MOF-based Ag NPs/Co3O4 nanozyme for colorimetric detection of thiophanate-methyl based on analyte-enhanced sensing mechanism.

Silver nanoparticles supported on metal-organic framework (ZIF-67)-derived Co3O4 nanostructures (Ag NPs/Co3O4) were synthesized via a facile in situ reduction strategy. The resulting materials exhibited pH-switchable peroxidase/catalase-like catalytic activity. Ag NP doping greatly enhanced the catalytic activity of Ag NPs/Co3O4 towards 3,3',5,5'-tetramethylbenzidine (TMB) oxidation and H2O2 decomposition which were 59 times (A652 of oxTMB) and 3 times (A240 of H2O2) higher than that of ZIF-67, respectively. Excitingly, thiophanate-methyl (TM) further enhanced the peroxidase-like activity of Ag NPs/Co3O4 nanozyme due to the formation of Ag(I) species in TM-Ag NPs/Co3O4 and generation of more radicals resulting from strong interaction between Ag NPs and TM. The TM-Ag NPs/Co3O4 nanozyme exhibited lower Km and higher Vmax values towards H2O2 when compared with Ag NPs/Co3O4 nanozyme. A simple, bioelement-free colorimetric TM detection method based on Ag NPs/Co3O4 nanozyme via analyte-enhanced sensing strategy was successfully established with high sensitivity and selectivity. Our study demonstrated that hybrid noble metal NPs/MOF-based nanozyme can be a class of promising artificial nanozyme in environmental and food safety applications.

Advancing metabolic networks and mapping updated urinary metabolic fingerprints after exposure to typical carcinogenic heterocyclic aromatic amines.

Heterocyclic aromatic amines (HAAs) were not only present in cooked foods and cigarette smoke, but also measured in airborne particles and diesel-exhaust particles. Typical HAAs have been reported to induce carcinogenicity and metabolic disturbances, but how these hazardous compounds interfere with metabolic networks by regulating metabolic pathways and fingerprinting signature metabolites as biomarkers remains ambiguous. We developed an advanced strategy that adopted chemical isotope labeling ultrahigh-performance liquid chromatography coupled to quadrupole-Orbitrap high-resolution mass spectrometry for urinary nontargeted metabolomics analysis to gain new insight into in vivo physiological responses stimulated by exposure to typical HAAs. Rats were orally administered with a single dose of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) or 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) (1 and 10 mg/kg bw) and their D3-isotopic compounds, respectively, and urine samples were then continuously collected within 36 h. Metabolomics data were acquired and processed by classical multivariate statistical analysis, while urinary metabolites were further identified and characterized according to mass spectrometric fragmentation rules, time- and dose-dependent profiles, and calibration of synthesized standards. We monitored 23 and 37 urinary metabolites as the biotransformation products of PhIP and MeIQx, respectively, and first identified demethylated metabolites of PhIP, tentatively named 2-amino-6-phenylimidazo[4,5-b]pyridine, and dihydroxylation products of classical HAAs as short-term biomarkers of exposure to further unravel the metabolic networks. In addition, our findings revealed that both HAAs significantly disturb histidine metabolism, arginine and proline metabolism, tryptophan metabolism, pyrimidine metabolism, tricarboxylic acid cycle, etc. Furthermore, we found that histamine, methionine, alanine, and 4-guanidinobutanoic acid could be considered potential characteristic biomarkers for the oncogenicity or carcinogenicity of both PhIP and MeIQx and screened their specific key pivotal metabolites. The current metabolomics approach is applicable in mapping updated urinary metabolic fingerprints and identifying potential specific biomarkers for HAAs-induced early tumorigenesis.

Simple and sensitive determination of sulfites in Chinese herbal teas by ultrahigh-performance liquid chromatography tandem mass spectrometry.

