Dual signal amplification coupling dual inhibition effect for fabricating photoelectrochemical chlorpyrifos biosensor

Photoelectrochemical (PEC) detection is an attractive analytical tool as it allows for an elegant and sensitive assay. However, designing a novel detection strategy to achieve an excellent PEC analytical performance is still highly challenging. Herein we design a novel photoelectrochemical (PEC) chlorpyrifos biosensor based on dual signal amplification strategy coupling dual inhibition effect. Dual signal amplification strategy was achieved by coupling the graphene quantum dots sensitized CuFe2O4 magnetic nanocrystal clusters (GQDs-CuFe2O4 MNCs) with the amplification of enzymolysis products. In this biosensing architecture, the GQDs-CuFe2O4 MNCs prepared by electrostatic adsorption showed nearly 4-fold and 30-fold enhancement photocurrent compared with the pure CuFe2O4 MNCs and GQDs, respectively. And the contact angle measurement demonstrated that the GQDs-CuFe2O4 MNCs exhibited good biocompatibility. Based on all these above advantages, the GQDs-CuFe2O4 MNCs were immobilized on the magnetic electrode surface by a fast and simple magnetism-assisted assembly, and the acetylcholinesterase (AChE) was further coated on the surface of the as-prepared multifunctional electrode. Due to thiocholine (enzymolysis products) acts as a sacrificial electron donor to scavenge the holes, compared with the GQDs-CuFe2O4 MNCs modified electrode in the acetylthiocholine chloride solution, the photocurrent of the resulting AChE-based biosensor was further significantly enhanced. Based on the dual inhibition of AChE activity by chlorpyrifos and the formation of Cu-chlorpyrifos complex hindered the electron transfer of CuFe2O4 MNCs toward the electrode surface, the proposed AChE-based biosensor can be applied to the quantification of chlorpyrifos with a linear range from 0.001 μg mL−1 to 1 μg mL−1 and a detection limit of 0.3 ng mL−1 (S/N = 3). This novel dual signal amplification strategy opens up a new avenue for achieving high sensitivity in the field of PEC biosensing.