Amplified photoelectrochemical DNA biosensor based on a CdS quantum dot/WS2 nanosheet heterojunction and hybridization chain reaction-mediated enzymatic hydrolysis

An amplified photoelectrochemical biosensor was designed for the ultrasensitive monitoring of DNA by coupling a CdS quantum dot (QD)/WS2 nanosheet heterostructure with hybridization chain reaction (HCR)-programmed enzymatic hydrolysis. The sensing platform was constructed via the assembly of capture DNA on the CdS/WS2 modified ITO electrode surface. In the presence of target DNA, auxiliary DNA was immobilized and initiated the HCR process to form a long double-stranded DNA nanostructure with the aid of two biotin-labeled hairpin DNAs, which then bound with a large amount of avidin-labeled alkaline phosphatase via biological affinity interactions to catalyze the hydrolysis of ascorbic acid 2phosphate into ascorbic acid, which served as an efficient electron donor to facilitate the spatial separation of electron-hole pairs from QDs, followed by an enhancement in the photocurrent response. Under optimized conditions, the biosensor worked over a desirable linear range from 5 fM to 50 pM and exhibited a low detection limit of 2.29 fM as well as satisfactory selectivity and good stability, thus demonstrating its great prospects for applications in bioanalysis and clinical diagnostics.