Free-base porphyrins as chemical probes for heavy metal ions detection

Abstract

Heavy metals are one of the major contaminants in water. They come from various human activities which include mining, smelting, and industrial discharge to name a few. Heavy metals pose a toxic danger to human beings even at their minute concentration. Current methods of detection suffer from numerous limitations such as complicated sample preparation, high cost of instruments, and the need for professional chemists. These challenges make them unsuitable for in situ and real-time monitoring of samples. Fluorescence spectroscopy has emerged as an alternative for sensing applications. They have high sensitivity, good selectivity, and only require small amounts of fluorescent probes. In this study, free base porphyrins were selected as a fluorescent chemical probe to detect the presence of commonly discharge heavy metals - lead (Pb2+) ions and nickel (Ni2+) ions. Solution-based assay and fluorescent measurements were used throughout the study. From the fluorescent analysis, porphyrins showed more selective and sensitivity towards Pb2+ ions. The study also investigated the photostability of porphyrins when porphyrins solutions were put under ambiance light conditions. This solution-based assay fluorescent measurement shows promising potential application of porphyrins to be used as chemical probes on another sensor medium such as on optical fibre and thin film study.