Inter-laboratory validation of visual loop-mediated isothermal amplification assays for GM contents screening

Rapid detection of human cytomegalovirus by multienzyme isothermal rapid amplification and lateral flow dipsticks

Introduction

Human cytomegalovirus (HCMV) is the most common viral infection seen in newborns. The major route of transmission for acquired human cytomegalovirus infection is breast milk from mothers who are HCMV seropositive to the infants. Thus, a rapid, economical, and simple method to perform HCMV test in breast milk is crucial and necessary for preventing acquired HCMV infection, especially in underdeveloped regions with limited laboratory resources.

Methods

In this study, an effective technique for the detection of HCMV was constructed by combining multienzyme isothermal rapid amplification (MIRA) and lateral flow chromatography strip (LFD). Primers for the conserved HCMV sequence UL83 were utilized for MIRA-LFD testing.

Results

Our results showed that the entire MIRA reaction could be completed in 12 minutes at 37°C, and LFD outcomes could be observed visibly after 10 minutes. The detection sensitivity of this method reached 50 copy/μl. Samples of breast milk were examined to compare MIRA-LFD and conventional qPCR. The accuracy of MIRA-LFD was 100%.

Discussion

The straightforward, rapid, economic features of the test can provide the significant advantages for the prevention of breast milk-acquired cytomegalovirus infection, particularly in resource-limited locations with high seroprevalence of cytomegalovirus.

Development of a Naked Eye CRISPR-Cas12a and -Cas13a Multiplex Point-of-Care Detection of Genetically Modified Swine

The Rapid Visual CRISPR (RAVI-CRISPR) assay employs Cas12a and Cas13a enzymes for precise gene detection in a sample. However, RAVI-CRISPR is limited in single-tube multiplex detection applications due to the lack of specific single-strand (ss) DNA-fluorescently quenched (ssDNA-FQ) and RNA-fluorescently quenched (ssRNA-FQ) reporter cleavage mechanisms. We report the development of a sensitive and specific dual-gene Cas12a and Cas13a diagnostic system. To optimize the application for field testing, we designed a portable multiplex fluorescence imaging assay that could distinguish test results with the naked eye. Herein, dual gene amplified products from multiplex recombinase polymerase amplification (RPA) were simultaneously detected in a single tube using Cas12a and Cas13a enzymes. The resulting orthogonal DNA and RNA collateral cleavage specifically distinguishes individual and mixed ssDNA-FQ and ssRNA-FQ reporters using the green-red-yellow, fluorescent signal conversion reaction system, detectable with portable blue and ultraviolet (UV) light transilluminators. As a proof-of-concept, reliable multiplex RAVI-CRISPR detection of genome-edited pigs was demonstrated, exhibiting 100% sensitivity and specificity for the analysis of CD163 knockout, lactoferrin (LF) knock-in, and wild-type pig samples. This portable naked-eye multiplex RAVI-CRISPR detection platform can provide accurate point-of-care screening of genetically modified animals and infectious diseases in resource-limited settings.

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.

[Evaluation of a Species-specific, Stable, and Endogenous Sequence of Eggplant (Solanum melongena) using LAMP for the Detection of Genetically Modified Eggplants]

Species-specific endogenous reference sequences are indispensable in the development of methods to detect genetically modified (GM) crops for food and feed. We analyzed a partial sequence derived from the β-fructosidase gene among several solanaceous species and developed a new eggplant specific detection method using loop-mediated isothermal amplification (LAMP). LAMP is a rapid, specific, and cost-effective technique. The species-specificity and stability of the developed method were evaluated using 18 eggplant cultivars and other crops including solanaceous plants. The limit of detection was also evaluated. The developed method showed high specificity for eggplants and stability among the eggplant cultivars tested. These results suggested that the developed method would be useful as a positive control for the detection of GM eggplants with LAMP.

Colorimetric biosensing of nopaline synthase terminator using Fe3O4@Au and hemin-functionalized reduced graphene oxide

In this paper, we present a simple and label-free colorimetric biosensor for detection of the nopaline synthase (NOS) terminator in genetically modified (GM) plants. The "signal on" colorimetric biosensor was developed using a nanocomposite consisted of gold nanoparticles doped magnetic Fe₃O₄ nanoparticles (Fe₃O₄@Au NP), capture probe DNA (cDNA), and hemin-functionalized reduced graphene oxide nanosheets (H-GN). The nanocomposite was successfully prepared by means of Au-S bonds and the strong π interactions between cDNA and H-GN. The sensing approach is based on the excellent peroxidase-mimicking activity of H-GN and its different electrostatic interactions with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). In presence of the target NOS, the cDNA in the nanocomposite will hybridize with its complementary sequence, and form dsDNA structure. Due to the weak π interactions between dsDNA and H-GN, a portion of H-GN will be released from the surface of Fe₃O₄@Au NPs and transferred into solution. After magnetic separation was performed, the supernatant was incubated with 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂. The released H-GN can catalyze the oxidation reaction of TMB and turn the colorless solution blue. This "signal-on" colorimetric biosensor shows a broad linear range of 0.5-100 nM for the target NOS, with a 0.19 nM detection limit. The application of the biosensor for determination of NOS segments in samples of GM and non-GM tomatoes shows that it can discriminate between GM and non-GM plants. The reliability of the method for samples of NOS-spiked GM tomato suggests satisfactory recoveries in the range of 93.6%-94.2%.

Rapid DNA template preparation directly from a rice sample without purification for loop-mediated isothermal amplification (LAMP) of rice genes

Rapid DNA template preparation directly from a single rice (Oryza sativa) grain or rice flour of its equivalent weight was developed for loop-mediated isothermal amplification (LAMP). LAMP efficiency using DNA extract obtained from consecutive addition of alkaline lysis reagent (25 mM NaOH, 0.2 mM EDTA) and neutralizing reagent (40 mM Tris–HCl [pH 5]) was comparable to that using an equivalent amount of purified DNA as template. The stability of the prepared DNA extract was confirmed for up to six-day storage at room temperature. Without using any special laboratory devices, the developed method enabled a rapid, simple, and low-cost DNA template preparation method for reliable LAMP testing to detect rice genes.