Immunochromatography using colloidal gold-antibody probe for the detection of atrazine in water samples

Establishment of monoclonal antibody and scFv immuno-based assay for Cry2Aa toxin in spiked grain samples

Bacillus thuringiensis (Bt) Cry toxins have been widely used in the development of genetically modified organisms (GMOs) for pest control. This work aimed to establish more cost effective methods for used Cry2Aa toxins. Three immunoassay methods (IC-ELISA, DAS-ELISA, and CLEIA) were successfully developed in this work. The mAb was used as the detecting antibody, for the IC-ELISA, the range of IC20 to IC80 was 1.11 μg/mL - 60.70 μg/mL, and an IC50 of 10.65 μg/mL. For the DAS-ELISA, the limit of detection (LOD) and limit of quantitation (LOQ) were 10.76 ng/mL and 20.70 ng/mL, respectively. For the CLEIA, the LOD and LOQ were 6.17 ng/mL and 7.40 ng/mL, respectively. The scFv-based detections were the most sensitive for detecting Cry2Aa. The LOD and LOQ for the DAS-ELISA were 118.75 ng/mL and 633.48 ng/mL, respectively. The LOD and LOQ for the CLEIA, read as 37.47 ng/mL and 70.23 ng/mL, respectively. The fact that Cry2Aa toxin was recovered in spiked grain samples further demonstrated that the approaches might be used to identify field samples. These methods provided good sensitivity, stability, and applicability for detecting Cry2Aa toxin, promising ultrasensitive monitoring and references for Cry toxins risk assessment.

Obtaining a Monoclonal Antibody against a Novel Prometryn-Like Hapten and Characterization of Its Selectivity for Triazine Herbicides

In this study, a previously unreported 3-((4-(isopropylamino)-6-(methylthio)-1,3,5-triazin-2-yl) amino) butyric acid hapten was designed and synthesized. This maximized the exposure of the antigen-determinant isopropyl of prometryn to the immune system in animals to induce the production of anticipated highly specific anti-prometryn antibodies. The hapten has a molecular weight of 285.37 Da. The compound was confirmed by nuclear magnetic resonance hydrogen spectroscopy (¹H NMR), nuclear magnetic resonance carbon spectroscopy (¹³C NMR), and high-resolution mass spectrometry (HRMS). By using the active ester approach, immunogens and coated antigens were created. Bovine serum albumin (BSA) was used as an immunogen, along with the successfully produced hapten, to immunize mice. The IC₅₀ value of mouse monoclonal anti-prometryn antibody (mAb) 7D4 (the quantity of analyte that generated 50% prometryn inhibition) was 3.9 ng/mL. The anti-prometryn mAb was of the IgG1 subclass. The IC₂₀ (80% binding level (B/B₀) of prometryn)-IC₈₀ (20% binding level (B/B₀) of prometryn) range of the anti-prometryn monoclonal antibody standard curve working range was 0.9-18.1 ng/mL. The prepared mAb has good characteristics because it can specifically recognize prometryn, and the cross-reaction rates for ametryn, desmetryn, and terbumeton were 34.77%, 18.09%, and 7.64%, respectively. The cross-reaction rate with the other seven triazines was less than 1%. The hapten structure proposed can serve as an additional tool for modulating selectivity in detecting triazines.

Development of a test strip for rapid detection of Gymnodinium catenatum

Harmful algal blooms (HABs) are major ecological and environmental problems in China's coastal waters and seriously threaten the stability of the marine ecosystem and human health. Gymnodinium catenatum is a toxic red tide dinoflagellate. It can produce paralytic shellfish toxins (PSP), which cause serious hazards to marine organisms, public health, and safety. In this paper, a test strip based on colloidal gold immunochromatography (GICG) was developed for the rapid detection of Gymnodinium catenatum. The experimental results showed that the test strip has good specificity and sensitivity. It not only detects the different components of Gymnodinium catenatum but also may detect algal toxins. The lowest density of Gymnodinium catenatum that can be detected by this test strip is approximately 120 cells/mL. Cross-reaction indicated that the test strip had a high specificity for Gymnodinium catenatum. This test strip provides a rapid method for in situ detection of Gymnodinium catenatum and a reference method for the monitoring of other harmful algae to serve as an early warning of upcoming red tides. It also provides a new way to prepare more detection methods for toxic algal toxins.

