# Novel Quinoline Chemosensor with Dual-Mode Fluorescence and DFT-Backed Mechanism for Mercury(II) Sensing

## TL;DR

A new quinoline-based chemosensor called HMQC can detect mercury in water with high sensitivity and selectivity, using dual fluorescence modes at different pH levels.

## Contribution

The dual-mode fluorescence and DFT-backed mechanism of HMQC offer a novel approach for mercury detection.

## Key findings

- HMQC shows fluorescence enhancement at pH 7 with a low detection limit of 1.47 nM.
- At pH 5, HMQC exhibits quenching with a detection range suitable for higher mercury concentrations.
- The chemosensor is reusable and effective in real water samples with high recovery rates.

## Abstract

Mercury (Hg²⁺) contamination poses a significant threat to environmental and human health, necessitating the development of sensitive and selective detection methods. In this study, we report the design and application of a novel quinoline-based chemosensor, HMQC, for the detection of Hg²⁺ in aqueous environments. The probe exhibits dual fluorescence behavior, with quenching at acidic pH (pH 5) and enhancement at neutral pH (pH 7), enabling both qualitative and quantitative detection of Hg²⁺. Under optimized conditions at pH 7, HMQC demonstrated a broad linear range (4.84–50 nM), a low limit of detection (LOD) of 1.47 nM, and high selectivity toward Hg²⁺ over competing metal ions. At pH 5, the probe showed effective quenching with a linear range of 3.09–15 µM and an LOD of 0.93 µM, making it suitable for environments with higher mercury concentrations. The practical utility of HMQC was validated by detecting Hg²⁺ in spiked real water samples with recovery rates ranging from 92% to 108% and relative standard deviations (RSD) below 5%. The probe’s reversibility and reusability were confirmed through successive binding and displacement cycles with EDTA, highlighting its robustness for real-time and continuous monitoring. The adaptability of HMQC under different pH conditions aligns with international water quality standards, such as the World Health Organization (WHO) and European Union (EU) limits for mercury in drinking water (1 µg/L or 5 nM), demonstrating its suitability for environmental and industrial applications. Moreover, DFT calculations have been conducted to obtain atomistic insights into the binding complex and the quenching mechanism. This work provides a versatile and efficient platform for mercury detection, combining high sensitivity, selectivity, and robust performance in complex matrices. The dual fluorescence response of HMQC represents a novel approach in chemosensor design, offering significant potential for future advancements in environmental monitoring and public health protection. *Corresponding Authors. Gasser M. Khairy: gasser_mostafa@science.suez.edu.eg.

The online version contains supplementary material available at 10.1007/s10895-025-04702-3.