Conducting Polymer-based Aptamer Biosensor for in situ Monitoring of Cytokine
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Conducting Polymer-based Aptamer Biosensor for in situ Monitoring of Cytokine Wei Liao1, Bradly Randall1, Nicolas Alba1, and Xinyan Tracy Cui1,2 1 Bioengineering, University of Pittsburgh, Pittsburgh, PA, 15261 2 McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, 15261 ABSTRACT Neural prostheses often suffer from undesired chronic inflammatory tissue response. Therefore; a sensitive and real-time biosensor for inflammatory cytokine detection would provide invaluable information toward solving this problem. Such a biosensor based on an aptamer probe doped in polypyrrole and subsequent electrochemical impedance spectroscopy (EIS) has been developed. PDGF, an important inflammatory cytokine, has been successfully measured in both offline EIS characterization and real-time impedance monitoring. For in situ detection of PDGF, the best sensitivity of 10 ng/ml has been achieved. INTRODUCTION Neural prostheses often suffer from undesired chronic inflammatory tissue response. This can lead to neuronal loss and formation of glial scar tissue, which would serve as a barrier to neural signal transduction [1, 2]. In situ monitoring of neuro-inflammatory cytokines may improve our understanding of device-induced inflammatory responses. Furthermore, early detection of the onset and degree of inflammation and the release of drugs accordingly may lead to improved long-term performance of such implanted devices. We previously reported a promising reagentless aptamer biosensor which detects protein by monitoring surface state capacitance change before and after specific target binding using electrochemical impedance spectroscopy (EIS) [3]. Due to the unique electric properties of the immobilized aptamer probe, bias potential can be used to optimize the specific target binding while minimizing the non-specific adsorption to achieve high specificity. The limit of detection (LOD) for detecting the neuro-inflammatory cytokine Platelet Derived Growth Factor (PDGF) via this reagentless method is around 1 µg/ml. Such a detection limit is not enough for detecting PDGF in vitro as the actual concentration of PDGF is ~10 ng/ml in body fluid. To improve the sensitivity of impedimetric detection, one may increase the surface density of the immobilized probe, and/or induce redox molecules to elicit greater impedance change. In this report, in order to achieve much higher sensitivity, electropolymerized polypyrrole has been used as a supporting film and an electrochemical mediator [Fe(CN)6]3-/4- has been applied during detection. Polypyrrole (PPy), a biocompatible and electrically conductive polymer, has the ability to immobilize negatively charged molecules as dopants in the porous structure formed by the positively charged polypyrrole backbone [4]. In biosensing applications, polypyrole has been used to immobilize biorecoginition components as dopants in the conductive matrix for the electrochemical detection of glucose, protein, and DNA molecules [5, 6]. Incorporating proteins such as enzymes, ant
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