Naked-eye sensor for rapid determination of mercury ion

A naked-eye paper sensor for rapid determination of trace mercury ion in water samples was designed and demonstrated. The mercury-sensing rhodamine B thiolactone was immobilized in silica matrices and the silica matrices were impregnated firmly and uniformly in the filter paper. As water samples flow through the filter paper, the membrane color will change from white to purple red, which could be observed obviously with naked eye, when concentration of mercury ions equals to or exceeds 10 nM, the maximum residue level in drinking water recommended by U.S. EPA. The color change can also be recorded by a flatbed scanner and then digitized, reducing the detection limit of Hg2+ down to 1.2 nM. Moreover, this method is extremely specific for Hg2+ and shows a high tolerance ratio of interferent coexisting ions. The presence of Na+ (2 mM), K+ (2 mM), Fe3+ (0.1 mM), Zn2+ (0.1 mM), Mg2+ (0.1 mM), Ni2+ (50 μM), Co2+ (50 μM), Cd2+ (50 μM), Pb2+ (50 μM), Cu2+ (50 μM) and Ag+ (3.5 μM) did not interfere with the detection of Hg2+ (25 nM). Finally, the present method was applied in the detection of Hg2+ in mineral water, tap water and pond water.