Sulfites are used widely in food and beverage production to prevent browning or oxidation. However, the overingestion of sulfites is harmful to human health and may cause medical complications. Chinese herbal teas have been widely consumed for centuries. However, sulfite levels in Chinese herbal teas are rarely investigated and reported. Here, we present a simple, sensitive, and quantitative method to determine sulfites in Chinese herbal teas using ultrahigh-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) coupled with dispersive solid phase extraction. The method utilized a SeQuant ZIC-HILIC column for separation, and the optimal gradient eluents consisted of acetonitrile and aqueous solution with 0.1% acetic acid and 10 mM ammonium acetate. Porous chitosan/partially reduced graphene oxide/diatomite (CS/prGO/DM) composites were used as efficient dispersive solid phase extraction adsorbents for sample preparation. Several parameters were investigated during the extraction process, including sample-to-extraction solvent volume ratios, the extraction procedure and dosage of the adsorbent. Under the optimum conditions, the developed method gave a good determination coefficient (r2 > 0.99), low detection limits (0.51-12.1 µg kg-1) and high recoveries in the range of 83.8-102.7% at different spiked levels. The method has the great advantages of being time saving, good reproducibility and much lower detection limits when compared to titration methods. The method was further applied to analyze real herbal tea samples collected from the local market, demonstrating that our developed method is robust and useful for determining sulfites in practical application.

Porous chitosan/partially reduced graphene oxide/diatomite composite as an efficient adsorbent for quantitative colorimetric detection of pesticides in a complex matrix.

On-site, instrument free quantitative analysis of pesticides is of significant importance for food safety control. However, it is still a great challenge for pesticide detection in food via the current visual detection methods due to the presence of interferents in a complex matrix. In this study, a complex tea matrix had a strong effect on a gold nanoparticles (Au NPs) based colorimetric sensor for the detection of pesticides. Here, a porous chitosan/partially reduced graphene oxide/diatomite (CS/prGO/DM) composite was successfully synthesized via a facile hydrothermal treatment. It could act as an efficient adsorbent for removing different types of tea interferents. A colorimetric sensing platform for the quantitative detection of pesticides in a complex matrix was successfully established. The color changes of the aggregation of Au NPs induced by pesticides were captured using the camera of a smartphone and the images were processed with average RGB (red, green, and blue) values obtained using self-developed software. The G/R values and A700/525 values obtained from UV-vis spectra could be used for quantitative analysis of pesticides. The limits of detection of phosalone and thiram in tea were 90 nM and 13.8 nM, respectively. It is expected that graphene-based materials are attractive for wide application of on-site colorimetric quantitative detection in a variety of fields like environmental protection, food safety and bioanalysis.

Qualitative and Quantitative Analysis of Tumor Cell Invasion Using Au Clusters.

Tumor invasion/metastasis is still the major cause of death in cancer patients. Membrane type-1 matrix metalloproteinase (MT1-MMP) is directly related to tumor invasion/metastasis. To accurately and quickly distinguish the risk of invasion/metastasis of primary tumor cells, it is urgent to develop a simple and precise quantitative method to distinguish the expression level of MT1-MMP. In this work, we have constructed red fluorescent Au clusters with peroxidase-like properties that could specifically bind to MT1-MMP on human cervical cancer cells. After MT1-MMP was labelled with Au clusters, we could visually see red fluorescence of MT1-MMP on cervical cancer cells via fluorescence microscopy and catalytic color imaging using an ordinary optical microscope. The constructed Au clusters contained 26 Au atoms; thus, the amount of MT1-MMP on cervical cancer cells could be accurately quantified using inductively coupled plasma mass spectrometry (ICP-MS). More importantly, the invasion/metastasis capabilities of the cervical cancer Siha, Caski and Hela cells with different MT1-MMP amounts could be accurately distinguished by fluorescence/catalysis qualitative imaging and ICP-MS quantitative analysis. This method of qualitative/quantitative analysis of tumor-associated proteins on cancer cells has great potential for accurately diagnosing aggressive tumor cells and assessment of their invasion/metastasis risk.

Chitosan-reduced graphene oxide composites with 3D structures as effective reverse dispersed solid phase extraction adsorbents for pesticides analysis.

