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/Bi 2 S 3 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 Na 2 S 2 O 3 conversion to H 2 S with the aid of H 2 O 2 . The generated H 2 S could react with BiOBr nanoflowers (BiOBrNFs) modified on an indium tin oxide electrode, resulting in the in situ formation of BiOBr/Bi 2 S 3 heterostructures with enhanced photoelectric conversion efficiency. The BiOBr/Bi 2 S 3 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.