Ultrasensitive electrochemical sensing of Hg2+ based on thymine-Hg2+-thymine interaction and signal amplification of alkaline phosphatase catalyzed silver deposition

Publication date: 1 May 2018
Source:Biosensors and Bioelectronics, Volume 104
Author(s): Aigui Xu, Long Chao, Hongbo Xiao, Yuyun Sui, Jia Liu, Qingji Xie, Shouzhuo Yao
We report an ultrasensitive electrochemical sensor for Hg²⁺ detection, on the basis of two Hg²⁺-specific oligonucleotide probes (a thiolated capture probe and a biotinated signal probe), "terminal" signal amplification of alkaline phosphatase catalyzed deposition of silver and in situ microliter-droplet anodic stripping voltammetry (ASV). The thiolated capture probe is immobilized on an Au-plated glassy carbon electrode, and the biotinated signal probe is then attached to the electrode surface through the thymine-Hg²⁺-thymine interaction in the presence of Hg²⁺. A streptavidin-alkaline phosphatase (ALP) composite is then immobilized on the electrode surface via biotin–streptavidin interaction. The immobilized ALP can catalyze the hydrolyzation of ascorbic acid 2-phosphate trisodium salt to generate ascorbic acid, which can reduce AgNO3 to form silver deposit on the modified electrode. Quantitative analysis of Hg²⁺ is conducted through microliter-droplet ASV of silver after its simultaneous chemical dissolution and cathodic preconcentration on the modified electrode. The sensor can linearly respond to the common logarithm of Hg²⁺ concentration from 0.1nM to 250μM with a limit of detection of 0.01nM (2 ppt, S/N = 3) and a sensitivity as high as 227μAdec⁻¹.



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