A comparison of chemiluminescence immunoassay and radioimmunoassay for the detection of nortestosterone residues in meat samples

A chemiluminescence immunoassay, with a nantiserum raised against 19-nortestorone-3- carboxymethyloxime/bovine serum albumin and the N-(4-aminobutyl)-N-ethylisoluminol conjugate of 19-nortestosterone as tracer is compared to a radioimmunoassay, with an antiserum against 19-nortestosterone-17-hemisuccinate/bovine serum albumin and 19-(6,7-³H) nor testosterone as the radioactive label. Both methods have a similar sensitivity but the limit of quantification is much lower for radioimmunoassay (0.08 μg kg^-1) than for chemiluminescence immunoassay (0.6 μg kg^-1). A more practical appraoch, the limit of decision, is defined which is determined by the analytical results obtained from certified blank reference samples. This concept gives a good qualitative agreement between the two immunoassay techniques and the number of false positive and negative results, as ascertaind by GC/MS, is minimized; this is shown for assays of 38 meat samples.     

Evaluation of α-fetoprotein (AFP) in human serum by chemiluminescence enzyme immunoassay with magnetic particles and coated tubes as solid phases

In this work, the monoclonal antibodies (McAbs) to α-fetoprotein (AFP) were immobilized on two different solid phases, i.e., magnetic particles (MP) and coated tubes (CT). Based on this, a MP based chemiluminescence enzyme immunoassay (MP-CLEIA) and a CT based CLEIA (CT-CLEIA) were proposed for the evaluation of AFP in human serum and their analytical merits were studied and compared. By detailed discussion of several performance variants, including the concentration of immobilized McAb, dilution ratio of horseradish peroxidase (HRP) labeled McAb (HRP-McAb), total assay time, substrate volume, chemiluminescent kinetics, and hook effect concentration, the advantages of MP-CLEIA became conspicuously apparent. Moreover, in the presence of MP, the catalytic activity of labeled enzyme was kept to high extent and the stability of immunoreagents was satisfied. Finally, 59 human serum samples were detected by the MP-CLEIA and a good correlation was obtained when comparing the results with that from a commercial electrochemiluminescence immunoassay kit.     

New highly sensitive enzyme immunoassay for the determination of pravastatin in human plasma

New highly sensitive enzyme immunoassay (EIA) has been developed and validated for the determination of pravastatin (PRV) in human plasma samples. PRV was coupled to keyhole limpt hemocyanin (KLH) and bovine serum albumin (BSA) via its terminal carboxylic acid group by carbodiimide reagent. PRV-KLH conjugate was used as an immunogen for raising anti-PRV polyclonal antibody in rabbits. The generated anti-PRV antibody recognized PRV with high affinity and selectivity. PRV-BSA conjugate was immobilized onto microwell plates and used as a solid phase. The assay involved a competitive binding reaction between PRV, in plasma sample, and the immobilized PRV-BSA for the binding sites on a limited amount of the anti-PRV antibody. The anti-PRV antibody bound to the plate wells was quantified with horseradish peroxidase-labeled anti-immunoglobulin second anti-rabbit IgG antibody and 3,3′,5,5′-tetramethylbenzidine as a substrate for the peroxidase enzyme. The concentration of PRV in the sample was quantified by its ability to inhibit the binding of the anti-PRV antibody to the immobilized PRV-BSA and subsequently the color development in the assay wells. The conditions of the proposed EIA were investigated and the optimum conditions were employed in the determination of PRV in plasma samples. The assay limit of detection was 0.2 ng mL⁻¹ and the effective working range at relative standard deviation (RSD) of ≤5% was 0.5-20 ng mL⁻¹. The mean analytical recovery of PRV from spiked plasma was 100.9 ± 2.98%. The precision of the assay was satisfactory; RSD was 2.61-3.70 and 3.96-4.17% for intra- and inter-assay precision, respectively. The analytical procedure is convenient, and one can analyze ∼200 samples per working day, facilitating the processing of large-number batch of samples. The proposed EIA has a great value in the routine analysis of PRV in plasma samples for its therapeutic monitoring and pharmacokinetic studies.     

