Construction of an effective ratiometric fluorescent sensing platform for specific and visual detection of mercury ions based on target-triggered the inhibition on inner filter effect

Sensitive and selective determination of mercury ion (Hg2+) is critical for human health and environmental monitoring. Herein we construct an effective ratiometric fluorescent sensing platform by combining green fluorescent polymer carbon dots (PCDs) and red fluorescent tetraphenylporphyrin tetrasulfonic acid hydrate (TPPS) for specific and visual detection of Hg2+. The fluorescence of PCDs can be quenched by TPPS through inner filter effect (IEF). In the presence of both Mn2+ and Hg2+, however, Hg2+ can expedite the complexation of TPPS and Mn2+, which causes the decrease in both fluorescence and absorption of TPPS, accompanied by the fluorescence recovery of PCDs due to the subdued IFE between TPPS and PCDs. Based on the change of fluorescence signal, a ratiometric fluorescent sensing platform is constructed for specific and visual detection of Hg2+. The proposed approach presents a fine linear range for Hg2+ over the range of 10-200 nM with a detection limit of 0.038 nM. Moreover, an easily distinguishable fluorescence color change from pink to green with the increase of Hg2+ concentration can be observed by the naked eye under a UV lamp. Such a simple and effective method shows great potential for visual sensing of Hg2+ in on-site and resource-limited settings.