Rapid electrochemical quantification of trace Hg using a hairpin DNA probe and quantum dot modified screen-printed gold electrodes.

Rapid, simple, sensitive and specific approaches for mercury(ii) (Hg) detection are essential for toxicology assessment, environmental protection, food analysis and human health. In this study, a ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quaternary Zn-Ag-In-S quantum dot (QD) on screen-printed gold electrodes (SPGE), referred to as the HP-QDs-SPGE electrochemical biosensor in this study, was developed for Hg detection. Based on the "turn-off" reaction of a hairpin DNA probe binding with a mismatched target and Hg through the formation of T-Hg-T coordination, the HP-QDs-SPGE electrochemical biosensor can rapidly quantify trace Hg with high ultrasensitivity, specificity, repeatability and reproducibility. The conformational change of the hairpin DNA probe caused a significant decrease in electrochemical intensity, which could be used for the quantification of Hg. The linear dynamic range and high sensitivity of the HP-QDs-SPGE electrochemical biosensor for the detection of Hg was studied , with a broad linear dynamic range of 10 pM to 1 μM and detection limits of 0.11 pM. In particular, this HP-QDs-SPGE electrochemical biosensor showed excellent selectivity toward Hg ions in the presence of other metal ions. More importantly, this biosensor has been successfully used to detect Hg in deionized water, tap water, groundwater and urine samples with good recovery rate and small relative standard deviations. In summary, the developed HP-QDs-SPGE electrochemical biosensor exhibited promising potential for further applications in on-site analysis.