Highly selective visual sensing of copper based on fluorescence enhanced glutathione-Au nanoclusters

A Semi-Automatic Environmental Monitoring Device for Mercury and Cobalt Ion Detection

A syringe-based, semi-automatic environmental monitoring device is developed for on-site detection of harmful heavy metal ions in water. This portable device consists of a spring-embedded syringe and a polydimethylsiloxane (PDMS) membrane-based flow regulator for semi-automatic fix-and-release fluidic valve actuation, and a paper-based analytical device (PAD) with two kinds of gold nanoclusters (AuNCs) for sensitive Hg2+ and Co2+ ion detection, respectively. The thickness of the elastic PDMS membrane can be adjusted to stabilize and modulate the flow rates generated by the pushing force provided by the spring attached to the plunger. Also, different spring constants can drastically alter the response time. People of all ages can extract the fix-volume sample solutions and then release them to automatically complete the detection process, ensuring high reliability and repeatability. The PAD comprises two layers of modified paper, and each layer is immobilized with bovine serum albumin-capped gold nanoclusters (R-AuNCs) and glutathione-capped gold clusters (G-AuNCs), respectively. The ligands functionalized on the surface of the AuNCs not only can fine-tune the optical properties of the nanoclusters but also enable specific and simultaneous detection of Hg2+ and Co2+ ions via metallophilic Au+ -Hg2+ interaction and the Co2+ -thiol complexation effect, respectively. The feasibility of the device for detecting heavy metal ions at low concentrations in various environmental water samples is demonstrated. The Hg2+ and Co2+ ions can be seen simultaneously within 20 min with detection limits as low as 1.76 nm and 0.27 µm, respectively, lower than those of the regulatory restrictions on water by the US Environmental Protection Agency and the European Union. we expect this sensitive, selective, portable, and easy-to-use device to be valid for on-site multiple heavy metal ion pollution screenings in resource-constrained settings.

Umbelliferone and Its Synthetic Derivatives as Suitable Molecules for the Development of Agents with Biological Activities: A Review of Their Pharmacological and Therapeutic Potential

Umbelliferone (UMB), known as 7-hydroxycoumarin, hydrangine, or skimmetine, is a naturally occurring coumarin in the plant kingdom, mainly from the Umbelliferae family that possesses a wide variety of pharmacological properties. In addition, the use of nanoparticles containing umbelliferone may improve anti-inflammatory or anticancer therapy. Also, its derivatives are endowed with great potential for therapeutic applications due to their broad spectrum of biological activities such as anti-inflammatory, antioxidant, neuroprotective, antipsychotic, antiepileptic, antidiabetic, antimicrobial, antiviral, and antiproliferative effects. Moreover, 7-hydroxycoumarin ligands have been implemented to develop 7-hydroxycoumarin-based metal complexes with improved pharmacological activity. Besides therapeutic applications, umbelliferone analogues have been designed as fluorescent probes for the detection of biologically important species, such as enzymes, lysosomes, and endosomes, or for monitoring cell processes and protein functions as well various diseases caused by an excess of hydrogen peroxide. Furthermore, 7-hydroxy-based chemosensors may serve as a highly selective tool for Al3+ and Hg2+ detection in biological systems. This review is devoted to a summary of the research on umbelliferone and its synthetic derivatives in terms of biological and pharmaceutical properties, especially those reported in the literature during the period of 2017-2023. Future potential applications of umbelliferone and its synthetic derivatives are presented.

Ce3+ and Fe2+ co-enhanced ratiometric fluorescence probe utilizing copper nanoclusters and coumarin for sensitive assay of hydrogen peroxide and glucose

