Influence of the hapten design on the development of a competitive ELISA for the determination of the antifouling agent Irgarol 1051 at trace levels

The interaction analysis between human serum albumin with chlorpyrifos and its derivatives through sub-atomic docking and molecular dynamics simulation techniques

Chlorpyrifos (CPF) is an extensively used organophosphate pesticide for crop protection. However, there are concerns about it contaminating the environment and human health, with estimated three lakh deaths annually. The molecular modeling protocol was assisted in redesigning thirteen well-known CPF linkers and inserting them at five selectable CPF (R1-R5) positions of CPF to get 258 CPF derivatives. CPF and its derivatives were optimized using LigPrep and docked to a grid centralized on Trp214 using extra precision glide docking. The Binding free energy of complexes was calculated using molecular mechanics/generalized born surface area (MM-GBSA). CPF and CPFD-225 have glide scores of - 3.08 and - 6.152 kcal/mol, respectively, with human serum albumin and ΔG bind for CPF (- 33.041817 kcal/mol) (- 52.825 kcal/mol) for CPF-D225. The top ten CPF derivatives showed at least ninefold better binding free energy than the CPF proposed for polyclonal antibody production. Subsequently, molecular docking studies revealed that CPF and its derivatives could bind to human serum albumin (HSA). Furthermore, using the Desmond package, a 100-ns molecular dynamics (MD) simulation was performed on the potential binding site. The final systems of CPF-HSA and CPF-222D complexes consist of 76,014 and 76,026 atoms, respectively. The physical stability of both the systems (CPF-HSA and CPF-222D) was analyzed by considering the overall potential energy, RMSF, RMSD, Hydrophobic interactions, and water-mediated patterns, which showed total energy of - 141,610 kcal/mol and - 140,150 kcal/mol, respectively.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03344-7.

An Immunochemical Approach to Detect the Quorum Sensing-Regulated Virulence Factor 2-Heptyl-4-Quinoline N-Oxide (HQNO) Produced by Pseudomonas aeruginosa Clinical Isolates

Understanding quorum sensing (QS) and its role in the development of pathogenesis may provide new avenues for diagnosing, surveillance, and treatment of infectious diseases. For this purpose, the availability of reliable and efficient analytical diagnostic tools suitable to specifically detect and quantify these essential QS small molecules and QS regulated virulence factors is crucial. Here, we reported the development and evaluation of antibodies and an enzyme-linked immunosorbent assay (ELISA) for HQNO (2-heptyl-4-quinoline N-oxide), a QS product of the PqsR system, which has been found to act as a major virulence factor that interferes with the growth of other microorganisms. Despite the nonimmunogenic character of HQNO, the antibodies produced showed high avidity and the microplate-based ELISA developed could detect HQNO in the low nM range. Hence, a limit of detection (LOD) of 0.60 ± 0.13 nM had been reached in Müeller Hinton (MH) broth, which was below previously reported levels using sophisticated equipment based on liquid chromatography coupled to mass spectrometry. The HQNO profile of release of different Pseudomonas aeruginosa clinical isolates analyzed using this ELISA showed significant differences depending on whether the clinical isolates belonged to patients with acute or chronic infections. These data point to the possibility of using HQNO as a specific biomarker to diagnose P. aeruginosa infections and for patient surveillance. Considering the role of HQNO in inhibiting the growth of coinfecting bacteria, the present ELISA will allow the investigation of these complex bacterial interactions underlying infections. IMPORTANCE Bacteria use quorum sensing (QS) as a communication mechanism that releases small signaling molecules which allow synchronizing a series of activities involved in the pathogenesis, such as the biosynthesis of virulence factors or the regulation of growth of other bacterial species. HQNO is a metabolite of the Pseudomonas aeruginosa-specific QS signaling molecule PQS (Pseudomonas quinolone signal). In this work, the development of highly specific antibodies and an immunochemical diagnostic technology (ELISA) for the detection and quantification of HQNO was reported. The ELISA allowed profiling of the release of HQNO by clinical bacterial isolates, showing its potential value for diagnosing and surveillance of P. aeruginosa infections. Moreover, the antibodies and the ELISA reported here may contribute to the knowledge of other underlying conditions related to the pathology, such as the role of the interactions with other bacteria of a particular microbiota environment.

