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ArticleJanuary 20, 2014

Detection and Spatial Mapping of Mercury Contamination in Water Samples Using a Smart-Phone
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Cite this: ACS Nano 2014, 8, 2, 1121–1129

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Abstract

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Detection of environmental contamination such as trace-level toxic heavy metal ions mostly relies on bulky and costly analytical instruments. However, a considerable global need exists for portable, rapid, specific, sensitive, and cost-effective detection techniques that can be used in resource-limited and field settings. Here we introduce a smart-phone-based hand-held platform that allows the quantification of mercury(II) ions in water samples with parts per billion (ppb) level of sensitivity. For this task, we created an integrated opto-mechanical attachment to the built-in camera module of a smart-phone to digitally quantify mercury concentration using a plasmonic gold nanoparticle (Au NP) and aptamer based colorimetric transmission assay that is implemented in disposable test tubes. With this smart-phone attachment that weighs <40 g, we quantified mercury(II) ion concentration in water samples by using a two-color ratiometric method employing light-emitting diodes (LEDs) at 523 and 625 nm, where a custom-developed smart application was utilized to process each acquired transmission image on the same phone to achieve a limit of detection of ∼3.5 ppb. Using this smart-phone-based detection platform, we generated a mercury contamination map by measuring water samples at over 50 locations in California (USA), taken from city tap water sources, rivers, lakes, and beaches. With its cost-effective design, field-portability, and wireless data connectivity, this sensitive and specific heavy metal detection platform running on cellphones could be rather useful for distributed sensing, tracking, and sharing of water contamination information as a function of both space and time.

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Since the recognition of severe neurotoxic effects of mercury in the 1960s, (1-3) the development of detection techniques for real-time and long-term monitoring of mercury contamination in environmental and biological samples has become a high priority. Various neurological effects of mercury exposure have been mainly attributed to the organic form of mercury, predominantly methylmercury (MeHg⁺), which is known to accumulate in the food chain (4) and cross the blood–brain barrier after human ingestion. (5, 6) While such findings have added weight to the severity of organic mercury contamination, the threat of inorganic mercury, namely, mercury(II) ions (Hg²⁺), should not be underestimated. In fact, mercury(II) ions are the primary mercury contamination in the aquatic system and the “precursor” form of methylmercury due to bacteria-assisted biotransformation processes. (7, 8) Furthermore, inorganic mercury is known to be more nephrotoxic than its organic form, as it primarily accumulates in the kidney proximal tubule cells. (9) Therefore, the detection and quantification of mercury(II) ion contamination in water systems are of paramount importance and could potentially be used to assist prevention of mercury ions from entering the food chain.

Toward this need, low nanomolar (nM) concentrations of mercury(II) ions have been traditionally detected by using spectroscopic methods, including, for example, atomic absorption spectroscopy (AAS), (10, 11) inductively coupled plasma mass spectrometry (ICP-MS), (12) and atomic fluorescence spectrometry (AFS). (13) However, these approaches require complex sample preparation procedures, expensive and bulky instruments, and professionally trained personnel running the tests. Therefore, they are not well suited for rapid on-site detection of mercury and may not even be available for use in developing countries. On the other hand, recent advances in microfabrication and nanoscience have enabled the development of portable detection assays that are integrated with lab-on-a-chip platforms, showing great potential for use in resource-limited environments. (14-18) Among these technologies, gold nanoparticle (Au NP)-based colorimetric assays are emerging as alternative approaches for heavy metal detection, (19-21) providing high sensitivity, specificity, and ease of signal read-out using, for example, UV–vis spectrometers (19-21) or glass slide readers. (14) However, these existing systems that utilize NPs are still limited due to their relatively bulky instrumentation, higher costs, and lack of wireless connectivity, which are important especially for distributed sensing and spatiotemporal mapping of contamination in remote locations and field settings. As an alternative to Au NP-based plasmonic techniques, detection of subppm levels of mercury(II) ions has recently been demonstrated by using dye-embedded polymer films as colorimetric substrates that are digitized using, for example, smart-phone cameras. (22) However, this recent approach does not utilize the processing/computational power of the phone, and it has limited detection sensitivity and repeatability due to unavoidable variations in ambient light conditions and user operation and/or alignment during the image capture process.

To provide a field-portable, cost-effective, and wirelessly connected platform to sensitively quantify heavy metal ion concentration in water samples, here we report a battery-powered mobile sensing device that consists of a lightweight (∼37 g) opto-mechanical attachment to a smart-phone along with a custom-developed Android application for quantification, reporting, and sharing of detection results. This lab-on-a-phone device is based on dual-wavelength illumination using light-emitting diodes (LEDs) at 523 and 625 nm and can quantify mercury-induced subtle transmission changes of a colorimetric assay utilizing citrate-stabilized plasmonic Au NPs and aptamers (Apt) mixed within disposable test tubes. Due to the shift in the plasmonic resonance wavelength of dispersed and aggregated Au NPs in response to mercury(II) ions, we demonstrated sensitive detection of mercury contamination in water samples with a limit of detection (LOD) of ∼3.5 ppb, which has the same order of magnitude as the maximum contaminant level (MCL) of mercury(II) recommended for drinking water, i.e., 2 and 6 ppb, as established by the U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO), respectively. (23, 24) With this cellphone-based colorimetric detection platform, we also demonstrated geospatial mapping of mercury(II) contamination in California by testing water samples collected at more than 50 locations, from tap water sources as well as natural sources such as rivers, lakes, and beaches. This heavy metal detection system running on smart-phones could provide a complementary addition to other mobile-phone-based imaging, sensing, and diagnostics devices (25-42) and holds significant potential for distributed sensing and spatiotemporal mapping and monitoring of mercury contamination globally. In fact, cellphone subscriptions worldwide have reached more than 7 billion by the end of 2013, and smart-phone penetration rate is globally increasing, which is estimated to reach more than 60%, 45%, and 25% by the end of 2015 in North America, Europe, and Africa, respectively. (43) Therefore, the use of mobile phones for bioanalytical measurement science as well as for reporting and sharing of results provides widely scalable, cost-effective, and yet rather powerful/competitive solutions to implement various tests and measurements even in resource-limited and field settings, which constitutes an important motivation for this work.

Results and Discussion

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Optical Design of the Smart-Phone-Based Mercury Reader

We created an optical imaging interface that is mechanically attached to the existing camera module of a smart-phone to quantify mercury concentration using a colorimetric nanoparticle and aptamer assay. This attachment contains two button cells (3 V), which are used to power two LEDs, as illustrated in Figure 1a. These LEDs are mounted at a sufficiently large distance (∼26.5 mm) away from the location of the rectangular test tubes (containing the sample and control solutions) and are scattered by optical diffusers to ensure uniform illumination of both tubes (Figure 1a). The emission wavelengths of these LEDs were selected to be 523 and 625 nm to follow the shift in the extinction wavelengths of the dispersed and aggregated Au NPs, respectively. In order to obtain multispectral information from a given water sample, the green LED illuminated the bottom half while the red LED illuminated the top half of each cuvette (Figure 1a). To avoid a possible crosstalk between the green and red lights, the optical paths of the two LEDs were separated by an opaque clapboard before they reached the cuvettes (Figure 1a, inset) and passed through two rectangular apertures (6.6 × 5 mm, one for each color) that are placed in front of each cuvette. The transmitted light through the sample and control cuvettes was then collected through two other rectangular apertures of the same size to be imaged onto the digital camera of the smart-phone using a plano-convex lens (f = 28 mm) (Figure 1a). This external lens was chosen to yield a demagnification factor of 7× so that the two 6.6-mm-wide sample cuvettes could be simultaneously imaged within the active area of the smart-phone CMOS imager chip. All of these electrical and optical elements were consolidated in an opaque cuboid (Figure 1a, gray part) and coupled to a base plate (Figure 1a, black part) with a total weight of ∼37 g. Although the current attachment is designed for an Android phone (Samsung Galaxy S II, Figure 1b), the same optical reader can be implemented on other smart-phones such as an iPhone, after slight mechanical modifications in the base attachment.

Figure 1. Design of the ratiometric optical reader on a smart-phone. (a) 3D schematic illustration of the internal structure of the opto-mechanical attachment. The inset image shows the same attachment with a slightly different observation angle. (b) Photograph of the actual optical reader installed on an Android-based smart-phone. The screen of the smart-phone displays a typical image of the sample and control cuvettes when illuminated by red (625 nm) and green (523 nm) LEDs simultaneously.

Plasmonic Colorimetric Assay and Measurement of Mercury(II) Ion Concentration

Spherical Au NPs have been previously studied as novel sensing probes for mercury(II) ion detection. (19-21) The characteristic color change of Au NPs from red to purple or blue upon aggregation that is induced by mercury(II) ion binding events constitutes the basis of the Au NP-based colorimetric detection assay. However, most Au NP-based probes require a surface modification step to conjugate mercury(II)-specific ligands onto Au NPs, and the LOD varies based on the capturing ligand that is selected. (44-48) Here, we adopt an alternative approach, which utilizes the strong affinity of the thymine-rich aptamer sequence to mercury(II) ions and citrate-stabilized Au NPs as colorimetric signal transducers to generate a high detection sensitivity. (49) In this protocol, Au NPs are used without the need for surface functionalization steps, which greatly facilitates field use. In a typical mercury detection experiment, 0.64 nM Au NPs (50 nm diameter) are mixed with 3 μM aptamer (5′-TTTTTTTTTT-3′) in 20 mM Tris-HCl buffer (pH 8.0) to form the probe solution. Next, 4 μL of water sample solution is added to the probe solution and incubated for 5–10 min (see Methods section for details). Aptamer forms a protective layer on the surface of Au NPs, which prevents them from aggregation even in a high-salt environment such as 10 mM NaCl. However, this aptamer layer will be stripped off by the presence of mercury(II) ions due to the formation of more stable T-Hg²⁺-T complexes. (50, 51) As a result, the unprotected Au NPs can undergo distinct color transition from red to blue in the presence of NaCl (Figure 2a), and this spectral shift is detected to quantify mercury concentration using our dual-wavelength smart-phone-based colorimetric reader.

A representative smart-phone-captured image of Au NP probe solutions with and without mercury(II) ions is depicted in Figure 2b. Each cuvette was illuminated by red and green LEDs at different spatial locations and separated by two rectangular apertures that are 3 mm apart from each other (Figure 2b). The illumination spots of the LEDs were sufficiently large to cover both the sample and control cuvettes (2 mm apart). This dual-illumination color and dual-cuvette configuration forms four readable signals in a single image frame, namely, red control (RC), red sample (RS), green control (GC), and green sample (GS) signals (Figure 2c). To quantify the mercury contamination in a given water sample, the acquired transmission image of these cuvettes (sample and control) is first digitally split into red (R) and green (G) channels (Figure 2c) to further minimize the spectral crosstalk between these two colors. The centroids of each rectangular aperture are automatically localized by a detection algorithm, and a rectangular region of interest (ROI, 400 × 300 pixels) around each of these four centroids is then used to calculate the averaged transmission signal for each ROI, yielding RC, RS, GC, and GS signals. Note that RC and RS are calculated using the red channel image, whereas GC and GS are calculated using the green channel image, both of which are digitally separated from the raw RGB image captured by the cellphone camera sensor (Figure 2c). The transmission intensity of the sample cuvette is further normalized to that of the control cuvette by placing two identical deionized water samples in both cuvette positions, leading to an illumination normalization factor of 1.15 for the red LED (R_Factor) and 0.98 for the green LED (G_Factor). The calibration ratio of the control cuvette (G/R_C) was obtained by taking the ratio of the GC and RC. Similarly, the calibration ratio of the sample cuvette (G/R_S) was obtained by taking the ratio of GS × G_Factor to RS × R_Factor. Finally, the ultimate normalized green-to-red signal (i.e., normalized G/R) for a given water sample was computed by taking the ratio of G/R_S to G/R_C (Figure 2c). These calculations are automatically implemented using a custom-designed Android application running on the same smart-phone, which will be detailed in the next section.

Figure 2. Principle of dual-color dual-cuvette colorimetric detection. (a) Scheme of the mercury sensing mechanism by using plasmonic Au NPs and aptamer. (b) Representative image captured on the smart-phone under dual-wavelength illumination. The left cuvette (control) contained a mixture of Au NPs (0.64 nM) and aptamer (30 nM), while the right cuvette (sample) contained a mixture of Au NPs and aptamer plus 500 nM Hg²⁺ (representative of a contaminated water sample). (c) Flow of image-processing steps to compute normalized green-to-red signal ratio (i.e., normalized G/R signal).

Android-Based Smart Application for Mercury Quantification

We created a custom-designed Android application that allows for mobile testing and sharing of mercury quantification results. After attaching the colorimetric mercury measurement device onto the smart-phone camera unit (Figure 1), the user can hold the cellphone horizontally and then run mercury tests using this smart application. From the main menu of the application, the user can start a new test, create a device-specific calibration curve, view previously run tests, share the test results, and review the operating instructions (Figure 3a). The user can calibrate the application for attachment-specific variations by imaging, for example, mercury-contaminated control samples at known concentrations (Figure 3b). These calibration curves can be stored and reused by various devices/attachments. After capturing a colorimetric transmission image of the sample, the user can first preview the image on the screen before proceeding to digitally analyze/process it (Figure 3c). The application can also use an image file already stored on the phone memory for processing/testing. After pressing on the “Process” button, the transmission signal ratios between the sample and control regions will be automatically computed on the phone, following the image-processing steps discussed in the previous section. A previously stored calibration curve is used to convert the calculated signal ratio into the mercury concentration level of the sample (in ppb), and the results are then displayed on the screen of the phone (Figure 3d). The total time taken for calculating the mercury concentration on the Android phone (Samsung Galaxy S II) is <7 s. The final test results can be saved on the phone memory with a stamp of time and GPS coordinates of the test and can also be shared with a secure server for spatiotemporal mapping using, for example, a Google Maps-based interface (Figure 3e). With the same Android application, the results can also be reviewed as a function of time per location using a graph-based interface (Figure 3f).

Figure 3. Screen shots of our mercury detection application running on an Android phone. (a) Main menu; (b) calibration menu; (c) preview of a captured or selected colorimetric image before proceeding to analyze/quantify the sample; (d) display of the results; (e) spatiotemporal mapping of mercury contamination using a Google Maps-based interface; (f) tracking of mercury levels as a function of time per location.

Calibration and Specificity Tests

In our cellphone-based mercury detection platform, each normalized G/R ratio computed from a captured RGB image corresponds to a specific mercury concentration value (ppb). The Android application includes a default calibration curve, which was obtained by measuring the normalized G/R ratios of a set of known concentration mercury(II) solutions ranging from 0 to 5 μM (see Figure 4). The values of these normalized G/R ratios increased as the concentration of mercury(II) ions rose above 10 nM and reached saturation at >1000 nM (Figure 4). The signal increase in the 10–1000 nM range is mainly due to the aggregation of Au NPs, which is triggered by the mercury(II) ion concentration. This Au NP aggregation process relatively enhances the extinction at the red wavelength (e.g., 625 nm), while it reduces the extinction at the green wavelength (e.g., 523 nm), which is also confirmed by our UV–vis spectroscopic measurements (see the Supporting Information, Figure S1a). This plasmon-resonance-based wavelength shift occurred rapidly after around 5 min (Supporting Information, Figure S2), demonstrating a quick response time for the NP/aptamer-based colorimetric assay, making it appropriate for use in field settings. As a result of these plasmonic changes due to NP aggregation, the transmission signal of the red channel relatively decreased, whereas the transmission of the green channel increased. Therefore, the final G/R ratio of a sample increased as the mercury(II) ion concentration is increased, which is also illustrated in the calibration curve presented in Figure 4.

