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-β-cyclodextrin as both the template and as effective modulators for increasing the peroxidase-like properties of the Cu-NCs. The β-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) H 2 O 2 in the concentration range of 0.02 to 10 mM using the β-CD/Cu-NC assisted oxidation of tetramethylbenzidine by H 2 O 2 , and (b) glucose in the concentration range of 0.04 to 20 mM after addition of glucose oxidase and formation of H 2 O 2 . The detection limits (at an S/N ratio of 3) are 0.2 μM for H 2 O 2 and 0.4 μM for glucose. The β-CD coating is found to result in a strong increase in the reaction rate, probably because the cavity of β-CD acts as a pocket for the recognition and catalysis of substrate. Hence, the binding specificity becomes similar to that of natural enzymes. The peroxidase-like catalytic activity of Cu-NCs in non-enzymatic sensors is strongly enhanced by utilizing mono-6-thio-β-cyclodextrin (mono-6-SH-β-CD) as both the template molecule and the effective rate modulator.