Design and Characterization of a Novel Hapten and Preparation of Monoclonal Antibody for Detecting Atrazine

This study provides the first design and synthetic protocol for preparing highly sensitive and specific atrazine (ATR) monoclonal antibodies (mAbs). In this work, a previously unreported hapten, 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine, was designed and synthesized, which maximally exposed the characteristic amino group ATR to an animal immune system to induce the expected antibody. The molecular weight of the ATR hapten was 259.69 Da, and its purity was 97.8%. The properties of the anti-ATR mAb were systematically characterized. One 9F5 mAb, which can detect ATR, was obtained with an IC₅₀ value (the concentration of analyte that produced 50% inhibition of ATR) of 1.678 µg/L for ATR. The molecular weight for the purified 9F5 mAb was approximately 52 kDa for the heavy chain and 15 kDa for the light chain. The anti-ATR mAb prepared in this study was the IgG₁ type. The working range of the standard curve (IC₂₀ (the concentration of analyte that produced 20% inhibition of ATR)_-IC₈₀ (the concentration of analyte that produced 80% inhibition of ATR)) was 0.384 to 11.565 µg/L. The prepared anti-ATR mAb had high specificity, sensitivity, and affinity with low cross-reactivity. The prepared anti-ATR mAb could provide the core raw material for establishing an ATR immunoassay.

A gold nanoparticle-based lateral flow immunoassay for atrazine point-of-care detection using a handhold scanning device as reader

A method is described to achieve accurate quantitative detection of atrazine (ATZ) in maize by using lateral flow strips based on gold nanoparticles (GNPs) and a handheld scanning reader. GNPs of 15 nm in diameter were applied as label, and a lateral flow immune assay strip was prepared. The linear range was 5.01-95.86 ng mL^-1 with a detection limit of 4.92 ng mL^-1 in phosphate buffer, 4 times better than the readout by the naked eye. ATZ-spiked corn samples were also analysed. The accuracy of results of spiked samples was confirmed by ELISA and liquid chromatography-tandem mass spectrometry (HPLC), which proved the reliability of the proposed method. A handhold device with an optical scanning system was designed for on-site quantitative detection. Combined with the pretreatment, the assay could be completed in less than 20 min.

Diagnostic Accuracy of Immunochromatographic Tests for the Detection of Norovirus in Stool Specimens: a Systematic Review and Meta-Analysis

Noroviruses are the leading cause of acute gastroenteritis in all age groups and constitute a major health and economic burden worldwide. This systematic review and meta-analysis aimed to determine the diagnostic accuracy of immunochromatographic tests (ICTs) for the detection of norovirus in stool specimens, which has not been performed previously. In this systematic review and meta-analysis (registered on PROSPERO, CRD42020186911), we searched Medline/PubMed, Embase, Cochrane Library, and Web of Science for all studies published up to 16 May 2020. The values for sensitivity, specificity, positive likelihood ratio (LR+), negative likelihood ratio (LR-), and diagnostic odds ratio (DOR) of ICTs with 95% confidence interval (CI) were pooled using a bivariate random-effects model. The summary receiver operating characteristic curve and area under the curve were used to summarize overall test accuracy. We included 43 studies describing 7,428 samples. The overall estimates of sensitivity, specificity, LR+, LR-, DOR, and accuracy of ICT for diagnosing norovirus were 0.61 (95% CI, 0.54 to 0.67), 0.97 (95% CI, 0.95 to 0.98), 17.08 (95% CI, 11.15 to 26.18), 0.40 (95% CI, 0.34 to 0.46), 53.9 (95% CI, 31.32 to 92.78), and 0.928, respectively. Significant differences in pooled sensitivities were noted between age groups and in pooled DOR and LR+ between genogroups of included samples. ICT provides low sensitivity but high specificity and accuracy for detecting norovirus. Thus, an ICT for norovirus can be a rapid and convenient way for identifying patients early; however, a negative result cannot rule out norovirus infection and should be confirmed by a reference test.