Chitosan-reduced graphene oxide composites with 3D structures (3D CS-rGO) were prepared via a facile solvothermal synthetic strategy. The reduction of GO and crosslinking of rGO nanosheets with CS into 3D structures were achieved simultaneously in one step. The resulting 3D CS-rGO composite achieves high adsorption capacities of catechins, caffeine and pigments from tea acetonitrile extraction, especially for catechins, which is 10 times higher than that of GO (179.3 mg g-1vs. 18.7 mg g-1). The 3D CS-rGO composite exhibits the best removal efficiency of matrix interference in comparison to other traditional adsorbents, which could diminish the matrix effect on targeted pesticides by 1%-55%. A determination method of 70 kinds of pesticides is successfully established for tea based on 3D CS-rGO composite as an efficient reverse dispersed solid phase extraction adsorbent. The established method has the great advantages of operation simplicity, being time saving and high purification performance using only one kind and a low amount of adsorbent. 3D graphene based materials are expected to be promising adsorbents for sample pretreatment in trace contaminant analysis of complex food samples.

Facile synthesis of amine-functional reduced graphene oxides as modified quick, easy, cheap, effective, rugged and safe adsorbent for multi-pesticide residues analysis of tea.

Amine-functional reduced graphene oxide (amine-rGO) with different carbon chain length amino groups were successfully synthesized. The graphene oxides (GO) reduction as well as amino grafting were achieved simultaneously in one step via a facile solvothermal synthetic strategy. The obtained materials were characterized by X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectrometry and X-ray photoelectron spectroscopy to confirm the modification of GO with different amino groups. The adsorption performance of catechins and caffeine from tea acetonitrile extracts on different amine functional rGO samples were evaluated. It was found that tributylamine-functional rGO (tri-BuA-rGO) exhibited the highest adsorption ability for catechins and caffeine compared to GO and other amino group functional rGO samples. It was worth to note that the adsorption capacity of catechins on tri-BuA-rGO was 11 times higher than that of GO (203.7mgg-1 vs 18.7mgg-1). Electrostatic interaction, π-π interaction and surface hydrophilic-hydrophobic properties of tri-BuA-rGO played important roles in the adsorption of catechins as well as caffeine. The gravimetric analysis confirmed that the tri-BuA-rGO achieved the highest efficient cleanup preformance compared with traditional dispersive solid phase extraction (dSPE) adsorbents like primary-secondary amine (PSA), graphitized carbon black (GCB) or C18. A multi-pesticides analysis method based on tri-BuA-rGO is validated on 33 representative pesticides in tea using gas chromatography coupled to tandem mass spectrometry or high-performance liquid chromatography coupled with tandem mass spectrometry. The analysis method gave a high coefficient of determination (r2>0.99) for each pesticide and satisfactory recoveries in a range of 72.1-120.5%. Our study demonstrated that amine functional rGO as a new type of QuEChERS adsorbent is expected to be widely applied for analysis of pesticides at trace levels.

Catalytic Activity Control via Crossover between Two Different Microstructures.

Metal nanocatalysts hold great promise for a wide range of heterogeneous catalytic reactions, while the optimization strategy of catalytic activity is largely restricted by particle size or shape control. Here, we demonstrate that a reversible microstructural control through the crossover between multiply twinned nanoparticle (MTP) and single crystal (SC) can be readily achieved by solvent post-treatment on gold nanoparticles (AuNPs). Polar solvents (e.g., water, methanol) direct the transformation from MTP to SC accompanied by the disappearance of twinning and stacking faults. A reverse transformation from SC to MTP is achieved in nonpolar solvent (e.g., toluene) mixed with thiol ligands. The transformation between two different microstructures is directly observed by in situ TEM and leads to a drastic modulation of catalytic activity toward the gas-phase selective oxidation of alcohols. On the basis of the combined experimental and theoretical investigations of alcohol chemisorption on these nanocatalysts, we propose that the exposure of {211}-like microfacets associated with twin boundaries and stack faults accounts for the strong chemisorption of alcohol molecules on MTP AuNPs and thus the exceptionally high catalytic activity.

Residue pattern of polycyclic aromatic hydrocarbons during green tea manufacturing and their transfer rates during tea brewing.

