Potential of cross-priming amplification and DNA-based lateral-flow strip biosensor for rapid on-site GMO screening.

The requirement to monitor the presence of genetically modified organisms (GMO) in a variety of marked products has generated an increasing demand for reliable, rapid, and time and cost-effective analytical methods. Here we report an on-site method for rapid detection of cauliflower mosaic virus promoter (CaMV 35S), a common element present in most GMO, using cross-priming amplification (CPA) technology. Detection was achieved using a DNA-based contamination-proof strip biosensor. The limit of detection was 30 copies for the pBI121 plasmid containing the CaMV 35S gene. The certified reference sample of GM maize line MON810 was detectable even at the low relative mass concentration of 0.05%. The developed CPA method had high specificity for the CaMV 35S gene, as compared with other GM lines not containing this gene and non-GM products. The method was further validated using nine real-world samples, and the results were confirmed by real-time PCR analysis. Because of its simplicity, rapidity, and high sensitivity, this method of detecting the CaMV 35S gene has great commercial prospects for rapid GMO screening of high-consumption food and agriculture products.

Robust Covalent Aptamer Strategy Enables Sensitive Detection and Enhanced Inhibition of SARS-CoV-2 Proteins.

Aptamer-based detection and therapy have made substantial progress with cost control and easy modification. However, the conformation lability of an aptamer typically causes the dissociation of aptamer-target complexes during harsh washes and other environmental stresses, resulting in only moderate detection sensitivity and a decreasing therapeutic effect. Herein, we report a robust covalent aptamer strategy to sensitively detect nucleocapsid protein and potently neutralize spike protein receptor binding domain (RBD), two of the most important proteins of SARS-CoV-2, after testing different cross-link electrophilic groups via integrating the specificity and efficiency. Covalent aptamers can specifically convert aptamer-protein complexes from the dynamic equilibrium state to stable and irreversible covalent complexes even in harsh environments. Covalent aptamer-based ELISA detection of nucleocapsid protein can surpass the gold standard, antibody-based sandwich ELISA. Further, covalent aptamer performs enhanced functional inhibition to RBD protein even in a blood vessel-mimicking flowing circulation system. The robust covalent aptamer-based strategy is expected to inspire more applications in accurate molecular modification, disease biomarker discovery, and other theranostic fields.

Detection of severe fever with thrombocytopenia syndrome virus by reverse transcription-cross-priming amplification coupled with vertical flow visualization.

A virus known as severe fever with thrombocytopenia syndrome virus (SFTSV) was recently identified as the etiological agent of severe fever with thrombocytopenia syndrome (SFTS) in China. Reliable laboratory detection and identification of this virus are likely to become clinically and epidemiologically desirable. We developed a nearly instrument-free, simple molecular method which incorporates reverse transcription-cross-priming amplification (RT-CPA) coupled with a vertical flow (VF) visualization strip for rapid detection of SFTSV. The RT-CPA-VF assay targets a conserved region of the M segment of the SFTSV genome and has a limit of detection of 100 copies per reaction, with no cross-reaction with other vector-borne bunyaviruses and bacterial pathogens. The performance of the RT-CPA-VF assay was determined with 175 human plasma specimens collected from 89 clinically suspected SFTS patients and 86 healthy donors. The sensitivity and specificity of the assay were 94.1% and 100.0%, respectively, compared with a combination of virus culture and real-time RT-PCR. The entire procedure, from specimen processing to result reporting, can be completed within 2 h. The simplicity and nearly instrument-free platform of the RT-CPA-VF assay make it practical for point-of-care testing.

EasyNAT MP Assay: A Simple, Rapid, and Low-Cost Method to Detect Mycoplasma pneumoniae Using Cross-Priming Amplification Technology.

BACKGROUND: Mycoplasma pneumoniae (MP) is the most common pathogen of atypical pneumonia and the main cause of community-acquired pneumonia (CAP) in infants and older adults. This study aimed at investigating a method based on the cross-priming amplification (CPA) technique for the rapid detection of MP in clinical specimens collected from patients with CAP. METHODS: The sensitivity and specificity of the EasyNAT MP assay were determined. Oropharyngeal swab specimens were collected from 162 in-patients of Hangzhou First People's Hospitals from January 2018 to December 2020. The patients were aged between 1 and 15 years with symptoms, signs, and chest radiographs consistent with CAP. This study evaluated the presence of MP in the clinical specimens using the EasyNAT method and the conventional fluorescence quantitative PCR technique. RESULTS: The limit of detection using the EasyNAT MP assay was 500 copies/mL, while the test results of the other 13 common pathogens causing CAP or colonizing in the upper respiratory tract showed no cross-reactivity. Of 162 specimens, EasyNAT MP gave a positive indication in 82 specimens. Compared with conventional fluorescence quantitative PCR, the positive coincidence rate and the negative coincidence rate of EasyNAT MP was found to be 100.00% and 97.56%, respectively. Of the 82 specimens, two specimens were determined to be negative by the conventional fluorescence quantitative PCR, but were positive for EasyNAT MP. The two samples were re-extracted and confirmed to be positive by conventional fluorescence quantitative PCR. CONCLUSION: EasyNAT MP is suitable as an initial test for MP diagnosis due to its simplicity, low turnaround time, and high sensitivity and specificity.