Washing-free chemiluminescence immunoassay for rapid detection of cardiac troponin Ⅰ in whole blood samples

Chemiluminescence immunoassay(CLⅠA) has always been a great challenge in detecting cardiac troponin Ⅰ(c Tn Ⅰ) in whole blood samples without centrifugation because of the interference of red blood cells and low sensitivity. Ⅰn this study, the antigens and erythrocytes in the blood were captured by the antibodies immobilized on the magnetic particles, recognized by another biotinconjugated c Tn Ⅰ antibody and detected by streptavidin/acridine aster-conjugated polychloromethylstyrene microspheres(...     

Homogeneous immunoassay based on gold nanoparticles and visible absorption detection

A sensitive homogeneous immunoassay, using human serum albumin (HSA) as a model analyte coupled with simple visible absorption detection, has been developed. The new assay is based on the use of gold nanoparticles functionalized with the target protein, which compete with the analyte for the binding of a specific polyclonal antibody. The binding of antibodies to the functionalized nanoparticles determines a shift of the visible absorption maximum of the gold colloid, and quantification of the analyte could be obtained as the competitive inhibition of the binding of antibodies to the nanoparticles. The proposed immunoassay has been optimized and successfully applied to measuring HSA in human urine samples, in which results agreed well with those obtained by a nephelometric reference method.     

A highly sensitive enzyme immunoassay for evaluation of 2′-deoxycytidine plasma level as a prognostic marker for breast cancer chemotherapy

A highly sensitive competitive enzyme immunoassay (EIA) has been developed and validated for the determination of the plasma level of 2′-deoxycytidine (dCyd), the potential prognostic marker for breast cancer chemotherapy. This assay employed a monoclonal antibody that recognizes dCyd with a high specificity, and 5′-succinyl-dCyd (5′sdCyd) conjugate of bovine serum albumin (5′sdCyd-BSA) immobilized onto microplate wells as a solid phase. The assay involved a competitive binding reaction between dCyd, in plasma sample, and the immobilized 5′sdCyd-BSA for the binding sites of the anti-dCyd antibody. The bound antibody was quantified with horseradish peroxidase-labeled anti-immunoglobulin second antibody and 3,3′,5,5′-tetramethylbenzidine as a peroxidase substrate. The concentration of dCyd in the sample was quantified by its ability to inhibit the binding of the antibody to the immobilized 5′sdCyd-BSA and subsequently the color formation in the assay. The assay limit of detection was 8 nM and the effective working range at relative standard deviations (R.S.D.s) of ≤10% was 20-800 nM. No cross-reactivity from the structurally related nucleobases, nucleosides, and nucleotides was observed in the proposed assay. Mean analytical recovery of added dCyd was 98-100 ± 3.2-8.2%. The precision of the assay was satisfactory; R.S.D. was 3.4-4.2 and 4.3-8.9% for intra- and inter-assay precision, respectively. The proposed EIA was compared favorably with HPLC method in its ability to accurately measure dCyd spiked into plasma samples. The analytical procedure is convenient, and one can analyze 200 samples per working day, facilitating the processing of large-number batch of samples. The proposed EIA is expected to contribute in further evaluation of dCyd as a prognostic marker for breast cancer chemotherapy and elucidation of the role of dCyd in various biological and biochemical systems.     

Surface Plasmon Resonance Immunoassay for Ochratoxin A Based on Nanogold Hollow Balls with Dendritic Surface