Polydopamine functionalized graphene sheets decorated with magnetic metal oxide nanoparticles as efficient nanozyme for the detection and degradation of harmful triazine pesticides

A facile and an eco-friendly reduction and functionalization of reduced graphene oxide (rGO) sheets is carried out using dopamine and decorated with magnetic Fe₃O₄ nanoparticles with an average size of 12 nm by a simple co-precipitation method which is established as an artificial nanozyme. Here, functionalization of graphene using dopamine has introduced several advantages and insights into this study. The Fe₃O₄ nanoparticles decorated functionalized rGO sheets (FDGs) nanozymes are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, atomic force microscopy (AFM), thermogravimetric (TGA) and vibrating sample magnetometer (VSM) analysis. FDGs nanozymes exhibits dual characteristics towards detection and degradation of harmful simazine pesticide. The hydrogen bonding interactions between pesticide molecules and 3,3',5,5'-tetramethylbenzidine (TMB) causes inhibition of the catalytic activity of the FDGs towards oxidation of TMB molecule. Based on that, the presence of simazine pesticide in an aqueous medium can be easily determined and a certain value (2.24 μM) of detection limit was achieved. The photocatalytic degradation of simazine is also executed and excellent photocatalytic activity was observed under irradiation of direct natural sunlight. The FDGs nanozyme is also reusable up to several times with insignificant loss in its catalytic activity towards simazine degradation.

An Open Sandwich Immunochromatography for Non-competitive Detection of Small Antigens

Immunochromatography assay is an easy and rapid on-site detection method. However, conventional sandwich immunochromatographies using two antibodies can only detect target molecules above a threshold size. Small molecules below 1000 in molecular weight are usually detected using competitive immunoassay. However, competitive immunoassay is not suitable for visual detection of low concentration samples. Based on the principles of open sandwich immunoassay, which detects small molecules via interchain interaction of separated variable region fragments (V_H and V_L) from a single antibody, we developed non-competitive open sandwich immunochromatography. Bone Gla protein (BGP)-C7, a peptide containing the seven C-terminal amino acids of human osteocalcin, was selected as the target. By using V_L fragments fixed on a nitrocellulose membrane, and colored cellulose bead-labeled V_H fragments, we specifically detected 10 ng/mL of BGP-C7. This is the first report of open sandwich immunochromatography, which is an easy and rapid method for on-site, signal-on detection of small molecules.

Immunochromatography for the diagnosis of Mycoplasma pneumoniae infection: A systematic review and meta-analysis

The aim of this study was to evaluate the diagnostic performance of immunochromatographic tests (ICTs) for the detection of Mycoplasma pneumoniae. Medline/Pubmed, Embase, the Cochrane Library, and ISI Web of Science were searched through June 12, 2019 for relevant studies that used ICTs for the detection of M. pneumoniae infection with polymerase chain reaction (PCR) or microbial culturing as reference standards. Pooled diagnostic accuracy with 95% confidence interval (CI) was calculated using a bivariate random effects model. We also constructed summary receiver operating characteristic curves and calculated the area under the curve (AUC). Statistical heterogeneity was evaluated by χ² test or Cochrane’s Q test. Thirteen studies including 2,235 samples were included in the meta-analysis. The pooled sensitivity and specificity for diagnosing M. pneumoniae infection were 0.70 (95% CI: 0.59–0.79) and 0.92 (95% CI: 0.87–0.95), respectively. The positive likelihood ratio (LR) was 8.94 (95% CI: 4.90–14.80), negative LR 0.33 (95% CI: 0.22–0.46), diagnostic odds ratio 29.20 (95% CI: 10.70–64.20), and AUC 0.904. In subgroup analysis, ICTs demonstrated similar pooled sensitivities and specificities in populations of children only and mixed populations (children + adults). Specimens obtained from oropharyngeal swabs exhibited a higher sensitivity and specificity than those of nasopharyngeal swab. Moreover, pooled estimates of sensitivity and accuracy for studies using PCR as a reference standard were higher than those using culture. The pooled sensitivity and specificity of Ribotest Mycoplasma^®, the commercial kit most commonly used in the included studies, were 0.66 and 0.89, respectively. Overall, ICT is a rapid user-friendly method for diagnosing M. pneumoniae infection with moderate sensitivity, high specificity, and high accuracy. This suggests that ICT may be useful in the diagnostic workup of M. pneumoniae infection; however, additional studies are needed for evaluating the potential impact of ICT in clinical practice.

