Weiping Wang

Facile synthesis of oxygen and sulfur co-doped graphitic carbon nitride fluorescent quantum dots and their application for mercury( ii ) detection and bioimaging

In this work, uniform oxygen and sulfur co-doped graphitic carbon nitride quantum dots (OS-GCNQDs) have been prepared by thermal treatment of citric acid and thiourea. The as-obtained OS-GCNQDs show strong blue photoluminescence (PL) with a relatively high quantum yield of 14.5%. Furthermore, OS-GCNQDs exhibit stable and specific concentration-dependent PL intensities in the presence of mercury(II) ions in the range of 0.001–20.0 μM, with a detection limit of 0.37 nM (3S/N). More importantly, OS-GCNQDs were explored for cell imaging with satisfactory biocompatibility, and so are a potential fluorescent probe in biosensing and bioimaging applications.

Determination of bisphenol A and naphthols in river water samples by capillary zone electrophoresis after cloud point extraction.

As a first attempt, cloud point extraction (CPE) was developed to preconcentrate bisphenol A (BPA), α-naphthol and β-naphthol prior to performing capillary zone electrophoresis (CZE) analysis. The parameters influencing the CPE efficiency, such as Triton X-114 concentrations, pH value, extraction time and temperature were systematically evaluated. After diluting with acetonitrile, the surfactant-rich phase of CPE can be injected directly into the CE instrument. The CZE baseline separation was achieved with running buffer (pH 9.5) composed of 50mM sodium tetraborate in 30% (v/v) methanol, and an applied voltage of 25 kV. Under the optimized CPE and CZE conditions, an preconcentration factor of 50 times could be obtained and the limit of quantification for the three analytes were found to be 1.67 μg L(-1), 0.80 μg L(-1) and 0.67 μg L(-1) for BPA, α-naphthol and β-naphthol, respectively. The proposed methods have shown to be a green, rapid and effective approach for determination of three analytes present in river water samples.

Facile synthesis of N, S-codoped fluorescent carbon nanodots for fluorescent resonance energy transfer recognition of methotrexate with high sensitivity and selectivity

In this report, N, S-codoped fluorescent carbon nanodots (NSCDs) were prepared by a facile, simple, low-cost, and green thermal treatment of ammonium persulfate, glucose, and ethylenediamine. The as-prepared NSCDs displayed bright blue emission with a relatively high fluorescent quantum yield of 21.6%, good water solubility, uniform morphology, and excellent chemical stability, compared to pure CDs. The fluorescence of NSCDs can be significantly quenched by methotrexate (MTX) via fluorescence resonance energy transfer (FRET) between NSCDs and MTX, which was used for highly selective and sensitive detection of MTX with a wide linear range up to 50.0 μM and a low detection limit of 0.33 nM (S/N = 3). Moreover, this method was explored for practical detection of MTX in human serum with satisfied results.

Fabrication of CoFe2O4–graphene nanocomposite and its application in the magnetic solid phase extraction of sulfonamides from milk samples

In the present study, a graphene-based magnetic nanocomposite (CoFe2O4-graphene, CoFe2O4-G) was synthesized and used successfully as an adsorbent for the magnetic solid phase extraction (MSPE) of sulfonamides for the first time. The surface morphologies and structures of the CoFe2O4-G nanocomposite were investigated by scanning electron microscopy (SEM), FT-IR, UV-vis spectroscopy, X-ray diffraction (XRD) and vibration sample magnetometer (VSM). Five sulfonamides, including sulfamerazine, sulfamethizole, sulfadoxine, sulfamethoxazole and sulfisoxazole were used as model analytes to evaluate the enrichment properties of the prepared adsorbent in MSPE. After preconcentration, the adsorbent could be conveniently separated from the aqueous samples by an external magnet, and the analytes desorbed from adsorbent were determined by high performance liquid chromatography-ultraviolet detection (HPLC-UV). Extraction parameters including sample pH, amount of sorbent, extraction time and desorption conditions were optimized in detail. Under the optimal conditions, good linear relationships between the peak areas and the concentrations of the analytes were obtained. The linear ranges were 0.02-50.00 mg L(-1) with correlation coefficients (r)≧0.9982. The limits of detection were less than 1.59 μg L(-1). Good reproducibility was obtained. The relative standard deviations of intra- and inter-day analysis were less than 4.3% and 6.5%, respectively. The proposed method was successfully applied for the analysis of sulfonamides in milk samples. The average recoveries determined for two milk samples spiked at levels from 5 to 20 μg L(-1) were 62.0-104.3% with relative standard deviations less than 14.0%. In addition, the CoFe2O4-G could be reused after cleaning with acetone and ultrapure water successively.

Graphene‐Fe3O4 as a magnetic solid‐phase extraction sorbent coupled to capillary electrophoresis for the determination of sulfonamides in milk

Graphene-Fe3 O4 nanoparticles were prepared using one-step solvothermal method and characterized by X-ray diffraction, FTIR spectroscopy, scanning electron microscopy, and vibrating sample magnetometry. The results demonstrated that Fe3 O4 nanoparticles were homogeneously anchored on graphene nanosheets. The as-synthesized graphene-Fe3 O4 nanoparticles were employed as sorbent for magnetic solid-phase extraction of sulfonamides in milk prior to capillary electrophoresis analysis. The optimal capillary electrophoresis conditions were as follows: 60 mmol/L Na2 HPO4 containing 2 mmol/L ethylenediaminetetraacetic acid disodium salt and 24% v/v methanol as running buffer, separation voltage of 14 kV, and detection wavelength of 270 nm. The parameters affecting extraction efficiency including desorption solution, the amount of graphene-Fe3 O4 nanoparticles, extraction time, and sample pH were investigated in detail. Under the optimal conditions, good linearity (5-200 μg/L) with correlation coefficients ≥0.9910 was obtained. The limits of detection were 0.89-2.31 μg/L. The relative standard deviations for intraday and interday analyses were 4.9-8.5 and 4.0-9.0%, respectively. The proposed method was successfully applied to the analysis of sulfonamides in milk samples with recoveries ranging from 62.7 to 104.8% and relative standard deviations less than 10.2%.

