Development of an immunoassay (ELISA) for the quantification of thiram in lettuce

Two competitive immunoassays, a laboratory assay based on microwell plates and a field test based on the use of polystyrene tubes, have been developed for the quantification of thiram in lettuces. Concerning the laboratory assay, the calibration curve for thiram had a linear range of 11 to 90 ng/mL and a detection limit of 5 ng/mL. Precision of the assay presented coefficient of variation values <9% and the recovery of thiram from lettuce averaged 89% across the range of the immunoassay method using 30 min extraction with water/acetone (50:50, v/v). The tube-based method was developed in order that an extract of lettuce, containing thiram at the MRL (8 ppm), would be found on the linear part of the standard curve. The calibration curve for thiram has a linear range of 100 to 800 ng/mL (1.39 to 11.1 ppm in lettuce) and a detection limit of 40 ng/mL.     

Identification and quantification of three genetically modified insect resistant cotton lines using conventional and TaqMan real-time polymerase chain reaction methods

As the genetically modified organisms (GMOs) labeling policies are issued in many countries, qualitative and quantitative polymerase chain reaction (PCR) techniques are increasingly used for the detection of genetically modified (GM) crops in foods. Qualitative PCR and TaqMan real-time quantitative PCR methods to detect and identify three varieties of insect resistant cotton, i.e., Mon531 cotton (Monsanto Co.) and GK19 and SGK321 cottons (Chinese Academy of Agricultural Sciences), which were approved for commercialization in China, were developed in this paper. Primer pairs specific to inserted DNAs, such as Cowpea trypsin inhibitor (CpTI) gene of SGK321 cotton and the specific junction DNA sequences containing partial Cry1A(c) gene and NOS terminator of Mon531, GK19, and SGK321 cotton varieties were designed to conduct the identified PCR assays. In conventional specific identified PCR assays, the limit of detection (LOD) was 0.05% for Mon531, GK19, or SGK321 in 100 ng of cotton genomic DNA for one reaction. Also, the multiplex PCR method for screening the three GM cottons was also established, which could save time and cost in practical detection. Furthermore, a real-time quantitative PCR assay based on TaqMan chemistry for detection of insect resistant gene, Cry1A(c), was developed. This assay also featured the use of a standard plasmid as a reference molecule, which contained both a specific region of the transgene Cry1A(c) and an endogenous stearoyl-acyl carrier protein desaturase (Sad1) gene of the cotton. In quantitative PCR assay, the quantification range was from 0.01 to 100% in 100 ng of the genome DNA template, and in the detection of 1.0, 3.0, and 5.0% levels of three insect resistant cotton lines, respectively, all of the relative standard deviations (RSDs) were less than 8.2% except for the GM cotton samples with 1.0% Mon531 or GK19, which meant that our real-time PCR assays involving the use of reference molecule were reliable and practical for GM insect resistant cottons quantification. All of these results indicated that our established conventional and TaqMan real-time PCR assays were applicable to detect the three insect resistant cottons qualitatively and quantitatively.     

Reliable enzyme-linked immunosorbent assay for the determination of soybean proteins in processed foods

Among allergenic foods, soybean is known as a food causing adverse reactions in allergenic patients. To clarify the validity of labeling, the specific and sensitive detection method for the analysis of the soybean protein would be necessary. The p34 protein, originally characterized to be p34 as an oil-body associated protein in soybean, has been identified as one of the major allergenic proteins and named Gly m Bd 30K. A novel sandwich enzyme-linked immunosorbent assay (ELISA) for the detection and quantification of the soybean protein in processed foods was developed using polyclonal antibodies raised against p34 as a soybean marker protein and the specific extraction buffer for extract. The developed sandwich ELISA method was highly specific for the soybean protein. The limit of detection (LOD) and the limit of quantification (LOQ) of the developed ELISA were 0.47 ng/mL (equivalent to 0.19 microg/g in foods) and 0.94 ng/mL (equivalent to 0.38 microg/g in foods), respectively. The recovery ranged from 87.7 to 98.7%, whereas the intra- and interassay coefficients of variation were less than 4.2 and 7.5%, respectively. This study showed that the developed ELISA method is a specific, precise, and reliable tool for the quantitative analysis of the soybean protein in processed foods.     