To determine the LOD of our smart-phone-based colorimetric assay, we measured the normalized G/R values of a control sample (i.e., [Hg²⁺] = 0, [Au NPs] = 0.64 nM, [Apt] = 30 nM), which resulted in a signal level of 0.940 ± 0.025 (μ_blank ± σ_blank). Our LOD was then determined by the mean of this control sample plus three times its standard deviation (μ_blank + 3σ_blank; see the blue dashed line in Figure 4), which corresponds to a mercury(II) ion concentration of approximately 17.3 nM, or ∼3.5 ppb. Quite interestingly, the LOD of our smart-phone-based dual-color ratiometric platform was more than 6 times better than the LOD of the exact same assay measured by a portable UV–vis spectrometer (Ocean Optics, HR2000+), which resulted in 123 nM, or 24.6 ppb, LOD (see the Supporting Information, Figure S1b). More importantly, the LOD of mercury(II) ions using our smart-phone-based field-portable sensor has the same order of magnitude as the EPA’s mercury(II) reference concentration for drinking water (i.e., 2 ppb) (23) and also satisfies the WHO guideline value for mercury(II) concentration (i.e., 6 ppb). (24)

Figure 4. Dose–response curve of the Au NP and aptamer based plasmonic colorimetric assay running on a smart-phone. Each measurement at a given concentration was repeated three times. The curve was fitted by an exponential function with a coefficient of determination (R²) of 0.96. An LOD of 3.5 ppb for Hg²⁺ was obtained based on the G/R ratios of a control sample ([Hg²⁺] = 0) plus 3 times the standard deviation of the control (blue dashed line).

Next, we performed specificity tests by challenging the same colorimetric plasmonic nanoparticle and aptamer assay with different metal ions, such as Fe³⁺, Ca²⁺, Cu²⁺, and Pb²⁺, as illustrated in Figure 5. The concentrations of all these metal ion samples were prepared to be 500 nM, and our experiments revealed that, except mercury(II) ions, the other metal ion samples yielded a signal level that is comparable to control samples (Figure 5), verifying the specificity of our assay toward detection of Hg²⁺. The same specificity performance was also confirmed independently by UV–vis spectroscopic measurements as summarized in the Supporting Information, Figure S1c,d.

Figure 5. Specificity tests of the Au NP and aptamer based plasmonic mercury assay for different metal ions (500 nM). Each measurement was repeated three times.

Mapping of Mercury Concentration in Water Samples in California

The performance of our smart-phone-based mercury sensor was also tested with water samples including city tap water and natural water samples collected at over 50 different locations in California. Figure 6 summarizes our measurement results for 19 of these samples collected from various apartments (tap water), rivers, lakes, and beaches on the California coast. The results suggest that all the city tap water samples have undetectable levels of mercury(II) ions since the signal readings are at the same level as our LOD (Figure 6). However, our measurements for the water samples collected from natural sources reveal higher mercury concentration levels, ranging from 3.7 to 8.6 ppb, as illustrated in Figure 6. The samples that are found to contain mercury(II) ion concentrations above 6 ppb, i.e., the safety level recommended by WHO, (24) are mostly from ocean samples, with the worst being from the San Francisco Bay (Figure 6). Our observation that the mercury content in ocean water samples is higher compared to fresh water is probably because the ocean is at the end of mercury’s global transport pathway in the environment (52) and thus might exhibit higher pollution levels.

Figure 6. Smart-phone-based mercury detection results for 11 tap water samples and eight natural samples collected in California, USA. Each measurement was repeated three times. Note that the measurements are plotted against the G/R ratios, which makes the presented scale of the mercury concentration (ppb) nonlinear, between 0.8 and 9.1 ppb.

As one of its major advantages, our hand-held smart-phone-based mercury detection platform is also able to generate spatiotemporal contamination maps for, for example, environmental monitoring. To do so, GPS coordinates were recorded for each water sample that was tested, and all the other sample-related information such as measurement results and dates was sent to a secure server using the smart-phone application for mapping of the results. Figure 7a–c represent three smart-phone-generated mercury-monitoring maps, where the spatial resolution of the maps is determined by the sampling density. For instance, in Figure 7a, samples were collected and measured at a low density of ∼0.2 measurements/km; in Figure 7b and c, higher resolution was shown by increasing the sampling density to 3.3 and 20 measurements/km, respectively. Figure 7d–f show histogram plots corresponding to the mercury(II) concentrations that are displayed in Figure 7a–c with a better visualization of the variation of mercury(II) levels within a given area. Interestingly, some locations such as points B and C in Figure 7a and d had statistically higher mercury(II) levels than the rest with very small p values (<0.001) determined by standard Student’s t test. Further investigation of this area indicated that the red ROI in Figure 7a included a marina hosting yachts and boats (Figure 7b), which possibly form the major source of heavy metal pollution in that particular region. Mercury(II) ion concentration near the marina also formed a weak gradient (from A to T), as illustrated in Figure 7b and e, with the closest point to the marina having the highest mercury(II) concentration (i.e., point T in Figure 7b and e). Point E in Figure 7e was statistically lower in mercury(II) concentration (p < 0.01) compared to other locations within the same region of interest, and this observation was confirmed by higher resolution mercury(II) mapping in Figure 7c and f. In addition to spatial mapping of contamination, the option of monitoring the level of mercury concentration as a function of time for a specific location is also feasible using our smart-phone-based sensing platform as illustrated in Figure 3f.

Figure 7. Spatiotemporal mapping of mercury contamination in Los Angeles coastal area. (a–c) Geospatial mercury concentration maps with different sampling densities; (b) zoomed-in area of the red ROI in (a); (c) enlarged region of the red ROI in (b). (d–f) Corresponding mercury concentration readings in (a)–(c). All the data points were measured three times. p values were calculated *via* two-sample Student’s t test by setting target data set as one population and the rest of the data sets as the other. ** represents p < 0.01, and *** represents p < 0.001.

Conclusions

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In summary, we introduced a sensitive and cost-effective smart-phone-based mercury(II) ion sensor platform, which utilizes a battery-powered opto-mechanical reader attached to the existing camera module of a smart-phone to digitally quantify mercury concentration using a plasmonic Au NP and aptamer based colorimetric assay. We employed a two-color ratiometric detection method using LEDs at 523 and 625 nm and a custom-developed Android application for rapid digital image processing of the captured transmission images on the same phone. The LOD of mercury(II) ions with this mobile device is found to be 3.5 ppb, which is on the same order of magnitude with the maximum allowable level of mercury(II) ions in drinkable water defined by the U.S. EPA (2 ppb) (23) and WHO (6 ppb). (24) Moreover, we generated a geospatial mercury(II) contamination map by measuring more than 50 samples collected in California from various sources including tap, river, lake, and ocean water samples. The cost-effective design, portability, and data connectivity of this sensitive heavy metal detection device integrated onto cellphones could be rather useful for distributed sensing, tracking, and sharing of water contamination information as a function of both space and time, globally.

Methods

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Hardware Design

Our optical imaging system was designed for an Android phone (Samsung Galaxy S II) in Autodesk (Inventor) and printed using a 3D printer (Elite, Dimension). Two LEDs (120 degree illumination angle, SuperBrightLEDs), one green (523 nm, RL5-G16120) and one red (625 nm, RL5-G12120), illuminated the test/sample and control cuvettes simultaneously and were powered by two button cells (3 V, CR1620, Energizer). An optical diffuser (made using three sheets of A4 printer paper) was inserted between the LEDs and the cuvettes for uniform illumination of each cuvette. The transmitted light through the cuvettes was then collected by a plano-convex lens (focal length f = 28 mm, NT65–576, Edmund Optics) and imaged using the smart-phone camera (f = 4 mm). This imaging configuration provides an optical demagnification factor of 28/4 = 7-fold, which permits imaging of both the test and control cuvettes (6.6 × 6.6 mm in cross section) within the field of view of the phone’s CMOS imager chip. To avoid crosstalk of the two-color illumination, a black clapboard was used to separate the light paths of the LEDs before entering the cuvettes, and four rectangular apertures (6.6 × 5 mm) were added both in front of and behind the cuvettes to spatially filter the transmitted light at each color (i.e., red and green). The acquired images were analyzed in digitally separated red and green channels to further reject possible spectral crosstalk between red and green illumination wavelengths.

Gold Nanoparticle and Aptamer Based Colorimetric Assay

Citrate-stabilized Au NPs (50 nm) were purchased from NanoComposix. Aptamer sequence of 5′-TTTTTTTTTT-3′ was obtained from Integrated DNA Technologies. All metal salts such as mercury(II) chloride were obtained from Sigma. Stock Au NP solution in 20 mM Tris-HCl buffer (TH, pH 8.0) was prepared by centrifugation of raw Au NP-citrate solution, aspiration of the supernatant, and redispersion in TH buffer with 20× dilution to give a working concentration of 0.64 nM. Water samples collected from rivers, lakes, and beaches were filtered by a 0.2 μm polyethersulfone membrane (Whatman) to remove sand and other solid particles within the test samples. Tap water samples and calibration solutions containing mercury(II) ions prepared in deionized water were used directly without further purification. In a typical measurement procedure, 4 μL of the sample of interest was mixed with 4 μL of 3 μM aptamer (20 mM TH buffer, pH 8.0), followed by a 5 min reaction period. Next, 400 μL of Au NPs (0.64 nM) in 20 mM TH buffer solution was added and allowed to react for 5 min. Finally, 8 μL of 10 mM NaCl was added and incubated for another 10 min before being analyzed by the smart-phone device.

UV–Vis Spectroscopic Investigation of Water Samples Using a Portable Spectrometer

In our comparison measurements against the smart-phone (see the Supporting Information), a white LED (RL5-W15120, SuperBrightLEDs) was used as the light source, and the transmission signal that passed through a standard 1 cm cuvette was collected by a 600-μm-diameter optical fiber and measured by a portable spectrometer (HR2000+, Ocean Optics). The background spectrum was recorded using deionized water as a blank control sample. Each spectrum was collected with an exposure time of 1 ms and scanned 500 times for averaging in order to improve the signal-to-noise ratio of each UV–vis spectroscopic measurement.

Supporting Information

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UV–vis spectroscopic measurement results of the Au NP and aptamer based colorimetric assay (calibration curve, specificity, and dynamics test). This material is available free of charge via the Internet at http://pubs.acs.org.

nn406571t_si_001.pdf (544.33 kb)

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Author Information

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Corresponding Author
- Aydogan Ozcan - †Electrical Engineering Department, ‡Bioengineering Department, §California NanoSystems Institute (CNSI), ∥Department of Physics & Astronomy, and ⊥Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, California 90095, United States; Email: [email protected]
Authors
- Qingshan Wei - †Electrical Engineering Department, ‡Bioengineering Department, §California NanoSystems Institute (CNSI), ∥Department of Physics & Astronomy, and ⊥Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, California 90095, United States
- Richie Nagi - †Electrical Engineering Department, ‡Bioengineering Department, §California NanoSystems Institute (CNSI), ∥Department of Physics & Astronomy, and ⊥Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, California 90095, United States
- Kayvon Sadeghi - †Electrical Engineering Department, ‡Bioengineering Department, §California NanoSystems Institute (CNSI), ∥Department of Physics & Astronomy, and ⊥Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, California 90095, United States
- Steve Feng - †Electrical Engineering Department, ‡Bioengineering Department, §California NanoSystems Institute (CNSI), ∥Department of Physics & Astronomy, and ⊥Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, California 90095, United States
- Eddie Yan - †Electrical Engineering Department, ‡Bioengineering Department, §California NanoSystems Institute (CNSI), ∥Department of Physics & Astronomy, and ⊥Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, California 90095, United States
- So Jung Ki - †Electrical Engineering Department, ‡Bioengineering Department, §California NanoSystems Institute (CNSI), ∥Department of Physics & Astronomy, and ⊥Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, California 90095, United States
- Romain Caire - †Electrical Engineering Department, ‡Bioengineering Department, §California NanoSystems Institute (CNSI), ∥Department of Physics & Astronomy, and ⊥Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, California 90095, United States
- Derek Tseng - †Electrical Engineering Department, ‡Bioengineering Department, §California NanoSystems Institute (CNSI), ∥Department of Physics & Astronomy, and ⊥Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, California 90095, United States
Author Contributions
R. Nagi and K. Sadeghi contributed equally to this project.
Notes
The authors declare the following competing financial interest(s): A. Ozcan is the cofounder of a start-up company that aims to commercialize computational microscopy tools.

Acknowledgment

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Ozcan Research Group gratefully acknowledges the support of the Presidential Early Career Award for Scientists and Engineers (PECASE), Army Research Office (ARO) Life Sciences Division, ARO Young Investigator Award, National Science Foundation (NSF) CAREER Award, NSF CBET Division Biophotonics Program, NSF Emerging Frontiers in Research and Innovation (EFRI) Award, Office of Naval Research (ONR), and National Institutes of Health (NIH) Director’s New Innovator Award DP2OD006427 from the Office of the Director, National Institutes of Health. We also thank Dr. Hangfei Qi from Prof. Ren Sun’s lab at the Department of Molecular and Medical Pharmacology (UCLA) for providing the aptamer sequence.