ELISA-Based Method for Variant-Independent Detection of Total Microcystins and Nodularins via a Multi-immunogen Approach

Required routine monitoring of microcystins (MCs) and nodularins (NODs) in water samples, as posed by U.S. EPA Unregulated Contaminant Monitoring Rule 4, demands cost-effective, reliable, and sensitive detection methods. To target as many MC and NOD variants as possible, we developed an indirect competitive enzyme-linked immunosorbent assay (ELISA) with group-specific monoclonal antibodies for variant-independent detection of total MCs and NODs. In this ELISA method, the mice monoclonal antibodies presenting both high affinities and broad-spectrum recognition capabilities against MCs and NODs were self-produced by designing MC hapten-based multi-immunogens to minimize specificity for the particular variant. Their high affinities and variant-independent binding capabilities against MCs and NODs were validated by both wet lab and in silico methods. The developed ELISA method achieved a limit of detection of below 0.3 μg/L for 13 MC/NOD variants, well with the reported best cross-reactivities of 60-127% relative to MC-LR. As a case study, this ELISA method was used to map the variations of intracellular and extracellular total MCs/NODs in the Luoma Lake drinking water source, China, in July, 2020. Its capability to measure total MCs/NODs with high sensitivity and high throughput in a simple and affordable way would truly be a disruptive technology capable of changing our understanding of bloom/toxin dynamics and having obvious implications for monitoring efforts.

An Immunochemical Approach to Quantify and Assess the Potential Value of the Pseudomonas Quinolone Signal as a Biomarker of Infection

Quorum sensing (QS) is a bacterial cell density-based communication system using low molecular weight signals called autoinducers (AIs). Identification and quantification of these molecules could provide valuable information related to the stage of colonization or infection as well as the stage of the disease. With this scenario, we report here for the first time the development of antibodies against the PQS (pseudomonas quinolone signal), the main signaling molecule from the pqs QS system of Pseudomonas aeruginosa, and the development of a microplate-based enzyme-linked immunosorbent assay (ELISA) able of quantifying this molecule in complex biological media in the low nanometer range (LOD, 0.36 ± 0.14 nM in culture broth media). Moreover, the PQS ELISA here reported has been found to be robust and reliable, providing accurate results in culture media. The technique allowed us to follow up the PQS profile of the release of bacterial clinical isolates obtained from patients of different disease status. A clear correlation was found between the PQS immunoreactivity equivalents and the chronic or acute infection conditions, which supports the reported differences on virulence and behavior of these bacterial strains due to their adaptation capability to the host environment. The results obtained point to the potential of the PQS as a biomarker of infection and to the value of the antibodies and the technology developed for improving diagnosis and management of P. aeruginosa infections based on the precise identification of the pathogen, appropriate stratification of the patients according to their disease status, and knowledge of the disease progression.

High-Throughput Immunochemical Method to Assess the 2-Heptyl-4-quinolone Quorum Sensing Molecule as a Potential Biomarker of Pseudomonas aeruginosa Infections

Bacterial quorum sensing (QS) is being contemplated as a promising target for developing innovative diagnostic and therapeutic strategies. Here we report for the first time the development of antibodies against 2-heptyl-4-quinolone (HHQ), a signaling molecule from the pqs QS system of Pseudomonas aeruginosa, involved in the production of important virulent factors and biofilm formation. The antibodies produced were used to develop an immunochemical diagnostic approach to assess the potential of this molecule as a biomarker of P. aeruginosa infection. The ELISA developed is able to reach a detectability in the low nM range (IC₅₀ = 4.59 ± 0.29 nM and LOD = 0.34 ± 0.13 nM), even in complex biological samples such as Müeller Hinton (MH) culture media. The ELISA developed is robust and reproducible and has been found to be specific to HHQ, with little interference from other related alkylquinolones from the pqs QS system. The ELISA has been used to analyze the HHQ production kinetics of P. aeruginosa clinical isolates grown in MH media, pointing to its potential as a biomarker of infection and at the possibility to use the technology developed to obtain additional information about the disease stage.

