Accurate ethanol determination in Chinese Baijiu based on red-emitted carbon quantum dots (CQDs) and a simple pH correction.

The quality control of Baijiu is necessary including ethanol content. In this work, red-emitted carbon quantum dots based on p-phenylenediamine (PPD-CQDs) were fabricated for accurate determination of ethanol in Baijiu. The good linear response of PPD-CQDs to ethanol-water solution (E-Ws; 20-80 vol%) offered the potential for ethanol determination in practice. However, further application of this procedure to Baijiu resulted in a certain deviation. After excluding interference from most of the ingredients involved, a simple pH correction on Baijiu made application of the process practicable. The red-emission of PPD-CQDs supported analysis of Baijiu with different flavors and ethanol monitoring. Therefore, a quick-response fluorescence method was established for Baijiu ethanol determination; this method can be applied to the many varieties of Chinese Baijiu available and also has potential for use in other alcoholic beverages.

A smart ratiometric fluoresence and colorimetry dual-responsive sensor for morin determination based on the complex between carbon quantum dots and polyethyleneimine.

As a representative flavonoid, morin exhibits multi-biological activities, but its abuse endangers human health. Developing advanced technology for morin determination is urgently needed. In this study, a dual-responsive approach was reported for morin based on the complexing of carbon quantum dots (CQDs) and polyethyleneimine (PEI). The CQDs were fabricated via an improved hydrothermal method employing tyrosine and malic acid. Binding with PEI induced an 8-fold emission enhancement and a slight red-shift to 445 nm of CQDs because of the complexing of PEI and CQDs. Further morin introduction led to the blue emission (445 nm) quenching of CQDs-PEI and a yellow emission (560 nm) generation, which contributed a ratiometric fluorescence approach for morin determination between 2.0 and 32 µM, with a limit of detection (LOD) of 45 nM. Meanwhile, under sunlight the color of CQDs-PEI became yellow upon morin addition, which developed a colorimetric method for morin determination in a wide range between 2.0 and 100 µM (LOD = 69 nM). The developed dual-responsive method either displayed accurate results for morin in diluted human and bovine serum, being potential for actual sample analysis. Finally, a visual detection based on the smartphone was constructed and applied for the real-time determination of morin.

High sensitive ratiometric fluorescence analysis of trypsin and dithiothreitol based on WS2 QDs.

In this paper, a simple tungsten disulfide quantum dots (WS2 QDs)-based ratiometric fluorescence method was established for the detection of trypsin and 1, 4-dithiothreitol. Trypsin can hydrolyze cytochrome c into heme-peptide fragments with peroxidase-like activity. In the presence of hydrogen peroxide, the fragments can generates hydroxyl radicals, which can oxidize o-phenylenediamine (OPD) to form 2,3-diaminophenazine (DAP) with a fluorescence peak at 568 nm. DAP can quench the fluorescence of WS2 QDs at 448 nm via fluorescence resonance energy transfer (FRET). When 1, 4-dithiothreitol was present, it can react with hydroxyl radicals, and less OPD was oxidized, which accompanied by the fluorescence intensity of WS2 QDs increased and the fluorescence intensity of DAP decreased. Therefore, the fluorescence intensity ratio (F568/F448) can be used to monitor trypsin and 1, 4-dithiothreitol. A good linear calibration between fluorescence intensity ratio F568/F448 versus trypsin activity and1, 4-dithiothreitol concentration were obtained within 0.2-140 µg mL-1 and 20-200 µmol L-1, respectively. And the detection limit was 0.09 µg mL-1 for trypsin and 6.8 µmol L-1 for 1, 4-dithiothreitol, respectively. Furthermore, the developed ratiometric fluorescence method was successfully applied for trypsin and 1, 4-dithiothreitol assay in human serum samples.

A label-free fluorescent sensor based on silicon quantum dots-MnO2 nanosheets for the detection of α-glucosidase and its inhibitor.

α-Glucosidase and its inhibitors play a key role in diagnosis and treatment of diabetes. In the present work, we established a facile, sensitive and selective fluorescence method based on silicon quantum dots (SiQDs) and MnO2 nanosheets for the determination of α-glucosidase and one of its inhibitors acarbose. The fluorescence of SiQDs was greatly quenched by MnO2 nanosheets due to the inner filter effect. α-Glucosidase could easily catalyze the hydrolysis of l-ascorbic acid-2-O-α-d-glucopyranosyl (AAG) to produce ascorbic acid (AA), which could reduce MnO2 nanosheets to Mn2+, resulting in dramatic recovery of the fluorescence of SiQDs. The proposed sensing platform could provide a good linear relationship between the fluorescence intensity of SiQDs and the concentration of α-glucosidase in the range of 0.02-2.5 U mL-1 with a detection limit of 0.007 U mL-1. In addition, the sensing platform could be used for α-glucosidase inhibition. Acarbose was one of the most common and typical inhibitors, and this sensing platform can be utilized to detect acarbose in the range of 1-1000 µM. The developed fluorescence method was successfully validated for the determination of α-glucosidase in human serum samples.

Fluorometric determination of the activity of alkaline phosphatase based on a system composed of WS2 quantum dots and MnO2 nanosheets.

A fluorometric method is described for the detection of alkaline phosphatase (ALP) activity. It is based on the use of the product of hydrolysis of the drug amifostine (a thiophosphoester) by ALP. It is known that MnO2 nanosheets quench the blue fluorescence of tungsten disulfide quantum dots (WS2 QDs) which have excitation/emission wavelengths of 320/448 nm. However, in the presence of ALP and amifostine, the product of hydrolysis [2-(3-aminopropylamino)ethanethiol] triggers the decomposition of the MnO2 nanosheets. This results in the recovery of fluorescence. Based on this finding, an assay for ALP activity was developed that works in the 0.09-1.6 U L-1 range, with a 40 mU L-1 detection limit. The relative standard deviation is 1.87% for five repeated measurements of 0.8 U L-1 ALP. The method was applied to the analysis of ALP in real samples and gave satifactory results. Graphical abstractSchematic representation of a fluorometric method for determination of the activity of alkaline phosphatase (ALP). The fluorescence of a system composed of WS2 quantum dots and MnO2 nanosheets is quenched. Hydrolysis of the cytoprotective adjuvant amifostine (a phosphothioester) by ALP leads to a thiol that causes the decomposition of the MnO2 nanosheets. As a result, the blue fluorescence of the system becomes increasingly restored.

Fluorometric determination and intracellular imaging of cysteine by using glutathione capped gold nanoclusters and cerium(III) induced aggregation.

A turn-on fluorometric method is described for selective and sensitive detection of cysteine (Cys). Gold nanoclusters (Au NCs) capped with glutathione (GSH) are used as a fluorescent probe. If Ce3+ ion are present, they will bind to the carboxy groups of the GSH-capped Au NC. This results in aggregation-induced emission enhancement (AIEE), best measured at excitation/emission wavelengths of 360/575 nm. On addition of Cys, which has less steric hindrance compared with GSH and higher affinity for Ce3+, it will bind to Ce3+ through the carboxyl group and link with Au NCs via Au-S bond. Hence, the AIEE is increased and Cys can be quantified via this effect with a linear response in the 0.4-120 µmol L-1 Cys concentration range and a detection limit of 0.15 µmol L-1. Graphical abstract Schematic presentation of cysteine detection via the Ce3+-triggered aggregation of glutathione capped gold nanoclusters which leads to increased yellow fluorescence.