Application of immunological methods for the determination of environmental pollutants in human biomonitoring. A review

Impedimetric immunoglobulin G immunosensor based on chemically modified graphenes

Immunosensors which display high sensitivity and selectivity are of utmost importance to the biomedical field. Graphene is a material which has immense potential for the fabrication of immunosensors. For the first time, we evaluate the immunosensing capabilities of various graphene surfaces in this work. We propose a simple and label-free electrochemical impedimetric immunosensor for immunoglobulin G (IgG) based on chemically modified graphene (CMG) surfaces such as graphite oxide, graphene oxide, thermally reduced graphene oxide and electrochemically reduced graphene oxide. Disposable electrochemical printed electrodes were first modified with CMG materials before anti-immunoglobulin G (anti-IgG), which is specific to IgG, was immobilized. The principle of detection lies in the changes in impedance spectra of the redox probe after the attachment of IgG to the immobilized anti-IgG. It was found that thermally reduced graphene oxide has the best performance when compared to the other CMG materials. In addition, the optimal concentration of anti-IgG to be deposited onto the modified electrode surface is 10 μg ml(-1) and the linear range of detection of the immunosensor is from 0.3 μg ml(-1) to 7 μg ml(-1). Finally, the fabricated immunosensor also displays selectivity for IgG.

Instantaneous Determination via Bimolecular Recognition: Usefulness of FRET in Phosphorylcholine Group Enriched Nanoparticles

This paper deals with smart bimolecular recognition for instantaneous determination. In particular, we installed the fluorescence resonance energy transfer (FRET) system in phosphorylcholine (PC) group enriched nanoparticles (NPs). The most favorable characteristics were as follows: (i) the suppression of nonspecific protein adsorption by the PC group enriched surface and (ii) simple bioassay protocol relative to the conventional enzyme-linked immunosorbent assay (ELISA). In the case of immunoassays, nonspecific interaction and complex protocols are known dominant problems. To address these issues, we designed FRET-installed NPs. Agglutination of NPs is a fundamental immunoassay technique; however, it is not quantitative. By evaluating the degree of agglutination based on the fluorescence intensity, the resulting information can be used for diagnosis. Therefore, we installed the FRET system on the surface of the NPs. In this paper, C-reactive protein (CRP) and osteopontin (OPN) were the target biomarkers for instantaneous determination, and the resulting fluorescence intensity correlated well with changes in the concentrations of the target molecules. The immunoassay protocol was quite simple, involving only the mixing of FRET-installed NPs and target molecules, such as CRP and OPN antigens. We successfully evaluated the concentration of the target biomarkers, even when human serum albumin was present as an interference molecule.

Poly- and monoclonal antibody-based ELISAs for fipronil

An enzyme-linked immunosorbent assay (ELISA) for fipronil was developed by using polyclonal antibodies (pABs) or monoclonal antibodies (mABs), and its suitability of the determination of this analyte in spiked water samples was studied. The pABs-based assay showed I50 = 17.95 ppb, I90 = 203.40 ppb, and I10 = 0.066 ppb, whereas the mABs-based assay showed I50 = 5.99 ppb, I90 = 485.40 ppb, and I10 = 0.074 ppb. The recoveries of fipronil from tap water samples by pABs-based ELISA were 93.00-124.00% in the range of 0-500 ng/mL, and those obtained from the samples by mABs-based ELISA were 94.70-108.00%. Different types of water from pool, river, and sea were spiked at different levels (ranging form 0.1 to 10 microg/L) and were assayed by the indirect ELISA with mABs. The recoveries of fipronil by this ELISA were in the range of 80-120%. The results demonstrate that this assay is suitable for the quantitative detection of fipronil at trace levels in water samples.

