ACS Publications. Most Trusted. Most Cited. Most Read
Interactions of Catalytic Enzymes with n-Type Polymers for High-Performance Metabolite Sensors
More

OR SEARCH CITATIONS

My Activity
Publications

Figure 1Loading Img
Download Hi-Res ImageDownload to MS-PowerPointCite This:ACS Appl. Mater. Interfaces 2023, 15, 7, 9726-9739
  • Open Access
Organic Electronic Devices

Interactions of Catalytic Enzymes with n-Type Polymers for High-Performance Metabolite Sensors
Click to copy article linkArticle link copied!

  • David Ohayon
    David Ohayon
    Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    More by David Ohayon
  • Dominik Renn
    Dominik Renn
    Catalysis Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    More by Dominik Renn
  • Shofarul Wustoni
    Shofarul Wustoni
    Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    More by Shofarul Wustoni
  • Keying Guo
    Keying Guo
    Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    More by Keying Guo
  • Victor Druet
    Victor Druet
    Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    More by Victor Druet
  • Adel Hama
    Adel Hama
    Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    More by Adel Hama
  • Xingxing Chen
    Xingxing Chen
    Physical Science and Engineering Division, KAUST, Thuwal 23955-6900, Saudi Arabia
    More by Xingxing Chen
  • Iuliana Petruta Maria
    Iuliana Petruta Maria
    Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, U.K.
    More by Iuliana Petruta Maria
  • Saumya Singh
    Saumya Singh
    Department of Chemistry, University of College London, 20 Gordon Street, London WC1H 0AJ, U.K.
    More by Saumya Singh
  • Sophie Griggs
    Sophie Griggs
    Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, U.K.
    More by Sophie Griggs
    Orcidhttps://orcid.org/0000-0002-5916-6609
  • Bob C. Schroeder
    Bob C. Schroeder
    Department of Chemistry, University of College London, 20 Gordon Street, London WC1H 0AJ, U.K.
    More by Bob C. Schroeder
  • Magnus Rueping
    Magnus Rueping
    Catalysis Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    More by Magnus Rueping
    Orcidhttps://orcid.org/0000-0003-4580-5227
  • Iain McCulloch
    Iain McCulloch
    Physical Science and Engineering Division, KAUST, Thuwal 23955-6900, Saudi Arabia
    Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, U.K.
    More by Iain McCulloch
    Orcidhttps://orcid.org/0000-0002-6340-7217
  • Sahika Inal*
    Sahika Inal
    Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    *Email: [email protected]
    More by Sahika Inal
    Orcidhttps://orcid.org/0000-0002-1166-1512
Open PDFSupporting Information (1)

ACS Applied Materials & Interfaces

Cite this: ACS Appl. Mater. Interfaces 2023, 15, 7, 9726–9739
Click to copy citationCitation copied!
https://doi.org/10.1021/acsami.2c20502
Published February 7, 2023

Copyright © 2023 American Chemical Society. This publication is licensed under

CC-BY 4.0 .

Abstract

Click to copy section linkSection link copied!
High Resolution Image
Download MS PowerPoint Slide

The tight regulation of the glucose concentration in the body is crucial for balanced physiological function. We developed an electrochemical transistor comprising an n-type conjugated polymer film in contact with a catalytic enzyme for sensitive and selective glucose detection in bodily fluids. Despite the promise of these sensors, the property of the polymer that led to such high performance has remained unknown, with charge transport being the only characteristic under focus. Here, we studied the impact of the polymer chemical structure on film surface properties and enzyme adsorption behavior using a combination of physiochemical characterization methods and correlated our findings with the resulting sensor performance. We developed five n-type polymers bearing the same backbone with side chains differing in polarity and charge. We found that the nature of the side chains modulated the film surface properties, dictating the extent of interactions between the enzyme and the polymer film. Quartz crystal microbalance with dissipation monitoring studies showed that hydrophobic surfaces retained more enzymes in a densely packed arrangement, while hydrophilic surfaces captured fewer enzymes in a flattened conformation. X-ray photoelectron spectroscopy analysis of the surfaces revealed strong interactions of the enzyme with the glycolated side chains of the polymers, which improved for linear side chains compared to those for branched ones. We probed the alterations in the enzyme structure upon adsorption using circular dichroism, which suggested protein denaturation on hydrophobic surfaces. Our study concludes that a negatively charged, smooth, and hydrophilic film surface provides the best environment for enzyme adsorption with desired mass and conformation, maximizing the sensor performance. This knowledge will guide synthetic work aiming to establish close interactions between proteins and electronic materials, which is crucial for developing high-performance enzymatic metabolite biosensors and biocatalytic charge-conversion devices.

This publication is licensed under

CC-BY 4.0 .
  • cc licence
  • by licence
Copyright © 2023 American Chemical Society

Subjects

what are subjects

Keywords

what are keywords

Introduction

Click to copy section linkSection link copied!
Protein adsorption at solid–liquid interfaces is critical for many biological events, such as cell adsorption, (1) transmembrane signaling, (2) and the blood coagulation cascade. (3) Protein adsorption is also one of the most challenging problems for biomedical device applications. For instance, thrombus formation on implants (and inflammatory responses) (3) and hemodialysis membranes, (4) biofouling of implanted devices and analytical chips intended for chronic use, (5) and dental plaque formation (6) are among the most common issues where protein adsorption leads to device failure. On the other hand, controlled protein adsorption is highly desirable for other devices and applications, such as biosensors and immunoassays, (7,8) genome analysis, (9) protein separation and purification, (10) membrane filtration, (11) and scaffold vascularization. (12) Effective control over the protein adsorption process necessitates understanding the underlying mechanisms and the involved interactions with the surface. Unfortunately, no single universal understanding exists, and the current literature displays contention, reflecting the complexity of the adsorption phenomenon and protein–surface interactions. (13) Various interfacial interactions (van der Waals, electrostatic, and hydrophobic) and surface physicochemical properties (charge, wettability, polarity, roughness, and morphology) and environmental conditions (protein bulk concentration, ionic strength, pH, and temperature) are thought to influence the adsorption behavior. (14,15) A robust empirical model that links substrate surface properties to the resulting protein adsorption behavior would greatly benefit the design of new materials, particularly electronic materials for biosensors.
Electrochemical biosensors typically use proteins, such as enzymes or antibodies, as the biorecognition unit that binds the analyte. (16) These proteins are often immobilized on the electrode or semiconductor surface. For the case of enzymatic metabolite sensors, the metabolite-binding and catalytic sites of the enzyme must be in a specific orientation with respect to the solution and the substrate, respectively, for efficient capture of the metabolite and transduction of the binding event. The enzyme immobilized on the surface should maintain its 3D solution structure as much as possible for efficient catalysis and target specificity. Therefore, the amount of protein bound, its orientation, and conformation are critical to sensor performance. Various strategies have been developed to immobilize enzymes on electronic surfaces. These include physical adsorption, covalent attachment, enzyme reconstitution, and protein engineering. (17,18) The enzyme shelf life stability is often higher when attached to a surface compared to that of its soluble form. (19,20) Among these methods, physical adsorption has been the most popular due to its simplicity. However, this approach lacks total control over the orientation of the protein, and denaturation or changes in the protein structure have been observed as a result of protein–surface interactions. (21) It is thus essential to choose or decorate the electronic surface to allow for stable immobilization of the adsorbed enzyme with the desired orientation.
We have recently developed an electronic metabolite sensor where the enzyme was physically adsorbed on the organic semiconductor surface. (22−24) The semiconductor was an electron-transporting (n-type) copolymer that was patterned on the channel and gate electrode of a microfabricated organic electrochemical transistor (OECT). For the case of the glucose sensor, glucose oxidase (GOx) was immobilized on the n-type polymer film. The device detected glucose (and lactate when lactate oxidase was used as the enzyme) in saliva with excellent sensitivity, selectivity, and a wide detection range of 6 orders of magnitude. The n-type polymer/GOx film also functioned as the anode of a glucose fuel cell, extracting enough power from biological media to drive small electronics. (22) The sensor operation relied mainly on the O2 sensitivity of the n-type film, where its conductivity increased as the O2 amount decreased in the solution when glucose bound to GOx. (25) The sensor results and spectroscopy analysis point to an intimate interface between the polymer film and the enzyme which allows the OECT to detect minute changes in O2 concentrations and, hence, enzyme activity at its surface. Despite the promise of this platform, it has not been clear why this particular polymer led to such high-performance sensors. Shedding light onto the enzyme adsorption process on this film would be very important to design new n-type semiconductors for biosensors, particularly when considering that the electronic performance of this polymer is behind that of the recently developed n-type materials. (26−28)
Here, we developed a series of n-type polymers based on the aforementioned polymer backbone (naphthalene diimide bi-thiophene, NDI-T2) but with various side chains (Figure 1a). All polymers had in common ethylene glycol (EG) side chains attached either to the NDI or the T2 unit, enabling solution processability and OECT operation in aqueous electrolytes. (29) The first group comprises two copolymers where one monomer has a branched alkyl side chain, and the other contains a linear EG-based side chain (P-75 and P-90). (29) We designed one homopolymer from the fully glycolated monomer (P-100) (29) and another for which we replaced the linear EG chain with a branched one (P-100B). (30) The last polymer of the series includes zwitterions on the side chain attached to the NDI unit (P-ZI). We first evaluated the glucose sensing performance of each film in the OECT configuration, as well as used a three-electrode setup to rule out any differences in the transistor performance of each polymer. We then characterized the film surface using water contact angle and ζ potential measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Using a quartz crystal microbalance with dissipation monitoring (QCM-D), we monitored the real-time enzyme adsorption behavior and quantified the amount of enzyme adhered to each polymer film. We calculated the resulting theoretical footprint of the enzyme and evaluated the viscoelastic properties of the adsorbed layer(s). We determined the structural composition of the protein layer on each film surface using circular dichroism (CD) and correlated the results with our GOx adsorption model. Our results show that although hydrophobic surfaces retain more enzymes, they also denature the enzyme to a higher degree than polar surfaces. On the hydrophilic/polar surfaces, GOx adsorbs loosely with a larger footprint, suggesting a flattened conformation. A hydrophilic, negatively charged, and smooth surface leads to the best-performing glucose sensors, indicating the need for a conformational change (flattening) to establish electronic communication with the semiconductor film. Focusing on semiconductor/enzyme interactions and the influence of side chains on enzyme adsorption (conformation) and sensor sensitivity, our work provides guidelines to design efficient bio-electronic hybrid materials with target application in enzyme-based electrochemical devices.

Figure 1

Figure 1. (a) Chemical structure of n-type polymers: the two copolymers with varying EG contents: P-75 and P-90, the fully glycolated (alkyl-free) analogue (P-100), P-100B with a branched EG side chain (branched analogue of P-100), and P-ZI with its zwitterions on the side chain. (b) OECT schematic highlighting the locations of the n-type film with adsorbed GOx (channel and gate). When glucose is present, it gets oxidized to gluconolactone by the active site (FAD) of GOx, following glucose + GOx (FAD) → gluconolactone + GOx (FADH2).

High Resolution Image
Download MS PowerPoint Slide

Materials and Methods

Click to copy section linkSection link copied!

Materials

P-75, P-90, and P-100 were synthesized according to the previous protocols. (29) The P-100B synthesis details can be found in a recent report (P-1G). (30) P-ZI synthesis is described in the Supporting Information with NMR spectra provided in Figures S1–S4. d-Glucose, phosphate buffered saline (PBS), and GOx (Aspergillus niger, type X–S, lyophilized powder, 50 KU) were purchased from Sigma-Aldrich and used as received.

Quartz Crystal Microbalance with Dissipation Monitoring

We conducted QCM-D measurements using a Q-sense analyzer (QE401, Biolin Scientific AB) with Cr/Au-coated quartz crystals before (used as a reference) and after coating with the polymer films. The changes in frequency (Δf) and dissipation (ΔD) signals of the quartz-coated sensor were first measured in air (100 μL/min) and then in PBS, which was flown at a speed of 20 μL/min. After stabilizing the film in PBS (Δf < 0.1 Hz per 5 min), we introduced GOx solution (10 mg/mL, PBS) in the chamber. The signals were recorded for 50 min, followed by a PBS rinsing step (10 min at 20 μL/min and then 200 μL/min for 1 h) to allow any loosely bound proteins to desorb. We measured the 3rd, 5th, 7th, 9th, and 11th harmonics and used the 7th one for analysis (see Supporting Information Discussion 2). The measured shifts in the frequency of the sensors were converted into changes in mass (Δm) using the Sauerbrey equation
Δm=−17.7nΔfn
(1)
where n is the number of the overtone selected for the mass quantification and −17.7 is a constant determined by the crystal’s resonant frequency, active area, density, and shear modulus. When examining surface events, such as protein adsorption, it is generally more desirable to focus on the higher harmonics of the quartz crystal. At lower harmonics, the trapping of the acoustic energy (assuming that the energy of the mechanical oscillations of the crystal is confined to its area) is relatively inefficient, and thus, the data are more likely to reflect bulk changes and external mechanical vibrations. (31) We, therefore, chose to analyze the data using the seventh overtone, representing the best compromise between surface sensitivity and noise from our setup. We also fit the data using viscoelastic modeling (Kelvin–Voigt model, Q-Tools software, Biolin). Four harmonics (third, fifth, seventh, and ninth) were used for this model.

Circular Dichroism

The GOx amino acid distribution and surface charge representation were obtained using the Expasy server and PyMOL Molecular Graphics System, Version 2.4.2, Schrödinger, LLC, respectively, by using the corresponding amino acid sequence (UniProtKB: P13006) for GOx for A. niger. PyMOL Molecular Graphics System, Version 2.4.2, Schrödinger, LLC was used to visualize the surface charges of GOx in its native state in solution.
CD spectra (190–270 nm) at 20 °C were recorded using a Jasco J-815 CD spectropolarimeter (Jasco Inc., Japan). A 1 mm-path-length quartz cell (Hellma GmbH) was used for solution samples. The GOx (UniProtKB: P13006) concentration in PBS was 1 mg/mL. Samples were prepared on quartz substrates by spin-coating the polymers using the same protocol as that mentioned above (see the Materials and Methods section). The enzyme was drop-casted on the polymer films and left to adsorb for 30 min. All spectra were recorded after accumulating 20 runs and smoothed using a fast Fourier-transform filter to minimize background effects. Quantitative prediction of the secondary structure was performed by deconvolution of the CD spectra using the CAPITO program. (32) The program extracts the helical content at 220 nm, the β-strand at 206 nm, and the irregular structure at 199 nm only (neglecting the respective contributions of the other two elements at those wavelengths). Hence, the sum of the three secondary structural elements can differ from 100%. The represented spectrum corresponds to the average CD signal over triplicate experiments.

Film Preparation

Polymer films were prepared on the corresponding substrates by spin-coating the polymers from a 4 mg/mL solution in chloroform (1000 rpm for 30 s, for P-75, P-90, P-100, and P-100B) or trifluoroethanol (1000 rpm for 30 s, for P-ZI).

Water Contact Angle and Surface Free Energy Determination

The water contact angle of the polymer films was determined from static contact angle measurements using a KRUSS DSA100E drop-shape analyzer and Advance software (Germany).

Atomic Force Microscopy

AFM measurements were performed using a Veeco Dimension 3100 scanning probe system. Samples were prepared on indium tin oxide substrates using the same conditions as those summarized above. The images of the films immersed in PBS were obtained using a Bruker ScanAsyst-fluid module mounted with ScanAsyst-fluid probes (nominal resonant frequency: 150 kHz, spring constant: 0.7 N/m). Gwyddion software was used for statistical data and post-treatment.

X-ray Photoelectron Spectroscopy

XPS measurements were performed using a Kratos Axis Supra instrument equipped with a monochromatic Al Kα X-ray source (hν = 1486.6 eV), which was operated at a power of 150 W and under ultra-high vacuum (in the range of 10–9 mbar). All spectra were recorded in the hybrid mode using electrostatic and magnetic lenses. The survey and high-resolution spectra were acquired at fixed S-5 analyzer pass energies of 80 and 20 eV, respectively. The obtained spectra were calibrated using the reference C 1s at 284.8 eV. We deconvoluted the spectra using XPSPeak4 software with Gaussian and Lorentzian methods and subtracted the background using the Tougaard method.

OECT Fabrication, Characterization, and Operation of the Biosensor

The OECTs were microfabricated on glass substrates based on established protocols using standard photolithography and Parylene-C peel-off techniques. (33) All polymers were spun at 1000 rpm for 30 s from a 4 mg/mL polymer solution (solvent: chloroform for P-75, P-90, P-100, and P-100B; trifluoroethanol for P-ZI). All devices had the same channel (width = 100 μm, length = 10 μm) and gate electrode (500 × 500 μm) dimensions. The OECT channel and gate surfaces were coated with the respective polymer. All channels and gates were incubated with a GOx solution (10 mg/mL in 1× PBS, pH 7.4) for 30 min at room temperature (20 °C). The sensing performance of the OECT biosensors was assessed via chronoamperometry using a Keithley 2602A source meter, where the drain voltage (VD) and gate voltage (VG) were fixed at 0.5 V. After a steady current baseline was obtained for the drain current (ID), we monitored the real-time changes in response to subsequent additions of increasing concentrations of glucose into the electrolyte. Solutions of the enzyme and glucose were stored at 4 °C. All electrical measurements were performed at room temperature. For all experiments, the electrolyte volume was kept at 40 μL. For an accurate comparison between devices, we normalized the device response to glucose
NROECT=|ID−I0I0|
(2)
where ID and I0 are the current output at a given analyte concentration and zero analyte concentration, respectively.
We also measured the glucose sensitivity of Au electrodes (3 mm diameter) coated with the respective polymers in a three-electrode setup. Each electrode was coated with the corresponding polymer and functionalized with GOx according to the protocol detailed above. The polymer electrode was used as the working electrode, in combination with a Ag/AgCl reference electrode and platinum (Pt) coil counter electrode. We first evaluated the O2 sensitivity of our polymers by recording the electrode current in degassed and ambient atmospheres. The three-electrode setup was placed in a sealed glovebox flushed with N2 gas. The O2 content in the glovebox and electrolyte was monitored using an optical microsensor (PreSens Precision Sensing GmbH, Germany). The needle-type O2 microsensor (NTH-PSt7) has a spatial resolution down to 50 μm and a temporal resolution down to 3 s with a limit of detection of 0.03% O2. Once the O2 detection limit was reached, we performed chronoamperometry measurements in PBS-1× at −0.6 V versus Ag/AgCl using a PalmSens potentiostat. Once a steady current value was obtained, we stopped the N2 flush and opened the box to allow O2 to diffuse while recording the current changes. The experiment was stopped once a steady-state current value was obtained at an ambient O2 concentration. The polymer/GOx response to 1 mM glucose was then recorded under ambient conditions. We normalized the electrode’s current response to glucose with its response to O2
NRelectrode=|ID−I0IO2−IN2|
(3)
ID represents the stabilized current upon 1 mM glucose addition, and I0 is the baseline current under ambient conditions before the glucose addition.

Safety Statement

No unexpected or unusually high safety hazards were encountered.

Results and Discussion

Click to copy section linkSection link copied!

OECT Device Characteristics and Glucose Sensing Performance

With Ag/AgCl as the gate electrode and PBS as the electrolyte, all devices showed enhancement mode OECT behavior (Figure S5). When using a planar Au electrode coated with the corresponding n-type polymer as the gate (as illustrated in Figure 1b), all channels displayed lower currents and transconductance (gm) values, while P-ZI could not be switched ON (Figure S6). We functionalized the active area of these devices with the enzyme. We evaluated the changes in the channel current (ID) as successive glucose concentrations were added to the measurement solution. As glucose was oxidized by GOx, the O2 amount in the electrolyte decreased as it was used for GOx regeneration. Since the n-type OECT current is inherently sensitive to changes in the O2 content of its environment, the GOx reaction with glucose led to an immediate increase in ID. (25) Although all polymers are sensitive to O2 and all polymers except P-ZI operated sufficiently as an OECT, only P-90, P-100, and P-100B OECTs showed a current response to the oxidation of glucose (Figure 2a). Figure 2b compares the glucose sensitivity of these devices (NROECT). P-90 and P-100 OECTs had similar sensing performance, while P-100B demonstrated the smallest response.

Figure 2

Figure 2. Performance of n-type OECTs and electrodes as glucose sensors. (a) Real-time response of the OECT (source-drain current, ID, as a function of time) as successive amounts of glucose are added to the electrolyte. The gate and drain voltages were kept constant at +0.5 V. The OECTs were operated using a planar gate configuration, where both the channel and gate were functionalized with GOx. Insets represent the real-time response of the devices to glucose concentrations lower than 250 μM. (b) Normalized response of the OECTs (NROECT) to glucose. Error bars represent the standard deviation of at least three different devices. (c) Amperometric response of n-type conjugated polymer electrodes to 1 mM glucose. The working electrode was the n-type film functionalized with GOx, the reference electrode was Ag/AgCl, and the counter electrode was a Pt coil. The arrow represents the time point when 1 mM glucose was added into the electrolyte. (d) NRelectrode to 1 mM glucose (plain bars) and to O2 (patterned bars).

High Resolution Image
Download MS PowerPoint Slide
As gm of each device differs (Figure S6), the OECT sensing performance may not be a direct indicator of enzyme/polymer interactions. To rule out the effect of the intrinsic OECT characteristics, we evaluated the glucose-sensing performances of our n-type polymers in a three-electrode configuration. However, the O2 sensitivity of each polymer may differ and hence their response to the same concentration of glucose. Therefore, first, we quantified the O2 sensitivity of our polymer-coated electrodes by measuring their respective reduction current in de-gassed and ambient atmospheres. All of our films showed an increase in their current when O2 was depleted from the electrolyte, with P-ZI and P-100B having the highest O2 sensitivity and P-90 and P-100 the lowest (Figure S7). We then measured the amperometric response of each polymer film to 1 mM glucose under ambient conditions (Figure 2c). All polymers, including P-75 and P-ZI which did not operate in OECTs, showed an increase in their current upon glucose oxidation. Figure 2d compares the normalized glucose- and the O2-triggered increases in the current of each electrode (see eq 3 in Materials and Methods). Although P-90 and P-100 are the least sensitive to O2, their current response to glucose is among the largest. Also, note that although P-100B is more sensitive to O2, the P100 and P100-B electrodes have comparable glucose sensing performance. On the other hand, the polymer with the highest O2 sensitivity, P-ZI, is not the most responsive to glucose. Given that these polymers sense glucose without relying on external mediators, their currents are not sensitive to hydrogen peroxide, (22,23) and their response to glucose does not scale with their O2 sensitivity, we conclude that the sensor performance is largely governed by the differences in enzyme/polymer interactions.

Surface Properties of n-Type Films

We sought to understand the origin of the differences in polymer/enzyme interactions by investigating first the film surface characteristics. Surface wettability and charge are thought to be the primary drivers of enzyme adsorption behavior (Supporting Information Discussion 1). (34) We measured the water contact angle on the films as shown in Figure S8. Surface hydrophilicity increases with the EG content (from P-75 to P-100B), and P-ZI has the most hydrophobic surface (Figure 3a). Zeta potential (ζ) measurements revealed a net and increasingly negative surface charge when going from P-75 to P-90 and P-100, while P-100B and P-ZI had a positive and neutral surface, respectively (Figure 3b). Xie et al. showed that the surface charge influences the orientation of the adsorbed GOx; i.e., a positively charged surface leads to a preferred front-lying orientation, while a negatively charged surface is expected to induce a more favorable back-lying orientation. (35) We used the PyMOL Molecular Graphics server to visualize the surface charges of GOx in its native state in solution (Figure S9) and estimated the possible orientation of GOx (i.e., assuming no conformational changes upon adsorption) on our films (Figure 3c). The front-lying orientation is expected to lead to a lower bioelectrocatalytic activity due to the hindered access to the substrate-binding site, (35) which is the case for the P-ZI film. The most ideal enzyme orientation, where the enzyme active site is easily accessible and remains close to the electrode surface (back-lying orientation), is likely to occur on the negatively charged polymers, i.e., P-75, P-90, and P-100.

Figure 3

Figure 3. Surface properties of n-type films. (a) Water contact angle and (b) ζ potential of the n-type polymer films. Error bars represent the standard deviation of (a) nine and (b) four different measurements. (c) Orientations of native GOx from A. niger (PDB: 3QVP) as a function of surface charge: (i) “front-lying” orientation on a charge-neutral surface; (ii) “standing” orientation on a positively charged surface; and (iii) “back-lying” orientation on a negatively charged surface. Surface colors on GOx indicate positive and negative electrostatic potentials contoured from 50 kT/e (blue) to −50 kT/e (red). The cofactor is shown in stick representation and highlighted in red.

High Resolution Image
Download MS PowerPoint Slide
The surface roughness and morphology may affect the adsorption behavior of proteins, mainly if the lateral dimensions of the surface (nano)structures correspond to the length scale of the protein. (14,36,37) We characterized the surface morphology of our films immersed in PBS using AFM. Although it is difficult to predict the effect of surface roughness alone on protein adsorption, (38) studies showed that topological factors (e.g., roughness, feature size), combined with surface chemical variabilities, can influence protein adsorption characteristics. (36) Empirically, the surface morphology became more fibrillary with the EG content, while the average surface roughness peaked for P-100B (7.3 nm), followed by P-90 (2.6 nm), P-100 (1.7 nm), and P-75 (1.5 nm). P-ZI displayed a morphology with small domains but no fibrillar content (Figure S11). Smaller-scale images (1 × 1 μm) exhibited features similar to those in larger scales (5 × 5 μm). The 3D representation of the morphologies highlighted differences in height and lateral dimensions of the nanostructures for each surface (Figure S11a). Except for P-100B, which displayed large “bumps” on the surface, all polymers had a “spikier” texture with a relatively homogeneous distribution, which was reflected in the average dimension distribution profiles of the surface (Figure S11b). We also analyzed the lateral surface dimensions by sampling each AFM image at three arbitrarily chosen regions (Figure S12). All polymers displayed much larger lateral dimensions (minimum 34.5 ± 3.6 nm) than the length scale of GOx (maximum 7.7 nm), suggesting that the surface morphology might not be the primary driver of enzyme adsorption and interactions with the polymers.

Monitoring Enzyme Adsorption and Characterization of the Adsorbed Layer

We used QCM-D to monitor, in real time, the amount of enzyme adsorbing on polymer films and the viscoelastic properties of the protein layer. Figure 4a shows the changes in the frequency (Δf) and dissipation (Δd) signals from an exemplary P-90 film as GOx physically adsorbs on it. The same plots for other films are shown in Figure S13. The films were first left to swell in PBS. Once they were fully hydrated, QCM-D signals stabilized. The enzyme was then introduced into the chamber, causing a decrease in Δf and an increase in Δd, indicative of protein accumulation on polymer films and the softness of the formed layer. The enzyme solution was then replaced with PBS to wash away any unbound species, resulting in a physically adsorbed, stable protein layer. Proteins at the solid–liquid interface are generally considered non-rigid; thus, it is intuitive to analyze the QCM-D data using a viscoelastic model (Voigt) rather than the Sauerbrey equation. (39) However, we could not consistently apply the Voigt model to all of our data (Figure S14) and determined the Sauerbrey model to be appropriate for our system. Figure 4b shows the mass increase on each sensor upon adsorption of GOx. We observed that the amount of hydrated enzyme remaining on the film depends on the polymer type. The P-75 film retained the highest GOx amount (769 ng cm–2), followed by P-90 (191 ng cm–2), P-ZI (126 ng cm–2), P-100B (97 ng cm–2), and P-100 (73 ng cm–2). P-75 has one of the most hydrophobic surfaces and a slight negative charge with a combination of alkyl and EG chains. Although P-ZI presents a similar hydrophobicity to P-75, the charge neutrality induced by its zwitterionic side chains seems to inhibit further mass uptake. As for negatively charged P-100 and positively charged P-100B, showing the most hydrophilic surfaces of the series, they do not attract more protein than P-90, where the protein amount is almost doubled compared to that on these surfaces. We conclude that protein absorption is more effective on hydrophobic surfaces populated with ideally a few negative charges. Alkyl side chains seem required for protein adsorption but should not dominate the surface. For example, when we tested a fully alkylated NDI-T2 analogue, namely, P-0, which has a much higher water contact angle (ca. 100°) than all the polymers studied, (29) we saw that the enzyme adsorption did not improve further; in fact, it is limited to only 49 ng cm2 (Figure S15). Note that the mass values are calculated based on the assumption of an even distribution of the enzyme on a laterally homogeneous surface, and we do not consider the formation of clusters or multilayers.

Figure 4

Figure 4. GOx adsorption on polymer films, analyzed using QCM-D. (a) P-90 QCM-D raw data reporting the change in frequency (Δfn) and dissipation (Δdn) for harmonics fifth, seventh, and ninth. (b) Corresponding mass taken up upon GOx adsorption on each film as a function of surface wettability [represented by cos(θ) where θ is the water contact angle]. The adsorbed mass per area was extracted from the data collected at the end of the rinsing process (see Figure S14). (c) Footprint of the enzyme on each polymer film. The footprint was calculated from the enzyme surface coverage and average dimensions of the crystal structure of a deglycosylated GOx molecule (60 Å × 52 Å × 77 Å), (40) assuming an even distribution of the enzyme on a laterally homogeneous surface. (d) P-90 Δd vs Δf plots (seventh harmonic). The numbers define the linear regions in the plots with different slopes. The red and blue dots demark the end of the adsorption and desorption processes, respectively. (e) Δd/Δf ratio, calculated from the values measured at the end of the adsorption and the rinsing steps, as a function of wettability cos(θ).

