Fe(III)-controlled dual-channel ratiometric colorimetric sensing of Pb(II)

Colorimetric detection methods are prosperous in the monitoring of contaminants in food and environmental matrices. However, the traditional single-channel color changes seriously restrict the enhancement of their sensitivity and facile applications. Herein, a Fe 3+ concentration-controlled dual-channel ratiometric colorimetric sensing platform for the sensitive detection of Pb 2+ was established. Generally, the low concentrations of Fe 3+ can trigger a typical absorption peak at 652   nm of the oxidized TMB (oxTMB). While high concentrations of Fe 3+ induce colorless-to-orange change due to the generation of biphenyl quinone with strong absorption peaks at 450   nm. Interestingly, the presence of Pb 2+ could convert Fe 3+ to Fe (3+x)+ by a displacement reaction, causing a blue-to-colorless change at low Fe 3+ concentrations or an orange-to-blue color change at high Fe 3+ concentrations. The latter dual-channel color variances corresponded to a more distinguished visual quantification of Pb 2+ compared to the former one-channel changes. As such, the Pb 2+ was detected over a range of 0.625-25   µM, with a low detection limit (LOD) of 70   nM. Additionally, by integrating smartphone optical equipment and color recognition software, an intelligent platform for the instant detection of Pb 2+ was established, with a LOD of 0.30   µM. In real samples detection, the developed smartphone sensing platform demonstrated excellent recovery rates (89.0±4.6% to 111.1±7.4%), comparable to the conventional UV-Vis spectroscopy. This work sheds light on fabrication dual-channel colorimetric detection methods for enhanced sensing performance and provides a rapid, sensitive, and intelligent platform for detecting small molecular hazards in the environment.