Triple quenching effect of nanozyme catalyzed precipitation combined with enzyme-free amplification for photoelectrochemical biosensing of circulating tumor DNA.

In this work, a new photoelectrochemical (PEC) biosensor based on triple quenching effect of nanozyme catalyzed precipitation to PEC signal of MgInS was constructed for ultrasensitive detection of circulating tumor DNA (ctDNA). Enzyme-free amplification technology was used to convert target ctDNA into a large number of product chains (PC) to improve the detection sensitivity. CoO nanozyme with excellent peroxidase (POD)-like activity was introduced to the surface of MgInS by PC. CoO could oxidize chromogenic agent 3-Amino-9-ethylcarbazole (AEC) to produce red insoluble precipitation in the presence of HO, resulting in the PEC signal "off" of MgInS to achieve ultrasensitive detection of ctDNA. In particular, CoO nanozyme showed three synergistic quenching effects on PEC signal of MgInS, which contributed greatly to improving the detection sensitivity. Firstly, the light absorption range of CoO could reach 1000 nm, and compete with MgInS for light absorption. Secondly, the produced red precipitation belonged to the insulating material and had large electrochemical impedance, which hindered the transmission of photogenerated carriers. Thirdly, the precipitation also prevented the electron donor ascorbic acid (AA) from transferring electrons to MgInS. This biosensor provided a promising sensitive PEC detection technology for ctDNA, and further broadened the application of nanozymes in the field of PEC analysis.