Enzyme-linked immunosorbent assay for the organophosphorus insecticide fenthion. Influence of hapten structure

Electrochemical biosensor based on cellulose nanofibers/graphene oxide and acetylcholinesterase for the detection of chlorpyrifos pesticide in water and fruit juice†

In this work, cellulose nanofibers and graphene oxide are used to fabricate a simple and reliable electrochemical biosensor, based on acetylcholinesterase (AChE) for the detection of highly dangerous organophosphates (OPs), utilizing chlorpyrifos as a representative sample. AChE is an enzyme that is essential for neurotransmission and catalyzes the conversion of acetylcholine (ATCh) into thiocholine and acetic acid. The pesticide used in this work, chlorpyrifos, inhibits the catalytic activity of AChE on ATCh, and this inhibition can be measured using square wave voltammetry (SWV). Utilizing a process of surface modification, layers of cellulose nanofibers, graphene oxide, a chitosan-graphene oxide composite, and acetylcholinesterase (AChE/CS-GO/GO/CNFs) were immobilized on a screen-printed carbon electrode (SPCE). The modified SPCE working electrode was characterized using scanning electron microscopy and graphene oxide trapped in the cellulose nanofibers was found to increase the sensitivity of the biosensor. The modified biosensor demonstrated good performance for detection of chlorpyrifos over a linear range of 25–1000 nM under optimum conditions, and the limits of detection and quantification were 2.2 nM and 73 nM, respectively. Our sophisticated technique might offer a more precise, straightforward, quick, and environmentally friendly way to assess chlorpyrifos contamination in water and juice samples.

Cellulose nanofibers and graphene oxide are used to fabricate an electrochemical biosensor based on acetylcholinesterase for detecting organophosphates. This biosensor is simple and reliable, and it utilizes chlorpyrifos as a representative sample of highly dangerous OPs.

Facile synthesis disposable MOF membrane filter: Growth of NH2-MIL-125 (Ti) on filter paper for fast removal of organophosphorus pesticides in aqueous solution and vegetables

Metal-organic frameworks (MOFs) have great potential to remove pesticide residues. However, the lack of affinity between the materials and target and the process of trivial sample preparation resulted in limited removal efficiency. Here, we report a one-pot method for the fast preparation of NH₂-MIL-125 (Ti)-based filter paper to synthesise NH₂-MIL-125 (Ti)-based filter paper membranes. The NH₂-MIL-125 (Ti)-based filter paper membrane takes advantage of π-π interactions between the organophosphorus pesticides (OPPs) and the benzene ring of MOFs. The affinity of amino groups and metal Ti for phosphorus atoms in the OPPs exhibits rapid removal efficiency for three OPPs, imidan, fenthion, and fenitrothion. The isothermal adsorption results for imidan, fenthion, and fenitrothion were consistent with the Langmuir, Freundlich, and Langmuir models, respectively. The kinetic results for imidan, fenthion, and fenitrothion agreed with the pseudo-second-order kinetic model, and the removal efficiency reached equilibrium within 1 min. There was no significant change in the adsorption capacity of OPPs in different pH solutions (pH = 2-10). Compared with that of MOFs, the NH₂-MIL-125 (Ti)-based filter paper membrane removal efficiency of OPPs is the same, and it also has better removal efficiency in actual spinach samples. As a result, the sample pretreatment procedure was simplified using a low-cost and simple-to-synthesize disposable NH₂-MIL-125 (Ti)-based filter paper membrane, samples' quick separation and the simultaneous fast removal of OPPs.

Fluoride-Free 2D Niobium Carbide MXenes as Stable and Biocompatible Nanoplatforms for Electrochemical Biosensors with Ultrahigh Sensitivity