Event-specific qualitative and quantitative polymerase chain reaction analysis for genetically modified canola T45

Polymerase chain reaction (PCR) methods have been the main technical support for the detection of genetically modified organisms (GMOs). To date, GMO-specific PCR detection strategies have been developed basically at four different levels, such as screening-, gene-, construct-, and event-specific detection methods. Event-specific PCR detection method is the primary trend in GMO detection because of its high specificity based on the flanking sequence of exogenous integrant. GM canola, event T45, with tolerance to glufosinate ammonium is one of the commercial genetically modified (GM) canola events approved in China. In this study, the 5'-integration junction sequence between host plant DNA and the integrated gene construct of T45 canola was cloned and revealed by means of TAIL-PCR. Specific PCR primers and TaqMan probes were designed based upon the revealed sequence, and qualitative and quantitative TaqMan real-time PCR detection assays employing these primers and probe were developed. In qualitative PCR, the limit of detection (LOD) was 0.1% for T45 canola in 100 ng of genomic DNA. The quantitative PCR assay showed limits of detection and quantification (LOD and LOQ) of 5 and 50 haploid genome copies, respectively. In addition, three mixed canola samples with known GM contents were detected employing the developed real-time PCR assay, and expected results were obtained. These results indicated that the developed event-specific PCR methods can be used for identification and quantification of T45 canola and its derivates.     

Immunoaffinity purification of chlorimuron-ethyl from soil extracts prior to quantitation by enzyme-linked immunosorbent assay

A competitive-indirect enzyme-linked immunosorbent assay (CI-ELISA) was developed to quantify chlorimuron-ethyl in soil. The linear working range of the assay was from 1 to 1000 ng mL(-)(1). The assay had an I(50) value of 54 ng mL(-)(1), with a limit of detection of 2 ng mL(-)(1) and a limit of quantification of 27 ng mL(-)(1). Three soils were extracted using a carbonate buffer (pH 9.0) and the extracts spiked with chlorimuron-ethyl. Because of the effects of coextractants (matrix effects) from soil on the accuracy and precision of the ELISA, immunoaffinity chromatography (IAC) was used to purify chlorimuron-ethyl from soil extracts prior to analysis. The immunoaffinity columns, which had a total binding capacity of 1350 ng of chlorimuron-ethyl mL(-)(1) of immunosorbent, were prepared by binding anti-chlorimuron-ethyl antibodies to protein G Sepharose 4B. Although the matrix effects were largely removed using the affinity column, they could be completely removed by first passing the extract through a column containing epoxy-coupled 1,6-diaminohexane (EAH) Sepharose 4B to remove organic acids prior to IAC. Assay sensitivity was increased 100-fold using IAC to purify and simultaneously concentrate chlorimuron-ethyl from soil extracts. The purification strategy (EAH followed by IAC chromatography) removed matrix effects from all three soils and allowed for the accurate quantitation of chlorimuron-ethyl in soil extracts.     

Comparison of a direct ELISA and an HPLC method for glyphosate determinations in water

A competitive direct enzyme-linked immunosorbent assay (ELISA) and high-pressure liquid chromatographic (HPLC) methods were compared in terms of accuracy and precision for the detection and quantification of glyphosate-spiked Nanopure, tap, and river waters. The ELISA had a detection limit of 0.6 ng mL(-)(1) and a linear working range of 1-25 ng mL(-)(1), whereas the HPLC method had a detection limit of 50 ng mL(-)(1) and a linear working range of 100-10000 ng mL(-)(l). No statistically significant differences (95% confidence interval) were found between the ELISA and HPLC analysis of the three water matrixes. The coefficients of variation obtained with the ELISA in tap water were between 10 and 19%, whereas the coefficients of variation for the HPLC analysis were between 7 and 15%. The use of ELISA for the analysis of glyphosate in water is a cost-effective and reliable method capable of meeting water quality guidelines established for Europe and North America.     

