Graphene-coated copper-doped ZnO quantum dots for sensitive photoelectrochemical bioanalysis of thrombin triggered by DNA nanoflowers

This work reports a photoelectrochemical (PEC) biosensing platform for the sensitive and specific screening of thrombin by using graphene oxide-coated copper-doped zinc oxide quantum dots (Cu0.3Zn0.7O-GO QDs) as the photoactive materials and glucose oxidase-encapsulated DNA nanoflowers (GOx-DFs) for signal amplification. Interestingly, the coated graphene oxide nanosheets on the surface of the Cu0.3Zn0.7O QDs could cause the charge to transfer rapidly and ameliorate the photocorrosion. The doped copper into the quantum dots could enhance the absorption of visible light by tuning the band gap of ZnO QDs, therefore increasing the photocurrent under visible irradiation. Upon addition of target thrombin, a sandwiched reaction was carried out between thrombin aptamer and GOx-DFs, accompanying the formation of nanocomposites with the magnetic microparticles (MMPs)/thrombin/GOx-DFs. Followed by magnetic separation, the carried GOx oxidized glucose to H2O2, thus resulting in the increasing photocurrent of the Cu0.3Zn0.7O-GO QD-modified electrode. Under optimum conditions, the developed PEC biosensing platform exhibited good analytical performance with a linear range of 50-10 000 fM thrombin and a limit of detection of 29 fM. Impressively, our strategy offers a new horizon in developing bridge-connected graphene-coated nanomaterials and novel signal amplification strategy for the development of PEC biosensors.