A novel photoelectrochemical sensor based on PPIX-functionalized WO3-rGO nanohybrid-decorated ITO electrode for detecting cysteine.

A universal photoelectrochemical (PEC) sensing platform was fabricated based on the composition of protoporphyrin IX (PPIX), tungsten trioxide (WO3) and reduced graphene oxide (rGO) on indium tin oxide (ITO) electrode for detecting cysteine in aqueous solution. The rGO layer was not only providing bridges for the ITO electrode to anchor tightly with the WO3 nanostructures, but behaved as an electron transfer medium to enhance the electron transport from the conduction band (CB) of WO3. Furthermore, the strong absorption coefficient of porphyrin adsorbed onto WO3 nanoplates by bidentate binding could significantly improve the photocurrent density and slow charge recombination kinetics through the ultrafast electron injection. The SEM, XRD, and DRS were employed to characterize the prepared nanomaterials and modified-ITO electrodes. The results showed that the PPIX-WO3-rGO/ITO electrode could render the capability of absorbing a broad UV-vis light and displayed excellent photocurrent response in 0.1M pH 7.0 PBS with excitation wavelength at 380 nm, which could be notably improved upon addition of cysteine at 0.3 V. Based on the enhanced photocurrent signal, a novel method for PEC detection of cysteine was developed with a linear range of 0.1 to 100 μM in 0.1M PBS (pH 7.0). The detection limit was 25 nM (3σ). And higher stability and selectivity were obtained. The novel strategy could provide a fast and sensitive method for cysteine analysis.