Development of monoclonal antibody-based sensitive ELISA for the determination of Cry1Ie protein in transgenic plant

RNA-based detection of genetically modified plants via current-voltage characteristic measurement

The widespread adoption of genetically modified (GM) crops has escalated concerns about their safety and ethical implications, underscoring the need for efficient GM crop detection methods. Conventional detection methods, such as polymerase chain reaction, can be costly, lab-bound, and time-consuming. To overcome these challenges, we have developed RapiSense, a cost-effective, portable, and sensitive biosensor platform. This sensor generates a measurable voltage shift (0.1-1 V) in the system's current-voltage characteristics, triggered by an increase in membrane's negative charge upon hybridization of DNA/RNA targets with a specific DNA probe. Probes designed to identify the herbicide resistance gene hygromycin phosphotransferase show a detection range from ∼1 nM to ∼10 μM and can discriminate between complementary, non-specific, and mismatched nucleotide targets. The incorporation of a small membrane sensor to detect fragmented RNA samples substantially improve the platform's sensitivity. In this study, RapiSense has been effectively used to detect specific DNA and fragmented RNA in transgenic variants of Arabidopsis, sweet potato, and rice, showcasing its potential for rapid, on-site GM crop screening.

Establishment of novel receptor-antibody sandwich assays to broadly detect Bacillus thuringiensis Cry1 and Cry2 toxins

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 and broader detection methods for commonly used Cry toxins. Using ligand blot and bio-layer interferometry, we confirmed that a recombinant toxin-binding fragments derived from Helicoverpa armigera cadherin-like protein (HaCad-TBR) could broadly bind Cry1Ab, Cry1Ac, Cry2Aa, and Cry2Ab with the affinity of 0.149, 0.402, 120, and 4.12 nM, respectively. Based on the affinity results, a novel receptor-antibody sandwich assay broadly detecting Cry1A and Cry2 toxins was developed by using HaCad-TBR as capture molecules, and anti-Cry1A/Cry2A polyclonal antibodies (pAbs) as the detection antibodies. The detection limit (LOD) for Cry1Ab, Cry1Ab, Cry2Aa, and Cry2Ab were 5.30, 5.75, 30.83 and 13.70 ng/mL. To distinguish Cry1A and Cry2A toxins in a singular test, anti-Cry1A pAbs and anti-Cry2A pAbs were labelled with different quantum dots (QDs). The LOD for the four toxins by receptor-QDs-pAbs sandwich assay were calculated to be 1.36, 4.71, 17.48, and 7.54 ng/mL, respectively. The two developed methods were validated by spiked rice and corn samples, suggesting they may potentially be used in monitoring and quantifying Cry toxins in food and environment.

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.

Quantum-Dot-Bead-Based Fluorescence-Linked Immunosorbent Assay for Sensitive Detection of Cry2A Toxin in Cereals Using Nanobodies

In this study, a quantum-dot-bead (QB)-based fluorescence-linked immunosorbent assay (FLISA) using nanobodies was established for sensitive determination of the Cry2A toxin in cereal. QBs were used as the fluorescent probe and conjugated with a Cry2A polyclonal antibody. An anti-Cry2A nanobody P2 was expressed and used as the capture antibody. The results revealed that the low detection limit of the developed QB-FLISA was 0.41 ng/mL, which had a 19-times higher sensitivity than the traditional colorimetric ELISA. The proposed assay exhibited a high specificity for the Cry2A toxin, and it had no evident cross-reactions with other Cry toxins. The recoveries of Cry2A from the spiked cereal sample ranged from 86.6–117.3%, with a coefficient of variation lower than 9%. Moreover, sample analysis results of the QB-FLISA and commercial ELISA kit correlated well with each other. These results indicated that the developed QB-FLISA provides a potential approach for the sensitive determination of the Cry2A toxin in cereals.

Development of a sensitive monoclonal antibody-based sandwich ELISA to detect Vip3Aa in genetically modified crops

Objectives

To develop a sensitive monoclonal antibody-based sandwich enzyme-linked immunosorbent assay (ELISA) to detect Vip3Aa in genetically modified (GM) crops and their products.

