A gadolinium(III)-coumarin complex based MRI/Fluorescence bimodal probe for the detection of fluoride ion in aqueous medium

Recent applications of coinage metal nanoparticles passivated with salicylaldehyde and salicylaldehyde-based Schiff bases

Salicylaldehyde (SD) and its derivatives are effective precursors for generating coinage metal (gold, silver, and copper) nanoparticles (NPs). These NPs have a variety of potential environmental applications, such as in water purification and sensing, and those arising from their antibacterial activity. The use of SD and its derivatives for synthesizing coinage NPs is attractive due to several factors. First, SD is a relatively inexpensive and readily available starting material. Second, the synthetic procedures are typically simple and can be carried out under mild conditions. Finally, the resulting NPs can be tailored to have specific properties, such as size, shape, and surface functionality, by varying the reaction conditions. In an alkaline solution, the phenolate form of SD was converted to its quinone form, while ionic coinage metal salts were converted to zero-valent nanoparticles. The capping in situ produced quinone of coinage metal nanoparticles generated metal-enhanced fluorescence under suitable experimental conditions. The formation of iminic bonds during the formation of Schiff bases altered the properties (especially metal-enhanced fluorescence) and applications.

Current progress on fluoride occurrence in the soil environment: Sources, transformation, regulations and remediation

Fluorine is a halogen element widely distributed in nature, but due to excessive emissions from industrial manufacturing and agricultural production, etc., the soil is over-enriched with fluoride and the normal growth of plants is under stress, and it also poses a great threat to human health. In this review, we summarized the sources of fluoride in soil, and then analyzed the potential mechanisms of fluoride uptake in soil-plant systems. In addition, the main influences of soil ecosystems on plant fluoride uptake were discussed, soil management options to mitigate fluoride accumulation in plants were also summarized. The bioremediation techniques were found to be a developmental direction to improve fluoride pollution. Finally, we proposed other research directions, including fluoride uptake mechanisms in soil-plant systems at the molecular expression levels, development of visualization techniques for fluoride transport in plants, interactions mechanisms between soil microhabitats and plant metabolism affecting fluoride uptake, as well as combining abiotic additives, nanotechnology and biotechnology to remediate fluoride contamination problems.

A portable and intelligent logic detector for simultaneous and in-situ detection of Al3+ and fluoride in groundwater

To develop a convenient and intelligent detector for simultaneous and in-situ detection of Al³⁺ and F^- in groundwater, a novel organic probe called RBP has been prepared. With the increase of Al³⁺, RBP showed a significant fluorescence enhancement at 588 nm, and the detection limit was 0.130 mg/L. After combining with fluorescent internal standard CDs, the fluorescence of RBP-Al-CDs at 588 nm was quenched due to the replace of F^- for Al³⁺, while the CDs at 460 nm remained unchanged, and the detection limit was 0.0186 mg/L. For convenient and intelligent detection, an RBP-based logic detector has been developed for simultaneous detection of Al³⁺ and F^-. Within the ultra-trace, low concentration, and high concentration range of Al³⁺ and F^-, the logic detector can achieve rapid feedback on their concentration levels ("U", "L" and "H") through different output modes of the signal lamps. The development of logical detector is of great significance for studying the in-situ chemical behavior of Al³⁺ and F^- and for daily household detection.

Coumarin 6H-fused fluorescent probe for highly sensitive detection of coralyne using oligonucleotide-modified silver nanoparticles

In this study, a novel, rapid, and sensitive fluorescence sensing platform was developed for the detection of coralyne (COR) by the conjugation of coumarin 6H (C6H) fluorescent dye with oligonucleotide-modified silver nanoparticles [(dT)₃₂-AgNPs]. In the presence of COR, a remarkable and rapid decrease in the fluorescence signal of the probe with a quenching efficiency of around 62% was observed. The quenching response of the system towards COR was possibly due to the displacement of thymidine-rich deoxyoligonucleotides by COR on the surface of AgNPs. The complementary experiments with an adenine-rich single strand as well as with two different secondary structures (i.e., duplex and triplex) revealed a favorable sequence specificity of the sensing platform. The influence of key parameters including the incubation time and temperature was evaluated and optimized to achieve the highest performance. The linear range of 10-183 nM with a correlation coefficient of R = 0.9982 and a limit of detection of 5.24 nM were obtained under the optimized conditions. The selectivity of the proposed probe towards COR was revealed by the evaluation of its response to other small molecules that have molecular structures similar to COR. Finally, the successful applicability of the system was shown with the obtained average recoveries in the range of 87.28-104.52% in human urine samples.

