CdTe QDs-sensitized TiO2 nanocomposite for magnetic-assisted photoelectrochemical immunoassay of SARS-CoV-2 nucleocapsid protein.

[Display omitted] • A magnetic-assisted PEC immmunosensor was constructed to detect SARS-CoV-2 N protein. • Fe 3 O 4 @SiO 2 @Au/Ab 1 can extract targets in complex samples and simplify the process. • Active species were studied by free radical trapping assay and ESR test. • The mechanism of photogenerated e−/h+ of SiO 2 @TiO 2 @CdTe QDs transfer was deduced. • The immunosenor had a low detection limit of 1.8 pg mL−1. A sensitive, reliable, and cost-effective detection for SARS-CoV-2 was urgently needed due to the rapid spread of COVID-19. Here, a "signal-on" magnetic-assisted PEC immunosensor was constructed for the quantitative detection of SARS-CoV-2 nucleocapsid (N) protein based on Z-scheme heterojunction. Fe 3 O 4 @SiO 2 @Au was used to connect the capture antibody to act as a capture probe (Fe 3 O 4 @SiO 2 @Au/Ab 1). It can extract target analytes selectively in complex samples and multiple electrode rinsing and assembly steps were avoided effectively. CdTe QDs sensitized TiO 2 coated on the surface of SiO 2 spheres to form Z-scheme heterojunction (SiO 2 @TiO 2 @CdTe QDs), which broadened the optical absorption range and inhibited the quick recombination of photogenerated electron/hole of the composite. With fascinating photoelectric conversion performance, SiO 2 @TiO 2 @CdTe QDs were utilized as a signal label, thus further realizing signal amplification. The migration mechanism of photogenerated electrons was further deduced by active material quenching experiment and electron spin resonance (ESR) measurement. The elaborated immunosensor can detect SARS-CoV-2 N protein in the linear range of 0.005–50 ng mL−1 with a low detection limit of 1.8 pg mL−1 (S/N = 3). The immunosensor displays extraordinary sensitivity, strong anti-interference, and high reproducibility in detecting SARS-CoV-2 N protein, which envisages its potential application in the clinical diagnosis of COVID-19. [ABSTRACT FROM AUTHOR]