Water-soluble mercury ion sensing based on the thymine-Hg-thymine base pair using retroreflective Janus particle as an optical signaling probe.

Herein, we report an optical sensing platform for mercury ions (Hg) in water based on the integration of Hg-mediated thymine-thymine (T-T) stabilization, a biotinylated stem-loop DNA probe, and a streptavidin-modified retroreflective Janus particle (SA-RJP). Two oligonucleotide probes, including a stem-loop DNA probe and an assistant DNA probe, were utilized. In the absence of Hg, the assistant DNA probe does not hybridize with the stem-loop probe due to their T-T mismatch, so the surface-immobilized stem-loop DNA probe remains a closed hairpin structure. In the presence of Hg, the DNA forms a double-stranded structure with the loop region via Hg-mediated T-T stabilization. This DNA hybridization induces stretching of the stem-loop DNA probe, exposing biotin. To translate these Hg-mediated structural changes in DNA probe into measurable signal, SA-RJP, an optical signaling label, is applied to recognize the exposed biotin. The number of biospecifically bound SA-RJPs is proportional to the concentration of Hg, so that the concentration of Hg can be quantitatively analyzed by counting the number of RJPs. Using the system, a highly selective and sensitive measurement of Hg was accomplished with a limit of detection of 0.027nM. Considering the simplified optical instrumentation required for retroreflection-based RJP counting, RJP-assisted Hg measurement can be accomplished in a much easier and inexpensive manner. Moreover, the detection of Hg in real drinking water samples including tap and commercial bottled water was successfully carried out.