Plasmonic TiO@Au NPs//CdS QDs photocurrent-direction switching system for ultrasensitive and selective photoelectrochemical biosensing with cathodic background signal.

An ultrasensitive and selective photoelectrochemical (PEC) biosensor with cathodic background signal was developed for the detection of carcinoembryonic antigen (CEA) based on innovative plasmonic TiO@Au nanoparticles//CdS quantum dots (TiO@Au NPs//CdS QDs) photocurrent-direction switching system, coupling with hybridization chain reaction (HCR) for the signal amplification. Firstly, innovative TiO@Au NPs were successfully fabricated through in situ ascorbic acid-reduction of Au NPs dispersed on TiO surface, and TiO@Au NPs as the photoactive material showed a cathodic background signal. When target CEA existed, a sandwich-type reaction was performed in capture CEA aptamer-modified TiO@Au NPs and trigger CEA aptamer. Interestingly, after HCR triggered by target CEA, a mass of CdS QDs were introduced into the biosensing platform, resulting in the formation of TiO@Au NPs//CdS QDs system, along with the switch of photocurrents from cathodic to anodic. The obtained remarkable anodic photocurrent was depended on the localized surface plasmon resonance (LSPR) effect of Au between TiO and CdS. Under the optimal conditions, plasmonic TiO@Au NPs//CdS QDs photocurrent-direction switching PEC biosensing platform with cathodic background signal exhibited ultrasensitive for the determination of CEA with a low limit of detection of 18.9 fg/mL. Importantly, the proposed PEC biosensor can eliminate the interferences of the initial photocurrent and background signal, and has high-efficiency anti-interference ability, satisfactory stability and excellent reproducibility, which may have great potentials in bioanalysis and disease diagnosis.