Residues of polycyclic aromatic hydrocarbons (PAHs) in green tea and tea infusion were determined using gas chromatography-tandem mass spectrometry to study their dissipation pattern during green tea processing and infusion. Concentration and evaporation of PAHs during tea processing were the key factors affecting PAH residue content in product intermediates and in green tea. PAH residues in tea leaves increased by 2.4-3.1 times during the manufacture of green tea using the electric heating model. After correction to dry weight, PAH residue concentrations decreased by 33.5-48.4% during green tea processing because of PAH evaporation. Moreover, spreading and drying reduced PAH concentrations. The transfer rates of PAH residues from green tea to infusion varied from 4.6% to 7.2%, and PAH leaching was higher in the first infusion than in the second infusion. These results are useful for assessing exposure to PAHs from green tea and in formulating controls for the maximum residue level of PAHs in green tea.

Profiling elements in Puerh tea from Yunnan province, China.

Puerh tea, as the most representative Chinese dark tea, has attracted global interest in recent years. Profiling the levels of metal elements in Puerh tea is very important since its presence is related to human health. In this study, 41 elements in 98 Puerh tea samples from Yunnan province, China including Puerh raw tea and Puerh ripe tea were evaluated by microwave digestion combined with inductively coupled plasma mass spectrometry . The content of toxic elements, essential elements and rare earth elements of Puerh tea from different regions was discussed in detail. The concentrations of Ba, Cr, As, Pb, Bi, Fe, Zn, V, Mn, Be, Ag and Tl showed significant differences (p < 0.05) by ANOVA analysis. Principal component analysis and linear discriminant analysis were used to describe the relationship of Puerh tea from different regions. This study provided a comprehensive database for Puerh tea quality control and intake risk assessment.

Multiresidue Method for the Rapid Determination of Pesticide Residues in Tea Using Ultra Performance Liquid Chromatography Orbitrap High Resolution Mass Spectrometry and In-Syringe Dispersive Solid Phase Extraction.

A method based on in-syringe dispersive solid phase extraction (IS-D-SPE) and ultra performance liquid chromatography Orbitrap high resolution mass spectrometry for the multiresidue analysis of 117 pesticides in tea was developed. Full scan mode was acquired over an m/z range of 100-800 with Orbitrap resolution at 70000, followed by full scan/dd-MS2 mode for confirmation. The identification criteria of retention time and mass accuracy tolerance was ±0.20 min and ±5.0 ppm, respectively. MS/MS fragment ions obtained dd-MS2 were necessary to identify the pesticides with the same molecular mass weight. The IS-D-SPE technique involved a mixture of 200 mg PSA, 100 mg C18, and 15 mg multiwalled carbon nanotubes for the cleanup of tea matrix. Good linearity (R2 > 0.99) for 117 pesticides was obtained. Satisfactory recoveries in the range of 70-120% were obtained for 105 pesticides, while intraday and interday precisions were below 20%. Limits of quantification were generally 10 µg kg-1. Finally, this method was employed to analyze 117 pesticides in 70 tea samples.

Occurrence and Residue Pattern of Phthalate Esters in Fresh Tea Leaves and during Tea Manufacturing and Brewing.

The residues of 16 phthalate esters (PAEs) in fresh tea leaves and made tea were determined via gas chromatography-tandem mass spectrometry to study their distribution and degradation characteristics during tea planting and processing. Five PAEs were detected in all fresh tea leaves, and higher concentrations were detected in mature leaves. The distribution of PAEs in fresh tea leaves ranged from 69.7 to 2244.0 µg/kg. The degradative percentages of ∑5PAEs during green tea manufacturing ranged from 61 to 63% and were significantly influenced by the drying process. The transfer rates of PAEs-D4 ranged from 5.2 to 100.6%. PAEs with a high water solubility showed the highest transfer coefficient in the range of 91.8-100.6%, whereas PAEs with a high log Kow showed a low leaching efficiency below 11.9%. These results benefit the risk evaluation and establishment of a maximum residue limit for PAEs in tea.

Solid-phase purification and extraction for the determination of trace neonicotinoid pesticides in tea infusion.

