Development of a highly sensitive enzyme-linked immunosorbent assay for atrazine Performance evaluation by flow injection immunoassay

An integrated strategy for rapid on-site screening and determination of prometryn residues in herbs

We produced a prometryn-specific monoclonal antibody and propose a strategy for convenient on-site detection of prometryn residues in herbs for the first time. This strategy has perfect applicability in a complex herbal medicine matrix. The strategy combines a semiquantitative immunochromatographic strip assay with a heterologous indirect competitive ELISA. When there was no matrix interference, the ELISA had a half-maximal inhibitory concentration of 2.6 ng·mL^-1 and a limit of detection of 0.2 ng·mL^-1. The immunochromatographic strip assay can be completed within 5 min with a visual limit of detection of 1 ng·mL^-1. Although the sample matrix had different effects on the sensitivity of the antibody, excellent repeatability and accuracy were achieved. The method was successfully applied for the screening and determination of prometryn residue in multiple complex herb samples for the first time, and the results were in good agreement with those obtained by liquid chromatography-tandem mass spectrometry. The proposed strategy is rapid, of high-throughput, and of low cost, and may be a promising choice for on-site detection of prometryn in different kinds of herbs. Graphical abstract.

A competitive lateral flow assay for the detection of tenofovir

Proper management of an HIV infection requires that a patient be at least 80-95% adherent to a prescribed drug regimen to avoid poor health outcomes and the development of drug-resistant HIV strains. Clinicians generally monitor adherence habits indirectly through patient self-reporting, pill counting, and electronic drug monitoring. While direct measurement of patient samples like urine for monitoring drug levels is possible, it requires specialized equipment and training that is not readily available in resource-limited settings where the need is greatest. In this work we report the development of an antibody that binds to tenofovir (TFV), a key small molecule drug for both the treatment and prevention of HIV, and a competitive lateral flow assay that uses that antibody to monitor urine samples for the presence of the drug. TFV was conjugated to an immunogenic protein and injected into rabbits to raise polyclonal antibodies sensitive to the drug. The antibodies were verified for TFV-sensitivity by immunoprecipitation and HPLC. A gold nanoparticle-based competitive assay was developed to detect the presence of TFV in urine samples with a sensitivity of 1 μg mL-1. This TFV assay could be deployed as a point-of-care device for adherence monitoring in resource-limited settings as a low-cost, accurate, and speedy alternative to current methods to better inform changes in treatment.

A microfluidic device for the automated electrical readout of low-density glass-slide microarrays

Microarrays are a powerful platform for rapid and multiplexed analysis in a wide range of research fields. Electrical readout systems have emerged as an alternative to conventional optical methods for microarray analysis thanks to its potential advantages like low-cost, low-power and easy miniaturization of the required instrumentation. In this work an automated electrical readout system for low-cost glass-slide microarrays is described. The system enables the simultaneous conductimetric detection of up to 36 biorecognition events by incorporating an array of interdigitated electrode transducers. A polydimethylsiloxane microfluidic structure has been designed that creates microwells over the transducers and incorporates the microfluidic channels required for filling and draining them with readout and cleaning solutions, thus making the readout process fully automated. Since the capture biomolecules are not immobilized on the transducer surface this readout system is reusable, in contrast to previously reported electrochemical microarrays. A low-density microarray based on a competitive enzymatic immunoassay for atrazine detection was used to test the performance of the readout system. The electrical assay shows a detection limit of 0.22±0.03 μg L(-1) similar to that obtained with fluorescent detection and allows the direct determination of the pesticide in polluted water samples. These results proved that an electrical readout system such as the one presented in this work is a reliable and cost-effective alternative to fluorescence scanners for the analysis of low-density microarrays.

