A "signal-on" photoelectrochemical biosensor utilizing in-situ synthesis of SnS2/MgIn2S4 heterostructures and enzyme-assisted target cycling amplification for the sensitive detection of the mecA gene.

To address the urgent need for rapid detection of drug resistance biomarkers for methicillin-resistant Staphylococcus aureus (MRSA), particularly the mecA gene that encods the low-affinity penicillin-binding protein PBP2a, this study developed a dual-amplification photoelectrochemical biosensing platform utilizing in-situ synthesized SnS2/MgIn2S4 heterojunction photoanodes. This system synergistically combines the co-sensitization effect of AgInS2 nanoparticles with Exonuclease III-driven target circular amplification: a type II heterojunction structure was constructed through the low-temperature in-situ growth of MgIn2S4 on SnS2 nanosheets, significantly enhanced the separation efficiency of photogenerated carriers, while the band-matched AgInS2 nanoparticles (NPs) improved the directional charge transfer, thereby amplifying the photocurrent response. After recognizing the target mecA gene, the Exo III-triggered hairpin probe initiated a circular cleavage that triggered cascade amplification, resulting in the generation of a substantial amount of output DNA S1 strands. These strands were subsequently assembled into S1/S2-AgInS2 double-strand bridges on the electrode surface, achieving "signal-on" detection through the formation of co-sensitized nanostructures. The biosensor exhibits a wide dynamic range from 100 aM to 1 nM (R2 = 0.999), an exceptionally low detection limit of 12.9 aM (S/N = 3), and a quantitative recovery rate ranging from 98.30 % to 104.70 % for the mecA gene in environmental water matrices, establishing a reliable analytical tool for monitoring antibiotic resistance genes in aquatic ecosystems.