Of various chemosensory protocols, the color change observed by the naked eye is considered to be a conceivable and on-site way to indicate the presence of an analyte. We herein designed a ratiometric fluorescence probe by hybridizing dual-emission quantum dots (QDs) and demonstrated its efficiency for on-site visual determination of copper ions. The hybrid probe comprises two sizes of cadmium telluride QDs emitting red and green fluorescence, respectively, in which the red-emitting ones are embedded in silica nanoparticles and the green-emitting ones are covalently linked onto the surface. The fluorescence of the embedded QDs is insensitive to the analyte, whereas the green emissive QDs are functionalized to be selectively quenched by the analyte. Upon exposure to different amounts of copper ions, the variations of the dual emission intensity ratios display continuous color changes from green to red, which can be clearly observed by the naked eye. The limit of detection for copper is estimated to be 1.1 nM, much lower than the allowable level of copper (~20 μM) in drinking water set by U.S. Environmental Protection Agency. The probe is demonstrated for the determination of copper ions in lake water and mineral water samples, especially for visually monitoring copper residues on herb leaves. This prototype ratiometric probe is simple, fully self-contained, and thus potentially attractive for visual identification without the need for elaborate equipment.

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Mercury pollution is a widespread danger to human health and environment. To developed a effective method for mercury detecting is in high demand. This work demonstrated a novel bright fluorescent molecule DPDTC for the sensing of mercury. The approach was mainly based on the mercury-induced fluorescence turn-off of DPDTC. The probe was prepared by a simple method and exhibited high fluorescence. The fluorescence of DPDTC was very stable and immue to photobleaching. Results showed that DPDTC was a promising tool for mercury detection. Moreover, DPDTC could be immoblized on a paper to prepare an simple and portable sensor which expanded its real application.