Direct electrical detection of DNA synthesis

Molecular Detection of Respiratory Tract Viruses in Chickens at the Point of Need by Loop-Mediated Isothermal Amplification (LAMP)

Accurate and timely molecular diagnosis of respiratory diseases in chickens is essential for implementing effective control measures, preventing the spread of diseases within poultry flocks, minimizing economic loss, and guarding food security. Traditional molecular diagnostic methods like polymerase chain reaction (PCR) require expensive equipment and trained personnel, limiting their use to centralized labs with a significant delay between sample collection and results. Loop-mediated isothermal amplification (LAMP) of nucleic acids offers an attractive alternative for detecting respiratory viruses in broiler chickens with sensitivity comparable to that of PCR. LAMP's main advantages over PCR are its constant incubation temperature (∼65 °C), high amplification efficiency, and contaminant tolerance, which reduce equipment complexity, cost, and power consumption and enable instrument-free tests. This review highlights effective LAMP methods and variants that have been developed for detecting respiratory viruses in chickens at the point of need.

Rapid Detection of Broad-Spectrum Pathogenic Bacteria Based on Highly Sensitive Proton Response of the Nucleic Acid Amplification SPQC Platform

Pathogenic bacteria significantly contribute to elevated morbidity and mortality rates, highlighting the urgent need for early and precise detection. Currently, there is a paucity of effective broad-spectrum methods for detecting pathogenic bacteria. We have developed an innovative proton-responsive series piezoelectric quartz crystal (PR-SPQC) platform for the broad-spectrum identification of pathogenic bacteria. This was achieved by retrieving and aligning sequences from the NCBI GenBank database to identify and validate 16S rRNA oligonucleotide sequences that are signatures of pathogenic bacteria but absent in humans or fungi. The hyperbranched rolling circle amplification, activated exclusively by the screened target, exponentially generates protons that are detected by SPQC through a 2D polyaniline (PANI) film. The PR-SPQC platform demonstrates broad-spectrum capabilities in detecting pathogenic bacteria, with a detection limit of 2 CFU/mL within 90 min. Clinical testing of blood samples yielded satisfactory results. With its advantages in miniaturization, cost efficiency, and suitability for point-of-care testing, PR-SPQC has the potential to be extensively used for the rapid identification of diverse pathogenic bacteria within clinical practice and public health sectors.

Control of interface functions in solid-state biosensors for stable detection of molecular recognition

Significant progress has been achieved in the field of solid-state biosensors over the past 50 years. Various sensing devices with high-density integration and flexible configuration, as well as new applications for clinical diagnosis and healthcare, have been developed using blood, serum, and other body fluids such as sweat, tears, and saliva. A high-density array of ion-sensitive field effect transistors was developed by exploiting the advantages of advanced semiconductor technologies and commercialized in combination with an enzymatic primer extension reaction as a DNA sequencer in 2011. Different types of materials such as inorganic materials, metals, polymers, and biomolecules are mixed together on the surface of the gate while maintaining their own functions; therefore, compatibility among different materials has to be optimized so that the best detection performance of solid-state biosensors, including stability and reliability, is achieved as designed. Solid-state biosensors are suitable for the rapid, cost-effective, and noninvasive identification of biomarkers at various timepoints over the course of a disease.

Modified cytosines versus cytosine in a DNA polymerase: retrieving thermodynamic and kinetic constants at the single molecule level

DNA methylation plays key roles in various areas, such as gene expression, regulation, epigenetics, and cancers. Since 5-methylcytosine (5mC) is commonly present in methylated DNA, characterizing the binding kinetics and thermodynamics of the nucleotide to the enzymatic pocket can help to understand the DNA replication process. Furthermore, 5-carboxycytosine (5caC) is a form that appears through the iterative oxidation of 5mC, and its effect on the DNA replication process is still not well known. Here, we immobilized a DNA polymerase (DNAP) with an orientation control on a tip of an atomic force microscope (AFM), and observed the interaction between the immobilized deoxyguanosine triphosphate (dGTP) on the surface and the DNAP in the presence of a DNA duplex. The interaction probability increased as the concentration of the DNA strand, and the affinity constant between the DNAP and DNA was obtained by fitting the change. Increasing the concentration of dGTP in solution diminished the interaction probability, and a fitting allowed us to retrieve the affinity constant between dGTP and the DNAP holding the DNA in the reaction pocket. Because the dissociation constant could be obtained through the loading rate dependence of the unbinding force value, both affinity and kinetic constants for cytosine (C), 5mC, and 5caC in the DNAP were compared in the light of the steric and electronic effect of the substituents at 5-position of cytosine.

