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Conducting-Polymer Nanowire Immunosensor Arrays for Microbial Pathogens

Ashok Mulchandani
University of California-Riverside, Riverside, CA

A promising approach for the direct (label-free) electrical detection of biological macromolecules uses one-dimensional (1-D) nanostructures such as nanowires and nanotubes, configured as field-effect transistors that change conductance upon binding of charged macromolecules to receptors linked to the device surfaces. Combined with simple, rapid, and label-free detection, potentially to single molecule, these nanosensors are also attractive due to the small size, low power requirement and, most of all, the possibility of developing high-density arrays for simultaneous analyses of multiple species. Although current nanosensors based on carbon nanotubes and silicon nanowires has elucidated the power of 1-D nanostructures as biosensors, they have low throughput and limited controllability and are unattractive for fabrication of high-density sensor arrays. More importantly, surface modifications, typically required to incorporate specific antibodies, have to be performed postsynthesis and post-assembly, limiting our ability to individually address each nanostructured sensing elements with the desired specificity.

The overall objective of the proposed research is to develop a novel technique for the facile fabrication of bioreceptor (antibody)-functionalized nanowires that are individually addressable and scalable to high-density biosensor arrays and to demonstrate its application for label-free, real-time, rapid, sensitive and cost-effective detection of multiple pathogens in water. Electropolymerization of conducting polymers between two contact electrodes is a versatile method for fabricating nanowire biosensor arrays with the required controllability. The benign conditions of electropolymerization enable the sequential deposition of conducting-polymer nanowires with embedded antibodies onto a patterned electrode platform, providing a revolutionary route to create a "truly" high-density and individually addressable nanowire biosensor arrays. The nanowire immunosensor array's utility will be used to simultaneously quantify three important model pathogens: poliovirus, hepatitis A virus and rotarvirus.

We will use our recently reported (Ramanathan et al., 2004) simple, yet powerful, facile technique of electrochemical polymerization of biomolecule-friendly conducting polymers, such as polypyrrole, in prefabricated channels of tailor-made aspect ratio between two contact electrodes at site-specific position to synthesize nanowires of tailor-made properties for fabricating individually addressable high-density nanowires biosensors arrays. Detection of pathogens will be achieved by the extremely sensitive modulation of the electrical conductance of the nanowires brought about by the change in the electrostatic charges from binding of the pathogens to the antibodies.

Effects of monomer concentration, dopant type and concentration, aspect ratio and electrochemical polymerization mode on the sensitivity, selectivity and durability of poliovirus, HAV and rotavirus antibodies-functionalized polypyrrole nanowires as label-free bioaffinity sensor of these important model viral pathogens in water will be investigated to establish optimum synthesis conditions of biomolecules-functionalized nanowires to successfully realize our innovation to practice.

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