Biocatalysis-induced formation of BiOBr/Bi2S3 semiconductor heterostructures: A highly efficient strategy for establishing sensitive photoelectrochemical sensing system for organophosphorus pesticide detection

In this work, we present a highly sensitive photoelectrochemical (PEC) sensing platform for malathion (Mal) detection based on the biocatalysis-induced formation of BiOBr/Bi2S3 semiconductor heterostructures (BIFBSH). Initially, a double-stranded DNA consisting of an initiator strand and the anti-Mal aptamer was immobilized on magnetic beads surface. The target Mal could competitively bind with its aptamer and liberate the initiator strand from the double-stranded DNA. Subsequently, the initiator strand triggered a hybridization chain reaction (HCR) to produce a long DNA concatemer containing the sequence of G-quadruplex structure. The DNA concatemer was then endowed with HRP-like activity via the formation of hemin/G-quadruplex complexes and binding with MnTMPyP. The HCR-synthesized HRP-mimicking DNA concatemer (HSHMDC) was employed to catalyze Na2S2O3 conversion to H2S with the aid of H2O2. The generated H2S could react with BiOBr nanoflowers (BiOBrNFs) modified on an indium tin oxide electrode, resulting in the in situ formation of BiOBr/Bi2S3 heterostructures with enhanced photoelectric conversion efficiency. The BiOBr/Bi2S3 heterostructures could generate a strong photocurrent signal to indicate Mal recognition. Under the optimal conditions, a wide linear range between the Mal concentration and photocurrent intensity (0.001–1000 ng mL−1) and a limit of detection (LOD) as low as 0.12 pg mL−1 were achieved.