Nanogold bioconjugates for direct and sensitive multiplexed immunosensing

The use of nanogold bioconjugates for direct detection of the antibody-antigen immunoreaction is addressed. The integration of gold nanoparticles tracers as signal generators in microarray immunosensing and compact disc detection technique show important advantages to reach sensitive, selective, high throughput, reliable and cost-effective assays. For that, a thorough study of the performances of the size of spherical nanogold particles and coating density was developed. The size of the nanoparticle determines the optimal antibody dilution, being the smaller particles the best performing ones. Enhancement effect of lower size is also studied. The gold labeling method do not affects the recognition capability of the labeled proteins. As a proof of concept, the nanoconjugates were used for the simultaneous and direct determination of small molecules. Employing nanogold bioconjugates as recognition labels resulted in robust and reliable assays, reaching a sensitivity of 0.03 and 1.3μg/L for sulfasalazine and atrazine, respectively. This shows that the use of nanogold bioconjugates for direct immunosensing is very competitive, achieving highly sensitive and reproducible assays (RSD<10%). This approach would simultaneously determine both small and large molecular size targets, in different formats, using the same detection mode what paves the way for many other applications in different scenarios.

Preparation of antibodies and development of an enzyme-linked immunosorbent assay (ELISA) for the determination of doxycycline antibiotic in milk samples

This paper reports the development of an immunoassay for the specific analysis of doxycycline (DC), a congener of the tetracycline antibiotic family (TCs), in milk samples. This is the first time that DC antibody production is reported, based on a rationally designed and well-characterized immunizing hapten. The chemical structure of the immunizing hapten (13-[(2-carboxyethyl)thiol]-5-hydroxy-6-α-deoxytetracycline, TC1) was designed to maximize recognition of the tetracycline characteristic moiety defined as lower periphery of the TCs plus the region of the upper periphery composed by the hydroxyl group at position C(5) (B ring) and the dimethylamino group in ring A. Polyclonal antibodies raised against TC1 coupled to horseshoe crab hemocianyn (HCH) were used to develop a homologous indirect competitive enzyme-linked immunosorbent assay (ELISA). The microplate ELISA can detect DC in buffer down to 0.1 μg L(-1). The ELISA has been proven to tolerate a wide range of ionic strengths and pH values. The assay is very selective for DC with a minor recognition of methacycline (32% of cross-reactivity). Experiments performed with whole milk samples demonstrate that samples can be directly analyzed after a simple treatment method, reaching detectability values below 5 μg L(-1).

Development of an immunoassay for terbutryn: study of the influence of the immunization protocol

Heterologous immunization has proven to be useful to enhance the selectivity and specificity of catalytic antibodies. However, in the field of immunoassays, few studies have been done to establish how the immunization protocol influences the antibody characteristics. In the present study, we have developed an enzyme-linked immunosorbent assay (ELISA) for the detection of the pesticide terbutryn following a homologous and a heterologous immunization strategy. No significant differences have been observed between the immunization procedures regarding immunoassay sensitivity and selectivity. Thus, immunoassays with a limit of detection below the 25 ng/l established by current European regulations have been obtained with both immunization protocols. Initial studies have been performed to assess the applicability of these ELISAs to the analysis of real water matrixes.

Immunoaffinity chromatography: an introduction to applications and recent developments

Immunoaffinity chromatography (IAC) combines the use of LC with the specific binding of antibodies or related agents. The resulting method can be used in assays for a particular target or for purification and concentration of analytes prior to further examination by another technique. This review discusses the history and principles of IAC and the various formats that can be used with this method. An overview is given of the general properties of antibodies and of antibody-production methods. The supports and immobilization methods used with antibodies in IAC and the selection of application and elution conditions for IAC are also discussed. Several applications of IAC are considered, including its use in purification, immunodepletion, direct sample analysis, chromatographic immunoassays and combined analysis methods. Recent developments include the use of IAC with CE or MS, ultrafast immunoextraction methods and the use of immunoaffinity columns in microanalytical systems.

Generation of broad specificity antibodies for sulfonamide antibiotics and development of an enzyme-linked immunosorbent assay (ELISA) for the analysis of milk samples

