Colorimetric oligonucleotide-based sensor for ultra-low Hg²⁺ in contaminated environmental medium: Convenience,...

A colorimetric sensor for detection of Hg²⁺ is developed via graphene oxide/gold nanoparticles (GO/AuNPs) nanocomposite as peroxidase mimic. In the absence of Hg²⁺, the adsorption of ss-DNA on GO/AuNPs resulted in the decrease of peroxidase-like activity of GO/AuNPs, which catalyzed the oxidation of 3, 3, 5, 5-tetramethylbenzidine (TMB) to be very light blue. In the presence of Hg²⁺, the oligonucleotides of T-Hg²⁺-T conformation formed by thymine-Hg(II)-thymine interaction could not be adsorbed or bonded on GO/AuNPs, and the GO/AuNPs resumed their original high activity of peroxidase mimic and catalyzed the oxidation of TMB into distinct blue product. Under optimized conditions, the absorbance value at the wavelength of 655 nm (A₆₅₅) was linearly related with the concentration of Hg²⁺ in the range between 5.2 × 10^-9 M and 1.2 × 10^-7 M with a detection limit of 3.8 × 10^-10 M. By visual observation with the naked eye, Hg²⁺ as low as 3.3 × 10^-7 M could cause color change in solution. The specific T-Hg²⁺-T binding made it easy to selectively detect Hg²⁺. The results show that the colorimetric assay offers great potential for the detection of Hg²⁺ in real samples.