Abstract

A surface plasmon resonance (SPR)‐immunosensor based on nano‐size gold hollow ball (GHB) with dendritic surface has been developed for detection of Ochratoxin A (OTA). A thionine thin film was initially electropolymerized onto the SPR‐probe surface, and then anti‐OTA monoclonal antibody (anti‐OTA) was immobilized onto the SPR‐probe surface by means of GHB conjugation. The binding of target molecules onto the immobilized antibodies causes an increase in the resonant angle of the sensor chip, and the resonant angle shift was proportional to the OTA concentration in the range of 0.05–7.5 ng/ml with a detection limit of 0.01 ng/ml at a signal/noise ration of 3. A glycine‐HCl solution (pH 2.8) was used to release antigen‐antibody complexes from the biorecognition surface. Good reusability was exhibited. Moreover, spiking various levels of OTA into three milk samples was assayed using the proposed immunoassay. Analytical results show the precision of the developed immunoassay is acceptable. Compared with the conventional enzyme‐linked immunosorbent assay, the proposed immunoassay system was simple and rapid without multiple labeling and separation steps. Importantly, the proposed immunoassay system could be further developed for the immobilization of other antigens or biocompounds.     

Pretreatment-free immunochromatographic assay for the detection of streptomycin and its application to the control of milk and dairy products

A rapid pretreatment-free immunochromatographic assay was developed for the control of the streptomycin (STR) content in milk and dairy products. The assay is based on the competition between an immobilized STR–protein conjugate and STR in a sample to be tested for the binding to monoclonal anti-STR antibodies conjugated to colloidal gold during the flow of the sample along a membrane strip with immobilized reactants. It is possible to improve the cut-off level of positive and negative samples distinguished by a change in the molar STR to protein ratio in the immobilized conjugate. The cut-off level (500 ng mL⁻¹) thus achieved corresponds to the stated MRL of STR in milk and dairy products. For STR concentrations in the range of 16–250 ng mL⁻¹ its content can be quantitatively measured based on the degree of binding of a colloidal gold label in the test strip zone with the immobilized STR–protein conjugate. The duration of the assay is 10 min. The selected sizes of membrane pores and colloidal gold particles allow the assay to be carried out at room temperature without additional reactants and pretreatment. The applicability of the assay for milk, whole milk, sour clotted milk, and kefir with different fat content (from 0.5% to 6%) was confirmed. The results of quantitative immunochromatographic assay show good correlation with traditional ELISA (r was equal to 0.935 and 0.940 for the series tested).     

Microchip electrophoresis coupled with on-line magnetic separation and chemiluminescence detection for multiplexed immunoassay

A facile and universal strategy for multiplexed immunoassay is proposed. The strategy is based on microchip electrophoresis (MCE) coupled with on-line magnetic separation and chemiluminescence (CL) detection. The system consisted of a microchip, an electromagnet, and a photomultiplier. The realization of multiplexed immunoassay protocol involves sampling magnetic nanoparticles (MNPs) labeled antibodies, N-(4-aminobutyl)-N-ethyl-isoluminol (ABEI) labeled antigens and free antigens in the precolumn reactor, on-line immunoreaction, capturing the MNPs-immunocomplexes, and the separation of unconjugated ABEI-labeled antigens. After on-line magnetic separation, the free ABEI-labeled antigens were transported into the separation channel, and mixed with hydrogen peroxide (H(2) O(2) ) in the presence of horseradish peroxidase in the postcolumn reactor, and producing CL emission. Using this arrangement, multiple analytes could be measured simultaneously by performing the technical operations for a single assay. As a proof-of-concept, the multiplexed immunoassay was evaluated for the simultaneous determination of five model analytes (i.e. hydrocortisone, corticosterone, digoxin, testosterone, and estriol). The results exhibited excellent precision and sensitivity, the relative standard deviations for nine times detection were lower than 4.7% for all the five components, and the detection limits of five analytes were in the range of 3.6-4.9 nM. The MCE system was validated using two human serum-based control samples containing five analytes.     

