Biosensors for GMO Testing: Nearly 25 Years of Research

Sensitive detection of genetically modified maize based on a CRISPR/Cas12a system

With the vigorous development of biotechnology, genetically modified organisms (GMOs) have become more and more common. In order to effectively supervise and administrate them, the rapid and accurate detection of GMOs is urgently demanded. Here, GMO gene-specific sensing methods based on colorimetry and surface-enhanced Raman scattering (SERS) were proposed based on the lateral branch cleavage function of the CRISPR/Cas12a system. Two transgenes, pCaMV35S and M810 Cry1Ab, were chosen as targets for transgenic crops. By using these methods, we performed transgenic detection on five types of maize leaves and successfully distinguished transgenic from non-transgenic samples. The colorimetric method is rapid, economical and available for field detection. The SERS approach, giving a higher sensitivity to 100 fM, is more suitable for laboratory application scenarios. This study explores practical transgenic detection approaches and will be valuable for the supervision of GMOs.

Review of CRISPR/Cas Systems on Detection of Nucleotide Sequences

Nowadays, with the rapid development of biotechnology, the CRISPR/Cas technology in particular has produced many new traits and products. Therefore, rapid and high-resolution detection methods for biotechnology products are urgently needed, which is extremely important for safety regulation. Recently, in addition to being gene editing tools, CRISPR/Cas systems have also been used in detection of various targets. CRISPR/Cas systems can be successfully used to detect nucleic acids, proteins, metal ions and others in combination with a variety of technologies, with great application prospects in the future. However, there are still some challenges need to be addressed. In this review, we will list some detection methods of genetically modified (GM) crops, gene-edited crops and single-nucleotide polymorphisms (SNPs) based on CRISPR/Cas systems, hoping to bring some inspiration or ideas to readers.

CRISPR-Cas-based detection for food safety problems: Current status, challenges, and opportunities

Food safety is one of the biggest public issues occurring around the world. Microbiological, chemical, and physical hazards can lead to food safety issues, which may occur at all stages of the supply chain. In order to tackle food safety issues and safeguard consumer health, rapid, accurate, specific, and field-deployable detection methods meeting diverse requirements are one of the imperative measures for food safety assurance. CRISPR-Cas system, a newly emerging technology, has been successfully repurposed in biosensing and has demonstrated huge potential to establish conceptually novel detection methods with high sensitivity and specificity. This review focuses on CRISPR-Cas-based detection and its current status and huge potential specifically for food safety inspection. We firstly illustrate the pending problems in food safety and summarize the popular detection methods. We then describe the potential applications of CRISPR-Cas-based detection in food safety inspection. Finally, the challenges and futuristic opportunities are proposed and discussed. Generally speaking, the current food safety detection methods are still unsatisfactory in some ways such as being time-consuming, displaying unmet sensitivity and specificity standards, and there is a comparative paucity of multiplexed testing and POCT. Recent studies have shown that CRISPR-Cas-based biosensing is an innovative and fast-expanding technology, which could make up for the shortcomings of the existing methods or even replace them. To sum up, the implementation of CRISPR-Cas and the integration of CRISPR-Cas with other techniques is promising and desirable, which is expected to provide "customized" and "smart" detection methods for food safety inspection in the coming future.

Digital PCR-Based Characterization of a g10evo-epsps Gene-Specific Matrix Reference Material for Its Food and Feed Detection

g10evo-epsps is a novel glyphosate herbicide-resistant gene that has been transferred to various crops such as soybean, corn, cotton, and rice. Here, we developed a gene-specific digital Polymerase Chain Reaction (dPCR) detection method for absolute quantitative analysis of g10evo-epsps, and characterized g10evo-epsps certified reference materials (CRM) using ZUTS-33 soybean powder as the candidate material. Stability tests of matrix CRMs demonstrate that these CRMs can be stored stably for 6 months and transported for 10 days at room temperature and withstand summer high temperatures (below 60 °C). CRM characterization is based on the copy number ratio of g10evo-epsps to lectin. Eight qualified laboratories independently validated the CRM using dPCR method, with a measurement of 0.98 (copy/copy) and an extended uncertainty of 0.08 (copy/copy). The g10evo-epsps matrix CRM described here may be used for qualitative and quantitative testing, method evaluation, laboratory quality control, and other related fields.

Collaborative Ring Trial of the Applicability of a Reference Plasmid DNA Calibrant in the Quantitative Analysis of GM Maize Event MON810

Certified reference materials (CRMs) is one of the critical requirements in a quantitative analytical method, such as in the quantification of genetically modified (GM) contents in food/feed products. Plasmid-DNA-based CRMs are becoming essential in GM content quantification. Herein, we report the construction of one plasmid DNA calibrant, pMON810, for the quantification of the GM maize event MON810 which is commercially planted and used for food/feeds worldwide, and the collaborative ring trial was used to validate its applicability. pMON10 was proven to have high specificity for the MON810 event. The limit of detection (LOD) and limit of quantification (LOQ) of real-time PCR assays of MON810 event and maize endogenous gene using pMON810 as calibrant was 2 copies/μL and 5 copies/μL, respectively. A total of eight laboratories participated in the ring trial and returned valid test results. Each sample was performed with three repeats and three parallels in each repeat. Statistical analysis of the ring trial results showed that pMON810 as a calibrant had high PCR efficiency (ranging from 0.885 to 1.008) and good linearity (ranging from 0.9933 to 0.9997) in MON810 and endogenous gene real-time PCR assays. The bias between the test values and true values ranged from 4.60 to 20.00% in the quantification of five blind samples. These results indicate that pMON810 is suitable for use as a calibrant for the quantification of MON810 events in routine lab analysis or to evaluate detection methods for MON810, as well as being used as a substitute for the matrix-based CRM of MON810.

