Inhibition of α-glucosidase activity by curcumin loaded on ZnO@rGO nanocarrier for potential treatment of diabetes mellitus.

Curcumin (Cur) is an acidic polyphenol with some effects on α-glucosidase (α-Glu), but Cur has disadvantages such as being a weak target, lacking passing the blood-brain barrier and having low bioavailability. To enhance the curative effect of Cur, the hybrid composed of ZnO nanoparticles decorated on rGO was used to load Cur (ZnO@rGO-Cur). The use of the multispectral method and enzyme inhibition kinetics analysis certify the inhibitory effect and interaction mechanism of ZnO@rGO-Cur with α-Glu. The static quenching of α-Glu with both Cur and ZnO@rGO-Cur is primarily driven by hydrogen bond and van der Waals interactions. The conformation-changing ability by binding to the neighbouring phenolic hydroxyl group of Cur increased their ability to alter the secondary structure of α-Glu, resulting in the inhibition of enzyme activity. The inhibition constant (Ki, Cur > Kis,ZnO@rGO-Cur ) showed that the inhibition effect of ZnO@rGO-Cur on α-Glu was larger than that of Cur. The CCK-8 experiments proved that ZnO@rGO nanocomposites have good biocompatibility. These results suggest that the therapeutic potential of ZnO@rGO-Cur composite is an emerging nanocarrier platform for drug delivery systems for the potential treatment of diabetes mellitus.

Rapid, one-pot, protein-mediated green synthesis of water-soluble fluorescent nickel nanoclusters for sensitive and selective detection of tartrazine.

In the work, water-soluble bovine serum albumin-protected fluorescent nickel nanoclusters (BSA-NiNCs) are used as fluorescent probes to construct a label-free fluorescence quenching sensor for sensitive and selective detection of tartrazine. The fluorescent BSA-NiNCs are synthesized in one pot using BSA as both the template and reducing agent, and hydrogen peroxide as the additive. The as-prepared NiNCs are characterized by using various analytical techniques like transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-Vis absorption spectroscopy, circular dichroism spectroscopy, and fluorescence spectroscopy. The synthesized BSA-NiNCs have a quantum yield of ca. 8% by using quinine sulfate as a standard. The sensor for tartrazine detection shows a wide linear range of 0.01-3.5 µM, with a low detection limit of 4 nM. The fluorescence quenching very likely results from the combination of the intermolecular interactions and the secondary inner filter effect between BSA-NiNCs and tartrazine. Then, the proposed sensor is successfully employed for tartrazine detection in drink samples, and the results are comparable with those based on a reference HPLC method.

Green synthesis of luminescent graphitic carbon nitride quantum dots from human urine and its bioimaging application.

A hydrothermal synthetic approach is developed for the preparation of graphitic carbon nitride quantum dots (g-C3N4 QDs) from human urine. The reported synthetic method is green, simple, low-cost, less time-consuming, and can be used for the large-scale production of the g-C3N4 QDs. The as-prepared g-C3N4 QDs possess a high quantum yield of 15.7% by using quinine sulfate as a reference, and display excitation-wavelength dependent fluorescent emission. In addition, the g-C3N4 QDs exhibit high photostability, low cytotoxicity. and are successfully used as fluorescent probes for cell multicolor imaging. It is believed that the valuable nanomaterials, g-C3N4 QDs, which are transformed from the human bodily wastes, are promising in diverse chemical applications.

Label-free photoluminescence assay for nitrofurantoin detection in lake water samples using adenosine-stabilized copper nanoclusters as nanoprobes.

In this paper, we constructed a novel label-free analytical strategy for highly sensitive and selective detection of nitrofurantoin (NFT) based on adenosine-stabilized copper nanoclusters (CuNCs) as nanoprobes. It was found that NFT caused a rapid decrease in the photoluminescence intensity of CuNCs. The photoluminescence quenching was likely attributed to the inner filter effect between NFT and CuNCs. The CuNCs exhibited a wide linear range of 0.05-4.0µM with the detection limit of 30nM (7.1ngmL-1) for detection of NFT. And it was successfully applied for NFT detection in lake water samples.

Enhancing sensitivity and selectivity in a label-free colorimetric sensor for detection of iron(II) ions with luminescent molybdenum disulfide nanosheet-based peroxidase mimetics.

