Photoelectrochemical biosensing of leukemia gene based on CdS/AuNPs/FeOOH Z-scheme heterojunction and a facile reflective device

A new Z-scheme heterojunction of CdS/Au nanoparticles (AuNPs)/FeOOH was constructed on a fluorine-doped tin oxide (FTO) electrode for photoelectrochemical biosensing of leukemia gene fragment b3a2, where FeOOH was modified on FTO by hydrothermal synthesis, AuNPs were cathodically deposited on the FeOOH/FTO electrode, and CdS quantum dots were cast-coated on the AuNPs/FeOOH/FTO electrode. Thioglycolic acid was then cast-coated on the CdS/AuNPs/FeOOH/FTO electrode to tether a hairpin DNA (hDNA) by EDC/NHS coupling. The target DNA (tDNA, b3a2) can open the hDNA to form a G-tetrad, further forming a DNAzyme with chlorohemin. In the presence of H2O2, the horseradish peroxidase-like DNAzyme can catalyze the oxidation of 4-chloro-1-naphthol to form an insoluble precipitate. The anodic photocurrent in the presence of ascorbic acid was inhibited by the precipitate, and the tDNA was thus quantitatively analyzed, with a semilogarithmic linear detection range from 0.1 fM to 5 nM and a limit of detection of 33 aM (S/N = 3). A new, simple and efficient reflective device by covering the photoelectrochemical cell outer-walls with a Sn foil was used to improve the utilization of incident light for enhanced biosensing, which may be of some general reference value for photoelectrochemical analysis.