Guangyang Liu

Advances in characterisation and biological activities of chitosan and chitosan oligosaccharides.

Chitosan and chitosan oligosaccharides (COS) have been reported to possess various biomedical properties, including antimicrobial activities, immuno-enhancing effects, and anti-tumour activities. COS have attracted considerable interest due to their physicochemical properties, and potential applications in the food and pharmaceutical industries, especially in cancer therapies. This paper describes the preparation of COS and their physicochemical properties, and modification, which aids understanding of their biological activities. Based on the latest reports, several biological and anti-tumour activities of COS will be discussed. The proposed anti-tumour mechanisms of COS are summarised, to provide comprehensive insights into research on the molecular level. Finally, the potential applications and future development of the biopolymer will be discussed.

Competitive fluorescence assay for specific recognition of atrazine by magnetic molecularly imprinted polymer based on Fe3O4-chitosan

A novel fluorescence sensing strategy for determination of atrazine in tap water involving direct competition between atrazine and 5-(4,6-dichlorotriazinyl) aminofluorescein (5-DTAF), and which exploits magnetic molecularly imprinted polymer (MMIP), has been developed. The MMIP, based on Fe3O4-chitosan nanoparticles, was synthesized to recognize specific binding sites of atrazine. The recognition capability and selectivity of the MMIP for atrazine and other triazine herbicides was investigated. Under optimal conditions, the competitive reaction between 5-DTAF and atrazine was performed to permit quantitation. Fluorescence intensity changes at 515 nm was linearly related to the logarithm of the atrazine concentration for the range 2.32-185.4 μM. The detection limit for atrazine was 0.86μM (S/N=3) and recoveries were 77.6-115% in spiked tap water samples.

Colorimetric sensing of atrazine in rice samples using cysteamine functionalized gold nanoparticles after solid phase extraction

A simple and sensitive colorimetric assay for the determination of atrazine in rice samples using cysteamine–gold nanoparticles (AuNPs) after solid phase extraction has been developed. The approach exploited the benefits of a robust sample pretreatment scheme with a rapid and sensitive colorimetric sensing strategy based on cysteamine–AuNPs. As a result of the hydrogen bonding between atrazine and cysteamine, cysteamine–AuNPs were induced to aggregate with an accompanying distinct color change from wine red to blue. The color change was monitored by UV-vis spectrophotometry or with the naked eye. The difference of the absorbance value at 523 nm was linearly related to the atrazine concentration over the range 0.033 to 6.67 μg g−1, and the limit of detection (S/N = 3) was 0.0165 μg g−1. The spiked rice samples were extracted and purified using Oasis HLB cartridges and satisfactory recoveries (83.23–91.65%) were realized.

Molecularly imprinted polymer for selective extraction and simultaneous determination of four tropane alkaloids from Przewalskia tangutica Maxim. fruit extracts using LC-MS/MS

A class-specific molecularly imprinted polymer (MIP) for selective extraction and preconcentration of four tropane alkaloids has been successfully prepared by precipitation polymerization using anisodine (ASD) as the template, methacrylic (MAA) as the functional monomer, trimethylolpropane trimethacrylate (TRIM) as the crosslinker and acetonitrile as the porogen. The performances of the MIPs and the non-molecularly imprinted polymers (NIPs) were evaluated in terms of selective recognition capacity, adsorption isotherms and adsorption kinetics. The results indicated that the MIPs exhibited significant specific recognition toward TAs with a large adsorption capacity. To testify the feasibility of MIP in real sample preparation, the obtained MIPs were applied as the selective sorbents for the solid-phase extraction of four TAs in Przewalskia tangutica Maxim. Under optimized conditions, a rapid, convenient and efficient method for the determination of four TAs in Przewalskia tangutica Maxim. fruit samples was established by class-specific MIPs based MISPE coupling with high performance liquid chromatography tandem mass spectrometry (LC-MS/MS). The method gave excellent recoveries (82.1–102%) and precision (RSDs < 5%, n = 5) for Przewalskia tangutica Maxim. fruit extracts spiked at three concentration levels (50, 100, 200 μg L−1). The results demonstrated that the TAs in the extracts could be separated and purified through MIP-SPE from Przewalskia tangutica Maxim.

Electrochemical detection of ractopamine based on a molecularly imprinted poly-o-phenylenediamine/gold nanoparticle–ionic liquid–graphene film modified glass carbon electrode

An electrochemical sensor for sensitive detection of ractopamine (RAC) was fabricated by using molecularly imprinted polymer (MIP) incorporation with graphene (GR), ionic liquid (IL) and gold nanoparticle (AuNPs) nanocomposites. The AuNPs–IL–GR nanocomposite was utilized to improve the electrochemical response while MIP served as a recognition element. The MIPs were prepared by electropolymerization of o-phenylenediamine (oPD) on the AuNPs–IL–GR nanocomposite modified electrode. The resulting sensor was studied with respect to its response to hexacyanoferrate as a probe and characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Differential pulse voltammetry (DPV) was used to investigate the electrochemical behaviors of the proposed sensor in a phosphate buffer solution. Under optimal conditions, the peak current was linear to RAC concentration in the range from 10 μg L−1 to 5000 μg L−1, with a low detection limit of 0.46 μg L−1 (S/N = 3). The electrochemical MIP-sensor was applied to the determination of RAC in swine urine samples and satisfactory results were obtained.

