Colorimetric oligonucleotide-based sensor for ultra-low H2+ in contaminated environmental medium: Convenience, sensitivity and mechanism

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 (A(655)) was linearly related with the concentration of Hg2+ in the range between 5.2 x 10(-9) M and 1.2 x 10(-7) M with a detection limit of 3.8 x 10(-19) M. By visual observation with the naked eye, Hg2+ as low as 3.3 x 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. (C) 2020 Elsevier B.V. All rights reserved.