Indirect enzyme-antibody sandwich enzyme-linked immunosorbent assay for quantification of TAXI and XIP type xylanase inhibitors in wheat and other cereals

To quantify Triticum aestivum xylanase inhibitor (TAXI) and xylanase inhibiting protein (XIP) type proteins in cereals in general and wheat ( T. aestivum) in particular, a robust enzyme-linked immunosorbent assay (ELISA) using an uncommon enzyme-antibody sandwich format was developed. Bacillus subtilis glycoside hydrolase family (GH) 11 and Aspergillus oryzae GH 10 xylanases were selected for coating ELISA plate wells to capture TAXI and XIP, respectively, prior to probing with antibodies. The detection threshold of the developed ELISA was much lower than that of the currently used xylanase inhibitor assay and the recently described Western blot approach. Because of its broad dynamic range (TAXI, 30-600 ng/mL, and XIP, 3-60 ng/mL), one proper standard extract dilution can be used for analyzing different wheat varieties, whereas for the currently used colorimetric assay, often different dilutions need to be analyzed. The TAXI ELISA for wheat was successfully adapted for barley ( Hordeum vulgare) and could also be used for other cereals.     

Qualitative and quantitative polymerase chain reaction assays for an alfalfa (Medicago sativa)-specific reference gene to use in monitoring transgenic cultivars

Genetically modified (GM) alfalfa (Medicago sativa) was marketed for the first time in 2005. For countries with established thresholds for GM plants, methods to detect and quantify their adventitious presence are required. We selected acetyl CoA carboxylase as a reference gene for the detection and quantification of GM alfalfa. Two qualitative polymerase chain reaction (PCR) assays (Acc1 and Acc2) were designed to detect alfalfa. Both were specific to alfalfa, amplifying DNA from 12 separate cultivars and showing negative results for PCR of 15 nonalfalfa plants. The limits of detection for Acc1 and Acc2 were 0.2 and 0.01%, respectively. A quantitative real-time PCR assay was also designed, having high linearity (r > 0.99) over alfalfa standard concentrations ranging from 100 to 2.0 x 10(5) pg of alfalfa DNA per PCR. The real-time PCR assay was effective in quantifying alfalfa DNA from forage- and concentrate-based mixed diets containing different amounts of alfalfa meal.     

Qualitative and quantitative event-specific PCR detection methods for oxy-235 canola based on the 3' integration flanking sequence

As more genetically modified plant events are approved for commercialization worldwide, the event-specific PCR method has become the key method for genetically modified organism (GMO) identification and quantification. This study reveals the 3' flanking sequence of the exogenous integration of Oxy-235 canola employing thermal asymmetric interlaced PCR (TAIL-PCR). On the basis of the revealed 3' flanking sequence, PCR primers and TaqMan probe were designed and qualitative and quantitative PCR assays were established for Oxy-235 canola. The specificity and limits of detection (LOD) and quantification (LOQ) of these two PCR assays were validated to as low as 0.1% for the relative LOD of qualitative PCR assay; the absolute LOD and LOQ were low to 10 and 20 copies of canola genomic DNA in quantitative PCR assay, respectively. Furthermore, ideal quantified results were obtained in the practical canola sample detection. All of the results indicate that the developed qualitative and quantitative PCR methods based on the revealed 3' integration flanking sequence are suitable for GM canola Oxy-235 identification and quantification.     

Determination of triterpenic acids in human serum by high-performance liquid chromatography: triterpenoid interaction with serum protein

Terpenic acids are under development as therapeutic agents in numerous treatments. In support of pharmacokinetic and toxicological evaluations, a robust assay based on high-performance liquid chromatography (HPLC) was developed for the analysis of the terpenoids in human serum. For a clear understanding of the differences in biological activity of these compounds, the interactions between oleanolic or betulinic acids and human serum protein have been studied by ultraviolet-visible (UV-vis) absorption under physiological conditions. A combination of liquid/liquid extraction, centrifugation, and consecutive HPLC resulted in simultaneous separation, identification, and quantification of the oleanolic, betulinic, and ursolic acids. The validity of the developed method was established by determining linearity, recovery, precision, accuracy, limit of detection, and quantification. Detection limits were in the range of 3.3-4.3 ng/mL, and linearity values ranged up to 1 μg/mL. The repeatability of the method was good. All compounds can be well-distinguished by order of elution during liquid chromatography. The pentacyclic triterpenoids have been identified by retention time comparison to pure standards and quantified by an internal standard. The results by UV-vis absorption spectra experiments (240-340 nm) indicate that protein structures have been perturbed in the presence of oleanolic and betulinic acids.     