Dual responsive magnetic Fe3O4-TiO2/graphene nanocomposite as an artificial nanozyme for the colorimetric detection and photodegradation of pesticide in an aqueous medium

The Fe₃O₄-TiO₂/reduced graphene oxide (Fe₃O₄-TiO₂/rGO) nanocomposite was successfully prepared by one step hydrothermal method and exhibit intrinsic peroxidase mimic activity and photocatalytic efficiency. The as-prepared nanomaterials were characterized by several analytical tools including XRD, HRTEM, FESEM, XPS, VSM, FT-IR, AFM, TGA and zeta potential analysis. The average particle size of Fe₃O₄ and TiO₂ NPs on the rGO nanosheets are found to be 9 ± 0.2 nm. The synthesized nanocomposite showed dual responsive including highly sensitive colorimetric detection of harmful atrazine pesticide in an aqueous medium as well as photocatalytic degradation of atrazine pesticide. The Fe₃O₄-TiO₂/rGO nanocomposite showed the efficient peroxidase-like catalytic activity throughout the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) as a peroxidase substrate to the blue-colored oxidized product (ox-TMB) in presence of H₂O₂. Based on this observation, the colorimetric detection technique is applied for the sensing of atrazine as model pesticides using TMB as a peroxidase substrate molecule and 2.98 μg/L of the limit of detection (LOD) was obtained in the linear range of 2-20 μg/L. Thus the proposed colorimetric sensing technique is simple and low cost for the real-time monitoring of the pesticides in an aqueous medium. Further, the Fe₃O₄-TiO₂/rGO nanocomposite was also successfully utilized towards efficient photocatalytic degradation of atrazine molecule (100 %) under irradiation of natural sunlight. Moreover, Fe₃O₄-TiO₂/rGO nanocomposite was successfully recycled for 10 times without a significant loss of its photocatalytic efficiency. This work delivers a new insight for the dual responsive of the Fe₃O₄-TiO₂/rGO nanocomposite as an artificial nanozyme for colorimetric sensing of the water pollutant and also removal of the water pollutant by simple photocatalytic degradation method under natural sunlight irradiation.

Novel polyclonal antibody-based rapid gold sandwich immunochromatographic strip for detecting the major royal jelly protein 1 (MRJP1) in honey

Honey adulteration is becoming increasingly alarming incidents in food safety. Monitoring and detecting adulteration face greater challenges. Honey contains the major royal jelly proteins (MRJP) secreted by bee workers. To detect honey adulteration fast and accurately, a rapid gold sandwich immunochromatographic strip (GSIS) was developed based on two specific polyclonal antibodies (PoAbs) against the MRJP1, the most abundant protein of all MRJPs. We determined the best of pH value (pH 8.6) and PoAb SP-1 amount (5 μg/mL) in conjunction with colloidal. The cut-off value (sensitivity) of GSIS in detecting MRJP1 is 2.0 μg/mL in solution. Validation analysis with RJ, milk vetch honey, acacia honey and honey adulteration containing rice syrup and corn syrup with different ratios demonstrated that the GSIS could show consistent Test line (T line) when the test samples contain more than 30% pure honey or MRJP1 0.4 mg/g. The validation results by isotope ratio mass spectrometry on the same pure and all adulteration milk vetch honey samples showed the same information of GSIS test. The qualitative assay GSIS provided a valuable new way for honey authenticity and laid the foundation for the future application of GSIS with monoclonal antibodies in honey authentication.

