One-Dimensional Conducting Polymer Nanostructures for Chemical and Biological Sensor Applications
Despite of their short history, conducting polymers such as polypyrrole (PPy) have emerged as a novel building block for label-free chemiresistive/FET chemical/biological sensors owing to a great environmental stability, active functional monomers for direct covalent immobilization of bioreceptors, remarkable optical, magnetic, and electrical properties like a semiconductor as well as mechanical property and ease of fabrication possessed by polymers. Tunable electrical conductivity can also be realized by several orders of magnitude via the process called `doping' where anions or dopants is chemically or electrochemically incorporated to oxidized CP backbones to attain the charge neutrality.
Confining conducting polymers to one-dimensional (1-D) nanoscale has ultimately increased the surface area to volume ratio and facilitated the electron transport through the bulk of 1-D nanomaterials. Therefore, a small perturbation by adsorbed charged chemical/biological molecules on their surfaces significantly affected the charge distribution within the bulk of 1-D nanomaterials, enhancing the sensitivity and detection limits. While this nano-electronic chemical/biological sensor showed a potential for advanced technology in detection and monitoring, device fabrication and assembly for 1-D conducting polymer nanostructures still appeared challenging to be scalable and reproducible in a cost effective manner.
Herein, this dissertation focused on fabrication and assembly of 1-D conducting polymer nanostructures based chemiresistive/FET chemical/biological sensors in a cost effective manner. First, lithographically patterned nanowire electrodeposition (LPNE) was used to batch-scale fabricate single PPy nanoribbon with controlled dimensions and defined location on various substrates for NH3 detection. Various bioreceptors were also surface functionalized on LPNE grown PPy nanoribbon to investigate sensing performance in terms of sensitivity, selectivity, dynamic range, and detection limits towards the specific virus and the target protein. Polyclonal antibodies (pAbs) that recognized cucumber mosaic virus (CMV) were anchored on PPy nanoribbons for the detection of CMV. Single chain fragment variables (scFvs) specific for mycobacterium tuberculosis antigen 85 complex protein (Ag85) were functionalized on PPy nanoribbons to accommodate the electrostatic screening effect caused by dissolved salt concentration in buffer solution and diluted human serum. On the other hand, template-directed electrodeposition was employed to synthesize PPy nanowires using various dopants and solvents in order to evaluate the structure dependent sensing performances for detection of Ag85B protein.