Multiplexed Immunosensor Based on the Amperometric Transduction for Monitoring of Marine Pollutants in Sea Water

Environmental pollutants vigilance is one of the main problems that the aquaculture industry has to face with the objective to ensure the quality of their products and prevent entrance in the food chain that finally may arrive to the consumer. Contaminants such as hormones, antibiotics or biocides are especially relevant due to their toxicity, pharmacological effect or hormonal activity that can be considered harmful for the final consumer. The contaminants can be detected in the environment where the food is growing, and their concentration can be found (i.e., seawater) in the range of µg·L⁻¹, ng·L⁻¹ or even in lower concentrations. Thus, sensitive and selective methods for their monitoring are required to avoid their arrival in the food chain. Here, the development of a multiplexed amperometric biosensor is described, based on the use of specific antibodies to reach the necessary detectability to measure the targeted contaminants directly in seawater. The multiplexed immunosensor allows the detection of four relevant pollutants, such as el Irgarol 1051, sulfapyridine, chloramphenicol and estradiol, reaching an IC₅₀ of 5.04 ± 0.29, 3.45 ± 0.29, 4.17 ± 0.44 and 5.94 ± 0.28 µg·L⁻¹, directly measured in seawater.

Enzyme-linked immunosorbent assays for therapeutic drug monitoring coumarin oral anticoagulants in plasma

The development of high-throughput immunochemical assays to assist on precision medicine for patients treated with coumarin oral anticoagulants (OA) is reported. The assays are able to quantitate Warfarin (W) and/or Acenocoumarol (ACL) directly in plasma samples without any previous sample pretreatment. The detectabilities (W, 3.52 ± 2.25 nM and ACL, 1.56 ± 0.64 nM) and the working ranges achieved (W, 1.19 ± 0.73 to 12.05 ± 2.99 nM and ACL 0.63 ± 0.20 to 10.19 ± 6.69 nM) are within the therapeutic levels usually found in patients treated with these drugs. The assays are specific with only cross-recognition of 4'-NH₂-ACL on the ACL ELISA, which is one of the main metabolites of this drug. Moreover, accuracy studies performed with blind spiked samples show very good correlation between the spiked and the measured concentrations. Finally, a small clinical pilot study has been performed analyzing 96 plasma samples from treated and untreated patients, showing that the assay is able to quantitate ACL. The results obtained allow envisaging the possibility to use these assays for pharmacokinetic studies, dosage assessment or therapeutic drug monitoring.

Interferometric nanoimmunosensor for label-free and real-time monitoring of Irgarol 1051 in seawater

An interferometric nanobiosensor for the specific and label-free detection of the pollutant Irgarol 1051 directly in seawater has been settled. Due to the low molecular weight of Irgarol pollutant and its expected low concentration in seawater, the sensor is based on a competitive inhibition immunoassay. Parameters as surface biofunctionalization, concentration of the selective antibody and regeneration conditions have been carefully evaluated. The optimized immunosensor shows a limit of detection of only 3 ng/L, well below the 16 ng/L set by the EU as the maximum allowable concentration in seawater. It can properly operate during 30 assay-regeneration cycles using the same sensor biosurface and with a time-to-result of only 20 min for each cycle. Moreover, the interferometric nanosensor is able to directly detect low concentrations of Irgarol 1051 in seawater without requiring sample pre-treatments and without showing any background signal due to sea matrix effect.