Development of an immunochromatographic strip test for the rapid detection of zearalenone in wheat from Jiangsu province, China

A colloidal gold (ICS) test was developed for rapid detection of zearalenone (ZEN) in wheat samples. The mAb against ZEN was prepared in our laboratory and labelled with colloidal gold as a probe for the ICS test. The conditions were optimized and 30 nm colloidal gold nanoparticles were chosen for optimal performance. Millipore 135 was chosen as the NC membrane for its level of sensitivity. The optimum amount of coated antigen ZEN-OVA and anti-ZEN mAb was 0.5 mg/mL and 8 μg/mL, respectively. The ICS test, which has a detection limit of 15 ng/mL for ZEN, could be completed in 5 min. Analysis of ZEN in 202 wheat samples over three consecutive years revealed that data obtained from the ICS test were in a good agreement with LC-MS/MS data. This result demonstrated that the ICS test could be used as a qualitative tool to screen on-site for ZEN.

Development of a Calibration Strip for Immunochromatographic Assay Detection Systems

With many benefits and applications, immunochromatographic (ICG) assay detection systems have been reported on a great deal. However, the existing research mainly focuses on increasing the dynamic detection range or application fields. Calibration of the detection system, which has a great influence on the detection accuracy, has not been addressed properly. In this context, this work develops a calibration strip for ICG assay photoelectric detection systems. An image of the test strip is captured by an image acquisition device, followed by performing a fuzzy c-means (FCM) clustering algorithm and maximin-distance algorithm for image segmentation. Additionally, experiments are conducted to find the best characteristic quantity. By analyzing the linear coefficient, an average value of hue (H) at 14 min is chosen as the characteristic quantity and the empirical formula between H and optical density (OD) value is established. Therefore, H, saturation (S), and value (V) are calculated by a number of selected OD values. Then, H, S, and V values are transferred to the RGB color space and a high-resolution printer is used to print the strip images on cellulose nitrate membranes. Finally, verification of the printed calibration strips is conducted by analyzing the linear correlation between OD and the spectral reflectance, which shows a good linear correlation (R² = 98.78%).

Lipopolysaccharide Specific Immunochromatography Based Lateral Flow Assay for Serogroup Specific Diagnosis of Leptospirosis in India

BACKGROUND

Leptospirosis is a re-emerging infectious disease that is under-recognized due to low-sensitivity and cumbersome serological tests. MAT is the gold standard test and it is the only serogroup specific test used till date. Rapid reliable alternative serogroup specific tests are needed for surveillance studies to identify locally circulating serogroups in the study area.

METHODS/PRINCIPAL FINDINGS

In the present investigation the serological specificity of leptospiral lipopolysaccharides (LPS) was evaluated by enzyme linked immunosorbent assay (ELISA), dot blot assay and rapid immunochromatography based lateral flow assay (ICG-LFA). Sera samples from 120 MAT positive cases, 174 cases with febrile illness other than leptospirosis, and 121 seronegative healthy controls were evaluated for the diagnostic sensitivity and specificity of the developed assays. LPS was extracted from five locally predominant circulating serogroups including: Australis (27.5%), Autumnalis (11.7%), Ballum (25.8%), Grippotyphosa (12.5%), Pomona (10%) and were used as antigens in the diagnostics to detect IgM antibodies in patients' sera. The sensitivity observed by IgM ELISA and dot blot assay using various leptospiral LPS was >90% for homologous sera. Except for Ballum LPS, no other LPS showed cross-reactivity to heterologous sera. An attempt was made to develop LPS based ICG-LFA for rapid and sensitive serogroup specific diagnostics of leptospirosis. The developed ICG-LFA showed sensitivity in the range between 93 and 100% for homologous sera. The Wilcoxon analysis showed LPS based ICG-LFA did not differ significantly from the gold standard MAT (P>0.05).

CONCLUSION

The application of single array of LPS for serogroup specific diagnosis is first of its kind. The developed assay could potentially be evaluated and employed for as MAT alternative.

Competitive immunochromatographic assay for the detection of thiodiglycol sulfoxide, a degradation product of sulfur mustard

An immunochromatographic assay (ICA) based on the competitive antigen-coated format using colloidal gold as the label was developed for the detection of thiodiglycol sulfoxide (TDGO), an important metabolite and degradation compound of sulphur mustard (SM). The ICA test strip consisted of a membrane with a detection zone, a sample pad and an absorbent pad. The membrane was separately coated with hapten-OVA conjugate (test line) and anti-rabbit mouse IgG (control line). The visual detection limit for TDGO by ICA detection was found to be 10 μg mL(-1). For validation, the ICA results obtained for spiked water samples were in good agreement with those obtained by indirect competitive inhibition enzyme-linked immunosorbent assay (ELISA) for TDGO. The assay time for detection was less than 10 min. The developed ICA has the potential to be a useful on-site screening tool for the retrospective detection of SM in environmental samples.

