Diagnostics based on nucleic acid sequence variant profiling: PCR, hybridization, and NGS approaches

Single-molecule force spectroscopy of toehold-mediated strand displacement

Toehold-mediated strand displacement (TMSD) is extensively utilized in dynamic DNA nanotechnology and for a wide range of DNA or RNA-based reaction circuits. Investigation of TMSD kinetics typically relies on bulk fluorescence measurements providing effective, bulk-averaged reaction rates. Information on individual molecules or even base pairs is scarce. In this work, we explore the dynamics of strand displacement processes at the single-molecule level using single-molecule force spectroscopy with a microfluidics-enhanced optical trap supported by state-of-the-art coarse-grained simulations. By applying force, we can trigger and observe TMSD in real-time with microsecond and nanometer resolution. We find TMSD proceeds very rapidly under load with single step times of 1 µs. Tuning invasion efficiency by introducing mismatches allows studying thousands of forward/backward invasion events on a single molecule and analyze the kinetics of the invasion process. Extrapolation to zero force reveals single step times for DNA invading DNA four times faster than for RNA invading RNA. We also study the kinetics of DNA invading RNA, a process that in the absence of force would rarely occur. Our results reveal the importance of sequence effects for the TMSD process and have relevance for a wide range of applications in nucleic acid nanotechnology and synthetic biology.

Multi-omics analysis identified extracellular vesicles as biomarkers for cardiovascular diseases

Cell-derived extracellular vesicles (EVs) have emerged as a promising non-invasive liquid biopsy technique due to their accessibility and their ability to encapsulate and transport diverse biomolecules. EVs have garnered substantial research interest, notably in cardiovascular diseases (CVDs), where their roles in pathophysiology and as diagnostic and prognostic biomarkers are increasingly recognized. This review provides a comprehensive overview of EVs, starting with their origins, followed by the techniques used for their isolation and characterization. We explore the diverse cargo of EVs, including nucleic acids, proteins, lipids, and metabolites, highlighting their roles in intercellular communication and as potential biomarkers. We then delve into the application of genomics, transcriptomics, proteomics, and metabolomics in the analysis of EVs, particularly within the context of CVDs. Finally, we discuss how integrated multi-omics approaches are unveiling novel biomarkers, offering fresh insights into the diagnosis and prognosis of CVDs. This review underscores the growing importance of EVs in clinical diagnostics and the potential of multi-omics to propel future advancements in CVD biomarker discovery.

A comprehensive review of engineered exosomes from the preparation strategy to therapeutic applications

Exosomes exhibit high bioavailability, biological stability, targeted specificity, low toxicity, and low immunogenicity in shuttling various bioactive molecules such as proteins, lipids, RNA, and DNA. Natural exosomes, however, have limited production, targeting abilities, and therapeutic efficacy in clinical trials. On the other hand, engineered exosomes have demonstrated long-term circulation, high stability, targeted delivery, and efficient intracellular drug release, garnering significant attention. The engineered exosomes bring new insights into developing next-generation drug delivery systems and show enormous potential in therapeutic applications, such as tumor therapies, diabetes management, cardiovascular disease, and tissue regeneration and repair. In this review, we provide an overview of recent advancements associated with engineered exosomes by focusing on the state-of-the-art strategies for cell engineering and exosome engineering. Exosome isolation methods, including traditional and emerging approaches, are systematically compared along with advancements in characterization methods. Current challenges and future opportunities are further discussed in terms of the preparation and application of engineered exosomes.

A serotype-specific and tiled amplicon multiplex PCR method for whole genome sequencing of dengue virus

Dengue fever, a mosquito-borne viral disease of significant public health concern in tropical and subtropical regions, is caused by any of the four serotypes of the dengue virus (DENV1-4). Cutting-edge technologies like next-generation sequencing (NGS) are revolutionizing virology, enabling in-depth exploration of DENV's genetic diversity. Here, we present an optimized workflow for full-genome sequencing of DENV 1-4 utilizing tiled amplicon multiplex PCR and Illumina sequencing. Our assay, sequenced on the Illumina MiSeq platform, demonstrates its ability to recover the full-length dengue genome across various viral abundances in clinical specimens with high-quality base coverage. This high quality underscores its suitability for precise examination of intra-host diversity, enriching our understanding of viral evolution and holding potential for improved diagnostic and intervention strategies in regions facing dengue outbreaks.

Application of Next-Generation Sequencing (NGS) Techniques for Selected Companion Animals

Next-Generation Sequencing (NGS) techniques have revolutionized veterinary medicine for cats and dogs, offering insights across various domains. In veterinary parasitology, NGS enables comprehensive profiling of parasite populations, aiding in understanding transmission dynamics and drug resistance mechanisms. In infectious diseases, NGS facilitates rapid pathogen identification, characterization of virulence factors, and tracking of outbreaks. Moreover, NGS sheds light on metabolic processes by elucidating gene expression patterns and metabolic pathways, essential for diagnosing metabolic disorders and designing tailored treatments. In autoimmune diseases, NGS helps identify genetic predispositions and molecular mechanisms underlying immune dysregulation. Veterinary oncology benefits from NGS through personalized tumor profiling, mutation analysis, and identification of therapeutic targets, fostering precision medicine approaches. Additionally, NGS plays a pivotal role in veterinary genetics, unraveling the genetic basis of inherited diseases and facilitating breeding programs for healthier animals. Physiological investigations leverage NGS to explore complex biological systems, unraveling gene-environment interactions and molecular pathways governing health and disease. Application of NGS in treatment planning enhances precision and efficacy by enabling personalized therapeutic strategies tailored to individual animals and their diseases, ultimately advancing veterinary care for companion animals.

Application of CRISPR/Cas13a-based biosensors in serum marker detection

The detection of serum markers is important for the early diagnosis and monitoring of diseases, but conventional detection methods have the problem of low specificity or sensitivity. CRISPR/Cas13a-based biosensors have the characteristics of simple detection methods and high sensitivity, which have a certain potential to solve the problems of conventional detection. This paper focuses on the research progress of CRISPR/Cas13a-based biosensors in serum marker detection, introduces the principles and applications of fluorescence, electrochemistry, colorimetric, and other biosensors based on CRISPR/Cas13a in the detection of serum markers, compares and analyzes the differences between the above CRISPR/Cas13a-based biosensors, and looks forward to the future development direction of CRISPR/Cas13a-based biosensors.

Single-Atom Site SERS Chip for Rapid, Ultrasensitive, and Reproducible Direct-Monitoring of RNA Binding

Ribonucleic acids (RNA) play active roles within cells or viruses by catalyzing biological reactions, controlling gene expression, and communicating responses to cellular signals. Rapid monitoring RNA variation has become extremely important for appropriate clinical decisions and frontier biological research. However, the most widely used method for RNA detection, nucleic acid amplification, is restricted by a mandatory temperature cycling period of ≈1 h required to reach target detection criteria. Herein, a direct detection approach via single-atom site integrated surface-enhanced Raman scattering (SERS) monitoring nucleic acid pairing reaction, can be completed within 3 min and reaches high sensitivity and extreme reproducibility for COVID-19 and two other influenza viruses' detection. The mechanism is that a single-atom site on SERS chip, enabled by positioning a single-atom oxide coordinated with a specific complementary RNA probe on chip nanostructure hotspots, can effectively bind target RNA analytes to enrich them at designed sites so that the binding reaction can be detected through Raman signal variation. This ultrafast, sensitive, and reproducible single-atom site SERS chip approach paves the route for an alternative technique of immediate RNA detection. Moreover, single-atom site SERS is a novel surface enrichment strategy for SERS active sites for other analytes at ultralow concentrations.