Recently, 2D niobium carbide MXene has drawn vast attention due to its merits of large surface area, good metallic conductivity, and tunable band gap, making it desirable for various applications. However, the usage of highly toxic fluoride-containing etchant and quite long etching time in the conventional synthesis route has greatly hindered further exploration of MXene, especially restricting its biomedical application. Herein, novel fluoride-free Nb2CT x nanosheets are prepared by a facile strategy of electrochemical etching (E-etching) exfoliation. Taking advantage of rapid aluminum clearance, excellent chemical stability, and biocompatibility from the MXene by E-etching, fluoride-free Nb2CT x /acetylcholinesterase-based biosensors are constructed for phosmet detection with the limit of detection down to 0.046 ng mL-1. The fabricated Nb2CT x -based biosensor is superior to the counterpart from hydrofluoric acid-etched Nb2CT x , indicating that fluoride-free MXene can enhance the enzyme activity and electron transfer in the biosensor. The results prove that the fluorine-free MXene shows promise for developing biosensors with high performance of ultrahigh sensitivity and selectivity. It is highly expected that the fluoride-free MXene as a stable and biocompatible nanoplatform has great potential to be expanded to many other biomedical fields.

Metal Organic Framework steered electrosynthesis of anisotropic gold nanorods for specific sensing of organophosphate pesticides in vegetables collected from the field

The uncontrolled use of organophosphate (OP) group of pesticides has led to their accumulation in food and vegetables, causing major health issues. Hence, the development of a reliable sensor is imperative for the detection of neurotoxic organophosphates (OP). In the present study, we have intertwined the interfaces of a Metal Organic Framework (MOF), MOF-directed rapid electrochemically grown gold nanorods (aAuNR), cysteamine (Cys) functionalization, and the neurotransmitter acetylcholinesterase (AChE) to fabricate a novel electrochemical bioprobe AChE/Cys/aAuNR/MOF/ITO for sensing OP pesticides with an ultra-low detection limit of 3 ng L-1 over a linear range of 30 to 600 ng L-1. Prior to sensing, in silico docking studies were employed for tracking the structural aspects of the molecular recognition of specific OP as potential inhibitors. The sensor can quantify residues of sprayed OP (chlorpyrifos, malathion, parathion, methyl parathion, ethion) in field vegetables (Abelmoschus esculentus, Solanum melongena, Capsicum annuum, Momordica charantia Linn) using a single calibration curve designed using chlorpyrifos, and the results were validated via gas chromatography-electron capture detector (GC-ECD) measurements. The inhibition rate kinetics of structurally different OP (chlorpyrifos, malathion, methyl parathion) were studied via the bioprobe and further validated using the standard Ellman method, confirming the practical applicability of the sensor for the detection of a specific group of OP. The bioprobe AChE/Cys/aAuNR/MOF/ITO offers good stability, specificity, and anti-interference properties for the detection of OP in real samples.

Boosting the sensitivity of in vitro β-lactam allergy diagnostic tests

The synthesis of structurally new haptens and the development of suitable antigens are essential for boosting the sensitivity of drug allergy diagnostic testing.

High-performance electrochemical enzyme sensor for organophosphate pesticide detection using modified metal-organic framework sensing platforms

A practical electrochemical biosensor with high sensitivity was developed for detecting organophosphorus (OP). Initially, Ce metal was introduced into an UiO-66-template to form Ce/UiO-66. Later, graphene oxide (GO), carbon black (CB) and multi-walled carbon nanotubes (MWCNTs) were separately added to Ce/UiO-66 to compare the effect of different carbon-based material types on the performance of the biosensor. Exclusively, Ce/UiO-66/MWCNTs with a Ce (7%) and MWCNT (30%) matrix was found to not only load more acetylcholinesterase (AChE) onto vacant sites but also increase electron transfer and decrease the number of diffusion pathways between the thiocholine and electrode surface. Moreover, the appropriate oxophilicity of Ce coupled with the high surface area and good conductivity of MWCNTs in the UiO-66 structure revealed a high affinity to acetylthiocholine chloride (ATCl) and possible catalysis of the hydrolysis of ATCl with a Michaelis-Menten constant of 0.258 mM. This biosensor, under optimal conditions, demonstrated a rapid and sensitive detection of paraoxon over a wide linear range of 0.01-150 nM, with a low detection limit of 0.004 nM. As a result, the AChE/Ce/UiO-66/MWCNTs/GCE biosensor can be employed in laboratory and field experiments to determine paraoxon levels.