A novel amperometric immunosensor based on Fe3O4 magnetic nanoparticles/chitosan composite film for determination of ferritin

A novel amperometric immunosensor was developed by immobilizing ferritin antibody (FeAb) on the surface of Fe(3)O(4) magnetic nanoparticles/chitosan composite film modified glassy carbon electrode (GCE). This material combined the advantages of inorganic Fe(3)O(4) nanoparticles with the organic polymer chitosan. The stepwise assembly procedure of the immunosensor was characterized by means of differential pulse voltammetry (DPV) and ac impedance. The K(3)Fe(CN)(6)/K(4)Fe(CN)(6) was used as a marker to probe the interface and to determinate ferritin. The factors that could influence the performance of the resulting immunosensor were studied in detail. After the immunosensor was incubated with ferritin for 32 min at 35 degrees C, the DPV current decreased linearly with the logarithm of ferritin concentration in the range from 20 to 500 ng mL(-1) with a correlation coefficient of 0.995 and a detection limit of 7.0 ng mL(-1). This immunosensor was used to analyze ferritin in human serum samples. The analytical results showed that the developed immunoassay was comparable with the radioimmunoassay (RIA), and the studied immunosensor exhibited good accuracy, high sensitivity, and long-term stability for 3 weeks, which implies a promising alternative approach for detecting ferritin in clinical diagnosis.

Development of an enzyme-linked immunosorbent assay for quantitative determination of quizalofop-p-ethyl

Accurate quantification of quizalofop-p-ethyl is essential for it may do harm to humans and animals through both water and food. Currently, detection of quizalofop-p-ethyl mainly relies on methods such as gas chromatography, high performance liquid chromatography, and gas chromatography-mass spectrometry. Although these techniques are reliable, they are relatively expensive and time-consuming because of multistep sample cleanup. To address this, we developed a competitive indirect enzyme-linked immunosorbent assay (ciELISA) with a polyclonal antibody against quizalofop-p-ethyl that was generated in our lab. The IC(50) of detection was 0.03495 microg/mL, and the lowest detection limit reached 0.00192 microg/mL. Furthermore, the method had high specificity for it did not cross-react with other structure-related compounds. When water and soil samples that were fortified with quizalofop-p-ethyl were analyzed by this ELISA, recoveries were in the range of 89-110% from water and 81-108% from soil. Good correlations between this immunoassay and gas chromatography data were obtained for residues of quizalofop-p-ethyl in water and soil. Our data indicate that this method is a convenient analytical technique for monitoring quizalofop-p-ethyl in waters without extraction and the extra cleanup step and in soil without the cleanup step.

Development of an enzyme-linked immunosorbent assay for podophyllotoxin

A competitive indirect enzyme-linked immunosorbent assay (ciELISA) for podophyllotoxin was developed by using polyclonal antibody, and its suitability for the determination of this analyte in spiked water samples was studied. To avoid antibody production to the linker, the succinoyl-podophyllotoxin (hapten) mimicking the analyte was synthesized and conjugated with the carrier proteins bovine serum albumin (BSA) and ovalbumin (OVA) by mixed anhydride reaction (MAR) and active ester method (AEM). Polyclonal antibodies raised against Hapten-BSA(1) synthesized by MAR and Hapten-BSA(2) by AEM were screened and selected for the ciELISA. One set of antibodies from the rabbit M4440 immunized with Hapten--BSA(1) showed an I(50) value of 2.21 microg/mL with a detection limit of 0.12 microg/mL, and the other set from the rabbit M4469 immunized with Hapten-BSA(2) had an I(50) value of 0.7897 microg/mL with a detection limit of 0.0056 microg/mL. This assay showed the cross-reactivities with the structurally closely related compounds. Recoveries from the podophyllotoxin-fortified tap water in the assay were in the range of 72--115%. A good correlation between podophyllotoxin concentration measured by the ELISA and HPLC (R(2)=0.9924, Y=1.195X-0.257) was obtained from linear regression analysis. These results indicate that the ELISA could be a convenient and supplemental analytical tool for monitoring podophyllotoxin and its analogues in waters without previous extraction or cleanup.

