Highly sensitive colorimetric detection of glucose through glucose oxidase and Cu-catalyzed 3,3',5,5'-tetramethylbenzidine oxidation.

We develop a glucose oxidase (GOx)-mediated strategy for detecting glucose based on oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB), which is generated from Cu-catalyzed 3,3',5,5'-tetramethylbenzidine (TMB)-HO reaction, as colorimetric readout. The sensing system involves two processes: generation of HO from GOx-catalyzed oxidation of glucose, and HO-induced the oxidization of TMB via the catalysis of Cu. The HO formed by GOx-catalyzed oxidation of glucose oxidizes colorless TMB to blue oxTMB, thus enhancing the absorbance intensity at 670 nm. Therefore, we draw a conclusion that the enhancement in colorimetric signal relies directly on HO concentration, which, in turn, depends on glucose concentration. This color change can be used not only for visual detection of glucose by naked eyes but for reliable glucose quantification in the range from 1 to 100 nM with a detection limit of 0.21 nM. The method possesses the following advantages: simple design, low experimental cost, and no any additional experimental equipment for heating, illuminating, or bubbling.