A class-selective immunoassay for simultaneous analysis of anilinopyrimidine fungicides using a rationally designed hapten

The development of multianalyte immunoassays constitutes a main research issue in the field of bioanalytical techniques. In the present study, class-specific antibodies against the three members of the anilinopyrimidine family of fungicides (pyrimethanil, cyprodinil and mepanipyrim) were raised by using a bioconjugate of a rationally designed hapten [5-(6-methyl-2-(phenylamino)pyrimidin-4-yl)pentanoic acid]. Highly sensitive immunoassays were developed for the generic determination of these compounds, using the competitive enzyme-linked immunosorbent assay (ELISA). Particularly, a direct antibody-coated competitive ELISA afforded identical sensitivity for the three anilinopyrimidines, with IC₅₀ values of 0.26, 0.27 and 0.25 μg L^-1 for pyrimethanil, cyprodinil and mepanipyrim, respectively. This immunoassay was fully characterized and applied to the multianalyte determination of anilinopyrimidine fungicides in white and red wines, with a limit of quantification of 1 μg L^-1, average recoveries from 93.1 to 114.4%, and relative standard deviations lower than 20%. Commercial wine samples were analyzed and those containing detectable anilinopyrimide residues were verified by a reference chromatographic technique.

Detection of the Antimicrobial Triclosan in Environmental Samples by Immunoassay

A sensitive, competitive enzyme-linked immunosorbent assay (ELISA) for the detection of the antimicrobial triclosan (TCS; 2,4,4'-trichloro-2'-hydroxydiphenyl ether) was developed. Novel immunizing haptens were synthesized by derivatizing at the 4-Cl position of the TCS molecule. Compounds derived from substitutions at 4'-Cl and that replaced the 2'-OH with a Cl atom were designed as unique coating antigen haptens. Polyclonal rabbit antisera were screened against the coating antigen library to identify combinations of immunoreagents resulting in the most sensitive assays. The most sensitive assay identified was one utilizing antiserum no. 1155 and a heterologous competitive hapten, where the 2'-OH group was substituted with a Cl atom. An IC50 value and the detection range for TCS in assay buffer were 1.19 and 0.21-6.71 μg/L, respectively. The assay was selective for TCS, providing low cross-reactivity (<5%) to the major metabolites of TCS and to brominated diphenyl ether-47. A second assay utilizing a competitive hapten containing Br instead of Cl substitutions was broadly selective for both brominated and chlorinated diphenylethers. Using the most sensitive assay combination, we measured TCS concentrations in water samples following dilution. Biosolid samples were analyzed following the dilution of a simple solvent extract. The immunoassay results were similar to those determined by LC-MS/MS. This immunoassay can be used as a rapid and convenient tool to screen for human and environmental exposure.

Development of an enzyme linked immunosorbent assay for detection of cyathane diterpenoids

Background

So-called cyathane type diterpenoids are produced as secondary metabolites by basidiomycetes. Based on their antibacterial, fungicidal, and cytotoxic properties, cyathane type terpenoids represent interesting target compounds in fungal biotechnology.

Results

An indirect competitive enzyme linked immunosorbent assay has been developed for detection of cyathane type diterpenoids. Rabbit polyclonal antibodies were raised against a mixture of striatal A and B conjugated to bovine serum albumin. The conditions for direct attachment of the hapten striatal B to a solid phase by passive adsorption were optimized. The cross reactivities of the striatals A, C and D, of the striatins A and B, and of the erinacines C and P to striatal B were determined. The validation study showed that the ELISA was precise and sensitive. The average IC₅₀ of striatal B was 36.0 ng mL⁻¹ with an inter-assay coefficient of variation (CV) of 13.2% (n = 5). Recoveries from striatal B spiked samples in the assay were in the range of 97.3 – 125.9%. A good correlation between the striatal B concentration measured by the ELISA and by HPLC-DAD (y = 1.1122× – 0.1585, R² = 0.9942) was obtained from linear regression analysis. The suitability of the ELISA for detection of cyathane type diterpenoids in submerged cultures and fruiting bodies of H. erinaceus was studied. It showed cross reactivity with supernatants from submerged cultures and extracts thereof, but did not show cross reactivity with extracts from fruiting bodies.