References

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Minamata disease (M. d.) is methylmercury (MeHg) poisoning that occurred in humans who ingested fish and shellfish contaminated by MeHg discharged in waste water from a chemical plant (Chisso Co. Ltd.). It was in May 1956, that M. d. was first officially "discovered" in Minamata City, south-west region of Japan's Kyushu Island. The marine products in Minamata Bay displayed high levels of Hg contamination (5.61 to 35.7 ppm). The Hg content in hair of patients, their family and inhabitants of the Shiranui Sea coastline were also detected at high levels of Hg (max. 705 ppm). Typical symptoms of M. d. are as follows: sensory disturbances (glove and stocking type), ataxia, dysarthria, constriction of the visual field, auditory disturbances and tremor were also seen. Further, the fetus was poisoned by MeHg when their mothers ingested contaminated marine life (named congenital M. d.). The symptom of patients were serious, and extensive lesions of the brain were observed. While the number of grave cases with acute M. d. in the initial stage was decreasing, the numbers of chronic M. d. patients who manifested symptoms gradually over an extended period of time was on the increase. For the past 36 years, of the 2252 patients who have been officially recognized as having M. d., 1043 have died. This paper also discusses the recent remaining problems.
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TEACH. Organic Mercury, U.S. Environmental Protection Agency, 2007. http://www.epa.gov/teach/chem_summ/mercury_org_summary.pdf.
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Clarkson, T. W. The Toxicology of Mercury Crit. Rev. Clin. Lab. Sci. 1997, 34, 369– 403
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The toxicology of mercury
Clarkson, Thomas W.
Critical Reviews in Clinical Laboratory Sciences (1997), 34 (4), 369-403CODEN: CRCLBH; ISSN:1040-8363. (CRC)
A review and discussion with 80 refs. The major phys. forms of mercury to which humans are exposed are mercury vapor, Hg0, and methylmercury compds., CH3HgX. Mercury vapor emitted from both natural and anthropogenic sources is globally distributed in the atm. It is returned as a water-sol. form in pptn. and finds its way into bodies of fresh and ocean water. Land run-off also accounts for further input into lakes and oceans. Inorg. mercury, present in water sediments, is subject to bacterial conversion to methylmercury compds. that are bioaccumulated in the aquatic food chain to reach the highest concn. in predatory fish. Human exposure to mercury vapor is from dental amalgam and industries using mercury. Methylmercury compds. are found exclusively in seafood and freshwater fish. The health effects of mercury vapor have been known since ancient times. Severe exposure results in a triad of symptoms, erethism, tremor, and gingivitis. Today, there is concern with more subtle effects such as preclin. changes in kidney function and behavioral and cognitive changes assocd. with effects on the central nervous system. Methylmercury is a neurol. poison affecting primarily brain tissue. In adults, brain damage is focal affecting the function of such areas as the cerebellum (ataxia) and the visual cortex (constricted visual fields). Methylmercury also at high doses can cause severe damage to the developing brain. Today the chief concern is with the more subtle effects arising from prenatal exposure such as delayed development and cognitive changes in children.
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Wolfe, M. F.; Schwarzbach, S.; Sulaiman, R. A. Effects of Mercury on Wildlife: A Comprehensive Review Environ. Toxicol. Chem. 1998, 17, 146– 160
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Effects of mercury on wildlife: a comprehensive review
Wolfe, Marti F.; Schwarzbach, Steven; Sulaiman, Rini A.
Environmental Toxicology and Chemistry (1998), 17 (2), 146-160CODEN: ETOCDK; ISSN:0730-7268. (SETAC Press)
A review with 147 refs. Wildlife may be exposed to mercury (Hg) and methylmercury (MeHg) from a variety of environmental sources, including mine tailings, industrial effluent, agricultural drainwater, impoundments, and atm. deposition from elec. power generation. Terrestrial and aquatic wildlife may be at risk from exposure to waterborne Hg and MeHg. The transformation of inorg. Hg by anaerobic sediment microorganisms in the water column produces MeHg, which bioaccumulates at successive trophic levels in the food chain. If high trophic level feeders, such as piscivorous birds and mammals, ingest sufficient MeHg in prey and drinking water, Hg toxicoses, including damage to nervous, excretory and reproductive systems, result. Currently accepted no obsd. adverse effect levels (NOAELs) for waterborne Hg in wildlife have been developed from the piscivorous model in which most dietary Hg is in the Me form. Such model are not applicable to omnivores, insectivores, and other potentially affected groups, and have not incorporated data from other important matrixes, such as eggs and muscle. The purpose of this paper is to present a comprehensive review of the Hg literature as it relates to effects on wildlife, including previously understudied groups. The authors present a critique of the current state of knowledge about effects of Hg on wildlife as an aid to identifying missing information and to planning research needed for conducting a complete assessment of Hg risks to wildlife. This review summarizes the toxicity of Hg to birds and mammals, the mechanisms of Hg toxicity, the measurement of Hg in biota, and interpretation of residue data.
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TEACH. Inorganic Mercury, U.S. Environmental Protection Agency, 2007. http://www.epa.gov/teach/chem_summ/mercury_inorg_summary.pdf.
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Blum, J. D.; Popp, B. N.; Drazen, J. C.; Anela Choy, C.; Johnson, M. W. Methylmercury Production below the Mixed Layer in the North Pacific Ocean Nat. Geosci. 2013, 6, 879– 884
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Methylmercury production below the mixed layer in the North Pacific Ocean
Blum, Joel D.; Popp, Brian N.; Drazen, Jeffrey C.; Choy, C. Anela; Johnson, Marcus W.
Nature Geoscience (2013), 6 (10), 879-884CODEN: NGAEBU; ISSN:1752-0894. (Nature Publishing Group)
Mercury enters marine food webs in the form of microbially generated monomethylmercury. Microbial methylation of inorg. mercury, generating monomethylmercury, is widespread in low-oxygen coastal sediments. The degree to which microbes also methylate mercury in the open ocean has remained uncertain, however. Here, we present measurements of the stable isotopic compn. of mercury in nine species of marine fish that feed at different depths in the central North Pacific Subtropical Gyre. We document a systematic decline in δ202Hg, Δ199Hg and Δ201Hg values with the depth at which fish feed. We show that these mercury isotope trends can be explained only if monomethylmercury is produced below the surface mixed layer, including in the underlying oxygen min. zone, i.e., between 50 and more than 400 m depth. Specifically, we est. that about 20-40% of the monomethylmercury detected below the surface mixed layer originates from the surface and enters deeper waters either attached to sinking particles, or in zooplankton and micronekton that migrate to depth. We suggest that the remaining monomethylmercury found at depth is produced below the surface mixed layer by methylating microbes that live on sinking particles. We suggest that microbial prodn. of monomethylmercury below the surface mixed later contributes significantly to anthropogenic mercury uptake into marine food webs.
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Stacchiotti, A.; Morandini, F.; Bettoni, F.; Schena, I.; Lavazza, A.; Grigolato, P. G.; Apostoli, P.; Rezzani, R.; Aleo, M. F. Stress Proteins and Oxidative Damage in a Renal Derived Cell Line Exposed to Inorganic Mercury and Lead Toxicology 2009, 264, 215– 224
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Harnly, M.; Seidel, S.; Rojas, P.; Fornes, R.; Flessel, P.; Smith, D.; Kreutzer, R.; Goldman, L. Biological Monitoring for Mercury within a Community with Soil and Fish Contamination Environ. Health Perspect. 1997, 105, 424– 429
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Legrand, M.; Sousa Passos, C. J.; Mergler, D.; Chan, H. M. Biomonitoring of Mercury Exposure with Single Human Hair Strand Environ. Sci. Technol. 2005, 39, 4594– 4598
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Hightower, J. M.; Moore, D. Mercury Levels in High-End Consumers of Fish Environ. Health Perspect. 2003, 111, 604– 608
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McDowell, M. A.; Dillon, C. F.; Osterloh, J.; Bolger, P. M.; Pellizzari, E.; Fernando, R.; de Oca, R. M.; Schober, S. E.; Sinks, T.; Jones, R. L.et al. Hair Mercury Levels in U.S. Children and Women of Childbearing Age: Reference Range Data from NHANES 1999–2000 Environ. Health Perspect. 2004, 112, 1165– 1171
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Lee, J.-S.; Mirkin, C. A. Chip-Based Scanometric Detection of Mercuric Ion Using DNA-Functionalized Gold Nanoparticles Anal. Chem. 2008, 80, 6805– 6808
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Cho, E. S.; Kim, J.; Tejerina, B.; Hermans, T. M.; Jiang, H.; Nakanishi, H.; Yu, M.; Patashinski, A. Z.; Glotzer, S. C.; Stellacci, F.et al. Ultrasensitive Detection of Toxic Cations through Changes in the Tunnelling Current across Films of Striped Nanoparticles Nat. Mater. 2012, 11, 978– 985
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Ultrasensitive detection of toxic cations through changes in the tunnelling current across films of striped nanoparticles
Cho, Eun Seon; Kim, Jiwon; Tejerina, Baudilio; Hermans, Thomas M.; Jiang, Hao; Nakanishi, Hideyuki; Yu, Miao; Patashinski, Alexander Z.; Glotzer, Sharon C.; Stellacci, Francesco; Grzybowski, Bartosz A.
Nature Materials (2012), 11 (11), 978-985CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
Although multiple methods have been developed to detect metal cations, only a few offer sensitivities below 1 pM, and many require complicated procedures and sophisticated equipment. Here, the authors describe a class of simple solid-state sensors for the ultrasensitive detection of heavy-metal cations (notably, an unprecedented attomolar limit for the detection of CH3Hg+ in both standardized solns. and environmental samples) through changes in the tunneling current across films of nanoparticles (NPs) protected with striped monolayers of org. ligands. The sensors are also highly selective because of the ligand-shell organization of the NPs. On binding of metal cations, the electronic structure of the mol. bridges between proximal NPs changes, the tunneling current increases and highly conductive paths ultimately percolate the entire film. The nanoscale heterogeneity of the structure of the film broadens the range of the cation-binding consts., which leads to wide sensitivity ranges (remarkably, over 18 orders of magnitude in CH3Hg+ concn.).
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Gartia, M. R.; Braunschweig, B.; Chang, T.-W.; Moinzadeh, P.; Minsker, B. S.; Agha, G.; Wieckowski, A.; Keefer, L. L.; Liu, G. L. The Microelectronic Wireless Nitrate Sensor Network for Environmental Water Monitoring J. Environ. Monit. 2012, 14, 3068– 3075
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Lafleur, J. P.; Senkbeil, S.; Jensen, T. G.; Kutter, J. P. Gold Nanoparticle-Based Optical Microfluidic Sensors for Analysis of Environmental Pollutants Lab Chip 2012, 12, 4651– 4656
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Gold nanoparticle-based optical microfluidic sensors for analysis of environmental pollutants
Lafleur, Josiane P.; Senkbeil, Silja; Jensen, Thomas G.; Kutter, Joerg P.
Lab on a Chip (2012), 12 (22), 4651-4656CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
Conventional methods of environmental anal. can be significantly improved by the development of portable microscale technologies for direct in-field sensing at remote locations. This report demonstrates the vast potential of gold nanoparticle-based microfluidic sensors for the rapid, in-field, detection of two important classes of environmental contaminants - heavy metals and pesticides. Using gold nanoparticle-based microfluidic sensors linked to a simple digital camera as the detector, detection limits as low as 0.6 μg L-1 and 16 μg L-1 could be obtained for the heavy metal mercury and the dithiocarbamate pesticide ziram, resp. These results demonstrate that the attractive optical properties of gold nanoparticle probes combine synergistically with the inherent qualities of microfluidic platforms to offer simple, portable and sensitive sensors for environmental contaminants.
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Chung, E.; Gao, R.; Ko, J.; Choi, N.; Lim, D. W.; Lee, E. K.; Chang, S.-I.; Choo, J. Trace Analysis of Mercury(II) Ions Using Aptamer-Modified Au/Ag Core-Shell Nanoparticles and SERS Spectroscopy in a Microdroplet Channel Lab Chip 2013, 13, 260– 266
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Trace analysis of mercury(II) ions using aptamer-modified Au/Ag core-shell nanoparticles and SERS spectroscopy in a microdroplet channel
Chung, Eunsu; Gao, Rongke; Ko, Juhui; Choi, Namhyun; Lim, Dong Woo; Lee, Eun Kyu; Chang, Soo-Ik; Choo, Jaebum
Lab on a Chip (2013), 13 (2), 260-266CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
The authors report the rapid and highly sensitive trace anal. of mercury(II) ions in water using a surface-enhanced Raman scattering (SERS)-based microdroplet sensor. Aptamer-modified Au/Ag core-shell nanoparticles have been fabricated and utilized as highly functional sensing probes. All detection processes for the reaction between mercury(II) ions and aptamer-modified nanoparticles were performed in a specially designed microdroplet channel. Small water droplets that included sample reagents were sepd. from each other by an oil phase that continuously flowed along the channel. This two-phase liq.-liq. segmented flow system prevented the adsorption of aggregated colloids to the channel walls due to localized reagents within encapsulated droplets. The result was reduced residence time distributions. The limit of detection (LOD) of mercury(II) ions in water was detd. by the SERS-based microdroplet sensor to be below 10 pM, which is three orders below the EPA-defined max. contaminant level. This combination of a SERS-based microfluidic sensor with aptamer-based functional nanoprobes can be used for in-the-field sensing platforms, due to its size and simplicity.
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Lin, Y.-W.; Huang, C.-C.; Chang, H.-T. Gold Nanoparticle Probes for the Detection of Mercury, Lead and Copper Ions Analyst 2011, 136, 863– 871
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Liu, D.; Wang, Z.; Jiang, X. Gold Nanoparticles for the Colorimetric and Fluorescent Detection of Ions and Small Organic Molecules Nanoscale 2011, 3, 1421– 1433
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Gold nanoparticles for the colorimetric and fluorescent detection of ions and small organic molecules
Liu, Dingbin; Wang, Zhuo; Jiang, Xingyu
Nanoscale (2011), 3 (4), 1421-1433CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
A review. In recent years, gold nanoparticles (AuNPs) have drawn considerable research attention in the fields of catalysis, drug delivery, imaging, diagnostics, therapy, and biosensors due to their unique optical and electronic properties. In this review, recent advances are summarized in the development of AuNP-based colorimetric and fluorescent assays for ions including cations (such as Hg2+, Cu2+, Pb2+, As3+, Ca2+, Al3+, etc.) and anions (such as NO2-, CN-, PF6-, F-, I-, oxoanions), and small org. mols. (such as cysteine, homocysteine, trinitrotoluene, melamine ,and cocaine, ATP, glucose, dopamine, and so forth). Many of these species adversely affect human health and the environment. Moreover, particular attention is paid to AuNP-based colorimetric and fluorescent assays in practical applications.
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Du, J.; Jiang, L.; Shao, Q.; Liu, X.; Marks, R. S.; Ma, J.; Chen, X. Colorimetric Detection of Mercury Ions Based on Plasmonic Nanoparticles Small 2013, 9, 1467– 1481
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Colorimetric Detection of Mercury Ions Based on Plasmonic Nanoparticles
Du, Jianjun; Jiang, Lin; Shao, Qi; Liu, Xiaogang; Marks, Robert S.; Ma, Jan; Chen, Xiaodong
Small (2013), 9 (9-10), 1467-1481CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. The development of rapid, specific, cost-effective, and robust tools in monitoring Hg2+ levels in both environmental and biol. samples is of utmost importance due to the severe mercury toxicity to humans. A no. of techniques exist, but the colorimetric assay, which is reviewed herein, is a possible tool in monitoring the level of mercury. These assays allow transforming target sensing events into color changes, which have applicable potential for in-the-field application through naked-eye detection. Specifically, plasmonic nanoparticle-based colorimetric assay exhibits a much better propensity for identifying various targets in terms of sensitivity, soly., and stability compared to commonly used org. chromophores. In this review, recent progress in the development of gold nanoparticle-based colorimetric assays for Hg2+ is summarized, with a particular emphasis on examples of functionalized gold nanoparticle systems with oligonucleotides, oligopeptides, and functional mols. Besides highlighting the current design principle for plasmonic nanoparticle-based colorimetric probes, the discussions on challenges and the prospect of next-generation probes for in-the-field applications are also presented.
