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

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-d ichlorotriazinyl） amino fluorescein（DTAF） with a triazine ring, which s lightly resembles m elamine, w as selected as the fluorescent substance. The fluorescent competitive assay using DMIPs as t he 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 w ithin 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 wi th satisfactory recoveries（71.9 to 86.3%）. According to the comparative analysis, the result of optimized fluorescent competitive assay re vealed excellent agreement with the HPLC-MS/MS result for melamine.

Development of ELISA and immunochromatographic assay for ofloxacin

Two rapid, sensitive and reliable immunoassay methods, namely competitive indirect enzyme-linked immunosorbent assay (CI-ELISA) and colloidal gold-based immunochromatographic assay (CGIA), were developed to detect ofloxacin (OFL). The linear range of the CI-ELISA was from 0.5 to 128 ng/mL with a limit of detection (LOD) of 0.35 ng/mL. Good recoveries were obtained in analyzing simulated swine urine samples. The CGIA could accurately estimate OFL at concentrations as low as 10 ng/mL in less than 10 min, and test results were read visually without any instrument.

Aptamer-based competitive electrochemical assay of small biomolecules

A convenient aptamer-based competitive electrochemical biosensor for a small biomolecule,adenosine,was described. The sensing surface was fabricated by self-assembly of an aptamer/mercaptohexanol monolayer on a gold disk electrode. The principle of this aptasensor is based on the competition between an adenosine target molecule and a ferrocene-conjugated signaling DNA strand for the aptamer binding site on the sensing surface. Due to the competitive nature of this assay,the electrochemical responses of the surface captured ferrocene are inversely proportional to log[adenosine] in the range from 0.05 to 3.2 μM,with a detection limit of 25 nM. Moreover,the aptasensor also shows high selectivity for adenosine. The proposed aptasensor thus holds great potential for the detection of other small biomolecules.

Functional Characteristics of a Novel Chemosensory Protein in the Cotton Bollworm Helicoverpa armigera (Hübner)

A chemosensory protein named HarmCSP5 in cotton bollworm Helicoverpa armigera （Hvbner） was obtained from antennal eDNA libraries and expressed in Escherichia coll. The real time quantitative PCR （RT-qPCR） results indicated that HarmCSP5 gene was mainly expressed in male and female antennae but also expressed in female legs and wings. Competitive binding assays were performed to test the binding affinity of recombinant HarmCSP5 to 60 odor molecules including some cotton volatiles. The resules showed that HarmCSP5 showed strong binding abilities to 4-ehtylbenzaldehyde and 3,4-dimethlbenz aldehyde, whereas methyl phenylacetate, 2-decanone, 1-pentanol, carvenol, isobomeol, nerolidol, 2- nonanone and ethyl heptanoate have relatively weak binding affinity. Moreover, the predicted 3D model of HarmCSP5 consists of six α-helices located among residues 33-38 （αl）, 40-48 （α2）, 62-72 （α3）, 80-96 （α4）, 98-108 （α5）, and 116-119 （α6）, two pairs of disulfide bridges Cys49-Cys55, Cys75-Cys78. The two amino acid residues, Ile94 and Trpl01, may play crucial roles in HarmCSP5 binding with ligands and need further study for confirmation.

Microcystin-LR detection based on indirect competitive enzyme-linked immunosorbent assay

Microcystins(MCs)are a group of closely related toxic cyclic heptapeptides produced by common cyanobacte-ria,which cause lots of accidents and threatens human health.In this paper,an indirect competitive enzyme-linked immu-nosorbent assay(ic-ELISA)was established and used to detect microcystin-LR(MC-LR)in drinking and surface waters.The concentration of coating antigen was 5 mg/mL,the dilution of monoclonal antibody MC10E7 was 1:3000,the dilution of enzyme tracer(goat anti-mouse IgG-peroxidase)was 1:3000,the standard concentration of MC-LR ranged from 0.001 mg/L to 30 mg/L,and o-phenylenediamine was used as substrate.The assay showed high relativity with high performance liquid chromatography(HPLC)with a correlation coefficient of more than 99%.The relative standard deviation was less than 10%,the detection limit was achieved down to 0.01 mg/L and up to 5.1 mg/L.The quantitative detection range was from 0.03 mg/L to 3 mg/L,and the antibody had high specificity for[4-arginine]microcystins.It performed well in spite of the influence of the real samples.

Molecular and in vitro biochemical assessment of chemosensory protein 10 from brown planthopper Nilaparvata lugens at acidic pH

