New Concepts in Surface Modification for Biosensor Application-Polyaniline and Bacteriophage Surface Modification

Abstract

Polyaniline is one of the most promising conductive polymers for technological applications because of its unique electrooptical properties, ease of synthesis and low cost. An additional attribute is that polyanilines can be chemically modified straightforwardly in an electrochemical cell. Specifically, nucleophiles can reduce the polyaniline backbone from the oxidized emeraldine form to the leucoemaraldine form, leading to the formation of chemically modified polyaniline. In chapter 2 of this dissertation, we investigate electrochemically directed chemical modification of polyanilines for applications in heterogeneous immunosorbent assays. Electrochemical methods and surface enhanced Raman Spectroscopy (SERs) were used to characterize polyaniline films covalently modified with IgG antibody fragments containing nucleophilic thiol groups. The cyclic voltammetry signals from the protein sandwich assay were much higher on the oxidized state of polyaniline than those on the reduced state of polyaniline, indicating that the antibody fragment is covalently attached only to oxidized polyaniline. SERs results also provide evidence that the emeraldine form of polyaniline converted into the leucoemeraldine form after reacting with antibody solution. Assembly of biological molecules and nanoparticles to generate novel hybrid materials is an active area of investigation with applications ranging from sensor development to the diagnosis and treatment of certain diseases. Typically, the bonding between biomolecules and nanoparticles is based on hydrophobic interactions, van der Walls contact, and/or electrostatic forces. In chapter 3 of this work, we report on the covalent attachment of filamentous bacteriophage thiolated with 2-iminothiolane to gold nanoparticles. Results from UV-VIS spectroscopy indicate that the reaction between primary amines on phage and 2-iminothiolane takes place very rapidly. TEM and AFM imaging clearly shows that the formation of networks of bacteriophage and nanoparticles has occurred. Surface enhanced Raman spectroscopy was used to investigate nature of the interaction between thiol-functionalized fd bacteriophage and gold nanoparticles. The conjugate network generated in our work has promising applications in biosensor field. Preliminary investigations on the use of these materials to modify electrode surfaces will be discussed.