Fabrication of metal ion sensing devices based on porphyrin-immobilized papers

Abstract

Contaminations of heavy metals in water sources can pose serious hazards to human health and the environments. Commercially available techniques are usually expensive and require highly skilled operators. Thus, inexpensive and simple sensing devices for monitoring heavy metals have been developed in recent years. In this research, charged porphyrins including tetrakis(4-sulfonatophenyl)porphyrin (TSPP) and tetrakis(N-methyl-4-pyridyl)porphine tetraiodide (TMPyP) were synthesized and investigated for their abilities as sensors for metal ions via UV-vis absorption and fluorescence modes of detection. Furthermore, these molecules were also deposited on paper support to evaluate their abilities as paper-based sensors. It was found that both porphyrins could detect Hg²⁺ and Cd²⁺ via colorimetric changes, while both could sense Cu²⁺ via the reduction of fluorescence signals. However, due to the clearer color changes of TSPP and simpler synthetic methods, the molecule was selected as an exemplary module for integration between organic synthesis and real-world analytical applications in practical organic chemistry course. On the other hand, TMPyP, with its stronger interaction with cellulose surface, was fabricated as a more ready-to-use paper-based Cu²⁺ sensing device. This device was found to be able to sense Cu²⁺ with a limit of detection of 2.41 µM, and could be used to analyze Cu²⁺ in commercial drinking waters and tap water with the percent recovery in the range of 94-100%. Moreover, distance-based microfluidic paper devices based on fluorescence quenching were also developed – this could sense Cu²⁺ in the range of 13-57 µM.