Exploring a monothiolated β-cyclodextrin as the template to synthesize copper nanoclusters with exceptionally increased peroxidase-like activity

The authors describe a method for increasing the peroxidase-like catalytic properties of copper nanoclusters (Cu-NCs) that are used in non-enzymatic assays. The Cu-NCs were prepared by utilizing 6-thio-beta-cyclodextrin as both the template and as effective modulators for increasing the peroxidase-like properties of the Cu-NCs. The beta-CD-coated Cu-NCs have an average diameter of 2 nm, are stable in aqueous solutions, display strong fluorescence with excitation/emission peak wavelengths of 360/450 nm, and possess peroxidase-like catalytic activity which makes them a useful enzyme mimic. We have applied the findings to non-enzymatic photometric determination (at 650 nm) of (a) H2O2 in the concentration range of 0.02 to 10 mM using the beta-CD/Cu-NC assisted oxidation of tetramethylbenzidine by H2O2, and (b) glucose in the concentration range of 0.04 to 20 mM after addition of glucose oxidase and formation of H2O2. The detection limits (at an S/N ratio of 3) are 0.2 mu M for H2O2 and 0.4 mu M for glucose. The beta-CD coating is found to result in a strong increase in the reaction rate, probably because the cavity of beta-CD acts as a pocket for the recognition and catalysis of substrate. Hence, the binding specificity becomes similar to that of natural enzymes.