In the present study, we demonstrated that the luminescent molybdenum disulfide (MoS2) nanosheets, which were prepared hydrothermally by using sodium molybdate and thiourea as precursors, possessed peroxidase-like activity, and could catalyze the oxidation of peroxidase substrate o-phenylenediamine (OPD) in the presence of hydrogen peroxide (H2O2) to produce a yellow color reaction. Further addition of Fe(2+) into the nanosheets led to peroxidase mimetics with greatly enhanced catalytic activity. The observation was exploited to develop a label-free colorimetric nanozyme sensor for detection of Fe(2+). The fabricated MoS2/OPD/H2O2 sensor showed a wide linear range of 0.01-0.8 µM with a detection limit of 7 nM. Moreover, it was found that the MoS2/OPD/H2O2 sensor displayed enhanced sensitivity and selectivity toward Fe(2+) compared with the OPD/H2O2 sensor, suggesting that the MoS2 nanosheets could improve the performance of the Fe(2+) sensor. An advanced chemometrics algorithm, multivariate curve resolution by alternating least squares (MCR-ALS), was further applied to interpret the origin of enhancing sensitivity and selectivity in the Fe(2+) sensor with the MoS2 nanosheets. The time-dependent UV-vis spectral data of the studied systems were collected, and submitted to the MCR-ALS. The results showed that the increased sensitivity and selectivity of the MoS2/OPD/H2O2 sensor for Fe(2+) detection likely arose from its large reaction rate constant. Finally, the proposed MoS2/OPD/H2O2 sensor was successfully applied for detection of Fe(2+) in water samples.

Fluorescence analysis of 6-mercaptopurine with the use of a nano-composite consisting of BSA-capped Au nano-clusters and core-shell Fe3O4-SiO2 nanoparticles.

A magnetic and fluorescent nano-composite was prepared. It comprised of a core of Fe3O4 nanoparticles (NPs), a silica shell and satellitic Au nano-clusters (AuNCs) capped with bovine serum albumin (BSA). This nano-composite has many desirable properties, e.g. magnetism, red emission, high water solubility, and high resistance to photo-bleaching. On addition of the analyte, 6-mercaptopurine (6-MP) or indeed other similar thiols, AuNCs formed aggregates because the existing cross-links within the Fe3O4 NPs@SiO2 and AuNC structure were broken in favor of the gold-thiol bonds. On suitable irradiation of such aggregates, red fluorescence was emitted at 613 nm. It decreased significantly as a function of the added 6-MP concentration, and the quenching ratio (F0 - F) / F0 was related linearly to the concentration of 6-MP in the range of 0.01 to 0.5 µmol L(-1). The detection limit was 0.004 µmol L(-1) (S/N=3). The method was strongly selective for 6-MP in the presence of oxidants, phenols, heavy-metal ions, and especially bio-thiols.

Differentiation of mint (Mentha haplocalyx Briq.) from different regions in China using gas and liquid chromatography.

In this study, complex substances such as Mint (Mentha haplocalyx Briq.) samples from different growing regions in China were analyzed for phenolic compounds by high-performance liquid chromatography with diode array detection and for the volatile aroma compounds by gas chromatography with mass spectrometry. Chemometrics methods, e.g. principal component analysis, back-propagation artificial neural networks, and partial least squares discriminant analysis, were applied to resolve complex chromatographic profiles of Mint samples. A total of 49 aroma components and 23 phenolic compounds were identified in 79 Mint samples. Principal component analysis score plots from gas chromatography with mass spectrometry and high-performance liquid chromatography with diode array detection data sets showed a clear distinction among Mint from three different regions in China. Classification results showed that satisfactory performance of prediction ability for back-propagation artificial neural networks and partial least squares discriminant analysis. The major compounds that contributed to the discrimination were chlorogenic acid, unknown 3, kaempherol 7-O-rutinoside, salvianolic acid L, hesperidin, diosmetin, unknown 6 and pebrellin in Mint according to regression coefficients of the partial least squares discriminant analysis model. This study indicated that the proposed strategy could provide a simple and rapid technique to distinguish clearly complex profiles from samples such as Mint.

Automated headspace solid-phase microextraction and on-fiber derivatization for the determination of clenbuterol in meat products by gas chromatography coupled to mass spectrometry.

