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Molecular crowding was found to significantly facilitate synthesis of DNA-templated Ag nanoclusters, which offered an effective and general strategy for preparation of Ag nanoclusters with improved fluorescence emission and quantum yield.

The use of plant protein for the preparation of fluorescent gold nanoclusters (FGCs) is highly desirable owing to its abundance, low-cost, sustainability, and hypoallergenicity compared with protein from animals or microorganisms. In this work, zein, a protein derived from corn, was used as both a protecting ligand and reducing agent for FGC synthesis. Owing to the unique solubility of the protein, the zein-protected FGCs (Z-FGCs) can be separated from unreacted HAuCl4 and NaOH by simply mixing with an acidic buffer for several minutes. The Z-FGCs exhibit dual emission at 442 and 655 nm under excitation at 365 nm. Upon the introduction of Ag+/Hg2+ ions, the Z-FGC emission at 655 nm can be significantly enhanced/quenched while leaving the fluorescence at 442 nm almost unchanged. Accordingly, Z-FGCs can be employed as fluorescent ratiometric probes for the detection of Ag+/Hg2+ ions. The Z-FGC probes function well under a broad range of pH (pH 6–10) and temperatures (20–60 °C) and can thus be applied to determine Ag+/Hg2+ ions in tap water. Furthermore, the self-assembled film-forming property of zein is preserved after the FGC synthesis, which allows for the facile preparation of Z-FGC films for real-time visual sensing of Ag+/Hg2+ ions. [ABSTRACT FROM AUTHOR]

• An electrostatically confined method is developed for in-situ synthesis of CuNCs. • The preparation can be completed within 1 min without using any toxic agents. • CS-GSH-CuNCs shows much higher stability than GSH-CuNCs. • CS-GSH-CuNCs can be used as the fluorescence probe for detection of lysozyme. The fundamental challenges in application of copper nanoclusters (CuNCs) to fluorescence sensing are their poor stability, weak fluorescence intensity, and time-consuming preparation. In this work, an efficient and green method was developed by using a positively charged natural polysaccharide, chitosan (CS), as confining agent to electrostatically trap the negatively charged glutathione (GSH) as reducing-cum-protecting ligand for the in-situ synthesis of CuNCs. The synthesis can be completed within 1 min and CS-GSH-CuNCs emits intense orange fluorescence with an emission peak at 574 nm, which is much higher than that of GSH-CuNCs prepared in the absence of CS. Meanwhile, owning to both confinement and antioxidant effects of CS, CS-GSH-CuNCs shows excellent stability against time, temperature, salt, UV irradiation, and pH. Furthermore, the emission intensity of CS-GSH-CuNCs can be quenched by lysozyme (Lys) through the enzymatic hydrolysis of CS by Lys. Based on that, a fluorescence method was developed for the Lys determination with a linear range of 5–110 nM and a detection limit of 1.6 nM. Moreover, this approach shows high selectivity to Lys over various common substances in the biological environment, and thus can be used to determine Lys in human serum. [ABSTRACT FROM AUTHOR]

Fluorescence analysis has been regarded as one of the commonly used analytical methods because of its advantages of simple operation, fast response, low cost and high sensitivity. So far, various fluorescent probes, with noble metal nanoclusters, quantum dots, organic dyes and metal organic frameworks as representatives, have been widely reported. However, single fluorescent probe often suffers from some deficiencies, such as low quantum yield, poor chemical stability, low water solubility and toxicity. To overcome these disadvantages, the introduction of cyclodextrins into fluorescent probes has become a fascinating approach. This review (with 218 references) systematically covers the research progress of fluorescent composites based on cyclodextrins in recent years. Preparation strategies, fluorescence properties, response mechanisms and applications in sensing (ions, organic pollutants, bio-related molecules, temperature, pH) and bioimaging of fluorescent composites based on cyclodextrins are summarized in detail. Finally, the current challenges and future perspectives of these composites in relative research fields are discussed. [Display omitted] • Surveyed literatures about fluorescent composites based on cyclodextrins in recent years. • Discussed preparation strategies and fluorescence properties of fluorescent composites based on cyclodextrins. • Summarized applications in sensing and bioimaging of fluorescent composites based on cyclodextrins. • Outlooked challenges and future prospects of related research fields. [ABSTRACT FROM AUTHOR]

Sensitive detection of metoprolol tartrate (MPT) is extremely urgent in the therapy of cardiovascular diseases to guarantee the curative effectiveness. Herein, porous ZrO 2 was first employed as a matrix to spatially confine CuNCs (ZrO 2 @CuNCs), which simultaneously ameliorated the emission intensity and stability of CuNCs. Benefiting from the inner filter effect (IFE) and dynamic quenching effect (DQE) between ZrO 2 @CuNCs and AuNPs and the color fading of AuNPs induced by MPT, fluorometric and colorimetric methods for simple and sensitive determination of MPT were proposed. Besides, to meet the demand of convenient detection of MPT, a portable sensing platform was constructed including a dark box produced by a 3D printer and a smartphone. This method was further employed to determine MPT in human serum and urine samples with satisfactory results with the triple mode. This work is the first attempt to fabricate a multi-mode optical and portable sensor for MPT detection, which provides a novel approach for point-of-care monitoring of drugs in the treatment of diseases. [ABSTRACT FROM AUTHOR]