Conclusions

The developed method is appropriate for qualitative and quantitative detection of cyathane diterpenoids in complex mixtures. Due to its high sensitivity and specificity, it represents an ideal screening method for discovering new cyathane diterpenoids and new potential producers of them.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-014-0098-4) contains supplementary material, which is available to authorized users.

Quick and label-free detection for Coumaphos by using surface plasmon resonance biochip

Coumaphos is a common organophosphorus pesticide used in agricultural products. It is harmful to human health and has a strictly stipulated maximum residue limit (MRL) on fruits and vegetables. Currently existing methods for detection are complex in execution, require expensive tools and are time consuming and labor intensive. The surface plasmon resonance method has been widely used in biomedicine and many other fields. This study discusses a detection method based on surface plasmon resonance in organophosphorus pesticide residues. As an alternative solution, this study proposes a method to detect Coumaphos. The method, which is based on surface plasmon resonance (SPR) and immune reaction, belongs to the suppression method. A group of samples of Coumaphos was detected by this method. The concentrations of Coumaphos in the samples were 0 µg/L, 50 µg/L, 100 µg/L, 300 µg/L, 500 µg/L, 1000 µg/L, 3000 µg/L and 5000 µg/L, respectively. Through detecting a group of samples, the process of kinetic reactions was analyzed and the corresponding standard curve was obtained. The sensibility is less than 25 µg/L, conforming to the standard of the MRL of Coumaphos stipulated by China. This method is label-free, using an unpurified single antibody only and can continuously test at least 80 groups of samples continuously. It has high sensitivity and specificity. The required equipments are simple, environmental friendly and easy to control. So this method is promised for a large number of samples quick detection on spot and for application prospects.

Synthesis of haptens and development of an indirect enzyme-linked immunosorbent assay for tris(2,3-dibromopropyl) isocyanurate

A competitive indirect enzyme-linked immunosorbent assay (ciELISA) was developed for detection of tris(2,3-dibromopropyl) isocyanurate (TBC). Polyclonal antibodies against TBC were raised from synthesized haptens and then screened against various coating antigens. After optimization of the immunoassay conditions, the linear range and IC₅₀ value of the assay were 0.30-100 and 5.17 μg/L, respectively, with little cross-reactivity (≤2%). Recovery of various samples (water, serum, soil) was tested and the values ranged from 68% to 110%. This ciELISA was also applied to determine TBC in the riverside soil of the Liuyang River, and the results were compared with the data obtained by UHPLC-MS/MS. The experimental assay results confirmed that this proposed immunoassay is a specific, sensitive, and reliable method for determination and monitoring of TBC.

Soil contamination and persistence of pollutants following organophosphate sprays and explosions to control red-billed quelea (Quelea quelea)

BACKGROUND

Red-billed quelea (Quelea quelea) are controlled at breeding colonies and roosts by organophosphate sprays or explosions. Contamination with organophosphates after sprays and with petroleum products and phthalates after explosions was assessed.

RESULTS

Concentrations in soil of the organophosphate fenthion the day after sprays were uneven (0-29.5 µg g(-1)), which was attributable to excess depositions at vehicle turning points, incorrect positioning of nozzles and poor equipment maintenance. A laboratory study using field-collected samples provided an estimate of 47 days for the half-life of fenthion. After sprays, fenthion persisted in soil for up to 188 days. High concentrations were detected 5 months after negative results at the same sites, providing indirect evidence of leaching. Concentrations of total petroleum hydrocarbons (TPHs) and phthalates ranged from 0.05 to 130.81 (mean 18.69) µg g(-1) and from 0 to 1.62 (mean 0.55) µg g(-1) respectively in the craters formed by the explosions, but declined to means of 0.753 and 0.027 µg g(-1) at 10 m away. One year after an explosion, mean TPHs of 0.865 and mean phthalates of 0.609 were detected.

CONCLUSION

Localisation of high concentrations of fenthion likely to have effects on soil biota could be mitigated by improved spray management. Given a half-life in the soil of 47 days for fenthion and the possibility of its leaching months after applications raises concerns about its acceptability. The pollutants left behind after explosions have been quantified for the first time, and, given their long-term persistence, their continued use poses a threat to environmental health.