Fluorescent microarray for multiplexed quantification of environmental contaminants in seawater samples

The development of a fluorescent multiplexed microarray platform able to detect and quantify a wide variety of pollutants in seawater is reported. The microarray platform has been manufactured by spotting 6 different bioconjugate competitors and it uses a cocktail of 6 monoclonal or polyclonal antibodies raised against important families of chemical pollutants such as triazine biocide (i.e. Irgarol 1051®), sulfonamide and chloramphenicol antibiotics, polybrominated diphenyl ether flame-retardant (PBDE, i.e. BDE-47), hormone (17β-estradiol), and algae toxin (domoic acid). These contaminants were selected as model analytes, however, the platform developed has the potential to detect a broader group of compounds based on the cross-reactivity of the immunoreagents used. The microarray chip is able to simultaneously determine these families of contaminants directly in seawater samples reaching limits of detection close to the levels found in contaminated areas (Irgarol 1051®, 0.19 ± 0,06 µg L^-1; sulfapyridine, 0.17 ± 0.07 µg L^-1; chloramphenicol, 0.11 ± 0.03 µg L^-1; BDE-47, 2.71 ± 1.13 µg L^-1; 17β-estradiol, 0.94 ± 0.30 µg L^-1 and domoic acid, 1.71 ± 0.30 µg L^-1). Performance of the multiplexed microarray chip was assessed by measuring 38 blind spiked seawater samples containing either one of these contaminants or mixtures of them. The accuracy found was very good and the coefficient of variation was < 20% in all the cases. No sample pre-treatment was necessary, and the results could be obtained in just 1 h 30 min. The microarray shows high sample throughput capabilities, being able to measure simultaneously more than 68 samples and screen them for a significant number of chemical contaminants of interest in environmental screening programs.

Detection of contaminants in water supply: A review on state-of-the-art monitoring technologies and their applications

Water monitoring technologies are widely used for contaminants detection in wide variety of water ecology applications such as water treatment plant and water distribution system. A tremendous amount of research has been conducted over the past decades to develop robust and efficient techniques of contaminants detection with minimum operating cost and energy. Recent developments in spectroscopic techniques and biosensor approach have improved the detection sensitivities, quantitatively and qualitatively. The availability of in-situ measurements and multiple detection analyses has expanded the water monitoring applications in various advanced techniques including successful establishment in hand-held sensing devices which improves portability in real-time basis for the detection of contaminant, such as microorganisms, pesticides, heavy metal ions, inorganic and organic components. This paper intends to review the developments in water quality monitoring technologies for the detection of biological and chemical contaminants in accordance with instrumental limitations. Particularly, this review focuses on the most recently developed techniques for water contaminant detection applications. Several recommendations and prospective views on the developments in water quality assessments will also be included.

Label-Free Biosensors Based on Bimodal Waveguide (BiMW) Interferometers

The bimodal waveguide (BiMW) sensor is a novel common path interferometric transducer based on the evanescent field detection principle, which in combination with a bio-recognition element allows the direct detection of biomolecular interactions in a label-free scheme. Due to its inherent high sensitivity it has great potential to become a powerful analytical tool for monitoring substances of interest in areas such as environmental control, medical diagnostics and food safety, among others. The BiMW sensor is fabricated using standard silicon-based technology allowing cost-effective production, and meeting the requirements of portability and disposability necessary for implementation in a point-of-care (POC) setting.In this chapter we describe the design and fabrication of the BiMW transducer, as well as its application for bio-sensing purposes. We show as an example the biosensor capabilities two different applications: (1) the immunodetection of Irgarol 1051 biocide useful in the environmental field, and (2) the detection of human growth hormone as used in clinical diagnostics. The detection is performed in real time by monitoring changes in the intensity pattern of light exiting the BiMW transducer resulting from antigen-antibody interactions on the surface of the sensor.

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.