Nitronyl nitroxide monoradical TEMPO as new electrochemical label for ultrasensitive detection of nucleic acids

In this work, a novel electrochemical biosensor based on nitronyl nitroxide monoradical 2,2,6,6-tetramethylpiperidine 1-Oxyl (TEMPO) as new electrochemical label for facile nucleic acids detection is developed. This fast and convenient functional microelectrode was designed by fixing the capture probe peptide nucleic acid (PNA) and using the coordination interaction of Zr⁴⁺ with both phosphate groups and carboxyl groups. Differential pulse voltammetry (DPV) was used to study the oxidation current of TEMPO which was combined with the electrode surface and labeled. TEMPO electrochemical signal related to target deoxyribonucleic acid (tDNA) concentration was finally detected when tDNA was added on the surface of glassy carbon electrode (GCE). The detection principle, optimization of key factors and performance analysis of the biosensor are also discussed. A great linear relation is acquired within the scope of 10 pM-100 nM under optimal conditions and the detection limit of this experiment is calculated as low as 2.57 pM (R² = 0.996). In addition, complex serum samples were used to explore the practical application of this experiment. The results show the developed electrochemical DNA biosensor has wide application prospects in nucleic acids detection and clinical analysis.

Clinical Massively Parallel Sequencing

BACKGROUND

The newest advances in DNA sequencing are based on technologies that perform massively parallel sequencing (MPS). Since 2006, the output from MPS platforms has increased from 20 Mb to >7 Tb. First-generation MPS platforms amplify individual DNA molecules to multiple copies and then interrogate the sequence of those molecules. Second-generation MPS analyzes single unamplified molecules to generate much longer sequence reads but with less output than first-generation MPS and lower first-pass accuracy. With MPS technologies, it is now possible to analyze genomes, exomes, a defined subset of genes, transcriptomes, and even methylation across the genome. These technologies have and will continue to completely transform the clinical practice.

CONTENT

The major first- and second-generation MPS platforms and how they are used in clinical practice are discussed.

SUMMARY

The ability to sequence terabases of DNA per run on an MPS platform will dramatically change how DNA sequencing is used in clinical practice. Currently, MPS of targeted gene panels is the most common use of this technology clinically, but as the cost for genome sequencing inches downward to $100, this may soon become the method of choice (with the caveat that, at least in the near term, clinical-grade genome sequencing with interpretation may cost much more than $100). Other uses of this technology include sequencing of a mixture of bacterial and viral species (metagenomics), as well as the characterization of methylation across the genome.

Scalable Nanogap Sensors for Non-Redox Enzyme Assays

Clinical diagnostic assays that monitor redox enzyme activity are widely used in small, low-cost readout devices for point-of-care monitoring (e.g., a glucometer); however, monitoring non-redox enzymes in real-time using compact electronic devices remains a challenge. We address this problem by using a highly scalable nanogap sensor array to observe electrochemical signals generated by a model non-redox enzyme system, the DNA polymerase-catalyzed incorporation of four modified, redox-tagged nucleotides. Using deoxynucleoside triphosphates (dNTPs) tagged with para-aminophenyl monophosphate (pAPP) to form pAP-deoxyribonucleoside tetra-phosphates (AP-dN4Ps), incorporation of the nucleotide analogs by DNA polymerase results in the release of redox inactive pAP-triphosphates (pAPP₃) that are converted to redox active small molecules para-aminophenol (pAP) in the presence of phosphatase. In this work, cyclic enzymatic reactions that generated many copies of pAP at each base incorporation site of a DNA template in combination with the highly confined nature of the planar nanogap transducers ( z = 50 nm) produced electrochemical signals that were amplified up to 100,000×. We observed that the maximum signal level and amplification level were dependent on a combination of factors including the base structure of the incorporated nucleotide analogs, nanogap electrode materials, and electrode surface coating. In addition, electrochemical signal amplification by redox cycling in the nanogap is independent of the in-plane geometry of the transducer, thus allowing the nanogap sensors to be highly scalable. Finally, when the DNA template concentration was constrained, the DNA polymerase assay exhibited different zero-order reaction kinetics for each type of base incorporation reaction, resolving the closely related nucleotide analogs.

Targeted next-generation sequencing of 50 cancer-related genes in Japanese patients with oral squamous cell carcinoma

Somatic mutation analysis is a standard of practice for human cancers to identify therapeutic sensitization and resistance mutations. We performed a multigene sequencing screen to explore mutational hotspots in cancer-related genes using a semiconductor-based sequencer. DNA from oral squamous cell carcinoma samples was used as a template to amplify 207 regions from 50 cancer-related genes. Of the 80 oral squamous cell carcinoma specimens from Japanese patients, including formalin-fixed paraffin-embedded samples, 56 specimens presented at least one somatic mutation among the 50 investigated genes, and 17 of these samples showed multiple gene somatic mutations. TP53 was the most commonly mutated gene (50.0%), followed by CDKN2A (16.3%), PIK3CA (7.5%), HRAS (5.0%), MET (2.5%), and STK11 (2.5%). In total, 32 cases (40.0%) were human papillomavirus positive and they were significantly less likely to have a TP53, mutation than human papillomavirus-negative oral squamous cell carcinomas (8/32, 25.0% vs 32/48, 66.7%, p = 0.00026). We also detected copy number variations, in which segments of the genome could be duplicated or deleted from the sequencing data. We detected the tumor-specific TP53 mutation in the plasma cell-free DNA from two oral squamous cell carcinoma patients, and after surgery, the test for these mutations became negative. Our approach facilitates the simultaneous high-throughput detection of somatic mutations and copy number variations in oral squamous cell carcinoma samples.

