Highly sensitive and selective photoelectrochemical DNA sensor for the detection of Hg2+ in aqueous solutions

A turn-on photoelectrochemical sensor for Hg2+ detection based on thymine-Hg2+-thymine interaction is presented by using a thymine-rich oligonucleotide film and a double-strand DNA intercalator, Ru(bpy)(2)(dppz)(2+) (bpy=2,2'-bipyridine, dppz=dipyrido[3,2-a:2',3'-c]phenazine) as the photocurrent signal reporter. The presence of Hg2+ induces the formation of a double helical DNA structure which provides binding sites for Ru(bpy)2(dppz)2+. The double helical structure was confirmed by circular dichroism and fluorescence measurements. Under the optimized conditions, a linear relationship between photocurrent and Hg2+ concentration was obtained over the range of 0.1 nM to 10 nM Hg2+, with a detection limit of 20 pM. Interference by 10 other metal ions was negligible. Analytical results of Hg2+ spiked into tap water and lake water by the sensor were in good agreement with mass spectrometry data. With the advantages of high sensitivity and selectivity, simple sensor construction, low instrument cost and low sample volume, this method is potentially suitable for the on-site monitoring of Hg2+ contamination. (C) 2012 Elsevier B.V. All rights reserved.