Synthesis of site-heterologous haptens for high-affinity anti-pyraclostrobin antibody generation

The design and synthesis of functional chemical derivatives of small organic molecules is usually a key step for the intricate production of a variety of bioconjugates. In this respect, the derivatization site at which the spacer arm is introduced in immunizing conjugates constitutes a highly critical parameter for the generation of high-affinity and selective antibodies. However, due to the usual complexity of the required synthetic procedures, the appropriate comparison of alternative tethering positions has often been neglected. In the present study, meticulous strategies were followed to prepare synthetic derivatives of pyraclostrobin with the same linkers located at diverse rationally-chosen sites. Activity appraisal of antibodies and bioconjugates was carried out by bidimensional competitive direct and indirect immunoassays, and a superior performance of two of the three synthesized haptens was found. Finally, a detailed analysis of the conformations of the target molecule and the synthesized haptens in aqueous solution was done using computer assisted molecular modeling techniques. This study suggested that the lower titers and affinities of one set of antibodies are most probably due to conformational effects of the spacer arm in the immunizing bioconjugate.

Matrix Effects on the Microcystin-LR Fluorescent Immunoassay Based on Optical Biosensor

Matrix effects on the microcystin-LR fluorescent immunoassay based on the evanescent wave all-fiber immunosensor (EWAI) and their elimination methods were studied. The results indicated that PBS and humic acid did not affect the monitoring of samples under the investigated conditions. When the pH was less than 6 or higher than 8, the fluorescence signals detected by immunosensor systems were obviously reduced with the decrease or increase of pH. When the pH ranged from 6 to 8, IC₅₀ and the linear working range of MC-LR calculated from the detection curves were 1.01∼1.04 μg/L and 0.12∼10.5 μg/L, respectively, which was favourable for an MC-LR immunoassay. Low concentrations of Cu²⁺ rarely affected the detection performance of MC-LR. When the concentration of CuSO₄ was higher than 5 mg/L, the fluorescence signal detected by EWAI clearly decreased, and when the concentration of CuSO₄ was 10 mg/L, the fluorescence signal detected was reduced by 70%. The influence of Cu²⁺ on the immunoassay could effectively be compromised when chelating reagent EDTA was added to the pre-reaction mixture.

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.

Development of a monoclonal antibody-based broad-specificity ELISA for fluoroquinolone antibiotics in foods and molecular modeling studies of cross-reactive compounds

A competitive indirect enzyme-linked immunosorbent assay (ciELISA) using monoclonal antibodies (Mabs) having broad specificity for fluoroquinolone (FQ) antibiotics is described. Four FQs, ciprofloxacin (CIP), enrofloxacin (ENR), norfloxacin (NOR), and ofloxacin (OFL), were conjugated to bovine serum albumin for immunogens and to ovalbumin for coating antigens. A Mab C4A9H1 raised against the CIP hapten exhibited high cross-reactivity (35-100%) with 12 of 14 FQs and detected these FQs in a ciELISA below their maximum residue levels (MRLs) with good sensitivity at 50% binding inhibition (IC50). The quantitative structure-activity relationship (QSAR) between Mab C4A9H1 and various FQs by comparative molecular field analysis (CoMFA) showed a high predictive ability with a cross-validation q2 value of 0.866. Using a simple purification process and the broad-specificity ciELISA adapted for analysis of FQs in chicken muscle, chicken liver, honey, shrimp, and whole egg samples demonstrated recoveries of 60-93% for CIP, ENR, NOR, OFL, flumequine, and danofloxacin.

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.

Immunosensors for pollutants working in organic media. Study of performances of different tracers with luminescent detection

A comparative study of enzymatic and non-enzymatic labels combined with luminescence detection, developed for immunosensing of pesticide residues (carbaryl, 1-naphthol, irgarol 1051) in organic media, is presented. Peroxidase and alkaline phosphatase enzymes with fluorogenic (3-p-hydroxyphenylpropanoic acid) and luminogenic (AMPPD derivative) substrates, respectively, were assessed as enzymatic markers. As an alternative, terbium(III) chelate, with time-resolved fluorescence detection, was evaluated as a non-enzymatic label. The best sensitivity was achieved by use of alkaline phosphatase in an immunocomplex capture assay format (I (50) values 0.06, 0.27, and 7.45 microg L(-1) in buffer, 1:1 methanol-buffer, and methanol, respectively). Results were also good (I (50) 1.00 and 6.30 microg L(-1) for water and aqueous-organic mixture, respectively) for Tb(III) chelate in an immobilized conjugate assay format. Use of alkaline phosphatase label to measure carbaryl (100 ng L(-1)) in different spiked river water samples, after solid-phase extraction and analyte elution with an ethyl acetate-methanol mixture, resulted in recoveries ranging from 81 to 98%, with acceptable precision (CV 4-14%, n=4).