Profiling cancer-related gene mutations in oral squamous cell carcinoma from Japanese patients by targeted amplicon sequencing

Somatic mutation analysis is a standard practice in the study of human cancers to identify mutations that cause therapeutic sensitization and resistance. We performed comprehensive genomic analyses that used PCR target enrichment and next-generation sequencing on Ion Proton semiconductor sequencers. Forty-seven oral squamous cell carcinoma (OSCC) samples and their corresponding noncancerous tissues were used for multiplex PCR amplification to obtain targeted coverage of the entire coding regions of 409 cancer-related genes (covered regions: 95.4% of total, 1.69 megabases of target sequence). The number of somatic mutations in 47 patients with OSCC ranged from 1 to 20 with a mean of 7.60. The most frequent mutations were in TP53 (61.7%), NOTCH1 (25.5%), CDKN2A (19.1%), SYNE1 (14.9%), PIK3CA (10.6%), ROS1 (10.6%), and TAF1L (10.6%). We also detected copy number variations (CNVs) in the segments of the genome that could be duplicated or deleted from deep sequencing data. Pathway assessment showed that the somatic aberrations within OSCC genomes are mainly involved in several important pathways, including cell cycle regulation and RTK–MAPK-PI3K. This study may enable better selection of therapies and deliver improved outcomes for OSCC patients when combined with clinical diagnostics.

Detection of microRNA: A Point-of-Care Testing Method Based on a pH-Responsive and Highly Efficient Isothermal Amplification

Laborious and costly detection of miRNAs has brought challenges to its practical applications, especially for home health care, rigorous military medicine, and the third world. In this work, we present a pH-responsive miRNA amplification method, which allows the detection of miRNA just using a pH test paper. The operation is easy and no other costly instrument is involved, making the method very friendly. In our strategy, a highly efficient isothermal amplification of miRNA is achieved using an improved netlike rolling circle amplification (NRCA) technique. Large amounts of H⁺ can be produced as a byproduct during the amplification to induce significant changes of pH, which can be monitored directly using a pH test paper or pH-sensitive indicators. The degree of color changes depends on the amount of miRNA, making it possible for quantitative analysis. As an example, the method is successfully applied to quantify a miRNA (miR-21) in cancer cells. The results agree well with that from the prevalent qRT-PCR analysis. It is the first time that a paper-based point-of-care testing (POCT) is developed for the detection of miRNAs, which might promote the popularization of miRNAs working as biomarkers for diagnostic purposes.

Rapid Detection of Candida albicans by Polymerase Spiral Reaction Assay in Clinical Blood Samples

Candida albicans is the most common human yeast pathogen which causes mucosal infections and invasive fungal diseases. Early detection of this pathogen is needed to guide preventative and therapeutic treatment. The aim of this study was to establish a polymerase spiral reaction (PSR) assay that rapidly and accurately detects C. albicans and to assess the clinical applicability of PSR-based diagnostic testing. Internal transcribed spacer 2 (ITS2), a region between 5.8S and 28S fungal ribosomal DNA, was used as the target sequence. Four primers were designed for amplification of ITS2 with the PSR method, which was evaluated using real time turbidity monitoring and visual detection using a pH indicator. Fourteen non-C. albicans yeast strains were negative for detection, which indicated the specificity of PSR assay was 100%. A 10-fold serial dilution of C. albicans genomic DNA was subjected to PSR and conventional polimerase chain reaction (PCR) to compare their sensitivities. The detection limit of PSR was 6.9 pg/μl within 1 h, 10-fold higher than that of PCR (69.0 pg/μl). Blood samples (n = 122) were collected from intensive care unit and hematological patients with proven or suspected C. albicans infection at two hospitals in Beijing, China. Both PSR assay and the culture method were used to analyze the samples. Of the 122 clinical samples, 34 were identified as positive by PSR. The result was consistent with those obtained by the culture method. In conclusion, a novel and effective C. albicans detection assay was developed that has a great potential for clinical screening and point-of-care testing.

Genomic characterization of esophageal squamous cell carcinoma: Insights from next-generation sequencing

Two major types of cancer occur in the esophagus: squamous cell carcinoma, which is associated with chronic smoking and alcohol consumption, and adenocarcinoma, which typically arises in gastric reflux-associated Barrett's esophagus. Although there is increasing incidence of esophageal adenocarcinoma in Western counties, esophageal squamous cell carcinoma (ESCC) accounts for most esophageal malignancies in East Asia, including China and Japan. Technological advances allowing for massively parallel, high-throughput next-generation sequencing (NGS) of DNA have enabled comprehensive characterization of somatic mutations in large numbers of tumor samples. Recently, several studies were published in which whole exome or whole genome sequencing was performed in ESCC tumors and compared with matched normal DNA. Mutations were validated in several genes, including in TP53, CDKN2A, FAT1, NOTCH1, PIK3CA, KMT2D and NFE2L2, which had been previously implicated in ESCC. Several new recurrent alterations have also been identified in ESCC. Combining the clinicopathological characteristics of patients with information obtained from NGS studies may lead to the development of effective diagnostic and therapeutic approaches for ESCC. As this research becomes more prominent, it is important that gastroenterologist become familiar with the various NGS technologies and the results generated using these methods. In the present study, we describe recent research approaches using NGS in ESCC.