A method was developed for the determination of clenbuterol in meat using stable-isotope-dilution gas chromatography with mass spectrometry coupled with solid-phase microextraction and on-fiber derivatization. The samples were first homogenized with hydrochloric acid followed by protein deposition. After headspace solid-phase microextraction and on-fiber derivatization, the content of clenbuterol was measured with the aid of stable-isotope dilution. The condition of solid-phase microextraction was optimized by central composite design. The relative standard deviations, limit of detection, and recoveries for clenbuterol were 4.2-9.2%, 0.48 µg/kg, and 96-104%, respectively. The proposed method was satisfactory for analysis of real samples as compared with the Chinese standard method.

Molybdenum disulfide quantum dots as a photoluminescence sensing platform for 2,4,6-trinitrophenol detection.

Transition metal chalcogenides, especially molybdenum disulfide (MoS2), have recently attracted wide attention from researchers as graphene-analogous materials. However, until now, little literature has reported the synthesis of photoluminescent MoS2 materials and their applications in analytical chemistry. We herein presented a facile bottom-up hydrothermal route for the synthesis of photoluminescent MoS2 quantum dots (QDs) by using sodium molybdate and cysteine as precursors. The prepared MoS2 QDs were characterized by transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, photoluminescence spectroscopy, and UV-vis spectroscopy. The MoS2 QDs were then used as photoluminescent probes to construct a photoluminescence (PL) quenching sensor for detection of 2,4,6-trinitrophenol (TNP). The TNP sensor presented a wide linear range from 0.099 to 36.5 µM with a high detection limit of 95 nM. Furthermore, the sensor displayed a high sensitivity toward TNP over other structurally similar compounds like 2,4,6-trinitrotoluene, p-chlorophenol, phenol, and 2,6-di-tert-butyl-4-methylphenol. To understand the origin of the high sensitivity, we assessed the emission wavelength-dependent PL quenching behavior of MoS2 QDs by the above five compounds using Stem-Volmer equation in detail. The results showed that the novel approach we put forward can satisfactorily explain the interaction mechanisms between MoS2 QDs and the five compounds, and the high sensitivity for TNP very likely originated from a combination of the PL resonance energy transfer, electronic energy transfer, and electrostatic interactions between MoS2 QDs and TNP. Finally, the sensor was successfully applied for detection of TNP in water samples and test papers.

Competitive interactions of anti-carcinogens with serum albumin: a spectroscopic study of bendamustine and dexamethasone with the aid of chemometrics.

Interactions between the anti-carcinogens, bendamustine (BDM) and dexamethasone (DXM), with bovine serum albumin (BSA) were investigated with the use of fluorescence and UV-vis spectroscopies under pseudo-physiological conditions (Tris-HCl buffer, pH 7.4). The static mechanism was responsible for the fluorescence quenching during the interactions; the binding formation constant of the BSA-BDM complex and the binding number were 5.14×10(5)Lmol(-1) and 1.0, respectively. Spectroscopic studies for the formation of BDM-BSA complex were interpreted with the use of multivariate curve resolution - alternating least squares (MCR-ALS), which supported the complex formation. The BSA samples treated with site markers (warfarin - site I and ibuprofen - site II) were reacted separately with BDM and DXM; while both anti-carcinogens bound to site I, the binding constants suggested that DXM formed a more stable complex. Relative concentration profiles and the fluorescence spectra associated with BDM, DXM and BSA, were recovered simultaneously from the full fluorescence excitation-emission data with the use of the parallel factor analysis (PARAFAC) method. The results confirmed that on addition of DXM to the BDM-BSA complex, the BDM was replaced and the DXM-BSA complex formed; free BDM was released. This finding may have consequences for the transport of these drugs during any anti-cancer treatment.

Simultaneous kinetic spectrometric determination of three flavonoid antioxidants in fruit with the aid of chemometrics.

A simple, inexpensive and sensitive kinetic spectrophotometric method was developed for the simultaneous determination of three anti-carcinogenic flavonoids: catechin, quercetin and naringenin, in fruit samples. A yellow chelate product was produced in the presence neocuproine and Cu(I) - a reduction product of the reaction between the flavonoids with Cu(II), and this enabled the quantitative measurements with UV-vis spectrophotometry. The overlapping spectra obtained, were resolved with chemometrics calibration models, and the best performing method was the fast independent component analysis (fast-ICA/PCR (Principal component regression)); the limits of detection were 0.075, 0.057 and 0.063 mg L(-1) for catechin, quercetin and naringenin, respectively. The novel method was found to outperform significantly the common HPLC procedure.

