Smartphone‐Assisted Quinoline‐Based Chromogenic Probe for the Selective Detection of Hg²⁺ in Protic Media

Abstract

High selectivity and sensitivity detection of Hg 2 + in aqueous environment by the naked-eye has always been a challenge. In this paper, a simple ligand based on 2-(hydroxymethyl)quinolin-8-ol (L) was synthesized and its structure was confirmed by NMR, IR and mass analysis. The probe L showed distinct colorimetric upon interaction with Hg 2 + in CH 3 OH-H 2 O (8 : 2, v/v) media. The ligand L exhibit unique absorbance band at 243 nm due to ligand-to-ligand charge transfer (LLCT). Upon interaction with Hg 2 + , the L formed new UV-Vis bands at 269 and 316 nm due to ligand-to-metal charge transitions (LMCT). The UV-Vis spectral studies indicate the formation of a 1 : 1 host-guest complex between the L and Hg 2 + with an association constant of 8.6 × 10 4 M À 1. The ligand L can work in the pH range of 3-8 without interfering with other competing ions. The detection limit of Hg 2 + can reach a concentration of as low as 0.13 μM (2.6 ppb) with high selectivity, even in a solution containing diverse metal ions. Besides, the selective colour change of L with Hg 2 + was integrated with smartphone to monitor the change in RGB tool and test paper kit. The binding mechanism of L with Hg 2 + was studied by using 1 H NMR, SEM and TDDFT analysis. Overall, ligand L demonstrates a promising and potential for the detection of toxic contaminate in aqueous environment.