A test strip platform based on DNA-functionalized gold nanoparticles for on-site detection of mercury (II) ions

A test strip, based on DNA-functionalized gold nanoparticles for Hg2+ detection, has been developed, optimized and validated. The developed colorimetric mercury sensor system exhibited a highly sensitive and selective response to mercury. The measurement principle is based on thymine-Hg2+-thymine (T-Hg2+-T) coordination chemistry and streptavidin-biotin interaction. A biotin-labeled and thiolated DNA was immobilized on the gold nanoparticles (AuNPs) surface through a self-assembling method. Another thymine-rich DNA, which was introduced to form DNA duplexes on the AuNPs surface with thymine-Hg2+-thymine (T-Hg2+-T) coordination in the presence of Hg2+, was immobilized on the nitrocellulose membrane as the test zone. When Hg2+ ions were introduced into this system, they induced the two strands of DNA to intertwist by forming T-Hg2+-T bonds resulting in a red line at the test zone. The biotin-labeled and thiolated DNA-functionalized AuNPs could be captured by streptavidin which was immobilized on the nitrocellulose membrane as the control zone. Under optimized conditions, the detection limit for Hg2+ was 3 nM, which is lower than the 10 nM, maximum contaminant limit defined by the US Environmental Protection Agency (EPA) for drinking water. A parallel analysis of Hg2+ in pool water samples using cold vapor atomic absorption spectrometry showed comparable results to those obtained from the strip test. Therefore, the results obtained in this study could be used as basic research for the development of Hg2+ detection, and the method developed could be a potential on-site screening tool for the rapid detection of Hg2+ in different water samples without special instrumentation. All experimental variables that influence the test strip response were optimized and reported. (C) 2012 Elsevier B.V. All rights reserved.