Photoelectrochemical detection of enzymatically generated CdS nanoparticles: Application to development of immunoassay

We report an innovative photoelectrochemical process (PEC) based on graphite electrode modified with electroactive polyvinylpyridine bearing osmium complex (Os-PVP). The system relies on the in situ enzymatic generation of CdS quantum dots (QDs). Alkaline phosphatase (ALP) catalyzes the hydrolisis of sodium thiophosphate (TP) to hydrogen sulfide (H₂S) which in the presence Cd²⁺ ions yields CdS semiconductor nanoparticles (SNPs). Irradiation of SNPs with the standard laboratory UV-illuminator (wavelength of 365nm) results in photooxidation of 1-thioglycerol (TG) mediated by Os-PVP complex on the surface of graphite electrode at applied potential of 0.31V vs. Ag/AgCl. A novel immunoassay based on specific enzyme linked immunosorbent assay (ELISA) combined with the PEC methodology was developed. Having selected the affinity interaction between bovine serum albumine (BSA) with anti-BSA antibody (AB) as a model system, we built the PEC immunoassay for AB. The new assay displays a linear range up to 20ngmL^-1 and a detection limit (DL) of 2ngmL^-1 (S/N=3) which is lower 5 times that of the traditional chromogenic ELISA test employing p-nitro-phenyl phosphate (pNPP).