High Resolution Image
Download MS PowerPoint Slide
From the adsorbed mass, we calculated the theoretical enzyme footprint on the films (Figure 4c). GOx had the largest footprint on P-0 (542 nm2, Figure S15c), where we hypothesized that the enzyme underwent significant conformational rearrangements due to the surface hydrophobicity (Supporting Information Discussion 1). The smallest enzyme footprint (35 nm2) was on the second top hydrophobic surface, i.e., P-75, suggesting a densely packed enzyme layer when considering its high amount therein. Among the rest of the glycolated films, the enzyme had the smallest footprint (139 nm2) on P-90, indicating either a more packed or slightly flattened enzyme layer. The case of P-100 is interesting. It has the lowest amount of enzyme with the largest footprint (after P-0), suggesting that the enzyme has an expanded conformation on this surface which we found to be highly negatively charged. Overall, these calculated footprints are generally larger than the theoretical footprint of GOx predicted from its crystal structure (21, 67, or 195 nm2) (37,41,42) but are in line with other reported values on Au (between 528 and 823 nm2) (6) and Au nanoparticles (between 250 and 300 nm2), (43) suggesting that GOx flattens out to some degree during adsorption. (44,45) Note that the native GOx dimensions are those of a deglycosylated GOx molecule, thus implying a larger structure for the protein in solution. (46) We also stress the qualitative aspect of these calculations due to our assumptions. We conclude that the most hydrophobic surface without EG chains denatures the enzyme to the highest degree and that EG chains are required to minimize conformational changes. However, if EG chains fully dominate the surface, enzyme/polymer interactions are impaired, and the adsorbed proteins undergo partial denaturation. Note that we did not find a correlation between the amount adsorbed and the surface based on their charges (Figure 3a); however, the position of the binding site may still be necessary even after flattening of the enzyme on the surface, favoring the negatively charged surfaces.
Having determined the mass and the coverage area of the enzyme layer on each polymer surface, we next used the dissipation data to investigate the viscoelastic properties of the protein layer. The Δd versus Δf plots represent viscoelastic changes in the protein layer as the adsorption proceeds (31) and contain a series of linear regions, each representing specific viscoelastic properties of the protein layer(s) (Figures 4d and S16, Supporting Information Discussion 2). The sign and the amplitude of these slopes indicate the rigidity of the formed layer, where a positive value implies the formation of a loose protein layer. (31)Figures 4d and S16 show that all polymers, except P-ZI, presented three linear regions during the adsorption process, suggesting similar kinetic behavior of the enzyme adsorption on these films. The first phase indicates a relatively rigid (small dissipation vs frequency) attachment until a critical surface coverage is reached. The second phase, characterized by a much steeper slope than that of phase 1, suggests the attachment of a viscoelastic stratum onto the first layer or loose (imperfectly coupled) binding of an additional rigid layer on the first. The last phase is associated with a further increase in the frequency, with a slight rise in dissipation, related to film thickening and possibly the removal of water molecules from the adlayers. For the glycolated polymer series, i.e., P-75, P-90, P-100, and P-100B, we observed a general increase in the slope values for all phases with the EG content (see Table S1). Some unbound protein detaches from the surfaces as the films are rinsed with PBS. We observe a different behavior of the enzyme on different films during the rinsing process. The enzyme layer on P-75 and P-90 displayed a constant dissipation while the frequency decreased, leading to a looser protein layer upon stabilization.
P-100 and P-100B exhibited an increase in frequency and dissipation (more evident for P-100B), possibly leading to a looser and/or more hydrated layer (Supporting Information Discussion 2). The increase in the dissipation for P-100 and P-100B can be due to a more expanded protein conformation which would increase the viscoelasticity of the bound molecules, (47) implying that GOx adopts a more expanded conformation on these most hydrophilic surfaces. On the other hand, P-ZI displayed a very different adsorption behavior, presenting a two-phase process. The initial phase suggests the attachment of a very loose GOx layer, characterized by a high slope value (Table S1). In contrast, the second phase corresponding to the adsorption stabilization showed a negative slope value, indicating a stiffening of the enzyme layer as opposed to that on the glycolated surfaces. Furthermore, we observe a further rigidification of the enzyme layer upon rinsing, as illustrated by the negative dissipation value (Figure S16).
The final state of the enzyme layer(s) at the end of the adsorption and rinsing processes (red and blue dots in Figure 4d, respectively) is represented by the Δd/Δf ratio values. We examined the Δd/Δf ratios as a function of the polymer film surface wettability cos(θ), where θ is the water contact angle (Figure 4e). (48) The Δd/Δf ratio increased with wettability, suggesting a less rigid layer on a more polar/hydrophilic surface. Here, we note the unique case of P-ZI, showing a positive Δd/Δf ratio upon rinsing (due to a negative dissipation value with respect to the polymer baseline), presenting a significantly more rigid GOx layer than that on the glycolated surfaces. Furthermore, Figure 4b shows that the adsorbed GOx mass is generally inversely correlated with the surface wettability, where we found less dense layers, i.e., meaning a smaller amount of adsorbed protein, for more hydrophilic/loosely bound surfaces. We suggest that the hydrophobic character of P-75 and P-ZI led to an increased adsorbed mass due to stronger protein–protein interactions and denatured GOx. It has been postulated that in a denatured state, proteins tend to form more protein–surface and inter-protein interactions, leading to a more rigid layer, which correlates with the stiffer layer(s) we observed on P-75 and P-ZI. (48)
Next, we calculated the protein adsorption rate (dm/dt) and related it to the adsorbed mass (Figures 5 and S17). Figure 5a shows an exemplary plot of adsorption rate versus mass where we observed three main regions: (I) transport-limited regime, (II) reaction-limited regime, and (III) saturation regime. (39) The linearly decreasing rate of the region (II) is characteristic of Langmuir-like adsorption, whereas its negative gradient is consistent with random sequential adsorption (RSA). Neither of the adsorption models seems to describe the behavior we observed. We, therefore, followed the suggestion of Nelson et al., who consider a mixture of immobile and mobile proteins with partially excluded space. (39) We applied RSA model fitting (eq 4) for a qualitative understanding of the adsorption process:
dmdt=kacb×(1+C1m)
(4)
where ka is the rate constant (cm/s), C1 (cm2/ng) is a constant related to the steric factors of the adsorbed protein, and cb is the protein concentration. Here, ka concerns the rate constant of protein accumulation at low coverage (i.e., when protein–protein interactions are insignificant), whereas C1 reflects how the adsorbed protein molecules slow the subsequent adsorption of others. We found C1 to be linear to the surface area used by the enzyme at a given time during its adsorption (AAd) (Figure S18a), while ka was proportional to the adsorbed mass (Figure S18b); this indicates that the adsorption process is limited by the blocking effect of already adsorbed molecules. Figure 5b presents a plot of C1 versus ka, relating the adsorption kinetics to the footprint/affinity of the enzyme for the underlying surface. (39) This plot is composed of four quadrants, each corresponding to different behavior. Quadranti relates the adsorption of GOx on a surface to relatively low affinity. On such a surface, the protein footprint is expected to be relatively small. We found only P-90 in this quadrant, at the limit between Quadrantsi and iii, which correlates with the footprint calculated for P-90 in the range of other footprints reported on various gold surfaces. Quadrantii corresponds to preservation of a small protein footprint on surfaces for which it has high affinity. As postulated by Nelson et al., this is not an apparent behavior; however, it correlates with the calculated footprint and our hypothesis that GOx aggregates in the form of clusters or multilayers on P-75 due to strong protein–protein interactions. Quadrantiii represents protein adsorption with a large footprint on surfaces for which it has a low affinity, and P-100, P-100B, and P-ZI are in this quadrant. Finally, Quadrantiv illustrates a surface for which GOx would have a high affinity, adsorbing with a large footprint.

Figure 5

Figure 5. GOx adsorption kinetics. (a) dm/dt vs Sauerbrey mass uptake (seventh harmonic) plots for GOx adsorption on P-90 and (b) plot of C1 as a function of ka.

High Resolution Image
Download MS PowerPoint Slide
Note that except for P-ZI, we observed a trend where the steric parameter C1 increased with the surface wettability, as illustrated in Figure S19. The low values of C1 for less polar surfaces have been suggested to indicate a higher packing density of proteins. (48) Our results for P-75 are in agreement with this hypothesis. QCM-D measurements showed that the highest amount of GOx was adsorbed by the P-75 film, presenting the lowest C1 value, which could be due to the aggregation of the proteins in the form of clusters that leave a free surface for incoming proteins to adsorb on. (48) Furthermore, except for P-ZI, the adsorption rate constant ka decreased with surface hydrophilicity (Figure S19), suggesting slower adsorption kinetics on more polar surfaces, attributed to the lower enzyme affinity and possible flattening of the protein.

Characterization of Enzyme-Adsorbed n-Type Films

Since all the techniques that we used above are somehow indirect, we used XPS analysis to evidence the enzyme layer on the surface and identify which surface groups interacted with the protein. We recorded the XPS N 1s spectra shown in Figure 6 (Table S2) because GOx comprises various amino acids that contain nitrogen atoms (see the list of amino acids with their properties and fraction in the structure in Table S3). (49) On the other hand, all polymers have only one kind of nitrogen bond from the NDI moiety (N–C═O). Only P-ZI involves an additional nitrogen bond, −NMe2+, arising from its zwitterionic side chain. We compared the relative area of the NH2 peak to the total area of the N 1s region for each polymer to estimate which film contained more enzymes on its surface (Table 1). We observed that P-75 had the highest contribution from the −NH2 peak (attributed to various amino acids). This analysis confirmed that the zwitterionic polymer repelled to some extent the enzyme. XPS N 1s analysis suggests that increasing the amount of the EG content in the side chains decreased the amount of enzyme adsorbed. All these results are in agreement with our QCM-D results.

Figure 6

Figure 6. High-resolution N 1s XPS spectra of the polymer films after enzyme adsorption. Yellow circles highlight the chemical bonds involving N atoms in the polymers, including the NDI backbone and side chains and those in the primary amino acids present in GOx. The amino acids displayed in the figure correspond to a selected few in the protein sequence: lysine (LYS), glutamine (GLN), and arginine (ARG).

High Resolution Image
Download MS PowerPoint Slide
Table 1. Relative Contribution of the NH2 Area (ANH2) to the N 1s Region (ATOT)
polymersANH2/ATOT
P-750.840
P-900.805
P-1000.736
P-100B0.744
P-ZI0.661
We also investigated the C 1s spectra of the polymers before and after enzyme adsorption (Figures S20 and S21, respectively, Tables S4–S6 for the bonds). We could detect C–O bond signals from pristine films, suggesting that some EG chains are located on the uppermost surface. We observed an increase in the relative contribution of this bond with EG substitution or branching (Table S5), in agreement with previous reports. (50) Once the enzyme was added to the films, only P-100 displayed two additional peaks in the deconvoluted C 1s spectra (Figure S21 and Table S6), attributed to C═C–N (285.77 eV) and C–OOH (288.498 eV) from GOx amino acids. (51) S 2p XPS shows similar additional features only for this film (Figure S22 and Table S7). Considering that the enzyme mass on this film is not the highest in the series, these additional signals suggest an expanded/flattened conformation of the enzyme on the P-100 surface, exposing these amino acids.
Moreover, we observed a significant shift in the C═C bond in P-90 (−0.115 eV), P-100 (−0.081 eV), and P-100B (−0.028 eV), to lower binding energies, compared to that in P-75 (+0.024 eV) and P-ZI (+0.092 eV) which had instead shifted to higher binding energies (Table S8). These shifts indicate an increased electron density around the C═C bonds of P-90, P-100, and P-100B. P-90 and P-100 displayed the most drastic shift (>0.2 eV) of the C═O bonds of the NDI moieties to lower binding energies (Table S8). Previously, we found similar interactions of the enzyme GOx with the C═O and C═N peaks of the P-90 polymer using in situ Raman spectroscopy. (22) We also noticed important shifts in the C–O bonds in most polymers to higher binding energies, indicating interactions of GOx with the EG side chains of these polymers. (52) We found the largest shifts for P-100 (+0.409 eV) and P-90 (+0.135 eV), followed by P-ZI (+0.125 eV), P-75 (+0.123 eV), and lastly, P-100B (+0.063 eV). It is interesting to note that the shift of C–O is much larger for P-100 (+0.409 eV) compared to that for P-100B (+0.063 eV), implying stronger interactions of GOx with P-100 than with P-100B, in line with the higher sensitivity of the P-100-based glucose sensor. Branching makes the surface more hydrophilic and positively charged, which seems to hinder interactions with the enzyme and the position of the reaction center (Supporting Information Discussion 1).
Next, we used CD to investigate the secondary structure of the enzyme upon adsorption on different polymers. Proteins tend to lose the α-helical content and gain the β-sheets and random coil/irregular content upon adsorption on surfaces. (15,53) CD studies of GOx adsorbed or entrapped on various substrates, such as the Au nanoparticles, (43) Nafion matrix, (54) and self-assembled monolayers, (37,45,55) revealed a characteristic increase in the β-sheet content with a decrease in the α-helical content upon biohybrid formation. The α-helical content of GOx is closely linked to its activity. Glucose biosensors with GOx adsorbed in an α-helix conformation exhibited a much higher sensitivity to glucose than those with GOx adsorbed in a β-sheet conformation. (45) Thus, the α/β ratio is a good indication of the enzyme conformational change and resulting activity. The CD spectra that we collected for each polymer film/GOx complex are shown in Figure S23. We deconvoluted the raw CD spectra using the CAPITO program as a qualitative tool to compare the conformation adopted by GOx upon adsorption on our polymers. (32)Table 2 represents the assessment of the GOx secondary structure upon adsorption on each polymer film after CD spectrum deconvolution. Overall, the best-performing polymers in OECT sensors, P-90 and P-100, display a more conserved content of secondary structure elements of GOx, showing similar α/β ratios and the least decrease in the α content. A further loss in the helical content is observed for the more polar and hydrophilic P-100B. Together with the decrease in the α helix, the β sheet content increased more significantly for the more hydrophilic P-100 and P-100B compared to that for P-90. These results suggest a more flattened conformation on these surfaces compared to that on P-90, in agreement with our QCM-D and XPS results. Surprisingly, the CD data indicate changes in the GOx structure upon adsorption on P-75 similar to P-100B despite the surfaces presenting opposite charges and different hydrophilicity. Recall that we could not observe any response to the glucose with the P-75 OECT sensor, and the polymer showed the least amperometric response to glucose despite being the one with the highest oxygen sensitivity and the highest amount of GOx. A possible reason is the unfavorable enzyme orientation on P-75 due to the lower negative charge and higher hydrophobicity. The P-ZI film, on the other hand, exhibited significant changes with a complete loss of the α-helical content and an increase in the irregular structure, consistent with our hypothesis of significant unfolding/denaturation on this film.
Table 2. Relative Content of Secondary Structural Elements of GOx Protein upon Adsorption on n-Type Polymersa
 α-helixβ-sheetirregularα/β
GOx (native)0.090.480.520.19
P-750.010.530.530.02
P-900.020.510.530.04
P-1000.020.550.510.04
P-100B0.010.540.520.02
P-ZI0.000.520.560.00
a

The helical, β-strand, and irregular contents were calculated individually, and therefore, the sum of the three secondary structural elements may not be equal to 100%.

Discussion

Click to copy section linkSection link copied!
Our study points out the following conclusions: (i) GOx has different packing arrangements and conformations depending on the properties of each polymer surface. It adopts an expanded conformation on polar/hydrophilic surfaces and undergoes partial denaturation on hydrophobic surfaces; (ii) on hydrophobic surfaces, there is more enzyme, independent of the surface charge; (iii) the rigidity of the GOx layer decreases with the EG content of the surface, exhibiting a looser and flatter layer on more hydrophilic/polar surfaces; (iv) the orientation and conformation adopted upon adsorption, mainly dictated by the surface charge and hydrophobicity (see Supporting Information Discussion 1), influence the enzyme activity, indicating the need for a possible conformation change (flattening) to interact electrochemically with the underlying semiconducting film. We have summarized our findings in Figure 7.

Figure 7

Figure 7. Influence of n-type polymer film surface properties on GOx adsorption. The surface hydrophilicity and charge govern enzyme adsorption behavior on the film surface. Hydrophobic surfaces tend to retain more enzymes. Surfaces that are too hydrophobic, however, lead to complete denaturation of the enzyme structure. GOx adopts a flattened conformation on hydrophilic/polar surfaces. The surface charge influences GOx orientation. A neutral surface (left) leads to a “front-lying” orientation, where the active site of the enzyme faces downward and is inaccessible to the glucose. A positively charged surface (middle) leads to the enzyme adsorbing in a “standing” orientation, where the active site is accessible. A negatively charged surface (right) leads to a “back-lying” orientation, with the active site facing up and in closer proximity to the sensor surface than in a standing fashion. The latter surface, which is hydrophilic, negatively charged, and homogeneous, is most desirable to build top-performer glucose sensors.

High Resolution Image
Download MS PowerPoint Slide

Conclusions

Click to copy section linkSection link copied!
In this work, we investigated electronic film surface properties for the adsorption of an oxidase enzyme to achieve high-performance metabolite sensors. We correlated the sensor performance with the protein adsorption behavior by systematically probing the polymer surface properties and enzyme/polymer interactions. The nature of the conjugated polymer side chains governed the film surface properties and played a critical role in the enzyme orientation, conformation, and adsorption behavior. Our study revealed that GOx adopted different arrangements upon adsorption on each surface, influenced by the surface hydrophilicity and charge, while the morphology and roughness did not play a significant role. Hydrophobic surfaces retained more enzymes upon adsorption, where the protein presented a more rigid and densely packed arrangement with a smaller footprint than that on hydrophilic surfaces. However, increasing the hydrophobicity of surfaces led to the partial or total denaturation of the enzyme, thus decreasing the enzyme’s biological activity. We found that the enzymes specifically interacted with EG side chains, which were more favorable for the linear ones than the branched ones. The rigidity of the protein layer decreased with an increase in the EG content of the film surface, as we observed a looser and more flattened enzyme layer on more hydrophilic/polar surfaces. On the other hand, the performance of our sensors correlated with the orientation of GOx on the polymer surface (which was modulated by the surface charge), where a negatively charged surface led to the most favorable orientation for efficient catalysis.
Investigation of the surface chemical groups revealed an increased electron density around the C═C and C═O bonds upon enzyme adsorption, following the increase in the OECT-based sensor performance. These observations were supported by CD measurements, which showed that although GOx altered its conformation on all surfaces, it retained its native structure and, subsequently, activity on the polymers that made the best-performing sensors. Our studies suggest that a slightly negatively charged, smooth, and hydrophilic surface presents the best surface properties to maximize the sensor performance. This work establishes critical guidelines for designing conjugated polymers for mediator-free enzymatic metabolite sensors. Although these results could be applicable to other catalytic enzymes that share similar structural units with GOx, we note the robustness of GOx which may be playing a role in generating effective hybrids with n-type polymers. Although our core application concerns glucose sensors, our systematic analysis would benefit other enzyme-based bioelectronic applications, such as enzymatic biofuel cells and any organic electronic device that relies on protein/electronic material interactions.

Supporting Information

Click to copy section linkSection link copied!

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.2c20502.

  • Materials and methods; NMR spectrum of P-ZI; OECT output characteristics; O2 sensitivity of n-type films; water contact angle of n-type films; glucose oxidase surface charge distribution; AFM images of n-type films, QCM-D traces, models, and analysis of n-type films; list of amino acids in glucose oxidase; XPS signals of glucose oxidase adsorbed on n-type films and spectra deconvolutions; CD spectra of glucose oxidase in solution and when adsorbed on n-type films; discussions on the effect of surface charge and hydrophobicity on protein adsorption; and discussion on protein adsorption behavior on n-type films (PDF)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

Click to copy section linkSection link copied!
  • Corresponding Author
  • Authors
    • David Ohayon - Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    • Dominik Renn - Catalysis Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    • Shofarul Wustoni - Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    • Keying Guo - Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    • Victor Druet - Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    • Adel Hama - Organic Bioelectronics Laboratory, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
    • Xingxing Chen - Physical Science and Engineering Division, KAUST, Thuwal 23955-6900, Saudi Arabia
    • Iuliana Petruta Maria - Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, U.K.
    • Saumya Singh - Department of Chemistry, University of College London, 20 Gordon Street, London WC1H 0AJ, U.K.
    • Sophie Griggs - Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, U.K.;  Orcidhttps://orcid.org/0000-0002-5916-6609
    • Bob C. Schroeder - Department of Chemistry, University of College London, 20 Gordon Street, London WC1H 0AJ, U.K.
    • Magnus Rueping - Catalysis Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia;  Orcidhttps://orcid.org/0000-0003-4580-5227
    • Iain McCulloch - Physical Science and Engineering Division, KAUST, Thuwal 23955-6900, Saudi Arabia;  Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, U.K.;  Orcidhttps://orcid.org/0000-0002-6340-7217
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

Click to copy section linkSection link copied!

The authors thank Michael Payne and Dr. Daniel Seeman from Brookhaven Instruments for their assistance with ζ potential measurements. S.S. acknowledges the British Council Newton Fund Institutional Links (ref: 337067) for their support. B.C.S. thanks the UK Research and Innovation for Future Leaders Fellowship no. MR/S031952/1 for funding. This publication is based upon work supported by King Abdullah University of Science and Technology (KAUST) under award nos. REI/1/5130-01-01, REI/1/4577-01, OSR-2018-CRG7-3709, and ORA-2021-CRG10-4650. Figure 7 was produced by Ana Bigio, a scientific illustrator at KAUST.

References

Click to copy section linkSection link copied!

This article references 55 other publications.

