Thesis (M.Eng)--Chulalongkorn University, 2011

This research is the investigation of the modified screen-printed carbon electrode with gold nanoparticles (AuNPs) and polypyrrole (PPy) together with the immobilized horseradish peroxidase by electropolymerization approach for phenol detection. The optimized electropolymerization conditions were 5 mM of gold precursor concentration and 10 cycling numbers of electropolymerization, respectively. The results of UV-Vis spectroscopy indicated the non-denaurization of HRP when mixed in solutions containing pyrrole and gold precursor which were of spherical shape and an average diameter approximately 15±5 nm. After that, the synthesized modified electrodes were physically characterized by SEM and AFM. AuNPs/PPy film revealed small granular particles mixed withrod-like structure. Whereas EDX results confirmed the presence and uniform distribution of AuNPs on the effective electrode surface area. Futhermore, the direct electron transfer was a typical of surface-controlled quasi-reversible process with the electron transfer rate of 0.05s-1. The study of enzyme kinetic parameters, we found that the mechanism did not follow Michaelis-Menten kinetics. The resulting biosensor performed a linear range from 1-8 µM, with sensitivity of 4.585nA/µM (R2= 0.955), detection limit of 3.19 µM (n=10), (S/N=3), and fast response time of 23.5 s. this biosensor showed a storage stability of residual current was 83.37% after seven days of storage in dried form at 4°C, and reproducibility was 3.78% (n=10).