Identification of Genetic Mutations in Human Lung Cancer by Targeted Sequencing

Lung cancer remains the most prevalent malignancy and the primary cause of cancer-related deaths worldwide. Unique mutations patterns can be found in lung cancer subtypes, in individual cancers, or within a single tumor, and drugs that target these genetic mutations and signal transduction pathways are often beneficial to patients. In this study, we used the Ion Torrent AmpliSeq Cancer Panel to sequence 737 loci from 45 cancer-related genes and oncogenes to identify genetic mutations in 48 formalin-fixed, paraffin-embedded (FFPE) human lung cancer samples from Chinese patients. We found frequent mutations in EGFR, KRAS, PIK3CA, and TP53 genes. Moreover, we observed that a portion of the lung cancer samples harbored two or more mutations in these key genes. This study demonstrates the feasibility of using the Ion Torrent sequencing to efficiently identify genetic mutations in individual tumors for targeted lung cancer therapy.

A Dual-Mode Large-Arrayed CMOS ISFET Sensor for Accurate and High-Throughput pH Sensing in Biomedical Diagnosis

GOAL

The existing ISFET-based DNA sequencing detects hydrogen ions released during the polymerization of DNA strands on microbeads, which are scattered into microwell array above the ISFET sensor with unknown distribution. However, false pH detection happens at empty microwells due to crosstalk from neighboring microbeads. In this paper, a dual-mode CMOS ISFET sensor is proposed to have accurate pH detection toward DNA sequencing.

METHODS

Dual-mode sensing, optical and chemical modes, is realized by integrating a CMOS image sensor (CIS) with ISFET pH sensor, and is fabricated in a standard 0.18-μm CIS process. With accurate determination of microbead physical locations with CIS pixel by contact imaging, the dual-mode sensor can correlate local pH for one DNA slice at one location-determined microbead, which can result in improved pH detection accuracy. Moreover, toward a high-throughput DNA sequencing, a correlated-double-sampling readout that supports large array for both modes is deployed to reduce pixel-to-pixel nonuniformity such as threshold voltage mismatch.

RESULTS

The proposed CMOS dual-mode sensor is experimentally examined to show a well correlated pH map and optical image for microbeads with a pH sensitivity of 26.2 mV/pH, a fixed pattern noise (FPN) reduction from 4% to 0.3%, and a readout speed of 1200 frames/s.

CONCLUSION

A dual-mode CMOS ISFET sensor with suppressed FPN for accurate large-arrayed pH sensing is proposed and demonstrated with state-of-the-art measured results toward accurate and high-throughput DNA sequencing.

SIGNIFICANCE

The developed dual-mode CMOS ISFET sensor has great potential for future personal genome diagnostics with high accuracy and low cost.

Visual detection of isothermal nucleic acid amplification using pH-sensitive dyes

Nucleic acid amplification is the basis for many molecular diagnostic assays. In these cases, the amplification product must be detected and analyzed, typically requiring extended workflow time, sophisticated equipment, or both. Here we present a novel method of amplification detection that harnesses the pH change resulting from amplification reactions performed with minimal buffering capacity. In loop-mediated isothermal amplification (LAMP) reactions, we achieved rapid (<30 min) and sensitive (<10 copies) visual detection using pH-sensitive dyes. Additionally, the detection can be performed in real time, enabling high-throughput or quantitative applications. We also demonstrate this visual detection for another isothermal amplification method (strand-displacement amplification), PCR, and reverse transcription LAMP (RT-LAMP) detection of RNA. The colorimetric detection of amplification presented here represents a generally applicable approach for visual detection of nucleic acid amplification, enabling molecular diagnostic tests to be analyzed immediately without the need for specialized and expensive instrumentation.

Frequent KIT mutations in human gastrointestinal stromal tumors

Identifying gene mutations in individual tumors is critical to improve the efficacy of cancer therapy by matching targeted drugs to specific mutations. Gastrointestinal stromal tumors (GIST) are stromal or mesenchymal subepithelial neoplasms affecting the gastrointestinal tract and frequently contain activating gene mutations in either KIT or platelet-derived growth factor A (PDGFRA). Although GIST is highly responsive to several selective tyrosine kinase inhibitors, combined use of inhibitors targeting other mutations is needed to further prolong survival in patients with GIST. In this study, we aim to screen and identify genetic mutations in GIST for targeted therapy using the new Ion Torrent next-generation sequencing platform. Utilizing the Ion Ampliseq Cancer Panel, we sequenced 737 loci from 45 cancer-related genes using DNA extracted from formalin-fixed and paraffin-embedded (FFPE) samples of 121 human gastrointestinal stromal tumors, set up stringent parameters for reliable variant calling by filtering out potential raw base calling errors, and identified frequent mutations in the KIT gene. This study demonstrates the utility of using Ion Torrent sequencing to efficiently identify human cancer mutations. This may provide a molecular basis for clinically developing new drugs targeting these gene mutations for GIST therapy.

