Fabrication And Application Of Biosensors Based On Poly(5-Formylindole) And Its CNTs Composites

Conducting polymers (CPs) have attracted more and more attention in the fabrication of biosensors due to some unique properties, including rapid electron transfer, specificity, high sensitivity, and biocompatibility. These functional materials can not only act as suitable immobilization carriers for biomolecules, but also have active effects on the transduction of biosensors. Interactions between conducting polymers and carbon nanotubes (CNTs) play an important role in the ultimate performance of CPs/CNTs composites. These composites have improved and synergic properties of electrochemical activity and biocompatibility due to the excellent electrical conductivity and larger specific surface area of CNTs. A novel conducting poly(5-formylindole) and a nanostructured composite P5FIn/SWNTs have been successfully prepared by electrochemical polymerization and designed to construct biosensors. The major contents of the thesis are as follows:1. A novel conducting polyindole derivative, poly(5-formylindole)(P5FIn), was obtained by electrochemical polymerization of5-formylindole (5FIn) monomer in acetonitrile (ACN). Then a nanostructured composite was synthesized electrochemically by direct anodic oxidation of5FIn with single-walled carbon nanotubes (SWNTs) modified electrode. As revealed by the results of cyclic voltammetry (CV) studies, both the pure P5FIn film and P5FIn/SWNTs composite film showed good electrochemical activity and redox performances. Scanning electron microscope (SEM) showed that P5FIn film was loosely packed porous and net-like structure, while the composite presented as an uniform and compact membrane in the form of more homogeneous and intact fibrillar network. Compared with pure P5FIn, the nanocomposite possessed larger specific surface area and superior charge-transport properties. These properties make will help broaden the practical applications of CPs/CNTs composites in the biosensing field.2. A signal-on electrochemiluminescence (ECL) biosensor devoted to the detection of Ramos cells was fabricated based on the P5FIn film. This ECL platform was presented by covalently coupling the18-mer amino-substituted oligonucleotide (ODN) probes with aldehyde groups that are strongly reactive toward a variety of nucleophiles on the surface of solid substrates. The specfic identification and high-affnity between aptamers and target cells, gold nanoparticles (AuNPs) enhanced ECL nanoprobes, along with P5FIn induced ECL quenching contributed greatly to the sensitivity and selectivity. The ECL signals were logarithmically linear with the concentration of Ramos cells in a wide determination range from500to1.0×105cells mL-1, and the corresponding detection limit was300cells mL-3.A lable-free electrochemical immunosensor based on P5FIn/SWNTs composite was fabricated to detect AFP antigen by measuring the change of electrochemical responses before and after the immunoreaction, the detection limit was0.02ng mL-The proposed immunosensor showed excellent performances of simplicity, high sensitivity, good specificity and reproducibility. The improvement of sensitivity was mainly owing to a dual signal amplification mechanism. The nanostructured P5FIn/SWNTs composite provided large specific surface area and good biocompatibility for the immobilization of biomolecules. Gold nanoparticles could act as electronic channels or wires in the electrochemical reaction, thus had synergistic effects on the electron transfer process. This immunosensor not only provides a convenient and rapid method for the detection of tumor markers, but also extends the practical application of CPs/CNTs composite to the field of biosensors.