Molecular and immunochemical characteristics of monoclonal and recombinant antibodies selective for the triazine herbicide simetryn and application to environmental analysis

A monoclonal antibody (mab) selective for the thiomethyl-s-triazine herbicide simetryn was obtained and characterized in enzyme-linked immunosorbent assay (ELISA). An IC(50) value for simetryn was 8.5 ng/mL, and the detection range extended from 1.1 to 70 ng/mL in ELISA. The cDNAs encoding variable heavy chain (VH) and variable light chain (VL) of the mab were cloned to produce various recombinant antibodies. Single-chain variable fragment (scFv) antibodies derived from the mab were characterized in ELISA and showed similar reactivities and specificities to the parent mab. A urea denaturation test revealed that the scFv antibodies bound to simetryn were more stable than those in the absence of antigen. A sandwich ELISA based on VH and VL fragments of the mab was successfully developed and showed similar sensitivity to those based on the mab and scFv antibodies in ELISA. In the recovery experiments using spiked environmental samples, the results obtained in ELISA based on the mab were favorably correlated with those by HPLC.

Generation of antiserum to Irgarol 1051 and development of a sensitive enzyme immunoassay using a new heterologous hapten derivative

A polyclonal antiserum to Irgarol 1051 was developed in sheep and used to construct an enzyme immunoassay method for the measurement of the antifouling compound in river and seawater samples. The antiserum was generated by a hapten derivative, 2-(tert-butylamino)-4-(cyclopropylamino)-6-(thiopropionic acid)-1,3,5-triazine, coupled to a mixture of keyhole limpet hemocyanin and bovine serum albumin, and the competitive enzyme immunoassay was constructed using a plate-coating antigen made of a heterologous new hapten derivative, 2-(tert-butylamino)-4-(cyclopropylamino)-6-(phenoxybenzoic acid)-1,3,5-triazine, linked to gelatine. The assay showed a sensitivity of about 5 ng L(-1) in river and seawater matrices with reasonable specificity with respect to commonly used triazines such as atrazine (3%), simazine (>0.1%) and desethylatrazine (>0.01%). However, high cross-reactivity levels were found with ametryn (56%) and prometryn (60%). Tests on the effects of organic solvents on assay performance indicated a high tolerance to methanol but much less so to acetonitrile. The assay was found to be highly reproducible and robust owing to the stability of the sheep antibody and the highly optimised competitive assay reagents which included the use of the new triazine-O-phenoxybenzoic acid derivative.

Determination of Irgarol 1051 in Western Mediterranean sediments. Development and application of supercritical fluid extraction-immunoaffinity chromatography procedure

A supercritical fluid extraction (SFE) procedure for Irgarol 1051 (i.e. 2-(tert-butylamino)-4-(cyclopropylamino)-6-(methylthio)-1,3,5-triazine) determination in marine sediments, which minimises the solvent usage, is developed and compared to a conventional extraction technique (i.e. sonication). First, the use of methanol (MeOH) in the presence of trifluoroacetic acid (TFA) as secondary modifier of supercritical carbon dioxide was evaluated. Extraction efficiency was strongly dependent on the modifier content but lesser on pressure (100-410 bar) and temperature (60-200 degrees C). In the selected extraction conditions (20% MeOH/TFA 0.65M, 370 bar, 150 degrees C) recoveries higher than 87% were obtained and the limit of detection was 3 ngg(-1) and the relative standard deviation of 10% (N=3) by GC coupled to mass spectrometry (GC-MS) in the electron impact mode. The developed SFE procedure is more convenient to extract Irgarol 1051 than the agitation plus sonication methods concerning on solvent usage (1.5 vs. 20 mL) being compatible with immunochemical procedures avoiding any solvent transfer step. The developed SFE combined with immunoaffinity chromatography (IAC) is highly selective allowing the determination of Irgarol by gas chromatography with nitrogen-phosphorus detection or in sediments at low ngg(-1) level (11-35 ngg(-1)) from Mediterranean marina and harbour sediments.