Simultaneous quantitation of 2-acetyl-4-tetrahydroxybutylimidazole, 2- and 4-methylimidazoles, and 5-hydroxymethylfurfural in beverages by ultrahigh-performance liquid chromatography-tandem mass spectrometry

An ultrahigh-performance liquid chromatography (UHPLC) tandem mass spectrometric (MS/MS) method was developed for the simultaneous quantification of 2-acetyl-4-tetrahydroxybutylimidazole (THI), 2- and 4-methylimidazoles (2-MI and 4-MI), and 5-hydroxymethylfurfural (HMF) in beverage samples. A C30 reversed-phase column was used in this method, providing sufficient retention and total resolution for all targeted analytes, with an MS/MS instrument operated in selected reaction monitoring (SRM) mode for sensitive and selective detection using isotope-labeled 4-methyl-d(3)-imidazole (4-MI-d(3)) as the internal standard (IS). This method demonstrates lower limit of quantification (LLOQ) at 1 ng/mL and coefficient of determination (r(2)) >0.999 for each analyte with a calibration range established from 1 to 500 ng/mL. This method also demonstrates excellent quantification accuracy (84.6-105% at 5 ng/mL, n = 7), precision (RSD < 7% at 5 ng/mL, n = 7), and recovery (88.8-99.5% at 10, 100, and 200 ng/mL, n = 3). Seventeen carbonated beverage samples were tested (n = 2) in this study including 13 dark-colored beverage samples with different flavors and varieties and 4 light-colored beverage samples. Three target analytes were quantified in these samples with concentrations in the range from 284 to 644 ng/mL for 4-MI and from 706 to 4940 ng/mL for HMF. THI was detected in only one sample at 6.35 ng/mL.     

Rapid time-resolved immunofluorometric assay for the measurement of creatine kinase in serum and whole blood samples

A rapid and simple immunochemical method was developed for the assessment of the creatine kinase (MM) isoenzyme [CK(MM)], a protein marker linked with animal welfare and meat quality. The one-step time-resolved immunofluorometric assay produced quantitative results from serum or whole blood samples in 20 min. The analytical limit of detection (mean + 2s) for the immunoassay was 17 ng/mL (n = 6), and the functional limit of detection for the analysis of porcine whole blood samples was 426 ng/mL (n = 24). The working range of the method was linear up to 50 micro g/mL, and the within-assay precision varied between 2.1 and 10.9%. The analysis of porcine serum samples showed that the results from the immunoassay method and colorimetric CK enzyme activity determination were highly correlated (r(2) = 0.965, n = 17, p < 0.001). The practicability of the assay was demonstrated by the analysis of 300 porcine whole blood samples in a slaughterhouse environment.     

Event-specific quantitative detection of nine genetically modified maizes using one novel standard reference molecule

With the development of genetically modified organism (GMO) detection techniques, the Polymerase Chain Reaction (PCR) technique has been the mainstay for GMO detection, and real-time PCR is the most effective and important method for GMO quantification. An event-specific detection strategy based on the unique and specific integration junction sequences between the host plant genome DNA and the integrated gene is being developed for its high specificity. This study establishes the event-specific detection methods for TC1507 and CBH351 maizes. In addition, the event-specific TaqMan real-time PCR detection methods for another seven GM maize events (Bt11, Bt176, GA21, MON810, MON863, NK603, and T25) were systematically optimized and developed. In these PCR assays, the fluorescent quencher, TAMRA, was dyed on the T-base of the probe at the internal position to improve the intensity of the fluorescent signal. To overcome the difficulties in obtaining the certified reference materials of these GM maizes, one novel standard reference molecule containing all nine specific integration junction sequences of these GM maizes and the maize endogenous reference gene, zSSIIb, was constructed and used for quantitative analysis. The limits of detection of these methods were 20 copies for these different GM maizes, the limits of quantitation were about 20 copies, and the dynamic ranges for quantification were from 0.05 to 100% in 100 ng of DNA template. Furthermore, nine groups of the mixed maize samples of these nine GM maize events were quantitatively analyzed to evaluate the accuracy and precision. The accuracy expressed as bias varied from 0.67 to 28.00% for the nine tested groups of GM maize samples, and the precision expressed as relative standard deviations was from 0.83 to 26.20%. All of these indicated that the established event-specific real-time PCR detection systems and the reference molecule in this study are suitable for the identification and quantification of these GM maizes.     