Results

Vegetative insecticidal proteins (Vips) are secreted by Bacillus thuringiensis (Bt) and are known to be toxic to Lepidoptera species. Vip3Aa family proteins, Vip3Aa19 and Vip3Aa20, were successfully applied in GM crops to confer an effective and persistent insecticidal resistance. A sensitive monoclonal antibody-based sandwich ELISA was developed to detect Vip3Aa in GM crops and their products. Two monoclonal antibodies were raised against the overexpressed and purified His-Vip3Aa20, were purified from mouse ascites and characterized. A sandwich ELISA method was developed using the 2G3-1D7 monoclonal antibody for capture and the biotin-labeled 1F9-1F5 monoclonal antibody for detection of Vip3Aa20. The linear detection range of the method was found to be approximately 31.25–500 pg/ml, with a sensitivity of 10.24 pg/ml.

Conclusions

The established ELISA was effective for detecting Vip3Aa family proteins other than Vip3Aa8, and was successfully applied in the detection of Vip3Aa20 and Vip3Aa19 expressed in transgenic maize and cotton.

A novel electrochemical DNA biosensor for transgenic soybean detection based on triple signal amplification

A novel electrochemical DNA biosensor was developed and MON89788 of soybean transgenic gene sequence was detected based on a strategy of rolling circle amplification (RCA) and gold nanoparticle cube (AuNPC)-labeled multiple probes. First, the mercapto-modified capture DNA was immobilized on the surface of the Fe3O4@Au magnetic nanoparticles via an Au-S bond, and the capture DNA was opened and complementarily hybridized with the target DNA to form a double-stranded DNA. In the 10 × reaction buffer, Exonuclease III (ExoIII) specifically recognized and sheared the double-stranded DNA to release the target DNA, which led to the next round of reaction. Afterward, AuNP cube-loaded ssDNA (AuNPC/DNA) was added with the rolling circle reaction with the help of Phi29 DNA polymerase and T4 ligase. Finally, [Ru(NH3)6]3+ was attracted directly by the anionic phosphate of ssDNA via electrostatic interaction. The determination was carried out by using chronocoulometry (CC), and the CC signal was recorded. The mass amount of DNA strands extended infinitely on the AuNPs cube and numerous [Ru(NH3)6]3+ were absorbed, thus the detected signal was highly amplified. The corresponding CC signal showed a good linear relationship with the logarithm of the target DNA concentration in the range of 1 × 10-16 to 1 × 10-7 mol L-1, with a detection limit of 4.5 × 10-17 mol L-1. Specific gene sequence of MON89788 in soybean samples was determined, and the recoveries ranged from 97.3% to 102.0%. This sensor is one of the most sensitive sensors for genetic sequence assessment at present. Moreover, it demonstrates good selectivity, stability, and reproducibility.

RNA Interference to Control Asian Corn Borer Using dsRNA from a Novel Glutathione-S-Transferase Gene of Ostrinia furnacalis (Lepidoptera: Crambidae)

Glutathione-S-transferases (GST) comprise a multifunctional protein superfamily, which plays important roles as detoxifiers and antioxidants in insects. The GST in Asian corn borer has not been previously characterized. In this study, we cloned, characterized, and expressed the complete GST genes from the midgut of Asian corn borer. Furthermore, we designed htL4440-OfGST vector to exploit this gene for RNA interference (RNAi) strategy to control this pest. A complete GST cDNA sequence in Asian corn borer was obtained by reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends technology. The gene was 887bp in length and contained a 705bp open reading frame and 5' UTR and 3' UTR lengths of 89 and 93bp, respectively. The putative sequence encoded a putative 234 amino acid residue peptide and had a predicted molecular weight of ~26kDa. The GST protein of Asian corn borer is hydrophilic and may have a 30 amino acid signal peptide with a cleavage site between L30 and K31. A recombination vector pET28a-OfGST was constructed for purification and antibody preparation. Western blotting analysis showed that this protein reached the maximum expression level around 24 h in Asian corn borer larvae fed the plant toxin 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one. A second vector, htL4440-OfGST, was constructed to generate the dsRNA of the GST gene. A larval feeding bioassay showed that the expressed dsRNA significantly reduced the detoxification ability of Asian corn borer larvae and increased mortality rate up to 54%. Our data indicated that GST plays very important roles in detoxifying in Asian corn borer and can be used as an RNAi method to control this pest in the field.