Understanding exosomes: Part 1-Characterization, quantification and isolation techniques

Exosomes are the smallest subset of extracellular signaling vesicles secreted by most cells with a diameter in the range of 30-150 nm. Their use has gained great momentum recently due to their ability to be utilized as diagnostic tools with a vast array of therapeutic applications. Over 5000 publications are currently being published yearly on this topic, and this number is only expected to dramatically increase as novel therapeutic strategies continue to be investigated. This review article first focuses on understanding exosomes, including their cellular origin, biogenesis, function, and characterization. Thereafter, overviews of the quantification methods and isolation techniques are given with discussion over their potential use as novel therapeutics in regenerative medicine.

Lung adenocarcinoma with brain metastasis detected dual fusion of LOC399815-ALK and ALK-EML4 in combined treatment of Alectinib and CyberKnife: A case report

INTRODUCTION

The anaplastic lymphoma kinase (ALK) gene fusion occurs in approximately 3% to 7% of nonsmall cell lung cancer (NSCLC), in which occurs approximately 23% to 31% of brain metastasis patients in poor prognosis. ALK tyrosine kinase inhibitors have shown efficacy in treating ALK-positive (ALK+) NSCLC. More than 90 distinct subtypes of ALK fusions have been identified through sequencing technique and would lead to significant differences in clinical efficacy, it is necessary to guide clinical treatment effectively by gene detection.

PATIENT CONCERNS

A 56-year-old nonsmoking female admitted to hospital due to cough, expectoration, and chest pain. Chest computed tomography revealed a space-occupying lesion in the upper left lobe (5.0 cm × 2.4 cm × 2.9 cm), multiple enlarged lymph nodes in mediastinum 3A and 5 (largest size 1.5 cm × 1.4 cm), and evidence of thoracic vertebral metastasis, brain magnetic resonance imaging also showed brain metastasis.

DIAGNOSES

Lung adenocarcinoma with brain metastasis.

INTERVENTIONS

The patient initially received conventional first-line chemotherapy, which led to a deteriorated condition. Blood-base liquid biopsy by next-generation sequencing resulted in double ALK fusions, in which with a neo-partner of lncRNA (LOC399815-ALK). Following subsequent treatment with Alectinib and stereotactic radiotherapy (CyberKnife) was subsequently employed to manage the brain metastatic lesions, resulting in a substantial decreased in both the number and size of tumor lesions.

OUTCOMES

The patient's response to therapy efficacy resulted in a substantial decreased in both the number and size of tumor lesions that assessed comprehensively evaluated through computed tomography imaging and ctDNA sequencing. Patient's condition has been under control for over 29 months.

CONCLUSION

Liquid biopsy may reveal the rare fusion forms of ALK, precisely guiding personalized treatment, and providing a reference method for longitudinal monitoring and efficacy evaluation of ALK-tyrosine kinase inhibitors in NSCLC patients.

DNA-Aptamer-Based qPCR Using Light-Up Dyes for the Detection of Nucleic Acids

Quantitative polymerase chain reaction (qPCR) is widely used in detection of nucleic acids, but existing methods either lack sequence-specific detection or are costly because they use chemically modified DNA probes. In this work, we apply a DNA aptamer and light-up dye-based chemistry for qPCR for nucleic acid quantification. In contrast to the conventional qPCR, in our method, we observe an exponential decrease in fluorescence upon DNA amplification. The qPCR method we developed produced consistent Ct vs log10 (DNA amount) standard curves, which have a linearfit with R2 value > 0.99. This qPCR technique was validated by quantifying gene targets from Streptococcus zooepidemicus (SzhasB) and Mycobacterium tuberculosis (MtrpoB). We show that our strategy is able to successfully detect DNA at as low as 800 copies/μL. To the best of our knowledge, this is the first study demonstrating the application of light-up dyes and DNA aptamers in qPCR.

Identification of DNA variants at ultra-low variant allele frequencies via Taq polymerase cleavage of wild-specific blockers

Detecting mutations related to tumors holds immense clinical significance for cancer diagnosis and treatment. However, the presence of highly redundant wild DNA poses a challenge for the advancement of low-copy mutant ctDNA genotyping in cancer cases. To address this, a Taqman qPCR strategy to identify rare mutations at low variant allele fractions (VAFs) has been developed. This strategy combines mutant-specific primers with wild-specific blockers. Diverging from other blocker-mediated PCRs, which rely on primer-induced strand displacement or the use of modified oligos resistant to Taq polymerase, our innovation is built upon the cleavage of specific blockers by Taq polymerase. Given its unique design, which does not hinge on strand displacement or base modification, we refer to this novel method as unmodified-blocker cleavage PCR (UBC-PCR). Multiple experiments consistently confirmed that variant distinction was improved significantly by introduction of 5' unmatched blockers into the reaction. Moreover, UBC-PCR successfully detected mutant DNA at VAFs as low as 0.01% across six different variant contexts. Multiplex UBC-PCR was also performed to identify a reference target and three mutations with a sensitivity of 0.01% VAFs in one single tube. In profiling the gene status from 12 lung cancer ctDNA samples and 22 thyroid cancer FNA DNA samples, UBC-PCR exhibited a 100% concordance rate with ddPCR and a commercial ARMS kit, respectively. Our work demonstrates that UBC-PCR can identify low-abundance variants with high sensitivity in multiplex reactions, independent of strand displacement and base modification. This strategy holds the potential to significantly impact clinical practice and precision medicine.

Mismatch-Guided Deoxyribonucleic Acid Assembly Enables Ultrasensitive and Multiplex Detection of Low-Allele-Fraction Variants in Clinical Samples

Somatic mutations are important signatures in clinical cancer treatment. However, accurate detection of rare somatic mutations with low variant-allele frequencies (VAFs) in clinical samples is challenging because of the interference caused by high concentrations of wild-type (WT) sequences. Here, we report a post amplification SNV-specific DNA assembly (PANDA) technology that eliminates the high concentration pressure caused by WT through a mismatch-guided DNA assembly and enables the ultrasensitive detection of cancer mutations with VAFs as low as 0.1%. Because it generates an assembly product that only exposes a single-stranded domain with the minimal length for signal readout and thus eliminates possible interferences from secondary structures and cross-interactions among sequences, PANDA is highly versatile and expandable for multiplex testing. With ultrahigh sensitivity, PANDA enabled the quantitative analysis of EGFR mutations in cell-free DNA of 68 clinical plasma samples and four pleuroperitoneal fluid samples, with test results highly consistent with NGS deep sequencing. Compared to digital PCR, PANDA returned fewer false negatives and ambiguous cases of clinical tests. Meanwhile, it also offers much lower upfront instrumental and operational costs. The multiplexity was demonstrated by developing a 3-plex PANDA for the simultaneous analysis of three EGFR mutations in 54 pairs of tumor and the adjacent noncancerous tissue samples collected from lung cancer patients. Because of the ultrahigh sensitivity, multiplexity, and simplicity, we anticipate that PANDA will find wide applications for analyzing clinically important rare mutations in diverse devastating diseases.