  1. 1
    Ngandu Mpoyi, E.; Cantini, M.; Reynolds, P. M.; Gadegaard, N.; Dalby, M. J.; Salmerón-Sánchez, M. Protein Adsorption as a Key Mediator in the Nanotopographical Control of Cell Behavior. ACS Nano 2016, 10, 6638– 6647,  DOI: 10.1021/acsnano.6b01649
    Google Scholar
    1
    Protein Adsorption as a Key Mediator in the Nanotopographical Control of Cell Behavior
    Ngandu Mpoyi, Elie; Cantini, Marco; Reynolds, Paul M.; Gadegaard, Nikolaj; Dalby, Matthew J.; Salmeron-Sanchez, Manuel
    ACS Nano (2016), 10 (7), 6638-6647CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Surface nanotopog. is widely employed to control cell behavior and in particular controlled disorder is important in cell differentiation/maturation. However, extracellular matrix proteins, such as fibronectin (FN), initially adsorbed on a biomaterial surface are known to mediate the interaction of synthetic materials with cells. The authors examine the effect of nanotopog. on cell behavior through this adsorbed layer of adhesive proteins using a nanostructured polycarbonate surface comprising 150 nm-diam. pits originally defined using electron beam lithog. The authors address the effect of this nanopitted surface on FN adsorption and subsequently on cell morphol. and behavior using C2C12 myoblasts. Wettability measurements and at. force microscopy imaging showed that protein is adsorbed both within the interpits spaces and inside the nanopits. Cells responded to this coated nanotopog. with the formation of fewer but larger focal adhesions and by mimicking the pit patterns within their cytoskeleton, nanoimprinting, ultimately achieving higher levels of myogenic differentiation compared to a flat control. Both focal adhesion assembly and nanoimprinting are dependent on cell contractility and are adversely affected using blebbistatin. The authors' results demonstrate the central role of the nanoscale protein interface in mediating cell-nanotopog. interactions and implicate this interface as helping control the mechanotransductive cascade.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFeku7jK&md5=a72fcec8df98fc20cdf467ebfd407b72
  2. 2
    Cho, W.; Stahelin, R. V. Membrane-Protein Interactions in Cell Signaling and Membrane Trafficking. Annu. Rev. Biophys. Biomol. Struct. 2005, 34, 119– 151,  DOI: 10.1146/annurev.biophys.33.110502.133337
    Google Scholar
    2
    Membrane-protein interactions in cell signaling and membrane trafficking
    Cho, Wonhwa; Stahelin, Robert V.
    Annual Review of Biophysics and Biomolecular Structure (2005), 34 (), 119-151, 2 platesCODEN: ABBSE4; ISSN:1056-8700. (Annual Reviews Inc.)
    A review. Research in the past decade has revealed that many cytosolic proteins are recruited to different cellular membranes to form protein-protein and lipid-protein interactions during cell signaling and membrane trafficking. Membrane recruitment of these peripheral proteins is mediated by a growing no. of modular membrane-targeting domains, including C1, C2, PH, FYVE, PX, ENTH, ANTH, BAR, FERM, and tubby domains, that recognize specific lipid mols. in the membranes. Structural studies of these membrane-targeting domains demonstrate how they specifically recognize their cognate lipid ligands. However, the mechanisms by which these domains and their host proteins are recruited to and interact with various cell membranes are only beginning to unravel with recent computational studies, in vitro membrane binding studies using model membranes, and cellular translocation studies using fluorescent protein-tagged proteins. Here, the authors summarize recent progress in the understanding of how the kinetics and energetics of membrane-protein interactions are regulated during cellular membrane targeting and the activation of peripheral proteins.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXlslCkurc%253D&md5=926e12e451770454a652c6b166628711
  3. 3
    Xu, L.-C.; Bauer, J. W.; Siedlecki, C. A. Proteins, Platelets, and Blood Coagulation at Biomaterial Interfaces. Colloids Surf., B 2014, 124, 49– 68,  DOI: 10.1016/j.colsurfb.2014.09.040
    Google Scholar
    3
    Proteins, platelets, and blood coagulation at biomaterial interfaces
    Xu, Li-Chong; Bauer, James W.; Siedlecki, Christopher A.
    Colloids and Surfaces, B: Biointerfaces (2014), 124 (), 49-68CODEN: CSBBEQ; ISSN:0927-7765. (Elsevier B.V.)
    A review. Blood coagulation and platelet adhesion remain major impediments to the use of biomaterials in implantable medical devices. There is still significant controversy and question in the field regarding the role that surfaces play in this process. This manuscript addresses this topic area and reports on state of the art in the field. Particular emphasis is placed on the subject of surface engineering and surface measurements that allow for control and observation of surface-mediated biol. responses in blood and test solns. Appropriate use of surface texturing and chem. patterning methodologies allow for redn. of both blood coagulation and platelet adhesion, and new methods of surface interrogation at high resoln. allow for measurement of the relevant biol. factors.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs1Ohu73F&md5=cafe9f538645381e50d626c25d89854a
  4. 4
    Urbani, A.; Sirolli, V.; Lupisella, S.; Levi-Mortera, S.; Pavone, B.; Pieroni, L.; Amoroso, L.; Di Vito, R.; Bucci, S.; Bernardini, S.; Sacchetta, P.; Bonomini, M. Proteomic Investigations on the Effect of Different Membrane Materials on Blood Protein Adsorption During Haemodialysis. Blood Transfus. 2012, 10 Suppl 2, s101– s112,  DOI: 10.2450/2012.014S
    Google Scholar
    There is no corresponding record for this reference.
  5. 5
    Russo, M. J.; Han, M.; Desroches, P. E.; Manasa, C. S.; Dennaoui, J.; Quigley, A. F.; Kapsa, R. M. I.; Moulton, S. E.; Guijt, R. M.; Greene, G. W.; Silva, S. M. Antifouling Strategies for Electrochemical Biosensing: Mechanisms and Performance toward Point of Care Based Diagnostic Applications. ACS Sens. 2021, 6, 1482– 1507,  DOI: 10.1021/acssensors.1c00390
    Google Scholar
    5
    Antifouling Strategies for Electrochemical Biosensing: Mechanisms and Performance toward Point of Care Based Diagnostic Applications
    Russo, Matthew J.; Han, Mingyu; Desroches, Pauline E.; Manasa, Clayton S.; Dennaoui, Jessair; Quigley, Anita F.; Kapsa, Robert M. I.; Moulton, Simon E.; Guijt, Rosanne M.; Greene, George W.; Silva, Saimon Moraes
    ACS Sensors (2021), 6 (4), 1482-1507CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)
    A review. Although there exist numerous established lab.-based technologies for sample diagnostics and analyte detection, many medical and forensic science applications require point of care based platforms for rapid on-the-spot sample anal. Electrochem. biosensors provide a promising avenue for such applications due to the portability and functional simplicity of the technol. However, the ability to develop such platforms with the high sensitivity and selectivity required for anal. of low analyte concns. in complex biol. samples remains a paramount issue in the field of biosensing. Nonspecific adsorption, or fouling, at the electrode interface via the innumerable biomols. present in these sample types (i.e., serum, urine, blood/plasma, and saliva) can drastically obstruct electrochem. performance, increasing background "noise" and diminishing both the electrochem. signal magnitude and specificity of the biosensor. Consequently, this review aims to discuss strategies and concepts used throughout the literature to prevent electrode surface fouling in biosensors and to communicate the nature of the antifouling mechanisms by which they operate. Evaluation of each antifouling strategy is focused primarily on the fabrication method, exptl. technique, sample compn., and electrochem. performance of each technol. highlighting the overall feasibility of the platform for point of care based diagnostic/detection applications.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXntFGjtLw%253D&md5=02e2b991557f5f9263161d178143eed9
  6. 6
    Choi, W.; Park, S.; Kwon, J.-S.; Jang, E.-Y.; Kim, J.-Y.; Heo, J.; Hwang, Y.; Kim, B.-S.; Moon, J.-H.; Jung, S.; Choi, S.-H.; Lee, H.; Ahn, H.-W.; Hong, J. Reverse Actuation of Polyelectrolyte Effect for in Vivo Antifouling. ACS Nano 2021, 15, 6811– 6828,  DOI: 10.1021/acsnano.0c10431
    Google Scholar
    6
    Reverse Actuation of Polyelectrolyte Effect for In Vivo Antifouling
    Choi, Woojin; Park, Sohyeon; Kwon, Jae-Sung; Jang, Eun-Young; Kim, Ji-Yeong; Heo, Jiwoong; Hwang, YoungDeok; Kim, Byeong-Su; Moon, Ji-Hoi; Jung, Sungwon; Choi, Sung-Hwan; Lee, Hwankyu; Ahn, Hyo-Won; Hong, Jinkee
    ACS Nano (2021), 15 (4), 6811-6828CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Zwitterionic polymers have extraordinary properties, i.e., significant hydration and the so-called antipolyelectrolyte effect, which make them suitable for biomedical applications. The hydration induces an antifouling effect, and this has been investigated significantly. The antipolyelectrolyte effect refers to the extraordinary ion-responsive behavior of particular polymers that swell and hydrate considerably in physiol. solns. This actuation begins to attract attention to achieve in vivo antifouling that is challenging for general polyelectrolytes. In this study, we established the sophisticated cornerstone of the antipolyelectrolyte effect in detail, including (i) the essential parameters, (ii) exptl. verifications, and (iii) effect of improving antifouling performance. First, we find that both osmotic force and charge screening are essential factors. Second, we identify the antipolyelectrolyte effect by visualizing the swelling and hydration dynamics. Finally, we verify that the antifouling performance can be enhanced by exploiting the antipolyelectrolyte effect and report redn. of 85% and 80% in ex and in vivo biofilm formation, resp.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXnt1Witrg%253D&md5=c85795f577a131bbc0e83935e26fba70
  7. 7
    Park, M. Orientation Control of the Molecular Recognition Layer for Improved Sensitivity: A Review. BioChip J. 2019, 13, 82– 94,  DOI: 10.1007/s13206-019-3103-0
    Google Scholar
    7
    Orientation Control of the Molecular Recognition Layer for Improved Sensitivity: a Review
    Park, Min
    BioChip Journal (2019), 13 (1), 82-94CODEN: BJIODP; ISSN:1976-0280. (Korean BioChip Society)
    Biosensors have been used in various fields of biol. anal., such as for quantification of analytes and the study of mol.-mol. interactions. Orientation control of the mol. recognition layer is one of the easiest and most effective ways to improve the sensitivity of biosensors. In this review, the orientation control of mol. recognition mols., such as antibodies, aptamers, and enzymes, is discussed. The review compares the improvement in the sensitivity and binding activity of biosensors achieved through orientation control with that achieved through random orientation. Immobilization methods of antibodies for orientation control are first discussed, with a focus on immobilization of the fragment crystallizable region of antibodies, which is the most studied technique. Covalent and non-covalent immobilization strategies are also discussed, and their effect on the sensitivity of biosensors is summarized. Lastly, the orientation control of other mol. recognition mols. (aptamers and enzymes) was discussed and the applications of mol. recognition mols. as biosensors are discussed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXms1GjtLo%253D&md5=1178ff364fb328dca070b5af9795d154
  8. 8
    Bhakta, S. A.; Evans, E.; Benavidez, T. E.; Garcia, C. D. Protein Adsorption onto Nanomaterials for the Development of Biosensors and Analytical Devices: A Review. Anal. Chim. Acta 2015, 872, 7– 25,  DOI: 10.1016/j.aca.2014.10.031
    Google Scholar
    8
    Protein adsorption onto nanomaterials for the development of biosensors and analytical devices: A review
    Bhakta, Samir A.; Evans, Elizabeth; Benavidez, Tomas E.; Garcia, Carlos D.
    Analytica Chimica Acta (2015), 872 (), 7-25CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)
    A review on the use of nanomaterials, specifically nanoparticles and nanostructured films, for efficiently adsorbing a protein with a minimized structural change for its immobilization, and developing a biosensor or an anal. device.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvVGgtrjM&md5=8f94677bf281b72443cae973449d4603
  9. 9
    Lagraulet, A. Current Clinical and Pharmaceutical Applications of Microarrays: From Disease Biomarkers Discovery to Automated Diagnostics. JALA 2010, 15, 405– 413,  DOI: 10.1016/j.jala.2010.06.011
    Google Scholar
    9
    Current clinical and pharmaceutical applications of microarrays: From disease biomarkers discovery to automated diagnostics
    Lagraulet, Adriana
    JALA (2010), 15 (5), 405-413CODEN: JALLFO; ISSN:1535-5535. (Elsevier)
    A review. Microarrays used for measuring chromosomal aberrations in genomic DNA and for defining gene expression patterns have become almost routine. A microarray consists of an arrayed series of microscopic spots each contg. either DNA or protein mols. known as feature reporters. Advances in microarray fabrication and in feature detection systems, such as high-resoln. scanners and their assocd. software, lead to high-throughput screening of the genome or the transcriptome of a cell or a group of cells in only few days. Despite the potential of high-d. microarrays, several problems about data interpretation are still to be solved. In addn., targeted microarrays are shown to be useful tools for rapid and accurate diagnosis of diseases. The aim of this review was to discuss the impact of microarrays on different application levels from the definition of disease biomarkers to pharmaceutical and clin. diagnostics.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Wht77N&md5=994f6ce5505be06de67964e144ed9771
  10. 10
    Low, D.; O’Leary, R.; Pujar, N. S. Future of Antibody Purification. J. Chromatogr. B 2007, 848, 48– 63,  DOI: 10.1016/j.jchromb.2006.10.033
    Google Scholar
    10
    Future of antibody purification
    Low, Duncan; O'Leary, Rhona; Pujar, Narahari S.
    Journal of Chromatography B: Analytical Technologies in the Biomedical and Life Sciences (2007), 848 (1), 48-63CODEN: JCBAAI; ISSN:1570-0232. (Elsevier B.V.)
    A review. Antibody purifn. seems to be safely ensconced in a platform, now well-established by way of multiple commercialized antibody processes. However, natural evolution compels us to peer into the future. This is driven not only by a large, projected increase in the no. of antibody therapies, but also by dramatic improvements in upstream productivity, and process economics. Although disruptive technologies have yet escaped downstream processes, evolution of the so-called platform is already evident in antibody processes in late-stage development. Here we perform a wide survey of technologies that are competing to be part of that platform, and provide our [inherently dangerous] assessment of those that have the most promise.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXislWlsrw%253D&md5=1f62286a745fa1a2fc43488dc436b82a
  11. 11
    Saxena, A.; Tripathi, B. P.; Kumar, M.; Shahi, V. K. Membrane-Based Techniques for the Separation and Purification of Proteins: An Overview. Adv. Colloid Interface Sci. 2009, 145, 1– 22,  DOI: 10.1016/j.cis.2008.07.004
    Google Scholar
    11
    Membrane-based techniques for the separation and purification of proteins: An overview
    Saxena, Arunima; Tripathi, Bijay P.; Kumar, Mahendra; Shahi, Vinod K.
    Advances in Colloid and Interface Science (2009), 145 (1-2), 1-22CODEN: ACISB9; ISSN:0001-8686. (Elsevier B.V.)
    A review. Membrane processes are increasingly reported for various applications in both upstream and downstream technol., such as microfiltration, ultrafiltration, emerging processes as membrane chromatog., high performance tangential flow filtration, and electrophoretic membrane contactor. Membrane-based processes are playing crit. role in the field of sepn./purifn. of biotechnol. products. Membranes became an integral part of biotechnol. and improvements in membrane technol. are now focused on high resoln. of bioproduct. In biosepn., applications of membrane technologies include protein prodn./purifn., protein-virus sepn. This manuscript provides an overview of recent developments and published literature in membrane technol., focusing on special characteristics of the membranes and membrane-based processes that are now used for the prodn. and purifn. of proteins.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhsVKntLbK&md5=75f591c1a108d55da706f1495131b8e3
  12. 12
    Vogel, V.; Baneyx, G. The Tissue Engineering Puzzle: A Molecular Perspective. Annu. Rev. Biomed. Eng. 2003, 5, 441– 463,  DOI: 10.1146/annurev.bioeng.5.040202.121615
    Google Scholar
    12
    The tissue engineering puzzle: A molecular perspective
    Vogel, Viola; Baneyx, Gretchen
    Annual Review of Biomedical Engineering (2003), 5 (), 441-463, 2 platesCODEN: ARBEF7; ISSN:1523-9829. (Annual Reviews Inc.)
    A review. The inability of biomaterial scaffolds to functionally integrate into surrounding tissue is one of the major roadblocks to developing new biomaterials and tissue-engineering scaffolds. Despite considerable advances, current approaches to engineering cell-surface interactions fall short in mimicking the complexity of signals through which surrounding tissue regulates cell behavior. Cells adhere and interact with their extracellular environment via integrins, and their ability to activate assocd. downstream signaling pathways depends on the character of adhesion complexes formed between cells and their extracellular matrix. In particular, α5β1 and αvβ3 integrins are central to regulating downstream events, including cell survival and cell-cycle progression. In contrast to previous findings that αvβ3 integrins promote angiogenesis, recent evidence argues that αvβ3 integrins may act as neg. regulators of proangiogenic integrins such as α5β1. This suggests that fibronectin is crit. for scaffold vascularization because it is the only mammalian adhesion protein that binds and activates α5β1 integrins. Cells are furthermore capable of stretching fibronectin matrixes such that the protein partially unfolds, and recent computational simulations provide structural models of how mech. stretching affects fibronectin function. The authors propose a model whereby excessive tension generated by cells in contact to biomaterials may in fact render fibronectin fibrils nonangiogenic and potentially inhibit vascularization. The model could explain why current biomaterials independent of their surface chemistries and textures fail to vascularize.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXotlGqs74%253D&md5=f5e5599b7e4eecf287b8f1cc6ced90e0
  13. 13
    Vogler, E. A. Protein Adsorption in Three Dimensions. Biomaterials 2012, 33, 1201– 1237,  DOI: 10.1016/j.biomaterials.2011.10.059
    Google Scholar
    13
    Protein adsorption in three dimensions
    Vogler, Erwin A.
    Biomaterials (2012), 33 (5), 1201-1237CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)
    A review. Recent exptl. and theor. work clarifying the phys. chem. of blood-protein adsorption from aq.-buffer soln. to various kinds of surfaces is reviewed and interpreted within the context of biomaterial applications, esp. toward development of cardiovascular biomaterials. The importance of this subject in biomaterials surface science is emphasized by reducing the "protein-adsorption problem" to three core questions that require quant. answer. An overview of the protein-adsorption literature identifies some of the sources of inconsistency among many investigators participating in more than five decades of focused research. A tutorial on the fundamental biophys. chem. of protein adsorption sets the stage for a detailed discussion of the kinetics and thermodn. of protein adsorption, including adsorption competition between two proteins for the same adsorbent immersed in a binary-protein mixt. Both kinetics and steady-state adsorption can be rationalized using a single interpretive paradigm asserting that protein mols. partition from soln. into a three-dimensional (3D) interphase sepg. bulk soln. from the phys.-adsorbent surface. Adsorbed protein collects in one-or-more adsorbed layers, depending on protein size, soln. concn., and adsorbent surface energy (water wettability). The adsorption process begins with the hydration of an adsorbent surface brought into contact with an aq.-protein soln. Surface hydration reactions instantaneously form a thin, pseudo-2D interface between the adsorbent and protein soln. Protein mols. rapidly diffuse into this newly formed interface, creating a truly 3D interphase that inflates with arriving proteins and fills to capacity within milliseconds at mg/mL bulk-soln. concns. C B. This inflated interphase subsequently undergoes time-dependent (minutes-to-hours) decrease in vol. V I by expulsion of either-or-both interphase water and initially adsorbed protein. Interphase protein concn. C I increases as V I decreases, resulting in slow redn. in interfacial energetics. Steady state is governed by a net partition coeff. P=(CI/CB). In the process of occupying space within the interphase, adsorbing protein mols. must displace an equiv. vol. of interphase water. Interphase water is itself assocd. with surface-bound water through a network of transient hydrogen bonds. Displacement of interphase water thus requires an amt. of energy that depends on the adsorbent surface chem./energy. This "adsorption-dehydration" step is the significant free energy cost of adsorption that controls the max. amt. of protein that can be adsorbed at steady state to a unit adsorbent surface area (the adsorbent capacity). As adsorbent hydrophilicity increases, adsorbent capacity monotonically decreases because the energetic cost of surface dehydration increases, ultimately leading to no protein adsorption near an adsorbent water wettability (surface energy) characterized by a water contact angle θ→65°. Consequently, protein does not adsorb (accumulate at interphase concns. greater than bulk soln.) to more hydrophilic adsorbents exhibiting θ<65°. For adsorbents bearing strong Lewis acid/base chem. such as ion-exchange resins, protein/surface interactions can be highly favorable, causing protein to adsorb in multilayers in a relatively thick interphase. A straightforward, three-component free energy relationship captures salient features of protein adsorption to all surfaces predicting that the overall free energy of protein adsorption ΔGadso is a relatively small multiple of thermal energy for any surface chem. (except perhaps for bioengineered surfaces bearing specific ligands for adsorbing protein) because a surface chem. that interacts chem. with proteins must also interact with water through hydrogen bonding. In this way, water moderates protein adsorption to any surface by competing with adsorbing protein mols. This Leading Opinion ends by proposing several changes to the protein-adsorption paradigm that might advance answers to the three core questions that frame the "protein-adsorption problem" that is so fundamental to biomaterials surface science.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsF2ltrjJ&md5=0e2d118231562af07b8574a503f467b6
  14. 14
    Rabe, M.; Verdes, D.; Seeger, S. Understanding Protein Adsorption Phenomena at Solid Surfaces. Adv. Colloid Interface Sci. 2011, 162, 87– 106,  DOI: 10.1016/j.cis.2010.12.007
    Google Scholar
    14
    Understanding protein adsorption phenomena at solid surfaces
    Rabe, Michael; Verdes, Dorinel; Seeger, Stefan
    Advances in Colloid and Interface Science (2011), 162 (1-2), 87-106CODEN: ACISB9; ISSN:0001-8686. (Elsevier B.V.)
    A review. Protein adsorption at solid surfaces plays a key role in many natural processes and has therefore promoted a widespread interest in many research areas. Despite considerable progress in this field there are still widely differing and even contradictive opinions on how to explain the frequently obsd. phenomena such as structural rearrangements, cooperative adsorption, overshooting adsorption kinetics, or protein aggregation. In this review recent achievements and new perspectives on protein adsorption processes are comprehensively discussed. The main focus is put on commonly postulated mechanistic aspects and their translation into math. concepts and model descriptions. Relevant exptl. and computational strategies to practically approach the field of protein adsorption mechanisms and their impact on current successes are outlined.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXitFaks7g%253D&md5=f711d1ef1c3ef137808f1edcf0caeec1
  15. 15
    Secundo, F. Conformational Changes of Enzymes Upon Immobilisation. Chem. Soc. Rev. 2013, 42, 6250– 6261,  DOI: 10.1039/c3cs35495d
    Google Scholar
    15
    Conformational changes of enzymes upon immobilisation
    Secundo, Francesco
    Chemical Society Reviews (2013), 42 (15), 6250-6261CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Protein conformation plays a crucial role in detg. both the catalytic efficiency and the chemo-, regio- and enantioselectivity of enzymes, thus eventually influencing their exploitability in biotechnol. applications. Inevitably, immobilization processes alter the natural mol. environment of enzymes, and quite often affect their catalytic activity through different mechanisms such as reduced accessibility of the substrate to the catalytic active center, loss of the enzyme dynamic properties and alteration of the conformational integrity of the enzyme. This tutorial review outlines first the most common spectroscopic techniques used for investigating the conformation of immobilized proteins, and then examines how protein loading and polar and hydrophobic/hydrophilic interactions with the carrier affect the structural and dynamic features of enzymes. The nanoscale-level studies in which protein conformational changes, detd. either by exptl. approaches or by homol. modeling, are correlated with the size and shape of the support are also discussed. Altogether, these results should provide useful information on how supports and/or enzymes have to be tailored to improve biocatalyst performance.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtVKhtrrL&md5=343de02ca34fdaefa8942e66e200ba55
  16. 16
    Koklu, A.; Ohayon, D.; Wustoni, S.; Druet, V.; Saleh, A.; Inal, S. Organic Bioelectronic Devices for Metabolite Sensing. Chem. Rev. 2022, 122, 4581– 4635,  DOI: 10.1021/acs.chemrev.1c00395
    Google Scholar
    16
    Organic Bioelectronic Devices for Metabolite Sensing
    Koklu, Anil; Ohayon, David; Wustoni, Shofarul; Druet, Victor; Saleh, Abdulelah; Inal, Sahika
    Chemical Reviews (Washington, DC, United States) (2022), 122 (4), 4581-4635CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Electrochem. detection of metabolites is essential for early diagnosis and continuous monitoring of a variety of health conditions. This review focuses on org. electronic material-based metabolite sensors and highlights their potential to tackle crit. challenges assocd. with metabolite detection. We provide an overview of the distinct classes of org. electronic materials and biorecognition units used in metabolite sensors, explain the different detection strategies developed to date, and identify the advantages and drawbacks of each technol. We then benchmark state-of-the-art org. electronic metabolite sensors by categorizing them based on their application area (in vitro, body-interfaced, in vivo, and cell-interfaced). Finally, we share our perspective on using org. bioelectronic materials for metabolite sensing and address the current challenges for the devices and progress to come.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXitFKgsr%252FJ&md5=5e31573a5985b4d3804c9bc0d6caa0f0
  17. 17
    Saboe, P. O.; Conte, E.; Farell, M.; Bazan, G. C.; Kumar, M. Biomimetic and Bioinspired Approaches for Wiring Enzymes to Electrode Interfaces. Energy Environ. Sci. 2017, 10, 14– 42,  DOI: 10.1039/c6ee02801b
    Google Scholar
    17
    Biomimetic and bioinspired approaches for wiring enzymes to electrode interfaces
    Saboe, Patrick O.; Conte, Emelia; Farell, Megan; Bazan, Guillermo C.; Kumar, Manish
    Energy & Environmental Science (2017), 10 (1), 14-42CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
    Biomimetic and bioinspired approaches to redox enzyme wiring involve borrowing structures and strategies found in biol. electron transfer systems for use in engineered devices. Redox protein-electrode systems are evolving for several applications, including energy, biomedical and environmental purposes. This review is intended to be both "tutorial" and comprehensive in that we provide a guide to understand, design, and improve electrode interfaces for redox enzyme electron transfer processes in devices. The review examines electrode interfaces by directly comparing them with biol. electron transfer systems. First, the mechanisms, theory, and structures for electron transfer in biol. systems are provided, followed by anal. of the strategies and structures engineered in redox-protein devices. The review describes the challenges of constructing and applying redox enzyme devices, including the poor elec. contact between electrodes and enzymes and low lifetime and scalability of devices.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVShu7%252FJ&md5=515d95f56b44f7da8fb8139d3183971c
  18. 18
    Pinyou, P.; Blay, V.; Muresan, L. M.; Noguer, T. Enzyme-Modified Electrodes for Biosensors and Biofuel Cells. Mater. Horiz. 2019, 6, 1336– 1358,  DOI: 10.1039/c9mh00013e
    Google Scholar
    18
    Enzyme-modified electrodes for biosensors and biofuel cells
    Pinyou, Piyanut; Blay, Vincent; Muresan, Liana Maria; Noguer, Thierry
    Materials Horizons (2019), 6 (7), 1336-1358CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
    A review. In biosensors and biofuel cells, it is often desirable to accelerate the electron transfer rate between the enzyme and electrode surface to improve the performance of the devices (sensitivity or power output). To this end, in this review, we focus on three important strategies available to improve the performance of enzyme-modified electrodes: the use of protein engineering, designer polymers, and the introduction of nanomaterials. Engineering the protein or proteins that constitute the biocatalytic elements allow tuning their stability, activity, and specificity. It can also allow changing the enzyme immobilization efficiency (adsorption vs. covalent immobilization, for example). If direct electron transfer is not favorable, it may be possible to introduce polymers in the system that mediate the electron transfer to or from the electrode surface. Significant advances have recently been made on the design of polymers to modify electrodes, including molecularly imprinted polymers and responsive polymers. A third element that can be incorporated into electrodes is nanoparticles. These nanomaterials can act as scaffolds to immobilize the biocatalytic elements through adsorption or chem. reaction with functional groups, increasing the surface area and the robustness of the electrode. A wealth of nanomaterials is being tested as part of novel enzyme-modified electrode designs, including graphene, carbon nanotubes, metallic nanoparticles, silicas, and metal-org. frameworks. Some of these can also be designed as nanowires to enable or shorten the direct electron transfer from distal active sites in the enzymes. In addn. to these strategies, we also highlight selected applications of enzyme-modified electrodes, including glucose biosensing, self-powered biosensors, and self-charging biosupercapacitors. We conclude the review with a reflection on novel approaches, applications, and challenges that we foresee can impact how to design the enzyme-modified electrodes of tomorrow.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXntVSrtLY%253D&md5=4bc2b099a63cce0be35d935547dc72b9
  19. 19
    Mateo, C.; Palomo, J. M.; Fernandez-Lorente, G.; Guisan, J. M.; Fernandez-Lafuente, R. Improvement of Enzyme Activity, Stability and Selectivity Via Immobilization Techniques. Enzyme Microb. Technol. 2007, 40, 1451– 1463,  DOI: 10.1016/j.enzmictec.2007.01.018
    Google Scholar
    19
    Improvement of enzyme activity, stability and selectivity via immobilization techniques
    Mateo, Cesar; Palomo, Jose M.; Fernandez-Lorente, Gloria; Guisan, Jose M.; Fernandez-Lafuente, Roberto
    Enzyme and Microbial Technology (2007), 40 (6), 1451-1463CODEN: EMTED2; ISSN:0141-0229. (Elsevier B.V.)
    A review. In spite of their excellent catalytic properties, enzyme properties usually have to be improved before their implementation at industrial scale (where many cycles of high yield processes are desired). Generally, sol. enzymes have to be immobilized to be reused for long times in industrial reactors and, in addn. to that, some other crit. enzyme properties have to be improved like stability, activity, inhibition by reaction products, and selectivity toward non-natural substrates. Some strategies to improve these enzyme properties during the performance of tailor-made enzyme immobilization protocols are reviewed here. In this way, immobilized enzymes may also exhibit much better functional properties than the corresponding sol. enzymes by very simple immobilization protocols. For example, multi-point and multi-subunit covalent immobilization improve the stability of monomeric or multimeric enzymes. Moreover, enantioselectivity of different enzymes (e.g., lipases) may be also dramatically improved (from E = 1 to >100) by performing different immobilization protocols on the same enzyme. In all cases, enzyme engineering via immobilization techniques is perfectly compatible with other chem. or biol. approaches to improve enzyme functions and the final success depend on the availability of a wide battery of immobilization protocols.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXjsleisbk%253D&md5=7f09d763070f2e9ce47051f04cab3101
  20. 20
    Jesionowski, T.; Zdarta, J.; Krajewska, B. Enzyme Immobilization by Adsorption: A Review. Adsorption 2014, 20, 801– 821,  DOI: 10.1007/s10450-014-9623-y
    Google Scholar
    20
    Enzyme immobilization by adsorption: a review
    Jesionowski, Teofil; Zdarta, Jakub; Krajewska, Barbara
    Adsorption (2014), 20 (5-6), 801-821CODEN: ADSOFO; ISSN:0929-5607. (Springer)
    A review. Endowed with unparalleled high catalytic activity and selectivity, enzymes offer enormous potential as catalysts in practical applications. These applications, however, are seriously hampered by enzymes' low thermal and chem. stabilities. One way to improve these stabilities is the enzyme immobilization. Among various tested methods of this process that make use of different enzyme-carrier interactions, immobilization by adsorption on solid carriers has appeared most common. According to these findings, in this review we present a comparative anal. of the literature reports on the recent trends in the immobilization of the enzymes by adsorption. This thorough study was prepd. in order to provide a deeper understanding of the process. Both carriers, carrier modifiers and procedures developed for effective adsorption of the enzymes are discussed. The review may thus be helpful in choosing the right adsorption scheme for a given enzyme to achieve the improvement of its stability and activity for a specific application.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtVGgsbvJ&md5=3501929307ec70fb7c06df11fb45213c