Immunoreagents appropriately produced to detect a wide range of sulfonamide antibiotic congeners have been used to develop a highly sensitive enzyme-linked immunosorbent assay (ELISA). The selectivity has been achieved by combining antibodies raised against 5-[6-(4-aminobenzenesulfonylamino)pyridin-3-yl]-2-methylpentanoic acid (SA1), covalently coupled to horseshoe crab hemocyanin (HCH), and 5-[4-(amino)phenylsulfonamide]-5-oxopentanoic acid (SA2), coupled to ovalbumin (OVA), on an indirect ELISA format. The immunizing hapten has been designed to address selectivity against the common aminobenzenesulfonylamino moieties, using theoretical calculations and molecular modeling tools. Hapten SA1 has been synthesized in four steps from methyl 5-(4-amino-3-pyridinyl)-2-methyl-4-pentenoate through a Heck reaction, under Jeffery conditions, to avoid introduction of additional epitopes in the linker. The microplate immunoassay developed is able to reach the necessary detectability for the determination of the sulfonamide antibiotics most frequently used in the veterinary field, in compliance with the EC Regulation 2377/90. As an example, the IC(50) and LOD values accomplished for sulfapyridine are 2.86 +/- 0.24 and 0.13 +/- 0.03 microg L(-1), respectively. Studies performed with different types of milk samples demonstrate that direct and accurate measurements can be performed in this type of matrix without any previous sample cleanup method.

Development of an enzyme-linked immunosorbent assay for determination of the miticide bromopropylate

This paper reports for the first time the development of an immunoassay for the analysis of the miticide bromopropylate (BP). The chemical structure of the immunizing haptens was designed to maximize the recognition of the bis-bromophenyl group of BP. Thus, the assay uses polyclonal antibodies raised against 2,2-bis(4-bromophenyl)-N-2-hydroxyacetamide-butanoic acid (hapten 2) conjugated to keyhole limpet hemocyanin from horseshoe crab. A heterologous indirect competitive enzyme-linked immunosorbent assay (ELISA) has been developed that can detect BP down to 0.14 microg L(-1). The assay has been proven to tolerate a wide range of ionic strengths and pH values. Studies on the selectivity of this immunoassay have demonstrated a high recognition of related pesticides that contain a bis-halophenyl group in their structure. Other pesticides do not interfere in the analysis of BP using this immunochemical technique. Preliminary experiments have shown that BP can be directly analyzed in white wine samples down to 0.16 microg L(-1) without the necessity of a cleanup procedure prior to the ELISA.

Detection of pesticide residues using an immunodevice based on negative dielectrophoresis

The detection of atrazine using a novel optical immunosensing technique based on negative dielectrophoresis (n-DEP) in microfluidic channels is described. Atrazine is a toxic triazine herbicide within the most frequently used. Polystyrene microparticles (6 microm diameters) modified with bovine serum albumin conjugated with atrazine (atrazine-BSA) were manipulated and captured when subjected to intense n-DEP electric fields. Specifically, particles were trapped when AC voltages with amplitudes of 10 V(peak) and frequencies over 1 MHz were applied to the electrodes. The immunological reaction occurring on the particles for detecting atrazine is based on an indirect competitive assay using a secondary anti-mouse immunogloburin G (IgG) antibody labeled with fluorescein isothiocyanate. The microfluidic device, with three-dimensional microelectrodes, was fabricated comprising two caged areas, allowing two simultaneous measurements inside the same microfluidic channel. The performance of this n-DEP immunosensing technique was evaluated using wine samples. The immunodevice showed a limit of detection for atrazine in buffer samples of 0.11 microgL(-1) and in pre-treated wine samples of 6.8 microg L(-1); these detection limits are lower than the maximum residue level (MRL) established by the European Community for residues of this herbicide in wine (50 microg L(-1)). This methodology offers great promise for rapid, simple, cost effective, and on-site analysis of biological, foods and beverages, and environmental samples.

Advanced homogeneous-heterogeneous immunosensing format employing restricted access supports

A rapid immunosensing methodology that employs the so-called homogeneous-heterogeneous assay mode is presented. The immunosensor is based on the homogeneous competition among the analyte, a fluorescent tracer, and the antibody, followed by separation of free and bound species by means of a restricted access alkyl-diol silica C18 reversed-phase chromatographic support. In order to develop a general labeling methodology, fluorescent tracers are synthesized from oligonucleotides covalently bound to the hapten in 3' position and the marker in 5'. The immunosensor principle is demonstrated by determining atrazine in a completely automated manner at 2 min/sample without regeneration of the support and a limit of detection of 1.0 microg/L with the optimized system. Preliminary assays employing multilabeled tracers indicate that sensitivity can be improved. Organic solvents 2-propanol and acetonitrile up to 15% (v/v) are well tolerated, while methanol can be added to 50%. The sensor capabilities are demonstrated through the analysis of natural waters.