Genetic mutation analysis of human gastric adenocarcinomas using ion torrent sequencing platform

Gastric cancer is the one of the major causes of cancer-related death, especially in Asia. Gastric adenocarcinoma, the most common type of gastric cancer, is heterogeneous and its incidence and cause varies widely with geographical regions, gender, ethnicity, and diet. Since unique mutations have been observed in individual human cancer samples, identification and characterization of the molecular alterations underlying individual gastric adenocarcinomas is a critical step for developing more effective, personalized therapies. Until recently, identifying genetic mutations on an individual basis by DNA sequencing remained a daunting task. Recent advances in new next-generation DNA sequencing technologies, such as the semiconductor-based Ion Torrent sequencing platform, makes DNA sequencing cheaper, faster, and more reliable. In this study, we aim to identify genetic mutations in the genes which are targeted by drugs in clinical use or are under development in individual human gastric adenocarcinoma samples using Ion Torrent sequencing. We sequenced 737 loci from 45 cancer-related genes in 238 human gastric adenocarcinoma samples using the Ion Torrent Ampliseq Cancer Panel. The sequencing analysis revealed a high occurrence of mutations along the TP53 locus (9.7%) in our sample set. Thus, this study indicates the utility of a cost and time efficient tool such as Ion Torrent sequencing to screen cancer mutations for the development of personalized cancer therapy.

Noise limits of CMOS current interfaces for biosensors: a review

Current sensing readout is one of the most frequent techniques used in biosensing due to the charge-transfer phenomena occurring at solid-liquid interfaces. The development of novel nanodevices for biosensing determines new challenges for electronic interface design based on current sensing, especially when compact and efficient arrays need to be organized, such as in recent trends of rapid label-free electronic detection of DNA synthesis. This paper will review the basic noise limitations of current sensing interfaces with particular emphasis on integrated CMOS technology. Starting from the basic theory, the paper presents, investigates and compares charge-sensitive amplifier architectures used in both continuous-time and discrete-time approaches, along with their design trade-offs involving noise floor, sensitivity to stray capacitance and bandwidth. The ultimate goal of this review is providing analog designers with helpful design rules and analytical tools. Also, in order to present a comprehensive overview of the state-of-the-art, the most relevant papers recently appeared in the literature about this topic are discussed and compared.

Nanotextured superhydrophobic electrodes enable detection of attomolar-scale DNA concentration within a droplet by non-faradaic impedance spectroscopy

Label-free, rapid detection of biomolecules in microliter volumes of highly diluted solutions (sub-femtomolar) is of essential importance for numerous applications in medical diagnostics, food safety, and chem-bio sensing for homeland security. At ultra-low concentrations, regardless of the sensitivity of the detection approach, the sensor response time is limited by physical diffusion of molecules towards the sensor surface. We have developed a fast, low cost, non-faradaic impedance sensing method for detection of synthetic DNA molecules in DI water at attomolar levels by beating the diffusion limit through evaporation of a micro-liter droplet of DNA on a nanotextured superhydrophobic electrode array. Continuous monitoring of the impedance of individual droplets as a function of evaporation time is exploited to dramatically improve the sensitivity and robustness of detection. Formation of the nanostructures on the electrode surface not only increases the surface hydrophobicity, but also allows robust pinning of the droplet contact area to the sensor surface. These two features are critical for performing highly stable impedance measurements as the droplet evaporates. Using this scheme, the detection limit of conventional non-faradaic methods is improved by five orders of magnitude. The proposed platform represents a step-forward towards realization of ultra-sensitive lab-on-chip biomolecule detectors for real time point-of-care application. Further works are however needed to ultimately realize the full potential of the proposed approach to appraise biological samples in complex buffer solutions rather than in DI water.

The Sequencing Bead Array (SBA), a next-generation digital suspension array

Here we describe the novel Sequencing Bead Array (SBA), a complete assay for molecular diagnostics and typing applications. SBA is a digital suspension array using Next-Generation Sequencing (NGS), to replace conventional optical readout platforms. The technology allows for reducing the number of instruments required in a laboratory setting, where the same NGS instrument could be employed from whole-genome and targeted sequencing to SBA broad-range biomarker detection and genotyping. As proof-of-concept, a model assay was designed that could distinguish ten Human Papillomavirus (HPV) genotypes associated with cervical cancer progression. SBA was used to genotype 20 cervical tumor samples and, when compared with amplicon pyrosequencing, was able to detect two additional co-infections due to increased sensitivity. We also introduce in-house software Sphix, enabling easy accessibility and interpretation of results. The technology offers a multi-parallel, rapid, robust, and scalable system that is readily adaptable for a multitude of microarray diagnostic and typing applications, e.g. genetic signatures, single nucleotide polymorphisms (SNPs), structural variations, and immunoassays. SBA has the potential to dramatically change the way we perform probe-based applications, and allow for a smooth transition towards the technology offered by genomic sequencing.