Miniaturization of self-assembled solid phase extraction based on graphene oxide/chitosan coupled with liquid chromatography for the determination of sulfonamide residues in egg and honey

The miniaturization of self-assembled solid phase extraction (m-SASPE) based on graphene oxide/chitosan (GO/CS) coupled with liquid chromatography-ultraviolet detection was developed for rapid screening of five sulfonamide residues in egg and honey. GO/CS was synthesized by solution blending method and characterized by FT-IR, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Parameters that affected extraction efficiency including sample pH, amount of the GO/CS, elution solvent and rotation speed were optimized in detail. Under the optimal conditions, good linear relationships between the peak area and the concentrations of the analytes were obtained. The linear ranges were 0.01-10.00μgg(-1) with correlation coefficients (r)≧0.9989. The method detection limits (MDLs) were in the range of 0.71-0.98ngg(-1). The relative standard deviations (RSDs) of intra- and inter-day analysis were less than 3.5 and 7.1%, respectively. The proposed method was successfully applied for the analysis of sulfonamide residues in egg and honey. The average recoveries for two samples spiked at levels from 0.02 to 2.0μgg(-1) were in the range of 75.3-105.2% with RSDs less than 13.5%.

A simple colorimetric analytical assay using gold nanoparticles for specific detection of tetracycline in environmental water samples

In this work, an aptamer-based colorimetric method for the detection of tetracycline (TC) was established by employing gold nanoparticles (AuNPs) as the colorimetric probe. In the absence of TC, the aptamers are readily adsorbed on the surface of AuNPs, which prevents aggregation of AuNPs and stabilizes the red colloidal solution against high concentrations of NaCl. In the presence of TC, the aptamers are subsequently released from the surface of the AuNPs due to binding with TC molecules. A gradual color change from red to blue was observed due to the salt-induced aggregation of AuNPs. Furthermore, a linear relationship between the absorbance intensity and the concentration of TC was observed in the range of 0.10 to 5.00 μM. The limit of detection was 0.071 μM. The developed assay was employed for the determination of TC in environmental water samples. The recoveries ranged from 106.7% to 115.6% with relative standard deviations being less than 3.0%. The results demonstrate that the method serves as a promising tool for the rapid, simple and cost-effective detection of TC.

Magnetic Metal-Organic Framework/Graphene Oxide-Based Solid-Phase Extraction Combined with Spectrofluorimetry for the Determination of Enrofloxacin in Milk Sample

We have developed an analytical method for the extraction and determination of enrofloxacin in milk sample by magnetic solid-phase extraction with metal-organic framework/graphene oxide (Fe3O4/MIL-100(Fe)/GO) as a sorbent coupling to spectrofluorimetry. The prepared Fe3O4/MIL-100(Fe)/GO nanocomposite were characterized by scanning electron microscopy, FT-IR spectroscopy, x-ray diffraction, and vibration sample magnetometer. The parameters affecting extraction efficiency including sample pH, amounts of sorbent, adsorption time, and acidity of elution solvent were optimized systematically. The optimal extraction conditions were as follows: 100.0-mL sample at pH of 8.0, 20.0xa0mg of Fe3O4/MIL-100(Fe)/GO as sorbent, extraction time of 30xa0min, and 4.00xa0mL of 15% (v/v) formic acid in methanol as eluent. A matrix-matched linear relationship (10.00–350.00xa0μgxa0L−1) between the fluorescence intensity and the concentrations of enrofloxacin was obtained with correlation coefficient (r)xa0=xa00.9979. The limit of detection (S/Nxa0=xa03) and the limit of quantification (S/Nxa0=xa010) were 0.65 and 2.17xa0μgxa0L−1, respectively. The relative standard deviations of intraday and interday analysis (nxa0=xa05) were 1.64 and 2.86%, respectively. The proposed method was successfully applied for the determination of enrofloxacin in milk sample with recoveries ranged from 85.7 to 106.3%.

Determination of Sulfonamide Residues in Honey and Milk by HPLC Coupled with Novel Graphene Oxide/Polypyrrole Foam Material-Pipette Tip Solid Phase Extraction

A rapid, sensitive, and economical pipette tip solid phase extraction (PT-SPE) based on graphene oxide/polypyrrole (GO/PPy) coupled with high performance liquid chromatography (HPLC) was developed for the extraction and determination of sulfonamides (SAs) in honey and milk samples. The PT-SPE procedure involved only 3.0xa0mg of adsorbent, 3xa0min adsorptive extraction time, and less than 1.0xa0mL of solvent consumption (sample, washing, or eluent). Under the optimal conditions, good linearities (0.01–10.00xa0μgxa0mL−1) were obtained with correlation coefficients (r)u2009>u20090.9996. The limits of detection (S/Nu2009=u20093) were in the range of 1.04–1.50xa0ngxa0mL−1. Meanwhile, the proposed method was successfully applied for the analysis of SAs in honey and milk with average recoveries within 62.3–109.0% and relative standard deviations less than 11.2%. The results demonstrated that the developed PT-SPE-HPLC method was suitable for the analysis of SAs in complex matrix due to its high sensitivity and accuracy.