Ag-β-Cyclodextrin-Graphene Oxide Ternary Nanostructures with Peroxidase-Mimicking Activity for Hg2+ Detection

To strengthen the properties of nanozymes, a Ag-beta-cyclodextrin-graphene oxide ternary nanocomposite (Ag-beta-CD-GO) was developed first by a homogeneous redox-active self-assembly method. Taking advantage of the excellent environmental compatibility, high surface areas, and strong hydrogen-bonding ability of beta-cyclodextrin and graphene oxide, the proposed Ag-beta-CD-GO exhibited superior peroxidase-mimicking activity, high stability, and nontoxicity as well. It could accelerate the oxidation- reduction reaction of the common colorimetric substrate 3,3',5,5'-tetramethylbenzidine (TMB) and the oxidant H2O2 with Michaelis constants (K-m)/maximal reaction rates (V-max) of 3.3 mmol.L-1/2.45 X 10(-8) mol.L-1.s(-1) and 0.13 mmol.L-1/2.52 X 10(-8) mol.L-1.s(-1), respectively. Interestingly, toxic Hg2+ could decrease the characteristic UV-vis absorbance at 653 nm of the Ag-beta-CD-GO-TMB-H2O2 system exclusively with an obvious color change from blue to colorless, expressing a visual hypochromic effect. Under the optimal testing conditions (pH 4.0, 180 mu L of 1.5 mmol.L-1 TMB, 180 mu L of 1.0 mol.L-1 H2O2, incubation for 20 min at 25 degrees C), the target Ag-beta-CD-GO-TMB-H2O2 was efficiently utilized for visual monitoring of toxic He' in natural water, drink, and fruit juice samples with quite a low detection limit, i.e., 8.3 X 10(-10) mol. L-1 (S/N = 3), far below the 3.0 X 10(-8) mol/L-1 permitted in drinking water by the World Health Organization (WHO). The synergetic enhancement peroxidase-mimicking activity of Ag-beta-CD-GO and the exclusive recognition mechanism to Hg2+ were further investigated in detail.

Automated summary

The Ag-beta-cyclodextrin-graphene oxide ternary nanocomposite showed superior peroxidase-mimicking activity, stability, and non-toxicity, with potential for visual monitoring of toxic Hg2+ in water, drinks, and fruit juices at a low detection limit. The synergy between Ag-beta-CD-GO and the exclusive recognition mechanism for Hg2+ was further explored in detail to enhance its applications.