Easy sensing of lead and zinc in water using smart glass based on cationic porphyrin layers

Abstract

Spontaneous formation of meso-tetra(N-methyl-4-pyridyl)porphyrin (H2T4) layers on a glass surface is proven effective to assess the sensitivity and selectivity of solid chemosensors for spectrometric detection (at sub-ppm levels) of Pb²⁺ and Zn²⁺ ions in water. The obtained results, achieved by a simple, low cost and repeatable non-covalent glass surface functionalization, are suitable for application in water management and control where detection of contaminants at micromolar or even submicromolar concentrations is required. The most striking result is represented by the high sensitivity towards Zn²⁺ ions, unusual for cationic porphyrins in solution, herein associated with macrocycle ring distortion caused by immobilization onto a glass surface. Moreover, the co-presence of Pb²⁺ and Zn²⁺ in water promotes a trans-metalation process responsible for a peculiar fingerprint of contaminant abundance in solution within the selected (short) analysis time. The defined sensing strategy is extendible to other metal ions, thus making these H2T4 functionalised glass slides ideal for the rapid on site-real time detection of heavy metal ions in water.