Simultaneous DNA amplification and detection using a pH-sensing semiconductor system

We developed an integrated chip for real-time amplification and detection of nucleic acid using pH-sensing complementary metal-oxide semiconductor (CMOS) technology. Here we show an amplification-coupled detection method for directly measuring released hydrogen ions during nucleotide incorporation rather than relying on indirect measurements such as fluorescent dyes. This is a label-free, non-optical, real-time method for detecting and quantifying target sequences by monitoring pH signatures of native amplification chemistries. The chip has ion-sensitive field effect transistor (ISFET) sensors, temperature sensors, resistive heating, signal processing and control circuitry all integrated to create a full system-on-chip platform. We evaluated the platform using two amplification strategies: PCR and isothermal amplification. Using this platform, we genotyped and discriminated unique single-nucleotide polymorphism (SNP) variants of the cytochrome P450 family from crude human saliva. We anticipate this semiconductor technology will enable the creation of devices for cost-effective, portable and scalable real-time nucleic acid analysis.

Translating genomics to the clinic: implications of cancer heterogeneity

BACKGROUND

Sequencing of cancer genomes has become a pivotal method for uncovering and understanding the deregulated cellular processes driving tumor initiation and progression. Whole-genome sequencing is evolving toward becoming less costly and more feasible on a large scale; consequently, thousands of tumors are being analyzed with these technologies. Interpreting these data in the context of tumor complexity poses a challenge for cancer genomics.

CONTENT

The sequencing of large numbers of tumors has revealed novel insights into oncogenic mechanisms. In particular, we highlight the remarkable insight into the pathogenesis of breast cancers that has been gained through comprehensive and integrated sequencing analysis. The analysis and interpretation of sequencing data, however, must be considered in the context of heterogeneity within and among tumor samples. Only by adequately accounting for the underlying complexity of cancer genomes will the potential of genome sequencing be understood and subsequently translated into improved management of patients.

SUMMARY

The paradigm of personalized medicine holds promise if patient tumors are thoroughly studied as unique and heterogeneous entities and clinical decisions are made accordingly. Associated challenges will be ameliorated by continued collaborative efforts among research centers that coordinate the sharing of mutation, intervention, and outcomes data to assist in the interpretation of genomic data and to support clinical decision-making.

Rapid detection of the ACMG/ACOG-recommended 23 CFTR disease-causing mutations using ion torrent semiconductor sequencing

Cystic fibrosis (CF) is one of the most frequently diagnosed autosomal-recessive diseases in the Caucasian population. For general-population CF carrier screening, the American College of Medical Genetics (ACMG)/American College of Obstetricians and Gynecologists (ACOG) have recommended a core panel of 23 mutations that will identify 49-98% of carriers, depending on ethnic background. Using a genotyping technology that can rapidly identify disease-causing mutations is important for high-throughput general-population carrier screening, confirming clinical diagnosis, determining treatment options, and prenatal diagnosis. Here, we describe a proof-of-concept study to determine whether the Ion Torrent Personal Genome Machine (PGM) sequencer platform can reliably identify all ACMG/ACOG 23 CF transmembrane conductance regulator (CFTR) mutations. A WT CF specimen along with mutant DNA specimens representing all 23 CFTR mutations were sequenced bidirectionally on the Ion Torrent 314 chip to determine the accuracy of the PGM for CFTR variant detection. We were able to reliably identify all of the targeted mutations except for 2184delA, which lies in a difficult, 7-mer homopolymer tract. Based on our study, we believe PGM sequencing may be a suitable technology for identifying CFTR mutations in the future. However, as a result of the elevated rate of base-calling errors within homopolymer stretches, mutations within such regions currently need to be evaluated carefully using an alternative method.

Stepping stones in DNA sequencing

In recent years there have been tremendous advances in our ability to rapidly and cost-effectively sequence DNA. This has revolutionized the fields of genetics and biology, leading to a deeper understanding of the molecular events in life processes. The rapid technological advances have enormously expanded sequencing opportunities and applications, but also imposed strains and challenges on steps prior to sequencing and in the downstream process of handling and analysis of these massive amounts of sequence data. Traditionally, sequencing has been limited to small DNA fragments of approximately one thousand bases (derived from the organism's genome) due to issues in maintaining a high sequence quality and accuracy for longer read lengths. Although many technological breakthroughs have been made, currently the commercially available massively parallel sequencing methods have not been able to resolve this issue. However, recent announcements in nanopore sequencing hold the promise of removing this read-length limitation, enabling sequencing of larger intact DNA fragments. The ability to sequence longer intact DNA with high accuracy is a major stepping stone towards greatly simplifying the downstream analysis and increasing the power of sequencing compared to today. This review covers some of the technical advances in sequencing that have opened up new frontiers in genomics.