A novel ratiometric fluorescent probe was constructed for sensitive assay of hydrogen peroxide (H₂O₂) and glucose, which utilized the synergistically enhanced effects of Ce³⁺ and Fe²⁺ on copper nanoclusters (CuNCs) and coumarin. In the CuNCs-Ce³⁺/Fe²⁺-coumarin system, Ce³⁺ triggered the aggregation-induced emission phenomenon of CuNCs, and Fe²⁺ catalyzed the Fenton reaction to efficiently yield hydroxyl radical (•OH). In the presence of H₂O₂, the 625-nm red fluorescence of CuNCs was sharply quenched owing to the oxidation of CuNCs to Cu(II) by •OH, but the 460-nm blue fluorescence of 7-hydroxycoumarin from the oxidation of coumarin by •OH dramatically increased. Based on the reversible changes in two fluorescence signals, a satisfactorily ratiometric probe was constructed for H₂O₂ assay with a detection limit (LOD) of 0.6 μM accompanied by a visual color variation from red to blue. For glucose assay, this ratiometric probe gave a linear range of 3.2-160 μM and LOD of 0.96 μM owing to the oxidization of glucose to yield H₂O₂ in the presence of glucose oxidase and O₂. Overall, the newly developed ratiometric probe shows a great prospect in real applications for visual assay of H₂O₂ and glucose by our naked eyes.

A new fluorescence probe for detection of Cu+2 in blood samples: Circuit logic gate

A Fluorescence probe was designed based on 8-hydroxyquinoline chitosan silica precursor (HQCS) for selective detection of Al³⁺, Cu²⁺. The HQCS has no observable fluorescence signal, but after the addition of Al³⁺, a huge fluorescence signal appeared, and the selective quenching was absorbed after the addition of Cu²⁺. The effect of other different cations, including Cu²⁺, Mg²⁺, Ca²⁺, Pb²⁺, Zn²⁺, Hg²⁺, Ag⁺, Fe^3+, and K⁺ was studied. The addition of Cu²⁺ to the probe (HQCSAL) decreased the fluorescence very repeatable, and the variation of the fluorescence vs. Cu²⁺ was monotonic and linear. Therefore, the prepared probe was used to determine Cu²⁺ ions in real samples. The mechanism of fluorescence variation by adding cations to the probe solution was studied using the Stern-Volmer equation. Under the optimum conditions, the linear range and detection limit were 3.5-31 μM and 1 μM, respectively. The probe accuracy on the copper determination in the blood and tap waters was comparable to the ICP-OES results. The circuit logic gate mimic was designed for the fluorescence behavior of the probe constituents.

A visualized ratiometric fluorescence sensing system for copper ions based on gold nanoclusters/perovskite quantum dot@SiO2 nanocomposites

Excessive copper ions (Cu²⁺) cause serious environmental pollution and even endanger the health of organisms. Fluorescence chemosensing materials are widely used in the detection of metal ions due to their simple operation and high sensitivity. In this study, SiO₂-encapsulated single perovskite quantum dot (PQD@SiO₂) core-shell nanostructures which show strong, stable, and green fluorescence are synthesized and composited with gold nanoclusters (AuNCs) which show Cu²⁺-sensitive and red light-emitting fluorescence to obtain a visualized ratiometric fluorescence sensor (AuNCs/PQD@SiO₂) for the detection of Cu²⁺. In the visualized detection of Cu²⁺, the green fluorescence emitted from the ion-insensitive PQD@SiO₂ component is used as a reference signal and the red fluorescence emitted by ion-sensitive AuNC component is adopted as a sensing signal. In the presence of Cu²⁺, the red fluorescence is quenched whereas the green fluorescence remains stable, which results in a visualized fluorescence color change from orange-red to yellow and finally to green with increasing Cu²⁺ concentration. The significant change in the fluorescence color of AuNCs/PQD@SiO₂ in response to Cu²⁺ enables a rapid, sensitive, and visualized detection of Cu²⁺. Further accurate and sensitive ratiometric fluorescence analysis of Cu²⁺ can be accomplished by measuring the ratio of fluorescence intensities at 643 and 520 nm (I₆₄₃/I₅₂₀) at a certain Cu²⁺ level. The developed AuNCs/PQD@SiO₂-based sensor has been validated by its satisfactory application in the detection of Cu²⁺ in human serum and environmental water samples.