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.

Immuno-based sample preparation for trace analysis

Immuno-based sample preparation techniques are based upon molecular recognition. Thanks to the high affinity and high selectivity of the antigen-antibody interaction, they have been shown to be a unique tool in the sampling area. Immuno-based sample preparation methods include the widely encountered immunoaffinity extraction sorbents, so-called immunosorbents, as well as membrane-baed or ultrafiltration techniques. This review describes the new developments and applications that have occurred in recent years with emphasis on (i) the antigen-antibody interactions, (ii) and their importance for the properties and use of immunosorbents, (iii) multiresidue extractions, (iv) the on-line coupling to chromatographic or electrophoretic separations, and (v) the high potential for improving MS detection. The recent use of artificial antibodies for sample pretreatment, so-called molecularly imprinted polymers, is also described.

Experimental comparison of three monoclonal antibodies for the class-selective immunoextraction of triazines. Correlation with molecular modeling and principal component analysis studies

The specificity of three immunosorbents (ISs) based on different monoclonal anti-triazine antibodies has been characterized by extraction recoveries studies and with step elution experiments. Both indicated that the anti-dichloroatrazine IS is specific of terbutylazine and cyanazine. The anti-atrazine IS is specific of the chlorotriazines, whereas the anti-ametryn IS can trap all the triazines. This confirms the great influence of the hapten design on the specificity of the resulting antibodies, even if the target molecules are small. Moreover, the anti-ametryn IS is suitable for class-selective extraction of triazines contained in complex matrices. An approach designed to learn more about the specificity for a group of structurally related compounds of antibodies produced with a given compound is proposed and evaluated. Molecular modeling followed by principal component analysis has been used to obtain distribution maps with the relative position of each immunoconjugate and all the triazines. In all three cases, conclusions on specificity made with the analysis of the maps fit well with the experimental results. Consequently, molecular modeling coupled with principal component analysis seems to be a unique, inexpensive, and rapid tool to select the appropriate hapten providing highly specific or class-specific antibodies according to the given problem.

A multichannel microfluidic sensor that detects anodic redox reactions indirectly using anodic electrogenerated chemiluminescence

Here, we describe a new approach for detecting redoxactive targets by electrochemical oxidation and reporting their presence by electrogenerated chemiluminescence (ECL) based on electrochemical oxidation of Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) and tripropylamine (TPA). This new strategy, which complements our previous reports of using ECL to signal the presence of targets undergoing electrochemical reduction, takes advantage of many of the attractive attributes of microfluidic-based electrochemical cells. These attributes include close proximity of multiple flow channels and electrodes, ability to move reagents through channels under laminar flow conditions, and the capacity to precisely place device components relative to one another using photolithography. Specifically, the microfluidic electrochemical sensor described here consists of three channels. The analyte and ECL reporting cocktail flow through separate channels, but they share a common anode. The cathode resides in a channel containing a sacrificial reductant. In this configuration, the target analyte competes with Ru(bpy)3(2+) and TPA to provide electrons for the reductant. Accordingly, in this competitive assay approach, the presence of the analyte is signaled as a lowering of the ECL intensity. In this report, the device performance characteristics are reported, and the detection of both ferrocyanide and dopamine is demonstrated at micromolar concentrations.

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.