Biochemistry and semiconductor electronics--the next big hit for silicon?

Two recent developments portend a new era for silicon electronics in biomedical applications. Firstly, highly specific chemical recognition and massively parallel sample preparation techniques are being combined with VLSI to make new kinds of analytical chips. Secondly, critical dimensions are beginning to approach the size of biomolecules, opening new pathways for physical interactions between molecules and semiconductor structures. Future generations of hybrid chemical-CMOS devices could revolutionize diagnosis and make personalized medicine cheap enough to become widespread.

Toward the single-hour high-quality genome

Today, resequencing of a human genome can be performed in approximately a week using a single instrument. Thanks to a steady logarithmic rate of increase in performance for DNA sequencing platforms over the past seven years, DNA sequencing is one of the fastest developing technology fields. As the process becomes faster, it opens up possibilities within health care, diagnostics, and entirely new fields of research. Immediate genetic characterization of contagious outbreaks has been exemplified, and with such applications for the direct benefit of human health, expectations of future sensitive, rapid, high-throughput, and cost-effective technologies are steadily growing. Simultaneously, some of the limitations of a rapidly growing field have become apparent, and questions regarding the quality of some of the data deposited into databases have been raised. A human genome sequenced in only an hour is likely to become a reality in the future, but its definition may not be as certain.

Assemblathon 1: a competitive assessment of de novo short read assembly methods

Low-cost short read sequencing technology has revolutionized genomics, though it is only just becoming practical for the high-quality de novo assembly of a novel large genome. We describe the Assemblathon 1 competition, which aimed to comprehensively assess the state of the art in de novo assembly methods when applied to current sequencing technologies. In a collaborative effort, teams were asked to assemble a simulated Illumina HiSeq data set of an unknown, simulated diploid genome. A total of 41 assemblies from 17 different groups were received. Novel haplotype aware assessments of coverage, contiguity, structure, base calling, and copy number were made. We establish that within this benchmark: (1) It is possible to assemble the genome to a high level of coverage and accuracy, and that (2) large differences exist between the assemblies, suggesting room for further improvements in current methods. The simulated benchmark, including the correct answer, the assemblies, and the code that was used to evaluate the assemblies is now public and freely available from http://www.assemblathon.org/.

Assemblathon 1: a competitive assessment of de novo short read assembly methods

Low-cost short read sequencing technology has revolutionized genomics, though it is only just becoming practical for the high-quality de novo assembly of a novel large genome. We describe the Assemblathon 1 competition, which aimed to comprehensively assess the state of the art in de novo assembly methods when applied to current sequencing technologies. In a collaborative effort, teams were asked to assemble a simulated Illumina HiSeq data set of an unknown, simulated diploid genome. A total of 41 assemblies from 17 different groups were received. Novel haplotype aware assessments of coverage, contiguity, structure, base calling, and copy number were made. We establish that within this benchmark: (1) It is possible to assemble the genome to a high level of coverage and accuracy, and that (2) large differences exist between the assemblies, suggesting room for further improvements in current methods. The simulated benchmark, including the correct answer, the assemblies, and the code that was used to evaluate the assemblies is now public and freely available from http://www.assemblathon.org/.

The power of NGS technologies to delineate the genome organization in cancer: from mutations to structural variations and epigenetic alterations

The development of cancer is characterized by the joined occurrence of alterations on different levels--from single nucleotide changes via structural and copy number variations to epigenetic alterations. With the advent of advanced technologies such as next generation sequencing, we have now the tools in hands to put some light on complex processes and recognize systematic patterns that develop throughout cancer progression. The combination of single hypothesis-driven experiments with a system-wide genetic view enables us to prove so far not addressable questions such as the influence of DNA methylation on gene expression or the disruption of genome homeostasis by structural variations and miRNA expression patterns. Out of this enormous amount of information, specific biomarkers for cancer progression have been discovered, which pave the way for the development of new therapeutic strategies. Here, we will review the status quo of integrative cancer genomic approaches, give an overview over the power of next generation sequencing technologies in oncology, and outline future perspective. Both sides--clinical as well as basic research aspects--will be considered.

Electric detection of DNA with PDMS microgap electrodes and silver nanoparticles

In this work a novel microdevice sensor has been developed by plating gold on the PDMS surface to generate a sandwich-type gap electrode for DNA detection. The microdevice utilizes a gold band electrode-PDMS-gold band electrode configuration and the minimum detectable volume could be as low as 5 μL. The 20 μm PDMS-based gap was chemically modified with DNA capture probes and DNA sandwich hybrids were formed with the addition of DNA target and silver nanoparticle probes. To increase detection sensitivity, parallel detection zones have been developed in which the relevant resistances decrease substantially upon hybridyzation. By measuring the change in electrical conductivity, the DNA target in the concentration range of 1000-0.1 nM can be assayed and the limit of lowest detectable concentration was achieved at 0.01 nM.

