Signal Inhibition of AuNPs on Type II CdIn <sub>2</sub>S <sub>4</sub>/NH <sub>2</sub>-MIL-125(Ti) Heterojunction: Enhanced Sandwich-Type Photoelectrochemical Aptasensor for MiRNA-203 Detection

Utilizing the competitive nature of AuNPs, which quench the photocurrent by competing with the CdIn2S4/NH2-MIL-125(Ti) heterojunction for light absorption and electron donation, we constructed a signal inhibition photoelectrochemical aptasensor for the detection of miRNA-203 in biological samples. MiRNA-203 has recently emerged as an effective biomarker for the early diagnosis of head and neck squamous cell carcinoma. Combining the sandwich type sensing mechanism with the high activity of the photoelectrochemical electrode material, a highly sensitive and selective sensing performance was obtained. For the first time, type II CdIn2S4/NH2-MIL-125(Ti) heterojunction have been loaded into carbon paste electrodes (CPEs), allowing for the stable immobilization of the hairpin DNA-P1. Upon capturing the target miRNA-203, DNA-P1 unfolds, enabling further hybridization with AuNPs-labeled DNA-P2. The attached AuNPs quenches the photocurrent of the CdIn2S4/NH2-MIL-125(Ti) heterojunction, realizing a “signal off” detection of miRNA-203. Using the change of the photocurrent as the sensing signal, we achieved a wide linear range (0.1 pM to 1000 pM) and a low limit of detection (0.0942 pM) for miRNA-203 detection. Moreover, the utilization of CPE as the PEC electrode ensures excellent stability in the repeated incubation process, providing a reusable sensor through simply pushing out and polishing of the CPE electrode. Therefore, the designed PEC aptasensor offeres a new perspective for monitoring miRNA biomarkers in the biological samples, with potential practical applications in early research on head and neck squamous cell carcinoma.