Split-Type Photoelectrochemical/Visual Sensing Platform Based on SnO 2 /MgIn 2 S 4 /Zn 0.1 Cd 0.9 S Composites and Au@Fe 3 O 4 Nanoparticles for Ultrasensitive Detection of Neuron Specific Enolase.

Herein, a novel dual mode detection system of split-type photoelectrochemical (PEC) and visual immunoassay was developed to detect neuron specific enolase (NSE), which achieved simultaneous and reliable NSE detection due to the completely different signal readouts and transduction mechanism. Specifically, specific reactions of antigens and antibodies were performed in 96-microwell plates. Gold nanoparticle (Au NP)-loaded Fe 3 O 4 (Au@Fe 3 O 4 ) NPs were used as secondary antibody markers and signal regulators, which could produce a blue-colored solution in the presence of 3,3',5,5'-tetramethylbenzidine (TMB) and H 2 O 2 because of its peroxidase-like activity. Therefore, the visual detection of NSE was realized, making the results more intuitive. Meanwhile, the above biological process could also be used as part of the split-type PEC sensing platform. Oxidized TMB and Fe 3+ were consumptive agents of the electron donor, which both realized the double quenching of PEC signal generated by the SnO 2 /MgIn 2 S 4 /Zn 0.1 Cd 0.9 S composites. Owing to the waterfall band structure, SnO 2 /MgIn 2 S 4 /Zn 0.1 Cd 0.9 S composites partially absorb visible light and effectively inhibit the electron-hole recombination, thereby providing significantly enhanced and stable initial signal. On the basis of the multiple signal amplification strategy and the split-type mode, NSE could be sensitively detected with a low detection limit of 14.0 fg·mL -1 (S/N = 3) and a wide linear range from 50.0 fg·mL -1 to 50.0 ng·mL -1 .