Multichannel SPR biosensor for detection of endocrine-disrupting compounds

A surface plasmon resonance (SPR) biosensor for simultaneous detection of multiple organic pollutants exhibiting endocrine-disrupting activity, namely atrazine, benzo[a]pyrene, 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-nonylphenol, is reported. The biosensor utilizes a multichannel SPR sensor based on wavelength modulation of SPR and wavelength division multiplexing (WDM) of sensing channels, antibodies as biorecognition element and a competitive immunoassay detection format. An analysis time of 45 min (including 30-min incubation of the sample with antibodies) and limits of detection as low as 0.05, 0.07, 0.16 and 0.26 ng mL(-1) are demonstrated for benzo[a]pyrene, atrazine, 2,4-D and 4-nonylphenol, respectively. The biosensor is also shown to be regenerable and suitable for repeated use.

Development of an enzyme-linked immunosorbent assay for the determination of the linear alkylbenzene sulfonates and long-chain sulfophenyl carboxylates using antibodies generated by pseudoheterologous immunization

ELISA methods have been developed for screening contamination of water resources by linear alkyl benzene sulfonates (LAS) or the most immediate degradation products, the long chain sulfophenyl carboxylates, SPCs. The assay uses antibodies raised through pseudoheterologous immunization strategies using an equimolar mixture of two immunogens (SFA-KLH and 13C(13)-SPC-KLH) prepared by coupling N-(4-alkylphenyl)sulfonyl-3-aminopropanoic acid (SFA) and p-(1-carboxy-13-tridecyl)phenylsulfonic acid (13C(13)-SPC) to keyhole limpet hemocyanin (KLH). The immunizing haptens have been designed to address recognition versus two different epitopes of the molecule. The SFA hapten maximizes recognition of the alkyl moiety while preserving the complexity of the different alkyl chains present in the LAS technical mixture. The 13C(13)-SPC hapten addresses recognition of the common and highly antigenic phenylsulfonic group. The antisera raised using this strategy have been shown to be superior to those obtained through homologous immunization procedures using a single substance. By using an indirect ELISA format, LAS and long-chain SPCs can be detected down to 1.8 and 0.2 microg L(-1), respectively. Coefficients of variation of 6 and 12% within and between assays, respectively, demonstrate immunoassay reproducibility. The assay can be used in media with a wide range of pH and ionic strength values. Preliminary experiments performed to assess matrix effects have demonstrated the potential applicability of the method as a screening tool to assess contamination by these types of surfactants in natural water samples.

Part per trillion determination of atrazine in natural water samples by a surface plasmon resonance immunosensor

A new immunoassay for continuously monitoring atrazine in water has been developed. It uses a portable biosensor platform based on surface plasmon resonance (SPR) technology. This immunoassay is based on the binding inhibition format with purified polyclonal antibodies, with the analyte derivative covalently immobilized on a gold sensor surface. An alkanethiol self-assembled monolayer (SAM) was formed on the gold-coated sensor surface in order to obtain a reusable sensing surface. The low detection limit for the optimized assay, calculated as the concentration that produces a 10% decrease in the blank signal, is 20 ng/L. A complete assay cycle, including regeneration, is accomplished in 25 min. Additionally, a study of the matrix effects of different types of wastewater was performed. All measurements were carried out with the SPR sensor system (beta-SPR) commercialised by the company Sensia, S.L. (Spain). The small size and low response time of the beta-SPR platform would allow it to be used in real contaminated locations. The immunosensor was evaluated and validated by measuring the atrazine content of 26 natural samples collected from Ebro River. Solid-phase extraction followed by gas chromatography coupled to mass spectrometric detection (SPE-GC-MS) was used to validate the new immunoassay.

