Black phosphorus quantum dots are useful oxidase mimics for colorimetric determination of biothiols.

Abstract

Black phosphorus quantum dots (BP QDs) with small size are synthesized usingan easy to operate thermal method. It was found that BP QDs possess oxidase-mimicking activity. They can catalyze the oxidation of thesubstrate 3,3',5,5'-tetramethylbenzidine to produce a blue-colored product even in the absence of hydrogen peroxide. Active oxygen species are proved to be involved in the reaction through the experiments of radical scavenging and electron spin resonance. Biothiols including reduced glutathione and cysteine inactivate the oxidase-mimicking activity of BP QDs, concomitant to the fading of the blue solution. Thisprovides the base fora colorimetric method for the determination of glutathione and cysteine. The decreased absorbance at 652nm displays linear response to the concentrations of glutathione ranging from 0.1 to 5.0μmolL-1, and cysteine from 0.1 to 10.0μmolL-1. The detection limits are 0.02μmolL-1 and 0.03μmolL-1 for glutathione and cysteine, respectively. Successive determinations of 1.0μmolL-1 glutathione and 5.0μmolL-1 cysteine solution give relative standard deviations of 0.8% and 1.7% (n = 11), respectively. As a preliminary application, the practicability of the method was evaluated by the determination of glutathione in pharmaceutical preparations. This work not only discovers a useful oxidase mimics but also sets up a reliable platform based on BP QDs in colorimetric detection. Graphical abstract Schematic representation of colorimetric determination for biothiols through inactivating oxidase mimetic-like catalytic activity of black phosphorus quantum dots(BP QDs) on the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB)with dissolved oxygento produce its blue oxidized product(oxTMB).