[Display omitted] • It is the first attempt to prepare Tb3+@GS-AgCuNCs via Tb3+-modulated AIE of BMNCs. • Tb3+@GS-AgCuNCs exhibit high fluorescence intensity and excellent stability. • An "on-off" sensing platform for anticancer drugs was designed based on the IFE. • The sensor exhibits high sensitivity and selectivity toward anticancer drugs. The development of accurate and sensitive detection methods of anticancer drugs is of significant importance because they play vital roles in biological systems. In recent years, bimetallic nanoclusters (BMNCs) incorporating the advantages of two metals have gained more and more attention, and can be widely applied in sensing applications. In this work, for the first time, we designed a sensing platform based on terbium ion (Tb3+) triggered aggregation-induced emission (AIE) of BMNCs. Tb3+ hybrid glutathione (GS) protected Ag/Cu nanoclusters (Tb3+@GS-AgCuNCs) were facilely fabricated according to the complexation reaction between Tb3+ and the carboxyl group of GS. Due to the inner filter effect (IFE), the fluorescence of Tb3+@GS-AgCuNCs decreased significantly in the presence of anticancer drugs with 6-thioguanine and methotrexate as representatives. In addition, the sensing platform was applied to monitor 6-thioguanine and methotrexate in real serum samples, indicating that it has great potential in anticancer drugs related applications. [ABSTRACT FROM AUTHOR]

Abstract: An easy prepared fluorescence turn-on and colorimetric dual channel probe was developed for rapid assay of Hg2+ ions with high sensitivity and selectivity by using poly(acrylic acid)-templated silver nanoclusters (PAA-AgNCs). The PAA-AgNCs exhibited weak fluorescence, while upon the addition of Hg2+ ions, AgNCs gives a dramatic increase in fluorescence as a result of the changes of the AgNCs states. The detection limit was estimated to be 2nM, which is much lower than the Hg2+ detection requirement for drinking water of U.S. Environmental Protection Agency, and the turn-on sensing mode offers additional advantage to efficiently reduce background noise. Also, a colorimetric assay of Hg2+ ions can be realized due to the observed absorbance changes of the AgNCs. More importantly, the method was successfully applied to the determination of Hg2+ ions in real water samples, which suggests our proposed method has a great potential of application in environmental monitoring. [Copyright &y& Elsevier]

CH/PEO-SiO 2 @Eu3+ fiber is prepared by electrospinning. Due to the fluorescence of Eu3+ complex, the film appears red under the excitation of UV-light. When the Cu2+ solution is dropped to the film, the color of the film will no longer appear red, and the fluorescence of the composite chitosan nanofibers can be quickly and sensitively quenched. [Display omitted] • CH/PEO-SiO 2 @Eu3+ nanofiber is prepared by electrospinning. • Due to the fluorescence of Eu3+ complex, the film appears red under the excitation of UV-light. • The fluorescence of the CH/PEO-SiO 2 @Eu3+ film can be quenched after Cu2+ solution is dropped on it. Trace amounts of heavy metal ions in the human body are essential for maintaining health. However, heavy metal ion excess or deficiency causes toxicity or disease. This study examines the sensitivity of luminescent europium complexes for the detection of Cu2+. Here, Eu3+ is complexed with1,10-phenanthroline (phen) and 4,4′,4-trimethyltriphenylamine (TTA) to form luminescent [Eu3+(TTA) 3 phen] complexes, encapsulated in silica (SiO 2) nanoparticles. The silica nanoparticles are then formed into a composite with a blend of chitosan and polyethylene oxide (PEO), to make electrospun nanofibers. The combination of Eu3+ complexes with SiO 2 nanoparticles doped in chitosan enhances the fluorescence performance. Photophysical measurements show that when the Cu2+ concentration is 100 μmol/L, the fluorescence of the composite chitosan nanofibers can be quickly and sensitively quenched, and that concentrations as low as 10 μmol/L Cu2+ can be detected. Furthermore, the use of chitosan and PEO to prepare the material makes these new fluorescence-based copper sensing materials suitable for Cu2+ detection in biological systems. [ABSTRACT FROM AUTHOR]

• Fluorescence emission of GSH-GNCs and BSA-GNCs is modulated by molecular crowding. • Molecular crowding triggers the aggregation-induced enhanced emission of GSH-GNCs. • Molecular crowding promotes the interaction between GSH-GNCs and protamine. • An efficient method for detection of protamine and heparin is developed. In this work, we found that the fluorescence emission and sensing performance of gold nanoclusters (GNCs) could be modulated greatly under molecular crowding environment in a ligand-dependent manner. The fluorescence emission of glutathione-protected GNCs (GSH-GNCs) can be significantly improved by molecular crowding while that of bovine serum albumin (BSA)-capped GNCs is notably weakened. Further, it was observed that molecular crowding could facilitate the interaction between GSH-GNCs and protamine, thus triggering a synergetic aggregation-induced enhanced emission (AIEE) effect. The AIEE could be suppressed by subsequent addition of heparin, allowing the development of a simple and efficient fluorescence approach for determination of protamine and heparin. The proposed method presents detection ranges of 0.7–3.0 and 0.05–2.8 μg mL−1 for protamine and heparin with the detection limits of 7.5 and 1.7 ng mL-1, respectively. This work is the first study of how molecular crowding impacts the fluorescence emission of GNCs and their interaction with biomolecules. The results indicate that the modulated properties of GNCs in crowding condition may open new prospects for the development of GNCs-based sensing methods. [ABSTRACT FROM AUTHOR]