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

Two electrochemiluminescence immunosensors for the sensitive and quantitative detection of the CP4-EPSPS protein in genetically modified crops

Two different models of electrochemiluminescence (ECL) immunosensors for the sensitive and quantitative detection of the CP4-EPSPS protein in genetically modified (GM) crops were proposed in this study. One was a signal-reduced ECL immunosensor based on nitrogen-doped graphene, graphitic carbon nitride and polyamide-amine (GN-PAMAM-g-C₃N₄) composites as the electrochemically active substance. The other model was a signal-enhanced ECL immunosensor based on a GN-PAMAM modified electrode for the detection of CdSe/ZnS quantum dots (QDs)-labeled antigens. The ECL signal responses of the reduced and enhanced immunosensors linearly decreased as the increase of the soybean RRS and RRS-QDs content in the range of 0.05% to 1.5% and 0.025% to 1.0%, with the limits of detection of 0.03% and 0.01% (S/N = 3), respectively. Both of the ECL immunosensors showed good specificity, stability, accuracy, and reproducibility in the analysis of real samples. The results indicate that the two immunosensors provide an ultra-sensitive and quantitative approach for the determination of the CP4-EPSPS protein. Due to their outstanding performances, the two ECL immunosensors could be useful tools for achieving the effective regulation of GM crops.

A nanomaterial-free and thionine labeling-based lateral flow immunoassay for rapid and visual detection of the transgenic CP4-EPSPS protein

Nanomaterial-based lateral flow immunoassays (LFIAs) have been widely used for the on-site detection of genetically modified components. However, the practical applications are often limited by the complex matrix, such as in red samples. In this study, a thionine (Thi) labeling-based LFIA was developed for the first time to detect CP4-EPSPS protein. The optimal labeling concentration of Thi was 0.5 mg/mL, and the antibody could be rapidly coupled to Thi in 10 min. The visual limit of detection (vLOD) levels for transgenic soybean, sugar beet, and cotton containing the CP4-EPSPS protein reached 0.05%, 0.1%, and 0.1%, respectively, and had no interference from other proteins. After storage at 4 °C for three months, the LFIA sensitivity remained unchanged and showed good stability. This method could be used to screen and detect a variety of transgenic crops containing the CP4-EPSPS protein, and the results were consistent with the current standard assay. This study pioneered the development of an immunochromatographic method using Thi as a marker and applied it to the detection of the CP4-EPSPS protein in herbicide-tolerant transgenic crops. This provides a new method for the rapid immunoassay of Thi as a dye and has good prospects for practical application.

Strategies for capturing Bacillus thuringiensis spores on surfaces of (001) GaAs-based biosensors

Bacillus thuringiensis (Bt) is used as a bioinsecticide since it effectively kills insect larvae. Bt is also genetically similar to Bacillus cereus (Bc), a well recognized foodborne human pathogen; they are both members of the Bacillus cereus group (BC group). Although approved Bt bioinsecticide products have been confirmed to be non-pathogenic to humans, close monitoring of Bt during dissemination is important for cost considerations and to limit impact on biodiversity towards nontarget organisms. As such, developing rapid, sensitive, and specific tools for quantitative detection of Bt spores during and following spray operations is highly desirable. The goals of this study were to investigate commercially available detection reagents for sensitivity and selectivity in detecting Bt spores, and then functionalize a surface of (001) GaAs used in photonic biosensing. To achieve these goals, we (1) screened commercial antibodies for their capacity to bind recombinant proteins from Bt spores, (2) screened antibodies and aptamers for their sensitivity and selectivity against Bt spores, and (3) tested the efficiency of selected antibodies and aptamers in capturing Bt spores on the surface of functionalized GaAs biochips. Seven genes encoding Bt spore proteins were cloned and expressed in Escherichia coli. The binding of each purified spore antigen was tested by commercially available polyclonal and monoclonal antibodies claimed to exclusively target spores. Of the seven targets, Bacillus collagen-like protein A, was the most abundant protein on Bt spores and demonstrated the strongest binding affinity to all test antibodies. The commercial antibodies (Abs) were also tested for specificity to BC Group versus non-BC Group spores. Three of six commercial antibodies showed selectivity to Bt spores, with recombinant Abs providing the most robust lower range of detection (10² to 6 × 10³ spores/mL). The sensitivity and selectivity of three published DNA aptamer sequences demonstrated a wide range of detection sensitivity for Bt spores. Two of the three test aptamers also showed reasonable selectivity towards Bt spores while the third demonstrated reactivity to non-BC Group B. megaterium and B. subtilis. Of the reagents tested, a thiolated aptamer and llama recombinant Ab showed highest Bt spore capture efficiency as measured by spore coverage of the GaAs surface. These results confirm that the selected aptamer and llama rAb can be considered strong candidates for the development of GaAs-based biosensing devices.

A sensitive immunosensor based on graphene-PAMAM composites for rapid detection of the CP4-EPSPS protein in genetically modified crops

A simple electrochemical immunosensor based on nitrogen-doped graphene and polyamide-amine (GN-PAM) composites was proposed for the detection of the CP4-EPSPS protein in genetically modified (GM) crops. In this immunosensor, the amplification of the detection signal was realized through antibodies labeled with gold nanoparticles (AuNPs). The electrochemical responses of the immunosensor were linear (R2 = 0.9935 and 0.9912) when the GM soybean RRS and maize NK603 content ranged from 0.025% to 1.0% and 0.05% to 1.5%, respectively. The limits of detection for the GM soybean RRS and maize NK603 were as low as 0.01% and 0.03%, respectively. The immunosensor also exhibited high specificity, and satisfactory stability, reproducibility, and accuracy. Our findings indicated that the constructed immunosensor provides a new approach for the sensitive detection of the CP4-EPSPS protein. Notably, the sensor may be applied to other proteins or pathogenic bacteria by simply changing the antibodies, and may also be used for multi-component analysis.