Microscale Enzymatic Optical Biosensors Using Mass Transport Limiting Nanofilms. 1. Fabrication and Characterization Using Glucose as a Model Analyte

Erich W. Stein, Patrick S. Grant, Huiguang Zhu, and Michael J. McShane*§
Biomedical Engineering Program and The Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana 71272, and Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843
Anal. Chem., 2007, 79 (4), pp 1339–1348
DOI: 10.1021/ac061414z
Publication Date (Web): January 17, 2007
Copyright © 2007 American Chemical Society

Abstract

“Smart tattoo” sensorsfluorescent microspheres that can be implanted intradermally and interrogated noninvasively using lightare being developed as potential tools for in vivo biochemical monitoring. In this work, a platform for enzymatic tattoo-type sensors is described and prototype devices evaluated using glucose as a model analyte. Sensor particles were prepared by immobilizing Pt(II) octaethylporphine (PtOEP), a phosphorescent dye readily quenched by molecular oxygen, into hybrid silicate microspheres, followed by loading and subsequent covalent immobilization of glucose oxidase. Rhodamine B-doped multilayer nanofilms were subsequently assembled on the surfaces of the particles to provide a reference signal and provide critical control of glucose transport into the particle. The enzymatic oxidation of glucose within the sensor results in the glucose concentration-dependent depletion of local oxygen levels, enabling indirect monitoring of glucose by measuring relative changes in PtOEP emission. A custom testing apparatus was used to monitor the dynamic sensor response to varying bulk oxygen and glucose levels, respectively. For the prototypes tested, dynamic test results indicate that the sensors respond rapidly (t95 = 84 s) and reversibly to changes in bulk glucose levels, while demonstrating high baseline stability. The sensitivity (change in intensity ratio) of these devices was determined to be 4.16 ± 0.57%/mg dL-1. The analytical range for the prototypes was determined to be 2−120 mg/dl, though this can be extended to cover the physiologically relevant range by tailoring the nanofilm coatings. These findings confirm the potential for enzymatic microscale optical and pave the way for extension of this initial demonstration with glucose to target other biochemical species relevant to metabolic monitoring.

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History

  • Published In Issue February 15, 2007
  • Received for review July 31, 2006. Accepted December 4, 2006.

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