High sensitive detection of Cry1Ab protein using a quantum dot-based fluorescence-linked immunosorbent assay

Protein-based detection methods, enzyme-linked immunosorbent assay (ELISA) and lateral flow strip, have been widely used for rapid, spot, and sensitive detection of genetically modified organisms (GMOs). Herein, one novel quantum dot-based fluorescence-linked immunosorbent assay (QD-FLISA) was developed employing quantum dots (QDs) as the fluorescent marker for the detection of the Cry1Ab protein in MON810 maize. The end-point fluorescent detection system was carried out using QDs conjugated with goat anti-rabbit secondary antibody. The newly developed Cry1Ab QD-FLISA assay was highly specific to the Cry1Ab protein and had no cross-reactivity with other target proteins, such as Cry2Ab, Cry1F, and Cry3Bb. The quantified linearity was achieved in the value range of 0.05-5% (w/w). The limits of detection (LOD) and quantification (LOQ) of the QD-FLISA were 2.956 and 9.854 pg/mL, respectively, which were more sensitive than the conventional sandwich ELISA method. All of the results indicated that QD-FLISA was a highly specific and sensitive method for the monitoring of Cry1Ab in GMOs.     

Studies on the supramolecular interaction between dimethomorph and disulfide linked β-cyclodextrin dimer by spectrofluorimetry and its analytical application

The supramolecular interaction of disulfide linked β-cyclodextrin (β-CD) dimer and dimethomorph has been studied by spectrofluorimetry. Based on the significant enhancement of the fluorescence intensity of dimethomorph, a new spectrofluorimetric method with high sensitivity and selectivity was developed for the determination of dimethomorph in bulk aqueous in the presence of the disulfide linked β-CD dimer. The inclusion complexation behavior of β-CD dimer with dimethomorph was studied in a KH(2)PO(4)-H(3)PO(4) buffer solution of pH 3.86 at room temperature. The apparent association constant of the complex was 2.25 × 10(4) L/mol. The linear range was 12-7500 ng/mL with the detection limit 3.70 ng/mL, and the limit of quantification was 12.4 ng/mL. The proposed method had been successfully applied to the determination of dimethomorph residues in vegetables with recoveries of 89.0-115%.     

Development and application of a liquid chromatography-mass spectrometry method to evaluate the glyphosate and aminomethylphosphonic acid dissipation in maize plants after foliar treatment

A simple and fast method has been developed and validated to measure glyphosate (GLYP) and aminomethylphosphonic acid (AMPA), which were previously derivatized with 9-fluorenylmethylchloroformate (FMOC-Cl), in maize plants using liquid chromatography (LC) coupled to fluorescence (FLD) and electrospray ionization mass spectrometry (ESI-MS) detection. The method has shown to be consistent, reliable, precise, and efficient. Moreover, the limits of detection (LOD) and quantification (LOQ) reached with the proposed method for GLYP and AMPA are lower than the established maximum residue levels (MRLs). The validated method was applied to quantify GLYP and AMPA in genetically modified (GM) maize foliar treated with the herbicide. It has been found that the GLYP dissipation was mainly due to the progressive dilution effect after herbicide treatment. Finally, it was also observed that the GLYP residue dissipation trend in maize shoot (leaves and stem) tissue determined by LC-ESI-MS matched that determined by liquid scintillation.     