Comparison of homologous and heterologous formats in nanocolloidal gold-based immunoassays for parathion residue determination

The effectiveness of homologous and heterologous formats in a nanocolloidal gold-based immunoassay for pesticide residue determination was investigated. Parathion, one of the most toxic organophosphorus pesticides, was used as the target analyte. One-step homologous and heterologous test strips based on a nanocolloidal gold-labeled monoclonal antibody were developed for the rapid detection of parathion residues. The results showed that the heterologous format was more effective than the homologous format, being more sensitive, more specific to parathion and more tolerant of matrix interferences. The best competitive hapten was found to have a moderate heterology and the opposite electronic distribution to the immunizing hapten. The detection limits for parathion using the preferred heterologous strip were 1 μg/L in water samples and 5 μg/kg in soil and food samples.

An immunoassay for dibutyl phthalate based on direct hapten linkage to the polystyrene surface of microtiter plates

BACKGROUND

Dibutyl phthalate (DBP) is predominantly used as a plasticizer inplastics to make them flexible. Extensive use of phthalates in both industrial processes and other consumer products has resulted in the ubiquitous presence of phthalates in the environment. In order to better determine the level of pollution in the environment and evaluate the potential adverse effects of exposure to DBP, immunoassay for DBP was developed.

METHODOLOGY/PRINCIPAL FINDINGS

A monoclonal antibody specific to DBP was produced from a stable hybridoma cell line generated by lymphocyte hybridoma technique. An indirect competitive enzyme-linked immunosorbent assay (icELISA) employing direct coating of hapten on polystyrene microtiter plates was established for the detection of DBP. Polystyrene surface was first oxidized by permanganate in dilute sulfuric acid to generate carboxyl groups. Then dibutyl 4-aminophthalate, which is an analogue of DBP, was covalently linked to the carboxyl groups of polystyrene surface with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). Compared with conjugate coated format (IC(50)=106 ng/mL), the direct hapten coated format (IC(50)=14.6 ng/mL) improved assay sensitivity after careful optimization of assay conditions. The average recovery of DBP from spiked water sample was 104.4% and the average coefficient of variation was 9.95%. Good agreement of the results obtained by the hapten coated icELISA and gas chromatography-mass spectrometry further confirmed the reliability and accuracy of the icELISA for the detection of DBP in certain plastic and cosmetic samples.

CONCLUSIONS/SIGNIFICANCE

The stable and efficient hybridoma cell line obtained is an unlimited source of sensitive and specific antibody to DBP. The hapten coated format is proposed as generally applicable because the carboxyl groups on modified microtiter plate surface enables stable immobilization of aminated or hydroxylated hapten with EDC. The developed hapten coated icELISA can be used as a convenient quantitative tool for the sensitive and accurate monitoring DBP in water, plastic and cosmetic samples.

Omethoate modulates some oxidant/antioxidant parameters in frogs (Rana ridibunda Pallas)

The aim of this study was to investigate the effect of an organophosphorus insecticide omethoate (OM), on certain oxidative stress biomarkers (malondialdehyde (MDA), reduced glutathione (GSH), glutathione- S-transferase (GST), glutathione reductase (GR), catalase (CAT)) in tongue, lung, stomach and muscle tissues of adult frogs ( Rana ridibunda Pallas). Animals were exposed to 10 and 20 parts per million dosages of OM for 24, 48, 72 or 96 h. According to the results, MDA level increased significantly in lung and stomach tissues. GSH content fluctuated in lung and muscle while it elevated in tongue and stomach tissues. With regard to antioxidant enzymes (GST, GR and CAT), their activities reduced in tongue, while they increased in lung and fluctuated in stomach and muscle tissues. It can be concluded that exposure of frogs to OM are characterized by increased MDA levels and fluctuated enzyme activities and GSH contents. This may reflect the potential role of these parameters as useful biomarkers for assessment of OM toxicity.