  21. 21
    Tello, A.; Cao, R.; Marchant, M. J.; Gomez, H. Conformational Changes of Enzymes and Aptamers Immobilized on Electrodes. Bioconjugate Chem. 2016, 27, 2581– 2591,  DOI: 10.1021/acs.bioconjchem.6b00553
    Google Scholar
    21
    Conformational Changes of Enzymes and Aptamers Immobilized on Electrodes
    Tello, Alejandra; Cao, Roberto; Marchant, Maria Jose; Gomez, Humberto
    Bioconjugate Chemistry (2016), 27 (11), 2581-2591CODEN: BCCHES; ISSN:1043-1802. (American Chemical Society)
    A review. Conformation constitutes a vital property of biomols., esp. in the cases of enzymes and aptamers, and is essential in defining their mol. recognition ability. When biomols. are immobilized on electrode surfaces, it is very important to have a control on all the possible conformational changes that may occur, either upon the recognition of their targets or by undesired alterations. Both, enzymes and aptamers, immobilized on electrodes are susceptible to conformational changes as a response to the nature of the charge of the surface and of the surrounding environment (pH, temp., ionic strength, etc.). The main goal of this review is to analyze how the conformational changes of enzymes and aptamers immobilized on electrode surfaces have been treated in reports on biosensors and biofuel cells. This topic was selected due to an insufficient information found on the actual conformational changes involved in the function of these bioelectrochem. devices despite its importance.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1yjtb7P&md5=b00a7df3bbe14fd7c4cff3b7d56ecb13
  22. 22
    Ohayon, D.; Nikiforidis, G.; Savva, A.; Giugni, A.; Wustoni, S.; Palanisamy, T.; Chen, X.; Maria, I. P.; Di Fabrizio, E.; Costa, P. M. F. J.; McCulloch, I.; Inal, S. Biofuel Powered Glucose Detection in Bodily Fluids with an N-Type Conjugated Polymer. Nat. Mater. 2020, 19, 456– 463,  DOI: 10.1038/s41563-019-0556-4
    Google Scholar
    22
    Biofuel powered glucose detection in bodily fluids with an n-type conjugated polymer
    Ohayon, David; Nikiforidis, Georgios; Savva, Achilleas; Giugni, Andrea; Wustoni, Shofarul; Palanisamy, Tamilarasan; Chen, Xingxing; Maria, Iuliana Petruta; Di Fabrizio, Enzo; Costa, Pedro M. F. J.; McCulloch, Iain; Inal, Sahika
    Nature Materials (2020), 19 (4), 456-463CODEN: NMAACR; ISSN:1476-1122. (Nature Research)
    A promising class of materials for applications that rely on electron transfer for signal generation are the n-type semiconducting polymers. Here we demonstrate the integration of an n-type conjugated polymer with a redox enzyme for the autonomous detection of glucose and power generation from bodily fluids. The reversible, mediator-free, miniaturized glucose sensor is an enzyme-coupled org. electrochem. transistor with a detection range of six orders of magnitude. This n-type polymer is also used as an anode and paired with a polymeric cathode in an enzymic fuel cell to convert the chem. energy of glucose and oxygen into elec. power. The all-polymer biofuel cell shows a performance that scales with the glucose content in the soln. and a stability that exceeds 30 days. Moreover, at physiol. relevant glucose concns. and from fluids such as human saliva, it generates enough power to operate an org. electrochem. transistor, thus contributes to the technol. advancement of self-powered micrometre-scale sensors and actuators that run on metabolites produced in the body.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVertb3E&md5=c407e831fb7cc6f65ee35cc607157024
  23. 23
    Pappa, A. M.; Ohayon, D.; Giovannitti, A.; Maria, I. P.; Savva, A.; Uguz, I.; Rivnay, J.; McCulloch, I.; Owens, R. M.; Inal, S. Direct Metabolite Detection with an N-Type Accumulation Mode Organic Electrochemical Transistor. Sci. Adv. 2018, 4, eaat0911  DOI: 10.1126/sciadv.aat0911
    Google Scholar
    There is no corresponding record for this reference.
  24. 24
    Savva, A.; Ohayon, D.; Surgailis, J.; Paterson, A. F.; Hidalgo, T. C.; Chen, X.; Maria, I. P.; Paulsen, B. D.; Petty, A. J., II; Rivnay, J.; McCulloch, I.; Inal, S. Solvent Engineering for High-Performance N-Type Organic Electrochemical Transistors. Adv. Electron. Mater. 2019, 5, 1900249,  DOI: 10.1002/aelm.201900249
    Google Scholar
    There is no corresponding record for this reference.
  25. 25
    Druet, V.; Nayak, P. D.; Koklu, A.; Ohayon, D.; Hama, A.; Chen, X.; Moser, M.; McCulloch, I.; Inal, S. Operation Mechanism of N-Type Organic Electronic Metabolite Sensors. Adv. Electron. Mater. 2022, 8, 2200065,  DOI: 10.1002/aelm.202200065
    Google Scholar
    25
    Operation Mechanism of n-Type Organic Electronic Metabolite Sensors
    Druet, Victor; Nayak, Prem D.; Koklu, Anil; Ohayon, David; Hama, Adel; Chen, Xingxing; Moser, Maximilian; McCulloch, Iain; Inal, Sahika
    Advanced Electronic Materials (2022), 8 (10), 2200065CODEN: AEMDBW; ISSN:2199-160X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The integration of n-type (electron-transporting) polymers with oxidase enzymes has allowed building high-performance org. electrochem. transistor (OECT) based metabolite sensors. Yet, the operation mechanism of these devices is poorly understood. Here, the process is investigated for the conversion of metabolite oxidn. to elec. current in an n-type org. electrochem. transistor (n-OECT). By monitoring oxygen (O2), hydrogen peroxide, and pH changes in the electrolyte as well as the potential of each elec. contact of the n-OECT during glucose detection, light is shed on the phys. phenomena occurring at the polymer-enzyme interface. It is shown that the n-type film performs O2 redn. reaction in its doped state and that the n-OECT characteristics are sensitive to O2. A correlation is found between the consumption of electrolyte-dissolved O2 and the generation of n-OECT current during the metabolite oxidn. The results demonstrate how the sensitivity of a polymer to O2, species known to deteriorate the performance of many semiconductor devices, becomes a feature to exploit in sensor applications. The importance of in operando anal. of the electrolyte compn. and the terminal potentials is highlighted for understanding the operation mechanism of bioelectronic devices and for sensor design and materials development.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhsFCisbnP&md5=3051c68d3d8131a162f8a2c46f3acde7
  26. 26
    Feng, K.; Shan, W.; Wang, J.; Lee, J.-W.; Yang, W.; Wu, W.; Wang, Y.; Kim, B. J.; Guo, X.; Guo, H. Cyano-Functionalized N-Type Polymer with High Electron Mobility for High-Performance Organic Electrochemical Transistors. Adv. Mater. 2022, 34, 2201340,  DOI: 10.1002/adma.202201340
    Google Scholar
    26
    Cyano-functionalized n-type polymer with high electron mobility for high-performance organic electrochemical transistors
    Feng, Kui; Shan, Wentao; Wang, Junwei; Lee, Jin-Woo; Yang, Wanli; Wu, Wenchang; Wang, Yimei; Kim, Bumjoon J.; Guo, Xugang; Guo, Han
    Advanced Materials (Weinheim, Germany) (2022), 34 (24), 2201340CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    N-Type org. mixed ionic-electronic conductors (OMIECs) with high electron mobility are scarce and highly challenging to develop. As a result, the figure-of-merit (μC*) of n-type org. electrochem. transistors (OECTs) lags far behind the p-type analogs, restraining the development of OECT-based low-power complementary circuits and biosensors. Here, two n-type donor-acceptor (D-A) polymers based on fused bithiophene imide dimer f-BTI2 as the acceptor unit and thienylene-vinylene-thienylene (TVT) as the donor co-unit are reported. The cyanation of TVT enables polymer f-BTI2g-TVTCN with simultaneously enhanced ion-uptake ability, film structural order, and charge-transport property. As a result, it is able to obtain a high volumetric capacitance (C*) of 170 ± 22 F cm-3 and a record OECT electron mobility (μe,OECT) of 0.24 cm2 V-1 s-1 for f-BTI2g-TVTCN, subsequently achieving a state-of-the-art μC* of 41.3 F cm-1 V-1 s-1 and geometry-normalized transconductance (gm,norm) of 12.8 S cm-1 in n-type accumulation-mode OECTs. In contrast, only a moderate μC* of 1.50 F cm-1 V-1 s-1 is measured for the non-cyanated polymer f-BTI2g-TVT. These remarkable results demonstrate the great power of cyano functionalization of polymer semiconductors in developing n-type OMIECs with substantial electron mobility in aq. environment for high-performance n-type OECTs.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhtlGktbnO&md5=1ba499f4b6ddc43f8a0dbbc0b5c47b2c
  27. 27
    Wu, H.-Y.; Yang, C.-Y.; Li, Q.; Kolhe, N. B.; Strakosas, X.; Stoeckel, M.-A.; Wu, Z.; Jin, W.; Savvakis, M.; Kroon, R.; Tu, D.; Woo, H. Y.; Berggren, M.; Jenekhe, S. A.; Fabiano, S. Influence of Molecular Weight on the Organic Electrochemical Transistor Performance of Ladder-Type Conjugated Polymers. Adv. Mater. 2022, 34, 2106235,  DOI: 10.1002/adma.202106235
    Google Scholar
    27
    Influence of Molecular Weight on the Organic Electrochemical Transistor Performance of Ladder-Type Conjugated Polymers
    Wu, Han-Yan; Yang, Chi-Yuan; Li, Qifan; Kolhe, Nagesh B.; Strakosas, Xenofon; Stoeckel, Marc-Antoine; Wu, Ziang; Jin, Wenlong; Savvakis, Marios; Kroon, Renee; Tu, Deyu; Woo, Han Young; Berggren, Magnus; Jenekhe, Samson A.; Fabiano, Simone
    Advanced Materials (Weinheim, Germany) (2022), 34 (4), 2106235CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Org. electrochem. transistors (OECTs) hold promise for developing a variety of high-performance (bio-)electronic devices/circuits. While OECTs based on p-type semiconductors have achieved tremendous progress in recent years, n-type OECTs still suffer from low performance, hampering the development of power-efficient electronics. Here, it is demonstrated that fine-tuning the mol. wt. of the rigid, ladder-type n-type polymer poly(benzimidazobenzophenanthroline) (BBL) by only one order of magnitude (from 4.9 to 51 kDa) enables the development of n-type OECTs with record-high geometry-normalized transconductance (gm,norm ≈ 11 S cm-1) and electron mobility x volumetric capacitance (μC* ≈ 26 F cm-1 V-1 s-1), fast temporal response (0.38 ms), and low threshold voltage (0.15 V). This enhancement in OECT performance is ascribed to a more efficient intermol. charge transport in high-mol.-wt. BBL than in the low-mol.-wt. counterpart. OECT-based complementary inverters are also demonstrated with record-high voltage gains of up to 100 V V-1 and ultralow power consumption down to 0.32 nW, depending on the supply voltage. These devices are among the best sub-1 V complementary inverters reported to date. These findings demonstrate the importance of mol. wt. in optimizing the OECT performance of rigid org. mixed ionic-electronic conductors and open for a new generation of power-efficient org. (bio-)electronic devices.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXislaqu7bO&md5=95e3105723d712eb9ae3f0dd684382f4
  28. 28
    Tang, H.; Liang, Y.; Liu, C.; Hu, Z.; Deng, Y.; Guo, H.; Yu, Z.; Song, A.; Zhao, H.; Zhao, D.; Zhang, Y.; Guo, X.; Pei, J.; Ma, Y.; Cao, Y.; Huang, F. A Solution-Processed N-Type Conducting Polymer with Ultrahigh Conductivity. Nature 2022, 611, 271– 277,  DOI: 10.1038/s41586-022-05295-8
    Google Scholar
    28
    A solution-processed n-type conducting polymer with ultrahigh conductivity
    Tang, Haoran; Liang, Yuanying; Liu, Chunchen; Hu, Zhicheng; Deng, Yifei; Guo, Han; Yu, Zidi; Song, Ao; Zhao, Haiyang; Zhao, Duokai; Zhang, Yuanzhu; Guo, Xugang; Pei, Jian; Ma, Yuguang; Cao, Yong; Huang, Fei
    Nature (London, United Kingdom) (2022), 611 (7935), 271-277CODEN: NATUAS; ISSN:1476-4687. (Nature Portfolio)
    Conducting polymers (CPs) with high cond. and soln. processability have made great advances since the pioneering work on doped polyacetylene1-3, thus creating the new field of 'org. synthetic metals,4. Various high-performance CPs have been realized, which enable the applications of several org. electronic devices5,6. Nevertheless, most CPs exhibit hole-dominant (p-type) transport behavior7,8, whereas the development of n-type analogs lags far behind and only a few exhibit metallic state, typically limited by low doping efficiency and ambient instability. Here we present a facilely synthesized highly conductive n-type polymer poly(benzodifurandione) (PBFDO). The reaction combines oxidative polymn. and in situ reductive n-doping, greatly increasing the doping efficiency, and a doping level of almost 0.9 charges per repeating unit can be achieved. The resultant polymer exhibits a breakthrough cond. of more than 2,000 S cm-1 with excellent stability and an unexpected soln. processability without extra side chains or surfactants. Furthermore, detailed investigations on PBFDO show coherent charge-transport properties and existence of metallic state. The benchmark performances in electrochem. transistors and thermoelec. generators are further demonstrated, thus paving the way for application of the n-type CPs in org. electronics.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38Xis1eiurjK&md5=87de74d405fc23fe19c9d6feeeba535b
  29. 29
    Giovannitti, A.; Maria, I. P.; Hanifi, D.; Donahue, M. J.; Bryant, D.; Barth, K. J.; Makdah, B. E.; Savva, A.; Moia, D.; Zetek, M.; Barnes, P. R. F.; Reid, O. G.; Inal, S.; Rumbles, G.; Malliaras, G. G.; Nelson, J.; Rivnay, J.; McCulloch, I. The Role of the Side Chain on the Performance of N-Type Conjugated Polymers in Aqueous Electrolytes. Chem. Mater. 2018, 30, 2945– 2953,  DOI: 10.1021/acs.chemmater.8b00321
    Google Scholar
    29
    The Role of the Side Chain on the Performance of N-type Conjugated Polymers in Aqueous Electrolytes
    Giovannitti, Alexander; Maria, Iuliana P.; Hanifi, David; Donahue, Mary J.; Bryant, Daniel; Barth, Katrina J.; Makdah, Beatrice E.; Savva, Achilleas; Moia, Davide; Zetek, Matyas; Barnes, Piers R. F.; Reid, Obadiah G.; Inal, Sahika; Rumbles, Garry; Malliaras, George G.; Nelson, Jenny; Rivnay, Jonathan; McCulloch, Iain
    Chemistry of Materials (2018), 30 (9), 2945-2953CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    We report a design strategy that allows the prepn. of soln. processable n-type materials from low b.p. solvents for org. electrochem. transistors (OECTs). The polymer backbone is based on NDI-T2 copolymers where a branched alkyl side chain is gradually exchanged for a linear ethylene glycol-based side chain. A series of random copolymers was prepd. with glycol side chain percentages of 0, 10, 25, 50, 75, 90, and 100 with respect to the alkyl side chains. These were characterized to study the influence of the polar side chains on interaction with aq. electrolytes, their electrochem. redox reactions, and performance in OECTs when operated in aq. electrolytes. We obsd. that glycol side chain percentages of >50% are required to achieve volumetric charging, while lower glycol chain percentages show a mixed operation with high required voltages to allow for bulk charging of the org. semiconductor. A strong dependence of the electron mobility on the fraction of glycol chains was found for copolymers based on NDI-T2, with a significant drop as alkyl side chains are replaced by glycol side chains.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXotFelu7o%253D&md5=ed7e798bb78dfbee00e02f7d9a5c959d
  30. 30
    Rosas Villalva, D.; Singh, S.; Galuska, L. A.; Sharma, A.; Han, J.; Liu, J.; Haque, M. A.; Jang, S.; Emwas, A. H.; Koster, L. J. A.; Gu, X.; Schroeder, B. C.; Baran, D. Backbone-Driven Host–Dopant Miscibility Modulates Molecular Doping in Ndi Conjugated Polymers. Mater. Horiz. 2022, 9, 500– 508,  DOI: 10.1039/d1mh01357b
    Google Scholar
    30
    Backbone-driven host-dopant miscibility modulates molecular doping in NDI conjugated polymers
    Rosas Villalva, Diego; Singh, Saumya; Galuska, Luke A.; Sharma, Anirudh; Han, Jianhua; Liu, Jian; Haque, Md Azimul; Jang, Soyeong; Emwas, Abdul Hamid; Koster, L. Jan Anton; Gu, Xiaodan; Schroeder, Bob C.; Baran, Derya
    Materials Horizons (2022), 9 (1), 500-508CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
    Mol. doping is the key to enabling org. electronic devices, however, the design strategies to maximize doping efficiency demands further clarity and comprehension. Previous reports focus on the effect of the side chains, but the role of the backbone is still not well understood. In this study, we synthesize a series of NDI-based copolymers with bithiophene, vinylene, and acetylenic moieties (P1G, P2G, and P3G, resp.), all contg. branched triethylene glycol side chains. Using computational and exptl. methods, we explore the impact of the conjugated backbone using three key parameters for doping in org. semiconductors: energy levels, microstructure, and miscibility. Our exptl. results show that P1G undergoes the most efficient n-type doping owed primarily to its higher dipole moment, and better host-dopant miscibility with N-DMBI. In contrast, P2G and P3G possess more planar backbones than P1G, but the lack of long-range order, and poor host-dopant miscibility limit their doping efficiency. Our data suggest that backbone planarity alone is not enough to maximize the elec. cond. (σ) of n-type doped org. semiconductors, and that backbone polarity also plays an important role in enhancing σ via host-dopant miscibility. Finally, the thermoelec. properties of doped P1G exhibit a power factor of 0.077μW m-1 K-2, and ultra-low in-plane thermal cond. of 0.13 W m-1K-1 at 5 mol% of N-DMBI, which is among the lowest thermal cond. values reported for n-type doped conjugated polymers.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXislygur7P&md5=0c1373ff0923e96345a80c6b7ebd0bc9
  31. 31
    Singh, K.; Blanford, C. F. Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring: A Technique to Optimize Enzyme Use in Bioelectrocatalysis. ChemCatChem 2014, 6, 921– 929,  DOI: 10.1002/cctc.201300900
    Google Scholar
    31
    Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring: A Technique to Optimize Enzyme Use in Bioelectrocatalysis
    Singh, Kulveer; Blanford, Christopher F.
    ChemCatChem (2014), 6 (4), 921-929CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
    This Concept article outlines how an electrochem. quartz crystal microbalance with dissipation monitoring (E-QCM-D) is used as a tool to follow adsorption and inactivation processes of immobilized oxidoreductases and to det. their specific activity simultaneously. Plots that relate activity to the adsorbed mass and dissipation have distinct features that can be used to diagnose the mechanisms of long-term activity loss. Along with model plots, this article highlights some of the key advances made by using the technique and how it has been applied to biocatalytic processes in which electrons are transferred directly between an electrode and an immobilized enzyme.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlt1Wgu7s%253D&md5=1cbcb457e1ab07822d93ab72de21e54f
  32. 32
    Wiedemann, C.; Bellstedt, P.; Görlach, M. Capito─a Web Server-Based Analysis and Plotting Tool for Circular Dichroism Data. Bioinformatics 2013, 29, 1750– 1757,  DOI: 10.1093/bioinformatics/btt278
    Google Scholar
    32
    CAPITO-a web server-based analysis and plotting tool for circular dichroism data
    Wiedemann, Christoph; Bellstedt, Peter; Goerlach, Matthias
    Bioinformatics (2013), 29 (14), 1750-1757CODEN: BOINFP; ISSN:1367-4803. (Oxford University Press)
    Motivation: CD (CD) spectroscopy is one of the most versatile tools to study protein folding and to validate the proper fold of purified proteins. Here, we aim to provide a readily accessible, user-friendly and platform-independent tool capable of analyzing multiple CD datasets of virtually any format and returning results as high-quality graphical output to the user. Results: CAPITO (CD Anal. and Plotting Tool) is a novel web server-based tool for analyzing and plotting CD data. It allows reliable estn. of secondary structure content utilizing different approaches. CAPITO accepts multiple CD datasets and, hence, is well suited for a wide application range such as the anal. of temp. or pH-dependent (un)folding and the comparison of mutants.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtVOjsrjN&md5=1eedf83b9d1dd24330e87eb8dafff1b7
  33. 33
    Koklu, A.; Wustoni, S.; Musteata, V.-E.; Ohayon, D.; Moser, M.; McCulloch, I.; Nunes, S. P.; Inal, S. Microfluidic Integrated Organic Electrochemical Transistor with a Nanoporous Membrane for Amyloid-Β Detection. ACS Nano 2021, 15, 8130– 8141,  DOI: 10.1021/acsnano.0c09893
    Google Scholar
    33
    Microfluidic Integrated Organic Electrochemical Transistor with a Nanoporous Membrane for Amyloid-β Detection
    Koklu, Anil; Wustoni, Shofarul; Musteata, Valentina-Elena; Ohayon, David; Moser, Maximilian; McCulloch, Iain; Nunes, Suzana P.; Inal, Sahika
    ACS Nano (2021), 15 (5), 8130-8141CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Alzheimer's disease (AD) is a neurodegenerative disorder assocd. with a severe loss in thinking, learning, and memory functions of the brain. To date, no specific treatment has been proven to cure AD, with the early diagnosis being vital for mitigating symptoms. A common pathol. change found in AD-affected brains is the accumulation of a protein named amyloid-β (Aβ) into plaques. In this work, we developed a micron-scale org. electrochem. transistor (OECT) integrated with a microfluidic platform for the label-free detection of Aβ aggregates in human serum. The OECT channel-electrolyte interface was covered with a nanoporous membrane functionalized with Congo red (CR) mols. showing a strong affinity for Aβ aggregates. Each aggregate binding to the CR-membrane modulated the vertical ion flow toward the channel, changing the transistor characteristics. Thus, the device performance was not limited by the soln. ionic strength nor did it rely on Faradaic reactions or conformational changes of bioreceptors. The high transconductance of the OECT, the precise porosity of the membrane, and the compactness endowed by the microfluidic enabled the Aβ aggregate detection over eight orders of magnitude wide concn. range (femtomolar-nanomolar) in 1μL of human serum samples. We expanded the operation modes of our transistors using different channel materials and found that the accumulation-mode OECTs displayed the lowest power consumption and highest sensitivities. Ultimately, these robust, low-power, sensitive, and miniaturized microfluidic sensors helped to develop point-of-care tools for the early diagnosis of AD.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXnsVOhtr0%253D&md5=6707b09f300ef21444a3df82453c8c05
  34. 34
    Attwood, S. J.; Kershaw, R.; Uddin, S.; Bishop, S. M.; Welland, M. E. Understanding How Charge and Hydrophobicity Influence Globular Protein Adsorption to Alkanethiol and Material Surfaces. J. Mater. Chem. B 2019, 7, 2349– 2361,  DOI: 10.1039/c9tb00168a
    Google Scholar
    34
    Understanding how charge and hydrophobicity influence globular protein adsorption to alkanethiol and material surfaces
    Attwood, Simon J.; Kershaw, Rebecca; Uddin, Shahid; Bishop, Steven M.; Welland, Mark E.
    Journal of Materials Chemistry B: Materials for Biology and Medicine (2019), 7 (14), 2349-2361CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
    Every biosensor, bioengineered scaffold or biomedical implant depends crucially on an ability to control protein adsorption at the material surface. Yet the adsorption of proteins to solid surfaces in aq. media is a complex and poorly understood phenomenon. To gain further insights the authors study protein adsorption using the quartz crystal microbalance for 10 model globular proteins interacting with pos., neg., neutral, hydrophobic and mixed alkanethiol monolayers as well as silica, polystyrene and Teflon, equating to ∼200 protein-surface combinations. The charge state of the materials in liq. was measured with at. force microscopy using a colloidal probe and numerically solving the full non-linear Poisson-Boltzmann equation. This approach has allowed the authors to address some of the important questions surrounding the basic principles that govern protein adsorption including the relative importance of net charge and hydrophobicity and why some materials are protein resistant. With the authors' set of mixed monolayer surfaces, the authors can modulate charge over a wide range while eliminating hydrophobic interactions and vice versa - thus permitting detn. of the functional dependence of adsorption on these parameters. This led the authors to develop two empirical predictive models with up to 90% accuracy that together encompass most materials relevant to biotechnol. and biomedical applications.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXjvFSrtb4%253D&md5=f0d012683958f7558a81c96cbe731814
  35. 35
    Xie, Y.; Li, Z.; Zhou, J. Hamiltonian Replica Exchange Simulations of Glucose Oxidase Adsorption on Charged Surfaces. Phys. Chem. Chem. Phys. 2018, 20, 14587– 14596,  DOI: 10.1039/c8cp00530c
    Google Scholar
    35
    Hamiltonian replica exchange simulations of glucose oxidase adsorption on charged surfaces
    Xie, Yun; Li, Zhanchao; Zhou, Jian
    Physical Chemistry Chemical Physics (2018), 20 (21), 14587-14596CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    The Hamiltonian replica exchange Monte Carlo (H-REMC) algorithm was applied to study protein adsorption and its performance was compared with that of the temp. replica exchange Monte Carlo (T-REMC). Comparisons indicate that the simulation results are consistent but the computational efficiency is improved for H-REMC. H-REMC could accurately and efficiently identify the preferred orientations of glucose oxidase (GOx) on charged surfaces; different preferential GOx orientations on different surfaces and soln. conditions could be spotted with a much fewer no. of simulation runs. On pos. charged surfaces, when electrostatic interactions dominate, the neg. charged GOx can be easily adsorbed with the "standing" orientation for which the substrate-binding domain is accessible to substrates. As the surface charge densities decrease and ionic strengths increase, there is an increasing contribution from the van der Waals (vdW) interactions, and thus more possible orientations appear. When the vdW interactions dominate, the unfavorable "front-lying" becomes the preferred orientation for which the substrate-binding domain is blocked by the surface. On neg. charged surfaces, though GOx has a net charge of -30 e under physiol. conditions, the charged groups are unevenly distributed over the protein surface; the pos. potential regions in the "back" of GOx enable the protein to be adsorbed on neg. charged surfaces with the "back-lying" orientation. The H-REMC provides an alternative method to accurately and efficiently probe the lowest-energy orientation of proteins adsorbed on surfaces for biotechnol. applications.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXotVeht7k%253D&md5=2ad32de202c0a3364283aa780673d8da
  36. 36
    Cho, D. H.; Xie, T.; Truong, J.; Stoner, A. C.; Hahm, J.-i. Recent Advances Towards Single Biomolecule Level Understanding of Protein Adsorption Phenomena Unique to Nanoscale Polymer Surfaces with Chemical Variations. Nano Res. 2020, 13, 1295– 1317,  DOI: 10.1007/s12274-020-2735-7
    Google Scholar
    36
    Recent advances towards single biomolecule level understanding of protein adsorption phenomena unique to nanoscale polymer surfaces with chemical variations
    Cho, David H.; Xie, Tian; Truong, Johnson; Stoner, Andrew C.; Hahm, Jong-in
    Nano Research (2020), 13 (5), 1295-1317CODEN: NRAEB5; ISSN:1998-0000. (Springer GmbH)
    A review. Abstr.: Protein adsorption onto polymer surfaces is a very complex and ubiquitous phenomenon whose integrated process impacts essential applications in our daily lives such as food packaging materials, health devices, diagnostic tools, and medical products. Increasingly, novel polymer materials with greater chem. intricacy and reduced dimensionality are used for various applications involving adsorbed proteins on their surfaces. Hence, the nature of protein-surface interactions to consider is becoming much more complicated than before. A large body of literature exists for protein adsorption. However, most of these investigations have focused on collectively measured, ensemble-averaged protein behaviors that occur on macroscale and chem. unvarying polymer surfaces instead of direct measurements at the single protein or sub-protein level. In addn., interrogations of protein-polymer adsorption boundaries in these studies were typically carried out by indirect methods, whose insights may not be suitably applied for explaining individual protein adsorption processes occurring onto nanostructured, chem. varying polymer surfaces. Therefore, an important gap in our knowledge still exists that needs to be systematically addressed via direct measurement means at the single protein and sub-protein level. Such efforts will require multifaceted exptl. and theor. approaches that can probe multilength scales of protein adsorption, while encompassing both single proteins and their collective ensemble behaviors at the length scale spanning from the nanoscopic all the way to the macroscopic scale. In this review, key research achievements in nanoscale protein adsorption to date will be summarized. Specifically, protein adsorption studies involving polymer surfaces with their defining feature dimensions and assocd. chem. partitions comparable to the size of individual proteins will be discussed in detail. In this regard, recent works bridging the crucial knowledge gap in protein adsorption will be highlighted. New findings of intriguing protein surface assembly behaviors and adsorption kinetics unique to nanoscale polymer templates will be covered. Single protein and sub-protein level approaches to reveal unique nanoscale protein-polymer surface interactions and protein surface assembly characteristics will be also emphasized. Potential advantages of these research endeavors in laying out fundamentally guided design principles for practical product development will then be discussed. Lastly, important research areas still needed to further narrow the knowledge gap in nanoscale protein adsorption will be identified. [graphic not available: see fulltext].
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXlvVyjtr8%253D&md5=dfd2729e35dc40e8539cba3fd651c3b3
  37. 37
    Seehuber, A.; Dahint, R. Conformation and Activity of Glucose Oxidase on Homogeneously Coated and Nanostructured Surfaces. J. Phys. Chem. B 2013, 117, 6980– 6989,  DOI: 10.1021/jp401906h
    Google Scholar
    37
    Conformation and Activity of Glucose Oxidase on Homogeneously Coated and Nanostructured Surfaces
    Seehuber, A.; Dahint, R.
    Journal of Physical Chemistry B (2013), 117 (23), 6980-6989CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
    Protein unfolding and loss of protein function upon surface contact is a major problem in biotechnol. and biomedicine. Using glucose oxidase (GOx) as a model protein, we investigated the impact of surface chem., topog., and confinement on enzyme activity, conformation, and affinity. A particular focus lay on the question whether the conformation of surface-bound proteins can be stabilized by embedding nanoscale adsorption sites, here in the form of monodisperse gold nanoparticles (AuNPs), into a protein-repelling matrix material. It was found that on homogeneous surfaces, GOx activity is generally lower than that in its native state and strongly affected by surface chem. Loss of activity is related to an increasing amt. of β-sheets in the GOx secondary structure and a corresponding redn. of α-helical elements. In contrast, on AuNP surfaces, the effect of surface chem. is negligible, and the amt. of adsorbed protein only depends on particle size. The low activity of GOx on all nanostructures studied is again accompanied by an increase of β-sheet and a redn. of α-helical secondary structure. The major cause for protein unfolding on AuNPs thus seems to be the curvature of the surface. In addn., the data suggest that unfavorable orientation of the adsorbed enzyme also contributes to the loss of activity.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXnvVKgsr4%253D&md5=3b263957157b293a23fd8b7e0cdd52b3
  38. 38
    Han, M.; Sethuraman, A.; Kane, R. S.; Belfort, G. Nanometer-Scale Roughness Having Little Effect on the Amount or Structure of Adsorbed Protein. Langmuir 2003, 19, 9868– 9872,  DOI: 10.1021/la030132g
    Google Scholar
    38
    Nanometer-scale roughness having little effect on the amount or structure of adsorbed protein
    Han, Mina; Sethuraman, Ananthakrishnan; Kane, Ravi S.; Belfort, Georges
    Langmuir (2003), 19 (23), 9868-9872CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Neither the adsorbed amt. per unit actual surface area nor the structural stability of hen egg lysozyme is influenced by increasing the nanometer-scale roughness (5 < Rave < 60 nm) of a series of model substrates. Seven poly(ether sulfone) (PES) ultrafiltration membranes of increasing mean pore size with the same surface chem. were chosen as model rough surface substrates. Topog. images, using at. force microscopy, combined with attenuated total reflection Fourier transform IR spectroscopy (ATR/FTIR) and sessile captive bubble contact angle measurements were used to characterize the surface properties of the substrates. ATR/FTIR spectroscopy together with a newly developed optimization algorithm for predicting the content of secondary structure motifs is used to correlate the secondary structure and amt. of adsorbed lysozyme with the substrate surface roughness. From the adsorption measurements, the net adsorbed amt. (total minus nonspecific adsorbed amt.) of lysozyme corresponded to approx. one monolayer of coverage for all the substrates independent of the roughness. Although lysozyme was structurally disturbed through adsorption to PES substrates, no significant changes in its secondary structure were obsd. with the increasing roughness.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXnsl2ntb0%253D&md5=16dcf1d1af81c3cd9cac5e1a01403ffb
  39. 39
    Nelson, G. W.; Parker, E. M.; Singh, K.; Blanford, C. F.; Moloney, M. G.; Foord, J. S. Surface Characterization and in Situ Protein Adsorption Studies on Carbene-Modified Polymers. Langmuir 2015, 31, 11086– 11096,  DOI: 10.1021/acs.langmuir.5b01644
    Google Scholar
    39
    Surface Characterization and in situ Protein Adsorption Studies on Carbene-Modified Polymers
    Nelson, Geoffrey W.; Parker, Emily M.; Singh, Kulveer; Blanford, Christopher F.; Moloney, Mark G.; Foord, John S.
    Langmuir (2015), 31 (40), 11086-11096CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Polystyrene thin films were functionalized using a facile two-step chem. protocol involving carbene insertion followed by azo-coupling, permitting the introduction of a range of chem. functional groups, including aniline, hexyl, amine, carboxyl, Ph, phosphonate diester, and ethylene glycol. XPS confirmed the success of the two-step chem. modification with a grafting d. of at least 1/10th of the typical loading d. (1014-1015) of a self-assembled monolayer (SAM). In situ, real-time quartz crystal microbalance with dissipation (QCM-D) studies show that the dynamics of binding of bovine serum albumin (BSA) are different at each modified surface. Mass, viscoelastic, and kinetic data were analyzed, and compared to cheminformatic descriptors (i.e., c log P, polar surface area) typically used for drug discovery. Results show that functionalities may either resist or adsorb BSA, and uniquely influence its adsorption dynamics. It is concluded that carbene-based surface modification can usefully influence BSA binding dynamics in a manner consistent with, and more robust than, traditional systems based on SAM chem.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFejtL%252FF&md5=d50f614724ddf6468c214797815d087e
