A label-free thrombin photoelectrochemical aptasensor based on structure-switching in G-quadruplexes

In this work, an Au/GaN photoelectrode was prepared by sputtering a 30.0-nm–thick gold film on an n-type gallium nitride (GaN) surface. Guanine (G) was used as a hole trap in photoinduced charge separation due to its lowest oxidation potential and because it could be easily oxidized among the five common nucleobases. Guanosine-rich DNA sequences can form stable secondary structures known as G-quadruplexes. The efficiency of hole transport was significantly improved after G-quadruplexes formation. The thrombin aptamer rich in guanine could be modified on the electrode surface through Au–S bonds, forming stable G-quadruplexes in the presence of target thrombin. Due to the presence of the G-quadruplexes, the electron-hole recombination rate of the system decreased and the photocurrent increased. Under optimized conditions, high specificity, selectivity, and linearity could be achieved in the concentration range of 0.100–10.0 nm, and the limit of detection was approximately 20.0 pM. Thus, the detection results of human serum thrombin were satisfactory. © 2022 The Authors