Comparative study of strategies for antibody immobilization onto the surface of magnetic particles in pseudo-homogeneous enzyme immunoassay of aflatoxin B1

Pseudo-homogeneous enzyme immunoassay (EIA) of aflatoxin B1 (AFB1) was accomplished using anti-AFM1 monoclonal antibodies conjugated with magnetic particles (MPs). The assay includes the concentration of AFB1 from the test sample on the surface of the MP-antibody conjugate, the binding of the AFB1-peroxidase conjugate to free sites of the antibodies, the separation of the complexes that formed from unreacted components by means of magnetic field, and the evaluation of the enzymatic activity of MP-bound peroxidase. A comparative study of antibody conjugates, which were prepared by three different methods, namely, by physical adsorption on native MP and covalent binding to oleic acidor polystyrene-coated MPs, was performed. For these conjugates, the detection limits of EIA for AFB1 are 2.6, 0.4, and 0.6 ng/mL, respectively. The advantages of the pseudo-homogeneous EIA format as a tool for the highly sensitive control of toxic contaminants in food are the shorter time of incubation of immunoassay reagents (5 min; the total assay time is 20 min) and the possibility of concentrating the analyte from the test samples.     

Highly sensitive rapid chemiluminescent immunoassay using the DNAzyme label for signal amplification

A novel trace tag for chemiluminescent (CL) immunoassay was designed by using DNAzyme to functionalize antibody-labeled Au nanoparticles (AuNPs). The trace tag showed an excellent ability to catalyze the oxidation of luminol by hydrogen peroxide, leading to strong CL emission. By coupling the trace tag with a passive mixing accelerated immunoreaction system, a highly sensitive rapid flow-through CL immunoassay method was proposed. Using carcinoembryonic antigen (CEA) as a model analyte, the capture antibody for CEA was immobilized on paramagnetic microspheres, and DNAzyme-anti-CEA antibody functionalized AuNPs were prepared as trace tag. A three-dimensional helical glass tube kept at 37 °C in a water bath was used for passively mixing immunoreagents in a two-step sandwich immunoassay, with which each immunoreaction step could be finished within 150 s. With the help of a magnet, the immunocomplex could conveniently be separated from reactants. Compared with the horseradish peroxidase-based tag, the newly designed trace tag showed obvious signal amplification due to its strong catalytic ability and high loading ratio of DNAzyme on each AuNP. The proposed method showed a linear calibration range from 0.005 to 0.5 ng mL(-1) for CEA detection with a detection limit of 4.1 pg mL(-1) at a signal-to-noise ratio of 3 and acceptable detection reproducibility. The assay results of clinical serum samples were in acceptable agreement with the reference values. The designed immunoassay system with ultrahigh sensitivity provided a programmable and low-cost approach for high-throughput clinical application.     

A Highly Sensitive Enzyme Immunoassay of Anti-Insulin Antibodies in Guinea Pig Serum

Abstract

A highly sensitive enzyme immunoassay of anti-insulin antibodies in guinea pig serum is described. Guinea pig anti-insulin serum was diluted to various extents with nonspecific guinea pig serum and incubated with insulin. Insulin bound to anti-insulin antibodies was separated from free insulin by precipitation with polyethylene glycol. Anti-insulin antibodies in the precipitates were dissociated from insulin and inactivated by incubation with 0.1 mol/1 HCl. The amount of insulin dissociated was measured by sandwich enzyme immunoassay using anti-insulin IgG-coated polystyrene balls and affinity-purified anti-insulin Fab′-horseradish peroxidase conjugate. The detection limit of anti-insulin antibodies in guinea pig serum was improved 1,000-fold as compared with that of the enzyme immunoassay previously described, in which insulin-coated polystyrene balls were incubated with diluted guinea pig anti-insulin serum and subsequently with rabbit (anti-guinea pig IgG) Fab′-horseradish peroxidase conjugate.     

Double-antibody homogeneous fluorescence immunoassay of phenytoin

A homogeneous fluorescence immunoassay suitable for quantifying 5–25 mg l^?1 phenytoin (5,5-diphenyl-2,4-imidazolidenedione) in serum is described. The fluorophor-labeled phenytoin and unlabeled phenytoin (analyte) compete for a limited number of anti-phenytoin antibody binding sites in the presence of anti-fluorophor antibodies. The label employed is a sulfonamido derivative of 2-naphthol-8-sulfonic acid (2-8) which, at neutral pH, undergoes excited-state proton transfer. Binding of anti 2-8 antibodies to the drug-fluorophor conjugate results in quenching of the conjugate base emission at 480 nm. The relative standard deviations are about 5%.     