Glassy carbon electrodes modified with gold nanoparticles for the simultaneous determination of three food antioxidants.

Electrochemical behavior of three antioxidants: butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and butylated hydroquinone (TBHQ), was investigated at a glassy carbon electrode modified with gold nanoparticles (AuNPs/GCE). This electrode was characterized by scanning electron microscopy (SEM). The experimental results indicated that the modified electrode was strongly electroactive during the redox reactions of BHA, BHT and TBHQ, and this was confirmed by the observed increased redox peak currents and shifted potentials; in addition, the oxidation products of BHA and TBHQ were found to be the same. The experimental conditions were optimized and the oxidation peaks of BHA and BHT were clearly separated. Based on this, an electrochemical method was researched and developed for the simultaneous determination of BHA, BHT and TBHQ in mixtures with the use of first derivative voltammetry; the linear concentration ranges were 0.10-1.50 µg mL(-1), 0.20-2.20 µg mL(-1) and 0.20-2.80 µg mL(-1), and detection limits were 0.039, 0.080 and 0.079µgmL(-1), for BHA, BHT and TBHQ, respectively. The proposed method was successfully applied for the analysis of the three analytes in edible oil samples.

Voltammetric investigation of DNA damage induced by nitrofurazone and short-lived nitro-radicals with the use of an electrochemical DNA biosensor.

Electrochemical behavior of nitrofurazone (NFZ) was investigated with the use of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. The pH-dependence of NFZ was studied at a glassy carbon electrode (GCE) in ethanol/Britton-Robinson buffer (30:70), and short-lived nitro-radicals were generated by the reduction of NFZ at high pHs (>7.0). In the presence of DNA, the DPV peak current of NFZ decreased and the peak potential shifted negatively, which indicated that there was an electrostatic interaction between NFZ and DNA. An electrochemical dsDNA/GCE biosensor was prepared to study the DNA damage produced in the presence NFZ; this process was followed with the use of the Co(phen)(3)(2+) electroactive probe. Also, the oxidation peaks of guanosine (750 mV) and adenosine (980 mV) indicated that DNA damage was related directly to the nitro-radicals. Experiments demonstrated that DNA damage occurred via two different steps while NFZ was metabolized and nitro-radicals were produced. Novel work with AFM on the NFZ/DNA interaction supported the suggestion that in vivo, the nitro-radicals were more cytotoxic than the NFZ molecules. A linear DPV calibration plot was obtained for NFZ analysis at a modified dsDNA/GCE (concentration range: 2.50 × 10(-6)-3.75 × 10(-5) mol L(-1); limit of detection: 8.0 × 10(-7) mol L(-1)), and NFZ was determined successfully in pharmaceutical samples.

One- and two-dimensional gas chromatography-mass spectrometry and high performance liquid chromatography-diode-array detector fingerprints of complex substances: a comparison of classification performance of similar, complex Rhizoma Curcumae samples with the aid of chemometrics.

Many complex natural or synthetic products are analysed either by the GC-MS (gas chromatography-mass spectrometry) or HPLC-DAD (high performance liquid chromatography-diode-array detector) technique, each of which produces a one-dimensional fingerprint for a given sample. This may be used for classification of different batches of a product. GC-MS and HPLC-DAD analyses of complex, similar substances represented by the three common types of the TCM (traditional Chinese medicine), Rhizoma Curcumae were analysed in the form of one- and two-dimensional matrices firstly with the use of PCA (Principal component analysis), which showed a reasonable separation of the samples for each technique. However, the separation patterns were rather different for each analytical method, and PCA of the combined data matrix showed improved discrimination of the three types of object; close associations between the GC-MS and HPLC-DAD variables were observed. LDA (linear discriminant analysis), BP-ANN (back propagation-artificial neural networks) and LS-SVM (least squares-support vector machine) chemometrics methods were then applied to classify the training and prediction sets. For one-dimensional matrices, all training models indicated that several samples would be misclassified; the same was observed for each prediction set. However, by comparison, in the analysis of the combined matrix, all models gave 100% classification with the training set, and the LS-SVM calibration also produced a 100% result for prediction, with the BP-ANN calibration closely behind. This has important implications for comparing complex substances such as the TCMs because clearly the one-dimensional data matrices alone produce inferior results for training and prediction as compared to the combined data matrix models. Thus, product samples may be misclassified with the use of the one-dimensional data because of insufficient information.