Electrochemical Magnetoimmunosensing Strategy for the Detection of Pesticides Residues

A novel electrochemical immunosensing strategy for the detection of atrazine based on magnetic beads is presented. Different coupling strategies for the modification of the magnetic beads with the specific anti-atrazine antibody have been developed. The immunological reaction for the detection of atrazine performed on the magnetic bead is based on a direct competitive assay using a peroxidase (HRP) tracer as the enzymatic label. After the immunochemical reactions, the modified magnetic beads can be easily captured by a magnetosensor made of graphite-epoxy composite, which is also used as the transducer for the electrochemical immunosensing. The electrochemical detection is thus achieved through a suitable substrate and mediator for the enzyme HRP. The electrochemical approach is also compared with a novel magneto-ELISA based on optical detection. The performance of the electrochemical immunosensing strategy based on magnetic beads was successfully evaluated using spiked real orange juice samples. The detection limit for atrazine using the competitive electrochemical magnetoimmunosensing strategy with anti-atrazine-specific antibody covalent coupled with tosyl-activated magnetic beads was found to be 6 x 10(-3) microg L(-1) (0.027 nmol L(-1)). This strategy offers great promise for rapid, simple, cost-effective, and on-site analysis of biological, food, and environmental samples.

Analysis of nonylphenol: advances and improvements in the immunochemical determination using antibodies raised against the technical mixture and hydrophilic immunoreagents

The development of an enzyme-linked immunosorbent assay (ELISA) for the detection of technical nonylphenol (NP) is reported. The preparation of specific antibodies has been addressed using an immunizing hapten with a four-carbon atom spacer arm placed at the ortho position that preserves both the hydroxyl group and the complexity of the branched nonyl chain mixture of the technical NP. The synthesis of the immunizing hapten 5-(2-hydroxy-5-nonylphenyl)-pentanoic acid has been accomplished through a four-step synthetic pathway using the NP commercial technical mixture as the starting material. Three types of competitor haptens have also been prepared depending on the location of the spacer arm: in ortho position to the phenol group (type A), attached to the oxygen atom (type B), and in para position, substituting the nonyl chain (type C). Drawbacks produced by the hydrophobicity of the NP or of the hapten derivatives have been circumvented by using a highly hydrophilic carrier molecule such as a high-molecular-weight aminodextran as a coating support for antigen in an indirect ELISA format. A reproducible and sensitive indirect competitive ELISA has been finally obtained, reaching a limit of detection of 2.3 +/- 0.9 microg L(-1) and an IC50 value of 29 +/- 5 microg L(-1) (both N = 16). A coefficient of variation of 11% for assays performed on different days (N = 5; IC50 = 30 +/- 3 microg L(-1)) demonstrates the assay reproducibility. The assay also recognizes the nonylphenol polyethoxylates to a different degree depending on the length of the ethoxylate chain. Recovery values in the range between 96 and 100% have been obtained using spiked blind aqueous samples although the sample preparation procedure used has been shown to have a great influence on the method accuracy. A preliminary evaluation of the analytical protocol established has been performed using real water samples.

Development of a micro-plate magnetic chemiluminescence enzyme immunoassay (MMCLEIA) for rapid- and high-throughput analysis of 17β-estradiol in water samples

A novel method of micro-plate magnetic chemiluminescence enzyme immunoassay (MMCLEIA) for the screening of 17beta-estradiol in water samples was proposed. It used the micro-plate magnetic separator designed by ourselves which can achieve the high-throughput analysis without the samples pre-treatment and the sensitive chemiluminescence system of AMPPD-ALP system. The method showed specific recognition of estrogen, without cross-reactions for three other major estrogenic compounds (17beta-estradiol (E2), estriol (E3), ethinyl (E2)) commonly found in water. The MMCLEIA was also especially suitable for the large-scale samples processing. The working range for 17beta-estradiol was 10-3000 pg/ml. The assay sensitivity was 5.4 pg/ml. Both intra- and inter-assay had relative standard deviation of less 15%. The effect of several physico-chemical parameters, such as the ratio of antibody versus antigen, incubation time and the concentration of detergent were studied. This method has been successfully applied to the preliminary detection of the sea-water. Compared with the chemiluminescence enzyme-linked immunosorbed assay, the correlation was good.