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El Kaoutit, H.; Estévez, P.; García, F. C.; Serna, F.; García, J. M. Sub-ppm Quantification of Hg(II) in Aqueous Media Using Both the Naked Eye and Digital Information from Pictures of a Colorimetric Sensory Polymer Membrane Taken with the Digital Camera of a Conventional Mobile Phone Anal. Methods 2013, 5, 54– 58
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Sub-ppm quantification of Hg(ii) in aqueous media using both the naked eye and digital information from pictures of a colorimetric sensory polymer membrane taken with the digital camera of a conventional mobile phone
El Kaoutit, Hamid; Estevez, Pedro; Garcia, Felix C.; Serna, Felipe; Garcia, Jose M.
Analytical Methods (2013), 5 (1), 54-58CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)
The authors present colorimetric sensory membranes for detecting Hg(ii) in aq. media. The color response of the sensory materials can be tuned for detection with the naked eye, such as the max. contaminant level of Hg(ii) that is set by the United States Environmental Protection Agency (EPA) for drinking H2O. Also, the concn. of Hg(ii) can be monitored using digital pictures of the membranes taken with conventional cameras. Thus, nanomolar concn. of Hg(ii) could be detected by the naked eye due to color changes of membranes, and the concn. of Hg(ii) could be quantified, within the millimolar to nanomolar range, by analyzing the digital information of pictures taken of the membranes after dipping them in H2O contg. this environmentally poisonous cation.
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U.S. EPA. National Primary Drinking Water Regulations. US EPA, 2009. http://water.epa.gov/drink/contaminants/index.cfm#List.
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World Health Organization. Guidelines for Drinking Water Quality, 4th ed.; World Health Organization: Geneva, 2011. http://whqlibdoc.who.int/publications/2011/9789241548151_eng.pdf.
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Vashist, S.; Mudanyali, O.; Schneider, E. M.; Zengerle, R.; Ozcan, A. Cellphone-Based Devices for Bioanalytical Sciences Anal. Bioanal. Chem. 2013, DOI: 10.1007/s00216-013-7473-1
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Coskun, A. F.; Ozcan, A. Computational Imaging, Sensing and Diagnostics for Global Health Applications Curr. Opin. Biotechnol. 2013, 25, 8– 16
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Tseng, D.; Mudanyali, O.; Oztoprak, C.; Isikman, S. O.; Sencan, I.; Yaglidere, O.; Ozcan, A. Lensfree Microscopy on a Cellphone Lab Chip 2010, 10, 1787– 1792
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Lensfree microscopy on a cellphone
Tseng, Derek; Mudanyali, Onur; Oztoprak, Cetin; Isikman, Serhan O.; Sencan, Ikbal; Yaglidere, Oguzhan; Ozcan, Aydogan
Lab on a Chip (2010), 10 (14), 1787-1792CODEN: LCAHAM; ISSN:1473-0197. (Royal Society of Chemistry)
We demonstrate lensfree digital microscopy on a cellphone. This compact and light-wt. holog. microscope installed on a cellphone does not utilize any lenses, lasers or other bulky optical components and it may offer a cost-effective tool for telemedicine applications to address various global health challenges. Weighing ∼38 g (<1.4 oz), this lensfree imaging platform can be mech. attached to the camera unit of a cellphone where the samples are loaded from the side, and are vertically illuminated by a simple light-emitting diode (LED). This incoherent LED light is then scattered from each micro-object to coherently interfere with the background light, creating the lensfree hologram of each object on the detector array of the cellphone. These holog. signatures captured by the cellphone permit reconstruction of microscopic images of the objects through rapid digital processing. We report the performance of this lensfree cellphone microscope by imaging various sized micro-particles, as well as red blood cells, white blood cells, platelets and a waterborne parasite (Giardia lamblia).
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Zhu, H.; Mavandadi, S.; Coskun, A. F.; Yaglidere, O.; Ozcan, A. Optofluidic Fluorescent Imaging Cytometry on a Cell Phone Anal. Chem. 2011, 83, 6641– 6647
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Zhu, H.; Yaglidere, O.; Su, T.-W.; Tseng, D.; Ozcan, A. Cost-Effective and Compact Wide-Field Fluorescent Imaging on a Cell-Phone Lab Chip 2011, 11, 315– 322
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Cost-effective and compact wide-field fluorescent imaging on a cell-phone
Zhu, Hongying; Yaglidere, Oguzhan; Su, Ting-Wei; Tseng, Derek; Ozcan, Aydogan
Lab on a Chip (2011), 11 (2), 315-322CODEN: LCAHAM; ISSN:1473-0197. (Royal Society of Chemistry)
We demonstrate wide-field fluorescent and darkfield imaging on a cell-phone with compact, light-wt. and cost-effective optical components that are mech. attached to the existing camera unit of the cell-phone. For this purpose, we used battery powered light-emitting diodes (LEDs) to pump the sample of interest from the side using butt-coupling, where the pump light was guided within the sample cuvette to uniformly excite the specimen. The fluorescent emission from the sample was then imaged using an addnl. lens that was positioned right in front of the existing lens of the cell-phone camera. Because the excitation occurs through guided waves that propagate perpendicular to our detection path, an inexpensive plastic color filter was sufficient to create the dark-field background required for fluorescent imaging, without the need for a thin-film interference filter. We validate the performance of this platform by imaging various fluorescent micro-objects in 2 colors (i.e., red and green) over a large field-of-view (FOV) of ∼81 mm2 with a raw spatial resoln. of ∼20 μm. With addnl. digital processing of the captured cell-phone images, through the use of compressive sampling theory, we demonstrate ∼2 fold improvement in our resolving power, achieving ∼10 μm resoln. without a trade-off in our FOV. Further, we also demonstrate darkfield imaging of non-fluorescent specimen using the same interface, where this time the scattered light from the objects is detected without the use of any filters. The capability of imaging a wide FOV would be exceedingly important to probe large sample vols. (e.g., >0.1 mL) of e.g., blood, urine, sputum or water, and for this end we also demonstrate fluorescent imaging of labeled white-blood cells from whole blood samples, as well as water-borne pathogenic protozoan parasites such as Giardia Lamblia cysts. Weighing only ∼28 g (∼1 oz), this compact and cost-effective fluorescent imaging platform attached to a cell-phone could be quite useful esp. for resource-limited settings, and might provide an important tool for wide-field imaging and quantification of various lab-on-a-chip assays developed for global health applications, such as monitoring of HIV+ patients for CD4 counts or viral load measurements.
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Preechaburana, P.; Gonzalez, M. C.; Suska, A.; Filippini, D. Surface Plasmon Resonance Chemical Sensing on Cell Phones Angew. Chem., Int. Ed. 2012, 51, 11585– 11588
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Surface Plasmon Resonance Chemical Sensing on Cell Phones
Preechaburana, Pakorn; Gonzalez, Marcos Collado; Suska, Anke; Filippini, Daniel
Angewandte Chemie, International Edition (2012), 51 (46), 11585-11588CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
An angle-resolved surface plasmon resonance detection system is described that is based on a single disposable device configured to use conditioned illumination and optical detection from cell phones. The SPR coupler central to the implementation is compatible with regular lab-on-a-chip technol. and temporarily adheres to the phone screen surface during the measurement. It couples and conditions the illumination from the screen and directs the SPR image to the phone camera. SPR detection was illustrated with a com. assay for β2 microglobulin and with a custom-made chip including embedded calibration. Current cell phones provide the performance required for chem. sensing, thereby rendering the platform viable to develop tests that may complement routine monitoring.
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Shen, L.; Hagen, J. A.; Papautsky, I. Point-of-Care Colorimetric Detection with a Smartphone Lab Chip 2012, 12, 4240– 4243
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Point-of-care colorimetric detection with a smartphone
Shen, Li; Hagen, Joshua A.; Papautsky, Ian
Lab on a Chip (2012), 12 (21), 4240-4243CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
Paper-based immunoassays are becoming powerful and low-cost diagnostic tools, esp. in resource-limited settings. Inexpensive methods for quantifying these assays have been shown using desktop scanners, which lack portability, and cameras, which suffer from the ever changing ambient light conditions. In this work, we introduce a novel approach of quantifying colors of colorimetric diagnostic assays with a smartphone that allows high accuracy measurements in a wide range of ambient conditions, making it a truly portable system. Instead of directly using the red, green, and blue (RGB) intensities of the color images taken by a smartphone camera, we use chromaticity values to construct calibration curves of analyte concns. We demonstrate the high accuracy of this approach in pH measurements with linear response ranges of 1-12. These results are comparable to those reported using a desktop scanner or silicon photodetectors. To make the approach adoptable under different lighting conditions, we developed a calibration technique to compensate for measurement errors due to variability in ambient light. This technique is applicable to a no. of common light sources, such as sun light, fluorescent light, or smartphone LED light. Ultimately, the entire approach can be integrated in an "app" to enable one-click reading, making our smartphone based approach operable without any professional training or complex instrumentation.
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Mudanyali, O.; Dimitrov, S.; Sikora, U.; Padmanabhan, S.; Navruz, I.; Ozcan, A. Integrated Rapid-Diagnostic-Test Reader Platform on a Cellphone Lab Chip 2012, 12, 2678– 2686
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Integrated rapid-diagnostic-test reader platform on a cellphone
Mudanyali, Onur; Dimitrov, Stoyan; Sikora, Uzair; Padmanabhan, Swati; Navruz, Isa; Ozcan, Aydogan
Lab on a Chip (2012), 12 (15), 2678-2686CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
We demonstrate a cellphone-based rapid-diagnostic-test (RDT) reader platform that can work with various lateral flow immuno-chromatog. assays and similar tests to sense the presence of a target analyte in a sample. This compact and cost-effective digital RDT reader, weighing only ∼65 g, mech. attaches to the existing camera unit of a cellphone, where various types of RDTs can be inserted to be imaged in reflection or transmission modes under light-emitting diode (LED)-based illumination. Captured raw images of these tests are then digitally processed (within less than 0.2 s per image) through a smart application running on the cellphone for validation of the RDT, as well as for automated reading of its diagnostic result. The same smart application then transmits the resulting data, together with the RDT images and other related information (e.g., demog. data), to a central server, which presents the diagnostic results on a world map through geo-tagging. This dynamic spatio-temporal map of various RDT results can then be viewed and shared using internet browsers or through the same cellphone application. We tested this platform using malaria, tuberculosis (TB) and HIV RDTs by installing it on both Android-based smartphones and an iPhone. Providing real-time spatio-temporal statistics for the prevalence of various infectious diseases, this smart RDT reader platform running on cellphones might assist healthcare professionals and policymakers to track emerging epidemics worldwide and help epidemic preparedness.
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Zhu, H.; Sikora, U.; Ozcan, A. Quantum Dot Enabled Detection of Escherichia coli Using a Cell-Phone Analyst 2012, 137, 2541– 2544
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Quantum dot enabled detection of Escherichia coli using a cell-phone
Zhu, Hongying; Sikora, Uzair; Ozcan, Aydogan
Analyst (Cambridge, United Kingdom) (2012), 137 (11), 2541-2544CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)
The authors report a cell-phone based Escherichia coli (E. coli) detection platform for screening of liq. samples. In this compact and cost-effective design attached to a cell-phone, the authors use anti-E. coli O157:H7 antibody functionalized glass capillaries as solid substrates to perform a quantum dot based sandwich assay for specific detection of E. coli O157:H7 in liq. samples. Using battery-powered inexpensive light-emitting-diodes (LEDs), the authors excite/pump these labeled E. coli particles captured on the capillary surface, where the emission from the quantum dots is then imaged using the cell-phone camera unit through an addnl. lens that is inserted between the capillary and the cell-phone. By quantifying the fluorescent light emission from each capillary tube, the concn. of E. coli in the sample is detd. The authors exptl. confirmed the detection limit of this cell-phone based fluorescent imaging and sensing platform as ∼5 to 10 cfu mL-1 in buffer soln. The authors also tested the specificity of this E. coli detection platform by spiking samples with different species (e.g., Salmonella) to confirm that non-specific binding/detection is negligible. The authors further demonstrated the proof-of-concept of the authors' approach in a complex food matrix, e.g., fat-free milk, where a similar detection limit of ∼5 to 10 cfu mL-1 was achieved despite challenges assocd. with the d. of proteins that exist in milk. The authors' results reveal the promising potential of this cell-phone enabled field-portable and cost-effective E. coli detection platform for e.g., screening of water and food samples even in resource limited environments. The presented platform can also be applicable to other pathogens of interest through the use of different antibodies.
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Gallegos, D.; Long, K. D.; Yu, H.; Clark, P. P.; Lin, Y.; George, S.; Nath, P.; Cunningham, B. T. Label-Free Biodetection Using a Smartphone Lab Chip 2013, 13, 2124– 2132
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Label-free biodetection using a smartphone
Gallegos, Dustin; Long, Kenneth D.; Yu, Hojeong; Clark, Peter P.; Lin, Yixiao; George, Sherine; Nath, Pabitra; Cunningham, Brian T.
Lab on a Chip (2013), 13 (11), 2124-2132CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
Utilizing its integrated camera as a spectrometer, we demonstrate the use of a smartphone as the detection instrument for a label-free photonic crystal biosensor. A custom-designed cradle holds the smartphone in fixed alignment with optical components, allowing for accurate and repeatable measurements of shifts in the resonant wavelength of the sensor. Externally provided broadband light incident upon an entrance pinhole is subsequently collimated and linearly polarized before passing through the biosensor, which resonantly reflects only a narrow band of wavelengths. A diffraction grating spreads the remaining wavelengths over the camera's pixels to display a high resoln. transmission spectrum. The photonic crystal biosensor is fabricated on a plastic substrate and attached to a std. glass microscope slide that can easily be removed and replaced within the optical path. A custom software app was developed to convert the camera images into the photonic crystal transmission spectrum in the visible wavelength range, including curve-fitting anal. that computes the photonic crystal resonant wavelength with 0.009 nm accuracy. We demonstrate the functionality of the system through detection of an immobilized protein monolayer, and selective detection of concn.-dependent antibody binding to a functionalized photonic crystal. We envision the capability for an inexpensive, handheld biosensor instrument with web connectivity to enable point-of-care sensing in environments that have not been practical previously.
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O’Driscoll, S.; MacCraith, B. D.; Burke, C. S. A Novel Camera Phone-Based Platform for Quantitative Fluorescence Sensing Anal. Methods 2013, 5, 1904– 1908
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A novel camera phone-based platform for quantitative fluorescence sensing
