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.

Fumed-Si-Pr-PNS as a Photoluminescence sensor for the Detection of Hg2+ in Aqueous Media.

Fumed silica was functionalized by piperazine followed by the reaction with 2- naphthalenesulfonyl chloride to prepare Fumed-Si-Pr-Piperazine-Naphthalenesulfonyl chloride (Fumed-Si-Pr-PNS), which was characterized to demonstrate the effective attachment on the surface of fumed silica. The optical sensing ability of Fumed-Si-Pr-PNS was studied via diverse metal ions in H2O solution by photoluminescence spectroscopy. The results showed that Fumed-Si-Pr-PNS detected selectively Hg2+ ions. The prepared sensor showed almost high absorption at different pH for Hg ion. After drawing various diagrams, The detection limits were calculated at about 12.45 × 10-6 M for Hg2+.

Design of Fluorescent Hybrid Materials Based on POSS for Sensing Applications.

Polyhedral oligomeric silsesquioxane (POSS) has a nanoscale silicon core and eight organic functional groups on the surface, with sizes from 0.7 to 1.5 nm. The three-dimensional nanostructures of POSS can be used to build all types of hybrid materials with specific performance and controllable nanostructures. The applications of POSS-based fluorescent materials have spread across various fields. In particular, the employment of POSS-based fluorescent materials in sensing application can achieve high sensitivity, selectivity, and stability. As a result, POSS-based fluorescent materials are attracting increasing attention due to their fascinating vistas, including unique structural features, easy fabrication, and tunable optical properties by molecular design. Here, we summarize the current available POSS-based fluorescent materials from design to sensing applications. In the design section, we introduce synthetic strategies and structures of the functionalized POSS-based fluorescent materials, as well as photophysical properties. In the application section, the typical POSS-based fluorescent materials used for the detection of various target objects are summarized with selected examples to elaborate on their wide applications.

Designed Synthesis of Fluorescence 'Turn-on' Dual Sensor for Selective Detection of Al3+ and Zn2+ in Water.

1-(Pyridin-2-yl-hydrazonomethyl)-naphthalen-2-ol (PNOH) is a naphthalene-based fluorescence dual chemo-sensor for Al3+ and Zn2+. The probe (PNOH) is spectroscopically characterised and the chemo-sensing mechanism has been demonstrated through 1H NMR, absorption and both steady state and time resolved fluorescence study. The 'turn-on' luminescence property of PNOH is used for the selective detection of trace amount of Al3+and Zn2+via chelation enhanced fluorescence (CHEF) through complex formation. The 1:1 stoichiometry of each sensor-metal complex is observed from Job's plot based on UV-Vis titration. Most promising advantage of the probe (PNOH) is its application in the one-pot detection of Al3+ (λem- 460 nm) and Zn2+ (λem- 510 nm) exciting at same wavelength (λex- 420 nm) while high intense emission appears at two different wavelengths. Limit of detection (LOD) of PNOH towards Al3+ & Zn2+ are found to be 60 nM & 365 nM respectively. Real water sample analysis has also been demonstrated by using the probe PNOH.

Urolithin A and B Derivatives as ON-OFF Selective Fluorescent Sensors for Iron(III).

The detection and sensing of environmentally crucial metal ions has always been of great significance in various fields such as biological and environmental cycles. Our previous studies have indicated a new coumarin based lactone, Urolithin B (i.e., 3-Hydroxy[c]chromen-6-one) as a potent fluorescent probe for the selective detection of Iron (III). In order to question the extension of this application to other urolithins, we have synthesized the major urolithins that humans are exposed to through regular diet. Following the structure identifying studies, the compounds were tested in fluorescence titration to investigate their interaction with various metals. The results have indicated that each title compound is selective to interact with Iron (III) in ON-OFF mode, independent from the presence of another metal. Similar to the previous findings, the Job's plots displaying the ratio of complex formation 3:2 UROs:Fe3+ have indicated the significance of the lactone group solely.

Urolithin B as a Simple, Selective, Fluorescent Probe for Sensing Iron(III) in Semi-Aqueous Solution.

The development of simple, environmental friendly, and cheap reagents with metal binding properties are quite important not only for the treatment of environmental pollution but also for their application in medicine. Within this study, for the first time, we displayed a natural chromen analogue, Urolithin B, as a simple, selective, fluorescent iron (III) sensing probe. Following the synthesis and structure identification studies, the selective metal binding property of the compound was displayed employing fluorescence techniques. Accordingly, urolithin B has the capacity to coordinate selectively to iron (III) with a 3:2 stoichiometry.

Triphenylbenzene Sensor for Selective Detection of Picric Acid.