Urinary PAH metabolites as biomarkers of exposure in aquatic environments

While immunoassays have been extensively applied to evaluate environmental contamination, to date they have rarely been used for the analysis of biological fluids outside of human medicine. These media are important because pollutants such as polycyclic aromatic hydrocarbons (PAHs) and their metabolites become concentrated in tissues, body fluids, and excreta, thereby offering a measure of exposure to biologically available contaminants. Such analyses also provide a nondestructive tool for monitoring exposure. Crabs (Carcinus maenas) were exposed to phenanthrene and pyrene (separately) at concentrations ranging from 0 to 200 microg L(-1). After 48 h, urine samples were taken and analyzed by immunoassay and UV-fluorescence spectrophotometry. Urinary levels (calibrated against hydroxylated metabolites) proved to be dose dependent for both compounds, and good agreementwas demonstrated between the immunoassay and the fluorescence techniques. The cross reactivity of the immunochemical technique (ELISA) for pyrene and hydroxy-metabolites was lower than for phenanthrene. HPLC analyses demonstrated that urine from the crabs exposed to pyrene contained mainly conjugate PAH metabolites whose concentrations (the sum of the four main pyrene metabolites/conjugates) showed very good agreement with the ELISA (r2 > 0.94) and fluorescence (r2 > 0.91) data. Environmental samples were also analyzed by ELISA and UV-fluorescence, and both techniques detected PAH (mainly petrogenic) contamination in the urine samples from a polluted harbor. These data demonstrate the potential of urine analyses by ELISA and UV-fluorescence to measure exposure of crabs to PAH.

Novel amperometric immunosensor for rapid separation-free immunoassay of carcinoembryonic antigen

A novel immunosensor for rapid separation-free determination of carcinoembryonic antigen (CEA) in human serum is proposed. The immunosensor is prepared by co-immobilizing thionine and horseradish peroxidase (HRP)-labeled CEA antibody on a glassy carbon electrode (GCE) through covalently binding them to GCE with a glutaraldehyde (GA) linkage. The electrochemical behavior of the immobilized thionine displays a surface-controlled electrode process with an average electron transfer rate constant of 4.74+/-2.99 s(-1). It can be used as an electron transfer mediator for enzymatic activity detection of the HRP-labeled antibody to CEA. After the immunosensor is incubated with CEA solution at 23 degrees C for 40 min, the access of activity center of the HRP to thionine is partly inhibited, which leads to a linear decrease in the catalytic efficiency of the HRP to the oxidation of immobilized thionine by H(2)O(2) at -300 mV over two CEA concentration ranges from 0.5 to 3.0 and 3.0 to 167 ng/ml. Under optimal conditions, the detection limit for the CEA immunoassay is 0.1 ng/ml at three times background noise. The immunosensor shows good accuracy and acceptable storage stability, precision and reproducibility with intra-assay CVs of 6.1% and 5.8% at 2.5 and 50 ng/ml CEA, respectively, and an inter-assay CV of 6.3% at 50 ng/ml. This method is economical and shortens the analytical time, making it potentially attractive for clinical immunoassays.

Development of chemiluminescent ELISAs to DDT and its metabolites in food and environmental samples

Two enzyme-linked immunosorbent assays (ELISA) with chemiluminescent (CL) detection for the insecticide DDT and the group of DDT-related compounds have been optimized and characterized. Both conjugate-coated ELISAs are based on monoclonal antibodies (MAbs) of different specificity and homologous protein conjugates. Effects of several physicochemical factors (ionic strength, pH, Tween-20 and Bovine serum albumin (BSA) concentrations) and solvents (methanol, ethanol, acetone and N,N'-dimethylformamide) on the performance of the assays were studied and optimized. For the DDT-selective assay, the sensitivity, estimated as the I(50) value, was 0.6 microg/l, with a linear working range between 0.1 and 2 microg/l and a limit of detection of 0.06 microg/l. For the DDT group-selective assay, the sensitivity was 0.2 microg/l, with a linear working range between 0.07 and 1 microg/l and a limit of detection of 0.04 microg/l. CL-ELISAs were four times more sensitive compared to colorimetric ELISAs. Finally, both immunoassays were applied to the detection of DDT and group of DDT-related compounds in spiked real water, soil and food samples.