  40. 40
    Hecht, H.; Kalisz, H.; Hendle, J.; Schmid, R.; Schomburg, D. Crystal Structure of Glucose Oxidase from Aspergillus niger Refined at 2·3 Å Reslution. J. Mol. Biol. 1993, 229, 153– 172,  DOI: 10.1006/jmbi.1993.1015
    Google Scholar
    40
    Crystal structure of glucose oxidase from Aspergillus niger refined at 2.3 Å resolution
    Hecht, H. J.; Kalisz, H. M.; Hendle, J.; Schmid, R. D.; Schomburg, D.
    Journal of Molecular Biology (1993), 229 (1), 153-72CODEN: JMOBAK; ISSN:0022-2836.
    Glucose oxidase (EC 1.1.3.4) is an FAD-dependent enzyme that catalyzes the oxidn. of β-D-glucose by O2. The crystal structure of the partially deglycosylated enzyme from A. niger was detd. by isomorphous replacement and refined to 2.3 Å resoln. The final crystallog. R-value was 18.1% for reflections between 10.0 and 2.3 Å resoln. The refined model included 580 amino acid residues, the FAD cofactor, 6 N-acetylglucosamine residues, 3 mannose residues, and 152 solvent mols. The FAD-binding domain was topol. very similar to other FAD-binding proteins. The substrate-binding domain was formed from noncontinuous segments of sequence and was characterized by a deep pocket. One side of this pocket was formed by a 6-stranded antiparallel β-sheet with the flavin ring system of FAD located at the bottom of the pocket on the opposite side. Part of the entrance to the active site pocket was at the interface to the 2nd subunit of the dimeric enzyme and was formed by a 20-residue lid, which in addn. covered parts of the FAD-binding site. The carbohydrate moiety attached to Asn-89 at the tip of this lid formed a link between the subunits of the dimer.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXpslSqsg%253D%253D&md5=5ab908e41cb0fffa2b18a07e3e4a364e
  41. 41
    Jensen, U. B.; Ferapontova, E. E.; Sutherland, D. S. Quantifying Protein Adsorption and Function at Nanostructured Materials: Enzymatic Activity of Glucose Oxidase at Glad Structured Electrodes. Langmuir 2012, 28, 11106– 11114,  DOI: 10.1021/la3017672
    Google Scholar
    41
    Quantifying Protein Adsorption and Function at Nanostructured Materials: Enzymatic Activity of Glucose Oxidase at GLAD Structured Electrodes
    Jensen, Uffe B.; Ferapontova, Elena E.; Sutherland, Duncan S.
    Langmuir (2012), 28 (30), 11106-11114CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Nanostructured materials strongly modulate the behavior of adsorbed proteins; however, the characterization of such interactions is challenging. Here the authors present a novel method combining protein adsorption studies at nanostructured quartz crystal microbalance sensor surfaces (QCM-D) with optical (surface plasmon resonance SPR) and electrochem. methods (cyclic voltammetry CV) allowing quantification of both bound protein amt. and activity. The redox enzyme glucose oxidase was studied as a model system to explore alterations in protein functional behavior caused by adsorption onto flat and nanostructured surfaces. This enzyme and such materials interactions are relevant for biosensor applications. Novel nanostructured gold electrode surfaces with controlled curvature were fabricated using colloidal lithog. and glancing angle deposition (GLAD). The adsorption of enzyme to nanostructured interfaces is significantly larger compared to flat interfaces even after normalization for the increased surface area, and no substantial desorption was obsd. within 24 h. A decreased enzymic activity was obsd. over the same period of time, which indicates a slow conformational change of the adsorbed enzyme induced by the materials interface. Addnl., the authors make use of inherent localized surface plasmon resonances in these nanostructured materials to directly quantify the protein binding. The authors hereby demonstrate a QCM-D-based methodol. to quantify protein binding at complex nanostructured materials. The authors' approach allows label free quantification of protein binding at nanostructured interfaces.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xps1GisLo%253D&md5=6c1d3461cfa0901af4db7a11118bea5e
  42. 42
    Bergman, J.; Wang, Y.; Wigström, J.; Cans, A.-S. Counting the Number of Enzymes Immobilized onto a Nanoparticle-Coated Electrode. Anal. Bioanal. Chem. 2018, 410, 1775– 1783,  DOI: 10.1007/s00216-017-0829-1
    Google Scholar
    42
    Counting the number of enzymes immobilized onto a nanoparticle-coated electrode
    Bergman, Jenny; Wang, Yuanmo; Wigstroem, Joakim; Cans, Ann-Sofie
    Analytical and Bioanalytical Chemistry (2018), 410 (6), 1775-1783CODEN: ABCNBP; ISSN:1618-2642. (Springer)
    To immobilize enzymes at the surface of a nanoparticle-based electrochem. sensor is a common method to construct biosensors for nonelectroactive analytes. Studying the interactions between the enzymes and nanoparticle support is of great importance in optimizing the conditions for biosensor design. This can be achieved by using a combination of anal. methods to carefully characterize the enzyme nanoparticle coating at the sensor surface while studying the optimal conditions for enzyme immobilization. From this anal. approach, it was found that controlling the enzyme coverage to a monolayer was a key factor to significantly improve the temporal resoln. of biosensors. However, these characterization methods involve both tedious methodologies and working with toxic cyanide solns. Here the authors introduce a new anal. method that allows direct quantification of the no. of immobilized enzymes (glucose oxidase) at the surface of a gold nanoparticle coated glassy carbon electrode. This was achieved by exploiting an electrochem. stripping method for the direct quantification of the d. and size of gold nanoparticles coating the electrode surface and combining this information with quantification of fluorophore-labeled enzymes bound to the sensor surface after stripping off their nanoparticle support. This method is both significantly much faster compared to previously reported methods and with the advantage that this method presented is nontoxic.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXitVCmsb3E&md5=af1e9459012d64ebcd9941afa09cfe1e
  43. 43
    Wang, Y.; Jonkute, R.; Lindmark, H.; Keighron, J. D.; Cans, A.-S. Molecular Crowding and a Minimal Footprint at a Gold Nanoparticle Support Stabilize Glucose Oxidase and Boost Its Activity. Langmuir 2020, 36, 37– 46,  DOI: 10.1021/acs.langmuir.9b02863
    Google Scholar
    43
    Molecular crowding and a minimal footprint at a gold nanoparticle support stabilize glucose oxidase and boost its activity
    Wang, Yuanmo; Jonkute, Rima; Lindmark, Hampus; Keighron, Jacqueline D.; Cans, Ann-Sofie
    Langmuir (2020), 36 (1), 37-46CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Enzymes conjugated to nanomaterials are used in the design of various biotechnologies. In the development of biosensors, surface modifications with the enzyme glucose oxidase (GOx) serve to aid the detection of blood glucose. In order to optimize sensor effectiveness, the enzyme tertiary structure needs to be preserved upon immobilization to retain the enzyme's catalytic activity. Because of the nature of GOx, it suffers from a tendency to denature when immobilized at a solid surface; hence, methods to optimize enzyme stability are of great importance. Here, we introduce the study of the interaction of GOx to the highly curved surface of 20 nm gold nanoparticles (AuNP) with an absorbed monolayer coating of enzyme as detd. by flocculation assays and quantification of immobilized GOx at the nanoparticle surface. Enzyme crowding was detd. by comparing the no. of enzymes that bind to how many can phys. fit. These measurements show how placing a monolayer of enzyme where the enzyme spreads thin at the AuNP surface still provides stable catalytic performance of up to 14 days compared to enzymes free in soln. Moreover, by the increasing enzyme d. via increasing the amt. of GOx present in soln. during the GOx/AuNP conjugation step creates a molecularly crowded environment at the highly curved nanoparticle surface. This limits the size of the enzyme footprint for attachment and shows that the activity per enzyme can be enhanced up to 300%. This is of great importance for implementing stable and sensitive sensor technologies that are constructed by enzyme-based nanoparticle scaffolds. Here, we show by using the conditions that maintain GOx structure and function when limiting the enzyme coating to an ultrathin layer, the design and construction of an ultrafast responding diagnostic sensor technol. for glucose can be achieved, which is crucial for monitoring rapid fluctuations of, for instance, glucose in the brain.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVGhtrfN&md5=17e0e462760f98852bde35651a0c4bd9
  44. 44
    Szucs, A.; Hitchens, G. D.; Bockris, J. O. M. On the Adsorption of Glucose Oxidase at a Gold Electrode. J. Electrochem. Soc. 1989, 136, 3748,  DOI: 10.1149/1.2096541
    Google Scholar
    44
    On the adsorption of glucose oxidase at a gold electrode
    Szucs, Arpad; Hitchens, G. Duncan; Bockris, John O.
    Journal of the Electrochemical Society (1989), 136 (12), 3748-55CODEN: JESOAN; ISSN:0013-4651.
    The shape and size of glucose oxidase (GO) adsorbed on a gold electrode was detd. by ellipsometry. GO is a prolate ellipsoid mol. with a major axis of 140 Å and a minor axis of 50 Å. Two orientations of the mol. on the surface were obsd.: the major axis can be perpendicular to the surface (standing position) or parallel to the surface (laying position). Above a certain coverage, enzymes in the standing position are not stable and undergo a transition to the laying position due to increasing intermol. interaction. In the laying position, the enzyme-and-substrate contact area is large, and gradual unfolding occurs, leading to a significant change in the structure of the protein. It was possible to detect direct electron transfer between a gold electrode and GO. After a short contact time, two almost overlapping electron transfer processes were distinguished, but were gradually transformed to a single response that was characteristic for adsorbed FAD, thus showing that significant changes in the protein structure occur, leading the deactivation of the enzyme.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXmtlGqsg%253D%253D&md5=d47d835f4f9214ecfa3393411eea2b6b
  45. 45
    Wang, K.-H.; Lin, W.-D.; Wu, J.-Y.; Lee, Y.-L. Conformation Transitions of Adsorbed Proteins by Interfacial Forces at an Air–Liquid Interface and Their Effect on the Catalytic Activity of Proteins. Soft Matter 2013, 9, 2717– 2722,  DOI: 10.1039/c2sm27371c
    Google Scholar
    45
    Conformation transitions of adsorbed proteins by interfacial forces at an air-liquid interface and their effect on the catalytic activity of proteins
    Wang, Ke-Hsuan; Lin, Wei-Dong; Wu, Jau-Yann; Lee, Yuh-Lang
    Soft Matter (2013), 9 (9), 2717-2722CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
    An efficient method to monitor and control the secondary structures of globular proteins is developed by adsorption of proteins from a bulk soln. onto an air-liq. interface. By controlling the concn. of a protein in the aq. phase, as well as the attractive force exerted by the template layer, the adsorption of proteins can be classified into two stages according to the variation of surface pressure. In the first stage, the proteins adsorb as a single-mol. layer. The interface-mol. interactions induce a structural transition of the adsorbed proteins into a β-sheet conformation (α/β < 0.1). The second stage is initiated by further adsorption of proteins onto the interface, forming multilayer proteins, and triggering a conformational transition into α-helix (α/β > 10). The glucose sensing expts. demonstrate that GOx with α-helix conformation has a much higher sensitivity than β-sheet GOx, attributed to its lower charge transfer resistance at the GOx-electrolyte interface. The present study not only provides a new approach to monitor, control, and design protein conformations, but also raises the importance of adsorption states of proteins in performing bio-activities at bio-interfaces.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXitVCisLc%253D&md5=a3a3455620ae43fc2a9014589fd3109b
  46. 46
    Muguruma, H.; Kase, Y.; Murata, N.; Matsumura, K. Adsorption of Glucose Oxidase onto Plasma-Polymerized Film Characterized by Atomic Force Microscopy, Quartz Crystal Microbalance, and Electrochemical Measurement. J. Phys. Chem. B 2006, 110, 26033– 26039,  DOI: 10.1021/jp063755m
    Google Scholar
    46
    Adsorption of Glucose Oxidase onto Plasma-Polymerized Film Characterized by Atomic Force Microscopy, Quartz Crystal Microbalance, and Electrochemical Measurement
    Muguruma, Hitoshi; Kase, Yoshihiro; Murata, Naoya; Matsumura, Kazunari
    Journal of Physical Chemistry B (2006), 110 (51), 26033-26039CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
    Adsorption of glucose oxidase (GOD) onto plasma-polymd. thin films (PPF) with nanoscale thickness was characterized by at. force microscopy (AFM), quartz crystal microbalance (QCM), and electrochem. measurements. The PPF surface is very flat (less than 1-nm roughness), and its properties (charge and wettability) can be easily changed while retaining the backbone structure. We focused on three types of surfaces: (1) the pristine surface of hexamethyldisiloxane (HMDS) PPF (hydrophobic and neutral surface), (2) an HMDS PPF surface with nitrogen-plasma treatment (hydrophilic and pos.-charged surface), and (3) an HMDS PPF surface treated with oxygen plasma (hydrophilic and neg.-charged surface). The AFM image showed that the GOD mols. were densely adsorbed onto surface 2 and that individual GOD mols. could be obsd. The longer axis of GOD ellipsoid mols. were aligned parallel to the surface, called the "lying position", because of electrostatic assocn. On surface 1, clusters of GOD mols. did not completely cover the original PPF surface (surface coverage was ca. 60%). The 10-nm-size step height between the GOD clusters and the PPF surface suggests that the longer axes of individual GOD mols. were aligned perpendicular to the surface, called the "standing position". On surface 3, only a few of the GOD mols. were adsorbed because of electrostatic repulsion. These results indicate that the plasma polymn. process can facilitate enhancement or redn. of protein adsorption. The AFM images show a corresponding tendency with the QCM profiles. The QCM data indicate that the adsorption behavior obeys the Langmuir isotherm equation. The amperometric biosensor characteristics of the GOD-adsorbed PPF on a platinum electrode showed an increment in the current because of enzymic reaction with glucose addn., indicating that enzyme activity was mostly retained in spite of irreversible adsorption.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xht12itb%252FJ&md5=2038a83ae3c7a40de82fbf4171d40787
  47. 47
    Fogel, R.; Mashazi, P.; Nyokong, T.; Limson, J. Critical Assessment of the Quartz Crystal Microbalance with Dissipation as an Analytical Tool for Biosensor Development and Fundamental Studies: Metallophthalocyanine–Glucose Oxidase Biocomposite Sensors. Biosens. Bioelectron. 2007, 23, 95– 101,  DOI: 10.1016/j.bios.2007.03.012
    Google Scholar
    47
    Critical assessment of the Quartz Crystal Microbalance with Dissipation as an analytical tool for biosensor development and fundamental studies: Metallophthalocyanine-glucose oxidase biocomposite sensors
    Fogel, R.; Mashazi, P.; Nyokong, T.; Limson, J.
    Biosensors & Bioelectronics (2007), 23 (1), 95-101CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)
    One of the challenges in electrochem. biosensor design is gaining a fundamental knowledge of the processes underlying immobilization of the mols. onto the electrode surface. This is of particular importance in biocomposite sensors where concerns have arisen as to the nature of the interaction between the biol. and synthetic mols. immobilized. The authors examd. the use of the Quartz Crystal Microbalance with Dissipation (QCM-D) as a tool for fundamental analyses of a model sensor constructed by the immobilization of cobalt(II) phthalocyanine (TCACoPc) and glucose oxidase (GOx) onto a gold-quartz electrode (electrode surface) for the enhanced detection of glucose. The model sensor was constructed in aq. phase and covalently linked the gold surface to the TCACoPc, and the TCACoPc to the GOx, using the QCM-D. The aq. metallophthalocyanine (MPc) formed a multi-layer over the surface of the electrode, which could be removed to leave a monolayer with a mass loading that compared favorably to the theor. value expected. Anal. of frequency and dissipation plots indicated covalent attachment of glucose oxidase onto the metallophthalocyanine layer. The amt. of GOx bound using the model system compared favorably to calcns. derived from the maximal amperometric functioning of the electrochem. sensor, but not to theor. values derived from dimensions of GOx as established by crystallog. The strength of the binding of the GOx film with the TCACoPc layer was tested by using 2% SDS as a denaturant/surfactant, and the GOx film was not found to be significantly affected by exposure to this. This paper thus showed that QCM-D can be used in order to model essential processes and interactions that dictate the functional parameters of a biosensor.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtVOisL3M&md5=eae1f08ac390aebbe6637e710283c9a0
  48. 48
    Anand, G.; Sharma, S.; Dutta, A. K.; Kumar, S. K.; Belfort, G. Conformational Transitions of Adsorbed Proteins on Surfaces of Varying Polarity. Langmuir 2010, 26, 10803– 10811,  DOI: 10.1021/la1006132
    Google Scholar
    48
    Conformational Transitions of Adsorbed Proteins on Surfaces of Varying Polarity
    Anand, Gaurav; Sharma, Sumit; Dutta, Amit K.; Kumar, Sanat K.; Belfort, Georges
    Langmuir (2010), 26 (13), 10803-10811CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Combining a wide range of protein adsorption expts. (three globular proteins on eight well-defined homogeneous surfaces) with Monte Carlo simulations of lattice proteins at different concns. and on surfaces of varying "polarity", we explore the extent and rheol. behavior of adsorbed proteins as a function of substrate polarity, "on" rate consts. (ka) and steric parameters (|A1|) from the random sequential adsorption model, and demonstrate a folding to unfolding transition upon adsorption. We show that model globular proteins (hen egg lysozyme, RNase A, and insulin dimer) behave similarly with respect to adsorption. Exptl., above a substrate wettability cos θ > 0.4 (where θ is the sessile contact angle of water on a substrate in air), the adsorbed mass, rigidity, and ka of the proteins are diminished, while the steric factor |A1| is increased, suggesting a lower packing d. To analyze these results, we have invoked computer simulations. We show that changing surface polarity has two profound effects. First, the amt. adsorbed increases as the surfaces become more apolar. Further, the proteins become less stable as their adsorbed amt. increased because they gain a large no. of interprotein and protein-surface interactions. Finally, apolar surfaces served to reduce the unfolding free energy barriers, further facilitating the reorganizing of proteins on these surfaces. Thus, increasing the nonpolar nature of the surfaces resulted in a more rigid adsorbed layer, in good agreement with the expts.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXlsFWrsLk%253D&md5=c29e03539eaebcc8b4e67806b89582ee
  49. 49
    Frederick, K. R.; Tung, J.; Emerick, R. S.; Masiarz, F. R.; Chamberlain, S. H.; Vasavada, A.; Rosenberg, S.; Chakraborty, S.; Schopfer, L. M.; Schopter, L. M. Glucose Oxidase from Aspergillus Niger. Cloning, Gene Sequence, Secretion from Saccharomyces Cerevisiae and Kinetic Analysis of a Yeast-Derived Enzyme. J. Biol. Chem. 1990, 265, 3793– 3802,  DOI: 10.1016/s0021-9258(19)39664-4
    Google Scholar
    49
    Glucose oxidase from Aspergillus niger. Cloning, gene sequence, secretion from Saccharomyces cerevisiae and kinetic analysis of a yeast-derived enzyme
    Frederick, Katherine R.; Tung, James; Emerick, Richard S.; Masiarz, Frank R.; Chamberlain, Scott H.; Vasavada, Amit; Rosenberg, Steven; Chakraborty, Sumita; Schopfer, Lawrence M.; Massey, Vincent
    Journal of Biological Chemistry (1990), 265 (7), 3793-802CODEN: JBCHA3; ISSN:0021-9258.
    The gene for A. niger glucose oxidase (EC 1.1.3.4) was cloned from both cDNA and genomic libraries using oligonucleotide probes derived from the amino acid sequences of peptide fragments of the enzyme. The mature enzyme consists of 583 amino acids and is preceded by a 22-amino-acid presequence. No intervening sequences are found within the coding region. The enzyme contains 3 cysteine residues and 8 potential sites for N-linked glycosylation. The protein shows 26% identity with alc. oxidase of Hansenuela polymorpha, and the N terminus has a sequence homologous with the AMP-binding region of other flavoenzymes, such as p-hydroxybenzoate hydroxylase and glutathione reductase. Recombinant yeast expression plasmids were constructed contg. a hybrid yeast alc. dehydrogenase II-glyceraldehyde-3-phosphage dehydrogenase promoter, either the yeast α-factor pheromone leader or the glucose oxidase presequence, and the mature glucose oxidase-coding sequence. When transformed into yeast, these plasmids direct the synthesis and secretion of between 75 and 400 μg/mL of active glucose oxidase. Anal. of the yeast-derived enzymes shows that they are of comparable specific activity and have more extensive N-linked glycosylation than the A. niger protein.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXksFens74%253D&md5=225b51acfba464b3a07b68493b7b000d
  50. 50
    Zhang, Y.; Savva, A.; Wustoni, S.; Hama, A.; Maria, I. P.; Giovannitti, A.; McCulloch, I.; Inal, S. Visualizing the Solid–Liquid Interface of Conjugated Copolymer Films Using Fluorescent Liposomes. ACS Appl. Bio Mater. 2018, 1, 1348– 1354,  DOI: 10.1021/acsabm.8b00323
    Google Scholar
    50
    Visualizing the Solid-Liquid Interface of Conjugated Copolymer Films Using Fluorescent Liposomes
    Zhang, Yi; Savva, Achilleas; Wustoni, Shofarul; Hama, Adel; Maria, Iuliana P.; Giovannitti, Alexander; McCulloch, Iain; Inal, Sahika
    ACS Applied Bio Materials (2018), 1 (5), 1348-1354CODEN: AABMCB; ISSN:2576-6422. (American Chemical Society)
    Conjugated polymers are promising engineering tools for establishing bilateral elec. communication with living systems. The free energy of their films, the roughness, and charge d. play major roles in detg. their interactions with lipid bilayers, which form the membrane barrier around every living cell allowing for mol. exchange with the extracellular environment. In this work, we investigate lipid bilayer formation from synthetic lipid vesicles (liposomes) on a series of amphiphilic copolymer films based on naphthalene 1,4,5,8 tetracarboxylic diimide bithiophene (NDI-T2) backbone where the alkyl side chain is gradually exchanged for an ethylene glycol-based side chain. As the concn. of ethylene glycol in the compn. changes, the surface energy of the films varies drastically, which, in turn, effects the interactions with liposomes. By imaging the interactions of fluorophore-labeled liposomes with these surfaces via a fluorescence microscope, we show that the films can be cast such that ethylene glycol-rich regions, which liposomes favor, are accumulated on the surface and ext. information on the wettability behavior that has not been possible using other surface sensitive techniques. This approach uncovers the solid/liq. interface of a promising class of electron transporting conjugated polymer films and suggests synthetic strategies to maximize the no. of lipid-polymer contacts for the formation of supported lipid bilayers.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvFSjur%252FP&md5=b8289013ce918793d79c8b1c08c836b7
  51. 51
    Stevens, J. S.; de Luca, A. C.; Pelendritis, M.; Terenghi, G.; Downes, S.; Schroeder, S. L. M. Quantitative Analysis of Complex Amino Acids and Rgd Peptides by X-Ray Photoelectron Spectroscopy (Xps). Surf. Interface Anal. 2013, 45, 1238– 1246,  DOI: 10.1002/sia.5261
    Google Scholar
    51
    Quantitative analysis of complex amino acids and RGD peptides by X-ray photoelectron spectroscopy (XPS)
    Stevens, Joanna S.; Luca, Alba C.; Pelendritis, Michalis; Terenghi, Giorgio; Downes, Sandra; Schroeder, Sven L. M.
    Surface and Interface Analysis (2013), 45 (8), 1238-1246CODEN: SIANDQ; ISSN:0142-2421. (John Wiley & Sons Ltd.)
    The C 1 s, N 1 s, and O 1 s core level binding energies (BEs) of the functional groups in amino acids (glycine, aspartic acid, glutamic acid, arginine, and histidine) with varied side-chains and cell-binding RGD-based peptides have been detd. and characterized by XPS with a monochromatic Al Kα source. The zwitterionic nature of the amino acids in the solid state is unequivocally evident from the N 1 s signals of the protonated amine groups and the C 1 s signature of carboxylate groups. Significant adventitious carbon contamination is evident for all samples but can be quant. accounted for. No intrinsic differences in the XP spectra are evident between two polymorphs (α and γ) of glycine, indicating that the crystallog. differences have a minor influence on the core level BEs for this system. The two nitrogen centers in the imidazole group of histidine exhibit an N 1 s BE shift that is in line with previously reported data for theophylline and aq. imidazole solns., while the nitrogen and carbon chem. shifts reflect the unusual guanidinium chem. environment in arginine. It is shown that the complex envelopes of C 1 s and O 1 s photoemission spectra for short-chain peptides can be analyzed quant. by ref. to the less complex XP spectra of the constituent amino acids, provided the peptides are of high enough purity. The distinctive N 1 s photoemission from the amide linkages provides an indicator of peptide formation even in the presence of common impurities, and variations in the relative intensities of N 1 s were found to be diagnostic for each of the three peptides investigated (RGD, RGDS, and RGDSC). Copyright © 2013 John Wiley & Sons, Ltd.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXlvVWit7c%253D&md5=eeed0a6a94c15715622e532a7064e712
  52. 52
    Koklu, A.; Ohayon, D.; Wustoni, S.; Hama, A.; Chen, X.; McCulloch, I.; Inal, S. Microfluidics Integrated N-Type Organic Electrochemical Transistor for Metabolite Sensing. Sens. Actuators, B 2021, 329, 129251,  DOI: 10.1016/j.snb.2020.129251
    Google Scholar
    52
    Microfluidics integrated n-type organic electrochemical transistor for metabolite sensing
    Koklu, Anil; Ohayon, David; Wustoni, Shofarul; Hama, Adel; Chen, Xingxing; McCulloch, Iain; Inal, Sahika
    Sensors and Actuators, B: Chemical (2021), 329 (), 129251CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
    The org. electrochem. transistor (OECT) can translate biochem. binding events between a recognition unit and its analyte into an elec. signal. We present an OECT comprising an n-type (electron transporting) conjugated polymer-based channel and lateral gate electrode functionalized with the enzyme, glucose oxidase. The device is integrated with a microfluidic system for real-time glucose monitoring in a flow-through manner. The n-type polymer has direct elec. communication with glucose oxidase, allowing glucose detection while surpassing hydrogen peroxide prodn. The microfluidic-integrated OECT shows superior features compared to its microfluidic-free counterpart, including higher current and transconductance values as well as improved signal-to-noise (SNR) ratios, which enhances the sensor sensitivity and its detection limit. Thanks to the low noise endowed by the integrated microfluidics, the gate current changes upon metabolite recognition could be resolved, revealing that while the relative changes in gate and drain currents are similar, the drain current output has a higher SNR. This is the first demonstration of the integration of a microfluidic system with an n-type accumulation mode OECT for real-time enzymic metabolite detection. The microfluidic-integrated design provides new insights into the mechanisms leading to high sensor sensitivities, crucial for the development of portable and autonomous lab-on-a-chip technologies.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisFelsbvN&md5=9b2661b1ad6439a4b932de0899859ee7
  53. 53
    Sethuraman, A.; Vedantham, G.; Imoto, T.; Przybycien, T.; Belfort, G. Protein Unfolding at Interfaces: Slow Dynamics of Α-Helix to Β-Sheet Transition. Proteins: Struct., Funct., Bioinf. 2004, 56, 669– 678,  DOI: 10.1002/prot.20183
    Google Scholar
    53
    Protein unfolding at interfaces: Slow dynamics of α-helix to β-sheet transition
    Sethuraman, Ananthakrishnan; Vedantham, Ganesh; Imoto, Taiji; Przybycien, Todd; Belfort, Georges
    Proteins: Structure, Function, and Bioinformatics (2004), 56 (4), 669-678CODEN: PSFBAF ISSN:. (Wiley-Liss, Inc.)
    A two-phase sequential dynamic change in the secondary structure of hen egg lysozyme (Lys) adsorbed on solid substrates was obsd. The first phase involved fast conversion of α-helix to random/turns (within the first minute or at very low coverage or high substrate wettability) with no perceptible change in β-sheet content. The second phase (1-1200 min), however, involved a relatively slow conversion from α-helix to β-sheet without a noticeable change in random/turns. An important finding of this work is that the concn. of lysozyme in the adsorbed state has a substantial effect on the fractional content of secondary structures. Attenuated total reflection Fourier transform IR (ATR/FTIR) spectroscopy, along with a newly-developed optimization algorithm for predicting the content of secondary structure motifs, was used to correlate the secondary structure and the amt. of adsorbed lysozyme with the surface wettability of six different flat nanoporous substrates. Although three independent variables, surface wettability, soln. concn. and time for absorption, were used to follow the fractional structural changes of lysozyme, the results were all normalized onto a single plot with the amt. adsorbed as the universal independent variable. Consequently, lateral interactions among proteins likely drive the transition process. Direct intermol. force adhesion measurements between lysozyme and different functionalized self-assembled alkanethiol monolayers confirm that hydrophobic surfaces interact strongly with proteins. The lysozyme-unfolding pathway during early adsorption appears to be similar to that predicted by published mol. modeling results.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXmvVOjtLs%253D&md5=39ef1e42ead2342ba24e56615df424aa
  54. 54
    Mecheri, B.; D’Epifanio, A.; Geracitano, A.; Targon Campana, P.; Licoccia, S. Development of Glucose Oxidase-Based Bioanodes for Enzyme Fuel Cell Applications. J. Appl. Electrochem. 2013, 43, 181– 190,  DOI: 10.1007/s10800-012-0489-y
    Google Scholar
    54
    Development of glucose oxidase-based bioanodes for enzyme fuel cell applications
    Mecheri, Barbara; D'Epifanio, Alessandra; Geracitano, Antonio; Targon Campana, Patricia; Licoccia, Silvia
    Journal of Applied Electrochemistry (2013), 43 (2), 181-190CODEN: JAELBJ; ISSN:0021-891X. (Springer)
    We fabricated an enzyme fuel cell (EFC) device based on glucose as fuel and glucose oxidase (GOx) as biocatalyst. As a strategy to improve GOx stability, preserving at the same time the enzyme catalytic activity, we propose an immobilization procedure to entrap GOx in a polymer matrix based on Nafion and multiwalled carbon nanotubes. CD spectra were recorded to study changes in the 3D structure of GOx that might be generated by the immobilization procedure. The comparison between the CD features of GOx immobilized and free in soln. indicates that the shape of the spectra and position of peaks do not significantly change. The bioelectrocatalytic activity toward glucose oxidn. of immobilized GOx was studied by cyclic voltammetry and chronoamperometry expts. Such electrochem. expts. allow monitoring the rate of GOx-catalyzed glucose oxidn. and extrapolating GOx kinetic parameters. Results demonstrate that immobilized GOx has high catalytic efficiency, due the maintaining of regular and well-ordered structure of the immobilized enzyme, as indicated by spectroscopic findings. Once investigated the electrode structure-property relationship, an EFC device was assembled using the GOx-based bioanode, and sulfonated poly ether ether ketone as electrolyte membrane. Polarization and power d. curves of the complete EFC device were acquired, demonstrating the suitability of the immobilization strategy and materials to be used in EFCs.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXmvVCqtw%253D%253D&md5=4b45651e8c8956bde2069f3c2629316d
  55. 55
    Fears, K. P.; Sivaraman, B.; Powell, G. L.; Wu, Y.; Latour, R. A. Probing the Conformation and Orientation of Adsorbed Enzymes Using Side-Chain Modification. Langmuir 2009, 25, 9319– 9327,  DOI: 10.1021/la901885d
    Google Scholar
    55
    Probing the Conformation and Orientation of Adsorbed Enzymes Using Side-Chain Modification
    Fears, Kenan P.; Sivaraman, Balakrishnan; Powell, Gary L.; Wu, Yonnie; Latour, Robert A.
    Langmuir (2009), 25 (16), 9319-9327CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    The bioactivity of enzymes that are adsorbed on surfaces can be substantially influenced by the orientation of the enzyme on the surface and adsorption-induced changes in the enzyme's structure. CD is a powerful method for observing the secondary structure of proteins; however, it provides little information regarding the tertiary structure of a protein or its adsorbed orientation. In this study, we developed methods using side-chain-specific chem. modification of solvent-exposed tryptophan residues to complement CD spectroscopy and bioactivity assays to provide greater detail regarding whether changes in enzyme bioactivity following adsorption are due to adsorbed orientation and/or adsorption-induced changes in the overall structure. These methods were then applied to investigate how adsorption influences the bioactivity of hen egg white lysozyme (HEWL) and glucose oxidase (GOx) on alkanethiol self-assembled monolayers over a range of surface chemistries. The results from these studies indicate that surface chem. significantly influences the bioactive state of each of these enzymes but in distinctly different ways. Changes in the bioactive state of HEWL are largely governed by its adsorbed orientation, while the bioactive state of adsorbed GOx is influenced by a combination of both adsorbed orientation and adsorption-induced changes in conformation.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXoslWlsrw%253D&md5=7edcc42fcd06607665bbbbaa2c7c2895