Smart-Plexer: a breakthrough workflow for hybrid development of multiplex PCR assays

Developing multiplex PCR assays requires extensive experimental testing, the number of which exponentially increases by the number of multiplexed targets. Dedicated efforts must be devoted to the design of optimal multiplex assays ensuring specific and sensitive identification of multiple analytes in a single well reaction. Inspired by data-driven approaches, we reinvent the process of developing and designing multiplex assays using a hybrid, simple workflow, named Smart-Plexer, which couples empirical testing of singleplex assays and computer simulation to develop optimised multiplex combinations. The Smart-Plexer analyses kinetic inter-target distances between amplification curves to generate optimal multiplex PCR primer sets for accurate multi-pathogen identification. In this study, the Smart-Plexer method is applied and evaluated for seven respiratory infection target detection using an optimised multiplexed PCR assay. Single-channel multiplex assays, together with the recently published data-driven methodology, Amplification Curve Analysis (ACA), were demonstrated to be capable of classifying the presence of desired targets in a single test for seven common respiratory infection pathogens.

Utilizing MiSeq Sequencing to Detect Circulating microRNAs in Plasma for Improved Lung Cancer Diagnosis

Non-small cell lung cancer (NSCLC) is a major contributor to cancer-related deaths, but early detection can reduce mortality. NSCLC comprises mainly adenocarcinoma (AC) and squamous cell carcinoma (SCC). Circulating microRNAs (miRNAs) in plasma have emerged as promising biomarkers for NSCLC. However, existing techniques for analyzing miRNAs have limitations, such as restricted target detection and time-consuming procedures. The MiSeqDx System has been shown to overcome these limitations, making it a promising tool for routine clinical settings. We investigated whether the MiSeqDx could profile cell-free circulating miRNAs in plasma and diagnose NSCLC. We sequenced RNA from the plasma of patients with AC and SCC and from cancer-free smokers using the MiSeqDx to profile and compare miRNA expressions. The MiSeqDx exhibits high speed and accuracy when globally analyzing plasma miRNAs. The entire workflow, encompassing RNA to data analysis, was completed in under three days. We also identified panels of plasma miRNA biomarkers that can diagnose NSCLC with 67% sensitivity and 68% specificity, and detect SCC with 90% sensitivity and 94% specificity, respectively. This study is the first to demonstrate that rapid profiling of plasma miRNAs using the MiSeqDx has the potential to offer a straightforward and effective method for the early detection and classification of NSCLC.

Development and application of a TaqMan-based real-time PCR method for the detection of the ASFV MGF505-7R gene

African swine fever virus (ASFV), the etiological agent of African swine fever (ASF), causes deadly hemorrhagic fever in domestic pigs. ASF's high mortality and morbidity have had disastrous effects on the world's swine industry. In recent years, the number of African swine virus strains has increased and presented new challenges for detecting classical ASFV-p72-based viruses. In this study, we observed that the ASFV MGF505-7R gene, a member of the multigene family that can enhance ASFV virulence and pathogenesis, has the potential to be a candidate for vaccine formulations. We also developed a real-time PCR assay based on the ASFV MGF505-7R gene and validated it in multiple aspects. The results indicated that the approach could detect standard plasmids with a sensitivity and a specificity of up to 1 × 10¹ copies/μL. Moreover, the assay had no cross-reactions with other porcine viruses. In laboratory and clinical settings, the assay can detect ASFV-infected samples at an early stage (4 hpi) and show a consistency of 92.56% when compared with classical ASFV detection in clinically ASFV-infected materials. This study's results also indicated that the TaqMan-based quantitative real-time PCR assay we developed for detecting the ASFV MGF505-7R gene is both sensitive and specific. This assay can provide a quick and accurate method for detecting ASFV and has the potential to be used as an optional tool for screening and monitoring ASF outbreaks.

Efficient large-scale screening of viral pathogens by fragment length identification of pooled nucleic acid samples (FLIPNAS)

The necessity for the large-scale screening of viral pathogens has been amply demonstrated during the COVID-19 pandemic. During this time, SARS-CoV-2 nucleic acid pooled testing, such as Dorfman-based group testing, was widely adopted in response to the sudden increased demand for detection. However, the current approach still necessitates the individual retesting of positive pools. Here, we established an efficient method termed the fragment-length identification of pooled nucleic acid samples (FLIPNAS), where all subsamples (n = 8) can be uniquely labelled and tested in a single-time detection among pools of samples. We used a novel and simple design of unique primers (UPs) to generate amplicons of unique lengths after reverse transcription and polymerase chain reaction to reach this aim. As a result, the unique lengths of the amplicons can be recognized and traced back to the corresponding UPs and specific samples. Our results demonstrated that FLIPNAS could recognize one to eight positive subsamples in a single test without retesting positive pools. The system also showed sufficient sensitivity for the mass monitoring of SARS-CoV-2 and no cross-reactivity against three common respiratory diseases. Moreover, the FLIPNAS results of 40 samples with a positive ratio of 7.8% were in 100% agreement with their individual detection results using the gold standard. Collectively, this study shows that the efficiency of nucleic acid pooling detection can be further improved by FLIPNAS, which can speed up testing and mitigate the urgent demand for resources.

Antibiotic Resistance Diagnosis in ESKAPE Pathogens-A Review on Proteomic Perspective

Antibiotic resistance has emerged as an imminent pandemic. Rapid diagnostic assays distinguish bacterial infections from other diseases and aid antimicrobial stewardship, therapy optimization, and epidemiological surveillance. Traditional methods typically have longer turn-around times for definitive results. On the other hand, proteomic studies have progressed constantly and improved both in qualitative and quantitative analysis. With a wide range of data sets made available in the public domain, the ability to interpret the data has considerably reduced the error rates. This review gives an insight on state-of-the-art proteomic techniques in diagnosing antibiotic resistance in ESKAPE pathogens with a future outlook for evading the "imminent pandemic".

Digital detection of proteins

This paper reviews methods for detecting proteins based on molecular digitization, i.e., the isolation and detection of single protein molecules or singulated ensembles of protein molecules. The single molecule resolution of these methods has resulted in significant improvements in the sensitivity of immunoassays beyond what was possible using traditional "analog" methods: the sensitivity of some digital immunoassays approach those of methods for measuring nucleic acids, such as the polymerase chain reaction (PCR). The greater sensitivity of digital protein detection has resulted in immuno-diagnostics with high potential societal impact, e.g., the early diagnosis and therapeutic intervention of Alzheimer's Disease. In this review, we will first provide the motivation for developing digital protein detection methods given the limitations in the sensitivity of analog methods. We will describe the paradigm shift catalyzed by single molecule detection, and will describe in detail one digital approach - which we call digital bead assays (DBA) - based on the capture and labeling of proteins on beads, identifying "on" and "off" beads, and quantification using Poisson statistics. DBA based on the single molecule array (Simoa) technology have sensitivities down to attomolar concentrations, equating to ∼10 proteins in a 200 μL sample. We will describe the concept behind DBA, the different single molecule labels used, the ways of analyzing beads (imaging of arrays and flow), the binding reagents and substrates used, and integration of these technologies into fully automated and miniaturized systems. We provide an overview of emerging approaches to digital protein detection, including those based on digital detection of nucleic acids labels, single nanoparticle detection, measurements using nanopores, and methods that exploit the kinetics of single molecule binding. We outline the initial impact of digital protein detection on clinical measurements, highlighting the importance of customized assay development and translational clinical research. We highlight the use of DBA in the measurement of neurological protein biomarkers in blood, and how these higher sensitivity methods are changing the diagnosis and treatment of neurological diseases. We conclude by summarizing the status of digital protein detection and suggest how the lab-on-a-chip community might drive future innovations in this field.