Nano-gold capillary immunochromatographic assay for parvalbumin

A novel non-instrumental bioanalysis based on colloidal-gold immunochromatography in a modified glass capillary was developed and named capillary immunochromatographic assay (CICA). In this report, glass capillary was proposed as a support in immunochromatographic assay because of its excellent characteristics. Goat anti-rabbit IgG and parvalbumin (PV) were immobilized on the inner wall of the glass capillary as control zone and test zone, respectively. The CICA was constructed, and main variables for the performance were optimized. Using an important allergen of fish products (parvalbumin, PV) as the target, the analytical efficiency of the developed technique was investigated and the visual detection limit (VDL) and semi-quantitative limit of detection (LOD) were estimated to be 70 ng mL(-1) and 40 ng mL(-1), respectively. The coefficient of variation (CV) for the intra-assay and inter-assay was calculated for the PV concentration of 50 ng mL(-1), and the entire operation, including sample preparation, was consistently performed in 30 min. The developed technique was implemented and validated with different foodstuffs, including Scophthalmus maximus (Linnaeus), surimi products, and livestock, confirming sufficient accuracy and precision of results and verifying the method to be efficacious. These results enabled us to propose CICA as a new and promising technique for simple, rapid, and on-site screening of PV in biological samples.

Development of a manual self-assembled colloidal gold nanoparticle-immunochromatographic strip for rapid determination of human interferon-γ

Interferons (IFNs) play a role in inhibition of tumor growth and participate in immunoreactions. Among IFNs, interferon-γ (IFNγ) is one of the most important therapeutic proteins and its immunodulation ability is better than that of other types. The objective of this study is to develop a manual self-assembled colloidal gold nanoparticle-immunochromatographic strip for human IFNγ using anti-human IFNγ polyclonal and monoclonal antibodies. Colloidal gold with a 25 nm diameter was made from chloroauric acid (HAuCl4), and labeled on anti-IFNγ mAbs as a chrominance reagent. A good linear relationship existed between the pixel intensity and the human IFNγ concentrations from 10-1000 ng mL(-1) in mouse serum and buffer, respectively, the regression equation was Y = 0.159logX + 0.0648, R(2) = 0.992 in mouse serum; Y = 0.294logX + 0.091, R(2) = 0.9969 in phosphate buffer by this proposed strip. Moreover, in the determination for mouse serum samples no cross-reaction occurred and the detection time was approximately 10 minutes. The shelf life of the strip was above 28 days at room temperature. The major advantages of the manual operation model were no expensive instruments and less reagents required. This proposed strip was highly specific, economic, convenient, and no machine was needed in clinical diagnosis.

Rapid and sensitive immunochromatographic strip for on-site detection of sulfamethazine in meats and eggs

A rapid immunochromatographic (ICG) strip based on a conjugate of colloidal gold and monoclonal antibody (mAb) was developed for the rapid, sensitive, and on-site detection of sulfamethazine in meat and egg samples. The detection limit of the ICG strip is 2 ng/mL, and the assay can be completed in 10 min. A cross-reactivity test indicated that the ICG strip was highly specific to sulfamethazine with no cross-reaction with sulfonamide compounds and other antibiotics. The results of the recovery test from meat and egg samples spiked with sulfamethazine were in good agreement with those obtained by the indirect competitive enzyme-linked immunosorbent assay. These results demonstrated that the ICG strip can be used as a rapid and qualitative tool for on-site screening of sulfamethazine in meat and egg samples.