A C 3-symmetric triphenylbenzene based photoluminescent compound, 1,3,5-tris(4'-(N-methylamino)phenyl) benzene ([NHMe]3TAPB), has been synthesized by mono-N-methylation of 1,3,5-tris(4'-aminophenyl) benzene (TAPB) and structurally characterized. [NHMe]3TAPB acts as a selective fluorescent sensor for picric acid (PA) with a detection limit as low as 2.25 ppm at a signal to noise ratio of 3. Other related analytes (i.e. TNT, DNT and DNB) show very little effect on the fluorescence intensity of [NHMe]3TAPB. The selectivity is triggered by proton transfer from picric acid to the fluorophore and ground-state complex formation between the protonated fluorophore and picrate anion through hydrogen bonding interactions. The fluorescence lifetime measurements reveal static nature of fluorescence quenching.

A fluorescence chemo sensor approach for determination of finerenone in pharmaceutical formulation and human plasma: Method development and validation.

Finerenone, a non-steroidal mineralocorticoid receptor antagonist, has gained recent approval for treating cardiovascular and kidney-related conditions. Herein, an innovative fluorescence chemo sensor was developed for the determination of finerenone in the pharmaceutical dosage form and the plasma matrix. The method is basically based on chemical transformation of finerenone into a fluorescent product through sequential reactions. This transformation occurs through a sequence of steps involving the interaction of finerenone with trimethylamine, resulting in the formation of a nucleophilic intermediate that subsequently reacts with bromoacetyl bromide to form fluorescent product, (S)-N-(2-bromoacetyl)-4-(4-cyano-2-methoxyphenyl)-5-ethoxy-2,8-dimethyl-1,4-dihydro-1,6-naphthyridine-3-carboxamide. The formed fluorescent product exhibits defined emission peak at 338 nm when excited at 248 nm. Significant concentration-dependent fluorescence enhancement was obtained enabling precise finerenone determination in the pharmaceutical formulation and plasma matrix. The method was optimized and validated providing sensitive determination over linearity range of 1-200 ng/mL with a lower limit of detection at 0.280 ng/mL. This strategy provides an efficient, economical substitute and straightforward, more sensitive analytical method for finerenone assessment in various matrices, in contrast to the previously published method, high-performance liquid chromatography-tandem mass spectrometry, which is expensive and time-consuming.

A novel high sensitive Cd-MOF fluorescent probe for acetone vapor in air and picric acid in water: Synthesis, structure and sensing properties.

A novel three-dimensional luminescence Cd-MOF sensor with the molecular formula {[(CH3)2NH2]2 Cd3(ptptc)2} (complex 1) has been synthesized by using terphenyl-3,3',5,5'-tetracarboxylic acid (H4ptptc) and Cd(NO3)2·4H2O under solvothermal conditions. Single crystal X-ray diffraction analysis shows that complex 1 crystallizes in the monoclinic system C2/c space group and consists of one-dimensional channels. Complex 1 exhibits characteristic fluorescence emission (λem = 380 nm) both in solid state and solvents upon excitation at 300 nm. Real-time fluorescence quenching of complex 1 was observed in the fluorescence sensing of acetone vapor and picric acid. Intriguingly, ppm scale detection limit for acetone vapor in air and nano-mole scale detection limit for picric acid in water were observed. Moreover, good reusability and liner/nonlinear relationships were observed in the fluorescent titration.

A novel mitochondria-targeted phosphorescence probe for hypochlorite ions detection in living cells.

Monitoring hypochlorite anion (ClO-) in living cells is particularly meaningful and valuable, because over-exposure of the ClO- may cause a potential health hazard towards animals and humans. Considering the special structure and properties of the gemini surfactant, a novel amphiphilic gemini-iridium complex Ir[(ppy-iso)2(bpy-tma2Br2)] (Ir-iso) with isoniazide as a recognition site for ClO- was designed. The Ir-iso possessed an excellent water-solubility as well as a strong ClO- binding capacity, as revealed from the rapid response of emission signal towards ClO-. It was worth noting that such probe had a highly-specific selectivity with a low detection limit (20.5 nM) and was suitable in physiological environment. The cell viability assay, cell imaging, and co-location studies further proved that the Ir-iso had little cytotoxicity and was specifically localized in the mitochondria of breast cancer cells, being a promising candidate of chemo-sensor to detect the endogenous ClO- in living cells.

Remote Microwave and Field-Effect Sensing Techniques for Monitoring Hydrogel Sensor Response.

This paper presents two novel techniques for monitoring the response of smart hydrogels composed of synthetic organic materials that can be engineered to respond (swell or shrink, change conductivity and optical properties) to specific chemicals, biomolecules or external stimuli. The first technique uses microwaves both in contact and remote monitoring of the hydrogel as it responds to chemicals. This method is of great interest because it can be used to non-invasively monitor the response of subcutaneously implanted hydrogels to blood chemicals such as oxygen and glucose. The second technique uses a metal-oxide-hydrogel field-effect transistor (MOHFET) and its associated current-voltage characteristics to monitor the hydrogel's response to different chemicals. MOHFET can be easily integrated with on-board telemetry electronics for applications in implantable biosensors or it can be used as a transistor in an oscillator circuit where the oscillation frequency of the circuit depends on the analyte concentration.