Web hybrid chain reaction enhanced fluorescent magnetic bead array for digital nucleic acid detection

The detection of biomarkers at low concentrations is important in clinical diagnostic analyses and has attracted continuous research. In this work, absolute quantification of hepatitis B virus (HBV) DNA was achieved using magnetic beads with isothermal, enzyme-free DNA nanostructure for fluorescence amplification. Firstly, the DNA-functionalized bead captured the target nucleic acid in the form of sandwich hybridization, and the individual target lighted up the entire bead by isothermal web hybridization chain reaction (wHCR). After the microarray scanning, the target nucleic acids can be digitally quantified based on the Poisson statistics. Therefore, the fluorescent bead assay enabled precise detection of HBV DNA down to 5 fM level without external calibration curves. Moreover, this method not only specifically distinguished single-base mismatched sequences, but also obtained the quantitative detection of HBV DNA in serum samples. Unlike routine digital detection usually combined with complex compartment partitioning operations, the amplification structure immobilized on beads can be conducted in microcentrifuge tubes with a volume of microliter scale. This work expands the application of magnetic beads in the digital quantitative detection via enzyme-free and isothermal method.

Development and characterization of reference materials for EGFR, KRAS, NRAS, BRAF, PIK3CA, ALK, and MET genetic testing

BACKGROUND

Along with the dramatic development of molecular diagnostic testing for the detection of oncogene variations, reference materials (RMs) have become increasingly important in performance evaluation of genetic testing.

OBJECTIVE

In this study, we built a set of RMs for genetic testing based on next-generation sequencing (NGS).

METHOD

Solid tumor tissues were selected as the samples of RMs for preparation. NGS was used to determine and validate the variants and the mutation frequency in DNA samples. Digital PCR was used to determine the copy numbers of RNA samples. The performance of the RMs was validated by six laboratories.

RESULTS

Thirty common genetic alterations were designed based on these RMs. RMs consisted of a positive reference, a limit of detection reference, and a negative reference. The validation results confirmed the performance of the RMs.

CONCLUSION

These RMs may be an attractive tool for the development, validation, and quality monitoring of molecular genetic testing.

Improved PCR by the Use of Disruptors, a New Class of Oligonucleotide Reagents

As a powerful tool, polymerase chain reaction (PCR) has been indispensable and widely used in a large array of applications. In practice, many factors may affect the overall performance of a PCR. One such factor is the stability of intramolecular secondary structure formed within single-stranded template. The higher the stability of such a structure, the more likely it will have adverse effects on PCR performance. Traditionally, chemical reagents believed to reduce the stability of nucleic acid secondary structures, such as DMSO and betaine, have been used to mitigate their adverse effects on PCR performance. However, these reagents have apparent downsides including increasing replication error rate, inhibiting polymerase activity, and being ineffective against secondary structures of very high stabilities. Disruptors, a new class of oligonucleotide reagents, do not exhibit such downsides. They are specifically designed to target intramolecular secondary structures only without any effect on the replication of other regions of the template. Their effective concentration range for improving PCR performance is well tolerated by PCR. And they are very effective in improving PCR performance on templates that are notoriously difficult to amplify by PCR even in the presence of DMSO or betaine, e.g., the inverted terminal repeat of adeno-associated virus (AAV-ITR). In this chapter, the application of disruptors in PCR is described with AAV-ITR as the example template.

Comparison of Homologous Recombination Repair Gene Next-Generation Sequencing Analysis in Patients With Metastatic Castration-Resistant Prostate Cancer Between Local and Central Laboratories in Korea

Background

Following success of the phase III PROfound trial, the poly (ADP-ribose) polymerase (PARP) inhibitor olaparib was approved by the US Food and Drug Administration in May 2020 for adult patients with deleterious homologous recombination repair (HRR) gene-mutated metastatic castration-resistant prostate cancer (mCRPC). As locally adopted multigene panel next-generation sequencing (NGS) assays for selecting PARP inhibitor candidates have not been thoroughly evaluated, we compared the analytical performance of the FoundationOne CDx (Foundation Medicine, Inc., Cambridge, MA, USA) (central laboratory) and other NGS assays (local laboratory) with samples from the PROfound trial in Korea.

Methods

One hundred PROfound samples (60 HRR mutation [HRRm] cases and 40 non-HRRm cases) were analyzed. The results of HRR gene mutation analysis were compared between the FoundationOne CDx and two other NGS assays [SureSelect Custom Design assay (Agilent Technologies, Inc., Santa Clara, CA, USA) and Oncomine Comprehensive assay (Thermo Fisher Scientific, Inc., Waltham, MA, USA)].

Results

The positive percent agreement for single nucleotide variants (SNVs) and insertion/deletions (indels) between the central laboratory and local laboratory was 98.7%-100.0%. The negative percent agreement and overall percent agreement (OPA) for SNVs and indels between central and local laboratories were both 100%. Compared with that of the FoundationOne CDx assay, the OPA for copy number variations of the Oncomine Comprehensive and SureSelect Custom assays reached 99.8%-100%. Most mCRPC patients harboring a deleterious genetic variant were successfully identified with both local laboratory assays.

Conclusions

The NGS approach at a local laboratory showed comparable analytical performance for identifying HRRm status to the FoundationOne CDx assay used at the central laboratory.

Cooperative strand displacement circuit with dual-toehold and bulge-loop structure for single-nucleotide variations discrimination

Nucleic acid nanotechnologies based on toehold-mediated strand displacement are ideally suited for single-nucleotide variations (SNVs) detection. But only a limited number of means could be used to construct selective hybridization probes via finely designed toehold and regulation of branching migration. Herein, we present a cooperative hybridization strategy relying on a dual-toehold and bulge-loop (DT&BL) probe, coupled with the strand displacement catalytic (SDC) cycle to identify SNVs. The dual-toehold can simultaneously hybridize the 5' and 3' ends of the target, so that it possessed the mutual correction function for improving the specificity in comparison with the single target-binding domain. Insertion of BLs into the dual-toehold probe allows tuning of Gibbs free energy change (ΔG) and control of the reaction rate during branching migration. Using the SDC cycle, the reactivity and selectivity of the DT&BL probe were increased drastically without elaborate competitive sequences. The feasibilities of this platform were demonstrated by the identification of three cancer-related genes. Moreover, the applicability of this biosensor to detect clinical samples showed satisfactory accuracy and reliability. We envision it would offer a new perspective for the construction of highly specific probes based on dynamic DNA nanotechnology, and serves as a promising tool for clinical diagnostics.