Determination of aculeatisides based on immunoassay using a polyclonal antibody against aculeatiside A

An enzyme-linked immunosorbent assay (ELISA) was developed for determination of aculeatisides. Aculeatiside A was conjugated with bovine serum albumin (BSA) for immunization. The ratio of hapten in an antigen conjugate was determined by matrix-assisted laser desorption/ionization TOF mass spectrometry. Polyclonal antibody was developed in rabbits against an aculeatiside A-BSA conjugate. The antibody was specific for aculeatiside A and aculeatiside B. The range of the immunoassay extended from 100 ng ml(-1) to 5 pg ml(-1) of aculeatisides. Good correlation between ELISA and HPLC methods was obtained when crude extracts of plant samples were analyzed. The optimized ELISA was found to be applicable to the determination of total aculeatisides in various plant samples.     

Direct detection of Δ9-tetrahydrocannabinol in saliva using a novel homogeneous competitive immunoassay with fluorescence quenching

For the detection of the major active component of cannabis, Δ9-tetrahydrocannabinol (THC) in aqueous samples, a homogeneous competitive immunoassay based on fluorescence quenching induced by fluorescence resonance energy transfer (FRET) has been developed. The fluorescence of anti-THC-antibody, labeled with fluorescence dye DY-481XL, can be quenched after its binding to THC-BSA-quencher conjugate (bovine serum albumin coupled with THC and another fluorescence dye, DYQ-661, as quencher). This quenching effect is inhibited when the antibodies bind to free THC in aqueous sample, thus competing for binding sites with the THC-BSA-quencher conjugate. The extent of the inhibition corresponds to the concentration of THC in the samples. The assay principle is simple and the test duration is within 10 min. The detection limit for THC in buffer was 2 ng mL⁻¹. In pooled saliva samples a detection limit of 50 ng mL⁻¹ was achieved.     

Preparation of Polyclonal Antibodies with Application for an Organophosphorus Pesticide Immunoassay

Haptens of dichlorvos and paraoxon were conjugated to the carrier proteins of bovine serum albumin. The obtained conjugates were characterized by infrared and ultraviolet–visible spectroscopy. The binding ratios of dichlorvos and paraoxon-to-carrier proteins were also evaluated. The number of hapten molecules per protein molecule of dichlorvos–cationized bovine serum albumin conjugate was higher than for paraoxon–bovine serum albumin conjugate. The sheep polyclonal antibodies were produced against the dichlorvos and paraoxon. New multipolyclonal antibodies were obtained and characterized following the immunization of a 1:1 mixture of the immunogens for the simultaneous determination of dichlorvos and paraoxon by the immunoassay. An indirect enzyme-linked immunosorbent assay was used to characterize the reactivity of the antibodies to hapten conjugates. The multiantibodies showed lower affinities than the separate antibodies, but their affinities were sufficient for an immunoassay for the simultaneous determination of the analytes. The detection limit and linear range for the determination of dichlorvos and paraoxon alone and together were determined. The recovery was characterized to determine dichlorvos and paraoxon fortified in model solutions and milk. These results demonstrate the potential of this immunoassay for the quantitative screening of dichlorvos and paraoxon.     

Novel immunoassay for Toxoplasma gondii-specific immunoglobulin G using a silica nanoparticle-based biomolecular immobilization method