Miniaturization of a homogeneous fluorescence immunoassay based on energy transfer using nanotiter plates as high-density sample carriers

The miniaturization of a homogeneous competitive immunoassay to a final assay volume of 70 nL is described. As the sample carrier, disposable plastic nanotiter plates (NTP) with dimensions of 2 x 2 cm2 containing 25 x 25 wells, corresponding to approximately 15,000 wells on a traditional 96-well microtiter plate footprint, were used. Sample handling was accomplished by a piezoelectrically actuated micropipet. To reduce evaporation while pipetting the assays, the NTP was handled in a closed humid chamber and cooled to the point of condensation. To avoid washing steps, a homogeneous assay was developed that was based on energy-transfer (ET). As a model system, an antibody-based assay for the detection of the environmentally relevant compound, simazine, in drinking water was chosen. Antibodies were labeled with the long-wavelength-excitable sulfoindocyanine dye Cy5 (donor), and a tracer was synthesized by labeling BSA with a triazine derivative and the acceptor dye Cy5.5. At low analyte concentrations, the tracer was preferably bound to the antibody binding sites. As a result of the close proximity of Cy5.5 and Cy5, an efficient quenching of the Cy5 fluorescence occurred. Higher analyte concentrations led to a progressive binding of the analyte to the antibody binding sites. The increased Cy5 fluorescence was determined by using a scanning laser-induced fluorescence detector. The limit of detection (LOD), using an antibody concentration of 20 nM, was 0.32 microg/L, or 1.11 x 10(-16) mol of simazine. In comparison, the LOD of the 96-well microtiter-plate-based ET immunoassay (micro-ETIA) was 0.15 microg/L, or 1.87 x 10(-13) mol. The LOD of the optimized micro-ETIA at 1 nM IgG, was 0.01 microg/L.

Monitoring of antifouling agents in water samples by on-line solid-phase extraction–liquid chromatography–atmospheric pressure chemical ionization mass spectrometry

An automatic method for determining diuron, irgarol 1051, folpet and dichlofluanid in seawater samples have been developed. This method is based on the on-line coupling of solid-phase extraction (SPE) with a highly crosslinked polymeric sorbent, LiChrolut EN, to liquid chromatography followed by atmospheric pressure chemical ionization (APCI) and mass spectrometry. The operational parameters affecting the APCI interface have been studied in both positive and negative ionization modes. The use of LiChrolut EN in the SPE produced recoveries of over 85% for all the compounds when 100 ml of seawater sample was preconcentrated. Calibration was carried out in both ionization modes and in full-scan and selected-ion monitoring (SIM). The method allowed all the analytes to be detected at 5 ng l(-1) in SIM acquisition mode except folpet, which, because of its low response, could only be detected at 250 ng l(-1). The method was used to analyse water samples taken from five different marina and fishing ports along the coast of Tarragona, Catalonia (Spain), over a 5-month period. Diuron and irgarol 1051 were detected and quantified in most samples at concentration levels ranging from 27 to 420 ng l(-1) for diuron and from 15 to 511 ng l(-1) for irgarol 1051.

Development and application of immunoaffinity chromatography for the determination of the triazinic biocides in seawater

The development of an immunoaffinity chromatography (IAC) procedure for the selective extraction of the anti-fouling agent Irgarol 1051 [2-(tert.-butylamino)-4-(cyclopropylamino)-6-(methylthio)-1,3,5-triazine] from seawater is described. The anti-Irgarol 1051 antibodies were covalently bound to agarose-based beads support. IAC column capacities were higher than 400 ng and ethanol-water (70:30) was selected as eluting mixture. After percolation of 250 ml of water sample containing Irgarol 1051 at environmental levels (ng l(-1) ), the breakthrough volume was still not achieved. Other triazine herbicides percolated through the IAC column showed good recoveries. Thus, this IAC procedure may be useful to extract related compounds. The developed IAC column was applied to real seawater samples and compared with RP-C18 cartridges. The limit of detection (LOD) reached by using the IAC procedure was twenty times lower than the LOD achieved by the RP-C 18 cartridges using the same detection system. Irgarol 1051 was detected at ng l(-1) levels in the Barcelona marina (northwestern Mediterranean Sea). An acceptable correlation between enzyme-linked immunosorbent assay and gas chromatography with nitrogen-phosphorus detection was observed, thus analysis of Irgarol 1051 can be performed by either one of the methods. In this work, further confirmation of the analyte identity for real samples was accomplished by gas chromatography-electron impact mass spectrometry.

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.