Biological monitoring of 2,4,5-trichlorophenol (II): evaluation of an enzyme-linked immunosorbent assay for the analysis of water, urine, and serum samples

Chlorophenols are frequently found in the urine of the population as consequence of the widespread use of chlorophenols and other organochlorinated compounds. An immunoassay for 2,4,5-trichlorophenol (2,4,5-TCP) has been evaluated as a tool to assess risk exposure of the population to these substances. The immunoassay is stable in media with pH values ranging from 6.6 to 10.5 units and ionic strength values varying within 20 and 80 mS cm(-)(1). Considering these parameters, the optimized immunoassay shows a limit of detection of 0.05 microg L(-)(1) and the dynamic range is placed between 0.09 and 0.72 microg L(-)(1). It shows a good accuracy and the coefficients of variation within and between assays are around 12% or lower. However, matrix effects can diminish the efficiency and detectability of the immunochemical methods. In this paper, the effect of water and complex biological sample matrices, such as serum and urine, on the immunoassay for 2,4,5-TCP has been evaluated. Simple sample treatment procedures have been developed for the analysis of these matrices. The final analytical protocols allow straightforward immunochemical determination of 2,4,5-TCP in natural waters, urine, and serum with detection limits of 0.07, 0.26, and 0.8 microg L(-)(1), respectively.

Stabilization of bound polycyclic aromatic hydrocarbons by a pi-cation interaction

Proteins can use aromatic side-chains to stabilize bound cationic ligands through cation-pi interactions. Here, we report the first example of the reciprocal process, termed pi-cation, in which a cationic protein side-chain stabilizes a neutral aromatic ligand. Site-directed mutagenesis revealed that an arginine side-chain located in the deep binding pocket of a monoclonal antibody (4D5) is essential for binding the neutral polynuclear aromatic hydrocarbon benzo[a]pyrene. This Arg was very likely selected for in the primary response, further underscoring the importance of the pi-cation interaction for ligand binding, which should be considered in protein analysis and design when ligands include aromatic groups.

Immunochemical analysis for dioxins--progress and prospects

Recent developments in antibody design and sample preparation have considerably enhanced the use of enzyme immunoassay (EIA) as an alternative to the conventional techniques based on gas chromatography and mass spectroscopy for the analysis of the trace organic pollutants polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in source and environmental samples. The EIA-specific sample preparation technique for solid matrices using a compatible extracting solvent coupled with an assay using a more sensitive antibody permits screening of source and environmental samples to be undertaken with minimal sample preparation. EIA has been validated on an increasing range of environmental and source samples as a cost effective I-TEQ screening tool, exploiting the commonly recognised general strengths of immunoassays such as speed, simplicity, low cost and parallel processing of many samples, greatly reducing the number of samples requiring conventional GCMS analysis. Further research and developmental work is required in the areas of sample extraction and extract cleanup to ensure compatibility with the immunoassay from the outset, and to standardise as far as is possible an assay format relevant to the application of interest, covering sample preparation, sample cleanup, quality control, assay procedure and data analysis.

On-line sample preparation of paraquat in human serum samples using high-performance liquid chromatography with column switching

A new ion-pair high-performance liquid chromatographic method with column-switching has been developed for the determination of paraquat in human serum samples. The diluted serum sample was injected onto a precolumn packed with LiChroprep RP-8 (25-40 microm) and polar serum components were washed out by 3% acetonitrile in 0.05 M phosphate buffer (pH 2.0) containing 5 mM sodium octanesulfonate. After valve switching to inject position, concentrated compounds were eluted in the back-flush mode and separated on an Inertsil ODS-2 column with 17% acetonitrile in 0.05 M phosphate buffer (pH 2.0) containing 10 mM sodium octanesulfonate. The total analysis time per sample was about 30 min and mean recovery was 98.5+/-2.8% with a linear range of 0.1-100 microg/ml. This method has been successfully applied to serum samples from incidents by paraquat poisoning.

Environmental immunoassays and other bioanalytical methods: overview and update

Immunoassays and bioanalytical techniques can aid the cost effective detection and quantification of trace contaminants in the environment, food, and human and animal populations. This overview of recent progress shows that rapid advances have occurred in the development and validation, of assays for many contaminants of both industrial and agricultural origin. Promising antibody based techniques such as immunoaffinity chromatography, biosensors, and flow injection immunoanalysis continue to evolve. Such techniques can not only help lower costs and improve efficiency, but can also allow the range of hypotheses that can be tested in many environmental studies to be broadened by permitting the determination of trace residues in small volume samples that would be otherwise difficult to analyze.