Green emitting carbon dots for sensitive fluorometric determination of cartap based on its aggregation effect on gold nanoparticles.

A fluorometric method was developed for the determination of the insecticide cartap. It is based on the use of green emitting carbon dots (CDs) and gold nanoparticles (Au NPs). The CDs were prepared from phenol and ethylene diamine by a hydrothermal route. They have excitation/emission maxima at 410/513 nm) and a fluorescence quantum yield of 29%. They were characterized by TEM, Raman, XRD, XPS, FT-IR, UV and fluorescence spectroscopies. The green fluorescence of the CDs is strongly reduced by the red-colored Au NPs because of an inner filter effect. Upon addition of cartap, it will cause the aggregation of the Au NPs owing to Au-N interaction between Au NPs and cartap to form purple colored aggregates with spectra that do not overlap the green emission of the CDs. Hence, their fluorescence is restored. Under optimum conditions, the method allows for the quantitation of cartap in the 5-300 nM concentration range, and the detection limit is 3.8 nM. The method was successfully applied to the determination of cartap in spiked real samples and gave satisfactory results. Graphical abstract Schematic presentation of green emitting carbon dots for sensitive fluorometric determination of cartap based on its aggregation effect on gold nanoparticles.

In-situ growth of gold nanoparticles on a 3D-network consisting of a MoS2/rGO nanocomposite for simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid.

A glassy carbon electrode was modified with a 3D-networked nanostructure composed of MoS2, reduced graphene oxide and gold nanoparticles (3D-MoS2/rGO/Au). The composites were prepared through in-situ growth of gold nanoparticles on 3D-MoS2/rGO nanosheets via a hydrothermal method. The morphology and electrochemical features of the composite were investigated. The 3D-MoS2/rGO/Au sensor exhibits excellent electrocatalytic activity for simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The oxidation potentials are well separated at around -0.05 V for AA, 0.06 V for DA and 0.2 V for UA, respectively. The detection limits for individual detection and simultaneous detection (S/N = 3) are 0.93 µM and 1.46 µM for AA, 0.11 µM and 0.15 µM for DA, and 0.74 µM and 0.29 µM for UA. The method was applied to the quantitative analysis of AA, DA, and UA in spiked serum samples with satisfying results. Graphical abstract In-situ growth of gold nanoparticles on 3D-networked MoS2/rGO nanocomposite for individual and simultaneous determination of ascorbic acid, dopamine and uric acid.

Multi-factor analysis of the quality of cellar mud of Luzhou-flavor liquor in Yibin production area.

The aim of this study was to conduct a thorough scientific investigation into the similarities and differences in the quality of the cellars of different Luzhou-flavor liquor wineries in Yibin production area and the reasons for them. This study analyzed cellar mud samples from five wineries in Yibin production area. The analysis of volatile flavor compounds was carried out using headspace solid-phase microextraction and gas chromatography-mass spectrometry. The bacterial and archaeal community structures and their correlations were analyzed by high-throughput sequencing. The study indicates that the Distillery A had the highest levels of ammonium nitrogen and effective phosphorus, Distillery F had the highest humus levels, and Distillery I had the highest pH levels. The community structure of the principal bacterial and archaeal communities in the five subterranean clays exhibited similarity, and all samples were dominated by Firmicutes as the primary bacterial group. However, there was variation in bacterial abundance. The cellar mud also has obvious regional differences, and there are three genera of differentially dominant archaea in the archaea. In summary, significant differences were observed in the physicochemical indexes of bacterial and archaeal abundance across all five samples. These differences led to variations in both the content and composition of volatile constituents.

Fluorescent and colorimetric dual-readout sensor based on Griess assay for nitrite detection.

In this work, we presented a sensitive and selective colorimetric and fluorescent dual-readout sensor based on Griess assay for nitrite (NO2-) detection under acidic condition. The sensor system was constituted of acid-resistant carbon quantum dots (CQDs) and 3-aminophenol (3-Aph) with acidic condition regulated using HCl. During the sensing procedure, reaction of 3-Aph and NO2- under acidic condition can yield a yellow-colored azoic compound (AZO), which gives the colorimetric readout; meanwhile, the fluorescence of CQDs (fluorescence reporter) quenched due to the strong absorption of AZO, leading to fluorescent readout. Wherein, CQDs were synthesized via hydrothermal method through using polyacrylamide as precursor and characterized by AFM, XRD and XPS. Under the optimized condition, the sensor exhibit broad linear relationships towards NO2- in the range of 10 to 100 nM and 2.5 to 100 µM, with practical detection limits of 10 nM and 2.5 µM for the fluorescent and colorimetric readout, respectively. And the sensor displayed excellent capability of selectivity according to interferences study. Furthermore, testing of sprouts, bacon and ham sausage real samples demonstrated good recoveries and reproducibility of the sensor system. All these results suggested the presented colorimetric and fluorescent dual-readout sensor can be a promising candidate for the NO2- detection in real applications.

Simple and sensitive fluorescence sensor for methotrexate detection based on the inner filter effect of N, S co-doped carbon quantum dots.

Reliable and simple detection methods for chemotherapeutic agent contaminants, such as methotrexate, are required to minimize their possible toxic threat. However, detecting them remains a challenging in environmental and biological analysis. Here, we developed a fluorescent N, S co-doped carbon quantum dots (N, S co-doped CQDs) probe to detect methotrexate on the basis of the inner filter effect of fluorescence. Under optimized conditions, the fluorescent probe exhibits high sensitivity and specific selectivity with a linear detection range from 0.4 µg/mL to 41.3 µg/mL and a low detection limit of 12 ng/mL (S/N = 3). Further, this N, S co-doped CQDs fluorescent probe can be used to analyze extracellular fluids and wastewater samples satisfactorily, thereby showing a remarkable potential for broad applications in biological molecule determination and environmental analysis.

An enzyme-free sensitive electrochemical microRNA-16 biosensor by applying a multiple signal amplification strategy based on Au/PPy-rGO nanocomposite as a substrate.

In present study, a sensitive and effective electrochemical microRNA (miRNA) sensing platform is successfully developed by integrating gold nanoparticles/polypyrrole-reduced graphene oxide (Au/PPy-rGO), catalyzed hairpin assembly (CHA) and hybridization chain reaction (HCR) multiple signal amplification strategy. Firstly, Au/PPy-rGO was employed onto a bare GCE by electrodeposition that can greatly enhanced conductivity and effectively immobilize probes. Then, the thiolated capture probes (SH-CP) were self-assembled on the Au/PPy-rGO modified GCE via Au-S bond. The target miRNA triggered the dynamic assembly of the two hairpin substrates (H1 and H2), leading to the cyclicality of the target miRNA and the formation of H1-H2 complexes without the assistance of enzyme. Subsequently, the newly emerging DNA fragment of H2 triggered the HCR when a mixture solution (hairpins H3 and H4) and produced dsDNA polymers. Finally, a substantial amount of methylene blue (MB) as signal indicator was intercalated into the minor groove of the long dsDNA polymers to achieve detected electrochemical signal. The fabricated sensor is able to detect miRNA-16 (model target) with concentration range from 10 fM to 5 nM with a low detection limit (LOD) of 1.57 fM (S/N = 3). Current research suggests that the developed multiple signal amplification platform has a great potential for the applications in the field of biomedical research and clinical analysis.