Simultaneous Detection of Three Genotypes of Gene Methylene Tetrahydrofolate Reductase and Methionine Synthase Reductase Based on Multiplex Asymmetric Real-Time PCR-HRM Biosensing

Genotyping of folate metabolism genes is of great importance in disease diagnosis and prevention. However, most current detection methods used for folate metabolism gene genotyping are based on sequencing and chips, which suffer from a high cost and laborious and time-consuming procedures. Herein, we reported a multiplex asymmetric PCR-HRM strategy for identifying genotypes of folate metabolism genes in a single tube. The proposed multiplex PCR-HRM assay has been successfully applied to identify the genotypes of folate metabolism genes, methylene tetrahydrofolate reductase (C677T, A1298C) and methionine synthase reductase A66G, on 1 μL of genomic DNA (gDNA) samples directly released from blood specimens, and the genotyping results were 100% consistent with the results of sequencing. The assay allows us to accurately detect the genotypes of gDNA with the detection limit down to 1 ng, which meets the clinical requirement. What is more, the capacity of resistance to aerosol pollution of the multiplex asymmetric PCR-HRM biosensing was first addressed and has been evaluated as it can withstand contamination of roughly 12.5-25% interfering nucleic acids. Because of the advantages of multiplex detection, high accuracy, and resistance to aerosol pollution and having no open tube procedure, this approach would pave the way for establishing a fast and cost-effective platform for folate metabolism gene genotyping and other SNP genotyping in clinical diagnostics.

Expanding the genetic spectrum of tooth agenesis using whole-exome sequencing

BACKGROUND

Tooth agenesis is a high genetic heterogeneous disorder with more than eighty genes identified as associated molecular causes. The present study aimed to detect the possible pathogenic variants in a cohort of well-characterized probands with a clinical diagnosis of tooth agenesis.

METHODS

We performed whole-exome sequencing (WES) in 131 tooth agenesis patients with no previously identified molecular diagnosis. All the potential pathogenic variants were verified by Sanger sequencing in patients and their family members. Results Seventy-three patients were genetically diagnosed in 131 unrelated Chinese patients with tooth agenesis, providing a positive molecular diagnostic rate of 55.7%, including 53.8% (49/91) in the non-syndromic tooth agenesis (NSTA) group, and 60.0% (24/40) in syndromic tooth agenesis (STA) group. A total of 75 variants from 13 different genes were identified, including 33 novel variants, and WNT10A and EDA are the most common causative genes associated with non-syndromic and syndromic tooth agenesis, respectively.

CONCLUSIONS

This study further extends the variant spectrum and clinical profiles of tooth agenesis, which has a positive significance for clinical practice, genetic diagnosis, prenatal counseling and future treatment.

Evaluation of droplet digital PCR rapid detection method and precise diagnosis and treatment for suspected sepsis (PROGRESS): a study protocol for a multi-center pragmatic randomized controlled trial

Background

Sepsis is still a major public health concern and a medical emergency due to its high morbidity and mortality. Accurate and timely etiology diagnosis is crucial for sepsis management. As an emerging rapid and sensitive pathogen detection tool, digital droplet PCR (ddPCR) has shown promising potential in rapid identification of pathogens and antimicrobial resistance genes. However, the diagnostic value and clinical impact of ddPCR tests remains to be studied in patients with suspected sepsis. PROGRESS trial is aimed to evaluate the clinical effectiveness of a novel ddPCR assay compared with standard practice.

Methods

PROGRESS is a multicenter, open-label, pragmatic randomized controlled trial (pRCT) set in ten hospitals, including departments of infectious disease and intensive care units. In this study, a total of 2292 patients with suspected sepsis will be randomly assigned to two arms: the ddPCR group and the control group with a ratio of 3:1. The primary outcome is the diagnostic efficacy, that is, the sensitivity and specificity of the ddPCR assay compared with the synchronous blood culture. Secondary outcomes include the mortality rates and the mean Sequential Organ Failure Assessment (SOFA) score at follow-up time points, the length of stay in the hospital, the time to directed antimicrobial therapy, duration of broad-spectrum antibiotic use, and the EQ-5D-5L score on day 90.

Discussion

It is the first multicenter pragmatic RCT to explore the diagnostic efficacy and clinical impact of the ddPCR assay in patients with suspected sepsis, taking advantage of both RCT’s ability to establish causality and the feasibility of pragmatic approaches in real-world studies (RWS). This trial will help us to get a comprehensive view of the assay’s capacity for precise diagnosis and treatment of sepsis. It has the potential to monitor the pathogen load change and to guide the antimicrobial therapy, making a beneficial impact on the prognosis of sepsis patients.

Trial registration: ClinicalTrial.gov, NCT05190861. Registered January 13, 2022—‘Retrospectively registered’, https://clinicaltrials.gov/ct2/show/NCT05190861.

Site-specific insertion of endonuclease recognition sites into amplicons to improve post-PCR analysis sensitivity of gene mutation

Precise detection of low-frequency gene mutations surrounded by excess wild-type DNA is important in many aspects of medical fields. Most hybridization-based methods for high-resolution mutant allele analysis are hindered by competition of the complementary strand with single-strand probes for the target strand. Here, we demonstrate that site-specific insertion of endonuclease recognition sites into amplicons allows post-PCR generation of short dsDNA or ssDNA, whereby improves the sensitivity of both melting temperature analysis (MTA) and end-point detection following up. Using a three-staged PCR protocol, enrichment of target gene and incorporation of specific restriction sites in amplicons were ensued with hardly any loss in amplification efficiency and specificity. It enables simultaneous discrimination among a panel of totally 11 EGFR 19 exon deletion mutations via MTA after post-PCR digestion by either FokI only or cooperated with CRISPR-Cas12a, using SYBR green I. By replacement of one double-strand cleavage site with a nickase binding domain post-PCR generation of ssDNA of interest via strand displacement amplification (termed as iSDA) is realized. Our preliminary investigation shows that iSDA permits analysis of single nucleotide variants down to 0.1% allelic-frequency using end-point detection. Given the good compatibility with the majority of mutant-enrich PCR methods, we envision it would advance the current gene profiling technologies to a large extent.

High-Throughput Variant Detection Using a Color-Mixing Strategy

Many diseases are related to multiple genetic alterations along a single gene. Probing for highly multiple (>10) variants in a single quantitative PCR tube is not possible because of a limited number of fluorescence channels and one variant per channel, so many more tubes are needed. Herein, a novel color-mixing strategy that uses fluorescence combinations as digital color codes to probe multiple variants simultaneously was experimentally validated. The color-mixing strategy relies on a simple intratube assay that can probe for 15 variants as part of an intertube assay that can probe for an exponentially increased number of variants. This strategy is achieved by using multiplex double-stranded toehold probes modified with fluorophores and quenchers; the probes are designed to be quenched or luminous after binding to wild-type or variant templates. The color-mixing strategy was used to probe for 21 pathogenic variants in thalassemia and to distinguish between heterozygous and homozygous variants in six tubes, with a specificity of 99% and a sensitivity of 94%. To support tuberculosis diagnosis, the same strategy was applied to simultaneously probe in Mycobacterium tuberculosis for rifampicin-resistance mutations occurring within one 81-bp region and one 48-bp region in the rpoB gene, plus five isoniazid-resistance mutations in the inhA and katG genes.