Genetically Modified Soybean Detection Using a Biosensor Electrode with a Self-Assembled Monolayer of Gold Nanoparticles

In this study, we proposed a genosensor that can qualitatively and quantitatively detect genetically modified soybeans using a simple electrode with evenly distributed single layer gold nanoparticles. The DNA sensing electrode is made by sputtering a gold film on the substrate, and then sequentially depositing 1,6-hexanedithiol and gold nanoparticles with sulfur groups on the substrate. Then, the complementary to the CaMV 35S promoter (P35S) was used as the capture probe. The target DNA directly extracted from the genetically modified soybeans rather than the synthesized DNA segments was used to construct the detection standard curve. The experimental results showed that our genosensor could directly detect genetically modified genes extracted from soybeans. We obtained two percentage calibration curves. The calibration curve corresponding to the lower percentage range (1-6%) exhibits a sensitivity of 2.36 Ω/% with R2 = 0.9983, while the calibration curve corresponding to the higher percentage range (6-40%) possesses a sensitivity of 0.1 Ω/% with R2 = 0.9928. The limit of detection would be 1%. The recovery rates for the 4% and 5.7% GMS DNA were measured to be 104.1% and 102.49% with RSD at 6.24% and 2.54%. The gold nanoparticle sensing electrode developed in this research is suitable for qualitative and quantitative detection of genetically modified soybeans and can be further applied to the detection of other genetically modified crops in the future.

A simple electrochemical immunosensor for sensitive detection of transgenic soybean protein CP4-EPSPS in seeds

Soybean is the most produced crop in Argentina, and 99 % corresponds to genetically modified soybean. One of the main produced varieties is Roundup Ready® soybean (RR), which was modified to express the enzyme CP4 5-enolpyruvylshikimate 3-phosphate synthase (CP4 EPSPS), which confers resistance to glyphosate, the main herbicide worldwide used. The possible impact of genetically modified organisms (GMO) has generated public concerns, thus increasing interest in the development of GMOs detection devices. In this work, an electrochemical immunosensor for CP4 EPSPS detection in soybean seeds was obtained, by using a gold electrode modified with an anti-CP4 EPSPS polyclonal antibody produced in our laboratory. The presented immunosensor resulted in a simple, low-cost, fast, and reproducible device. Also, labeling and/or signal amplification system was not necessary, since the sensor showed high sensibility with a low detection limit (lower at 0,038 % RR soybean, 38 ng mL-1 CP4 EPSPS).

Optimization of Loop-Mediated Isothermal Amplification (LAMP) reaction mixture for biosensor applications

Genetically Modified (GM) foods are becoming the future of agriculture on surviving global natural disasters and climate change by their enhanced production efficiency and improved functional properties. On the other hand, their adverse health and environmental effects, ample evidence on transgene leakage of Genetically Modified Organisms (GMOs) to crops have raised questions on their benefits and risks. Consequently, low-cost, reliable, rapid, and practical detection of GMOs have been important. GMO-detection platforms should be capable of stably storing detection reagents for long-delivery distances with varying ambient temperatures. In this study, we developed an event-specific, closed tube colorimetric GMO detection method based on Loop-Mediated Isothermal Amplification (LAMP) technique which can be integrated into GMO-detection platforms. The entire detection process optimized to 30 min and isothermally at 65 °C. The durability of the LAMP mixture in the test tubes showed that the LAMP reaction mixture, in which Bst polymerase and DNA sample was later included, yielded DNA amplicons for 3 days at room temperature, and for 6 days at 4 °C.•Simple, stable, and cheap storage method of LAMP reaction mixture for GMO-detection technologies.•GMO-detection platforms can stably store detection reagents for long-delivery distances with varying ambient temperatures.•Any DNA sample can be used in the field or resource-limited setting by untrained personnel.

An electrochemical DNA biosensor based on nitrogen-doped graphene nanosheets decorated with gold nanoparticles for genetically modified maize detection

A reliable electrochemical biosensor is reported based on nitrogen-doped graphene nanosheets and gold nanoparticle (Au/N-G) nanocomposites for the event-specific detection of GM maize MIR162. The differential pulse voltammetry response of methylene blue (MB) was chosen to monitor the target DNA hybridization event. Under the optimum conditions, the peak current increased linearly with the logarithm of the concentration of DNA in the range 1.0 × 10^-14 to 1.0 × 10^-8 M, and the detection limit was 2.52 × 10^-15 M (S/N = 3). It is also demonstrated that the DNA biosensor has high selectivity, good stability, and fabrication reproducibility. The biosensor has been effectively applied to detect MIR162 in real samples, showing its potential as an effective tool for GM crop analysis. These results will contribute to the development of new portable transgenic detection systems. Graphical abstract .