Reagents in microfluidics: an 'in' and 'out' challenge

Microfluidic devices are excellent at downscaling chemical and biochemical reactions and thereby can make reactions faster, better and more efficient. It is therefore understandable that we are seeing these devices being developed and used for many applications and research areas. However, microfluidic devices are more complex than test tubes or microtitre plates and the integration of reagents into them is a real challenge. This review looks at state-of-the-art methods and strategies for integrating various classes of reagents inside microfluidics and similarly surveys how reagents can be released inside microfluidics. The number of methods used for integrating and releasing reagents is surprisingly large and involves reagents in dry and liquid forms, directly-integrated reagents or reagents linked to carriers, as well as active, passive and hybrid release methods. We also made a brief excursion into the field of drug release and delivery. With this review, we hope to provide a large number of examples of integrating and releasing reagents that can be used by developers and users of microfluidics for their specific needs.

Development of immunochromatography-based methods for detection of leptospiral lipopolysaccharide antigen in urine

Leptospirosis is an infectious disease caused by the spirochete bacteria Leptospira spp. and is commonly found throughout the world. Diagnosis of leptospirosis performed by culture and microscopic agglutination tests is laborious and time-consuming. Therefore, we aimed to develop a novel immunochromatography (ICG)-based method for detecting Leptospira antigen in the urine of patients and animals. We used the 1H6 monoclonal antibody (MAb), which is specific to the lipopolysaccharide (LPS) that is common among Leptospira spp. The MAb was coupled to 40-nm-diameter colloidal gold, and the amounts of labeled antibody and immobilized antibody were 23 μg and 2 μg per test, respectively. Several strains of Leptospira and other bacterial species were used to evaluate the sensitivities and specificities of the assays we developed. The detection limit of the assays was 10(6) cells/ml when disrupted whole bacterial cells were used. The assays were Leptospira specific since they did not cross-react with non-Leptospira bacteria used in the study. Application of diagnostic assays was done on the urine samples of 46 Leptospira-infected hamsters, 44 patients with suspected leptospirosis, and 14 healthy individuals. Pretreatment of the urine samples by boiling and centrifugation (for ultrafiltration and concentration) eliminated nonspecific reactions that occurred in the assay. The sensitivity and specificity of the ICG-based lateral flow assay (LFA) were 89% and 87%, respectively, which were higher than those of the dipstick assay, which were 80% and 74%, respectively. In summary, this ICG-based LFA can be used as an alternative diagnostic assay for leptospirosis. Further development is still necessary to improve the assay.

Importance of membrane selection in the development of immunochromatographic assays for low-molecular weight compounds

This study was performed to demonstrate the importance of selecting an appropriate membrane when developing immunochromatographic assays (ICAs) for the sensitive detection of low-molecular weight compounds. Based on our findings, we propose a theoretical basis for selecting such a membrane. When eluting the sample solution for the competitive ICA using colloidal gold label for low-molecular analytes, the degree of binding inhibition is proportional to the collision frequency between the antibody-colloidal gold (Ab-CG) and analyte before Ab-CG binding to the capture antigen and a higher concentration of pesticides around the Ab-CG leads to a greater degree of inhibition. Therefore, we propose that the relative migration speed of the analyte and Ab-CG on the test strip is critically important for selecting a membrane in the development of sensitive competitive ICAs. We developed a novel method to estimate such a relative migration speed. We demonstrated the applicability of this proposal by using it to select an appropriate membrane for the development of an ICA of the pesticide diazinon.

Signal amplification using colloidal gold in a biolayer interferometry-based immunosensor for the mycotoxin deoxynivalenol

Deoxynivalenol (DON) is a toxin produced by certain species of Fusarium fungi that can infest wheat, barley and corn. The fungi cause diseases in crops worldwide and some of the secondary metabolites, such as DON, can adversely affect animal health and food safety. To monitor DON in wheat rapidly, a biosensor using the principle of biolayer interferometry (BLI) was developed. The signal from the sensor was substantially amplified through the use of a primary antibody-colloidal gold conjugate. The amplification was much greater in the presence of wheat matrix than in buffered solution, suggesting matrix components may have contributed to the enhancement. The improved signal provided by the amplification allowed for the development of rapid qualitative and quantitative assays. The limit of detection of the method was 0.09 mg kg(-1); the limit of quantitation was 0.35 mg kg(-1). Recovery from wheat spiked over the range from 0.2 to 5 mg kg(-1) averaged 103% (RSD = 12%). The quantitative assay compared favourably (r(2) = 0.9698) with a reference chromatographic method for 40 naturally contaminated wheats. The qualitative assay was able to classify accurately the same group of 40 samples as either above or below a 0.5 mg kg(-1) threshold. These results suggest that the BLI technique can be used to measure DON in wheat rapidly.