Application of PCR-LDR-nucleic acid detection strip in detection of YMDD mutation in hepatitis B patients treated with lamivudine.

Chronic hepatitis B virus (CHBV) infection causes cirrhosis and hepatocellular carcinoma. Lamivudine (LAM) has been successfully used to treat CHBV infections but prolonged use leads to the emergence of drug-resistant variants. This is primarily linked to a mutation in the tyrosine-methionine-aspartate-aspartate (YMDD) motif of the HBV polymerase gene at position 204. Rapid diagnosis of drug-resistant HBV is necessary for a prompt treatment response. Common diagnostic methods such as sequencing and restriction fragment length polymorphism (RFLP) analysis lack sensitivity and require significant processing. The aim of this study was to demonstrate the usefulness of a novel diagnostic method that combines polymerase chain reaction (PCR), ligase detection reaction (LDR) and a nucleic acid detection strip (NADS) in detecting site-specific mutations related to HBV LAM resistance. We compared this method (PLNA) to direct sequencing and RFLP analysis in 50 clinical samples from HBV infected patients. There was 90% concordance between all three results. PLNA detected more samples containing mutant variants than both sequencing and RFLP analysis and was more sensitive in detecting mixed variant populations. Plasmid standards indicated that the sensitivity of PLNA is at or below 3,000 copies per ml and that it can detect a minor variant at 5% of the total viral population. This warrants its further development and suggests that the PLNA method could be a useful tool in detecting LAM resistance.

Cross-priming amplification for rapid detection of Mycobacterium tuberculosis in sputum specimens.

Cross-priming amplification (CPA) technology for tuberculosis diagnosis from sputum specimens was evaluated. The sensitivity of CPA from smear- and liquid culture-positive specimens was 96.9%, and that from smear-negative and liquid culture-positive specimens was 87.5%. The specificity of CPA in culture-negative specimens was 98.8%.

Application of isothermal helicase-dependent amplification with a disposable detection device in a simple sensitive stool test for toxigenic Clostridium difficile.

Enzyme immunoassays (EIAs) are commonly used for the diagnosis of cases of Clostridium difficile-associated diarrhea (CDAD). However, these EIAs have high false-negative rates, even in patients with severe clinical disease. We have developed an IsoAmp CDAD test using a simple and user-friendly procedure to identify toxigenic C. difficile in feces. After DNA extraction from fecal samples, both the conserved sequence of the 5'-end fragment of the C. difficile tcdA toxin gene and competitive amplification internal control sequence were amplified using helicase-dependent amplification. Amplification products were detected using a novel amplicon-containment detection device. The analytical sensitivity of the assay was 20 copies of C. difficile genomic DNA per reaction. Evaluation of the clinical sensitivity and specificity of the IsoAmp CDAD test versus an EIA method using a PCR method as the reference standard revealed 100% sensitivity and 100% specificity for the IsoAmp CDAD test compared with 90.9% sensitivity and 100% specificity for the EIA method. Because the IsoAmp CDAD test requires no expensive equipments for nucleic acid amplification or detection and can be performed on a random access basis, the test provides a practical alternative to immunoassays for the diagnosis of CDAD with improved sensitivity.

Microfluidic PicoArray synthesis of oligodeoxynucleotides and simultaneous assembling of multiple DNA sequences.

Large DNA constructs of arbitrary sequences can currently be assembled with relative ease by joining short synthetic oligodeoxynucleotides (oligonucleotides). The ability to mass produce these synthetic genes readily will have a significant impact on research in biology and medicine. Presently, high-throughput gene synthesis is unlikely, due to the limits of oligonucleotide synthesis. We describe a microfluidic PicoArray method for the simultaneous synthesis and purification of oligonucleotides that are designed for multiplex gene synthesis. Given the demand for highly pure oligonucleotides in gene synthesis processes, we used a model to improve key reaction steps in DNA synthesis. The oligonucleotides obtained were successfully used in ligation under thermal cycling conditions to generate DNA constructs of several hundreds of base pairs. Protein expression using the gene thus synthesized was demonstrated. We used a DNA assembly strategy, i.e. ligation followed by fusion PCR, and achieved effective assembling of up to 10 kb DNA constructs. These results illustrate the potential of microfluidics-based ultra-fast oligonucleotide parallel synthesis as an enabling tool for modern synthetic biology applications, such as the construction of genome-scale molecular clones and cell-free large scale protein expression.

Cross priming amplification: mechanism and optimization for isothermal DNA amplification.

CPA is a class of isothermal amplification reactions that is carried out by a strand displacement DNA polymerase and does not require an initial denaturation step or the addition of a nicking enzyme. At the assay temperature of 63°C, the formation of a primer-template hybrid at transient, spontaneous denaturation bubbles in the DNA template is favored over re-annealing of the template strands by the high concentration of primer relative to template DNA. Strand displacement is encouraged by the annealing of cross primers with 5' ends that are not complementary to the template strand and the binding of a displacement primer upstream of the crossing primer. The resulting exponential amplification of target DNA is highly specific and highly sensitive, producing amplicons from as few as four bacterial cells. Here we report on the basic CPA mechanism - single crossing CPA - and provide details on alternative mechanisms.