Simultaneous determination of four organotins in food packaging by high-performance liquid chromatography–tandem mass spectrometry

A simple method based on high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the simultaneous determination of organotins-tri-n-butyltin chloride (TBT), triphenyltin chloride (TPT), dibutyltin dichloride (DBT), and diphenyltin dichloride (DPT)-in plastic food packaging. Samples were prepared by ultrasonic extraction with dichloromethane, followed by dissolution in acetonitrile containing 0.1% formic acid, and purification by an MCX column. The extracts were analyzed by LC-MS/MS in multiple reaction monitoring and positive modes with a C18 column; elution was carried out with a gradient of 0.1% formic acid and methanol containing 0.1% formic acid. The limits of detection for TBT, TPT, DBT, and DPT were 0.1, 0.6, 0.8, and 0.3 μg kg(-1), respectively. The recovery of organotins in spiked samples ranged from 68% to 113% (relative standard deviation: 0.4-4.2%). The proposed method was successfully employed to identify the target analytes in plastic packaging used for milk and cake.

Preparation of magnetic metal organic framework composites for the extraction of neonicotinoid insecticides from environmental water samples

MOF-199/Fe3O4 nanoparticles were explored for the first time to purify environmental water samples and adsorb neonicotinoid insecticides as hybrid adsorbents. The composites were successfully synthesized by an in situ method at room temperature with electrostatic interaction to chemically stabilize the nanoparticles and metal ions. The nanoparticles were uniformly encoded with metal organic frameworks (MOFs). With the lowest loading amount of Fe3O4 applied to magnetic solid-phase extraction (MSPE) of six neonicotinoid insecticides in environmental water samples followed by high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) analysis, the extraction efficiency was the highest. The main influencing factors including the solution ionic strength, solution pH, extraction time, desorbing organic solvent, and solvent volume, were also evaluated. Considering the adsorbing conditions and insecticide structures, the adsorbing mechanism was preliminarily discovered to be largely dependent upon the π–π interaction with the benzene ring in MOF-199 and delocalized large π bonds in the insecticide molecules. Under optimal conditions, the limits of detection (LODs) were 0.3–1.5 ng mL−1 with a signal-to-noise ratio (S/N) of 3. All the analytes exhibited good linearity with correlation coefficients (r2) of higher than 0.9947. The relative standard deviations (RSDs) for six neonicotinoid insecticides in environmental samples in five replicates ranged from 1.5% to 11.6%, and good recoveries from 88.0% to 107.0% were obtained, indicating that the MOF-199/Fe3O4 composites are feasible for analysis of trace analytes in environmental water samples.

Fluorescent competitive assay for melamine using dummy molecularly imprinted polymers as antibody mimics

Abstract A fluorescent competitive assay for melamine was first developed utilizing dummy molecularly imprinted polymers (DMIPs) as artificial antibodies. This method is based on the competition between fluorescent substances and the unlabeled analyte for binding sites in synthesized DMIPs and the decreased binding of fluorescent substances to DMIPs due to increased concentrations of melamine in the solutions. DMIPs for melamine were synthesized under a hot water bath in the presence of the initiator azobisisobutyronitrile (AIBN) using 2,4-diamino-6-methyl-1,3,5-triazine (DAMT) as a dummy template, methacrylic acid (MAA) as a functional monomer, and ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent. The adsorption capacity and selectivity of DMIPs for melamine were evaluated by the isothermal adsorption curve and Scatchard analysis. The evaluation results showed that the synthesized DMIPs had specific recognition sites for melamine and the maximum adsorption amount was 1 066.33 μg g−1. Later, 5-(4,6-dichlorotriazinyl) amino fluorescein (DTAF) with a triazine ring, which slightly resembles melamine, was selected as the fluorescent substance. The fluorescent competitive assay using DMIPs as the antibody mimics was finally established by selecting and optimizing the reaction solvents, DMIPs amount, DTAF concentration, and incubation time. The optimal detection system showed a linear response within range of 0.05–40 mg L−1 and the limit of detection (LOD) was 1.23 μg L−1. It was successfully applied to the detection of melamine in spiked milk samples with satisfactory recoveries (71.9 to 86.3%). According to the comparative analysis, the result of optimized fluorescent competitive assay revealed excellent agreement with the HPLC-MS/MS result for melamine.