A colorimetric/fluorescent dual-mode sensor for ultra-sensitive detection of Hg2+

A highly sensitive colorimetric/fluorescent dual-mode sensor based on hybridization chain reaction (HCR) combining multifunctional Au NPs is presented for the detection of Hg2+ in aqueous solution. In Hg2+ absent solution, the surface of Au NPs was covered by hairpin auxiliary DNAs and a single strand DNA (ssDNA), which prevented Au NPs from salt-induced aggregation. At the same time, the fluorescence intensity of the dye-labeled hairpin probes was significantly quenched by Au NPs. In the presence of Hg2+, T-He-T coordination chemistry between helper DNA and the hairpin probes was induced which triggered the formation of extended double stranded DNA (dsDNA) polymers via HCR. The formed dsDNA polymers were stiffer which couldn't attach to Au NPs, resulting in a red-to-blue color change along with salt-induced aggregation of Au NPs for colorimetric sensing. Meanwhile, the fluorescence of dye-labeled DNA turns on. Due to the HCR amplification effect, a highly sensitive detection of Hg2+ was achieved with detection limit of 0.1 nM. Colorimetry is suitable fox the analysis in salt solution with concentration lower than 100 mM. It serves as an intuitive method that He, down to 1.0 nM could be identified by naked eyes. For high-concentration salt solutions such as industrial effluent, fluorescent sensing acts as a better choice. Both the color and fluorescence changes of the proposed sensor exhibited high selectivity against other metal ions. Lake water was collected and analyzed using the dual-mode sensor, the results confirmed the practicability of the proposed approach.