A direct and highly sensitive piezoelectric immunoassay for Toxoplasma gondii-specific IgG (Tg-IgG) in infected rabbit serum (IRS) has been proposed on the basis of a new biomolecular immobilization strategy incorporating silica nanoparticles/matrix and a plasma-polymerized film (PPF) of n-butyl amine. SiO₂ nanoparticles prepared by using a water-in-oil microemulsion route were chemically activated and then used to conjugate T. gondii antigens (TgAg) onto the PPF-deposited crystal. Compared to the commonly applied methods, i.e. the glutaraldehyde (GLU) cross-linking procedure, this strategy could allow for antigens immobilized with higher loading amount and better retained immunoactivity, as demonstrated by the immunofluorescence measurements. Moreover, a mild reduction agent 2-mercaptoethanol (2-ME) which can deactivate T. gondii-specific IgM in the analytical samples was utilized to achieve the direct determination of Tg-IgG. Some applications including an optimized assay medium, a blocking reagent and a versatile regenerating solution may facilitate a sensitivity amplified, non-specific adsorption-minimized and renewable sensing system. A dynamic dilution range of ∼1:5000 to 1:70 and detection limit of 1:5350 dilution were observed. Results obtained by evaluating IRS samples indicate that the detection sensitivity of the developed immunoassay is comparable to that of the ELISA method and superior to that of the dot-immunogold test.     

Displacement immunoassay for the detection of ochratoxin A using ochratoxin B modified glass beads

We report here the development of a new assay for the detection of ochratoxin A (OTA) based on the use of its dechlorinated analogue, ochratoxin B (OTB), in a displacement immunoassay. OTB was immobilised on controlled-pore glass beads followed by the binding of anti-OTA antibody, with anti-IgG antibody peroxidase conjugate used as a label. In this manner, an original bio-sensing material was obtained. Upon incubation of this material with OTA, the toxin competes with OTB for the binding sites of the anti-OTA antibodies and releases the antibody-tagged peroxidase complex into the solution. Compared to classic competitive immunoassays, this newly developed displacement immunoassay presents a similar detection limit and assay time. Moreover, the detection, based on the activity of the horseradish peroxidase, is performed for the first time in situ using wine samples.     

Immune Complex Transfer Enzyme Immunoassay for Anti-Thyroglobulin IgG Using 2,4-Dinitrophenyl-thyroglobulin,Biotinyl-thyroglobulin and Streptavidin-β-D-galactosidase Conjugate

Abstract

A sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for anti-thyroglobulin IgG in serum is described. Anti-thyroglobulin IgG in serum was reacted simultaneously with 2,4-dinitrophenyl-thyroglobulin and biotinyl-thyroglobulin. The immune complex formed of the three components was trapped onto polystyrene balls coated with (anti-2,4-dinitrophenyl group) IgG and, after washing, reacted with streptavidin-β-D-galactosidase conjugate. After washing, the immune complex was eluted from the polystyrene balls with εN-2,4-dinitrophenyl-L-lysine and transferred to polystyrene balls coated with (anti-human IgG γ-chain) IgG. β-D-Galactosidase activity bound to the last polystyrene balls was assayed by fluorometry. Biotinylthyroglobulin and streptavidin-β-D-galactosidase conjugate could be prepared more easily than thyroglobulin-β-D-galactosidase conjugate used in the previous immunoassay. Inactive β-D-galactosidase, used to eliminate interference by anti-β-D-galactosidase antibodies in the previous immunoassay, was not required. The present immunoassay was 300-fold more sensitive than the conventional enzyme immunoassay, although 10-fold less sensitive than the previous immunoassay. Antithyroglobulin IgG was demonstrated in all patients with autoimmune thyroid diseases and 54% of healthy subjects.     

Solid-phase chemiluminescence immunoassay for screening of anabolic agents in application sites in slaughtered cattle

A solid-phase chemiluminescence immunoassay for 19-nortestosterone (NT) is presented; NT-3-carboxymethyloxime/N-(4-aminobutyl)-N-ethylisoluminol serves as the label with an antiserum raised against NT-3-carboxymethyloxime/bovine serum albumin. Some other anabolic compounds (e.g., testosterone and trenbolone) showed substantial cross-reactivity. The assay can be used generally for the detection of anabolic agents in application sites. Because of the high sensitivity (0.1 pg NT/tube at 90% relative binding), only 250 μg of muscle tissue is needed for the assay. Apparent NT contents of 0.4 to 16 000 μg kg^?1 tissue can be measured. With a simplified isolation method, about 40 samples can be screened in a working day.