Two-photon ratiometric sensing of Hg2+ by using cysteine functionalized Ag nanoparticles

We have demonstrated a novel two-photon sensing strategy to detect mercury ions with high selectivity and sensitivity. This sensing approach is based on the observation that addition of Hg2+ into a cysteine functionalized Ag nanoparticle solution could significantly enhance their two-photon emission. An enhancement factor of up to 100 fold was obtained when mercury was added. A detection limit of as low as 65 nM could be achieved. The sensitivity and sensing range can be easily tuned. Compared to the conventional colorimetric or extinction spectrum based methods, this scheme offers improved sensitivity, quantitative detection of Hg2+ with a larger dynamic range, and allows detection deep into biological environments such as cells and tissues where deep penetration is required. The sensitivity could be further improved by using two-photon microscopy with the additional advantages of 3D detection and mapping.