Inhibitor effects on molecular beacon-based mercury assays for tuning of detection range

A series of inhibitors were incorporated to modulate the detection range of mercury assay. A single-strand DNA-based mercury probe (ssDNA-Hg) containing 5 thymine (T) bases at both termini, which forms a hairpin structure in the presence of mercuric (Hg2+) ions via the T⋯Hg2+⋯T interaction, was designed. Although many previous studies focused on mercury detection to improve the sensitivity and selectivity, few studies have been reported to tune the detection range to cover a wide range of target concentrations in different environments. In the present study, a new Hg2+ detection scheme was designed to extend, narrow and shift the range of mercury detection using inhibitors. The complementary DNA (ssDNA-C) and cationic conjugated polyelectrolyte (CPE) induced a shift or broadening of the spectral response range by functioning as an allosteric inhibitor. Iodide and cyanide ions worked as efficient depletants, adjusting the binding constant of ssDNA-Hg and Hg2+ (1.1 × 107 M−1) by ∼10 times (up to ∼1.4 × 106 M−1) in the presence of I− or CN− ions, resulting in a large shift in the detection range according to [I−] or [CN−] with a sharp titration curve via a sequestration mechanism. Similar Hg2+ detection range shift was successfully demonstrated using same series of inhibitors in real samples such as Han River and tap water. This study suggests that the binding affinity of probe can be tuned toward a target and the resulting detection response range can be controlled using a range of inhibitors.