Highly sensitive colorimetric sensor for Hg2+ detection based on cationic polymer/DNA interaction

The detection of ultralow concentrations of mercury is a currently significant challenge. Here, a novel strategy is proposed: the colorimetric detection of Hg2+ based on the aggregation of gold nanoparticles (AuNPs) driven by a cationic polymer. In this three-component system, DNA combines electrostatically with phthalic diglycol diacrylate (PDDA) in a solution of AuNPs. In the presence of Hg2+, thymine (T)-Hg2+-T induced hairpin turns are formed in the DNA strands, which then do not interact with PDDA, enabling the freed PDDA to subsequently facilitate aggregation of the AuNPs. Thus, according to the change in color from wine-red to blue-purple upon AuNPs aggregation, a colorimetric sensor is established to detect Hg2+. Under optimal conditions, the color change is clearly seen with the naked eye. A linear range of 0.25-500 nM was obtained by absorption spectroscopy with a detection limit of approximately 0.15 nM. Additionally, the proposed method shows high selectivity toward Hg2+ in the presence of other heavy metal ions. Real sample analysis was evaluated with the use of lake water and the results suggest good potential for practical application.