Using fast gas chromatography-mass spectrometry with auto-headspace solid-phase microextraction to determine ultra trace residues of organophosphorus pesticides in fruits.

Organophosphorus pesticides (OPs) in apple and tomato were determined by using fast gas chromatography-mass spectrometry (FGC-MS) coupled with auto-headspace solid-phase microextraction (SPME). The experimental conditions of FGC were investigated and developed. Three different fibers were studied and compared and it was found that the polydimethysiloxane (PDMS) was the best. Factors affecting the extract efficiency, such as extraction time, temperature, ion strength, agitator speed, and content of organic solvents, were investigated and optimized. The limits of detection (LOD) of OPs were achieved between 0.002 ng/g and 0.955 ng/g; the RSD was less than 20.9%, and the recoveries were from 79% to 117%. For most commercial fruit samples, ultra trace residues of OPs were found, mainly on the surface, and their concentrations were generally lower than LOD of conventional methods.

Simultaneous determination of iron and aluminium by differential kinetic spectrophotometric method and chemometrics.

A differential kinetic spectrophotometric method was researched and developed for the simultaneous determination of iron and aluminium in food samples. It was based on the direct reaction kinetics and spectrophotometry of these two metal ions with Chrome Azurol S (CAS) in ethylenediamine-hydrochloric acid buffer (pH 6.3). The results were interpreted with the use of chemometrics. The kinetic runs and the visible spectra of the complex formation reaction were studied between 540 and 750 nm every 30 s over a total period of 285 s. A set of synthetic metal mixture samples was used to build calibrations models. These were based on the spectral and kinetic two-way data matrices, which were processed separately by the radial basis function-artificial neural network (global RBF-ANN) method. The prediction performance of these models was poorer than that from the combined kinetic-spectral three-way array, which was similarly processed by the same method (% relative prediction error (RPE(T))=5.6). These results demonstrate that improved predictions can be obtained from the data array, which has more information, and that appropriate chemometrics methods can enhance analytical performance of simple techniques such as spectrophotometry. Other chemometrics models were then applied: N-way partial least squares (NPLS), parallel factor analysis (PARAFAC), back propagation-artificial neural network (BP-ANN), single radial basis function-artificial neural network (RBF-ANN), and principal component neural network (PC-RBF-ANN). There was no substantial difference between the methods with the overall %RPE(T) range being 5.0-5.8. These two values corresponded to the NPLS and BP-ANN models, respectively. The proposed method was applied for the determination of iron and aluminium in some commercial food samples with satisfactory results.

Simultaneous enzymatic kinetic determination of pesticides, carbaryl and phoxim, with the aid of chemometrics.

A sensitive and selective enzymatic kinetic method for the simultaneous determination of mixtures of carbaryl and phoxim pesticides was researched and developed. It was based on the inhibitory effect of the pesticides on acetylcholinesterase (AChE), and the use of 5,5'-dithiobis(2-nitrobenzoic) acid (DTNB) as a chromogenic reagent for the thiocholine iodide (TChI) released from the acetylthiocholine iodide (ATChI) substrate. The DTNB-thiocholine reaction was investigated by a spectrophotometric-kinetic approach. The complex rate equation for the formation of the chromogenic product, P, was solved under certain experimental conditions, which enabled the absorbance (A(P), at lambda(max)=412 nm) from the mixtures of the two pesticide inhibitors to be directly related to their concentrations provided the absorbance additivity was followed. The spectra were measured for mixtures of carbaryl and phoxim at different concentrations, and at t=904 s, T=35 degrees C, pH=7.5, c(ATChI)=0.14, and c(AChE)=0.10 mg mL(-1). The detection limits of the enzymatic kinetic spectrophotometric procedures for the determination of the carbaryl and phoxim were 4.7 and 0.59 microg L(-1), respectively. Calibration models for chemometrics methods, such as principal component regression (PCR), partial least squares (PLS) and radial basis function-artificial neural network (RBF-ANN) were constructed and verified with synthetic samples of the mixtures of the two pesticides. The best performing model was based on the RBF-ANN method yielding at approximately 10 ppb analyte concentrations, %RPE(T) (carbaryl=5.2; phoxim=6.5), %Recovery (approx.105%) and %RPE(T) (6.5). Various spiked town-water samples produced recoveries in the range of 98.8-103% for each pesticide.