Cited By

Click to copy section linkSection link copied!

This article is cited by 14 publications.

  1. Yan Jiang, Ricardo Javier Vázquez, Samantha R. McCuskey, Benjamin Rui Peng Yip, Glenn Quek, David Ohayon, Binu Kundukad, Xuehang Wang, Guillermo C. Bazan. Recyclable Conjugated Polyelectrolyte Hydrogels for Pseudocapacitor Fabrication. ACS Applied Materials & Interfaces 2024, 16 (16) , 19968-19976. https://doi.org/10.1021/acsami.3c13137
  2. Tania Cecilia Hidalgo Castillo, Wentao Shan, Guorong Ma, Haoyu Zhao, Yunfei Wang, Victor Druet, Abdulelah Saleh, Xiaodan Gu, Sahika Inal. Thermal Annealing for High Performance and Memory Behavior in n‐Type Organic Electrochemical Transistors. Advanced Materials 2024, https://doi.org/10.1002/adma.202411214
  3. Zhenyu Hu, Puzhong Gu, Xiao Yang, Zejun Sun, Linlin Lu, Xing Liang, Xiaoyu Zhang, Zhiying Deng, Muxiang Liu, Guoqing Zu, Jia Huang. Nanoporous Conjugated Polymer Aerogel Films for High‐Performance Electrochemical Transistors. Advanced Functional Materials 2024, 34 (52) https://doi.org/10.1002/adfm.202410788
  4. Maryam Alsufyani, Benjamin Moss, Claudia E. Tait, William K. Myers, Maryam Shahi, Katherine Stewart, Xiaolei Zhao, Reem B. Rashid, Dilara Meli, Ruiheng Wu, Bryan D. Paulsen, Karl Thorley, Yuanbao Lin, Craig Combe, Charlie Kniebe‐Evans, Sahika Inal, Sang Young Jeong, Han Young Woo, Grant Ritchie, Ji‐Seon Kim, Jonathan Rivnay, Alexandra Paterson, James R Durrant, Iain McCulloch. The Effect of Organic Semiconductor Electron Affinity on Preventing Parasitic Oxidation Reactions Limiting Performance of n‐Type Organic Electrochemical Transistors. Advanced Materials 2024, 36 (44) https://doi.org/10.1002/adma.202403911
  5. Cheng Shi, Xingyu Jiang, Qi Wang, Chuan Xiang, Xinyu Dong, Lifeng Chi, Lizhen Huang. Blending enzyme immobilization enabled high performance glucose sensor based on an n-channel organic electrochemical transistor. Materials Research Express 2024, 11 (11) , 115903. https://doi.org/10.1088/2053-1591/ad95e1
  6. Christina J. Kousseff, Shofarul Wustoni, Raphaela K. S. Silva, Ariel Lifer, Achilleas Savva, Gitti L. Frey, Sahika Inal, Christian B. Nielsen. Single‐Component Electroactive Polymer Architectures for Non‐Enzymatic Glucose Sensing. Advanced Science 2024, 11 (27) https://doi.org/10.1002/advs.202308281
  7. Abdulelah Saleh, Anil Koklu, Ilke Uguz, Anna-Maria Pappa, Sahika Inal. Bioelectronic interfaces of organic electrochemical transistors. Nature Reviews Bioengineering 2024, 2 (7) , 559-574. https://doi.org/10.1038/s44222-024-00180-7
  8. Kétura Ferreira, Kethylen Cardoso, Romero Brandão-Costa, Joana T. Martins, Cláudia Botelho, Anna Neves, Thiago Nascimento, Juanize Batista, Éverton Ferreira, Fernando Damasceno, Amanda Sales-Conniff, Wendell Albuquerque, Ana Porto, José Teixeira. Physicochemical Properties of a Bioactive Polysaccharide Film from Cassia grandis with Immobilized Collagenase from Streptomyces parvulus (DPUA/1573). Cosmetics 2024, 11 (3) , 86. https://doi.org/10.3390/cosmetics11030086
  9. Haojie Dai, Wan Yue. n‐Type Organic Mixed Ionic‐Electronic Conductors for Organic Electrochemical Transistors. Advanced Engineering Materials 2024, 26 (9) https://doi.org/10.1002/adem.202301860
  10. Yazhou Wang, Shofarul Wustoni, Jokubas Surgailis, Yizhou Zhong, Anil Koklu, Sahika Inal. Designing organic mixed conductors for electrochemical transistor applications. Nature Reviews Materials 2024, 9 (4) , 249-265. https://doi.org/10.1038/s41578-024-00652-7
  11. Michele Catacchio, Mariapia Caputo, Lucia Sarcina, Cecilia Scandurra, Angelo Tricase, Verdiana Marchianò, Eleonora Macchia, Paolo Bollella, Luisa Torsi. Spiers Memorial Lecture: Challenges and prospects in organic photonics and electronics. Faraday Discussions 2024, 250 , 9-42. https://doi.org/10.1039/D3FD00152K
  12. Zhuo Shi, Zifeng Wang, Kaiwen Li, Yuwei Wang, Zhanhong Li, Zhigang Zhu. MXene fibers-based molecularly imprinted disposable electrochemical sensor for sensitive and selective detection of hydrocortisone. Talanta 2024, 266 , 125100. https://doi.org/10.1016/j.talanta.2023.125100
  13. Yuqiu Lei, Peiyun Li, Yuting Zheng, Ting Lei. Materials design and applications of n-type and ambipolar organic electrochemical transistors. Materials Chemistry Frontiers 2023, 8 (1) , 133-158. https://doi.org/10.1039/D3QM00828B
  14. Anton Weissbach, Matteo Cucchi, Hsin Tseng, Karl Leo, Hans Kleemann. Unraveling the Electrochemical Electrode Coupling in Integrated Organic Electrochemical Transistors. Advanced Functional Materials 2023, 33 (46) https://doi.org/10.1002/adfm.202302205
Download PDF
Go to ACS Applied Materials & Interfaces
Get e-Alerts
Get e-Alerts

ACS Applied Materials & Interfaces

Cite this: ACS Appl. Mater. Interfaces 2023, 15, 7, 9726–9739
Click to copy citationCitation copied!
https://doi.org/10.1021/acsami.2c20502
Published February 7, 2023

Copyright © 2023 American Chemical Society. This publication is licensed under

CC-BY 4.0 .

Article Views

3003

Altmetric

-

Citations

14
Learn about these metrics

Article Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.

Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.

The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated.

  • Abstract

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 1

    Figure 1. (a) Chemical structure of n-type polymers: the two copolymers with varying EG contents: P-75 and P-90, the fully glycolated (alkyl-free) analogue (P-100), P-100B with a branched EG side chain (branched analogue of P-100), and P-ZI with its zwitterions on the side chain. (b) OECT schematic highlighting the locations of the n-type film with adsorbed GOx (channel and gate). When glucose is present, it gets oxidized to gluconolactone by the active site (FAD) of GOx, following glucose + GOx (FAD) → gluconolactone + GOx (FADH2).

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 2

    Figure 2. Performance of n-type OECTs and electrodes as glucose sensors. (a) Real-time response of the OECT (source-drain current, ID, as a function of time) as successive amounts of glucose are added to the electrolyte. The gate and drain voltages were kept constant at +0.5 V. The OECTs were operated using a planar gate configuration, where both the channel and gate were functionalized with GOx. Insets represent the real-time response of the devices to glucose concentrations lower than 250 μM. (b) Normalized response of the OECTs (NROECT) to glucose. Error bars represent the standard deviation of at least three different devices. (c) Amperometric response of n-type conjugated polymer electrodes to 1 mM glucose. The working electrode was the n-type film functionalized with GOx, the reference electrode was Ag/AgCl, and the counter electrode was a Pt coil. The arrow represents the time point when 1 mM glucose was added into the electrolyte. (d) NRelectrode to 1 mM glucose (plain bars) and to O2 (patterned bars).

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 3

    Figure 3. Surface properties of n-type films. (a) Water contact angle and (b) ζ potential of the n-type polymer films. Error bars represent the standard deviation of (a) nine and (b) four different measurements. (c) Orientations of native GOx from A. niger (PDB: 3QVP) as a function of surface charge: (i) “front-lying” orientation on a charge-neutral surface; (ii) “standing” orientation on a positively charged surface; and (iii) “back-lying” orientation on a negatively charged surface. Surface colors on GOx indicate positive and negative electrostatic potentials contoured from 50 kT/e (blue) to −50 kT/e (red). The cofactor is shown in stick representation and highlighted in red.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 4

    Figure 4. GOx adsorption on polymer films, analyzed using QCM-D. (a) P-90 QCM-D raw data reporting the change in frequency (Δfn) and dissipation (Δdn) for harmonics fifth, seventh, and ninth. (b) Corresponding mass taken up upon GOx adsorption on each film as a function of surface wettability [represented by cos(θ) where θ is the water contact angle]. The adsorbed mass per area was extracted from the data collected at the end of the rinsing process (see Figure S14). (c) Footprint of the enzyme on each polymer film. The footprint was calculated from the enzyme surface coverage and average dimensions of the crystal structure of a deglycosylated GOx molecule (60 Å × 52 Å × 77 Å), (40) assuming an even distribution of the enzyme on a laterally homogeneous surface. (d) P-90 Δd vs Δf plots (seventh harmonic). The numbers define the linear regions in the plots with different slopes. The red and blue dots demark the end of the adsorption and desorption processes, respectively. (e) Δd/Δf ratio, calculated from the values measured at the end of the adsorption and the rinsing steps, as a function of wettability cos(θ).

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 5

    Figure 5. GOx adsorption kinetics. (a) dm/dt vs Sauerbrey mass uptake (seventh harmonic) plots for GOx adsorption on P-90 and (b) plot of C1 as a function of ka.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 6

    Figure 6. High-resolution N 1s XPS spectra of the polymer films after enzyme adsorption. Yellow circles highlight the chemical bonds involving N atoms in the polymers, including the NDI backbone and side chains and those in the primary amino acids present in GOx. The amino acids displayed in the figure correspond to a selected few in the protein sequence: lysine (LYS), glutamine (GLN), and arginine (ARG).

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 7

    Figure 7. Influence of n-type polymer film surface properties on GOx adsorption. The surface hydrophilicity and charge govern enzyme adsorption behavior on the film surface. Hydrophobic surfaces tend to retain more enzymes. Surfaces that are too hydrophobic, however, lead to complete denaturation of the enzyme structure. GOx adopts a flattened conformation on hydrophilic/polar surfaces. The surface charge influences GOx orientation. A neutral surface (left) leads to a “front-lying” orientation, where the active site of the enzyme faces downward and is inaccessible to the glucose. A positively charged surface (middle) leads to the enzyme adsorbing in a “standing” orientation, where the active site is accessible. A negatively charged surface (right) leads to a “back-lying” orientation, with the active site facing up and in closer proximity to the sensor surface than in a standing fashion. The latter surface, which is hydrophilic, negatively charged, and homogeneous, is most desirable to build top-performer glucose sensors.

    High Resolution Image
    Download MS PowerPoint Slide

  • References

    This article references 55 other publications.

