Visible-Light-Stimulated Enzymelike Activity of Graphene Oxide and Its Application for Facile Glucose Sensing

A novel and interesting enzyme-mimicking activity of chitosan-functionalized graphene oxide (CS-GO) upon phototriggering was demonstrated. CS-GO could catalyze oxidation of a typical chromogenic substrate (3,3',5,5'-tetramethylbenzidine, TMB) under visible light (lambda >= 400 nm) stimulation, which was independent of destructive H2O2. Visible light triggering was a rapid, clean, and versatile means for inducing the enzymelike activity of CS-GO, which was superior to the current peroxidase or peroxidase mimetics that use H2O2 as an oxidant. Compared to the natural enzyme horseradish peroxidase (HRP), CS-GO had a higher affinity for TMB. The mechanism of the phototriggered enzyme-mimicking activity of CS-GO was investigated in detail. In addition, a novel and facile colorimetric method was realized for detection of glucose based on the photoactivated CS-GO enzyme-mimicking system and the competitive interaction of concanavalin A with chitosan or glucose. The methodology showed a linear response for glucose in the range 2.5-5.0 mmol/L with a detection limit as low as 0.5 mu mol/L. The sensing system was applied for detection of glucose in human serum with satisfactory results.