Coumarin functionalized molecular scaffolds for the effectual detection of hazardous fluoride and cyanide

Fluoride and cyanide contamination in drinking water imposes detrimental impacts on human health above their permissible limits. Hence, the quantitative detection of these colourless water-soluble toxins has attracted attention. Even though a plethora of chemosensors have been reported so far for the detection of fluoride and cyanide from various matrices, still their applicability is limited to a few examples. Nevertheless, recent advances in the syntheses of coumarin derivatives have shown significant impact on fluoride and cyanide detection. Therefore, this present review provides a brief overview of the application of coumarin-coupled molecular scaffolds towards the detection of perilous fluoride and cyanide along with their sensing mechanisms in order to develop more innovative, simple, sensitive, real-time responsive and cost-effective coumarin-based supramolecular chemosensors to promote next generation approaches towards the ultra-trace quantitative detection of these toxic anions.

2-Sulfanylhydroquinone Dimer as a Switchable Fluorescent Dye

A new dye was developed, the photoluminescence properties of which are controlled by a chemical reaction. The fluorescence properties of 2-sulfanylhydroquinone dimers depend on the number of hydroxyl groups that are acylated. Unprotected or monoacylated 2-sulfanylhydroquinone dimers displayed good fluorescence properties, whereas diacylated and tetraacylated 2-sulfanylhydroquinone dimers showed dramatically decreased fluorescence. A monomesylated derivative was devised, which shows good fluorescence characteristics as a switching fluorescence dye through a chemical reaction.

Coumarin-Based Small-Molecule Fluorescent Chemosensors

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

Manganese oxide-carbon quantum dots nano-composites for fluorescence/magnetic resonance (T1) dual mode bioimaging, long term cell tracking, and ROS scavenging

Multimodal long-term imaging probes with capability of extracting complementary information are highly important in biomedical engineering for disease diagnosis and monitoring of therapeutics distribution. However, most of the theranostics probes used are transient and have inherent problem of toxicity mostly related to generation of free radicals. In current study, a simple microwave assisted synthesis of multimodal imaging nanoprobe (T1 contrast in MR/fluorescence) is reported via doping carbon quantum dots into manganese oxide nanoparticles. The nanostructures were characterized by US-Vis spectroscopy, fluorescence spectroscopy, FTIR, Raman spectroscopy, TEM, XRD, AFM and XPS. The average particle size was observed to be around 20-40 nm with a height of 7-9 nm and approximate quantum yield of 0.23. The nanostructures were useful for bio imaging and cell tracking via fluorescence microscopy up to 12 generations with nominal cytotoxicity. The material was capable of scavenging free radicals from cellular microenvironment and downregulate gene expression of free radical scavenging enzymes. The material has significant relaxivity (r1) value of 3.98 mM^-1.sec^-1 at 1.5 T. It was also observed to create significant contrast with high circulation time (30 min) and renal clearance property. The histological analysis of kidney and liver sections were observed to have no significant toxicity from the nanostructure.

A coumarin based highly sensitive fluorescent chemosensor for selective detection of zinc ion

A very effective and highly sensitive fluorescent chemosensor, based on 4-hydroxycoumarin skeleton substituted by benzothiazole moiety was synthesized and investigated for the detection of zinc ion. This chemosensor displays highly selective and sensitive fluorescence enhancement to Zn²⁺ over other metal ions examined in solution and in biological systems. The detection limit for the fluorescent chemosensor 1 toward Zn²⁺ was 3.58 × 10^-8 M. A simple and efficient approach was improved for the synthesis of chemosensor 1 starting from 4-hydroxycoumarin.

A novel glucosamine-linked fluorescent chemosensor for the detection of pyrophosphate in an aqueous medium and live cells

A glucosamine-linked Cu²⁺ ensemble has been successfully developed for detection of pyrophosphate (PPi) in aqueous medium and in live MD-AMB-231 cells.