Construction of photoelectrochemical thrombin aptasensor via assembling multilayer of graphene–CdS nanocomposites

A photoelectrochemical (PEC) aptasensor for highly sensitive and specific detection of thrombin was developed by using graphene–CdS nanocomposites multilayer as photoactive species and electroactive mediator hexaammineruthenium(III) chloride (RuNH363+) as signal enhancer. Graphene–CdS nanocomposites (G–CdS) were synthesized by one-pot reduction of oxide graphene and CdCl2 with thioacetamide. The photoactive multilayer was prepared by alternative assembly of the negatively charged 3-mercaptopropionic acid modified graphene–CdS nanocomposites (MPA-G–CdS) and the positively charged polyethylenimine (PEI) on ITO electrode. This layer-by-layer assembly method enhanced the stability and homogeneity of the photocurrent readout of G–CdS. Thrombin aptamer was covalently bound to the multilayer by using glutaraldehyde as cross-linking. Electroactive mediator RuNH363+ could interact with the DNA phosphate backbone and thus facilitated the electron transfer between G–CdS multilayer and electrode and enhanced the photocurrent. Hybridizing of a long complementary DNA with thrombin aptamer could increase the adsorption amount of RuNH363+, which in turn boosted the signal readout. In the presence of target thrombin, the affinity interaction between thrombin and its aptamer resulted in the long complementary DNA releasing from the G–CdS multilayer and decreasing of photocurrent signal. On the basis of G–CdS multilayer as the photoactive species, RuNH363+ as an electroactive mediator, and aptamer as a recognition module, a high sensitive PEC aptasensor for thrombin detection was proposed. The thrombin aptasensor displayed a linear range from 2.0pM to 600.0pM and a detection limit of 1.0pM. The present strategy provided a promising ideology for the future development of PEC biosensor. •Graphene–CdS nanocomposites were synthesized by one-pot reduction of oxide graphene and CdCl2.•Photoactive multilayer by alternative assembly of G–CdS and PEI showed excellent homogeneity.•RuNH363+ as electroactive mediator improved the photo-to-current conversion efficiency.•The aptasensor exhibited high sensitivity and efficiency for thrombin determination.