Direct Competitive Enzyme-Linked Immunosorbent Assay for the Determination of the Highly Polar Short-Chain Sulfophenyl Carboxylates

A direct enzyme-linked immunosorbent assay for the detection of the short-chain sulfophenylcarboxylic acids (SPCs), the main metabolites of the linear alkylbenzenesulfonates, is reported. Six SPCs (2C3, 2C4, 3C4, 2C5, 3C5, 3C6), differing in the length of the alkyl chain (between C3 and C6) and in the position of the phenylsulfonic group versus the carboxylic group, have been synthesized. Antibodies have been raised against a mixture of the corresponding horseshoe crab hemocyanin conjugates prepared by coupling the carboxylic acid to the lysine amino acid residues. The immunoassay As115/3C4-HRP achieves an IC50 value of 23 nM (6.67 microg L(-1)) and a detection limit of 0.85 nM (0.24 microg L(-1)), using as standard analyte an equimolar mixture of the six SPCs. The immunoassay has found to work better in media with low or moderate ionic strength (4-30 mS cm(-1)). The decrease in the detectability produced by the potential formation of SPC salts with divalent cations such as Ca2+ can be prevented by lowering the pH of the assay medium below the pKa value of the SPC carboxylic group and using a buffer chelating with properties such as citrate buffer. The assay can be considered specific for short-chain SPCs since congeners with longer alkyl chains and other pollutants containing sulfonic groups in their structure do not interfere significantly in the assay. Preliminary experiments addressed to evaluate the potential application of this assay to environmental water samples demonstrate the usefulness of the assay.

Determination of atrazine and carbaryl pesticide residues in vegetable samples using a multianalyte dipstick immunoassay format

A dipstick assay for the simultaneous determination of atrazine and carbaryl in vegetable samples was developed. The analytical method involved a fast extraction procedure followed by a multi-strip membrane test. The assay took 10 min, with a detection limit (naked eye) of 10 and 200 micro g l(-1) for atrazine and carbaryl, respectively. The cross-reactivities to related compounds tested were negligible except for propazine. Quantification of the pesticides was carried out by measuring the dot colour with a spectrophotometer. IC(50) values (inhibition constant at 50% of the maximum binding) of 2.04 microg l(-1) for atrazine and 92.8 microg l(-1) for carbaryl were achieved by this approach. Vegetable samples were extracted with MeOH. The proposed methodology was used to analyse atrazine and carbaryl and check for compliance with European Union maximum residue levels for vegetables. Recoveries (75-105%) were in agreement with those obtained by GC/MS or HPLC. Standard curves using 25% methanol/75% TBS were used for food sample assays using a multi-analyte dipstick. IC(50) values were 9.2 microg kg(-1) for atrazine and 179.2 microg kg(-1) for cabaryl.

Immunochemical determination of 2,4,6-trichloroanisole as the responsible agent for the musty odor in foods. 1. Molecular modeling studies for antibody production

Nine antisera have been raised against 2,4,6-trichloroanisole (2,4,6-TCA) by immunizing them with three different haptens. With the spacer arm at the meta position, hapten A (3-(2,4,6-trichloro-3-methoxyphenyl)propanoic acid) preserved all of the functional groups of the target analyte. In hapten B (5-(2,4,6-trichlorophenoxy)pentanoic acid), the spacer was placed in the molecule substituting the methoxy group. Finally, hapten C (3-(3,5-dichloro-4-methoxyphenyl)propanoic acid) held the spacer arm at the para position instead of the chlorine atom of the target analyte. Using theoretical models, we have studied how the molecular geometry and the electronic distribution are affected by the introduction of the linker. The evaluation of the avidity of the resulting antibodies demonstrates that the orientation produced by the spacer arm must also be considered an essential aspect. The screening for competitive assays performed after synthesizing a battery of heterologous competitors has provided with these antibodies eight indirect enzyme-linked immunosorbent assays with acceptable properties. From the number of assays obtained, their maximal absorbance, their signal-to-noise ratio, the slope, and the IC(50) values obtained, it can be concluded that hapten C provided the best antibodies.

Immunochemical determination of 2,4,6-trichloroanisole as the responsible agent for the musty odor in foods. 2. Immunoassay evaluation

Immunoassays for 2,4,6-trichloroanisol (TCA) have been evaluated. The assays were developed after raising antibodies against three different immunizing haptens (1). Lack of reproducibility has been one of the main problems of these assays. Precision was worse on these assays, reaching lower limits of detection. The high lipophilicity of TCA and its, consequently, low water solubility have been found to be the major cause of this problem. A reliable microplate-based enzyme-linked immunosorbent assay (ELISA) has been set after consideration of the TCA physicochemical features and evaluation of important parameters affecting immunoassay performance. The immunoassay uses As78 (developed against hapten B-KLH) and C9-OVA as the coating antigen. The selectivity is high although the brominated analogue 2,4,6-TBA is also recognized. In buffered media containing 7% ethanol, the resulting assay shows a good accuracy with an IC(50) value of 0.53 microgram L(-)(1) and a limit of detection of 0.044 microgram L(-)(1). Red and white wine samples caused important interferences in the immunoassay demonstrating the necessity of a cleanup procedure prior to the ELISA.