O'Driscoll, Stephen; MacCraith, Brian D.; Burke, Conor S.
Analytical Methods (2013), 5 (8), 1904-1908CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)
We describe a novel camera phone-based optical sensing platform capable of real-time quant. fluorescence-based measurements. The platform employs the phone's camera as a photodetector in a non-imaging optical configuration that simultaneously detects fluorescence from a no. of sensor spots on a disposable optical sensor chip. The platform combines the functionality of the camera with the phone's data-processing capabilities to facilitate on-phone anal. of detected fluorescence intensity. It is envisaged that such a platform will have significant potential in application areas such as environmental monitoring and healthcare where there is a growing demand for decentralized diagnostics using low-cost, portable devices, particularly in remote or low-resource environments.
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Oncescu, V.; O’Dell, D.; Erickson, D. Smartphone Based Health Accessory for Colorimetric Detection of Biomarkers in Sweat and Saliva Lab Chip 2013, 13, 3232– 3238
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Smartphone based health accessory for colorimetric detection of biomarkers in sweat and saliva
Oncescu, Vlad; O'Dell, Dakota; Erickson, David
Lab on a Chip (2013), 13 (16), 3232-3238CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
The mobile health market is rapidly expanding and portable diagnostics tools offer an opportunity to decrease costs and increase the availability of healthcare. Here we present a smartphone based accessory and method for the rapid colorimetric detection of pH in sweat and saliva. Sweat pH can be correlated to sodium concn. and sweat rate in order to indicate to users the proper time to hydrate during phys. exercise and avoid the risk of muscle cramps. Salivary pH below a crit. threshold is correlated with enamel decalcification, an acidic breakdown of calcium in the teeth. We conduct a no. of human trials with the device on a treadmill to demonstrate the ability to monitor changes in sweat pH due to exercise and electrolyte intake and predict optimal hydration. Addnl., we perform trials to measure salivary pH over time to monitor the effects of diet on oral health risks.
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Lillehoj, P. B.; Huang, M.-C.; Truong, N.; Ho, C.-M. Rapid Electrochemical Detection on a Mobile Phone Lab Chip 2013, 13, 2950– 2955
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Rapid electrochemical detection on a mobile phone
Lillehoj, Peter B.; Huang, Ming-Chun; Truong, Newton; Ho, Chih-Ming
Lab on a Chip (2013), 13 (15), 2950-2955CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
We present a compact mobile phone platform for rapid, quant. biomol. detection. This system consists of an embedded circuit for signal processing and data anal., and disposable microfluidic chips for fluidic handling and biosensing. Capillary flow is employed for sample loading, processing, and pumping to enhance operational portability and simplicity. Graphical step-by-step instructions displayed on the phone assists the operator through the detection process. After the completion of each measurement, the results are displayed on the screen for immediate assessment and the data is automatically saved to the phone's memory for future anal. and transmission. Validation of this device was carried out by detecting Plasmodium falciparum histidine-rich protein 2 (PfHRP2), an important biomarker for malaria, with a lower limit of detection of 16 ng mL-1 in human serum. The simple detection process can be carried out with two loading steps and takes 15 min to complete each measurement. Due to its compact size and high performance, this device offers immense potential as a widely accessible, point-of-care diagnostic platform, esp. in remote and rural areas. In addn. to its impact on global healthcare, this technol. is relevant to other important applications including food safety, environmental monitoring and biosecurity.
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Zhu, H.; Sencan, I.; Wong, J.; Dimitrov, S.; Tseng, D.; Nagashima, K.; Ozcan, A. Cost-Effective and Rapid Blood Analysis on a Cell-Phone Lab Chip 2013, 13, 1282– 1288
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Cost-effective and rapid blood analysis on a cell-phone
Zhu, Hongying; Sencan, Ikbal; Wong, Justin; Dimitrov, Stoyan; Tseng, Derek; Nagashima, Keita; Ozcan, Aydogan
Lab on a Chip (2013), 13 (7), 1282-1288CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
We demonstrate a compact and cost-effective imaging cytometry platform installed on a cell-phone for the measurement of the d. of red and white blood cells as well as Hb concn. in human blood samples. Fluorescent and bright-field images of blood samples are captured using sep. optical attachments to the cell-phone and are rapidly processed through a custom-developed smart application running on the phone for counting of blood cells and detg. Hb d. We evaluated the performance of this cell-phone based blood anal. platform using anonymous human blood samples and achieved comparable results to a std. bench-top hematol. analyzer. Test results can either be stored on the cell-phone memory or be transmitted to a central server, providing remote diagnosis opportunities even in field settings.
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Coskun, A. F.; Nagi, R.; Sadeghi, K.; Phillips, S.; Ozcan, A. Albumin Testing in Urine Using a Smart-Phone Lab Chip 2013, 13, 4231– 4238
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Albumin testing in urine using a smart-phone
Coskun, Ahmet F.; Nagi, Richie; Sadeghi, Kayvon; Phillips, Stephen; Ozcan, Aydogan
Lab on a Chip (2013), 13 (21), 4231-4238CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
We demonstrate a digital sensing platform, termed Albumin Tester, running on a smart-phone that images and automatically analyses fluorescent assays confined within disposable test tubes for sensitive and specific detection of albumin in urine. This light-wt. and compact Albumin Tester attachment, weighing approx. 148 g, is mech. installed on the existing camera unit of a smart-phone, where test and control tubes are inserted from the side and are excited by a battery powered laser diode. This excitation beam, after probing the sample of interest located within the test tube, interacts with the control tube, and the resulting fluorescent emission is collected perpendicular to the direction of the excitation, where the cellphone camera captures the images of the fluorescent tubes through the use of an external plastic lens that is inserted between the sample and the camera lens. The acquired fluorescent images of the sample and control tubes are digitally processed within one second through an Android application running on the same cellphone for quantification of albumin concn. in the urine specimen of interest. Using a simple sample prepn. approach which takes ∼5 min per test (including the incubation time), we exptl. confirmed the detection limit of our sensing platform as 5-10 μg mL-1 (which is more than 3 times lower than the clin. accepted normal range) in buffer as well as urine samples. This automated albumin testing tool running on a smart-phone could be useful for early diagnosis of kidney disease or for monitoring of chronic patients, esp. those suffering from diabetes, hypertension, and/or cardiovascular diseases.
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Coskun, A. F.; Wong, J.; Khodadadi, D.; Nagi, R.; Tey, A.; Ozcan, A. A Personalized Food Allergen Testing Platform on a Cellphone Lab Chip 2013, 13, 636– 640
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A personalized food allergen testing platform on a cellphone
Coskun, Ahmet F.; Wong, Justin; Khodadadi, Delaram; Nagi, Richie; Tey, Andrew; Ozcan, Aydogan
Lab on a Chip (2013), 13 (4), 636-640CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
We demonstrate a personalized food allergen testing platform, termed iTube, running on a cellphone that images and automatically analyses colorimetric assays performed in test tubes toward sensitive and specific detection of allergens in food samples. This cost-effective and compact iTube attachment, weighing approx. 40 g, is mech. installed on the existing camera unit of a cellphone, where the test and control tubes are inserted from the side and are vertically illuminated by two sep. light-emitting-diodes. The illumination light is absorbed by the allergen assay, which is activated within the tubes, causing an intensity change in the acquired images by the cellphone camera. These transmission images of the sample and control tubes are digitally processed within 1 s using a smart application running on the same cellphone for detection and quantification of allergen contamination in food products. We evaluated the performance of this cellphone-based iTube platform using different types of com. available cookies, where the existence of peanuts was accurately quantified after a sample prepn. and incubation time of ∼20 min per test. This automated and cost-effective personalized food allergen testing tool running on cellphones can also permit uploading of test results to secure servers to create personal and/or public spatio-temporal allergen maps, which can be useful for public health in various settings.
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Navruz, I.; Coskun, A. F.; Wong, J.; Mohammad, S.; Tseng, D.; Nagi, R.; Phillips, S.; Ozcan, A. Smart-Phone Based Computational Microscopy Using Multi-Frame Contact Imaging on a Fiber-Optic Array Lab Chip 2013, 13, 4015– 4023
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Smart-phone based computational microscopy using multi-frame contact imaging on a fiber-optic array
Navruz, Isa; Coskun, Ahmet F.; Wong, Justin; Mohammad, Saqib; Tseng, Derek; Nagi, Richie; Phillips, Stephen; Ozcan, Aydogan
Lab on a Chip (2013), 13 (20), 4015-4023CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
We demonstrate a cellphone based contact microscopy platform, termed Contact Scope, which can image highly dense or connected samples in transmission mode. Weighing approx. 76 g, this portable and compact microscope is installed on the existing camera unit of a cellphone using an opto-mech. add-on, where planar samples of interest are placed in contact with the top facet of a tapered fiber-optic array. This glass-based tapered fiber array has ∼9 fold higher d. of fiber optic cables on its top facet compared to the bottom one and is illuminated by an incoherent light source, e.g., a simple light-emitting-diode (LED). The transmitted light pattern through the object is then sampled by this array of fiber optic cables, delivering a transmission image of the sample onto the other side of the taper, with ∼3× magnification in each direction. This magnified image of the object, located at the bottom facet of the fiber array, is then projected onto the CMOS image sensor of the cellphone using two lenses. While keeping the sample and the cellphone camera at a fixed position, the fiber-optic array is then manually rotated with discrete angular increments of e.g., 1-2 degrees. At each angular position of the fiber-optic array, contact images are captured using the cellphone camera, creating a sequence of transmission images for the same sample. These multi-frame images are digitally fused together based on a shift-and-add algorithm through a custom-developed Android application running on the smart-phone, providing the final microscopic image of the sample, visualized through the screen of the phone. This final computation step improves the resoln. and also removes spatial artifacts that arise due to non-uniform sampling of the transmission intensity at the fiber optic array surface. We validated the performance of this cellphone based Contact Scope by imaging resoln. test charts and blood smears.
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Colorimetric detection of mercuric ion (Hg2+) in aqueous media using DNA-functionalized gold nanoparticles
Lee, Jae-Seung; Han, Min Su; Mirkin, Chad A.
Angewandte Chemie, International Edition (2007), 46 (22), 4093-4096CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Color is everything: Hg2+ in aq. media is detected by the formation of thymidine-Hg2+-thymidine coordination complexes, which raises the melting temp. of the DNA-hybridized gold nanoparticle probes and thus the temp. at which the probes disperse and effect a purple-to-red color change. The method has very high sensitivity and selectivity, and it provides a simple and fast colorimetric readout.
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Li, Li; Li, Baoxin; Qi, Yingying; Jin, Yan
Analytical and Bioanalytical Chemistry (2009), 393 (8), 2051-2057CODEN: ABCNBP; ISSN:1618-2642. (Springer)
The authors report a simple and sensitive aptamer-based colorimetric detection of mercury ions (Hg2+) using unmodified gold nanoparticles as colorimetric probe. It is based on the fact that bare gold nanoparticles interact differently with short single-strand DNA and double-stranded DNA. The anti-Hg2+ aptamer is rich in thymine (T) and readily forms T-Hg2+-T configuration in the presence of Hg2+. By measuring color change or adsorption ratio, the bare gold nanoparticles can effectively differentiate the Hg2+-induced conformational change of the aptamer in the presence of a given salt with high concn. The assay shows a linear response toward Hg2+ concn. through a five-decade range of 1 × 10-4 mol L-1 to 1 × 10-9 mol L-1. Even with the naked eye, the authors could identify micromolar Hg2+ concns. within minutes. By using the spectrometric method, the detection limit was improved to the nanomolar range (0.6 nM). The assay shows excellent selectivity for Hg2+ over other metal cations including K+, Ba2+, Ni2+, Pb2+, Cu2+, Cd2+, Mg2+, Ca2+, Zn2+, Al3+, and Fe3+. The major advantages of this Hg2+ assay are its water-soly., simplicity, low cost, visual colorimetry, and high sensitivity. This method provides a potentially useful tool for the Hg2+ detection.
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Miyake, Y.; Togashi, H.; Tashiro, M.; Yamaguchi, H.; Oda, S.; Kudo, M.; Tanaka, Y.; Kondo, Y.; Sawa, R.; Fujimoto, T.et al. MercuryII-Mediated Formation of Thymine-HgII-Thymine Base Pairs in DNA Duplexes J. Am. Chem. Soc. 2006, 128, 2172– 2173
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MercuryII-Mediated Formation of Thymine-HgII-Thymine Base Pairs in DNA Duplexes
Miyake, Yoko; Togashi, Humika; Tashiro, Mitsuru; Yamaguchi, Hiroshi; Oda, Shuji; Kudo, Megumi; Tanaka, Yoshiyuki; Kondo, Yoshinori; Sawa, Ryuichi; Fujimoto, Takashi; Machinami, Tomoya; Ono, Akira
Journal of the American Chemical Society (2006), 128 (7), 2172-2173CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The very specific binding of the HgII ion unexpectedly and significantly stabilizes naturally occurring thymine-thymine base mispairing in DNA duplexes. Following this finding, we prepd. DNA duplexes contg. metal-mediated base pairs at the desired sites, as well as novel double helical architectures consisting only of thymine-HgII-thymine pairs.
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Tanaka, Y.; Oda, S.; Yamaguchi, H.; Kondo, Y.; Kojima, C.; Ono, A. 15n-15n J-Coupling across HgII: Direct Observation of HgII-Mediated T-T Base Pairs in a DNA Duplex J. Am. Chem. Soc. 2006, 129, 244– 245
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Ecological effects, transport, and fate of mercury: a general review
Boening, Dean W.
Chemosphere (2000), 40 (12), 1335-1351CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Science Ltd.)
A review and discussion with many refs. Mercury at low concns. represents a major hazard to microorganisms. Inorg. mercury has been reported to produce harmful effects at 5 μg/l in a culture medium. Organomercury compds. can exert the same effect at concns. 10 times lower than this. The org. forms of mercury are generally more toxic to aquatic organisms and birds than the inorg. forms. Aquatic plants are affected by mercury in water at concns. of 1 mg/l for inorg. mercury and at much lower concns. of org. mercury. Aquatic invertebrates widely vary in their susceptibility to mercury. In general, organisms in the larval stage are most sensitive. Me mercury in fish is caused by bacterial methylation of inorg. mercury, either in the environment or in bacteria assocd. with fish gills or gut. In aquatic matrixes, mercury toxicity is affected by temp., salinity, dissolved oxygen and water hardness. A wide variety of physiol., reproductive and biochem. abnormalities have been reported in fish exposed to sublethal concns. of mercury. Birds fed inorg. mercury show a redn. in food intake and consequent poor growth. Other (more subtle) effects in avian receptors have been reported (i.e., increased enzyme prodn., decreased cardiovascular function, blood parameter changes, immune response, kidney function and structure, and behavioral changes). The form of retained mercury in birds is more variable and depends on species, target organ and geog. site. With few exceptions, terrestrial plants (woody plants in particular) are generally insensitive to the harmful effects of mercury compds.

