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Green emitting copper nanoclusters (G-Cu NCs), yellow emitting Cu NCs (Y-Cu NCs), orange emitting Cu NCs (O-Cu NCs) and red emitting Cu NCs (R-Cu NCs) were prepared using chicken egg white as the stabilizer by changing the reaction conditions. This is a green, facile and cheap method to explore different color emitting CuNCs by the same precursor and stabilizers. The G-Cu NCs were employed for the detection of ethanol due to their aggregation induced emission enhancement (AIEE) effect. The fluorescence emission of Cu NCs at 526 nm under the excitation of 444 nm can be effectively enhanced in the presence of ethanol due to AIEE effect, thus realizing the quantitative determination of ethanol content in the range 5–60%. In addition, a visual dual-emission fluorescence probe with the combination of G-Cu NCs and silicon nanoparticles (Si NPs/G-Cu NCs) was designed to evaluate ethanol content conveniently and rapidly. Desirable linear relationship is observed between ratio of fluorescence intensity (I525/I441) and ethanol content under the excitation of 383 nm. Visible color transformation of this probe is observed in the ethanol content range 2–20%. Moreover, the ethanol sensing platforms were applied to the detection and evaluation of the alcohol content of liquor, and the recoveries in liquor were in the range 99.7% to 113%, broadening the applications of Cu NCs and providing a sensitive detection method for ethanol. [ABSTRACT FROM AUTHOR]

A facile method for fabricating polymer carbon dots (PCDs) with characteristic dual-emission at 570 and 620 nm by 1,8-naphthalenediol in n-propanol solvents was designed. The synthesised PCDs possessed fluorescence enhancement performance toward the water in organic solvents. Based on this peculiar phenomenon, a highly efficient fluorescent probe for water detection in organic solvents such as N,N-dimethylformamide, dimethyl sulfoxide and n-propanol was established with a wide detection range from 0 to 50%. The probe can also be utilised to determine water content in other organic solvents. The practical application was explored by studying the response of PCDs toward the water in various spirit samples. This method may offer a new way of detecting water in organic solvents by PCDs. [ABSTRACT FROM AUTHOR]

In this work, a novel naked eye and fluorescence sensor for acetylcholinesterase (AChE) determination based on copper/silver nanoclusters (Cu/Ag NCs) was developed. L‐Histidine protected Cu/Ag NCs were prepared and exhibited superior properties compared with copper nanoclusters, with the quantum yield increased from 4.3% to 13.2%. The fluorescence of Cu/Ag NCs can be easily quenched by 2‐nitro‐5‐thiobenzoate anion (TNB) owing to the inner filter effect. TNB is the product between 5′‐Dithiobis‐(2‐nitrobenzoic acid) (DTNB) and thiols. However, AChE can specially catalyze acetylthiocholine (ATCh) to hydrolyze and release biothiols (TCh). Based on this, the determination of AChE was achieved by introducing DTNB. A naked eye sensor was also constructed owing to the color change. [ABSTRACT FROM AUTHOR]

We fabricated a new and selective fluorescent sensor for the detection of citrate by employing g-C3N4 quantum dots (g-CNQDs) and MgFe layered double hydroxide (MgFe-LDH). The g-CNQDs interacted with MgFe-LDH via electrostatic interaction and the fluorescence of g-CNQDs was effectively quenched by MgFe-LDH due to inner filter effect. Upon addition of citrate, the fluorescence of the g-CNQDs was significantly enhanced, arising from the replacement of g-CNQDs by citrate because citrate competed with g-CNQDs to form more stable complexes with MgFe-LDH. Therefore, we developed a "turn-off–on" fluorescence assay method for the detection of citrate. This method enabled the selective detection of citrate with linear range of 0.5–3.0 μM and 3.0–10.0 μM with a 12.3 nM limit of detection. This method exhibited advantages including easy preparation, environmentally friendly process and rapid response toward citrate. [ABSTRACT FROM AUTHOR]

A rapid method is described for synthesis of copper nanoclusters (CuNCs) by utilizing L-histidine as the stabilizer and ascorbic acid (AA) as the reductant. The CuNCs display blue-green fluorescence with excitation/emission peaks at 390/485 nm. A sensitive fluorometric assay was worked out for determination of alkaline phosphatase (ALP) activity. If the ALP substrate p-nitrophenylphosphate (PNPP) is enzymatically hydrolyzed, it forms p-nitrophenol (PNP) which reduces the fluorescence of CuNCs because its absorption band at 410 nm overlaps the excitation peak of CuNCs at 390 nm. In addition, the amino groups and imidazole groups on the surface of CuNCs possibly form a complex with the phenol groups of PNP. This induces aggregation-induced quenching of the fluorescence of CuNCs. The fluorescent probe has a linear analytical range that extends from 0.5 mU·mL−1 to 40 mU·mL−1 and a detection limit of 45 μU·mL−1.Schematic illustration of a fluorometric assay for alkaline phosphatase (ALP) activity that uses L-histidine protected copper nanoclusters (CuNCs), aggregation-induced quenching, and the inner filter effect between PNP and CuNCs. [ABSTRACT FROM AUTHOR]

In this work, we developed a "naked-eye" colorimetric and ratiometric fluorescence probe for a very important biomarker of uric acid (UA). The method was based on the oxidation of UA by uricase to allantoin and hydrogen peroxide, and then o-Phenylenediamine (OPD) was oxidized to the yellow-colored 2,3-diaminophenazine (oxOPD) in the presence of horseradish peroxidase (HRP) and hydrogen peroxide. The fluorescence emission of glutathione functionalized Ti 3 C 2 MQDs (GSH-Ti 3 C 2 MQDs) centered at 430 nm overlaps with the UV absorption of oxOPD at 425 nm to a large extent, which facilitates fluorescence resonance energy transfer (FRET) between GSH-Ti 3 C 2 MQDs and oxOPD. With the increase of the UA concentration, the emission at 430 nm of GSH-Ti 3 C 2 MQDs is progressively quenched and the emission at 568 nm of oxOPD was gradually increased. Moreover, the probe we designed is easier to distinguish with color change by naked eye for the detection of UA. This is the first report about the determination of UA by a "naked-eye" colorimetric and ratiometric fluorescence method combining GSH-Ti 3 C 2 MQDs and uricase/HRP enzymes. This work enables assays to perform fluorescence and visual detection of biomarker in biological fluids based on Ti 3 C 2 MQDs. We established a method for "naked eye" colorimetric and ratiometric fluorescence detection of uric acid based on glutathione functionalized MXene quantum dots (GSH-Ti 3 C 2 MQDs). Image 1 • We developed a ratiometric fluorescence probe for UA based on GSH-Ti 3 C 2 MQDs and oxOPD. • OPD was oxidized to the yellow oxOPD under HRP and H 2 O 2 to realize the naked-eye detection of UA. • The ratiometric fluorescence probe had detection limit of 125 nM for UA. [ABSTRACT FROM AUTHOR]