An analytical protocol that includes solid-phase purification and extraction is successfully developed for the determination of trace neonicotinoid pesticides in tea infusion. The method consists of a purification on amino-functionalized mesoporous silica SBA-15 followed by a solid-phase extraction based on graphene oxide before ultra high performance liquid chromatography with tandem mass spectrometry analysis. Parameters that significantly affected the extraction of the neonicotinoids onto graphene oxide, such as the amount of adsorbent, extraction time, pH, elution solvent, etc. were optimized. The amino-functionalized mesoporous silica SBA-15 has been proved to be an efficient adsorbent for removal of polyphenols especially catechins from tea infusion. Graphene oxide exhibits a very rapid adsorption rate (within 10 min) and high adsorption capacities for neonicotinoids at low initial concentration (0.01-0.5 mg/L). The analysis method gave a good determination coefficient (r(2) > 0.99) for each pesticide and high recoveries in the range of 72.2-95.0%. Powder X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and UV-vis spectroscopy were utilized to identify the structure and morphology of graphene oxide. The adsorption driving force of neonicotinoids on graphene oxide mainly depends on π-π electron donor-acceptor interaction and electrostatic interaction.

High Density Gold Nanoparticles Within Three-Dimensionally Mesoporous SBA-15: Adsorption Behavior and Optical Properties.

Unprecedentedly high-density (up to 79 wt%) immobilization of monodispersed gold nanoparticles (AuNPs) within mesoporous silica SBA-15 is achieved by variation of their pore size and pore-pore connectivity to enable a full access of AuNPs to the large and high-affinity internal surface of mesoporous silica (MPS) SBA-15. In addition, according to the adsorption kinetics, dipole-induced dipole interaction is suggested to be the primary driving force for adsorption of AuNPs on silica. Interestingly, the high internal surface of MPS shows much higher affinity to AuNPs than the external surface. The optical properties of these densely immobilized AuNPs are also investigated, demonstrating that a plasma coupling exists between closely spaced AuNPs.

Determination of 16 phthalate esters in tea samples using a modified QuEChERS sample preparation method combined with GC-MS/MS.

A modified QuEChERS method for the determination of 16 phthalate esters (PAEs) in tea samples using GC-MS/MS was developed and validated. The kinds and amounts of adsorbents were optimised, and the crude extracts were purified using primary secondary amine (PSA), graphitised carbon black (GCB) and anhydrous magnesium sulphate (MgSO4). Compared with extraction without matrix hydration, the addition of water could achieve higher extraction efficiency. The recoveries for PAEs obtained against matrix-matched standards at spiking levels of 50, 200 and 500 µg kg(-1) ranged from 84.7% to 112.7% with relative standard deviations below 20% (n = 6) for all cases. Limits of detection (0.6-36.0 µg kg(-1)) and quantitation (2.0-120.0 µg kg(-1)) were achieved using the proposed method for all PAEs. A total of 105 tea samples were found to be contaminated with PAEs.

Ordered, extra-large mesopores with highly loaded gold nanoparticles: a new sintering- and coking-resistant catalyst system.

Ordered, extra-large mesopores with highly loaded gold nanoparticles (AuNPs) exhibits unique sintering- and coking-resistant properties in gas-phase, cyclohexanol selective aerobic oxidation.

Stabilizing gold clusters by heterostructured transition-metal oxide-mesoporous silica supports for enhanced catalytic activities for CO oxidation.

A strategy for stabilizing ultrasmall gold clusters under thermal treatment has been developed. The essence of this methodology lies in construction of heterostructured transition-metal oxide-mesoporous silica supports. The supported clusters have been demonstrated to be sintering resistant and highly active for catalytic CO oxidation.

Ordered nanoporous silica with periodic 30-60 nm pores as an effective support for gold nanoparticle catalysts with enhanced lifetime.

We demonstrate that supermolecular templating allows tuning the pore size of ordered mesoporous materials in the once elusive range from 30 nm to more than 60 nm through simple control of synthetic variables (salt/supermolecule concentration and hydrothermal temperature). Gold nanoparticles (AuNPs) within the extra-large pores exhibit dramatically increased lifetime compared to those located within relatively small mesopores due to the enhanced mass diffusion that suppresses coke deposition on AuNPs.