    1. 1
      Ngandu Mpoyi, E.; Cantini, M.; Reynolds, P. M.; Gadegaard, N.; Dalby, M. J.; Salmerón-Sánchez, M. Protein Adsorption as a Key Mediator in the Nanotopographical Control of Cell Behavior. ACS Nano 2016, 10, 6638– 6647,  DOI: 10.1021/acsnano.6b01649
      1
      Protein Adsorption as a Key Mediator in the Nanotopographical Control of Cell Behavior
      Ngandu Mpoyi, Elie; Cantini, Marco; Reynolds, Paul M.; Gadegaard, Nikolaj; Dalby, Matthew J.; Salmeron-Sanchez, Manuel
      ACS Nano (2016), 10 (7), 6638-6647CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Surface nanotopog. is widely employed to control cell behavior and in particular controlled disorder is important in cell differentiation/maturation. However, extracellular matrix proteins, such as fibronectin (FN), initially adsorbed on a biomaterial surface are known to mediate the interaction of synthetic materials with cells. The authors examine the effect of nanotopog. on cell behavior through this adsorbed layer of adhesive proteins using a nanostructured polycarbonate surface comprising 150 nm-diam. pits originally defined using electron beam lithog. The authors address the effect of this nanopitted surface on FN adsorption and subsequently on cell morphol. and behavior using C2C12 myoblasts. Wettability measurements and at. force microscopy imaging showed that protein is adsorbed both within the interpits spaces and inside the nanopits. Cells responded to this coated nanotopog. with the formation of fewer but larger focal adhesions and by mimicking the pit patterns within their cytoskeleton, nanoimprinting, ultimately achieving higher levels of myogenic differentiation compared to a flat control. Both focal adhesion assembly and nanoimprinting are dependent on cell contractility and are adversely affected using blebbistatin. The authors' results demonstrate the central role of the nanoscale protein interface in mediating cell-nanotopog. interactions and implicate this interface as helping control the mechanotransductive cascade.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtFeku7jK&md5=a72fcec8df98fc20cdf467ebfd407b72
    2. 2
      Cho, W.; Stahelin, R. V. Membrane-Protein Interactions in Cell Signaling and Membrane Trafficking. Annu. Rev. Biophys. Biomol. Struct. 2005, 34, 119– 151,  DOI: 10.1146/annurev.biophys.33.110502.133337
      2
      Membrane-protein interactions in cell signaling and membrane trafficking
      Cho, Wonhwa; Stahelin, Robert V.
      Annual Review of Biophysics and Biomolecular Structure (2005), 34 (), 119-151, 2 platesCODEN: ABBSE4; ISSN:1056-8700. (Annual Reviews Inc.)
      A review. Research in the past decade has revealed that many cytosolic proteins are recruited to different cellular membranes to form protein-protein and lipid-protein interactions during cell signaling and membrane trafficking. Membrane recruitment of these peripheral proteins is mediated by a growing no. of modular membrane-targeting domains, including C1, C2, PH, FYVE, PX, ENTH, ANTH, BAR, FERM, and tubby domains, that recognize specific lipid mols. in the membranes. Structural studies of these membrane-targeting domains demonstrate how they specifically recognize their cognate lipid ligands. However, the mechanisms by which these domains and their host proteins are recruited to and interact with various cell membranes are only beginning to unravel with recent computational studies, in vitro membrane binding studies using model membranes, and cellular translocation studies using fluorescent protein-tagged proteins. Here, the authors summarize recent progress in the understanding of how the kinetics and energetics of membrane-protein interactions are regulated during cellular membrane targeting and the activation of peripheral proteins.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXlslCkurc%253D&md5=926e12e451770454a652c6b166628711
    3. 3
      Xu, L.-C.; Bauer, J. W.; Siedlecki, C. A. Proteins, Platelets, and Blood Coagulation at Biomaterial Interfaces. Colloids Surf., B 2014, 124, 49– 68,  DOI: 10.1016/j.colsurfb.2014.09.040
      3
      Proteins, platelets, and blood coagulation at biomaterial interfaces
      Xu, Li-Chong; Bauer, James W.; Siedlecki, Christopher A.
      Colloids and Surfaces, B: Biointerfaces (2014), 124 (), 49-68CODEN: CSBBEQ; ISSN:0927-7765. (Elsevier B.V.)
      A review. Blood coagulation and platelet adhesion remain major impediments to the use of biomaterials in implantable medical devices. There is still significant controversy and question in the field regarding the role that surfaces play in this process. This manuscript addresses this topic area and reports on state of the art in the field. Particular emphasis is placed on the subject of surface engineering and surface measurements that allow for control and observation of surface-mediated biol. responses in blood and test solns. Appropriate use of surface texturing and chem. patterning methodologies allow for redn. of both blood coagulation and platelet adhesion, and new methods of surface interrogation at high resoln. allow for measurement of the relevant biol. factors.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs1Ohu73F&md5=cafe9f538645381e50d626c25d89854a
    4. 4
      Urbani, A.; Sirolli, V.; Lupisella, S.; Levi-Mortera, S.; Pavone, B.; Pieroni, L.; Amoroso, L.; Di Vito, R.; Bucci, S.; Bernardini, S.; Sacchetta, P.; Bonomini, M. Proteomic Investigations on the Effect of Different Membrane Materials on Blood Protein Adsorption During Haemodialysis. Blood Transfus. 2012, 10 Suppl 2, s101– s112,  DOI: 10.2450/2012.014S
      There is no corresponding record for this reference.
    5. 5
      Russo, M. J.; Han, M.; Desroches, P. E.; Manasa, C. S.; Dennaoui, J.; Quigley, A. F.; Kapsa, R. M. I.; Moulton, S. E.; Guijt, R. M.; Greene, G. W.; Silva, S. M. Antifouling Strategies for Electrochemical Biosensing: Mechanisms and Performance toward Point of Care Based Diagnostic Applications. ACS Sens. 2021, 6, 1482– 1507,  DOI: 10.1021/acssensors.1c00390
      5
      Antifouling Strategies for Electrochemical Biosensing: Mechanisms and Performance toward Point of Care Based Diagnostic Applications
      Russo, Matthew J.; Han, Mingyu; Desroches, Pauline E.; Manasa, Clayton S.; Dennaoui, Jessair; Quigley, Anita F.; Kapsa, Robert M. I.; Moulton, Simon E.; Guijt, Rosanne M.; Greene, George W.; Silva, Saimon Moraes
      ACS Sensors (2021), 6 (4), 1482-1507CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)
      A review. Although there exist numerous established lab.-based technologies for sample diagnostics and analyte detection, many medical and forensic science applications require point of care based platforms for rapid on-the-spot sample anal. Electrochem. biosensors provide a promising avenue for such applications due to the portability and functional simplicity of the technol. However, the ability to develop such platforms with the high sensitivity and selectivity required for anal. of low analyte concns. in complex biol. samples remains a paramount issue in the field of biosensing. Nonspecific adsorption, or fouling, at the electrode interface via the innumerable biomols. present in these sample types (i.e., serum, urine, blood/plasma, and saliva) can drastically obstruct electrochem. performance, increasing background "noise" and diminishing both the electrochem. signal magnitude and specificity of the biosensor. Consequently, this review aims to discuss strategies and concepts used throughout the literature to prevent electrode surface fouling in biosensors and to communicate the nature of the antifouling mechanisms by which they operate. Evaluation of each antifouling strategy is focused primarily on the fabrication method, exptl. technique, sample compn., and electrochem. performance of each technol. highlighting the overall feasibility of the platform for point of care based diagnostic/detection applications.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXntFGjtLw%253D&md5=02e2b991557f5f9263161d178143eed9
    6. 6
      Choi, W.; Park, S.; Kwon, J.-S.; Jang, E.-Y.; Kim, J.-Y.; Heo, J.; Hwang, Y.; Kim, B.-S.; Moon, J.-H.; Jung, S.; Choi, S.-H.; Lee, H.; Ahn, H.-W.; Hong, J. Reverse Actuation of Polyelectrolyte Effect for in Vivo Antifouling. ACS Nano 2021, 15, 6811– 6828,  DOI: 10.1021/acsnano.0c10431
      6
      Reverse Actuation of Polyelectrolyte Effect for In Vivo Antifouling
      Choi, Woojin; Park, Sohyeon; Kwon, Jae-Sung; Jang, Eun-Young; Kim, Ji-Yeong; Heo, Jiwoong; Hwang, YoungDeok; Kim, Byeong-Su; Moon, Ji-Hoi; Jung, Sungwon; Choi, Sung-Hwan; Lee, Hwankyu; Ahn, Hyo-Won; Hong, Jinkee
      ACS Nano (2021), 15 (4), 6811-6828CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Zwitterionic polymers have extraordinary properties, i.e., significant hydration and the so-called antipolyelectrolyte effect, which make them suitable for biomedical applications. The hydration induces an antifouling effect, and this has been investigated significantly. The antipolyelectrolyte effect refers to the extraordinary ion-responsive behavior of particular polymers that swell and hydrate considerably in physiol. solns. This actuation begins to attract attention to achieve in vivo antifouling that is challenging for general polyelectrolytes. In this study, we established the sophisticated cornerstone of the antipolyelectrolyte effect in detail, including (i) the essential parameters, (ii) exptl. verifications, and (iii) effect of improving antifouling performance. First, we find that both osmotic force and charge screening are essential factors. Second, we identify the antipolyelectrolyte effect by visualizing the swelling and hydration dynamics. Finally, we verify that the antifouling performance can be enhanced by exploiting the antipolyelectrolyte effect and report redn. of 85% and 80% in ex and in vivo biofilm formation, resp.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXnt1Witrg%253D&md5=c85795f577a131bbc0e83935e26fba70
    7. 7
      Park, M. Orientation Control of the Molecular Recognition Layer for Improved Sensitivity: A Review. BioChip J. 2019, 13, 82– 94,  DOI: 10.1007/s13206-019-3103-0
      7
      Orientation Control of the Molecular Recognition Layer for Improved Sensitivity: a Review
      Park, Min
      BioChip Journal (2019), 13 (1), 82-94CODEN: BJIODP; ISSN:1976-0280. (Korean BioChip Society)
      Biosensors have been used in various fields of biol. anal., such as for quantification of analytes and the study of mol.-mol. interactions. Orientation control of the mol. recognition layer is one of the easiest and most effective ways to improve the sensitivity of biosensors. In this review, the orientation control of mol. recognition mols., such as antibodies, aptamers, and enzymes, is discussed. The review compares the improvement in the sensitivity and binding activity of biosensors achieved through orientation control with that achieved through random orientation. Immobilization methods of antibodies for orientation control are first discussed, with a focus on immobilization of the fragment crystallizable region of antibodies, which is the most studied technique. Covalent and non-covalent immobilization strategies are also discussed, and their effect on the sensitivity of biosensors is summarized. Lastly, the orientation control of other mol. recognition mols. (aptamers and enzymes) was discussed and the applications of mol. recognition mols. as biosensors are discussed.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXms1GjtLo%253D&md5=1178ff364fb328dca070b5af9795d154
    8. 8
      Bhakta, S. A.; Evans, E.; Benavidez, T. E.; Garcia, C. D. Protein Adsorption onto Nanomaterials for the Development of Biosensors and Analytical Devices: A Review. Anal. Chim. Acta 2015, 872, 7– 25,  DOI: 10.1016/j.aca.2014.10.031
      8
      Protein adsorption onto nanomaterials for the development of biosensors and analytical devices: A review
      Bhakta, Samir A.; Evans, Elizabeth; Benavidez, Tomas E.; Garcia, Carlos D.
      Analytica Chimica Acta (2015), 872 (), 7-25CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)
      A review on the use of nanomaterials, specifically nanoparticles and nanostructured films, for efficiently adsorbing a protein with a minimized structural change for its immobilization, and developing a biosensor or an anal. device.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvVGgtrjM&md5=8f94677bf281b72443cae973449d4603
    9. 9
      Lagraulet, A. Current Clinical and Pharmaceutical Applications of Microarrays: From Disease Biomarkers Discovery to Automated Diagnostics. JALA 2010, 15, 405– 413,  DOI: 10.1016/j.jala.2010.06.011
      9
      Current clinical and pharmaceutical applications of microarrays: From disease biomarkers discovery to automated diagnostics
      Lagraulet, Adriana
      JALA (2010), 15 (5), 405-413CODEN: JALLFO; ISSN:1535-5535. (Elsevier)
      A review. Microarrays used for measuring chromosomal aberrations in genomic DNA and for defining gene expression patterns have become almost routine. A microarray consists of an arrayed series of microscopic spots each contg. either DNA or protein mols. known as feature reporters. Advances in microarray fabrication and in feature detection systems, such as high-resoln. scanners and their assocd. software, lead to high-throughput screening of the genome or the transcriptome of a cell or a group of cells in only few days. Despite the potential of high-d. microarrays, several problems about data interpretation are still to be solved. In addn., targeted microarrays are shown to be useful tools for rapid and accurate diagnosis of diseases. The aim of this review was to discuss the impact of microarrays on different application levels from the definition of disease biomarkers to pharmaceutical and clin. diagnostics.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Wht77N&md5=994f6ce5505be06de67964e144ed9771
    10. 10
      Low, D.; O’Leary, R.; Pujar, N. S. Future of Antibody Purification. J. Chromatogr. B 2007, 848, 48– 63,  DOI: 10.1016/j.jchromb.2006.10.033
      10
      Future of antibody purification
      Low, Duncan; O'Leary, Rhona; Pujar, Narahari S.
      Journal of Chromatography B: Analytical Technologies in the Biomedical and Life Sciences (2007), 848 (1), 48-63CODEN: JCBAAI; ISSN:1570-0232. (Elsevier B.V.)
      A review. Antibody purifn. seems to be safely ensconced in a platform, now well-established by way of multiple commercialized antibody processes. However, natural evolution compels us to peer into the future. This is driven not only by a large, projected increase in the no. of antibody therapies, but also by dramatic improvements in upstream productivity, and process economics. Although disruptive technologies have yet escaped downstream processes, evolution of the so-called platform is already evident in antibody processes in late-stage development. Here we perform a wide survey of technologies that are competing to be part of that platform, and provide our [inherently dangerous] assessment of those that have the most promise.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXislWlsrw%253D&md5=1f62286a745fa1a2fc43488dc436b82a
    11. 11
      Saxena, A.; Tripathi, B. P.; Kumar, M.; Shahi, V. K. Membrane-Based Techniques for the Separation and Purification of Proteins: An Overview. Adv. Colloid Interface Sci. 2009, 145, 1– 22,  DOI: 10.1016/j.cis.2008.07.004
      11
      Membrane-based techniques for the separation and purification of proteins: An overview
      Saxena, Arunima; Tripathi, Bijay P.; Kumar, Mahendra; Shahi, Vinod K.
      Advances in Colloid and Interface Science (2009), 145 (1-2), 1-22CODEN: ACISB9; ISSN:0001-8686. (Elsevier B.V.)
      A review. Membrane processes are increasingly reported for various applications in both upstream and downstream technol., such as microfiltration, ultrafiltration, emerging processes as membrane chromatog., high performance tangential flow filtration, and electrophoretic membrane contactor. Membrane-based processes are playing crit. role in the field of sepn./purifn. of biotechnol. products. Membranes became an integral part of biotechnol. and improvements in membrane technol. are now focused on high resoln. of bioproduct. In biosepn., applications of membrane technologies include protein prodn./purifn., protein-virus sepn. This manuscript provides an overview of recent developments and published literature in membrane technol., focusing on special characteristics of the membranes and membrane-based processes that are now used for the prodn. and purifn. of proteins.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhsVKntLbK&md5=75f591c1a108d55da706f1495131b8e3
    12. 12
      Vogel, V.; Baneyx, G. The Tissue Engineering Puzzle: A Molecular Perspective. Annu. Rev. Biomed. Eng. 2003, 5, 441– 463,  DOI: 10.1146/annurev.bioeng.5.040202.121615
      12
      The tissue engineering puzzle: A molecular perspective
      Vogel, Viola; Baneyx, Gretchen
      Annual Review of Biomedical Engineering (2003), 5 (), 441-463, 2 platesCODEN: ARBEF7; ISSN:1523-9829. (Annual Reviews Inc.)
      A review. The inability of biomaterial scaffolds to functionally integrate into surrounding tissue is one of the major roadblocks to developing new biomaterials and tissue-engineering scaffolds. Despite considerable advances, current approaches to engineering cell-surface interactions fall short in mimicking the complexity of signals through which surrounding tissue regulates cell behavior. Cells adhere and interact with their extracellular environment via integrins, and their ability to activate assocd. downstream signaling pathways depends on the character of adhesion complexes formed between cells and their extracellular matrix. In particular, α5β1 and αvβ3 integrins are central to regulating downstream events, including cell survival and cell-cycle progression. In contrast to previous findings that αvβ3 integrins promote angiogenesis, recent evidence argues that αvβ3 integrins may act as neg. regulators of proangiogenic integrins such as α5β1. This suggests that fibronectin is crit. for scaffold vascularization because it is the only mammalian adhesion protein that binds and activates α5β1 integrins. Cells are furthermore capable of stretching fibronectin matrixes such that the protein partially unfolds, and recent computational simulations provide structural models of how mech. stretching affects fibronectin function. The authors propose a model whereby excessive tension generated by cells in contact to biomaterials may in fact render fibronectin fibrils nonangiogenic and potentially inhibit vascularization. The model could explain why current biomaterials independent of their surface chemistries and textures fail to vascularize.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXotlGqs74%253D&md5=f5e5599b7e4eecf287b8f1cc6ced90e0
    13. 13
      Vogler, E. A. Protein Adsorption in Three Dimensions. Biomaterials 2012, 33, 1201– 1237,  DOI: 10.1016/j.biomaterials.2011.10.059
      13
      Protein adsorption in three dimensions
      Vogler, Erwin A.
      Biomaterials (2012), 33 (5), 1201-1237CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)
      A review. Recent exptl. and theor. work clarifying the phys. chem. of blood-protein adsorption from aq.-buffer soln. to various kinds of surfaces is reviewed and interpreted within the context of biomaterial applications, esp. toward development of cardiovascular biomaterials. The importance of this subject in biomaterials surface science is emphasized by reducing the "protein-adsorption problem" to three core questions that require quant. answer. An overview of the protein-adsorption literature identifies some of the sources of inconsistency among many investigators participating in more than five decades of focused research. A tutorial on the fundamental biophys. chem. of protein adsorption sets the stage for a detailed discussion of the kinetics and thermodn. of protein adsorption, including adsorption competition between two proteins for the same adsorbent immersed in a binary-protein mixt. Both kinetics and steady-state adsorption can be rationalized using a single interpretive paradigm asserting that protein mols. partition from soln. into a three-dimensional (3D) interphase sepg. bulk soln. from the phys.-adsorbent surface. Adsorbed protein collects in one-or-more adsorbed layers, depending on protein size, soln. concn., and adsorbent surface energy (water wettability). The adsorption process begins with the hydration of an adsorbent surface brought into contact with an aq.-protein soln. Surface hydration reactions instantaneously form a thin, pseudo-2D interface between the adsorbent and protein soln. Protein mols. rapidly diffuse into this newly formed interface, creating a truly 3D interphase that inflates with arriving proteins and fills to capacity within milliseconds at mg/mL bulk-soln. concns. C B. This inflated interphase subsequently undergoes time-dependent (minutes-to-hours) decrease in vol. V I by expulsion of either-or-both interphase water and initially adsorbed protein. Interphase protein concn. C I increases as V I decreases, resulting in slow redn. in interfacial energetics. Steady state is governed by a net partition coeff. P=(CI/CB). In the process of occupying space within the interphase, adsorbing protein mols. must displace an equiv. vol. of interphase water. Interphase water is itself assocd. with surface-bound water through a network of transient hydrogen bonds. Displacement of interphase water thus requires an amt. of energy that depends on the adsorbent surface chem./energy. This "adsorption-dehydration" step is the significant free energy cost of adsorption that controls the max. amt. of protein that can be adsorbed at steady state to a unit adsorbent surface area (the adsorbent capacity). As adsorbent hydrophilicity increases, adsorbent capacity monotonically decreases because the energetic cost of surface dehydration increases, ultimately leading to no protein adsorption near an adsorbent water wettability (surface energy) characterized by a water contact angle θ→65°. Consequently, protein does not adsorb (accumulate at interphase concns. greater than bulk soln.) to more hydrophilic adsorbents exhibiting θ<65°. For adsorbents bearing strong Lewis acid/base chem. such as ion-exchange resins, protein/surface interactions can be highly favorable, causing protein to adsorb in multilayers in a relatively thick interphase. A straightforward, three-component free energy relationship captures salient features of protein adsorption to all surfaces predicting that the overall free energy of protein adsorption ΔGadso is a relatively small multiple of thermal energy for any surface chem. (except perhaps for bioengineered surfaces bearing specific ligands for adsorbing protein) because a surface chem. that interacts chem. with proteins must also interact with water through hydrogen bonding. In this way, water moderates protein adsorption to any surface by competing with adsorbing protein mols. This Leading Opinion ends by proposing several changes to the protein-adsorption paradigm that might advance answers to the three core questions that frame the "protein-adsorption problem" that is so fundamental to biomaterials surface science.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsF2ltrjJ&md5=0e2d118231562af07b8574a503f467b6
    14. 14
      Rabe, M.; Verdes, D.; Seeger, S. Understanding Protein Adsorption Phenomena at Solid Surfaces. Adv. Colloid Interface Sci. 2011, 162, 87– 106,  DOI: 10.1016/j.cis.2010.12.007
      14
      Understanding protein adsorption phenomena at solid surfaces
      Rabe, Michael; Verdes, Dorinel; Seeger, Stefan
      Advances in Colloid and Interface Science (2011), 162 (1-2), 87-106CODEN: ACISB9; ISSN:0001-8686. (Elsevier B.V.)
      A review. Protein adsorption at solid surfaces plays a key role in many natural processes and has therefore promoted a widespread interest in many research areas. Despite considerable progress in this field there are still widely differing and even contradictive opinions on how to explain the frequently obsd. phenomena such as structural rearrangements, cooperative adsorption, overshooting adsorption kinetics, or protein aggregation. In this review recent achievements and new perspectives on protein adsorption processes are comprehensively discussed. The main focus is put on commonly postulated mechanistic aspects and their translation into math. concepts and model descriptions. Relevant exptl. and computational strategies to practically approach the field of protein adsorption mechanisms and their impact on current successes are outlined.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXitFaks7g%253D&md5=f711d1ef1c3ef137808f1edcf0caeec1
    15. 15
      Secundo, F. Conformational Changes of Enzymes Upon Immobilisation. Chem. Soc. Rev. 2013, 42, 6250– 6261,  DOI: 10.1039/c3cs35495d
      15
      Conformational changes of enzymes upon immobilisation
      Secundo, Francesco
      Chemical Society Reviews (2013), 42 (15), 6250-6261CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Protein conformation plays a crucial role in detg. both the catalytic efficiency and the chemo-, regio- and enantioselectivity of enzymes, thus eventually influencing their exploitability in biotechnol. applications. Inevitably, immobilization processes alter the natural mol. environment of enzymes, and quite often affect their catalytic activity through different mechanisms such as reduced accessibility of the substrate to the catalytic active center, loss of the enzyme dynamic properties and alteration of the conformational integrity of the enzyme. This tutorial review outlines first the most common spectroscopic techniques used for investigating the conformation of immobilized proteins, and then examines how protein loading and polar and hydrophobic/hydrophilic interactions with the carrier affect the structural and dynamic features of enzymes. The nanoscale-level studies in which protein conformational changes, detd. either by exptl. approaches or by homol. modeling, are correlated with the size and shape of the support are also discussed. Altogether, these results should provide useful information on how supports and/or enzymes have to be tailored to improve biocatalyst performance.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtVKhtrrL&md5=343de02ca34fdaefa8942e66e200ba55
    16. 16
      Koklu, A.; Ohayon, D.; Wustoni, S.; Druet, V.; Saleh, A.; Inal, S. Organic Bioelectronic Devices for Metabolite Sensing. Chem. Rev. 2022, 122, 4581– 4635,  DOI: 10.1021/acs.chemrev.1c00395
      16
      Organic Bioelectronic Devices for Metabolite Sensing
      Koklu, Anil; Ohayon, David; Wustoni, Shofarul; Druet, Victor; Saleh, Abdulelah; Inal, Sahika
      Chemical Reviews (Washington, DC, United States) (2022), 122 (4), 4581-4635CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Electrochem. detection of metabolites is essential for early diagnosis and continuous monitoring of a variety of health conditions. This review focuses on org. electronic material-based metabolite sensors and highlights their potential to tackle crit. challenges assocd. with metabolite detection. We provide an overview of the distinct classes of org. electronic materials and biorecognition units used in metabolite sensors, explain the different detection strategies developed to date, and identify the advantages and drawbacks of each technol. We then benchmark state-of-the-art org. electronic metabolite sensors by categorizing them based on their application area (in vitro, body-interfaced, in vivo, and cell-interfaced). Finally, we share our perspective on using org. bioelectronic materials for metabolite sensing and address the current challenges for the devices and progress to come.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXitFKgsr%252FJ&md5=5e31573a5985b4d3804c9bc0d6caa0f0
    17. 17
      Saboe, P. O.; Conte, E.; Farell, M.; Bazan, G. C.; Kumar, M. Biomimetic and Bioinspired Approaches for Wiring Enzymes to Electrode Interfaces. Energy Environ. Sci. 2017, 10, 14– 42,  DOI: 10.1039/c6ee02801b
      17
      Biomimetic and bioinspired approaches for wiring enzymes to electrode interfaces
      Saboe, Patrick O.; Conte, Emelia; Farell, Megan; Bazan, Guillermo C.; Kumar, Manish
      Energy & Environmental Science (2017), 10 (1), 14-42CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
      Biomimetic and bioinspired approaches to redox enzyme wiring involve borrowing structures and strategies found in biol. electron transfer systems for use in engineered devices. Redox protein-electrode systems are evolving for several applications, including energy, biomedical and environmental purposes. This review is intended to be both "tutorial" and comprehensive in that we provide a guide to understand, design, and improve electrode interfaces for redox enzyme electron transfer processes in devices. The review examines electrode interfaces by directly comparing them with biol. electron transfer systems. First, the mechanisms, theory, and structures for electron transfer in biol. systems are provided, followed by anal. of the strategies and structures engineered in redox-protein devices. The review describes the challenges of constructing and applying redox enzyme devices, including the poor elec. contact between electrodes and enzymes and low lifetime and scalability of devices.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhvVShu7%252FJ&md5=515d95f56b44f7da8fb8139d3183971c
    18. 18
      Pinyou, P.; Blay, V.; Muresan, L. M.; Noguer, T. Enzyme-Modified Electrodes for Biosensors and Biofuel Cells. Mater. Horiz. 2019, 6, 1336– 1358,  DOI: 10.1039/c9mh00013e
      18
      Enzyme-modified electrodes for biosensors and biofuel cells
      Pinyou, Piyanut; Blay, Vincent; Muresan, Liana Maria; Noguer, Thierry
      Materials Horizons (2019), 6 (7), 1336-1358CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
      A review. In biosensors and biofuel cells, it is often desirable to accelerate the electron transfer rate between the enzyme and electrode surface to improve the performance of the devices (sensitivity or power output). To this end, in this review, we focus on three important strategies available to improve the performance of enzyme-modified electrodes: the use of protein engineering, designer polymers, and the introduction of nanomaterials. Engineering the protein or proteins that constitute the biocatalytic elements allow tuning their stability, activity, and specificity. It can also allow changing the enzyme immobilization efficiency (adsorption vs. covalent immobilization, for example). If direct electron transfer is not favorable, it may be possible to introduce polymers in the system that mediate the electron transfer to or from the electrode surface. Significant advances have recently been made on the design of polymers to modify electrodes, including molecularly imprinted polymers and responsive polymers. A third element that can be incorporated into electrodes is nanoparticles. These nanomaterials can act as scaffolds to immobilize the biocatalytic elements through adsorption or chem. reaction with functional groups, increasing the surface area and the robustness of the electrode. A wealth of nanomaterials is being tested as part of novel enzyme-modified electrode designs, including graphene, carbon nanotubes, metallic nanoparticles, silicas, and metal-org. frameworks. Some of these can also be designed as nanowires to enable or shorten the direct electron transfer from distal active sites in the enzymes. In addn. to these strategies, we also highlight selected applications of enzyme-modified electrodes, including glucose biosensing, self-powered biosensors, and self-charging biosupercapacitors. We conclude the review with a reflection on novel approaches, applications, and challenges that we foresee can impact how to design the enzyme-modified electrodes of tomorrow.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXntVSrtLY%253D&md5=4bc2b099a63cce0be35d935547dc72b9
    19. 19
      Mateo, C.; Palomo, J. M.; Fernandez-Lorente, G.; Guisan, J. M.; Fernandez-Lafuente, R. Improvement of Enzyme Activity, Stability and Selectivity Via Immobilization Techniques. Enzyme Microb. Technol. 2007, 40, 1451– 1463,  DOI: 10.1016/j.enzmictec.2007.01.018
      19
      Improvement of enzyme activity, stability and selectivity via immobilization techniques
      Mateo, Cesar; Palomo, Jose M.; Fernandez-Lorente, Gloria; Guisan, Jose M.; Fernandez-Lafuente, Roberto
      Enzyme and Microbial Technology (2007), 40 (6), 1451-1463CODEN: EMTED2; ISSN:0141-0229. (Elsevier B.V.)
      A review. In spite of their excellent catalytic properties, enzyme properties usually have to be improved before their implementation at industrial scale (where many cycles of high yield processes are desired). Generally, sol. enzymes have to be immobilized to be reused for long times in industrial reactors and, in addn. to that, some other crit. enzyme properties have to be improved like stability, activity, inhibition by reaction products, and selectivity toward non-natural substrates. Some strategies to improve these enzyme properties during the performance of tailor-made enzyme immobilization protocols are reviewed here. In this way, immobilized enzymes may also exhibit much better functional properties than the corresponding sol. enzymes by very simple immobilization protocols. For example, multi-point and multi-subunit covalent immobilization improve the stability of monomeric or multimeric enzymes. Moreover, enantioselectivity of different enzymes (e.g., lipases) may be also dramatically improved (from E = 1 to >100) by performing different immobilization protocols on the same enzyme. In all cases, enzyme engineering via immobilization techniques is perfectly compatible with other chem. or biol. approaches to improve enzyme functions and the final success depend on the availability of a wide battery of immobilization protocols.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXjsleisbk%253D&md5=7f09d763070f2e9ce47051f04cab3101
    20. 20
      Jesionowski, T.; Zdarta, J.; Krajewska, B. Enzyme Immobilization by Adsorption: A Review. Adsorption 2014, 20, 801– 821,  DOI: 10.1007/s10450-014-9623-y
      20
      Enzyme immobilization by adsorption: a review
      Jesionowski, Teofil; Zdarta, Jakub; Krajewska, Barbara
      Adsorption (2014), 20 (5-6), 801-821CODEN: ADSOFO; ISSN:0929-5607. (Springer)
      A review. Endowed with unparalleled high catalytic activity and selectivity, enzymes offer enormous potential as catalysts in practical applications. These applications, however, are seriously hampered by enzymes' low thermal and chem. stabilities. One way to improve these stabilities is the enzyme immobilization. Among various tested methods of this process that make use of different enzyme-carrier interactions, immobilization by adsorption on solid carriers has appeared most common. According to these findings, in this review we present a comparative anal. of the literature reports on the recent trends in the immobilization of the enzymes by adsorption. This thorough study was prepd. in order to provide a deeper understanding of the process. Both carriers, carrier modifiers and procedures developed for effective adsorption of the enzymes are discussed. The review may thus be helpful in choosing the right adsorption scheme for a given enzyme to achieve the improvement of its stability and activity for a specific application.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtVGgsbvJ&md5=3501929307ec70fb7c06df11fb45213c
    21. 21
      Tello, A.; Cao, R.; Marchant, M. J.; Gomez, H. Conformational Changes of Enzymes and Aptamers Immobilized on Electrodes. Bioconjugate Chem. 2016, 27, 2581– 2591,  DOI: 10.1021/acs.bioconjchem.6b00553
      21
      Conformational Changes of Enzymes and Aptamers Immobilized on Electrodes
      Tello, Alejandra; Cao, Roberto; Marchant, Maria Jose; Gomez, Humberto
      Bioconjugate Chemistry (2016), 27 (11), 2581-2591CODEN: BCCHES; ISSN:1043-1802. (American Chemical Society)
      A review. Conformation constitutes a vital property of biomols., esp. in the cases of enzymes and aptamers, and is essential in defining their mol. recognition ability. When biomols. are immobilized on electrode surfaces, it is very important to have a control on all the possible conformational changes that may occur, either upon the recognition of their targets or by undesired alterations. Both, enzymes and aptamers, immobilized on electrodes are susceptible to conformational changes as a response to the nature of the charge of the surface and of the surrounding environment (pH, temp., ionic strength, etc.). The main goal of this review is to analyze how the conformational changes of enzymes and aptamers immobilized on electrode surfaces have been treated in reports on biosensors and biofuel cells. This topic was selected due to an insufficient information found on the actual conformational changes involved in the function of these bioelectrochem. devices despite its importance.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1yjtb7P&md5=b00a7df3bbe14fd7c4cff3b7d56ecb13
    22. 22
      Ohayon, D.; Nikiforidis, G.; Savva, A.; Giugni, A.; Wustoni, S.; Palanisamy, T.; Chen, X.; Maria, I. P.; Di Fabrizio, E.; Costa, P. M. F. J.; McCulloch, I.; Inal, S. Biofuel Powered Glucose Detection in Bodily Fluids with an N-Type Conjugated Polymer. Nat. Mater. 2020, 19, 456– 463,  DOI: 10.1038/s41563-019-0556-4
      22
      Biofuel powered glucose detection in bodily fluids with an n-type conjugated polymer
      Ohayon, David; Nikiforidis, Georgios; Savva, Achilleas; Giugni, Andrea; Wustoni, Shofarul; Palanisamy, Tamilarasan; Chen, Xingxing; Maria, Iuliana Petruta; Di Fabrizio, Enzo; Costa, Pedro M. F. J.; McCulloch, Iain; Inal, Sahika
      Nature Materials (2020), 19 (4), 456-463CODEN: NMAACR; ISSN:1476-1122. (Nature Research)
      A promising class of materials for applications that rely on electron transfer for signal generation are the n-type semiconducting polymers. Here we demonstrate the integration of an n-type conjugated polymer with a redox enzyme for the autonomous detection of glucose and power generation from bodily fluids. The reversible, mediator-free, miniaturized glucose sensor is an enzyme-coupled org. electrochem. transistor with a detection range of six orders of magnitude. This n-type polymer is also used as an anode and paired with a polymeric cathode in an enzymic fuel cell to convert the chem. energy of glucose and oxygen into elec. power. The all-polymer biofuel cell shows a performance that scales with the glucose content in the soln. and a stability that exceeds 30 days. Moreover, at physiol. relevant glucose concns. and from fluids such as human saliva, it generates enough power to operate an org. electrochem. transistor, thus contributes to the technol. advancement of self-powered micrometre-scale sensors and actuators that run on metabolites produced in the body.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVertb3E&md5=c407e831fb7cc6f65ee35cc607157024
    23. 23
      Pappa, A. M.; Ohayon, D.; Giovannitti, A.; Maria, I. P.; Savva, A.; Uguz, I.; Rivnay, J.; McCulloch, I.; Owens, R. M.; Inal, S. Direct Metabolite Detection with an N-Type Accumulation Mode Organic Electrochemical Transistor. Sci. Adv. 2018, 4, eaat0911  DOI: 10.1126/sciadv.aat0911
      There is no corresponding record for this reference.
    24. 24
      Savva, A.; Ohayon, D.; Surgailis, J.; Paterson, A. F.; Hidalgo, T. C.; Chen, X.; Maria, I. P.; Paulsen, B. D.; Petty, A. J., II; Rivnay, J.; McCulloch, I.; Inal, S. Solvent Engineering for High-Performance N-Type Organic Electrochemical Transistors. Adv. Electron. Mater. 2019, 5, 1900249,  DOI: 10.1002/aelm.201900249
      There is no corresponding record for this reference.
    25. 25
      Druet, V.; Nayak, P. D.; Koklu, A.; Ohayon, D.; Hama, A.; Chen, X.; Moser, M.; McCulloch, I.; Inal, S. Operation Mechanism of N-Type Organic Electronic Metabolite Sensors. Adv. Electron. Mater. 2022, 8, 2200065,  DOI: 10.1002/aelm.202200065
      25
      Operation Mechanism of n-Type Organic Electronic Metabolite Sensors
      Druet, Victor; Nayak, Prem D.; Koklu, Anil; Ohayon, David; Hama, Adel; Chen, Xingxing; Moser, Maximilian; McCulloch, Iain; Inal, Sahika
      Advanced Electronic Materials (2022), 8 (10), 2200065CODEN: AEMDBW; ISSN:2199-160X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The integration of n-type (electron-transporting) polymers with oxidase enzymes has allowed building high-performance org. electrochem. transistor (OECT) based metabolite sensors. Yet, the operation mechanism of these devices is poorly understood. Here, the process is investigated for the conversion of metabolite oxidn. to elec. current in an n-type org. electrochem. transistor (n-OECT). By monitoring oxygen (O2), hydrogen peroxide, and pH changes in the electrolyte as well as the potential of each elec. contact of the n-OECT during glucose detection, light is shed on the phys. phenomena occurring at the polymer-enzyme interface. It is shown that the n-type film performs O2 redn. reaction in its doped state and that the n-OECT characteristics are sensitive to O2. A correlation is found between the consumption of electrolyte-dissolved O2 and the generation of n-OECT current during the metabolite oxidn. The results demonstrate how the sensitivity of a polymer to O2, species known to deteriorate the performance of many semiconductor devices, becomes a feature to exploit in sensor applications. The importance of in operando anal. of the electrolyte compn. and the terminal potentials is highlighted for understanding the operation mechanism of bioelectronic devices and for sensor design and materials development.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhsFCisbnP&md5=3051c68d3d8131a162f8a2c46f3acde7
    26. 26
      Feng, K.; Shan, W.; Wang, J.; Lee, J.-W.; Yang, W.; Wu, W.; Wang, Y.; Kim, B. J.; Guo, X.; Guo, H. Cyano-Functionalized N-Type Polymer with High Electron Mobility for High-Performance Organic Electrochemical Transistors. Adv. Mater. 2022, 34, 2201340,  DOI: 10.1002/adma.202201340
      26
      Cyano-functionalized n-type polymer with high electron mobility for high-performance organic electrochemical transistors
      Feng, Kui; Shan, Wentao; Wang, Junwei; Lee, Jin-Woo; Yang, Wanli; Wu, Wenchang; Wang, Yimei; Kim, Bumjoon J.; Guo, Xugang; Guo, Han
      Advanced Materials (Weinheim, Germany) (2022), 34 (24), 2201340CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      N-Type org. mixed ionic-electronic conductors (OMIECs) with high electron mobility are scarce and highly challenging to develop. As a result, the figure-of-merit (μC*) of n-type org. electrochem. transistors (OECTs) lags far behind the p-type analogs, restraining the development of OECT-based low-power complementary circuits and biosensors. Here, two n-type donor-acceptor (D-A) polymers based on fused bithiophene imide dimer f-BTI2 as the acceptor unit and thienylene-vinylene-thienylene (TVT) as the donor co-unit are reported. The cyanation of TVT enables polymer f-BTI2g-TVTCN with simultaneously enhanced ion-uptake ability, film structural order, and charge-transport property. As a result, it is able to obtain a high volumetric capacitance (C*) of 170 ± 22 F cm-3 and a record OECT electron mobility (μe,OECT) of 0.24 cm2 V-1 s-1 for f-BTI2g-TVTCN, subsequently achieving a state-of-the-art μC* of 41.3 F cm-1 V-1 s-1 and geometry-normalized transconductance (gm,norm) of 12.8 S cm-1 in n-type accumulation-mode OECTs. In contrast, only a moderate μC* of 1.50 F cm-1 V-1 s-1 is measured for the non-cyanated polymer f-BTI2g-TVT. These remarkable results demonstrate the great power of cyano functionalization of polymer semiconductors in developing n-type OMIECs with substantial electron mobility in aq. environment for high-performance n-type OECTs.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhtlGktbnO&md5=1ba499f4b6ddc43f8a0dbbc0b5c47b2c
    27. 27
      Wu, H.-Y.; Yang, C.-Y.; Li, Q.; Kolhe, N. B.; Strakosas, X.; Stoeckel, M.-A.; Wu, Z.; Jin, W.; Savvakis, M.; Kroon, R.; Tu, D.; Woo, H. Y.; Berggren, M.; Jenekhe, S. A.; Fabiano, S. Influence of Molecular Weight on the Organic Electrochemical Transistor Performance of Ladder-Type Conjugated Polymers. Adv. Mater. 2022, 34, 2106235,  DOI: 10.1002/adma.202106235
      27
      Influence of Molecular Weight on the Organic Electrochemical Transistor Performance of Ladder-Type Conjugated Polymers
      Wu, Han-Yan; Yang, Chi-Yuan; Li, Qifan; Kolhe, Nagesh B.; Strakosas, Xenofon; Stoeckel, Marc-Antoine; Wu, Ziang; Jin, Wenlong; Savvakis, Marios; Kroon, Renee; Tu, Deyu; Woo, Han Young; Berggren, Magnus; Jenekhe, Samson A.; Fabiano, Simone
      Advanced Materials (Weinheim, Germany) (2022), 34 (4), 2106235CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Org. electrochem. transistors (OECTs) hold promise for developing a variety of high-performance (bio-)electronic devices/circuits. While OECTs based on p-type semiconductors have achieved tremendous progress in recent years, n-type OECTs still suffer from low performance, hampering the development of power-efficient electronics. Here, it is demonstrated that fine-tuning the mol. wt. of the rigid, ladder-type n-type polymer poly(benzimidazobenzophenanthroline) (BBL) by only one order of magnitude (from 4.9 to 51 kDa) enables the development of n-type OECTs with record-high geometry-normalized transconductance (gm,norm ≈ 11 S cm-1) and electron mobility x volumetric capacitance (μC* ≈ 26 F cm-1 V-1 s-1), fast temporal response (0.38 ms), and low threshold voltage (0.15 V). This enhancement in OECT performance is ascribed to a more efficient intermol. charge transport in high-mol.-wt. BBL than in the low-mol.-wt. counterpart. OECT-based complementary inverters are also demonstrated with record-high voltage gains of up to 100 V V-1 and ultralow power consumption down to 0.32 nW, depending on the supply voltage. These devices are among the best sub-1 V complementary inverters reported to date. These findings demonstrate the importance of mol. wt. in optimizing the OECT performance of rigid org. mixed ionic-electronic conductors and open for a new generation of power-efficient org. (bio-)electronic devices.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXislaqu7bO&md5=95e3105723d712eb9ae3f0dd684382f4
    28. 28
      Tang, H.; Liang, Y.; Liu, C.; Hu, Z.; Deng, Y.; Guo, H.; Yu, Z.; Song, A.; Zhao, H.; Zhao, D.; Zhang, Y.; Guo, X.; Pei, J.; Ma, Y.; Cao, Y.; Huang, F. A Solution-Processed N-Type Conducting Polymer with Ultrahigh Conductivity. Nature 2022, 611, 271– 277,  DOI: 10.1038/s41586-022-05295-8
      28
      A solution-processed n-type conducting polymer with ultrahigh conductivity
      Tang, Haoran; Liang, Yuanying; Liu, Chunchen; Hu, Zhicheng; Deng, Yifei; Guo, Han; Yu, Zidi; Song, Ao; Zhao, Haiyang; Zhao, Duokai; Zhang, Yuanzhu; Guo, Xugang; Pei, Jian; Ma, Yuguang; Cao, Yong; Huang, Fei
      Nature (London, United Kingdom) (2022), 611 (7935), 271-277CODEN: NATUAS; ISSN:1476-4687. (Nature Portfolio)
      Conducting polymers (CPs) with high cond. and soln. processability have made great advances since the pioneering work on doped polyacetylene1-3, thus creating the new field of 'org. synthetic metals,4. Various high-performance CPs have been realized, which enable the applications of several org. electronic devices5,6. Nevertheless, most CPs exhibit hole-dominant (p-type) transport behavior7,8, whereas the development of n-type analogs lags far behind and only a few exhibit metallic state, typically limited by low doping efficiency and ambient instability. Here we present a facilely synthesized highly conductive n-type polymer poly(benzodifurandione) (PBFDO). The reaction combines oxidative polymn. and in situ reductive n-doping, greatly increasing the doping efficiency, and a doping level of almost 0.9 charges per repeating unit can be achieved. The resultant polymer exhibits a breakthrough cond. of more than 2,000 S cm-1 with excellent stability and an unexpected soln. processability without extra side chains or surfactants. Furthermore, detailed investigations on PBFDO show coherent charge-transport properties and existence of metallic state. The benchmark performances in electrochem. transistors and thermoelec. generators are further demonstrated, thus paving the way for application of the n-type CPs in org. electronics.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38Xis1eiurjK&md5=87de74d405fc23fe19c9d6feeeba535b
    29. 29
      Giovannitti, A.; Maria, I. P.; Hanifi, D.; Donahue, M. J.; Bryant, D.; Barth, K. J.; Makdah, B. E.; Savva, A.; Moia, D.; Zetek, M.; Barnes, P. R. F.; Reid, O. G.; Inal, S.; Rumbles, G.; Malliaras, G. G.; Nelson, J.; Rivnay, J.; McCulloch, I. The Role of the Side Chain on the Performance of N-Type Conjugated Polymers in Aqueous Electrolytes. Chem. Mater. 2018, 30, 2945– 2953,  DOI: 10.1021/acs.chemmater.8b00321
      29
      The Role of the Side Chain on the Performance of N-type Conjugated Polymers in Aqueous Electrolytes
      Giovannitti, Alexander; Maria, Iuliana P.; Hanifi, David; Donahue, Mary J.; Bryant, Daniel; Barth, Katrina J.; Makdah, Beatrice E.; Savva, Achilleas; Moia, Davide; Zetek, Matyas; Barnes, Piers R. F.; Reid, Obadiah G.; Inal, Sahika; Rumbles, Garry; Malliaras, George G.; Nelson, Jenny; Rivnay, Jonathan; McCulloch, Iain
      Chemistry of Materials (2018), 30 (9), 2945-2953CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      We report a design strategy that allows the prepn. of soln. processable n-type materials from low b.p. solvents for org. electrochem. transistors (OECTs). The polymer backbone is based on NDI-T2 copolymers where a branched alkyl side chain is gradually exchanged for a linear ethylene glycol-based side chain. A series of random copolymers was prepd. with glycol side chain percentages of 0, 10, 25, 50, 75, 90, and 100 with respect to the alkyl side chains. These were characterized to study the influence of the polar side chains on interaction with aq. electrolytes, their electrochem. redox reactions, and performance in OECTs when operated in aq. electrolytes. We obsd. that glycol side chain percentages of >50% are required to achieve volumetric charging, while lower glycol chain percentages show a mixed operation with high required voltages to allow for bulk charging of the org. semiconductor. A strong dependence of the electron mobility on the fraction of glycol chains was found for copolymers based on NDI-T2, with a significant drop as alkyl side chains are replaced by glycol side chains.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXotFelu7o%253D&md5=ed7e798bb78dfbee00e02f7d9a5c959d
    30. 30
      Rosas Villalva, D.; Singh, S.; Galuska, L. A.; Sharma, A.; Han, J.; Liu, J.; Haque, M. A.; Jang, S.; Emwas, A. H.; Koster, L. J. A.; Gu, X.; Schroeder, B. C.; Baran, D. Backbone-Driven Host–Dopant Miscibility Modulates Molecular Doping in Ndi Conjugated Polymers. Mater. Horiz. 2022, 9, 500– 508,  DOI: 10.1039/d1mh01357b
      30
      Backbone-driven host-dopant miscibility modulates molecular doping in NDI conjugated polymers
      Rosas Villalva, Diego; Singh, Saumya; Galuska, Luke A.; Sharma, Anirudh; Han, Jianhua; Liu, Jian; Haque, Md Azimul; Jang, Soyeong; Emwas, Abdul Hamid; Koster, L. Jan Anton; Gu, Xiaodan; Schroeder, Bob C.; Baran, Derya
      Materials Horizons (2022), 9 (1), 500-508CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
      Mol. doping is the key to enabling org. electronic devices, however, the design strategies to maximize doping efficiency demands further clarity and comprehension. Previous reports focus on the effect of the side chains, but the role of the backbone is still not well understood. In this study, we synthesize a series of NDI-based copolymers with bithiophene, vinylene, and acetylenic moieties (P1G, P2G, and P3G, resp.), all contg. branched triethylene glycol side chains. Using computational and exptl. methods, we explore the impact of the conjugated backbone using three key parameters for doping in org. semiconductors: energy levels, microstructure, and miscibility. Our exptl. results show that P1G undergoes the most efficient n-type doping owed primarily to its higher dipole moment, and better host-dopant miscibility with N-DMBI. In contrast, P2G and P3G possess more planar backbones than P1G, but the lack of long-range order, and poor host-dopant miscibility limit their doping efficiency. Our data suggest that backbone planarity alone is not enough to maximize the elec. cond. (σ) of n-type doped org. semiconductors, and that backbone polarity also plays an important role in enhancing σ via host-dopant miscibility. Finally, the thermoelec. properties of doped P1G exhibit a power factor of 0.077μW m-1 K-2, and ultra-low in-plane thermal cond. of 0.13 W m-1K-1 at 5 mol% of N-DMBI, which is among the lowest thermal cond. values reported for n-type doped conjugated polymers.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXislygur7P&md5=0c1373ff0923e96345a80c6b7ebd0bc9
    31. 31
      Singh, K.; Blanford, C. F. Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring: A Technique to Optimize Enzyme Use in Bioelectrocatalysis. ChemCatChem 2014, 6, 921– 929,  DOI: 10.1002/cctc.201300900
      31
      Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring: A Technique to Optimize Enzyme Use in Bioelectrocatalysis
      Singh, Kulveer; Blanford, Christopher F.