Preparation of antibodies and development of an enzyme-linked immunosorbent assay for determination of dealkylated hydroxytriazines

The development of an indirect competitive enzyme-linked immunosorbent assay (ELISA) for dealkylated hydroxytriazines is reported here for the first time. The assay uses polyclonal antibodies raised against N-(4-amine-6-hydroxy-[1,3,5]triazin-2-yl)-4-aminobutanoic acid (hapten 2g) conjugated to keyhole limpet hemocyanin by the active ester method. The immunizing hapten was synthesized by first introducing the amino group to the triazine ring in a protected form in order to increase its solubility in organic media. Subsequent steps consisted of reacting this compound with an appropriate spacer arm, followed by removal of the protecting group in acidic media. The resulting assay uses a homologous competitor hapten coupled to conalbumin by the mixed anhydride method. Coating antigens prepared using a homologous covalent coupling procedure failed to produce competitive immunoassays. The assay tolerates media with high ionic strength (up to 70 mS cm(-)(1)) and basic pH values (7.5-9.5 units). Under the optimized conditions, this ELISA is specific for dealkylated hydroxytriazines, reaching suitable limits of detection.

Biological monitoring of 2,4,5-trichlorophenol (I): preparation of antibodies and development of an immunoassay using theoretical models

Antibodies against 2,4,5-trichlorophenol have been prepared after theoretical and molecular modeling chemical studies of three potential immunizing haptens with the aim to find out the one mimicking best the target analyte. Competitive direct and indirect ELISAs have been developed after screening a battery of haptenized enzyme tracers and coating antigens, respectively. The relation between the degree of heterology of the competitor and the resulting immunoassay detectability has been investigated according to the electronic similarities of the competitor haptens with the target analyte taking in consideration their pK(a) values. These studies have been performed using theoretical and molecular modeling tools to find out their electronic distribution at their minimum energetic levels. The results suggest that the competitors should have a high homology to produced assays with good detectability values. On the other hand detectability improves when lowering the hapten density of the competitors. An indirect competitive ELISA has been finally selected for further investigation. The immunoassay has an IC(50) value of 0.6 microg L(-)(1) and a limit of detection of 0.084 microg L(-)(1). The selectivity of the assay is high in relation to other chlorophenols frequently present in real samples. In contrast, the brominated analogues may also be recognized with this assay.

Microfluidic enzyme immunoassay using silicon microchip with immobilized antibodies and chemiluminescence detection

Silicon microchips with immobilized antibodies were used to develop microfluidic enzyme immunoassays using chemiluminescence detection and horseradish peroxidase (HRP) as the enzyme label. Polyclonal anti-atrazine antibodies were coupled to the silicon microchip surface with an overall dimension of 13.1 x 3.2 mm, comprising 42 porous flow channels of 235-microm depth and 25-microm width. Different immobilization protocols based on covalent or noncovalent modification of the silica surface with 3-aminopropyltriethoxysilane (APTES) or 3-glycidoxypropyltrimethoxysilane (GOPS), linear polyethylenimine (LPEI, MW 750,000), or branched polyethylenimine (BPEI, MW 25,000), followed by adsorption or covalent attachment of the antibody, were evaluated to reach the best reusability, stability, and sensitivity of the microfluidic enzyme immunoassay (microFEIA). Adsorption of antibodies on a LPEI-modified silica surface and covalent attachment to physically adsorbed BPEI lead to unstable antibody coatings. Covalent coupling of antibodies via glutaraldehyde (GA) to three different functionalized silica surfaces (APTES-GA, LPEI-GA, and GOPS-BPEI-GA) resulted in antibody coatings that could be completely regenerated using 0.4 M glycine/HCl, pH 2.2. The buffer composition was shown to have a dramatic effect on the assay stability, where the commonly used phosphate buffer saline was proved to be the least suitable choice. The best long-term stability was obtained for the LPEI-GA surface with no loss of antibody activity during one month. The detection limits in the microFEIA for the three different immuno surfaces were 45, 3.8, and 0.80 ng/L (209, 17.7, and 3.7 pM) for APTES-GA, LPEI-GA, and GOPS-BPEI-GA, respectively.

