A sandwiched photoelectrochemical biosensing platform for detecting Cytokeratin-19 fragments based on AgS-sensitized BiOI/BiS heterostructure amplified by sulfur and nitrogen co-doped carbon quantum dots.

A sandwiched photoelectrochemical (PEC) immunosensor based on BiOI/BiS/AgS was designed for the quantitative detection of cytokeratin-19 fragments (CYFRA21-1) in serum. In this work, due to the intervention of the narrow band gap BiS, the absorption of the light source by the BiOI/BiS heterostructure has been significantly enhanced. Meanwhile, the matched band structure of BiOI, BiS and AgS promoted the rapid transfer of electrons between the conduction bands and effectively inhibited the recombination of electron-hole pairs, thus enhanced the photoelectric signals. Sulfur and nitrogen co-doped carbon quantum dots (S,N-CQDs) with up-conversion luminescence properties provided more light energy for the base materials. On the other hand, S,N-CQDs were combined with Ab through polydopamine (PDA), as secondary antibody labels, further enhanced the sensitivity of the sensor. Herein, the linear range of the sensor was from 0.001 to 100 ng mL and the detection limit was 1.72 pg mL. In addition, the sensor provides a feasible way for the detection of tumor markers due to its excellent selectivity, repeatability and good stability.