Maojun Jin

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.

A Competitive Bio-Barcode Amplification Immunoassay for Small Molecules Based on Nanoparticles

A novel detection method of small molecules, competitive bio-barcode amplification immunoassay, was developed and described in this report. Through the gold nanoparticles (AuNPs) probe and magnetic nanoparticles (MNPs) probe we prepared, only one monoclonal antibody can be used to detect small molecules. The competitive bio-barcode amplification immunoassay overcomes the obstacle that the bio-barcode assay cannot be used in small molecular detection, as two antibodies are unable to combine to one small molecule due to its small molecular structure. The small molecular compounds, triazophos, were selected as targets for the competitive bio-barcode amplification immunoassay. The linear range of detection was from 0.04 ng mL−1 to 10 ng mL−1, and the limit of detection (LOD) was 0.02 ng mL−1, which was 10–20 folds lower than ELISA (Enzyme Linked Immunosorbent Assay). A practical application of the proposed immunoassay was evaluated by detecting triazophos in real samples. The recovery rate ranged from 72.5% to 110.5%, and the RSD was less than 20%. These results were validated by GC-MS, which indicated that this convenient and sensitive method has great potential for small molecular in real samples.

A rapid immunomagnetic-bead-based immunoassay for triazophos analysis

An immunomagnetic-bead-based enzyme-linked immunosorbent assay (IMB-ELISA) was developed for detection of pesticides by using carboxyl functionalized magnetic Fe3O4 nanoparticles (CMNPs). The CMNPs were prepared by co-precipitation of Fe2+/Fe3+ with oleic acid as a surfactant and subsequent oxidation of CC into COOH by KMnO4 solution in situ. Then, anti-pesticide (triazophos) monoclonal antibodies were directly bonded onto the magnetic nanoparticles, which significantly increased the sensitivity compared with classic ELISA. The detection limit was 0.10 ng mL−1. Addition-recovery and high-precision experiments were performed on blank samples that were determined to be without triazophos. The average recovery rate for three types of samples (with each spiking concentration measured 5 times in parallel) ranged from 83.1% to 115.9%, with a relative standard deviation (RSD) of less than 10%, which meets the requirement of pesticide residue analysis. The application results were in accordance with the gas chromatography-mass spectrometry (GC-MS) method, suggesting that IMB-ELISA is rapid and reliable for pesticide detection.

A sensitive chemiluminescent enzyme immunoassay for carbofuran residue in vegetable, fruit and environmental samples

Using the direct competitive chemiluminescent enzyme immunoassay (CLEIA), a rapid, highly selective and sensitive method for carbofuran determination was developed. Several physicochemical parameters such as chemiluminescent sensitiser, assay buffer, blocking substance and working concentration were optimised. Under the optimum conditions, the CLEIA method for carbofuran determination was generated successfully. The detection sensitivity of the IC50 value was 4.2 ng/mL at a practical working concentration ranging from 0.4 to 50 ng/mL, and the limit of detection (LOD) for carbofuran was 0.5 ng/mL. Recoveries of carbofuran spiked into vegetable, fruit and environmental samples were determined by CLEIA after sample matrix effect testing. Finally, the confirmation test between CLEIA and LC-MS/MS was finished. The results showed that CLEIA method had higher sensitivity than enzyme-linked immunosorbent assay method, and the LOD of a variety of samples reached the carbofurans maximum residue limit value laid down by Codex Alimentarius Commission.

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.

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.

Selective solid-phase extraction based on molecularly imprinted technology for the simultaneous determination of 20 triazole pesticides in cucumber samples using high-performance liquid chromatography-tandem mass spectrometry

A selective analytical method for the simultaneous determination of 20 triazole fungicides and plant growth regulators in cucumber samples was developed using solid-phase extraction with specific molecularly imprinted polymers (MIPs) as adsorbents. The MIPs were successfully prepared by precipitation polymerization using triadimefon as the template molecule, methacrylic acid as the functional monomer, trimethylolpropane trimethacrylate as the crosslinker, and acetonitrile as the porogen. The performance and recognition mechanism for both the MIPs and non-molecularly imprinted polymers were evaluated using adsorption isotherms and adsorption kinetics. Liquid chromatography-tandem quadrupole mass spectrometry was used to identify and quantify the target analytes. The solid-phase extraction using the MIPs was rapid, convenient, and efficient for extraction and enrichment of the 20 triazole pesticides from cucumber samples. The recoveries obtained at three concentration levels (1, 2, and 10μgL-1) ranged from 82.3% to 117.6% with relative standard deviations of less than 11.8% (n=5) for all analytes. The limits of detection for the 20 triazole pesticides were all less than 0.4μgL-1, and were sufficient to meet international standards.

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.