Fluorescent noble metal nanoclusters for contaminants analysis in food matrix

Recently, food safety issues caused by contaminants have aroused great public concern. The development of innovative and efficient sensing techniques for contaminants detection in food matrix is in urgent demand. As fluorescent nanomaterials, noble metal nanoclusters have attracted much attention because of their ease of synthesis, enhanced catalytic activity and biocompatibility, and most importantly, excellent photoluminescence property that provides promising analytical applications. This review comprehensively introduced the synthesis method of noble metal nanoclusters, and summarized the application of metal nanoclusters as fluorescent sensing materials in the detection of pollutants, including pesticides, heavy metal, mycotoxin, food additives, and other contaminants in food. The detection mechanism of pesticide residues mostly relies on the inhibition of natural enzymes. For heavy metals, the detection mechanism is mainly related to the interaction between metal ions and nanoclusters or ligands. It is evidenced that metal nanoclusters have great potential application in the field of food safety monitoring. Moreover, challenges and future trends of nanoclusters were discussed. We hope that this review can provide insights and directions for the application of nanoclusters in contaminants detection.

Gold nanoclusters: An ultrasmall platform for multifaceted applications

Gold nanoclusters (Au NCs) with a core size below 2 nm form an exciting class of functional nano-materials with characteristic physical and chemical properties. The properties of Au NCs are more prominent and extremely different from their bulk counterparts. The synthesis of Au NCs is generally assisted by template or ligand, which impart excellent cluster stability and high quantum yield. The tunable and sensitive physicochemical properties of Au NCs open horizons for their advanced applications in various interdisciplinary fields. In this review, we briefly summarize the solution phase synthesis and origin of the characteristic properties of Au NCs. A vast review of recent research work introducing biosensors based on Au NCs has been presented along with their specifications and detection limits. This review also highlights recent progress in the use of Au NCs as bio-imaging probe, enzyme mimic, temperature sensing probe and catalysts. A speculation on present challenges and certain future prospects have also been provided to enlighten the path for advancement of multifaceted applications of Au NCs.

Glutathione stabilized green-emission gold nanoclusters for selective detection of cobalt ion

A glutathione stabilized Au nanoclusters (GSH-Au NCs) was synthesized here and used to selective detection of cobalt ion. The as-prepared GSH-Au NCs had strong green light emission around 500 nm, and the features of the NCs have been systematically characterized by UV-vis absorption, X-ray photoelectronic spectroscopic, Fourier transform infrared spectroscopy and transmission electron microscope characterization. The interactions between the GSH-Au NCs and metal ions was studied, and the results indicated that the fluorescence of the GSH-Au NCs could be quenched in the presence of Co²⁺ ion at pH of 6.0. The quenching ratio was linear with the concentration of Co²⁺ ions, and the calibration curve was I₀/I = 0.1187c_co + 0.6085 in the Co²⁺ concentration ranges from 2.0 to 50.0 μM with correlation coefficient (R²) of 0.9950 and the limit of detection (LOD, 3σ) of 0.124 μM. In addition, we collected environmental water samples to test the reliability of the method and demonstrated this method is simple, rapid, and selective.

Red-emitting GSH-Cu NCs as a triplet induced quenched fluorescent probe for fast detection of thiol pollutants

Thiol compounds exist widely on the Earth and have certain significance in the fields of the circulation of the sulfur element and industrial production. However, the odor and biological toxicity of thiol compounds make them pollutants that seriously threaten the environmental safety and the living quality of human. In this study, a novel triplet induced fluorescence "turn-off" strategy was designed for the detection of thiol pollutants via a glutathione-stabilized copper nanocluster (GSH-Cu NC) probe. The as-prepared GSH-Cu NCs not only have small size and good water-solubility, but also exhibit strong red-emitting fluorescence at 630 nm, which could be quenched quantitatively with the increase of the concentration of thiol pollutants. So they were employed to detect thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), 2-mercaptoethanol (ME) and 2-(diethylamino)ethanethiol (2-AT) in a wide linear range of 1-100 μM with detection limits of 0.73 μM, 0.43 μM, 0.37 μM, and 0.69 μM, respectively. This method was successfully applied to detect the above thiol pollutants in lake water with good recoveries. Moreover, their further application was also expanded as luminous test strips based on the excellent fluorescence characteristics of GSH-Cu NCs for fast real-time detection of thiol pollutants.