      ChemCatChem (2014), 6 (4), 921-929CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
      This Concept article outlines how an electrochem. quartz crystal microbalance with dissipation monitoring (E-QCM-D) is used as a tool to follow adsorption and inactivation processes of immobilized oxidoreductases and to det. their specific activity simultaneously. Plots that relate activity to the adsorbed mass and dissipation have distinct features that can be used to diagnose the mechanisms of long-term activity loss. Along with model plots, this article highlights some of the key advances made by using the technique and how it has been applied to biocatalytic processes in which electrons are transferred directly between an electrode and an immobilized enzyme.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlt1Wgu7s%253D&md5=1cbcb457e1ab07822d93ab72de21e54f
    32. 32
      Wiedemann, C.; Bellstedt, P.; Görlach, M. Capito─a Web Server-Based Analysis and Plotting Tool for Circular Dichroism Data. Bioinformatics 2013, 29, 1750– 1757,  DOI: 10.1093/bioinformatics/btt278
      32
      CAPITO-a web server-based analysis and plotting tool for circular dichroism data
      Wiedemann, Christoph; Bellstedt, Peter; Goerlach, Matthias
      Bioinformatics (2013), 29 (14), 1750-1757CODEN: BOINFP; ISSN:1367-4803. (Oxford University Press)
      Motivation: CD (CD) spectroscopy is one of the most versatile tools to study protein folding and to validate the proper fold of purified proteins. Here, we aim to provide a readily accessible, user-friendly and platform-independent tool capable of analyzing multiple CD datasets of virtually any format and returning results as high-quality graphical output to the user. Results: CAPITO (CD Anal. and Plotting Tool) is a novel web server-based tool for analyzing and plotting CD data. It allows reliable estn. of secondary structure content utilizing different approaches. CAPITO accepts multiple CD datasets and, hence, is well suited for a wide application range such as the anal. of temp. or pH-dependent (un)folding and the comparison of mutants.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtVOjsrjN&md5=1eedf83b9d1dd24330e87eb8dafff1b7
    33. 33
      Koklu, A.; Wustoni, S.; Musteata, V.-E.; Ohayon, D.; Moser, M.; McCulloch, I.; Nunes, S. P.; Inal, S. Microfluidic Integrated Organic Electrochemical Transistor with a Nanoporous Membrane for Amyloid-Β Detection. ACS Nano 2021, 15, 8130– 8141,  DOI: 10.1021/acsnano.0c09893
      33
      Microfluidic Integrated Organic Electrochemical Transistor with a Nanoporous Membrane for Amyloid-β Detection
      Koklu, Anil; Wustoni, Shofarul; Musteata, Valentina-Elena; Ohayon, David; Moser, Maximilian; McCulloch, Iain; Nunes, Suzana P.; Inal, Sahika
      ACS Nano (2021), 15 (5), 8130-8141CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Alzheimer's disease (AD) is a neurodegenerative disorder assocd. with a severe loss in thinking, learning, and memory functions of the brain. To date, no specific treatment has been proven to cure AD, with the early diagnosis being vital for mitigating symptoms. A common pathol. change found in AD-affected brains is the accumulation of a protein named amyloid-β (Aβ) into plaques. In this work, we developed a micron-scale org. electrochem. transistor (OECT) integrated with a microfluidic platform for the label-free detection of Aβ aggregates in human serum. The OECT channel-electrolyte interface was covered with a nanoporous membrane functionalized with Congo red (CR) mols. showing a strong affinity for Aβ aggregates. Each aggregate binding to the CR-membrane modulated the vertical ion flow toward the channel, changing the transistor characteristics. Thus, the device performance was not limited by the soln. ionic strength nor did it rely on Faradaic reactions or conformational changes of bioreceptors. The high transconductance of the OECT, the precise porosity of the membrane, and the compactness endowed by the microfluidic enabled the Aβ aggregate detection over eight orders of magnitude wide concn. range (femtomolar-nanomolar) in 1μL of human serum samples. We expanded the operation modes of our transistors using different channel materials and found that the accumulation-mode OECTs displayed the lowest power consumption and highest sensitivities. Ultimately, these robust, low-power, sensitive, and miniaturized microfluidic sensors helped to develop point-of-care tools for the early diagnosis of AD.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXnsVOhtr0%253D&md5=6707b09f300ef21444a3df82453c8c05
    34. 34
      Attwood, S. J.; Kershaw, R.; Uddin, S.; Bishop, S. M.; Welland, M. E. Understanding How Charge and Hydrophobicity Influence Globular Protein Adsorption to Alkanethiol and Material Surfaces. J. Mater. Chem. B 2019, 7, 2349– 2361,  DOI: 10.1039/c9tb00168a
      34
      Understanding how charge and hydrophobicity influence globular protein adsorption to alkanethiol and material surfaces
      Attwood, Simon J.; Kershaw, Rebecca; Uddin, Shahid; Bishop, Steven M.; Welland, Mark E.
      Journal of Materials Chemistry B: Materials for Biology and Medicine (2019), 7 (14), 2349-2361CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
      Every biosensor, bioengineered scaffold or biomedical implant depends crucially on an ability to control protein adsorption at the material surface. Yet the adsorption of proteins to solid surfaces in aq. media is a complex and poorly understood phenomenon. To gain further insights the authors study protein adsorption using the quartz crystal microbalance for 10 model globular proteins interacting with pos., neg., neutral, hydrophobic and mixed alkanethiol monolayers as well as silica, polystyrene and Teflon, equating to ∼200 protein-surface combinations. The charge state of the materials in liq. was measured with at. force microscopy using a colloidal probe and numerically solving the full non-linear Poisson-Boltzmann equation. This approach has allowed the authors to address some of the important questions surrounding the basic principles that govern protein adsorption including the relative importance of net charge and hydrophobicity and why some materials are protein resistant. With the authors' set of mixed monolayer surfaces, the authors can modulate charge over a wide range while eliminating hydrophobic interactions and vice versa - thus permitting detn. of the functional dependence of adsorption on these parameters. This led the authors to develop two empirical predictive models with up to 90% accuracy that together encompass most materials relevant to biotechnol. and biomedical applications.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXjvFSrtb4%253D&md5=f0d012683958f7558a81c96cbe731814
    35. 35
      Xie, Y.; Li, Z.; Zhou, J. Hamiltonian Replica Exchange Simulations of Glucose Oxidase Adsorption on Charged Surfaces. Phys. Chem. Chem. Phys. 2018, 20, 14587– 14596,  DOI: 10.1039/c8cp00530c
      35
      Hamiltonian replica exchange simulations of glucose oxidase adsorption on charged surfaces
      Xie, Yun; Li, Zhanchao; Zhou, Jian
      Physical Chemistry Chemical Physics (2018), 20 (21), 14587-14596CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      The Hamiltonian replica exchange Monte Carlo (H-REMC) algorithm was applied to study protein adsorption and its performance was compared with that of the temp. replica exchange Monte Carlo (T-REMC). Comparisons indicate that the simulation results are consistent but the computational efficiency is improved for H-REMC. H-REMC could accurately and efficiently identify the preferred orientations of glucose oxidase (GOx) on charged surfaces; different preferential GOx orientations on different surfaces and soln. conditions could be spotted with a much fewer no. of simulation runs. On pos. charged surfaces, when electrostatic interactions dominate, the neg. charged GOx can be easily adsorbed with the "standing" orientation for which the substrate-binding domain is accessible to substrates. As the surface charge densities decrease and ionic strengths increase, there is an increasing contribution from the van der Waals (vdW) interactions, and thus more possible orientations appear. When the vdW interactions dominate, the unfavorable "front-lying" becomes the preferred orientation for which the substrate-binding domain is blocked by the surface. On neg. charged surfaces, though GOx has a net charge of -30 e under physiol. conditions, the charged groups are unevenly distributed over the protein surface; the pos. potential regions in the "back" of GOx enable the protein to be adsorbed on neg. charged surfaces with the "back-lying" orientation. The H-REMC provides an alternative method to accurately and efficiently probe the lowest-energy orientation of proteins adsorbed on surfaces for biotechnol. applications.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXotVeht7k%253D&md5=2ad32de202c0a3364283aa780673d8da
    36. 36
      Cho, D. H.; Xie, T.; Truong, J.; Stoner, A. C.; Hahm, J.-i. Recent Advances Towards Single Biomolecule Level Understanding of Protein Adsorption Phenomena Unique to Nanoscale Polymer Surfaces with Chemical Variations. Nano Res. 2020, 13, 1295– 1317,  DOI: 10.1007/s12274-020-2735-7
      36
      Recent advances towards single biomolecule level understanding of protein adsorption phenomena unique to nanoscale polymer surfaces with chemical variations
      Cho, David H.; Xie, Tian; Truong, Johnson; Stoner, Andrew C.; Hahm, Jong-in
      Nano Research (2020), 13 (5), 1295-1317CODEN: NRAEB5; ISSN:1998-0000. (Springer GmbH)
      A review. Abstr.: Protein adsorption onto polymer surfaces is a very complex and ubiquitous phenomenon whose integrated process impacts essential applications in our daily lives such as food packaging materials, health devices, diagnostic tools, and medical products. Increasingly, novel polymer materials with greater chem. intricacy and reduced dimensionality are used for various applications involving adsorbed proteins on their surfaces. Hence, the nature of protein-surface interactions to consider is becoming much more complicated than before. A large body of literature exists for protein adsorption. However, most of these investigations have focused on collectively measured, ensemble-averaged protein behaviors that occur on macroscale and chem. unvarying polymer surfaces instead of direct measurements at the single protein or sub-protein level. In addn., interrogations of protein-polymer adsorption boundaries in these studies were typically carried out by indirect methods, whose insights may not be suitably applied for explaining individual protein adsorption processes occurring onto nanostructured, chem. varying polymer surfaces. Therefore, an important gap in our knowledge still exists that needs to be systematically addressed via direct measurement means at the single protein and sub-protein level. Such efforts will require multifaceted exptl. and theor. approaches that can probe multilength scales of protein adsorption, while encompassing both single proteins and their collective ensemble behaviors at the length scale spanning from the nanoscopic all the way to the macroscopic scale. In this review, key research achievements in nanoscale protein adsorption to date will be summarized. Specifically, protein adsorption studies involving polymer surfaces with their defining feature dimensions and assocd. chem. partitions comparable to the size of individual proteins will be discussed in detail. In this regard, recent works bridging the crucial knowledge gap in protein adsorption will be highlighted. New findings of intriguing protein surface assembly behaviors and adsorption kinetics unique to nanoscale polymer templates will be covered. Single protein and sub-protein level approaches to reveal unique nanoscale protein-polymer surface interactions and protein surface assembly characteristics will be also emphasized. Potential advantages of these research endeavors in laying out fundamentally guided design principles for practical product development will then be discussed. Lastly, important research areas still needed to further narrow the knowledge gap in nanoscale protein adsorption will be identified. [graphic not available: see fulltext].
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXlvVyjtr8%253D&md5=dfd2729e35dc40e8539cba3fd651c3b3
    37. 37
      Seehuber, A.; Dahint, R. Conformation and Activity of Glucose Oxidase on Homogeneously Coated and Nanostructured Surfaces. J. Phys. Chem. B 2013, 117, 6980– 6989,  DOI: 10.1021/jp401906h
      37
      Conformation and Activity of Glucose Oxidase on Homogeneously Coated and Nanostructured Surfaces
      Seehuber, A.; Dahint, R.
      Journal of Physical Chemistry B (2013), 117 (23), 6980-6989CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
      Protein unfolding and loss of protein function upon surface contact is a major problem in biotechnol. and biomedicine. Using glucose oxidase (GOx) as a model protein, we investigated the impact of surface chem., topog., and confinement on enzyme activity, conformation, and affinity. A particular focus lay on the question whether the conformation of surface-bound proteins can be stabilized by embedding nanoscale adsorption sites, here in the form of monodisperse gold nanoparticles (AuNPs), into a protein-repelling matrix material. It was found that on homogeneous surfaces, GOx activity is generally lower than that in its native state and strongly affected by surface chem. Loss of activity is related to an increasing amt. of β-sheets in the GOx secondary structure and a corresponding redn. of α-helical elements. In contrast, on AuNP surfaces, the effect of surface chem. is negligible, and the amt. of adsorbed protein only depends on particle size. The low activity of GOx on all nanostructures studied is again accompanied by an increase of β-sheet and a redn. of α-helical secondary structure. The major cause for protein unfolding on AuNPs thus seems to be the curvature of the surface. In addn., the data suggest that unfavorable orientation of the adsorbed enzyme also contributes to the loss of activity.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXnvVKgsr4%253D&md5=3b263957157b293a23fd8b7e0cdd52b3
    38. 38
      Han, M.; Sethuraman, A.; Kane, R. S.; Belfort, G. Nanometer-Scale Roughness Having Little Effect on the Amount or Structure of Adsorbed Protein. Langmuir 2003, 19, 9868– 9872,  DOI: 10.1021/la030132g
      38
      Nanometer-scale roughness having little effect on the amount or structure of adsorbed protein
      Han, Mina; Sethuraman, Ananthakrishnan; Kane, Ravi S.; Belfort, Georges
      Langmuir (2003), 19 (23), 9868-9872CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Neither the adsorbed amt. per unit actual surface area nor the structural stability of hen egg lysozyme is influenced by increasing the nanometer-scale roughness (5 < Rave < 60 nm) of a series of model substrates. Seven poly(ether sulfone) (PES) ultrafiltration membranes of increasing mean pore size with the same surface chem. were chosen as model rough surface substrates. Topog. images, using at. force microscopy, combined with attenuated total reflection Fourier transform IR spectroscopy (ATR/FTIR) and sessile captive bubble contact angle measurements were used to characterize the surface properties of the substrates. ATR/FTIR spectroscopy together with a newly developed optimization algorithm for predicting the content of secondary structure motifs is used to correlate the secondary structure and amt. of adsorbed lysozyme with the substrate surface roughness. From the adsorption measurements, the net adsorbed amt. (total minus nonspecific adsorbed amt.) of lysozyme corresponded to approx. one monolayer of coverage for all the substrates independent of the roughness. Although lysozyme was structurally disturbed through adsorption to PES substrates, no significant changes in its secondary structure were obsd. with the increasing roughness.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXnsl2ntb0%253D&md5=16dcf1d1af81c3cd9cac5e1a01403ffb
    39. 39
      Nelson, G. W.; Parker, E. M.; Singh, K.; Blanford, C. F.; Moloney, M. G.; Foord, J. S. Surface Characterization and in Situ Protein Adsorption Studies on Carbene-Modified Polymers. Langmuir 2015, 31, 11086– 11096,  DOI: 10.1021/acs.langmuir.5b01644
      39
      Surface Characterization and in situ Protein Adsorption Studies on Carbene-Modified Polymers
      Nelson, Geoffrey W.; Parker, Emily M.; Singh, Kulveer; Blanford, Christopher F.; Moloney, Mark G.; Foord, John S.
      Langmuir (2015), 31 (40), 11086-11096CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Polystyrene thin films were functionalized using a facile two-step chem. protocol involving carbene insertion followed by azo-coupling, permitting the introduction of a range of chem. functional groups, including aniline, hexyl, amine, carboxyl, Ph, phosphonate diester, and ethylene glycol. XPS confirmed the success of the two-step chem. modification with a grafting d. of at least 1/10th of the typical loading d. (1014-1015) of a self-assembled monolayer (SAM). In situ, real-time quartz crystal microbalance with dissipation (QCM-D) studies show that the dynamics of binding of bovine serum albumin (BSA) are different at each modified surface. Mass, viscoelastic, and kinetic data were analyzed, and compared to cheminformatic descriptors (i.e., c log P, polar surface area) typically used for drug discovery. Results show that functionalities may either resist or adsorb BSA, and uniquely influence its adsorption dynamics. It is concluded that carbene-based surface modification can usefully influence BSA binding dynamics in a manner consistent with, and more robust than, traditional systems based on SAM chem.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFejtL%252FF&md5=d50f614724ddf6468c214797815d087e
    40. 40
      Hecht, H.; Kalisz, H.; Hendle, J.; Schmid, R.; Schomburg, D. Crystal Structure of Glucose Oxidase from Aspergillus niger Refined at 2·3 Å Reslution. J. Mol. Biol. 1993, 229, 153– 172,  DOI: 10.1006/jmbi.1993.1015
      40
      Crystal structure of glucose oxidase from Aspergillus niger refined at 2.3 Å resolution
      Hecht, H. J.; Kalisz, H. M.; Hendle, J.; Schmid, R. D.; Schomburg, D.
      Journal of Molecular Biology (1993), 229 (1), 153-72CODEN: JMOBAK; ISSN:0022-2836.
      Glucose oxidase (EC 1.1.3.4) is an FAD-dependent enzyme that catalyzes the oxidn. of β-D-glucose by O2. The crystal structure of the partially deglycosylated enzyme from A. niger was detd. by isomorphous replacement and refined to 2.3 Å resoln. The final crystallog. R-value was 18.1% for reflections between 10.0 and 2.3 Å resoln. The refined model included 580 amino acid residues, the FAD cofactor, 6 N-acetylglucosamine residues, 3 mannose residues, and 152 solvent mols. The FAD-binding domain was topol. very similar to other FAD-binding proteins. The substrate-binding domain was formed from noncontinuous segments of sequence and was characterized by a deep pocket. One side of this pocket was formed by a 6-stranded antiparallel β-sheet with the flavin ring system of FAD located at the bottom of the pocket on the opposite side. Part of the entrance to the active site pocket was at the interface to the 2nd subunit of the dimeric enzyme and was formed by a 20-residue lid, which in addn. covered parts of the FAD-binding site. The carbohydrate moiety attached to Asn-89 at the tip of this lid formed a link between the subunits of the dimer.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXpslSqsg%253D%253D&md5=5ab908e41cb0fffa2b18a07e3e4a364e
    41. 41
      Jensen, U. B.; Ferapontova, E. E.; Sutherland, D. S. Quantifying Protein Adsorption and Function at Nanostructured Materials: Enzymatic Activity of Glucose Oxidase at Glad Structured Electrodes. Langmuir 2012, 28, 11106– 11114,  DOI: 10.1021/la3017672
      41
      Quantifying Protein Adsorption and Function at Nanostructured Materials: Enzymatic Activity of Glucose Oxidase at GLAD Structured Electrodes
      Jensen, Uffe B.; Ferapontova, Elena E.; Sutherland, Duncan S.
      Langmuir (2012), 28 (30), 11106-11114CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Nanostructured materials strongly modulate the behavior of adsorbed proteins; however, the characterization of such interactions is challenging. Here the authors present a novel method combining protein adsorption studies at nanostructured quartz crystal microbalance sensor surfaces (QCM-D) with optical (surface plasmon resonance SPR) and electrochem. methods (cyclic voltammetry CV) allowing quantification of both bound protein amt. and activity. The redox enzyme glucose oxidase was studied as a model system to explore alterations in protein functional behavior caused by adsorption onto flat and nanostructured surfaces. This enzyme and such materials interactions are relevant for biosensor applications. Novel nanostructured gold electrode surfaces with controlled curvature were fabricated using colloidal lithog. and glancing angle deposition (GLAD). The adsorption of enzyme to nanostructured interfaces is significantly larger compared to flat interfaces even after normalization for the increased surface area, and no substantial desorption was obsd. within 24 h. A decreased enzymic activity was obsd. over the same period of time, which indicates a slow conformational change of the adsorbed enzyme induced by the materials interface. Addnl., the authors make use of inherent localized surface plasmon resonances in these nanostructured materials to directly quantify the protein binding. The authors hereby demonstrate a QCM-D-based methodol. to quantify protein binding at complex nanostructured materials. The authors' approach allows label free quantification of protein binding at nanostructured interfaces.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xps1GisLo%253D&md5=6c1d3461cfa0901af4db7a11118bea5e
    42. 42
      Bergman, J.; Wang, Y.; Wigström, J.; Cans, A.-S. Counting the Number of Enzymes Immobilized onto a Nanoparticle-Coated Electrode. Anal. Bioanal. Chem. 2018, 410, 1775– 1783,  DOI: 10.1007/s00216-017-0829-1
      42
      Counting the number of enzymes immobilized onto a nanoparticle-coated electrode
      Bergman, Jenny; Wang, Yuanmo; Wigstroem, Joakim; Cans, Ann-Sofie
      Analytical and Bioanalytical Chemistry (2018), 410 (6), 1775-1783CODEN: ABCNBP; ISSN:1618-2642. (Springer)
      To immobilize enzymes at the surface of a nanoparticle-based electrochem. sensor is a common method to construct biosensors for nonelectroactive analytes. Studying the interactions between the enzymes and nanoparticle support is of great importance in optimizing the conditions for biosensor design. This can be achieved by using a combination of anal. methods to carefully characterize the enzyme nanoparticle coating at the sensor surface while studying the optimal conditions for enzyme immobilization. From this anal. approach, it was found that controlling the enzyme coverage to a monolayer was a key factor to significantly improve the temporal resoln. of biosensors. However, these characterization methods involve both tedious methodologies and working with toxic cyanide solns. Here the authors introduce a new anal. method that allows direct quantification of the no. of immobilized enzymes (glucose oxidase) at the surface of a gold nanoparticle coated glassy carbon electrode. This was achieved by exploiting an electrochem. stripping method for the direct quantification of the d. and size of gold nanoparticles coating the electrode surface and combining this information with quantification of fluorophore-labeled enzymes bound to the sensor surface after stripping off their nanoparticle support. This method is both significantly much faster compared to previously reported methods and with the advantage that this method presented is nontoxic.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXitVCmsb3E&md5=af1e9459012d64ebcd9941afa09cfe1e
    43. 43
      Wang, Y.; Jonkute, R.; Lindmark, H.; Keighron, J. D.; Cans, A.-S. Molecular Crowding and a Minimal Footprint at a Gold Nanoparticle Support Stabilize Glucose Oxidase and Boost Its Activity. Langmuir 2020, 36, 37– 46,  DOI: 10.1021/acs.langmuir.9b02863
      43
      Molecular crowding and a minimal footprint at a gold nanoparticle support stabilize glucose oxidase and boost its activity
      Wang, Yuanmo; Jonkute, Rima; Lindmark, Hampus; Keighron, Jacqueline D.; Cans, Ann-Sofie
      Langmuir (2020), 36 (1), 37-46CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Enzymes conjugated to nanomaterials are used in the design of various biotechnologies. In the development of biosensors, surface modifications with the enzyme glucose oxidase (GOx) serve to aid the detection of blood glucose. In order to optimize sensor effectiveness, the enzyme tertiary structure needs to be preserved upon immobilization to retain the enzyme's catalytic activity. Because of the nature of GOx, it suffers from a tendency to denature when immobilized at a solid surface; hence, methods to optimize enzyme stability are of great importance. Here, we introduce the study of the interaction of GOx to the highly curved surface of 20 nm gold nanoparticles (AuNP) with an absorbed monolayer coating of enzyme as detd. by flocculation assays and quantification of immobilized GOx at the nanoparticle surface. Enzyme crowding was detd. by comparing the no. of enzymes that bind to how many can phys. fit. These measurements show how placing a monolayer of enzyme where the enzyme spreads thin at the AuNP surface still provides stable catalytic performance of up to 14 days compared to enzymes free in soln. Moreover, by the increasing enzyme d. via increasing the amt. of GOx present in soln. during the GOx/AuNP conjugation step creates a molecularly crowded environment at the highly curved nanoparticle surface. This limits the size of the enzyme footprint for attachment and shows that the activity per enzyme can be enhanced up to 300%. This is of great importance for implementing stable and sensitive sensor technologies that are constructed by enzyme-based nanoparticle scaffolds. Here, we show by using the conditions that maintain GOx structure and function when limiting the enzyme coating to an ultrathin layer, the design and construction of an ultrafast responding diagnostic sensor technol. for glucose can be achieved, which is crucial for monitoring rapid fluctuations of, for instance, glucose in the brain.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXisVGhtrfN&md5=17e0e462760f98852bde35651a0c4bd9
    44. 44
      Szucs, A.; Hitchens, G. D.; Bockris, J. O. M. On the Adsorption of Glucose Oxidase at a Gold Electrode. J. Electrochem. Soc. 1989, 136, 3748,  DOI: 10.1149/1.2096541
      44
      On the adsorption of glucose oxidase at a gold electrode
      Szucs, Arpad; Hitchens, G. Duncan; Bockris, John O.
      Journal of the Electrochemical Society (1989), 136 (12), 3748-55CODEN: JESOAN; ISSN:0013-4651.
      The shape and size of glucose oxidase (GO) adsorbed on a gold electrode was detd. by ellipsometry. GO is a prolate ellipsoid mol. with a major axis of 140 Å and a minor axis of 50 Å. Two orientations of the mol. on the surface were obsd.: the major axis can be perpendicular to the surface (standing position) or parallel to the surface (laying position). Above a certain coverage, enzymes in the standing position are not stable and undergo a transition to the laying position due to increasing intermol. interaction. In the laying position, the enzyme-and-substrate contact area is large, and gradual unfolding occurs, leading to a significant change in the structure of the protein. It was possible to detect direct electron transfer between a gold electrode and GO. After a short contact time, two almost overlapping electron transfer processes were distinguished, but were gradually transformed to a single response that was characteristic for adsorbed FAD, thus showing that significant changes in the protein structure occur, leading the deactivation of the enzyme.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXmtlGqsg%253D%253D&md5=d47d835f4f9214ecfa3393411eea2b6b
    45. 45
      Wang, K.-H.; Lin, W.-D.; Wu, J.-Y.; Lee, Y.-L. Conformation Transitions of Adsorbed Proteins by Interfacial Forces at an Air–Liquid Interface and Their Effect on the Catalytic Activity of Proteins. Soft Matter 2013, 9, 2717– 2722,  DOI: 10.1039/c2sm27371c
      45
      Conformation transitions of adsorbed proteins by interfacial forces at an air-liquid interface and their effect on the catalytic activity of proteins
      Wang, Ke-Hsuan; Lin, Wei-Dong; Wu, Jau-Yann; Lee, Yuh-Lang
      Soft Matter (2013), 9 (9), 2717-2722CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
      An efficient method to monitor and control the secondary structures of globular proteins is developed by adsorption of proteins from a bulk soln. onto an air-liq. interface. By controlling the concn. of a protein in the aq. phase, as well as the attractive force exerted by the template layer, the adsorption of proteins can be classified into two stages according to the variation of surface pressure. In the first stage, the proteins adsorb as a single-mol. layer. The interface-mol. interactions induce a structural transition of the adsorbed proteins into a β-sheet conformation (α/β < 0.1). The second stage is initiated by further adsorption of proteins onto the interface, forming multilayer proteins, and triggering a conformational transition into α-helix (α/β > 10). The glucose sensing expts. demonstrate that GOx with α-helix conformation has a much higher sensitivity than β-sheet GOx, attributed to its lower charge transfer resistance at the GOx-electrolyte interface. The present study not only provides a new approach to monitor, control, and design protein conformations, but also raises the importance of adsorption states of proteins in performing bio-activities at bio-interfaces.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXitVCisLc%253D&md5=a3a3455620ae43fc2a9014589fd3109b
    46. 46
      Muguruma, H.; Kase, Y.; Murata, N.; Matsumura, K. Adsorption of Glucose Oxidase onto Plasma-Polymerized Film Characterized by Atomic Force Microscopy, Quartz Crystal Microbalance, and Electrochemical Measurement. J. Phys. Chem. B 2006, 110, 26033– 26039,  DOI: 10.1021/jp063755m
      46
      Adsorption of Glucose Oxidase onto Plasma-Polymerized Film Characterized by Atomic Force Microscopy, Quartz Crystal Microbalance, and Electrochemical Measurement
      Muguruma, Hitoshi; Kase, Yoshihiro; Murata, Naoya; Matsumura, Kazunari
      Journal of Physical Chemistry B (2006), 110 (51), 26033-26039CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      Adsorption of glucose oxidase (GOD) onto plasma-polymd. thin films (PPF) with nanoscale thickness was characterized by at. force microscopy (AFM), quartz crystal microbalance (QCM), and electrochem. measurements. The PPF surface is very flat (less than 1-nm roughness), and its properties (charge and wettability) can be easily changed while retaining the backbone structure. We focused on three types of surfaces: (1) the pristine surface of hexamethyldisiloxane (HMDS) PPF (hydrophobic and neutral surface), (2) an HMDS PPF surface with nitrogen-plasma treatment (hydrophilic and pos.-charged surface), and (3) an HMDS PPF surface treated with oxygen plasma (hydrophilic and neg.-charged surface). The AFM image showed that the GOD mols. were densely adsorbed onto surface 2 and that individual GOD mols. could be obsd. The longer axis of GOD ellipsoid mols. were aligned parallel to the surface, called the "lying position", because of electrostatic assocn. On surface 1, clusters of GOD mols. did not completely cover the original PPF surface (surface coverage was ca. 60%). The 10-nm-size step height between the GOD clusters and the PPF surface suggests that the longer axes of individual GOD mols. were aligned perpendicular to the surface, called the "standing position". On surface 3, only a few of the GOD mols. were adsorbed because of electrostatic repulsion. These results indicate that the plasma polymn. process can facilitate enhancement or redn. of protein adsorption. The AFM images show a corresponding tendency with the QCM profiles. The QCM data indicate that the adsorption behavior obeys the Langmuir isotherm equation. The amperometric biosensor characteristics of the GOD-adsorbed PPF on a platinum electrode showed an increment in the current because of enzymic reaction with glucose addn., indicating that enzyme activity was mostly retained in spite of irreversible adsorption.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xht12itb%252FJ&md5=2038a83ae3c7a40de82fbf4171d40787
    47. 47
      Fogel, R.; Mashazi, P.; Nyokong, T.; Limson, J. Critical Assessment of the Quartz Crystal Microbalance with Dissipation as an Analytical Tool for Biosensor Development and Fundamental Studies: Metallophthalocyanine–Glucose Oxidase Biocomposite Sensors. Biosens. Bioelectron. 2007, 23, 95– 101,  DOI: 10.1016/j.bios.2007.03.012
      47
      Critical assessment of the Quartz Crystal Microbalance with Dissipation as an analytical tool for biosensor development and fundamental studies: Metallophthalocyanine-glucose oxidase biocomposite sensors
      Fogel, R.; Mashazi, P.; Nyokong, T.; Limson, J.
      Biosensors & Bioelectronics (2007), 23 (1), 95-101CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)
      One of the challenges in electrochem. biosensor design is gaining a fundamental knowledge of the processes underlying immobilization of the mols. onto the electrode surface. This is of particular importance in biocomposite sensors where concerns have arisen as to the nature of the interaction between the biol. and synthetic mols. immobilized. The authors examd. the use of the Quartz Crystal Microbalance with Dissipation (QCM-D) as a tool for fundamental analyses of a model sensor constructed by the immobilization of cobalt(II) phthalocyanine (TCACoPc) and glucose oxidase (GOx) onto a gold-quartz electrode (electrode surface) for the enhanced detection of glucose. The model sensor was constructed in aq. phase and covalently linked the gold surface to the TCACoPc, and the TCACoPc to the GOx, using the QCM-D. The aq. metallophthalocyanine (MPc) formed a multi-layer over the surface of the electrode, which could be removed to leave a monolayer with a mass loading that compared favorably to the theor. value expected. Anal. of frequency and dissipation plots indicated covalent attachment of glucose oxidase onto the metallophthalocyanine layer. The amt. of GOx bound using the model system compared favorably to calcns. derived from the maximal amperometric functioning of the electrochem. sensor, but not to theor. values derived from dimensions of GOx as established by crystallog. The strength of the binding of the GOx film with the TCACoPc layer was tested by using 2% SDS as a denaturant/surfactant, and the GOx film was not found to be significantly affected by exposure to this. This paper thus showed that QCM-D can be used in order to model essential processes and interactions that dictate the functional parameters of a biosensor.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtVOisL3M&md5=eae1f08ac390aebbe6637e710283c9a0
    48. 48
      Anand, G.; Sharma, S.; Dutta, A. K.; Kumar, S. K.; Belfort, G. Conformational Transitions of Adsorbed Proteins on Surfaces of Varying Polarity. Langmuir 2010, 26, 10803– 10811,  DOI: 10.1021/la1006132
      48
      Conformational Transitions of Adsorbed Proteins on Surfaces of Varying Polarity
      Anand, Gaurav; Sharma, Sumit; Dutta, Amit K.; Kumar, Sanat K.; Belfort, Georges
      Langmuir (2010), 26 (13), 10803-10811CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Combining a wide range of protein adsorption expts. (three globular proteins on eight well-defined homogeneous surfaces) with Monte Carlo simulations of lattice proteins at different concns. and on surfaces of varying "polarity", we explore the extent and rheol. behavior of adsorbed proteins as a function of substrate polarity, "on" rate consts. (ka) and steric parameters (|A1|) from the random sequential adsorption model, and demonstrate a folding to unfolding transition upon adsorption. We show that model globular proteins (hen egg lysozyme, RNase A, and insulin dimer) behave similarly with respect to adsorption. Exptl., above a substrate wettability cos θ > 0.4 (where θ is the sessile contact angle of water on a substrate in air), the adsorbed mass, rigidity, and ka of the proteins are diminished, while the steric factor |A1| is increased, suggesting a lower packing d. To analyze these results, we have invoked computer simulations. We show that changing surface polarity has two profound effects. First, the amt. adsorbed increases as the surfaces become more apolar. Further, the proteins become less stable as their adsorbed amt. increased because they gain a large no. of interprotein and protein-surface interactions. Finally, apolar surfaces served to reduce the unfolding free energy barriers, further facilitating the reorganizing of proteins on these surfaces. Thus, increasing the nonpolar nature of the surfaces resulted in a more rigid adsorbed layer, in good agreement with the expts.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXlsFWrsLk%253D&md5=c29e03539eaebcc8b4e67806b89582ee
    49. 49
      Frederick, K. R.; Tung, J.; Emerick, R. S.; Masiarz, F. R.; Chamberlain, S. H.; Vasavada, A.; Rosenberg, S.; Chakraborty, S.; Schopfer, L. M.; Schopter, L. M. Glucose Oxidase from Aspergillus Niger. Cloning, Gene Sequence, Secretion from Saccharomyces Cerevisiae and Kinetic Analysis of a Yeast-Derived Enzyme. J. Biol. Chem. 1990, 265, 3793– 3802,  DOI: 10.1016/s0021-9258(19)39664-4
      49
      Glucose oxidase from Aspergillus niger. Cloning, gene sequence, secretion from Saccharomyces cerevisiae and kinetic analysis of a yeast-derived enzyme
      Frederick, Katherine R.; Tung, James; Emerick, Richard S.; Masiarz, Frank R.; Chamberlain, Scott H.; Vasavada, Amit; Rosenberg, Steven; Chakraborty, Sumita; Schopfer, Lawrence M.; Massey, Vincent
      Journal of Biological Chemistry (1990), 265 (7), 3793-802CODEN: JBCHA3; ISSN:0021-9258.
      The gene for A. niger glucose oxidase (EC 1.1.3.4) was cloned from both cDNA and genomic libraries using oligonucleotide probes derived from the amino acid sequences of peptide fragments of the enzyme. The mature enzyme consists of 583 amino acids and is preceded by a 22-amino-acid presequence. No intervening sequences are found within the coding region. The enzyme contains 3 cysteine residues and 8 potential sites for N-linked glycosylation. The protein shows 26% identity with alc. oxidase of Hansenuela polymorpha, and the N terminus has a sequence homologous with the AMP-binding region of other flavoenzymes, such as p-hydroxybenzoate hydroxylase and glutathione reductase. Recombinant yeast expression plasmids were constructed contg. a hybrid yeast alc. dehydrogenase II-glyceraldehyde-3-phosphage dehydrogenase promoter, either the yeast α-factor pheromone leader or the glucose oxidase presequence, and the mature glucose oxidase-coding sequence. When transformed into yeast, these plasmids direct the synthesis and secretion of between 75 and 400 μg/mL of active glucose oxidase. Anal. of the yeast-derived enzymes shows that they are of comparable specific activity and have more extensive N-linked glycosylation than the A. niger protein.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXksFens74%253D&md5=225b51acfba464b3a07b68493b7b000d
    50. 50
      Zhang, Y.; Savva, A.; Wustoni, S.; Hama, A.; Maria, I. P.; Giovannitti, A.; McCulloch, I.; Inal, S. Visualizing the Solid–Liquid Interface of Conjugated Copolymer Films Using Fluorescent Liposomes. ACS Appl. Bio Mater. 2018, 1, 1348– 1354,  DOI: 10.1021/acsabm.8b00323
      50
      Visualizing the Solid-Liquid Interface of Conjugated Copolymer Films Using Fluorescent Liposomes
      Zhang, Yi; Savva, Achilleas; Wustoni, Shofarul; Hama, Adel; Maria, Iuliana P.; Giovannitti, Alexander; McCulloch, Iain; Inal, Sahika
      ACS Applied Bio Materials (2018), 1 (5), 1348-1354CODEN: AABMCB; ISSN:2576-6422. (American Chemical Society)
      Conjugated polymers are promising engineering tools for establishing bilateral elec. communication with living systems. The free energy of their films, the roughness, and charge d. play major roles in detg. their interactions with lipid bilayers, which form the membrane barrier around every living cell allowing for mol. exchange with the extracellular environment. In this work, we investigate lipid bilayer formation from synthetic lipid vesicles (liposomes) on a series of amphiphilic copolymer films based on naphthalene 1,4,5,8 tetracarboxylic diimide bithiophene (NDI-T2) backbone where the alkyl side chain is gradually exchanged for an ethylene glycol-based side chain. As the concn. of ethylene glycol in the compn. changes, the surface energy of the films varies drastically, which, in turn, effects the interactions with liposomes. By imaging the interactions of fluorophore-labeled liposomes with these surfaces via a fluorescence microscope, we show that the films can be cast such that ethylene glycol-rich regions, which liposomes favor, are accumulated on the surface and ext. information on the wettability behavior that has not been possible using other surface sensitive techniques. This approach uncovers the solid/liq. interface of a promising class of electron transporting conjugated polymer films and suggests synthetic strategies to maximize the no. of lipid-polymer contacts for the formation of supported lipid bilayers.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhvFSjur%252FP&md5=b8289013ce918793d79c8b1c08c836b7
    51. 51
      Stevens, J. S.; de Luca, A. C.; Pelendritis, M.; Terenghi, G.; Downes, S.; Schroeder, S. L. M. Quantitative Analysis of Complex Amino Acids and Rgd Peptides by X-Ray Photoelectron Spectroscopy (Xps). Surf. Interface Anal. 2013, 45, 1238– 1246,  DOI: 10.1002/sia.5261
      51
      Quantitative analysis of complex amino acids and RGD peptides by X-ray photoelectron spectroscopy (XPS)
      Stevens, Joanna S.; Luca, Alba C.; Pelendritis, Michalis; Terenghi, Giorgio; Downes, Sandra; Schroeder, Sven L. M.
      Surface and Interface Analysis (2013), 45 (8), 1238-1246CODEN: SIANDQ; ISSN:0142-2421. (John Wiley & Sons Ltd.)
      The C 1 s, N 1 s, and O 1 s core level binding energies (BEs) of the functional groups in amino acids (glycine, aspartic acid, glutamic acid, arginine, and histidine) with varied side-chains and cell-binding RGD-based peptides have been detd. and characterized by XPS with a monochromatic Al Kα source. The zwitterionic nature of the amino acids in the solid state is unequivocally evident from the N 1 s signals of the protonated amine groups and the C 1 s signature of carboxylate groups. Significant adventitious carbon contamination is evident for all samples but can be quant. accounted for. No intrinsic differences in the XP spectra are evident between two polymorphs (α and γ) of glycine, indicating that the crystallog. differences have a minor influence on the core level BEs for this system. The two nitrogen centers in the imidazole group of histidine exhibit an N 1 s BE shift that is in line with previously reported data for theophylline and aq. imidazole solns., while the nitrogen and carbon chem. shifts reflect the unusual guanidinium chem. environment in arginine. It is shown that the complex envelopes of C 1 s and O 1 s photoemission spectra for short-chain peptides can be analyzed quant. by ref. to the less complex XP spectra of the constituent amino acids, provided the peptides are of high enough purity. The distinctive N 1 s photoemission from the amide linkages provides an indicator of peptide formation even in the presence of common impurities, and variations in the relative intensities of N 1 s were found to be diagnostic for each of the three peptides investigated (RGD, RGDS, and RGDSC). Copyright © 2013 John Wiley & Sons, Ltd.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXlvVWit7c%253D&md5=eeed0a6a94c15715622e532a7064e712
    52. 52
      Koklu, A.; Ohayon, D.; Wustoni, S.; Hama, A.; Chen, X.; McCulloch, I.; Inal, S. Microfluidics Integrated N-Type Organic Electrochemical Transistor for Metabolite Sensing. Sens. Actuators, B 2021, 329, 129251,  DOI: 10.1016/j.snb.2020.129251
      52
      Microfluidics integrated n-type organic electrochemical transistor for metabolite sensing
      Koklu, Anil; Ohayon, David; Wustoni, Shofarul; Hama, Adel; Chen, Xingxing; McCulloch, Iain; Inal, Sahika
      Sensors and Actuators, B: Chemical (2021), 329 (), 129251CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
      The org. electrochem. transistor (OECT) can translate biochem. binding events between a recognition unit and its analyte into an elec. signal. We present an OECT comprising an n-type (electron transporting) conjugated polymer-based channel and lateral gate electrode functionalized with the enzyme, glucose oxidase. The device is integrated with a microfluidic system for real-time glucose monitoring in a flow-through manner. The n-type polymer has direct elec. communication with glucose oxidase, allowing glucose detection while surpassing hydrogen peroxide prodn. The microfluidic-integrated OECT shows superior features compared to its microfluidic-free counterpart, including higher current and transconductance values as well as improved signal-to-noise (SNR) ratios, which enhances the sensor sensitivity and its detection limit. Thanks to the low noise endowed by the integrated microfluidics, the gate current changes upon metabolite recognition could be resolved, revealing that while the relative changes in gate and drain currents are similar, the drain current output has a higher SNR. This is the first demonstration of the integration of a microfluidic system with an n-type accumulation mode OECT for real-time enzymic metabolite detection. The microfluidic-integrated design provides new insights into the mechanisms leading to high sensor sensitivities, crucial for the development of portable and autonomous lab-on-a-chip technologies.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisFelsbvN&md5=9b2661b1ad6439a4b932de0899859ee7
    53. 53
      Sethuraman, A.; Vedantham, G.; Imoto, T.; Przybycien, T.; Belfort, G. Protein Unfolding at Interfaces: Slow Dynamics of Α-Helix to Β-Sheet Transition. Proteins: Struct., Funct., Bioinf. 2004, 56, 669– 678,  DOI: 10.1002/prot.20183
      53
      Protein unfolding at interfaces: Slow dynamics of α-helix to β-sheet transition
      Sethuraman, Ananthakrishnan; Vedantham, Ganesh; Imoto, Taiji; Przybycien, Todd; Belfort, Georges
      Proteins: Structure, Function, and Bioinformatics (2004), 56 (4), 669-678CODEN: PSFBAF ISSN:. (Wiley-Liss, Inc.)
      A two-phase sequential dynamic change in the secondary structure of hen egg lysozyme (Lys) adsorbed on solid substrates was obsd. The first phase involved fast conversion of α-helix to random/turns (within the first minute or at very low coverage or high substrate wettability) with no perceptible change in β-sheet content. The second phase (1-1200 min), however, involved a relatively slow conversion from α-helix to β-sheet without a noticeable change in random/turns. An important finding of this work is that the concn. of lysozyme in the adsorbed state has a substantial effect on the fractional content of secondary structures. Attenuated total reflection Fourier transform IR (ATR/FTIR) spectroscopy, along with a newly-developed optimization algorithm for predicting the content of secondary structure motifs, was used to correlate the secondary structure and the amt. of adsorbed lysozyme with the surface wettability of six different flat nanoporous substrates. Although three independent variables, surface wettability, soln. concn. and time for absorption, were used to follow the fractional structural changes of lysozyme, the results were all normalized onto a single plot with the amt. adsorbed as the universal independent variable. Consequently, lateral interactions among proteins likely drive the transition process. Direct intermol. force adhesion measurements between lysozyme and different functionalized self-assembled alkanethiol monolayers confirm that hydrophobic surfaces interact strongly with proteins. The lysozyme-unfolding pathway during early adsorption appears to be similar to that predicted by published mol. modeling results.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXmvVOjtLs%253D&md5=39ef1e42ead2342ba24e56615df424aa
    54. 54
      Mecheri, B.; D’Epifanio, A.; Geracitano, A.; Targon Campana, P.; Licoccia, S. Development of Glucose Oxidase-Based Bioanodes for Enzyme Fuel Cell Applications. J. Appl. Electrochem. 2013, 43, 181– 190,  DOI: 10.1007/s10800-012-0489-y
      54
      Development of glucose oxidase-based bioanodes for enzyme fuel cell applications
      Mecheri, Barbara; D'Epifanio, Alessandra; Geracitano, Antonio; Targon Campana, Patricia; Licoccia, Silvia
      Journal of Applied Electrochemistry (2013), 43 (2), 181-190CODEN: JAELBJ; ISSN:0021-891X. (Springer)
      We fabricated an enzyme fuel cell (EFC) device based on glucose as fuel and glucose oxidase (GOx) as biocatalyst. As a strategy to improve GOx stability, preserving at the same time the enzyme catalytic activity, we propose an immobilization procedure to entrap GOx in a polymer matrix based on Nafion and multiwalled carbon nanotubes. CD spectra were recorded to study changes in the 3D structure of GOx that might be generated by the immobilization procedure. The comparison between the CD features of GOx immobilized and free in soln. indicates that the shape of the spectra and position of peaks do not significantly change. The bioelectrocatalytic activity toward glucose oxidn. of immobilized GOx was studied by cyclic voltammetry and chronoamperometry expts. Such electrochem. expts. allow monitoring the rate of GOx-catalyzed glucose oxidn. and extrapolating GOx kinetic parameters. Results demonstrate that immobilized GOx has high catalytic efficiency, due the maintaining of regular and well-ordered structure of the immobilized enzyme, as indicated by spectroscopic findings. Once investigated the electrode structure-property relationship, an EFC device was assembled using the GOx-based bioanode, and sulfonated poly ether ether ketone as electrolyte membrane. Polarization and power d. curves of the complete EFC device were acquired, demonstrating the suitability of the immobilization strategy and materials to be used in EFCs.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXmvVCqtw%253D%253D&md5=4b45651e8c8956bde2069f3c2629316d
    55. 55
      Fears, K. P.; Sivaraman, B.; Powell, G. L.; Wu, Y.; Latour, R. A. Probing the Conformation and Orientation of Adsorbed Enzymes Using Side-Chain Modification. Langmuir 2009, 25, 9319– 9327,  DOI: 10.1021/la901885d
      55
      Probing the Conformation and Orientation of Adsorbed Enzymes Using Side-Chain Modification
      Fears, Kenan P.; Sivaraman, Balakrishnan; Powell, Gary L.; Wu, Yonnie; Latour, Robert A.
      Langmuir (2009), 25 (16), 9319-9327CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      The bioactivity of enzymes that are adsorbed on surfaces can be substantially influenced by the orientation of the enzyme on the surface and adsorption-induced changes in the enzyme's structure. CD is a powerful method for observing the secondary structure of proteins; however, it provides little information regarding the tertiary structure of a protein or its adsorbed orientation. In this study, we developed methods using side-chain-specific chem. modification of solvent-exposed tryptophan residues to complement CD spectroscopy and bioactivity assays to provide greater detail regarding whether changes in enzyme bioactivity following adsorption are due to adsorbed orientation and/or adsorption-induced changes in the overall structure. These methods were then applied to investigate how adsorption influences the bioactivity of hen egg white lysozyme (HEWL) and glucose oxidase (GOx) on alkanethiol self-assembled monolayers over a range of surface chemistries. The results from these studies indicate that surface chem. significantly influences the bioactive state of each of these enzymes but in distinctly different ways. Changes in the bioactive state of HEWL are largely governed by its adsorbed orientation, while the bioactive state of adsorbed GOx is influenced by a combination of both adsorbed orientation and adsorption-induced changes in conformation.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXoslWlsrw%253D&md5=7edcc42fcd06607665bbbbaa2c7c2895

  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.2c20502.

    • Materials and methods; NMR spectrum of P-ZI; OECT output characteristics; O2 sensitivity of n-type films; water contact angle of n-type films; glucose oxidase surface charge distribution; AFM images of n-type films, QCM-D traces, models, and analysis of n-type films; list of amino acids in glucose oxidase; XPS signals of glucose oxidase adsorbed on n-type films and spectra deconvolutions; CD spectra of glucose oxidase in solution and when adsorbed on n-type films; discussions on the effect of surface charge and hydrophobicity on protein adsorption; and discussion on protein adsorption behavior on n-type films (PDF)


    Terms & Conditions

    Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.