Exosome Processing and Characterization Approaches for Research and Technology Development

Exosomes are extracellular vesicles that share components of their parent cells and are attractive in biotechnology and biomedical research as potential disease biomarkers as well as therapeutic agents. Crucial to realizing this potential is the ability to manufacture high-quality exosomes; however, unlike biologics such as proteins, exosomes lack standardized Good Manufacturing Practices for their processing and characterization. Furthermore, there is a lack of well-characterized reference exosome materials to aid in selection of methods for exosome isolation, purification, and analysis. This review informs exosome research and technology development by comparing exosome processing and characterization methods and recommending exosome workflows. This review also provides a detailed introduction to exosomes, including their physical and chemical properties, roles in normal biological processes and in disease progression, and summarizes some of the on-going clinical trials.

Construction of branched DNA-based nanostructures for diagnosis, therapeutics and protein engineering

Branched DNA with multibranch-like anisotropic topology serves as a promising and powerful building block in constructing multifunctional-integrated nanomaterials in a programmable and controllable manner. Recently, a series of branched DNA-based functional nanomaterials were developed by elaborate molecular design. In this review, we focused on the construction of branched DNA-based nanostructures for biological and biomedical applications. First, the molecular design and synthesis method of branched DNA monomer were briefly described. Then, the construction strategies of branched DNA-based nanostructures were categorially discussed, including target-triggered polymerization, enzymatic extension and hybrid assembly. Finally, the biological and biomedical applications including diagnosis, therapeutics and protein engineering were summarized. We envision that the review will contribute to the further development of branched DNA-based nanomaterials with great application potential in the field of biomedicine, thus building a new bridge between material chemistry and biomedicine.

Designing highly multiplex PCR primer sets with Simulated Annealing Design using Dimer Likelihood Estimation (SADDLE)

One major challenge in the design of highly multiplexed PCR primer sets is the large number of potential primer dimer species that grows quadratically with the number of primers to be designed. Simultaneously, there are exponentially many choices for multiplex primer sequence selection, resulting in systematic evaluation approaches being computationally intractable. Here, we present and experimentally validate Simulated Annealing Design using Dimer Likelihood Estimation (SADDLE), a stochastic algorithm for design of multiplex PCR primer sets that minimize primer dimer formation. In a 96-plex PCR primer set (192 primers), the fraction of primer dimers decreases from 90.7% in a naively designed primer set to 4.9% in our optimized primer set. Even when scaling to 384-plex (768 primers), the optimized primer set maintains low dimer fraction. In addition to NGS, SADDLE-designed primer sets can also be used in qPCR settings to allow highly multiplexed detection of gene fusions in cDNA, with a single-tube assay comprising 60 primers detecting 56 distinct gene fusions recurrently observed in lung cancer.

The design of highly multiplex PCR primers to amplify and enrich many different DNA sequences is increasing in biomedical importance as new mutations and pathogens are identified. The authors present and experimentally validate Simulated Annealing Design using Dimer Likelihood Estimation (SADDLE), a stochastic algorithm for design of highly multiplex PCR primer sets that minimize primer dimer formation.

Discrimination of Single-Nucleotide Variants Based on an Allele-Specific Hybridization Chain Reaction and Smartphone Detection

Massive DNA testing requires novel technologies to support a sustainable health system. In recent years, DNA superstructures have emerged as alternative probes and transducers. We, herein, report a multiplexed and highly sensitive approach based on an allele-specific hybridization chain reaction (AS-HCR) in the array format to detect single-nucleotide variants. Fast isothermal amplification was developed before activating the HCR process on a chip to work with genomic DNA. The assay principle was demonstrated, and the variables for integrating the AS-HCR process and smartphone-based detection were also studied. The results were compared to a conventional polymerase reaction chain (PCR)-based test. The developed multiplex method enabled higher selectivity against single-base mismatch sequences at concentrations as low as 10³ copies with a limit of detection of 0.7% of the mutant DNA percentage and good reproducibility (relative error: 5% for intra-assay and 17% for interassay). As proof of concept, the AS-HCR method was applied to clinical samples, including human cell cultures and biopsied tissues of cancer patients. Accurate identification of single-nucleotide mutations in KRAS and NRAS genes was validated, considering those obtained from the reference sequencing method. To conclude, AS-HCR is a rapid, simple, accurate, and cost-effective isothermal method that detects clinically relevant genetic variants and has a high potential for point-of-care demands.

Plasmonic LAMP: Improving the Detection Specificity and Sensitivity for SARS-CoV-2 by Plasmonic Sensing of Isothermally Amplified Nucleic Acids

The ability to detect pathogens specifically and sensitively is critical to combat infectious diseases outbreaks and pandemics. Colorimetric assays involving loop-mediated isothermal amplification (LAMP) provide simple readouts yet suffer from the intrinsic non-template amplification. Herein, a highly specific and sensitive assay relying on plasmonic sensing of LAMP amplicons via DNA hybridization, termed as plasmonic LAMP, is developed for the severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) RNA detection. This work has two important advances. First, gold and silver (Au-Ag) alloy nanoshells are developed as plasmonic sensors that have 4-times stronger extinction in the visible wavelengths and give a 20-times lower detection limit for oligonucleotides over Au counterparts. Second, the integrated method allows cutting the complex LAMP amplicons into short repeats that are amendable for hybridization with oligonucleotide-functionalized Au-Ag nanoshells. In the SARS-CoV-2 RNA detection, plasmonic LAMP takes ≈75 min assay time, achieves a detection limit of 10 copies per reaction, and eliminates the contamination from non-template amplification. It also shows better detection specificity and sensitivity over commercially available LAMP kits due to the additional sequence identification. This work opens a new route for LAMP amplicon detection and provides a method for virus testing at its early representation.

Stoichiometric approach to quantitative analysis of biomolecules: the case of nucleic acids

Majority of protocols for quantitative analysis of biomarkers (including nucleic acids) require calibrations and target standards. In this work, we developed a principle for quantitative analysis that eliminates the need for a standard of a target molecule. The approach is based on stoichiometric reporting. While stoichiometry is a simple and robust analytical platform, its utility toward the analysis of biomolecules is very limited due to the lack of general methodologies for detecting the equivalence point. In this work, we engineer a new target/probe-binding model that enables detecting the equivalence point while maintaining an appropriate level of specificity. We establish the probe design principles through theoretical simulations and experimental confirmation. Further, we demonstrate the utility of the stoichiometric analysis via a proof-of-concept system based on oligonucleotide hybridization. Overall, the approach that requires neither standard nor calibration yields quantitative results with an adequate accuracy (> 90-110%) and a high specificity. The principles established in our work are very general and can extend beyond oligonucleotide targets toward quantitative analysis of many other biomolecules such as antibodies and proteins.

The CRISPR-Cas toolbox and gene editing technologies

The emergence of CRISPR-Cas systems has accelerated the development of gene editing technologies, which are widely used in the life sciences. To improve the performance of these systems, workers have engineered and developed a variety of CRISPR-Cas tools with a broader range of targets, higher efficiency and specificity, and greater precision. Moreover, CRISPR-Cas-related technologies have also been expanded beyond making cuts in DNA by introducing functional elements that permit precise gene modification, control gene expression, make epigenetic changes, and so on. In this review, we introduce and summarize the characteristics and applications of different types of CRISPR-Cas tools. We discuss certain limitations of current approaches and future prospects for optimizing CRISPR-Cas systems.