Phage-Mediated Competitive Chemiluminescent Immunoassay for Detecting Cry1Ab Toxin by Using an Anti-Idiotypic Camel Nanobody

Cry toxins have been widely used in genetically modified organisms for pest control, raising public concern regarding their effects on the natural environment and food safety. In this work, a phage-mediated competitive chemiluminescent immunoassay (c-CLIA) was developed for determination of Cry1Ab toxin using anti-idiotypic camel nanobodies. By extracting RNA from camels' peripheral blood lymphocytes, a naive phage-displayed nanobody library was established. Using anti-Cry1Ab toxin monoclonal antibodies (mAbs) against the library for anti-idiotypic antibody screening, four anti-idiotypic nanobodies were selected and confirmed to be specific for anti-Cry1Ab mAb binding. Thereafter, a c-CLIA was developed for detection of Cry1Ab toxin based on anti-idiotypic camel nanobodies and employed for sample testing. The results revealed a half-inhibition concentration of developed assay to be 42.68 ± 2.54 ng/mL, in the linear range of 10.49-307.1 ng/mL. The established method is highly specific for Cry1Ab recognition, with negligible cross-reactivity for other Cry toxins. For spiked cereal samples, the recoveries of Cry1Ab toxin ranged from 77.4% to 127%, with coefficient of variation of less than 9%. This study demonstrated that the competitive format based on phage-displayed anti-idiotypic nanobodies can provide an alternative strategy for Cry toxin detection.

Development of Monoclonal Antibodies Recognizing Linear Epitope: Illustration by Three Bacillus thuringiensis Crystal Proteins of Genetically Modified Cotton, Maize, and Tobacco

Bacillus thuringiensis Cry1Ac, Cry1Ia1, and Cry1Ie are δ-endotoxin insecticidal proteins widely implemented in genetically modified organisms (GMO), such as cotton, maize, and potato. Western blot assay integrates electrophoresis separation power and antibody high specificity for monitoring specific exogenous proteins expressed in GMO. Procedures for evoking monoclonal antibody (mAb) for Western blot were poorly documented. In the present study, Cry1Ac partially denatured at 100 °C for 5 min was used as an immunogen to develop mAbs selectively recognizing a linear epitope of Cry1Ac for Western blot. mAb 5E9C6 and 3E6E2 selected with sandwich ELISA strongly recognized the heat semidenatured Cry1Ac. Particularly, 3E6E2 recognized both E. coli and cotton seed expressed Cry1Ac in Western blot. Such strategy of using partially denatured proteins as immunogens and using sandwich ELISA for mAb screening was also successfully demonstrated with production of mAbs against Cry1Ie for Western blot assay in maize.

Consumption of Bt Maize Pollen Containing Cry1Ie Does Not Negatively Affect Propylea japonica (Thunberg) (Coleoptera: Coccinellidae)

Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) are prevalent predators and pollen feeders in East Asian maize fields. They are therefore indirectly (via prey) and directly (via pollen) exposed to Cry proteins within Bt-transgenic maize fields. The effects of Cry1Ie-producing transgenic maize pollen on the fitness of P. japonica was assessed using two dietary-exposure experiments in the laboratory. In the first experiment, survival, larval developmental time, adult fresh weight, and fecundity did not differ between ladybirds consuming Bt or non-Bt maize pollen. In the second experiment, none of the tested lethal and sublethal parameters of P. japonica were negatively affected when fed a rapeseed pollen-based diet containing Cry1Ie protein at 200 μg/g dry weight of diet. In contrast, the larval developmental time, adult fresh weight, and fecundity of P. japonica were significantly adversely affected when fed diet containing the positive control compound E-64. In both experiments, the bioactivity of the Cry1Ie protein in the food sources was confirmed by bioassays with a Cry1Ie-sensitive lepidopteran species. These results indicated that P. japonica are not affected by the consumption of Cry1Ie-expressing maize pollen and are not sensitive to the Cry1Ie protein, suggesting that the growing of Bt maize expressing Cry1Ie protein will pose a negligible risk to P. japonica.