A “signal on” photoelectrochemical biosensor for miRNA-21 detection based on layer-by-layer assembled n-n type Bi2S3@CdIn2S4 heterojunction

MicroRNA (miRNA) is an ideal biomarker, and the sensitive monitoring of low-abundance miRNA is of great significance for the treatment of cancer at the onset stage. Herein, a novel Y-shaped DNA-mediated photoelectrochemical (PEC) sensing platform based on the Bi2S3@CdIn2S4 photoanode is proposed for the detection of miRNA-21. First, an n-n type Bi2S3@CdIn2S4 heterojunction with tight interface is formed for the first time through a layer-by-layer assembly strategy due to the matched band structures of Bi2S3 and CdIn2S4. The photocurrent intensity of Bi2S3@CdIn2S4/GCE electrode is 1.7-fold higher than that of Bi2S3/GCE electrode and 2.5-fold higher than that of CdIn2S4/GCE electrode under visible light irradiation. Additionally, miRNA-21-triggered catalytic hairpin assembly facilitates the formation of Y-shaped DNA structure with CdS quantum dots (CdS QDs). As the photosensitizer of Bi2S3@CdIn2S4 heterojunction, CdS QDs accelerate the separation of electron-hole pairs in the sensing system and realizes photocurrent signal enhancement, thus realizing the “signal on” detection of the miRNA-21. The proposed PEC biosensor exhibits a superior sensitivity of 0.18 fM and the recoveries of human serum range from 98.0% to 104% with a relative standard deviation of 5.8–8.9%. Therefore, the constructed PEC biosensor has potential application value in the early diagnosis and treatment of miRNA-related diseases.