Ultra-specific nucleic acid testing by target-activated nucleases

Specific and sensitive detection of nucleic acids is essential to clinical diagnostics and biotechnological applications. Currently, amplification steps are necessary for most detection methods due to the low concentration of nucleic acid targets in real samples. Although amplification renders high sensitivity, poor specificity is prevalent because of the lack of highly accurate precise strategies, resulting in significant false positives and false negatives. Nucleases exhibit high catalytic activity for nucleic acid cleavage which is regulated in a programmable manner. This review focuses on the latest progress in nucleic acid testing methods based on the target-activated nucleases. It summarizes the property of enzymes such as CRISPR/Cas, Argonautes, and some gene-editing irrelevant nucleases, which have been leveraged to create highly specific and sensitive nucleic acid testing tools. We elaborate on recent advances in the field of nuclease-mediated DNA recognition techniques for nucleic acid detection, and discuss its future applications and challenges in molecular diagnostics.

Single-Molecule Detection of SARS-CoV-2 by Plasmonic Sensing of Isothermally Amplified Nucleic Acids

Single-molecule detection of pathogens such as SARS-CoV-2 is key to combat infectious diseases outbreak and pandemic. Currently colorimetric sensing with loop-mediated isothermal amplification (LAMP) provides simple readouts but suffers from intrinsic non-template amplification. Herein, we report that plasmonic sensing of LAMP amplicons via DNA hybridization allows highly specific and single-molecule detection of SARS-CoV-2 RNA. Our work has two important advances. First, we develop gold and silver alloy (Au-Ag) nanoshells as plasmonic sensors that have 4-times stronger extinction in the visible wavelengths and give 20-times lower detection limit for oligonucleotides than Au nanoparticles. Second, we demonstrate that the diagnostic method allows cutting the complex LAMP amplicons into short repeats that are amendable for hybridization with oligonucleotide-functionalized nanoshells. This additional sequence identification eliminates the contamination from non-template amplification. The detection method is a simple and single-molecule diagnostic platform for virus testing at its early representation.

TABLE OF CONTENT

Aplicación del modelo de pérdida de ADN para el diseño de cebadores en Potamotrygon magdalenae (Potamotrygonidae)

El diseño de cebadores es fundamental para amplificar regiones de genes debido a que la especificidad que mantienen cebador-secuencia de interés puede causar el éxito o fracaso en la reacción de PCR. En relación a Potamotrygon magdalenae (especie de interés de acuerdo al PAN Tiburones-Colombia), existe poca información disponible de aspectos relacionados con la genética poblacional de esta Raya. El objetivo del presente trabajo consistió en diseñar cebadores bajo los criterios del Modelo de Pérdida de ADN (DNA-LM), que permitan evaluar el estado genético de las poblaciones de P. magdalenae. Alineamos secuencias de la superfamilia Dayastoidea, disponibles en el NCBI, de los genes mitocondriales Citocromo C Oxidasa 1 (MT-CO1) y Citocromo b (MT-CYB). Se guimos los parámetros Gap open penalty (5), Gap extension penalti (0,2) y Terminal gap penalties (0,1) y seleccionamos dos pares de cebadores de acuerdo con el DNA-LM. Estimamos el producto amplificado del gen MT-CO1 en 916 pb y del gen MT-CYB en 774 pb, en muestras de P. magdalenae procedentes de diferentes ciénagas del Magdalena medio. Discutimos los resultados desde la perspectiva de validar la especificidad de los cebadores diseñados, teniendo en cuenta la correspondencia e identidad de las secuencias de los genes considerados. Los cebadores aquí reportados pueden contribuir a ampliar el conocimiento de la genética poblacional, biogeografía y filogenética de la raya de agua dulce P. magdalenae.

Evaluation of an automated insulated isothermal polymerase chain reaction system for rapid and reliable, on-site detection of African swine fever virus

OBJECTIVE

To evaluate the utility of an automated insulated isothermal PCR (iiPCR) system for rapid and reliable on-site detection of African swine fever virus (ASFV) in swine biological samples.

SAMPLE

Lymph node, tissue homogenate, whole blood, serum, spleen, and tonsil samples collected from swine in North and South Vietnam.

PROCEDURES

Analytic sensitivity of the iiPCR system was determined by serial dilution and analysis of 2 samples (swine tissue homogenate and blood) predetermined to be positive for ASFV. Analytic specificity was assessed by analysis of 2 samples predetermined to be negative for ASFV and positive or negative for other swine pathogens (classical swine fever virus, porcine reproductive and respiratory syndrome virus, foot-and-mouth disease virus, and porcine circovirus type 2). Diagnostic performance of the iiPCR system for detection of ASFV was determined by analysis of the various tissue sample types. For all tests, a real-time PCR assay was used as the reference method.

RESULTS

The iiPCR system was able to detect ASFV in swine blood or tissue homogenate at dilutions up to 10⁶, whereas the real-time PCR assay was able to detect dilutions of up to 10⁵ or 10⁶. The iiPCR system had high analytic specificity for detection of ASFV versus other swine pathogens. Between 97% and 100% agreement was found between results of the iiPCR system for the various tissue samples and results of real-time PCR assay.

CONCLUSIONS AND CLINICAL RELEVANCE

The evaluated iiPCR system was found to be a rapid, reliable, and sample-flexible method for ASFV detection and may be useful for disease surveillance and quarantine in national strategies for early ASF control.

Evaluation of a hybridization capture-based hereditary cancer panel for the ion semiconductor-based next-generation sequencing system

BACKGROUND

There is an unmet need to use the ThermoFisher Ion sequencing platform with a hybridization capture-based next-generation sequencing(NGS) panel. However, the analytical performance of combining an ion semiconductor-based sequencing system and a hybridization capture-based NGS panel has not been thoroughly evaluated. Therefore, we compared the analytic performance of Illumina's NextSeq and Ion S5 XL using a hybridization capture-based target enrichment method.

METHODS

We included 31 clinical samples and NA12878 reference material for comparing two different NGS instruments using a hybridization capture-based panel. The hybridization-based capture hereditary cancer predisposition (HCP) panel was designed for Ion S5 XL Sequencer and Illumina platforms, respectively.

RESULTS

We obtained comparable data involving sequencing run metrics and analytical performance of two different NGS systems using a hybridization-based capture panel designed for each NGS platform. The sensitivity, specificity, and accuracy of single-nucleotide variant and indel calling were 97.06%, 100%, and 100% for the Ion S5™ XL system and 98.53%, 100%, and 100% for NextSeq 550Dx platform, respectively.

CONCLUSIONS

This study demonstrated that a hybrid capture panel kit can be successfully implemented using the ThermoFisher Scientific Ion S5 XL instrument and offers the opportunity to select a variety of hybridization-based capture panels from various manufacturers.