Development and evaluation of an immunoassay for biological monitoring chlorophenols in urine as potential indicators of occupational exposure

Trichlorophenols (TCP) eliminated by the urine can be considered as potential biomarkers of exposure of many chemicals (chlorophenols, chlorophenoxy acid herbicides, prochloraz, lindane, hexachlorobenzene, etc). High-throughput screening methods are necessary to carry out efficient monitoring programs that may help to prevent certain occupational health diseases. For this purpose, an indirect enzyme-linked immunosorbent assay (ELISA) for 2,4,6-trichlorophenol detection has been developed using polyclonal antisera raised against 3-(3-hydroxy-2,4,6-trichlorophenyl)propanoic acid (hapten 5) covalently coupled by the mixed anhydride (MA) method to keyhole limpet hemocyanin (KLH). The indirect ELISA uses a heterologous coating antigen prepared by conjugation of 3-(2-hydroxy-3,6-dichlorophenyl)propanoic acid (hapten 4) to bovine serum albumin (BSA) using the active ester (AE) method. The optimum hapten density for the coating antigen was found to be 3 mol of hapten/mol of protein. The assay shows a limit of detection of 0.245 +/- 0.116 microg L(-1), and it is performed on 96-well microtiter plates in about 1.5 h. The ELISA reported recognizes on a much less extent other chlorinated phenols, such as 2,3,4,6-tetrachlorophenol (2,3,4,6-TtCP, 21%), 2,4,5-TCP (12%) and 2,3,5-TCP (15%); however, brominated phenols (BP) are even more recognized than the corresponding chlorinated analogues (ex. 2,4,6-TBP, 710%; 2,4-DBP, 119%). With the aim of finding an explanation for this behavior, theoretical calculations have been performed for those and other halogenated phenols (2,4,6-triiodophenol and 2,4,6-trifluorophenol) to clarify which physicochemical parameter can explain better the recognition pattern observed. Finally, the assay has been adapted to the analysis of urine samples. The studies have shown that a limit of detection of 1 microg L(-1) can be accomplished on this biological matrix by combining the ELISA procedure with a C18 solid-phase extraction method.

Comparison of multianalyte immunosensor formats for on-line determination of organic compounds

Studies leading to the development of multianalyte immunosensing approaches are presented herein. Competitive capture formats are developed for carbaryl, atrazine, and irgarol 1051 as target compounds. Three proposals have been tested: sequential, additive, and simultaneous formats. For individual determinations, the best format is the sequential mode; the additive mode is useful only for qualitative analyses; and the simultaneous mode is preferable for screening purposes. The proposed systems show to be advantageous over single-analyte sensors and other multianalyte approaches. In all cases, the sensitivity reached (limit of detection) is high enough for the analysis of samples containing levels of each pesticide lower than 0.1 microg/L, and sensor reusability is very good (>600 determinations). The applicability of the multianalyte immunosensors to on-line pollution surveillance in natural waters, as well as their advantages and limitations, is discussed.

Development of an immunochemical technique for the analysis of trichlorophenols using theoretical models

An immunoassay has been developed for trichlorophenol analysis on the basis of theoretical chemistry modeling studies. These data have allowed us to choose the optimum chemical structure of the immunizing hapten according to realistic similarities with the target analyte. The synthesis of this hapten and the subsequent application of an appropriate immunization protocol have lead to the production of polyclonal antibodies against the target analyte. A homologous direct competitive ELISA has been developed that can be carried out in about 1 h. It has a limit of detection of 0.2 +/- 0.06 microg/L (1.01 +/- 0.3 nM) and it has been proven to tolerate a wide range of ionic strengths and pH values. Thus, the assay has acceptable features in samples with ionic strength between 4 and 56 mS/cm and pH values between 5.5 and 9.5. Studies on the selectivity of this immunoassay have demonstrated a high recognition of the corresponding brominated analogues. Other phenolic compounds do not interfere significantly in the analysis of 2,4,6-trichorophenol using this immunochemical technique. The accuracy of the assay has been evaluated using certified and spiked samples.