Development of a monoclonal antibody-based, congener-specific and solvent-tolerable direct enzyme-linked immunosorbent assay for the detection of 2,2',4,4'-tetrabromodiphenyl ether in environmental samples

A sensitive direct enzyme-linked immunosorbent assay (ELISA) for the specific detection of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in environmental samples was developed. A hapten mimicking BDE-47 was synthesized by introducing a butyric acid spacer into 5-hydroxy-BDE-47 and coupled to keyhole limpet hemocyanin to form an immunogen for the production of monoclonal antibodies (Mabs) against BDE-47. The most sensitive direct ELISA was formatted with a Mab, designated as 4F2, in combination with 5-(2,4-dibromophenoxy)pentanoic acid peroxidase as a tracer. The inhibition half-maximum concentrations and limit of detection of BDE-47 in phosphate buffered saline with 25% DMSO were 1.4 ± 0.05 and 0.1 ng mL(-1), respectively. Cross-reactivity values of the ELISA with the tested BDE congeners and metabolites were ≤5.8%. This assay was used to determine BDE-47 in soil, sediment and house dust samples after ultrasonic extraction, simple cleanup and concentration steps. The average recoveries, repeatabilities (intraday extractions and analyses), and intra-laboratory reproducibilities (interday extractions and analyses) were in a range of 92-126%, 8-19% and 9-25%, respectively. Applied to 44 real samples, the results of this assay displayed a statistically significant correlation with those of a gas chromatography-mass spectrometry method (R(2)=0.79-0.85), indicating this ELISA is a suitable tool for environmental analyses of BDE-47.

Neurotoxic and immunotoxic effects of fenthion and omethoate on frogs at acute exposure

The study was carried out to investigate the neurotoxic and immunotoxic effects of fenthion- and omethoate-used agricultural areas on frogs (Rana ridibunda) at acute exposure. The neurotoxic effects of the chemicals were evaluated by measuring the activities of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Biomarkers selected for immunotoxic monitoring were the activities of adenosine deaminase (ADA) and myeloperoxidase (MPO) in various tissues of frogs exposed to 10 or 20 parts per million (ppm) dosages of fenthion and omethoate for 24, 48, 72 and 96 hours. Results showed that the administrations of chemicals fluctuated AChE and BChE activities in some tissues of frogs treated with both dosages at all the periods. With regard to the immunotoxic effects, MPO activity was increased in almost all the tissues of frogs after 10 and 20 ppm dosages and for 24, 48, 72 and 96 hours exposure of fenthion and omethoate as compared to those of control whereas ADA activity did not change in all the tissues. This may reflect the potential role of these parameters as useful biomarkers for toxicity of fenthion and omethoate.

Enzyme-linked immunosorbent assays for doping control of 5alpha-reductase inhibitors finasteride and dutasteride

Finasteride and dutasteride are 5alpha-reductase inhibitors included in the World Anti-Doping Agency's list of banned substances. Two highly sensitive and selective ELISA assays were developed for these compounds. Polyclonal rabbit antibodies were raised using synthesized haptens and other commercial products. The best immunoassay obtained, based on an antibody-coated format, showed a limit of detection of 0.01 microg L(-1) and an IC(50) of 0.75 microg L(-1) for finasteride (cross-reactivity with dutasteride<4%). The second assay allowed finasteride and dutasteride determination, with limits of detection of 0.013 and 0.021 microg L(-1), and IC(50) values 0.18 and 1.18 microg L(-1), respectively. Both assays were highly selective to a set of anabolic steroids, but they showed 37% and 30% cross-reactivity with the major urinary metabolite of finasteride, allowing its determination. The developed ELISA had better sensitivity than HPLC/MS/MS method and was applied as a screening technique to quantify dutasteride, finasteride, and its main metabolite in human urine without sample pre-treatment. Moreover, the analysis of dutasteride's excretion urines by ELISA was used to obtain its human excretion rate, essential to improve the analytical strategies about this type of drugs (permitted as medicines and prohibited in sport) and to establish an effective anti-doping policy.