Development of the visual loop-mediated isothermal amplification assays for seven genetically modified maize events and their application in practical samples analysis

As more and more genetically modified (GM) crops are approved for commercialization and planting, the development of quick and on-spot methods for GM crops and their derivates is required. Herein, we established the polymerase chain reaction and agarose gel electrophoresis-free system for the identification of seven GM maize events (DAS-59122-7, T25, BT176, TC1507, MON810, BT11, and MON863) employing a loop-mediated isothermal amplification (LAMP) technique. The LAMP assay was performed using a set of four specific primers at 60-65 °C in less than 40 min, and the results were observed by direct visual observation. In these developed assays, the specificity targeted at each GM maize event based on the event-specific sequence was well confirmed, and the limits of detection were as low as four copies of maize haploid genomic DNA with an exception of 40 copies for MON810 assay. Furthermore, these developed assays were successfully used to test six practical samples with different GM maize events and contents (ranged from 0.0 to 2.0%). All of the results indicated that the established event-specific visual LAMP assays are more convenient, rapid, and low-cost for GM maize routine analysis.     

Solid-phase extraction followed by liquid chromatography-mass spectrometry for trace determination of beta-lactam antibiotics in bovine milk.

A confirmatory assay able to unambiguously identify and quantify 10 approved-for-use beta-lactam antibiotics in milk below stipulated U.S. and EU tolerance levels is presented. beta-Lactams are extracted from 10 mL of intact milk by a Carbograph 4 cartridge. After solvent removal, residue reconstitution, and filtration, a completely transparent and uncolored extract is injected into a liquid chromatography -mass spectrometry (LC-MS) instrument equipped with an electrospray (ES) ion source and a single quadrupole. During the chromatographic run, the ES/MS system is operated first in the positive-ion mode (PI) and then in the negative-ion (NI) mode. This is done to circumvent matrix interferences resulting in remarkable signal weakening of the last-eluted analytes, when detecting them as [M+H]+ adduct ions. MS data acquisition is performed by a time-scheduled three-ion selected ion monitoring program. At the 5 ng/mL level, recoveries of the beta-lactams are between 70 (nafcillin) and 108% (cephalin), with relative standard deviations ranging between 5 (oxacillin) and 11% (amoxicillin and ceftiofur). The response of the ES/MS detector is linearly related to injected amounts up to 500 ng, irrespective of the chemical characteristics of the beta-lactams and the acquisition mode selected (PI or NI modes). Limits of quantification, based on a minimal value of the signal-to-noise ratio of 10, were estimated to be within 0.4 (cephalin) and 3 ng/mL (dicloxacillin). Analyses of milk samples taken after intramammary application of amoxicillin showed that 1.2 ng/mL of this penicillin was still present 6 days after treatment. At this concentration level, the identification power of the method is not weakened, as signals of the three product ions of amoxicillin are still well distinguishable from the background noise.     

Application of an ELISA to the determination of benalaxyl in red wines

The applicability of an ELISA for detection and quantification of benalaxyl in red wine samples is described. The study of the influence of this matrix on the reliability of the assay indicates that red wine samples require a rapid and simple cleanup step before ELISA assay. Recovery and precision of the method were evaluated by spiking red wine samples with benalaxyl in the 0.5-24 ng/mL range. Benalaxyl can be determined with good accuracy and precision up to 0. 5 ng/mL in starting red wine samples (detection limit of 0.13 ng/mL). No false negative or positive results were obtained. Authentic red wine samples were analyzed by ELISA and by RP-HPLC. The amounts of benalaxyl found by ELISA were in good agreement with RP-HPLC analysis.     

Detection of streptomycin residues in whole milk using an optical immunobiosensor.

The development of an assay for the detection of streptomycin residues in pasteurized whole milk using an optical biosensor (Biacore) is reported. Streptomycin-adipic hydrazide coupled to bovine thyroglobulin was used to produce a sheep polyclonal antibody. The antibody displayed excellent cross-reactivity with dihydrostreptomycin (106%). There was no significant cross-reaction with other aminoglycosides or common antibiotics. Streptomycin was also immobilized onto a CM5 sensor chip to provide a stable, reusable surface. The developed assay permitted the direct analysis of whole milk samples ( approximately 3.5% fat) without prior centrifugation and defatting. Results were available in 5 min. The limit of detection of the assay was determined as 4.1 ng/mL, well below the European maximum residue limit (MRL) of 200 ng/mL. Repeatability (or coefficient of variation) between runs was determined as 3.5% (100 ng/mL; 0.5 x MRL), 5.7% (200 ng/mL; MRL), and 7.6% (400 ng/mL; 2 x MRL).