A sensitive photoelectrochemical aptasensor for oxytetracycline based on a signal “switch off-on” strategy

A sensitive photoelectrochemical (PEC) aptasensor has been successfully constructed for oxytetracycline (OTC) biosensing based on a signal “switch off-on” strategy. When the conjugates of hairpin DNA probe and CdTe QD (H-DNA@QD) was immobilized on the ITO/TiO2 electrode by AuS bonds to form an ITO/TiO2/H-DNA@QD system, CdTe QDs at 3′ end of hairpin DNA close to the electrode surface led to the relatively strong photocurrent under visible light irradiation due to the effective electron transfer. After hybridized with aptamer of OTC, the hairpin DNA probe changed to a rigid, rod-like double helix, and CdTe QDs was far away from the electrode surface, resulting in significantly decrease of photocurrent. The photocurrent signal of the ITO/TiO2/H-DNA@QD/aptamer would recovery when immersing in the OTC solution, the recovery value increased with the increase of OTC concentration. Therefore, the aptasensor for OTC based on signal “switch off-on” mode have successfully been constructed, which exhibited a satisfying linear range (2-300 nM), low limit of detection (0.19 nM), good reproducibility and stability, and could offer an analytical application in complex food or environmental samples.