Ultrasensitive photoelectrochemical immunosensor for insulin detection based on dual inhibition effect of CuS-SiO2 composite on CdS sensitized C-TiO2.

High sensitivity of biosensor is one of the most important factor to realize the accurate detection of biomarkers. To achieve this purpose, enhancing initial signal and amplifying the value of signal change are two main approaches. In this study, a novel signal-off photoelectrochemical (PEC) immunosensor for highly sensitive determination of insulin was developed upon dual inhibition effect of CuS-SiO 2 composites toward CdS sensitized carbon doped titanium dioxide (C-TiO 2 /CdS). Due to the doping of carbon and sensitization of CdS, C-TiO 2 /CdS sensitized structure was employed as ideal photoactive matrix, which provided stable and enhanced basal signal. To achieve the amplification of signal change value, CuS-SiO 2 composites were prepared and used as labels. On account of the competitively light harvesting and electron donors consuming by p-type semiconductor CuS, less light energy and electron donors arrived at the C-TiO 2 /CdS sensitized structure. Besides, the remarkable steric hindrance effect of CuS-SiO 2 labeled secondary antibodies (CuS-SiO 2 -Ab 2 ) conjugates obstructed the transfer of electrons and diffusion of the electron donors to the photoelectrode surface, leading to further decrease of photocurrent compared with the pure CuS nanoparticles. Greatly enhanced sensitivity is achieved due to the dual inhibition effect of CuS-SiO 2 composites on C-TiO 2 /CdS. Taking advantage of the synergy effect of C-TiO 2 /CdS sensitized structure and dual inhibition effect of CuS-SiO 2 -Ab 2 bioconjugates, the as-prepared immunosensor for insulin exhibited high sensitivity and good stability with a low detection limit of 0.03 pg mL −1 . Additionally, the strategy provided an efficient and simple approach for signal amplification and held great promise for other PEC immunoassay development. [ABSTRACT FROM AUTHOR]