Fen 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.

Study on Enhancement Principle and Stabilization for the Luminol-H2O2-HRP Chemiluminescence System

A luminol-H2O2-HRP chemiluminescence system with high relative luminescent intensity (RLU) and long stabilization time was investigated. First, the comparative study on the enhancement effect of ten compounds as enhancers to the luminol-H2O2-HRP chemiluminescence system was carried out, and the results showed that 4-(imidazol-1-yl)phenol (4-IMP), 4-iodophenol (4-IOP), 4-bromophenol (4-BOP) and 4-hydroxy-4’-iodobiphenyl (HIOP) had the best performance. Based on the experiment, the four enhancers were dissolved in acetone, acetonitrile, methanol, and dimethylformamide (DMF) with various concentrations, the results indicated that 4-IMP, 4-IOP, 4-BOP and HIOP dissolved in DMF with the concentrations of 0.2%, 3.2%, 1.6% and 3.2% could get the highest RLU values. Subsequently, the influences of pH, ionic strength, HRP, 4-IMP, 4-IOP, 4-BOP, HIOP, H2O2 and luminol on the stabilization of the luminol-H2O2-HRP chemiluminescence system were studied, and we found that pH value, ionic strength, 4-IMP, 4-IOP, 4-BOP, HIOP, H2O2 and luminol have little influence on luminescent stabilization, while HRP has a great influence. In different ranges of HRP concentration, different enhancers should be selected. When the concentration is within the range of 0~6 ng/mL, 4-IMP should be selected. When the concentration of HRP ranges from 6 to 25ng/mL, 4-IOP was the best choice. And when the concentration is within the range of 25~80 ng/mL, HIOP should be selected as the enhancer. Finally, the three well-performing chemiluminescent enhanced solutions (CESs) have been further optimized according to the three enhancers (4-IMP, 4-IOP and HIOP) in their utilized HRP concentration ranges.

The Rapid Screening of Triazophos Residues in Agricultural Products by Chemiluminescent Enzyme Immunoassay

A highly sensitive chemiluminescent enzyme immunoassay (CLEIA) method was developed in this study for efficient screening of triazophos residues in a large number of samples. Based on the maximum residue limits (MRLs) set by China and CAC for triazophos in different agro-products, the representative apple, orange, cabbage, zucchini, and rice samples were selected as spiked samples, and the triazophos at the concentrations of the MRL values were spiked to blank samples. Subsequently, the five samples with the spiked triazophos standard were measured by CLEIA 100 times, and the detection results indicated that the correction factors of the apple, orange, cabbage, zucchini, and rice were determined as 0.79, 0.66, 0.85, 0.76, and 0.91, respectively. In this experiment, 1500 real samples were detected by both the CLEIA and the GC-MS methods. With the GC-MS method, 1462 samples were identified as negative samples and 38 samples as positive samples. Based on the correction factors, the false positive rate of the CLEIA method was 0.13%, and false negative rate was 0. The results showed that the established CLEIA method could be used to screen a large number of real samples.

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.

Determination of hymexazol in 26 foods of plant origin by modified QuEChERS method and liquid chromatography tandem-mass spectrometry

A rapid and sensitive method based on modified QuEChERS for hymexazol determination in 26 plant-derived foods using liquid chromatography tandem-mass spectrometry (LC-MS/MS) was developed. Variables affecting the separation (LC column, mobile phase additives) and clean-up effects of various dispersive phases, such as PSA, C18, GCB, MWCNTs, PEP-2, Al2O3, Florisil, and PVPP were evaluated. The method was validated using 26 matrices at spiked levels of 0.01 or 0.02, 0.05, 0.1, and 0.5mg/kg (0.05, 0.2, 0.5, and 1.0mg/kg for green tea). Mean recoveries were between 71.2% and 113.8%, and intra and inter-day precisions were below 14.8%. The limit of quantitation for 26 matrices ranged from 10 to 50μg/kg. Matrix-matched calibration was used. The method was subsequently applied for real sample analysis, and hymexazol was detected in a cucumber (below the LOQ) and was not detected in any other sample. The method is simple and effective, and meets the routine monitoring requirements for hymexazol residue in foods.

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.