Competitive immunochromatographic assay for the detection of the organophosphorus pesticide chlorpyrifos

An immunochromatographic assay (ICA) based on competitive antigen-coated format using colloidal gold as the label was developed for the detection of the organophosphorus insecticide chlorpyrifos. The ICA test strip consisted of a membrane with a detection zone, a sample pad and an absorbent pad. The membrane was separately coated with chlorpyrifos Hapten-OVA conjugate (test line) and anti-mouse IgG (control line). Based on the fact that the competition is between the migrating analyte in the sample and the analyte hapten immobilized on the test strip for the binding sites of the antibody-colloidal gold (Ab-CG) conjugate migrating on the test strip, this study suggests that the relative migration speed between the two migrating substances is a critically important factor for the sensitive detection by competitive ICA. This criterion was utilized for the confirmation of appropriateness of a nitrocellulose (NC) membrane for chlorpyrifos ICA. The detection limit of the ICA for chlorpyrifos standard and chlorpyrifos spiked into agricultural samples were 10 and 50 ng mL(-1), respectively. The assay time for the ICA test was less than 10 min, suitable for rapid on-site testing of chlorpyrifos.

Sensitive enzyme-linked immunosorbent assay and rapid one-step immunochromatographic strip for fumonisin B1 in grain-based food and feed samples

BACKGROUND

Maize contaminated with mycotoxin fumonisin B1 poses a global threat to agricultural production. In this study, polyclonal antibodies (pAb) specific to fumonisin B1 were generated from rabbits immunised with fumonisin B1-keyhole limpet haemocyanin (KLH). These antibodies were used to establish a sensitive competitive direct enzyme-linked immunosorbent assay (cdELISA) and gold nanoparticle immunochromatographic strip for detecting fumonisin B1 levels in maize-based foods and feeds.

RESULTS

In cdELISA, fumonisins B1, B2 and B3 at concentrations of 0.42, 0.58 and 81.5 ng mL(-1) respectively caused 50% inhibition (IC(50)) of binding of fumonisin B1-horseradish peroxidase (HRP) to the antibodies. Effective on-site detection of fumonisin B1 was achieved by developing a rapid and sensitive pAb-based gold nanoparticle immunochromatographic strip. This strip had a detection limit of 5 ng mL(-1) for fumonisin B1 in maize-based samples. Additionally, the whole analytical process could be completed within 10 min. Close examination of 15 maize-based samples by cdELISA revealed that 11 were fumonisin-positive, with a mean concentration of 435 +/- 20.1 ng g(-1). These results correlated well with those obtained by immunochromatographic strip.

CONCLUSION

Both cdELISA and immunochromatographic strip methods established in this study are sensitive for rapid detection of fumonisins in agricultural commodities.

Development and validation of a gold nanoparticle immunochromatographic assay (ICG) for the detection of zearalenone

A monoclonal antibody (mAb)-based gold nanoparticle immunochromatographic assay (ICG) for zearalenone detection was developed, optimized, and validated. The detection limits of ICG optimized with appropriate amounts of zearalenone-bovine serum albumin and gold nanoparticle-mAb to zearalenone were 2.5 ng/mL and 30 μg/kg for the standard solution and spike sample, respectively, and a weak cross-reaction for α-zearalenol and β-zearalenol was observed. The assay required only 15 min to obtain results and one step to perform the assay. In validation, the results obtained from spiked corn (10, 20, 30, 50, and 100 μg/kg) and naturally contaminated corn samples by the ICG were in good agreement with those obtained by direct competitive enzyme-linked immunosorbent assay (DC-ELISA) and high-performance liquid chromatography (HPLC). Therefore, the results obtained in this study could be used as basic research for the development of zearalenone-ICG, and the ICG developed could be a useful on-site screening tool for the rapid detection of zearalenone in corn without special instrumentation.