Nucleic Acid Tests for Clinical Translation

Nucleic acids, including deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are natural biopolymers composed of nucleotides that store, transmit, and express genetic information. Overexpressed or underexpressed as well as mutated nucleic acids have been implicated in many diseases. Therefore, nucleic acid tests (NATs) are extremely important. Inspired by intracellular DNA replication and RNA transcription, in vitro NATs have been extensively developed to improve the detection specificity, sensitivity, and simplicity. The principles of NATs can be in general classified into three categories: nucleic acid hybridization, thermal-cycle or isothermal amplification, and signal amplification. Driven by pressing needs in clinical diagnosis and prevention of infectious diseases, NATs have evolved to be a rapidly advancing field. During the past ten years, an explosive increase of research interest in both basic research and clinical translation has been witnessed. In this review, we aim to provide comprehensive coverage of the progress to analyze nucleic acids, use nucleic acids as recognition probes, construct detection devices based on nucleic acids, and utilize nucleic acids in clinical diagnosis and other important fields. We also discuss the new frontiers in the field and the challenges to be addressed.

Empirical evaluation of methods for de novo genome assembly

Technologies for next-generation sequencing (NGS) have stimulated an exponential rise in high-throughput sequencing projects and resulted in the development of new read-assembly algorithms. A drastic reduction in the costs of generating short reads on the genomes of new organisms is attributable to recent advances in NGS technologies such as Ion Torrent, Illumina, and PacBio. Genome research has led to the creation of high-quality reference genomes for several organisms, and de novo assembly is a key initiative that has facilitated gene discovery and other studies. More powerful analytical algorithms are needed to work on the increasing amount of sequence data. We make a thorough comparison of the de novo assembly algorithms to allow new users to clearly understand the assembly algorithms: overlap-layout-consensus and de-Bruijn-graph, string-graph based assembly, and hybrid approach. We also address the computational efficacy of each algorithm's performance, challenges faced by the assem- bly tools used, and the impact of repeats. Our results compare the relative performance of the different assemblers and other related assembly differences with and without the reference genome. We hope that this analysis will contribute to further the application of de novo sequences and help the future growth of assembly algorithms.

Detection of the SARS-CoV-2 D614G mutation using engineered Cas12a guide RNA

Detection of pathogens with single-nucleotide variations is indispensable for the disease tracing, but remains technically challenging. The D614G mutation in the SARS-CoV-2 spike protein is known to markedly enhance viral infectivity but is difficult to detect. Here, we report an effective approach called "synthetic mismatch integrated crRNA guided Cas12a detection" (symRNA-Cas12a) to detect the D614 and G614 variants effectively. Using this method, we systemically screened a pool of crRNAs that contain all the possible nucleotide substitutions covering the -2 to +2 positions around the mutation and identify one crRNA that can efficiently increase the detection specificity by 13-fold over the ancestral crRNA. With this selected crRNA, the symRNA-Cas12a assay can detect as low as 10 copies of synthetic mutant RNA and the results are confirmed to be accurate by Sanger sequencing. Overall, we have developed the symRNA-Cas12a method to specifically, sensitively and rapidly detect the SARS-CoV-2 D614G mutation.

Ultra-fast detection and quantification of nucleic acids by amplification-free fluorescence assay

Two types of clinically important nucleic acid biomarkers, microRNA (miRNA) and circulating tumor DNA (ctDNA) were detected and quantified from human serum using an amplification-free fluorescence hybridization assay. Specifically, miRNAs hsa-miR-223-3p and hsa-miR-486-5p with relevance for rheumatoid arthritis and cancer related mutations BRAF and KRAS of ctDNA were directly measured. The required oligonucleotide probes for the assay were rationally designed and synthesized through a novel "clickable" approach which is time and cost-effective. With no need for isolating nucleic acid components from serum, the fluoresence-based assay took only 1 hour. Detection and absolute quantification of targets was successfully achieved despite their notoriously low abundance, with a precision down to individual nucleotides. Obtained miRNA and ctDNA amounts showed overall a good correlation with current techniques. With appropriate probes, our novel assay and signal boosting approach could become a useful tool for point-of-care measuring other low abundance nucleic acid biomarkers.

Disruptors, a new class of oligonucleotide reagents, significantly improved PCR performance on templates containing stable intramolecular secondary structures

Intramolecular secondary structures within templates have been shown to lower PCR performance. Whereas many approaches have been developed to mitigate such impairment on PCR, their effects can vary greatly depending on template sequences. Here we present a novel, universally effective approach to improve PCR performance involving specifically designed oligonucleotides called disruptors. A disruptor contained three functional components, an anchor designed to initiate template binding, an effector to disrupt intramolecular secondary structure, and a 3' blocker to prevent its elongation by DNA polymerase. A functional mechanism for a disruptor to improve PCR efficiency was proposed where anchor first binds to template followed by effector-mediated strand displacement to unwind intramolecular secondary structure. Such a mechanism was consistent with the observation that anchor played a more critical role for disruptor function. As an example of potential disruptor applications, inverted terminal repeat sequences of recombinant adeno-associated virus vectors were successfully amplified in the presence of disruptors despite their well-known reputation as some of the most difficult templates for PCR amplification and Sanger sequencing due to their ultra-stable T-shaped hairpin structures. In stark contrast, both DMSO and betaine, two PCR additives routinely used to facilitate PCR amplification and Sanger sequencing of GC-rich templates, did not demonstrate any improving effect.

Enhanced asymmetric blocked qPCR method for affordable detection of point mutations in KRAS oncogene

An accurate genetic diagnostic is key for adequate patient management and the suitability of healthcare systems. The scientific challenge lies in developing methods to discriminate those patients with certain genetic variations present in tumor cells at low concentrations. We report a method called enhanced asymmetric blocked qPCR (EAB-qPCR) that promotes the blocker annealing against the primer-template hybrid controlling thermal cycling and reaction conditions with nonmodified oligonucleotides. Real-time fluorescent amplification curves of wild-type alleles were delayed by about eight cycles for EAB-qPCR, compared to conventional blocked qPCR approaches. This method reduced the amplification of native DNA variants (blocking percentage 99.7%) and enabled the effective enrichment of low-level DNA mutations. Excellent performance was estimated for the detection of mutated alleles in sensitivity (up to 0.5% mutant/total DNA) and reproducibility terms, with a relative standard deviation below 2.8%. The method was successfully applied to the mutational analysis of metastatic colorectal carcinoma from biopsied tissues. The determined single-nucleotide mutations in the KRAS oncogene (codon 12-13) totally agreed with those obtained from next-generation sequencing. EAB-qPCR is an accurate cheap method and can be easily incorporated into daily routine to detect mutant alleles. Hence, these features are especially interesting to facilitate the diagnosis and prognosis of several clinical diseases.

Emerging Options for the Diagnosis of Bacterial Infections and the Characterization of Antimicrobial Resistance

Precise and rapid identification and characterization of pathogens and antimicrobial resistance patterns are critical for the adequate treatment of infections, which represent an increasing problem in intensive care medicine. The current situation remains far from satisfactory in terms of turnaround times and overall efficacy. Application of an ineffective antimicrobial agent or the unnecessary use of broad-spectrum antibiotics worsens the patient prognosis and further accelerates the generation of resistant mutants. Here, we provide an overview that includes an evaluation and comparison of existing tools used to diagnose bacterial infections, together with a consideration of the underlying molecular principles and technologies. Special emphasis is placed on emerging developments that may lead to significant improvements in point of care detection and diagnosis of multi-resistant pathogens, and new directions that may be used to guide antibiotic therapy.