Chemosensory proteins(CSPs)are important molecular components of the insect olfactory system,which are involved in capturing,binding,and transporting hydrophobic odour molecules across the sensillum in sensillar lymph in regulating insect behavior.This protein family(CSPs)is also involved in many other systems that are not linked to olfactory receptors in olfactory sensilla.The brown planthopper(BPH)is a monophagous pest of rice that causes damage by sucking phloem sap and transmitting a number of diseases caused by viruses.In this study,fluorescence competitive binding assay and fluorescence quenching assay at acidic p H were performed as well as homology modelling to describe the binding affinity of Nlug CSP10.Fluorescence competitive binding assay(FCBA)demonstrated that Nlug CSP10 bound strongly to nonadecane,farnesene,and 2-tridecanone at acidic p H.The results of FCBA indicated that Nlug CSP10 bound different ligands at the physiological p H(5.0)of the bulk sensillum lymph.Fluorescence quenching assay demonstrated that Nlug CSP10 generated a stable complex with 2-tridecanone,while two ligands nonadecane and farnesene collided due to molecular collisions.The interaction of selected ligands with the modelled structure of Nlug CSP10 was also analyzed,which found the key amino acids(Gln23,Gln24,Gln25,Asn27,Met33,Ser34,Ile35,Tyr36,Asn42,Met43,Val45,Asn46,Asn93,Arg96,Ala97,Lys99,and Ala100)in Nlug CSP10 that were involved in binding of volatile compounds.The present study contributes to the binding profile of Nlug CSP10 that promotes the development of behaviorally active ligands based on BPH olfactory system.

Preparation of high-affinity rabbit monoclonal antibodies for ciprofloxacin and development of an indirect competitive ELISA for residues in milk

A convenient competitive enzyme-linked immunosorbent assay(ELISA) for ciprofloxacin(CPFX) was developed by using rabbit monoclonal antibodies(RabMAbs) against a hapten-protein conjugate of CPFX-bovine serum albumin(BSA).The indirect competitive ELISA of CPFX had a concentration at 50% inhibition(IC50) of 1.47 ng/ml and a limit of detection(LOD) of 0.095 ng/ml.The mAb exhibited some cross-reactivity,however,not so high with enrofloxacin(28.8%),ofloxacin(13.1%),norfloxacin(11.0%),fleroxacin(22.6%),and pefloxacin(20.4%).And it showed almost no cross-reactivity with other antibiotics or sulfonamides evaluated in this study.The competitive ELISA kit developed here could be used as a screening tool to detect and control illegal addition of CPFX in food products.This kit had been applied to milk detection and the recovery rates from samples spiked by CPFX were in a range of 63.02%-84.60%,with coefficients of variation of less than 12.2%.

Organophosphate esters cause thyroid dysfunction via multiple signaling pathways in zebrafish brain

Organophosphate esters(OPEs)are widespread in various environmental media,and can disrupt thyroid endocrine signaling pathways.Mechanisms by which OPEs disrupt thyroid hormone(TH)signal transduction are not fully understood.Here,we present in vivo-in vitro-in silico evidence establishing OPEs as environmental THs competitively entering the brain to inhibit growth of zebrafish via multiple signaling pathways.OPEs can bind to transthyretin(TTR)and thyroxine-binding globulin,thereby affecting the transport of TH in the blood,and to the brain by TTR through the blood-brain barrier.When GH3 cells were exposed to OPEs,cell proliferation was significantly inhibited given that OPEs are competitive inhibitors of TH.Cresyl diphenyl phosphate was shown to be an effective antagonist of TH.Chronic exposure to OPEs significantly inhibited the growth of zebrafish by interfering with thyroperoxidase and thyroglobulin to inhibit TH synthesis.Based on comparisons of modulations of gene expression with the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases,signaling pathways related to thyroid endocrine functions,such as receptor-ligand binding and regulation of hormone levels,were identified as being affected by exposure to OPEs.Effects were also associated with the biosynthesis and metabolism of lipids,and neuroactive ligand-receptor interactions.These findings provide a comprehensive understanding of the mechanisms by which OPEs disrupt thyroid pathways in zebrafish.

Effect of Puerarin on the Pharmacokinetics of Baicalin in Gegen Qinlian Decoction (葛根芩连汤) in Mice

Objective： To study the pharmacokinetics of puerarin（PUE） in Gegen Qinlian Decoction（葛根芩连汤, GQD）, and the effects of PUE dosage variations on the pharmacokinetics of baicalin（BAL） in mice. Methods： GQD is composed of the concentrated granules of four Chinese herbs. Three dosages with different levels of PUE, including GQD, GQD co-administered with PUE, and GQD co-administration with two times the amount of PUE, were used to research the pharmacokinetics of PUE and BAL in mice. The indirect competitive enzyme-linked immunosorbent assay（ic ELISA） methods based on an anti PUE-monoclonal antibody（MAb） and BAL-MAb were employed to determine the concentration of PUE and BAL in mice blood. Results： After the co-administration of GQD with PUE, the area under the curves（AUC0-14 h） of PUE increased 2.8 times compared with GQD. At the dose of GQD co-administration at two times that of PUE, the AUC0-14 h of PUE was almost equal to that of GQD co-administration of PUE, showing non-linear pharmacokinetics. The AUC0-48 h of BAL showed a good dose-related increase of PUE（r=0.993） in the range from 100 to 300 mg/kg, indicating that PUE dramatically affects the absorption of BAL in mice. There was no significant difference in the other pharmacokinetic parameters, such as the first time of maximum concentration（Tmax）, the second Tmax, or the mean residence time. Conclusions： The ic ELISA methods were successfully applied to pharmacokinetic studies of PUE and BAL in GQD in mice. The dosage variability of PUE of the main ingredient in GQD affects its own pharmacokinetic characteristics and the absorption characteristics of BAL.