Molecular machine and gold/graphene quantum dot hybrid based dual amplification strategy for voltammetric detection of VEGF165

Graphene quantum dots (GQDs) were prepared via pyrolysis of citric acid and glutamic acid, then reacted with chlorauric acid to form agold/graphene quantum dot hybrid (Au/GQD), and finally connected with hairpin DNA probe 1 (H1) and thionine (Thi). The H1-Au/GQD-Thi composite is found to be a viable redox probe for electrochemical and aptamer-based determination of vascular endothelial growth factor VEGF165. A dual amplification strategy is employed based on the use of molecular machine and theAu/GQD. Each single VEGF165 molecule can bind two DNA probes via specific aptamer-target recognition to produce a molecular machine. Surface-tethered hairpin DNA 2 (H2) hybridizes with the molecular machine through proximity effect, and the prelocked toehold domain of H2 becomes exposed. This part binds to H1-Au/GQD-Thi to release the molecular machine which then moves to the neighboring H2 upon which a surface programmatic chain reaction is initiated. By continuous molecular machine travel, many H1-Au/GQD-Thi probes are present on the gold electrode surface. This implies an efficient signal amplification capability. The Au/GQD based redox probes in-situ catalyzes the redox activity of thionine and further enhances the detection signal. The aptasensor exhibits ultrahigh sensitivity and selectivity for VEGF165. The square wave voltammetric signal, best measured at -0.18V vs. Ag/AgCl, increases linearly in the1.0 fM to 120 pM VEGF165 concentration range, and the detection limit is 0.3 fM. Conceivably, the method may be applied to other target proteins if the corresponding high-affinity aptamers are available.