Ultrasensitive photoelectrochemical immunosensor of cardiac troponin I detection based on dual inhibition effect of Ag@Cu2O core-shell submicron-particles on CdS QDs sensitized TiO2 nanosheets.

Rapidity and high sensitivity are the critical factors for the diagnoses of heart attacks and cardiac troponin I (cTnI) is used as a gold standard marker for its diagnosis. To realize the accurate detection of cTnI, a novel ultrasensitive photoelectrochemical (PEC) immunosensor for cTnI determination was developed upon dual inhibition effect of Ag@Cu2O core-shell submicron-particles(SPs) toward CdS sensitized the (001) facets of anatase titanium dioxide nanosheets (TiO2/CdS). In this study, the TiO2/CdS composite not only indicated stable and excellent photoelectric signal but also provided abundant functional group to immobilized cTnI antibodies (Ab1). To obtain the high sensitivity, Ag@Cu2O core-shell SPs were used as labels of the secondary antibodies (Ab2), owning to competitive absorption of light and consumption of electron donor, less light energy and electron donors arrived at the TiO2/CdS sensitization structure. Besides, the remarkable steric hindrance effect of Ag@Cu2O core-shell SPs labeled secondary antibodies (Ab2) conjugates obstructed the transfer of electrons and diffusion of the electron donors to the photoelectrode surface, leading to further decrease of photocurrent. Therefore, the constructed immunosensor has an ultrasensitive response to cTnI in a liner range of 0.02 pg/mL to 50 ng/mL with a low detection limit of 6.7 fg/mL, and exhibits good sensitivity and admirable stability. Moreover, the strategy provided an efficient and novel approach for dual inhibition effect in PEC immunoassay development.