Colorimetric detection of Hg2+ and Pb2+ based on peroxidase-like activity of graphene oxide–gold nanohybrids

Abstract

In recent years, considerable efforts have been devoted to the construction of efficient enzyme mimetics, which have significant advantages of simple synthesis and good stability. In this paper, we prepared novel graphene oxide–gold (GO–AuNP) nanohybrids that exhibited fascinating peroxidase-like activity and could catalyze the oxidation of the peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) by H₂O₂, while simultaneously developing a blue color in an aqueous solution. Furthermore, single-stranded DNA (ssDNA) were able to resist the salt-induced aggregation of GO–AuNP nanohybrids, whereas double-stranded DNA (dsDNA) did not inhibit salt-induced GO–AuNP nanohybrids aggregation. Based on these unique properties, we developed a label-free colorimetric method for the detection of Hg²⁺ and Pb²⁺. In the presence of Hg²⁺ or Pb²⁺, ssDNA formed a hairpin-like or a quadruplex structure, and these conformational changes facilitated the salt-induced aggregation of GO–AuNP nanohybrids, leaving behind a transparent supernatant after centrifugation. After incubation with TMB and H₂O₂, the colorimetric signal of the centrifugal supernatant was significantly decreased compared to that in the absence of Hg²⁺ or Pb²⁺. The response to Hg²⁺ and Pb²⁺ were in the range of 0–50 μM. Finally, this simple and sensitive sensor could be successfully applied for the detection of Hg²⁺ and Pb²⁺ in river water.