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Abstract
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Figure 1
Figure 1. Design of the ratiometric optical reader on a smart-phone. (a) 3D schematic illustration of the internal structure of the opto-mechanical attachment. The inset image shows the same attachment with a slightly different observation angle. (b) Photograph of the actual optical reader installed on an Android-based smart-phone. The screen of the smart-phone displays a typical image of the sample and control cuvettes when illuminated by red (625 nm) and green (523 nm) LEDs simultaneously.
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Figure 2
Figure 2. Principle of dual-color dual-cuvette colorimetric detection. (a) Scheme of the mercury sensing mechanism by using plasmonic Au NPs and aptamer. (b) Representative image captured on the smart-phone under dual-wavelength illumination. The left cuvette (control) contained a mixture of Au NPs (0.64 nM) and aptamer (30 nM), while the right cuvette (sample) contained a mixture of Au NPs and aptamer plus 500 nM Hg²⁺ (representative of a contaminated water sample). (c) Flow of image-processing steps to compute normalized green-to-red signal ratio (i.e., normalized G/R signal).
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Figure 3
Figure 3. Screen shots of our mercury detection application running on an Android phone. (a) Main menu; (b) calibration menu; (c) preview of a captured or selected colorimetric image before proceeding to analyze/quantify the sample; (d) display of the results; (e) spatiotemporal mapping of mercury contamination using a Google Maps-based interface; (f) tracking of mercury levels as a function of time per location.
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Figure 4
Figure 4. Dose–response curve of the Au NP and aptamer based plasmonic colorimetric assay running on a smart-phone. Each measurement at a given concentration was repeated three times. The curve was fitted by an exponential function with a coefficient of determination (R²) of 0.96. An LOD of 3.5 ppb for Hg²⁺ was obtained based on the G/R ratios of a control sample ([Hg²⁺] = 0) plus 3 times the standard deviation of the control (blue dashed line).
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Figure 5
Figure 5. Specificity tests of the Au NP and aptamer based plasmonic mercury assay for different metal ions (500 nM). Each measurement was repeated three times.
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Figure 6
Figure 6. Smart-phone-based mercury detection results for 11 tap water samples and eight natural samples collected in California, USA. Each measurement was repeated three times. Note that the measurements are plotted against the G/R ratios, which makes the presented scale of the mercury concentration (ppb) nonlinear, between 0.8 and 9.1 ppb.
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Figure 7
Figure 7. Spatiotemporal mapping of mercury contamination in Los Angeles coastal area. (a–c) Geospatial mercury concentration maps with different sampling densities; (b) zoomed-in area of the red ROI in (a); (c) enlarged region of the red ROI in (b). (d–f) Corresponding mercury concentration readings in (a)–(c). All the data points were measured three times. p values were calculated via two-sample Student’s t test by setting target data set as one population and the rest of the data sets as the other. ** represents p < 0.01, and *** represents p < 0.001.
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References
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  Harada M
  Critical reviews in toxicology (1995), 25 (1), 1-24 ISSN:1040-8444.
  Minamata disease (M. d.) is methylmercury (MeHg) poisoning that occurred in humans who ingested fish and shellfish contaminated by MeHg discharged in waste water from a chemical plant (Chisso Co. Ltd.). It was in May 1956, that M. d. was first officially "discovered" in Minamata City, south-west region of Japan's Kyushu Island. The marine products in Minamata Bay displayed high levels of Hg contamination (5.61 to 35.7 ppm). The Hg content in hair of patients, their family and inhabitants of the Shiranui Sea coastline were also detected at high levels of Hg (max. 705 ppm). Typical symptoms of M. d. are as follows: sensory disturbances (glove and stocking type), ataxia, dysarthria, constriction of the visual field, auditory disturbances and tremor were also seen. Further, the fetus was poisoned by MeHg when their mothers ingested contaminated marine life (named congenital M. d.). The symptom of patients were serious, and extensive lesions of the brain were observed. While the number of grave cases with acute M. d. in the initial stage was decreasing, the numbers of chronic M. d. patients who manifested symptoms gradually over an extended period of time was on the increase. For the past 36 years, of the 2252 patients who have been officially recognized as having M. d., 1043 have died. This paper also discusses the recent remaining problems.
4. 4
  TEACH. Organic Mercury, U.S. Environmental Protection Agency, 2007. http://www.epa.gov/teach/chem_summ/mercury_org_summary.pdf.
  There is no corresponding record for this reference.
5. 5
  Clarkson, T. W. The Toxicology of Mercury Crit. Rev. Clin. Lab. Sci. 1997, 34, 369– 403
  5
  The toxicology of mercury
  Clarkson, Thomas W.
  Critical Reviews in Clinical Laboratory Sciences (1997), 34 (4), 369-403CODEN: CRCLBH; ISSN:1040-8363. (CRC)
  A review and discussion with 80 refs. The major phys. forms of mercury to which humans are exposed are mercury vapor, Hg0, and methylmercury compds., CH3HgX. Mercury vapor emitted from both natural and anthropogenic sources is globally distributed in the atm. It is returned as a water-sol. form in pptn. and finds its way into bodies of fresh and ocean water. Land run-off also accounts for further input into lakes and oceans. Inorg. mercury, present in water sediments, is subject to bacterial conversion to methylmercury compds. that are bioaccumulated in the aquatic food chain to reach the highest concn. in predatory fish. Human exposure to mercury vapor is from dental amalgam and industries using mercury. Methylmercury compds. are found exclusively in seafood and freshwater fish. The health effects of mercury vapor have been known since ancient times. Severe exposure results in a triad of symptoms, erethism, tremor, and gingivitis. Today, there is concern with more subtle effects such as preclin. changes in kidney function and behavioral and cognitive changes assocd. with effects on the central nervous system. Methylmercury is a neurol. poison affecting primarily brain tissue. In adults, brain damage is focal affecting the function of such areas as the cerebellum (ataxia) and the visual cortex (constricted visual fields). Methylmercury also at high doses can cause severe damage to the developing brain. Today the chief concern is with the more subtle effects arising from prenatal exposure such as delayed development and cognitive changes in children.
6. 6
  Wolfe, M. F.; Schwarzbach, S.; Sulaiman, R. A. Effects of Mercury on Wildlife: A Comprehensive Review Environ. Toxicol. Chem. 1998, 17, 146– 160
  6
  Effects of mercury on wildlife: a comprehensive review
  Wolfe, Marti F.; Schwarzbach, Steven; Sulaiman, Rini A.
  Environmental Toxicology and Chemistry (1998), 17 (2), 146-160CODEN: ETOCDK; ISSN:0730-7268. (SETAC Press)
  A review with 147 refs. Wildlife may be exposed to mercury (Hg) and methylmercury (MeHg) from a variety of environmental sources, including mine tailings, industrial effluent, agricultural drainwater, impoundments, and atm. deposition from elec. power generation. Terrestrial and aquatic wildlife may be at risk from exposure to waterborne Hg and MeHg. The transformation of inorg. Hg by anaerobic sediment microorganisms in the water column produces MeHg, which bioaccumulates at successive trophic levels in the food chain. If high trophic level feeders, such as piscivorous birds and mammals, ingest sufficient MeHg in prey and drinking water, Hg toxicoses, including damage to nervous, excretory and reproductive systems, result. Currently accepted no obsd. adverse effect levels (NOAELs) for waterborne Hg in wildlife have been developed from the piscivorous model in which most dietary Hg is in the Me form. Such model are not applicable to omnivores, insectivores, and other potentially affected groups, and have not incorporated data from other important matrixes, such as eggs and muscle. The purpose of this paper is to present a comprehensive review of the Hg literature as it relates to effects on wildlife, including previously understudied groups. The authors present a critique of the current state of knowledge about effects of Hg on wildlife as an aid to identifying missing information and to planning research needed for conducting a complete assessment of Hg risks to wildlife. This review summarizes the toxicity of Hg to birds and mammals, the mechanisms of Hg toxicity, the measurement of Hg in biota, and interpretation of residue data.
7. 7
  TEACH. Inorganic Mercury, U.S. Environmental Protection Agency, 2007. http://www.epa.gov/teach/chem_summ/mercury_inorg_summary.pdf.
  There is no corresponding record for this reference.
8. 8
  Blum, J. D.; Popp, B. N.; Drazen, J. C.; Anela Choy, C.; Johnson, M. W. Methylmercury Production below the Mixed Layer in the North Pacific Ocean Nat. Geosci. 2013, 6, 879– 884
  8
  Methylmercury production below the mixed layer in the North Pacific Ocean
  Blum, Joel D.; Popp, Brian N.; Drazen, Jeffrey C.; Choy, C. Anela; Johnson, Marcus W.
  Nature Geoscience (2013), 6 (10), 879-884CODEN: NGAEBU; ISSN:1752-0894. (Nature Publishing Group)
  Mercury enters marine food webs in the form of microbially generated monomethylmercury. Microbial methylation of inorg. mercury, generating monomethylmercury, is widespread in low-oxygen coastal sediments. The degree to which microbes also methylate mercury in the open ocean has remained uncertain, however. Here, we present measurements of the stable isotopic compn. of mercury in nine species of marine fish that feed at different depths in the central North Pacific Subtropical Gyre. We document a systematic decline in δ202Hg, Δ199Hg and Δ201Hg values with the depth at which fish feed. We show that these mercury isotope trends can be explained only if monomethylmercury is produced below the surface mixed layer, including in the underlying oxygen min. zone, i.e., between 50 and more than 400 m depth. Specifically, we est. that about 20-40% of the monomethylmercury detected below the surface mixed layer originates from the surface and enters deeper waters either attached to sinking particles, or in zooplankton and micronekton that migrate to depth. We suggest that the remaining monomethylmercury found at depth is produced below the surface mixed layer by methylating microbes that live on sinking particles. We suggest that microbial prodn. of monomethylmercury below the surface mixed later contributes significantly to anthropogenic mercury uptake into marine food webs.
9. 9
  Stacchiotti, A.; Morandini, F.; Bettoni, F.; Schena, I.; Lavazza, A.; Grigolato, P. G.; Apostoli, P.; Rezzani, R.; Aleo, M. F. Stress Proteins and Oxidative Damage in a Renal Derived Cell Line Exposed to Inorganic Mercury and Lead Toxicology 2009, 264, 215– 224
  There is no corresponding record for this reference.
10. 10
  Harnly, M.; Seidel, S.; Rojas, P.; Fornes, R.; Flessel, P.; Smith, D.; Kreutzer, R.; Goldman, L. Biological Monitoring for Mercury within a Community with Soil and Fish Contamination Environ. Health Perspect. 1997, 105, 424– 429
  There is no corresponding record for this reference.
11. 11
  Legrand, M.; Sousa Passos, C. J.; Mergler, D.; Chan, H. M. Biomonitoring of Mercury Exposure with Single Human Hair Strand Environ. Sci. Technol. 2005, 39, 4594– 4598
  There is no corresponding record for this reference.
12. 12
  Hightower, J. M.; Moore, D. Mercury Levels in High-End Consumers of Fish Environ. Health Perspect. 2003, 111, 604– 608
  There is no corresponding record for this reference.
13. 13
  McDowell, M. A.; Dillon, C. F.; Osterloh, J.; Bolger, P. M.; Pellizzari, E.; Fernando, R.; de Oca, R. M.; Schober, S. E.; Sinks, T.; Jones, R. L.et al. Hair Mercury Levels in U.S. Children and Women of Childbearing Age: Reference Range Data from NHANES 1999–2000 Environ. Health Perspect. 2004, 112, 1165– 1171
  There is no corresponding record for this reference.
14. 14
  Lee, J.-S.; Mirkin, C. A. Chip-Based Scanometric Detection of Mercuric Ion Using DNA-Functionalized Gold Nanoparticles Anal. Chem. 2008, 80, 6805– 6808
  There is no corresponding record for this reference.
15. 15
  Cho, E. S.; Kim, J.; Tejerina, B.; Hermans, T. M.; Jiang, H.; Nakanishi, H.; Yu, M.; Patashinski, A. Z.; Glotzer, S. C.; Stellacci, F.et al. Ultrasensitive Detection of Toxic Cations through Changes in the Tunnelling Current across Films of Striped Nanoparticles Nat. Mater. 2012, 11, 978– 985
  15
  Ultrasensitive detection of toxic cations through changes in the tunnelling current across films of striped nanoparticles
  Cho, Eun Seon; Kim, Jiwon; Tejerina, Baudilio; Hermans, Thomas M.; Jiang, Hao; Nakanishi, Hideyuki; Yu, Miao; Patashinski, Alexander Z.; Glotzer, Sharon C.; Stellacci, Francesco; Grzybowski, Bartosz A.
  Nature Materials (2012), 11 (11), 978-985CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
  Although multiple methods have been developed to detect metal cations, only a few offer sensitivities below 1 pM, and many require complicated procedures and sophisticated equipment. Here, the authors describe a class of simple solid-state sensors for the ultrasensitive detection of heavy-metal cations (notably, an unprecedented attomolar limit for the detection of CH3Hg+ in both standardized solns. and environmental samples) through changes in the tunneling current across films of nanoparticles (NPs) protected with striped monolayers of org. ligands. The sensors are also highly selective because of the ligand-shell organization of the NPs. On binding of metal cations, the electronic structure of the mol. bridges between proximal NPs changes, the tunneling current increases and highly conductive paths ultimately percolate the entire film. The nanoscale heterogeneity of the structure of the film broadens the range of the cation-binding consts., which leads to wide sensitivity ranges (remarkably, over 18 orders of magnitude in CH3Hg+ concn.).
16. 16
  Gartia, M. R.; Braunschweig, B.; Chang, T.-W.; Moinzadeh, P.; Minsker, B. S.; Agha, G.; Wieckowski, A.; Keefer, L. L.; Liu, G. L. The Microelectronic Wireless Nitrate Sensor Network for Environmental Water Monitoring J. Environ. Monit. 2012, 14, 3068– 3075
  There is no corresponding record for this reference.
17. 17
  Lafleur, J. P.; Senkbeil, S.; Jensen, T. G.; Kutter, J. P. Gold Nanoparticle-Based Optical Microfluidic Sensors for Analysis of Environmental Pollutants Lab Chip 2012, 12, 4651– 4656
  17
  Gold nanoparticle-based optical microfluidic sensors for analysis of environmental pollutants
  Lafleur, Josiane P.; Senkbeil, Silja; Jensen, Thomas G.; Kutter, Joerg P.
  Lab on a Chip (2012), 12 (22), 4651-4656CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  Conventional methods of environmental anal. can be significantly improved by the development of portable microscale technologies for direct in-field sensing at remote locations. This report demonstrates the vast potential of gold nanoparticle-based microfluidic sensors for the rapid, in-field, detection of two important classes of environmental contaminants - heavy metals and pesticides. Using gold nanoparticle-based microfluidic sensors linked to a simple digital camera as the detector, detection limits as low as 0.6 μg L-1 and 16 μg L-1 could be obtained for the heavy metal mercury and the dithiocarbamate pesticide ziram, resp. These results demonstrate that the attractive optical properties of gold nanoparticle probes combine synergistically with the inherent qualities of microfluidic platforms to offer simple, portable and sensitive sensors for environmental contaminants.
18. 18
  Chung, E.; Gao, R.; Ko, J.; Choi, N.; Lim, D. W.; Lee, E. K.; Chang, S.-I.; Choo, J. Trace Analysis of Mercury(II) Ions Using Aptamer-Modified Au/Ag Core-Shell Nanoparticles and SERS Spectroscopy in a Microdroplet Channel Lab Chip 2013, 13, 260– 266
  18
  Trace analysis of mercury(II) ions using aptamer-modified Au/Ag core-shell nanoparticles and SERS spectroscopy in a microdroplet channel
  Chung, Eunsu; Gao, Rongke; Ko, Juhui; Choi, Namhyun; Lim, Dong Woo; Lee, Eun Kyu; Chang, Soo-Ik; Choo, Jaebum
  Lab on a Chip (2013), 13 (2), 260-266CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  The authors report the rapid and highly sensitive trace anal. of mercury(II) ions in water using a surface-enhanced Raman scattering (SERS)-based microdroplet sensor. Aptamer-modified Au/Ag core-shell nanoparticles have been fabricated and utilized as highly functional sensing probes. All detection processes for the reaction between mercury(II) ions and aptamer-modified nanoparticles were performed in a specially designed microdroplet channel. Small water droplets that included sample reagents were sepd. from each other by an oil phase that continuously flowed along the channel. This two-phase liq.-liq. segmented flow system prevented the adsorption of aggregated colloids to the channel walls due to localized reagents within encapsulated droplets. The result was reduced residence time distributions. The limit of detection (LOD) of mercury(II) ions in water was detd. by the SERS-based microdroplet sensor to be below 10 pM, which is three orders below the EPA-defined max. contaminant level. This combination of a SERS-based microfluidic sensor with aptamer-based functional nanoprobes can be used for in-the-field sensing platforms, due to its size and simplicity.
19. 19
  Lin, Y.-W.; Huang, C.-C.; Chang, H.-T. Gold Nanoparticle Probes for the Detection of Mercury, Lead and Copper Ions Analyst 2011, 136, 863– 871
  There is no corresponding record for this reference.
20. 20
  Liu, D.; Wang, Z.; Jiang, X. Gold Nanoparticles for the Colorimetric and Fluorescent Detection of Ions and Small Organic Molecules Nanoscale 2011, 3, 1421– 1433
  20
  Gold nanoparticles for the colorimetric and fluorescent detection of ions and small organic molecules
  Liu, Dingbin; Wang, Zhuo; Jiang, Xingyu
  Nanoscale (2011), 3 (4), 1421-1433CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
  A review. In recent years, gold nanoparticles (AuNPs) have drawn considerable research attention in the fields of catalysis, drug delivery, imaging, diagnostics, therapy, and biosensors due to their unique optical and electronic properties. In this review, recent advances are summarized in the development of AuNP-based colorimetric and fluorescent assays for ions including cations (such as Hg2+, Cu2+, Pb2+, As3+, Ca2+, Al3+, etc.) and anions (such as NO2-, CN-, PF6-, F-, I-, oxoanions), and small org. mols. (such as cysteine, homocysteine, trinitrotoluene, melamine ,and cocaine, ATP, glucose, dopamine, and so forth). Many of these species adversely affect human health and the environment. Moreover, particular attention is paid to AuNP-based colorimetric and fluorescent assays in practical applications.
