Mercury (Hg2+) Sensing Using Coumarin-Derived Fluorescent Chemo-Sensors: An Intuitive Development from 2015 to 2023

Mercury is known as a highly toxic metal that is poisonous even if present in a trace amount. Generally, it enters in the food chain (especially fish) and water resources via different pathways and leads to harmful effects. Owing to the detrimental nature of the metal, traditionally several methods were employed by researchers for regular monitoring of the mercury metal ions. However, these methods are associated with many limitations like high cost of technical expertise, and intricacy of the detection procedure. So, using these methods to detect mercury ions in real time is challenging. Therefore, in recent years fluorescent-based analytical tools emerged rapidly. Among the various fluorescent organic scaffolds, coumarin has been scorching, owing to quick response, light stability, high sensitivity, good selectivity, excellent fluorescence intensity, and fluorescence quantum yield. This review provides a deep dive into the coumarin-derived chemo-sensors development throughout 2015-2023. We anticipate that the review will assist to broad scientific community as a reference document to design more interesting sensors.

A novel bifunctional fluorescent and colorimetric probe for detection of mercury and fluoride ions

A fluorescent and colorimetric probe L1 based on a simple coumarin derivative for detection of Hg²⁺ and F^- ions was developed. Upon addition of Hg²⁺ and F^- ions, L1 underwent desulfurization and desilylation, respectively, to induce marked increase in the fluorescence intensity and sharp color change from light yellow to dark purple and light brown, respectively. Probe L1 could be used for sensing and for quantitative measurement of Hg²⁺ and F^- ions by both UV-vis and fluorescence spectra. The bifunctional probe exhibited a high selectivity over other competitive cations and anions and could be used in both organic and aqueous media over a wide pH range.

Use of a Smartphone as a Colorimetric Analyzer in Paper-based Devices for Sensitive and Selective Determination of Mercury in Water Samples

A smartphone application, called CAnal, was developed as a colorimetric analyzer in paper-based devices for sensitive and selective determination of mercury(II) in water samples. Measurement on the double layer of a microfluidic paper-based analytical device (μPAD) fabricated by alkyl ketene dimer (AKD)-inkjet printing technique with special design doped with unmodified silver nanoparticles (AgNPs) onto the detection zones was performed by monitoring the gray intensity in the blue channel of AgNPs, which disintegrated when exposed to mercury(II) on μPAD. Under the optimized conditions, the developed approach showed high sensitivity, low limit of detection (0.003 mg L^-1, 3SD blank/slope of the calibration curve), small sample volume uptake (two times of 2 μL), and short analysis time. The linearity range of this technique ranged from 0.01 to 10 mg L^-1 (r² = 0.993). Furthermore, practical analysis of various water samples was also demonstrated to have acceptable performance that was in agreement with the data from cold vapor atomic absorption spectrophotometry (CV-AAS), a conventional method. The proposed technique allows for a rapid, simple (instant report of the final mercury(II) concentration in water samples via smartphone display), sensitive, selective, and on-site analysis with high sample throughput (48 samples h^-1, n = 3) of trace mercury(II) in water samples, which is suitable for end users who are unskilled in analyzing mercury(II) in water samples.