Dual modes of fluorescence sensing and smartphone readout for sensitive and visual detection of mercury ions in Porphyra

A convenient and intuitive method for detecting trace heavy metal ions is vital for food safety and quality monitoring. Herein, a dual-emission ratiometric fluorescence probe based on Zr-based metal-organic frameworks (Zr-MOF) and silver nanoclusters (AgNCs) was assembled to sensitive and visual detect mercury ions (Hg²⁺). The sensor exhibits good sensitivity from 0.010 to 0.5 μg mL^-1 with a low detection limit of 1.8 μg L^-1 (corresponding to 0.72 μg kg^-1 by weight). The proposed method was finally applied to determine Hg²⁺ in the Porphyra matrix with satisfactory outcomes, the analytical recoveries were in the range of 94.74%-101.1%, indicating the practicability of the developed method. Meanwhile, the smartphone-based colorimetric method was established by capturing the changes in fluorescence colors of the probes exposed to different Hg²⁺ concentrations, with a quick sample-to-answer monitoring time of 10 min. The fluorescence probe, with these merits of simplicity, rapid response, and high sensitivity, offered a promising means for evaluating the safety of food polluted with Hg²⁺.