A novel ultrasensitive photoelectrochemical biosensor for detecting microRNA 21 based on cosensitization strategy and p-n heterojunction quenching mode

Highly sensitive detection of biomarkers has a vital role in clinical diagnosis and disease treatment. Integrating cosensitization strategy and p-n heterojunction quenching mode, we have established a novel ultrasensitive “signal off” photoelectrochemical (PEC) biosensor for detecting microRNA 21 (miRNA 21) via target-triggered catalytic hairpin assembly (CHA) cycling amplification. The n-type nano-hybrid (Bi2S3-ZnS) wrapped by toluidine blue O dye ([email protected]2S3-ZnS composite) has been synthesized, in which TBO and Bi2S3 as photosensitizers for photoactive matrix of ZnS. Since the cosensitization effect of Bi2S3 and TBO, 136-fold enhancement in PEC signal of [email protected]2S3-ZnS has been acquired compared with ZnS. Trace miRNA 21 can be transformed to abundant p-type copper sulfide (CuS) labeled signal tags to form p-n heterojunction with [email protected]2S3-ZnS, leading to obvious quenching effect. Thus, the PEC signals decrease with the increasing concentration of miRNA 21 and achieve the quantitative detection. The proposed PEC biosensor exhibits good linear relationship to miRNA 21 ranging from 1.0 × 10−17 to 1.0 × 10−11 mol·L−1 with a limit of detection of 3.3 × 10−18 mol·L−1. This biosensor based on TBO used as photosensitizer for the first time may offer new opportunities for detecting other biomarkers and facilitate the application of organic dyes in PEC sensing field.