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

We report an ultrasensitive electrochemical sensor for Hg detection, on the basis of two Hg-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-Hg-thymine interaction in the presence of Hg. 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 AgNO to form silver deposit on the modified electrode. Quantitative analysis of Hg 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 Hg 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.