21. 21
  Du, J.; Jiang, L.; Shao, Q.; Liu, X.; Marks, R. S.; Ma, J.; Chen, X. Colorimetric Detection of Mercury Ions Based on Plasmonic Nanoparticles Small 2013, 9, 1467– 1481
  21
  Colorimetric Detection of Mercury Ions Based on Plasmonic Nanoparticles
  Du, Jianjun; Jiang, Lin; Shao, Qi; Liu, Xiaogang; Marks, Robert S.; Ma, Jan; Chen, Xiaodong
  Small (2013), 9 (9-10), 1467-1481CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review. The development of rapid, specific, cost-effective, and robust tools in monitoring Hg2+ levels in both environmental and biol. samples is of utmost importance due to the severe mercury toxicity to humans. A no. of techniques exist, but the colorimetric assay, which is reviewed herein, is a possible tool in monitoring the level of mercury. These assays allow transforming target sensing events into color changes, which have applicable potential for in-the-field application through naked-eye detection. Specifically, plasmonic nanoparticle-based colorimetric assay exhibits a much better propensity for identifying various targets in terms of sensitivity, soly., and stability compared to commonly used org. chromophores. In this review, recent progress in the development of gold nanoparticle-based colorimetric assays for Hg2+ is summarized, with a particular emphasis on examples of functionalized gold nanoparticle systems with oligonucleotides, oligopeptides, and functional mols. Besides highlighting the current design principle for plasmonic nanoparticle-based colorimetric probes, the discussions on challenges and the prospect of next-generation probes for in-the-field applications are also presented.
22. 22
  El Kaoutit, H.; Estévez, P.; García, F. C.; Serna, F.; García, J. M. Sub-ppm Quantification of Hg(II) in Aqueous Media Using Both the Naked Eye and Digital Information from Pictures of a Colorimetric Sensory Polymer Membrane Taken with the Digital Camera of a Conventional Mobile Phone Anal. Methods 2013, 5, 54– 58
  22
  Sub-ppm quantification of Hg(ii) in aqueous media using both the naked eye and digital information from pictures of a colorimetric sensory polymer membrane taken with the digital camera of a conventional mobile phone
  El Kaoutit, Hamid; Estevez, Pedro; Garcia, Felix C.; Serna, Felipe; Garcia, Jose M.
  Analytical Methods (2013), 5 (1), 54-58CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)
  The authors present colorimetric sensory membranes for detecting Hg(ii) in aq. media. The color response of the sensory materials can be tuned for detection with the naked eye, such as the max. contaminant level of Hg(ii) that is set by the United States Environmental Protection Agency (EPA) for drinking H2O. Also, the concn. of Hg(ii) can be monitored using digital pictures of the membranes taken with conventional cameras. Thus, nanomolar concn. of Hg(ii) could be detected by the naked eye due to color changes of membranes, and the concn. of Hg(ii) could be quantified, within the millimolar to nanomolar range, by analyzing the digital information of pictures taken of the membranes after dipping them in H2O contg. this environmentally poisonous cation.
23. 23
  U.S. EPA. National Primary Drinking Water Regulations. US EPA, 2009. http://water.epa.gov/drink/contaminants/index.cfm#List.
  There is no corresponding record for this reference.
24. 24
  World Health Organization. Guidelines for Drinking Water Quality, 4th ed.; World Health Organization: Geneva, 2011. http://whqlibdoc.who.int/publications/2011/9789241548151_eng.pdf.
  There is no corresponding record for this reference.
25. 25
  Vashist, S.; Mudanyali, O.; Schneider, E. M.; Zengerle, R.; Ozcan, A. Cellphone-Based Devices for Bioanalytical Sciences Anal. Bioanal. Chem. 2013, DOI: 10.1007/s00216-013-7473-1
  There is no corresponding record for this reference.
26. 26
  Coskun, A. F.; Ozcan, A. Computational Imaging, Sensing and Diagnostics for Global Health Applications Curr. Opin. Biotechnol. 2013, 25, 8– 16
  There is no corresponding record for this reference.
27. 27
  Tseng, D.; Mudanyali, O.; Oztoprak, C.; Isikman, S. O.; Sencan, I.; Yaglidere, O.; Ozcan, A. Lensfree Microscopy on a Cellphone Lab Chip 2010, 10, 1787– 1792
  27
  Lensfree microscopy on a cellphone
  Tseng, Derek; Mudanyali, Onur; Oztoprak, Cetin; Isikman, Serhan O.; Sencan, Ikbal; Yaglidere, Oguzhan; Ozcan, Aydogan
  Lab on a Chip (2010), 10 (14), 1787-1792CODEN: LCAHAM; ISSN:1473-0197. (Royal Society of Chemistry)
  We demonstrate lensfree digital microscopy on a cellphone. This compact and light-wt. holog. microscope installed on a cellphone does not utilize any lenses, lasers or other bulky optical components and it may offer a cost-effective tool for telemedicine applications to address various global health challenges. Weighing ∼38 g (<1.4 oz), this lensfree imaging platform can be mech. attached to the camera unit of a cellphone where the samples are loaded from the side, and are vertically illuminated by a simple light-emitting diode (LED). This incoherent LED light is then scattered from each micro-object to coherently interfere with the background light, creating the lensfree hologram of each object on the detector array of the cellphone. These holog. signatures captured by the cellphone permit reconstruction of microscopic images of the objects through rapid digital processing. We report the performance of this lensfree cellphone microscope by imaging various sized micro-particles, as well as red blood cells, white blood cells, platelets and a waterborne parasite (Giardia lamblia).
28. 28
  Zhu, H.; Mavandadi, S.; Coskun, A. F.; Yaglidere, O.; Ozcan, A. Optofluidic Fluorescent Imaging Cytometry on a Cell Phone Anal. Chem. 2011, 83, 6641– 6647
  There is no corresponding record for this reference.
29. 29
  Zhu, H.; Yaglidere, O.; Su, T.-W.; Tseng, D.; Ozcan, A. Cost-Effective and Compact Wide-Field Fluorescent Imaging on a Cell-Phone Lab Chip 2011, 11, 315– 322
  29
  Cost-effective and compact wide-field fluorescent imaging on a cell-phone
  Zhu, Hongying; Yaglidere, Oguzhan; Su, Ting-Wei; Tseng, Derek; Ozcan, Aydogan
  Lab on a Chip (2011), 11 (2), 315-322CODEN: LCAHAM; ISSN:1473-0197. (Royal Society of Chemistry)
  We demonstrate wide-field fluorescent and darkfield imaging on a cell-phone with compact, light-wt. and cost-effective optical components that are mech. attached to the existing camera unit of the cell-phone. For this purpose, we used battery powered light-emitting diodes (LEDs) to pump the sample of interest from the side using butt-coupling, where the pump light was guided within the sample cuvette to uniformly excite the specimen. The fluorescent emission from the sample was then imaged using an addnl. lens that was positioned right in front of the existing lens of the cell-phone camera. Because the excitation occurs through guided waves that propagate perpendicular to our detection path, an inexpensive plastic color filter was sufficient to create the dark-field background required for fluorescent imaging, without the need for a thin-film interference filter. We validate the performance of this platform by imaging various fluorescent micro-objects in 2 colors (i.e., red and green) over a large field-of-view (FOV) of ∼81 mm2 with a raw spatial resoln. of ∼20 μm. With addnl. digital processing of the captured cell-phone images, through the use of compressive sampling theory, we demonstrate ∼2 fold improvement in our resolving power, achieving ∼10 μm resoln. without a trade-off in our FOV. Further, we also demonstrate darkfield imaging of non-fluorescent specimen using the same interface, where this time the scattered light from the objects is detected without the use of any filters. The capability of imaging a wide FOV would be exceedingly important to probe large sample vols. (e.g., >0.1 mL) of e.g., blood, urine, sputum or water, and for this end we also demonstrate fluorescent imaging of labeled white-blood cells from whole blood samples, as well as water-borne pathogenic protozoan parasites such as Giardia Lamblia cysts. Weighing only ∼28 g (∼1 oz), this compact and cost-effective fluorescent imaging platform attached to a cell-phone could be quite useful esp. for resource-limited settings, and might provide an important tool for wide-field imaging and quantification of various lab-on-a-chip assays developed for global health applications, such as monitoring of HIV+ patients for CD4 counts or viral load measurements.
30. 30
  Preechaburana, P.; Gonzalez, M. C.; Suska, A.; Filippini, D. Surface Plasmon Resonance Chemical Sensing on Cell Phones Angew. Chem., Int. Ed. 2012, 51, 11585– 11588
  30
  Surface Plasmon Resonance Chemical Sensing on Cell Phones
  Preechaburana, Pakorn; Gonzalez, Marcos Collado; Suska, Anke; Filippini, Daniel
  Angewandte Chemie, International Edition (2012), 51 (46), 11585-11588CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  An angle-resolved surface plasmon resonance detection system is described that is based on a single disposable device configured to use conditioned illumination and optical detection from cell phones. The SPR coupler central to the implementation is compatible with regular lab-on-a-chip technol. and temporarily adheres to the phone screen surface during the measurement. It couples and conditions the illumination from the screen and directs the SPR image to the phone camera. SPR detection was illustrated with a com. assay for β2 microglobulin and with a custom-made chip including embedded calibration. Current cell phones provide the performance required for chem. sensing, thereby rendering the platform viable to develop tests that may complement routine monitoring.
31. 31
  Shen, L.; Hagen, J. A.; Papautsky, I. Point-of-Care Colorimetric Detection with a Smartphone Lab Chip 2012, 12, 4240– 4243
  31
  Point-of-care colorimetric detection with a smartphone
  Shen, Li; Hagen, Joshua A.; Papautsky, Ian
  Lab on a Chip (2012), 12 (21), 4240-4243CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  Paper-based immunoassays are becoming powerful and low-cost diagnostic tools, esp. in resource-limited settings. Inexpensive methods for quantifying these assays have been shown using desktop scanners, which lack portability, and cameras, which suffer from the ever changing ambient light conditions. In this work, we introduce a novel approach of quantifying colors of colorimetric diagnostic assays with a smartphone that allows high accuracy measurements in a wide range of ambient conditions, making it a truly portable system. Instead of directly using the red, green, and blue (RGB) intensities of the color images taken by a smartphone camera, we use chromaticity values to construct calibration curves of analyte concns. We demonstrate the high accuracy of this approach in pH measurements with linear response ranges of 1-12. These results are comparable to those reported using a desktop scanner or silicon photodetectors. To make the approach adoptable under different lighting conditions, we developed a calibration technique to compensate for measurement errors due to variability in ambient light. This technique is applicable to a no. of common light sources, such as sun light, fluorescent light, or smartphone LED light. Ultimately, the entire approach can be integrated in an "app" to enable one-click reading, making our smartphone based approach operable without any professional training or complex instrumentation.
32. 32
  Mudanyali, O.; Dimitrov, S.; Sikora, U.; Padmanabhan, S.; Navruz, I.; Ozcan, A. Integrated Rapid-Diagnostic-Test Reader Platform on a Cellphone Lab Chip 2012, 12, 2678– 2686
  32
  Integrated rapid-diagnostic-test reader platform on a cellphone
  Mudanyali, Onur; Dimitrov, Stoyan; Sikora, Uzair; Padmanabhan, Swati; Navruz, Isa; Ozcan, Aydogan
  Lab on a Chip (2012), 12 (15), 2678-2686CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  We demonstrate a cellphone-based rapid-diagnostic-test (RDT) reader platform that can work with various lateral flow immuno-chromatog. assays and similar tests to sense the presence of a target analyte in a sample. This compact and cost-effective digital RDT reader, weighing only ∼65 g, mech. attaches to the existing camera unit of a cellphone, where various types of RDTs can be inserted to be imaged in reflection or transmission modes under light-emitting diode (LED)-based illumination. Captured raw images of these tests are then digitally processed (within less than 0.2 s per image) through a smart application running on the cellphone for validation of the RDT, as well as for automated reading of its diagnostic result. The same smart application then transmits the resulting data, together with the RDT images and other related information (e.g., demog. data), to a central server, which presents the diagnostic results on a world map through geo-tagging. This dynamic spatio-temporal map of various RDT results can then be viewed and shared using internet browsers or through the same cellphone application. We tested this platform using malaria, tuberculosis (TB) and HIV RDTs by installing it on both Android-based smartphones and an iPhone. Providing real-time spatio-temporal statistics for the prevalence of various infectious diseases, this smart RDT reader platform running on cellphones might assist healthcare professionals and policymakers to track emerging epidemics worldwide and help epidemic preparedness.
33. 33
  Zhu, H.; Sikora, U.; Ozcan, A. Quantum Dot Enabled Detection of Escherichia coli Using a Cell-Phone Analyst 2012, 137, 2541– 2544
  33
  Quantum dot enabled detection of Escherichia coli using a cell-phone
  Zhu, Hongying; Sikora, Uzair; Ozcan, Aydogan
  Analyst (Cambridge, United Kingdom) (2012), 137 (11), 2541-2544CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)
  The authors report a cell-phone based Escherichia coli (E. coli) detection platform for screening of liq. samples. In this compact and cost-effective design attached to a cell-phone, the authors use anti-E. coli O157:H7 antibody functionalized glass capillaries as solid substrates to perform a quantum dot based sandwich assay for specific detection of E. coli O157:H7 in liq. samples. Using battery-powered inexpensive light-emitting-diodes (LEDs), the authors excite/pump these labeled E. coli particles captured on the capillary surface, where the emission from the quantum dots is then imaged using the cell-phone camera unit through an addnl. lens that is inserted between the capillary and the cell-phone. By quantifying the fluorescent light emission from each capillary tube, the concn. of E. coli in the sample is detd. The authors exptl. confirmed the detection limit of this cell-phone based fluorescent imaging and sensing platform as ∼5 to 10 cfu mL-1 in buffer soln. The authors also tested the specificity of this E. coli detection platform by spiking samples with different species (e.g., Salmonella) to confirm that non-specific binding/detection is negligible. The authors further demonstrated the proof-of-concept of the authors' approach in a complex food matrix, e.g., fat-free milk, where a similar detection limit of ∼5 to 10 cfu mL-1 was achieved despite challenges assocd. with the d. of proteins that exist in milk. The authors' results reveal the promising potential of this cell-phone enabled field-portable and cost-effective E. coli detection platform for e.g., screening of water and food samples even in resource limited environments. The presented platform can also be applicable to other pathogens of interest through the use of different antibodies.
34. 34
  Gallegos, D.; Long, K. D.; Yu, H.; Clark, P. P.; Lin, Y.; George, S.; Nath, P.; Cunningham, B. T. Label-Free Biodetection Using a Smartphone Lab Chip 2013, 13, 2124– 2132
  34
  Label-free biodetection using a smartphone
  Gallegos, Dustin; Long, Kenneth D.; Yu, Hojeong; Clark, Peter P.; Lin, Yixiao; George, Sherine; Nath, Pabitra; Cunningham, Brian T.
  Lab on a Chip (2013), 13 (11), 2124-2132CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  Utilizing its integrated camera as a spectrometer, we demonstrate the use of a smartphone as the detection instrument for a label-free photonic crystal biosensor. A custom-designed cradle holds the smartphone in fixed alignment with optical components, allowing for accurate and repeatable measurements of shifts in the resonant wavelength of the sensor. Externally provided broadband light incident upon an entrance pinhole is subsequently collimated and linearly polarized before passing through the biosensor, which resonantly reflects only a narrow band of wavelengths. A diffraction grating spreads the remaining wavelengths over the camera's pixels to display a high resoln. transmission spectrum. The photonic crystal biosensor is fabricated on a plastic substrate and attached to a std. glass microscope slide that can easily be removed and replaced within the optical path. A custom software app was developed to convert the camera images into the photonic crystal transmission spectrum in the visible wavelength range, including curve-fitting anal. that computes the photonic crystal resonant wavelength with 0.009 nm accuracy. We demonstrate the functionality of the system through detection of an immobilized protein monolayer, and selective detection of concn.-dependent antibody binding to a functionalized photonic crystal. We envision the capability for an inexpensive, handheld biosensor instrument with web connectivity to enable point-of-care sensing in environments that have not been practical previously.
35. 35
  O’Driscoll, S.; MacCraith, B. D.; Burke, C. S. A Novel Camera Phone-Based Platform for Quantitative Fluorescence Sensing Anal. Methods 2013, 5, 1904– 1908
  35
  A novel camera phone-based platform for quantitative fluorescence sensing
  O'Driscoll, Stephen; MacCraith, Brian D.; Burke, Conor S.
  Analytical Methods (2013), 5 (8), 1904-1908CODEN: AMNEGX; ISSN:1759-9679. (Royal Society of Chemistry)
  We describe a novel camera phone-based optical sensing platform capable of real-time quant. fluorescence-based measurements. The platform employs the phone's camera as a photodetector in a non-imaging optical configuration that simultaneously detects fluorescence from a no. of sensor spots on a disposable optical sensor chip. The platform combines the functionality of the camera with the phone's data-processing capabilities to facilitate on-phone anal. of detected fluorescence intensity. It is envisaged that such a platform will have significant potential in application areas such as environmental monitoring and healthcare where there is a growing demand for decentralized diagnostics using low-cost, portable devices, particularly in remote or low-resource environments.
36. 36
  Oncescu, V.; O’Dell, D.; Erickson, D. Smartphone Based Health Accessory for Colorimetric Detection of Biomarkers in Sweat and Saliva Lab Chip 2013, 13, 3232– 3238
  36