Development of enzyme-linked immunosorbent assays for the organophosphorus insecticide EPN

Competitive enzyme-linked immunosorbent assays (ELISAs) in indirect and direct format were developed for the quantitative detection of the organophosphorus insecticide EPN. Five EPN derivatives (haptens) were synthesized and coupled to carrier proteins to use as an immunogen or as a competitor. Rabbits were immunized with two of the five haptens coupled to KLH for production of polyclonal antibodies, and the sera were screened against one of the haptens coupled to ovalbumin (OVA). Using the serum with the highest specificity and a coating antigen (hapten-OVA conjugate), an indirect (antigen-coated) ELISA was developed, which showed an IC(50) of 5.6 ng/mL with a detection limit of 0.2 ng/mL (20% inhibition). A direct (antibody-coated) ELISA using an enzyme tracer (hapten-enzyme conjugate) was also developed, which showed an IC(50) of 8.4 ng/mL with a detection limit of 0.9 ng/mL (20% inhibition). The antibodies showed negligible cross-reactivity with other organophosphorus pesticides except with the insecticide parathion-ethyl only in the direct ELISA. The recoveries of EPN from spiked samples determined by the indirect ELISAs were between 37 and 164%.

Selective enzyme-linked immunosorbent assay for triclosan. Application to wastewater treatment plant effluents

A sensitive and highly selective enzyme-linked immunosorbent assay was developed for triclosan, one of the most common bactericides in personal care products, which is also considered as an emerging contaminant, given its presence in the effluents of sewage and wastewater treatment plants. From synthesized haptens, polyclonal rabbit antibodies against triclosan were raised. The best ELISA immunoassay was based on an antibody-coated format, yielding a detection limit of 0.03 microg L(-1), an I50 of 3.85 microg L(-1), and a dynamic range from 0.22 to 42.16 microg L(-1), with little or no cross-reactivity (< 10%) to similarly structured compounds, including its metabolite methyltriclosan (CR < 6%). The assay was applied as a screening method to quantify triclosan in surface water and in wastewaters. After C18 solid-phase extraction, nanogram per liter concentrations were determined in effluents of urban wastewater treatment plants. The satisfactory recoveries achieved as well as the agreement between immunochemical and chromatographic methods (GC-MS) indicate its potential for either screening or laboratory quantification.

Hapten heterology for a specific and sensitive indirect enzyme-linked immunosorbent assay for organophosphorus insecticide fenthion

Five haptens with different spacer-arm attachment sites on the structure of the organophosphorus insecticide fenthion were designed and synthesized. All of the haptens were conjugated with ovalbumin (OVA) for the coating antigen, and three haptens containing all or most of the structure of fenthion were conjugated with bovine serum albumin (BSA) for the immunogen. Six polyclonal antisera were raised against the three BSA conjugates, and 30 antibody/coating conjugate combinations were selected for studies of assay sensitivity and specificity for fenthion. The study revealed the best combination with high sensitivity (I50 of 0.08 ng mL(-1)) and high assay specificity, which indicated that when structural difference between the analyte and an immunizing hapten is less than that between a coating hapten and the immunizing hapten, a high sensitive enzyme-linked immunosorbent assay (ELISA) in the heterologous system may stand a good chance to be developed. The immunity results showed that heterology in the hapten spacer-arm attachment site of the immunogen could achieve a remarkable improvement in the quantity, sensitivity, and/or specificity of antibody, and that the moiety of an analyte, which is the same as the moiety near/on the immunizing spacer-arm hapten attachment site, contributes greatly to the interaction of antibody and hapten.

Enzyme-linked immunosorbent assays for the insecticide fenitrothion. Influence of hapten conformation and sample matrix on assay performance

This study aimed at developing competitive enzyme-linked immunosorbent assays (ELISAs) for the organophosphorus (OP) insecticide fenitrothion using a monoclonal antibody. The hapten used to obtain the antibody had an ideal structural feature that allowed minimal functional group sacrifice. By using the antibody and a coating antigen, a competitive indirect ELISA was developed, which showed an IC50 of 14 ng mL(-1) with a detection limit of 3.0 ng mL(-1). A competitive direct ELISA using an enzyme tracer was also developed, which showed an IC50 of 17 ng mL(-1) with a detection limit of 1.6 ng mL(-1). The antibodies in both assays showed negligible cross-reactivity with the metabolites of fenitrothion and other OP pesticides except with the insecticides parathion-methyl and parathion-ethyl. Recoveries of fenitrothion from fortified rice and lettuce samples were determined and the bias in the recovery values was rationalized by using the standard curves obtained in the matrix extract.