  Smartphone based health accessory for colorimetric detection of biomarkers in sweat and saliva
  Oncescu, Vlad; O'Dell, Dakota; Erickson, David
  Lab on a Chip (2013), 13 (16), 3232-3238CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  The mobile health market is rapidly expanding and portable diagnostics tools offer an opportunity to decrease costs and increase the availability of healthcare. Here we present a smartphone based accessory and method for the rapid colorimetric detection of pH in sweat and saliva. Sweat pH can be correlated to sodium concn. and sweat rate in order to indicate to users the proper time to hydrate during phys. exercise and avoid the risk of muscle cramps. Salivary pH below a crit. threshold is correlated with enamel decalcification, an acidic breakdown of calcium in the teeth. We conduct a no. of human trials with the device on a treadmill to demonstrate the ability to monitor changes in sweat pH due to exercise and electrolyte intake and predict optimal hydration. Addnl., we perform trials to measure salivary pH over time to monitor the effects of diet on oral health risks.
37. 37
  Lillehoj, P. B.; Huang, M.-C.; Truong, N.; Ho, C.-M. Rapid Electrochemical Detection on a Mobile Phone Lab Chip 2013, 13, 2950– 2955
  37
  Rapid electrochemical detection on a mobile phone
  Lillehoj, Peter B.; Huang, Ming-Chun; Truong, Newton; Ho, Chih-Ming
  Lab on a Chip (2013), 13 (15), 2950-2955CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  We present a compact mobile phone platform for rapid, quant. biomol. detection. This system consists of an embedded circuit for signal processing and data anal., and disposable microfluidic chips for fluidic handling and biosensing. Capillary flow is employed for sample loading, processing, and pumping to enhance operational portability and simplicity. Graphical step-by-step instructions displayed on the phone assists the operator through the detection process. After the completion of each measurement, the results are displayed on the screen for immediate assessment and the data is automatically saved to the phone's memory for future anal. and transmission. Validation of this device was carried out by detecting Plasmodium falciparum histidine-rich protein 2 (PfHRP2), an important biomarker for malaria, with a lower limit of detection of 16 ng mL-1 in human serum. The simple detection process can be carried out with two loading steps and takes 15 min to complete each measurement. Due to its compact size and high performance, this device offers immense potential as a widely accessible, point-of-care diagnostic platform, esp. in remote and rural areas. In addn. to its impact on global healthcare, this technol. is relevant to other important applications including food safety, environmental monitoring and biosecurity.
38. 38
  Zhu, H.; Sencan, I.; Wong, J.; Dimitrov, S.; Tseng, D.; Nagashima, K.; Ozcan, A. Cost-Effective and Rapid Blood Analysis on a Cell-Phone Lab Chip 2013, 13, 1282– 1288
  38
  Cost-effective and rapid blood analysis on a cell-phone
  Zhu, Hongying; Sencan, Ikbal; Wong, Justin; Dimitrov, Stoyan; Tseng, Derek; Nagashima, Keita; Ozcan, Aydogan
  Lab on a Chip (2013), 13 (7), 1282-1288CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  We demonstrate a compact and cost-effective imaging cytometry platform installed on a cell-phone for the measurement of the d. of red and white blood cells as well as Hb concn. in human blood samples. Fluorescent and bright-field images of blood samples are captured using sep. optical attachments to the cell-phone and are rapidly processed through a custom-developed smart application running on the phone for counting of blood cells and detg. Hb d. We evaluated the performance of this cell-phone based blood anal. platform using anonymous human blood samples and achieved comparable results to a std. bench-top hematol. analyzer. Test results can either be stored on the cell-phone memory or be transmitted to a central server, providing remote diagnosis opportunities even in field settings.
39. 39
  Coskun, A. F.; Nagi, R.; Sadeghi, K.; Phillips, S.; Ozcan, A. Albumin Testing in Urine Using a Smart-Phone Lab Chip 2013, 13, 4231– 4238
  39
  Albumin testing in urine using a smart-phone
  Coskun, Ahmet F.; Nagi, Richie; Sadeghi, Kayvon; Phillips, Stephen; Ozcan, Aydogan
  Lab on a Chip (2013), 13 (21), 4231-4238CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  We demonstrate a digital sensing platform, termed Albumin Tester, running on a smart-phone that images and automatically analyses fluorescent assays confined within disposable test tubes for sensitive and specific detection of albumin in urine. This light-wt. and compact Albumin Tester attachment, weighing approx. 148 g, is mech. installed on the existing camera unit of a smart-phone, where test and control tubes are inserted from the side and are excited by a battery powered laser diode. This excitation beam, after probing the sample of interest located within the test tube, interacts with the control tube, and the resulting fluorescent emission is collected perpendicular to the direction of the excitation, where the cellphone camera captures the images of the fluorescent tubes through the use of an external plastic lens that is inserted between the sample and the camera lens. The acquired fluorescent images of the sample and control tubes are digitally processed within one second through an Android application running on the same cellphone for quantification of albumin concn. in the urine specimen of interest. Using a simple sample prepn. approach which takes ∼5 min per test (including the incubation time), we exptl. confirmed the detection limit of our sensing platform as 5-10 μg mL-1 (which is more than 3 times lower than the clin. accepted normal range) in buffer as well as urine samples. This automated albumin testing tool running on a smart-phone could be useful for early diagnosis of kidney disease or for monitoring of chronic patients, esp. those suffering from diabetes, hypertension, and/or cardiovascular diseases.
40. 40
  Coskun, A. F.; Wong, J.; Khodadadi, D.; Nagi, R.; Tey, A.; Ozcan, A. A Personalized Food Allergen Testing Platform on a Cellphone Lab Chip 2013, 13, 636– 640
  40
  A personalized food allergen testing platform on a cellphone
  Coskun, Ahmet F.; Wong, Justin; Khodadadi, Delaram; Nagi, Richie; Tey, Andrew; Ozcan, Aydogan
  Lab on a Chip (2013), 13 (4), 636-640CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  We demonstrate a personalized food allergen testing platform, termed iTube, running on a cellphone that images and automatically analyses colorimetric assays performed in test tubes toward sensitive and specific detection of allergens in food samples. This cost-effective and compact iTube attachment, weighing approx. 40 g, is mech. installed on the existing camera unit of a cellphone, where the test and control tubes are inserted from the side and are vertically illuminated by two sep. light-emitting-diodes. The illumination light is absorbed by the allergen assay, which is activated within the tubes, causing an intensity change in the acquired images by the cellphone camera. These transmission images of the sample and control tubes are digitally processed within 1 s using a smart application running on the same cellphone for detection and quantification of allergen contamination in food products. We evaluated the performance of this cellphone-based iTube platform using different types of com. available cookies, where the existence of peanuts was accurately quantified after a sample prepn. and incubation time of ∼20 min per test. This automated and cost-effective personalized food allergen testing tool running on cellphones can also permit uploading of test results to secure servers to create personal and/or public spatio-temporal allergen maps, which can be useful for public health in various settings.
41. 41
  Navruz, I.; Coskun, A. F.; Wong, J.; Mohammad, S.; Tseng, D.; Nagi, R.; Phillips, S.; Ozcan, A. Smart-Phone Based Computational Microscopy Using Multi-Frame Contact Imaging on a Fiber-Optic Array Lab Chip 2013, 13, 4015– 4023
  41
  Smart-phone based computational microscopy using multi-frame contact imaging on a fiber-optic array
  Navruz, Isa; Coskun, Ahmet F.; Wong, Justin; Mohammad, Saqib; Tseng, Derek; Nagi, Richie; Phillips, Stephen; Ozcan, Aydogan
  Lab on a Chip (2013), 13 (20), 4015-4023CODEN: LCAHAM; ISSN:1473-0189. (Royal Society of Chemistry)
  We demonstrate a cellphone based contact microscopy platform, termed Contact Scope, which can image highly dense or connected samples in transmission mode. Weighing approx. 76 g, this portable and compact microscope is installed on the existing camera unit of a cellphone using an opto-mech. add-on, where planar samples of interest are placed in contact with the top facet of a tapered fiber-optic array. This glass-based tapered fiber array has ∼9 fold higher d. of fiber optic cables on its top facet compared to the bottom one and is illuminated by an incoherent light source, e.g., a simple light-emitting-diode (LED). The transmitted light pattern through the object is then sampled by this array of fiber optic cables, delivering a transmission image of the sample onto the other side of the taper, with ∼3× magnification in each direction. This magnified image of the object, located at the bottom facet of the fiber array, is then projected onto the CMOS image sensor of the cellphone using two lenses. While keeping the sample and the cellphone camera at a fixed position, the fiber-optic array is then manually rotated with discrete angular increments of e.g., 1-2 degrees. At each angular position of the fiber-optic array, contact images are captured using the cellphone camera, creating a sequence of transmission images for the same sample. These multi-frame images are digitally fused together based on a shift-and-add algorithm through a custom-developed Android application running on the smart-phone, providing the final microscopic image of the sample, visualized through the screen of the phone. This final computation step improves the resoln. and also removes spatial artifacts that arise due to non-uniform sampling of the transmission intensity at the fiber optic array surface. We validated the performance of this cellphone based Contact Scope by imaging resoln. test charts and blood smears.
42. 42
  Wei, Q.; Qi, H.; Luo, W.; Tseng, D.; Ki, S. J.; Wan, Z.; Göröcs, Z.; Bentolila, L. A.; Wu, T.-T.; Sun, R.et al. Fluorescent Imaging of Single Nanoparticles and Viruses on a Smart Phone ACS Nano 2013, 7, 9147– 9155
  There is no corresponding record for this reference.
43. 43
  Portio Research Limited. Portio Research Mobile Factbook 2013. http://www.portioresearch.com/media/3986/Portio%20Research%20Mobile%20Factbook%202013.pdf.
  There is no corresponding record for this reference.
44. 44
  Kim, Y.; Johnson, R. C.; Hupp, J. T. Gold Nanoparticle-Based Sensing of “Spectroscopically Silent” Heavy Metal Ions Nano Lett. 2001, 1, 165– 167
  There is no corresponding record for this reference.
45. 45
  Lee, J.-S.; Han, M. S.; Mirkin, C. A. Colorimetric Detection of Mercuric Ion (Hg²⁺) in Aqueous Media Using DNA-Functionalized Gold Nanoparticles Angew. Chem., Int. Ed. 2007, 46, 4093– 4096
  45
  Colorimetric detection of mercuric ion (Hg2+) in aqueous media using DNA-functionalized gold nanoparticles
  Lee, Jae-Seung; Han, Min Su; Mirkin, Chad A.
  Angewandte Chemie, International Edition (2007), 46 (22), 4093-4096CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Color is everything: Hg2+ in aq. media is detected by the formation of thymidine-Hg2+-thymidine coordination complexes, which raises the melting temp. of the DNA-hybridized gold nanoparticle probes and thus the temp. at which the probes disperse and effect a purple-to-red color change. The method has very high sensitivity and selectivity, and it provides a simple and fast colorimetric readout.
46. 46
  Huang, C.-C.; Chang, H.-T. Parameters for Selective Colorimetric Sensing of Mercury(II) in Aqueous Solutions Using Mercaptopropionic Acid-Modified Gold Nanoparticles Chem. Commun. 2007, 1215– 1217
  There is no corresponding record for this reference.
47. 47
  Darbha, G. K.; Singh, A. K.; Rai, U. S.; Yu, E.; Yu, H.; Chandra Ray, P. Selective Detection of Mercury(II) Ion Using Nonlinear Optical Properties of Gold Nanoparticles J. Am. Chem. Soc. 2008, 130, 8038– 8043
  There is no corresponding record for this reference.
48. 48
  Liu, D.; Wang, S.; Swierczewska, M.; Huang, X.; Bhirde, A. A.; Sun, J.; Wang, Z.; Yang, M.; Jiang, X.; Chen, X. Highly Robust, Recyclable Displacement Assay for Mercuric Ions in Aqueous Solutions and Living Cells ACS Nano 2012, 6, 10999– 11008
  There is no corresponding record for this reference.
49. 49
  Li, L.; Li, B.; Qi, Y.; Jin, Y. Label-Free Aptamer-Based Colorimetric Detection of Mercury Ions in Aqueous Media Using Unmodified Gold Nanoparticles as Colorimetric Probe Anal. Bioanal. Chem. 2009, 393, 2051– 2057
  49
  Label-free aptamer-based colorimetric detection of mercury ions in aqueous media using unmodified gold nanoparticles as colorimetric probe
  Li, Li; Li, Baoxin; Qi, Yingying; Jin, Yan
  Analytical and Bioanalytical Chemistry (2009), 393 (8), 2051-2057CODEN: ABCNBP; ISSN:1618-2642. (Springer)
  The authors report a simple and sensitive aptamer-based colorimetric detection of mercury ions (Hg2+) using unmodified gold nanoparticles as colorimetric probe. It is based on the fact that bare gold nanoparticles interact differently with short single-strand DNA and double-stranded DNA. The anti-Hg2+ aptamer is rich in thymine (T) and readily forms T-Hg2+-T configuration in the presence of Hg2+. By measuring color change or adsorption ratio, the bare gold nanoparticles can effectively differentiate the Hg2+-induced conformational change of the aptamer in the presence of a given salt with high concn. The assay shows a linear response toward Hg2+ concn. through a five-decade range of 1 × 10-4 mol L-1 to 1 × 10-9 mol L-1. Even with the naked eye, the authors could identify micromolar Hg2+ concns. within minutes. By using the spectrometric method, the detection limit was improved to the nanomolar range (0.6 nM). The assay shows excellent selectivity for Hg2+ over other metal cations including K+, Ba2+, Ni2+, Pb2+, Cu2+, Cd2+, Mg2+, Ca2+, Zn2+, Al3+, and Fe3+. The major advantages of this Hg2+ assay are its water-soly., simplicity, low cost, visual colorimetry, and high sensitivity. This method provides a potentially useful tool for the Hg2+ detection.
50. 50
  Miyake, Y.; Togashi, H.; Tashiro, M.; Yamaguchi, H.; Oda, S.; Kudo, M.; Tanaka, Y.; Kondo, Y.; Sawa, R.; Fujimoto, T.et al. MercuryII-Mediated Formation of Thymine-HgII-Thymine Base Pairs in DNA Duplexes J. Am. Chem. Soc. 2006, 128, 2172– 2173
  50
  MercuryII-Mediated Formation of Thymine-HgII-Thymine Base Pairs in DNA Duplexes
  Miyake, Yoko; Togashi, Humika; Tashiro, Mitsuru; Yamaguchi, Hiroshi; Oda, Shuji; Kudo, Megumi; Tanaka, Yoshiyuki; Kondo, Yoshinori; Sawa, Ryuichi; Fujimoto, Takashi; Machinami, Tomoya; Ono, Akira
  Journal of the American Chemical Society (2006), 128 (7), 2172-2173CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The very specific binding of the HgII ion unexpectedly and significantly stabilizes naturally occurring thymine-thymine base mispairing in DNA duplexes. Following this finding, we prepd. DNA duplexes contg. metal-mediated base pairs at the desired sites, as well as novel double helical architectures consisting only of thymine-HgII-thymine pairs.
51. 51
  Tanaka, Y.; Oda, S.; Yamaguchi, H.; Kondo, Y.; Kojima, C.; Ono, A. 15n-15n J-Coupling across HgII: Direct Observation of HgII-Mediated T-T Base Pairs in a DNA Duplex J. Am. Chem. Soc. 2006, 129, 244– 245
  There is no corresponding record for this reference.
52. 52
  Boening, D. W. Ecological Effects, Transport, and Fate of Mercury: A General Review Chemosphere 2000, 40, 1335– 1351
  52
  Ecological effects, transport, and fate of mercury: a general review
  Boening, Dean W.
  Chemosphere (2000), 40 (12), 1335-1351CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Science Ltd.)
  A review and discussion with many refs. Mercury at low concns. represents a major hazard to microorganisms. Inorg. mercury has been reported to produce harmful effects at 5 μg/l in a culture medium. Organomercury compds. can exert the same effect at concns. 10 times lower than this. The org. forms of mercury are generally more toxic to aquatic organisms and birds than the inorg. forms. Aquatic plants are affected by mercury in water at concns. of 1 mg/l for inorg. mercury and at much lower concns. of org. mercury. Aquatic invertebrates widely vary in their susceptibility to mercury. In general, organisms in the larval stage are most sensitive. Me mercury in fish is caused by bacterial methylation of inorg. mercury, either in the environment or in bacteria assocd. with fish gills or gut. In aquatic matrixes, mercury toxicity is affected by temp., salinity, dissolved oxygen and water hardness. A wide variety of physiol., reproductive and biochem. abnormalities have been reported in fish exposed to sublethal concns. of mercury. Birds fed inorg. mercury show a redn. in food intake and consequent poor growth. Other (more subtle) effects in avian receptors have been reported (i.e., increased enzyme prodn., decreased cardiovascular function, blood parameter changes, immune response, kidney function and structure, and behavioral changes). The form of retained mercury in birds is more variable and depends on species, target organ and geog. site. With few exceptions, terrestrial plants (woody plants in particular) are generally insensitive to the harmful effects of mercury compds.
Supporting Information
Supporting Information
UV–vis spectroscopic measurement results of the Au NP and aptamer based colorimetric assay (calibration curve, specificity, and dynamics test). This material is available free of charge via the Internet at http://pubs.acs.org.
- nn406571t_si_001.pdf (544.33 kb)
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Detection and Spatial Mapping of Mercury Contamination in Water Samples Using a Smart-PhoneClick to copy article linkArticle link copied!

ACS Nano

Abstract

Results and Discussion

Optical Design of the Smart-Phone-Based Mercury Reader

Figure 1

Plasmonic Colorimetric Assay and Measurement of Mercury(II) Ion Concentration

Figure 2

Android-Based Smart Application for Mercury Quantification

Figure 3

Calibration and Specificity Tests

Figure 4

Figure 5

Mapping of Mercury Concentration in Water Samples in California

Figure 6

Figure 7

Conclusions

Methods

Hardware Design

Gold Nanoparticle and Aptamer Based Colorimetric Assay

UV–Vis Spectroscopic Investigation of Water Samples Using a Portable Spectrometer

Supporting Information

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Acknowledgment

References

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Detection and Spatial Mapping of Mercury Contamination in Water Samples Using a Smart-Phone
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