Electrochemical detection of oligonucleotide by attaching redox probes onto its backbone

An approach was demonstrated to detect oligonucleotide by attaching redox probes onto its backbone. First, peptide nucleic acid (PNA) with a neutral backbone was immobilized onto a gold (Au) electrode surface as a capture. Second, when the PNA capture hybridized with a target oligonucleotide (a short DNA), an assembly of Au-PNA-DNA formed and phosphate groups were thus brought into the assembly from the DNA's backbone. The linker ion of Zr(4+) exhibits a strong coordination interaction with the phosphate group and the carboxylic group. The hybridized target DNA provides the phosphate group while a derivatized redox probe of ferrocene (Fc) carboxyl acid offers the carboxylic group. Therefore, the redox probe can be attached to the phosphate group by the linker to form an assembly of Au-PNA-DNA-Zr-Fc. Its redox process was studied and the detection conditions of oligonucleotide were optimized. A limit of detection of 1.0×10(-12) M or ∼2 attomol was reached.

Electrical detection of oligonucleotide using an aggregate of gold nanoparticles as a conductive tag

Sequence-specific DNA detection is a routine job in medical diagnostics and genetic screening. Alternative to a fluorescence readout scheme or electrophoresis approach, various kinds of rapid, low-cost, facile, and label-free methods have also been developed in last decades. Among these, direct electrical detection of DNA received increasing attention but more research is desirable. Particularly, enhancement with high discrimination must be employed to selectively amplify the responding signal. A chip-based biosensor was developed in this work to electrically detect 22-mer oligonucleotide DNA at low concentration, from 50 fM to 10 pM. First, a gold nanoparticle (NP) was capped with 3-mercaptopropionic acid through a thiol-gold bond. The derivatized carboxylic acid group showed strong complex interaction with an inorganic linker, Zr(4+). As a result, Zr(4+) could link several hundreds of individual gold NPs together to form an aggregate of nanoparticles (ANP), which was capable of being used as a conductive tag for the electrical detection of DNA. Second, in order to achieve the discriminative localization of ANP to bridge two comb-shaped electrodes (with height of approximately 50 nm and interdistance of 300-350 nm) gapped with insulative material of silicon oxide, peptide nucleic acids were covalently bonded to the silicon oxide in the gap as capture sites for DNA. After hybridization with target DNA, the charged phosphate-containing backbone of DNA was introduced into the gap. Phosphate groups also exhibited strong complex interaction with the linker of Zr(4+) and could react with the residual Zr(4+) on the ANP surface. As a consequence, the conductive tags were linked to the phosphate groups and localized into the gap, which could modify the conductance between the two comb-shaped electrodes in turn. The degree of modification correlated directly to the amount of hybridized DNA and to the concentration of target DNA in sample solution. Compared with the individual NPs used as the tag, a strong enhancement from the gold ANP was obtained.

Electron transfer mediating properties of hydrocarbons as a function of chain length: a differential scanning conductive tip atomic force microscopy investigation

The development of novel molecular and biomolecular devices relies on the understanding of charge transport across molecule-substrate interfaces. However, different strategies adopted so far for fabricating and studying transport through metal-molecule-metal junctions yield values for the transport coefficients that differ by up to orders of magnitude even for the same junction. Conductive tip atomic force microscopy (CT-AFM) allows for the simultaneous measurement of transport and morphological properties of molecular assemblies, but absolute transport measurements depend on the nature of the AFM tip-molecule contact. In this work we present a differential approach to the study of metal-molecule-metal junctions based on the combination of AFM-driven nanolithography and CT-AFM. We nanograft patches of alkanethiol molecules in a self-assembled monolayer of alkanethiol molecules of different chain length and measure by CT-AFM the morphology and the transport properties of the nanopatches and of the reference layer. The method allows for the determination of the differential resistance between the two molecular layers and is thus independent of environmental factors. The validity of this approach is demonstrated by measuring the tunneling decay constant of alkanethiols as a function of their length.

A System for Multiplexed Direct Electrical Detection of DNA Synthesis

An electronic system for the multiplexed detection of DNA polymerization is designed and characterized. DNA polymerization is detected by the measurement of small transient currents arising from ion diffusion during polymerization. A transimpedance amplifier is used to detect these small currents; we implemented a twenty-four channel recording system on a single printed circuit board. Various contributions to the input-referred current noise are analyzed and characterized, as it limits the minimum detectable current and thus the biological limit of detection. We obtained 8.5 pA RMS mean noise current (averaged over all 24 channels) over the recording bandwidth (DC to 2 kHz). With digital filtering, the input-referred current noise of the acquisition system is reduced to 2.4 pA, which is much lower than the biological noise. Electrical crosstalk between channels is measured, and a model for the crosstalk is presented. Minimizing the crosstalk is critical because it can lead to erroneous microarray data. With proper precautions, crosstalk is reduced to a negligible value (less than 1.4%). Using a micro-fabricated array of 24 gold electrodes, we demonstrated system functionality by detecting the presence of a target DNA oligonucleotide which hybridized onto its corresponding target.

Single molecule transcription profiling with AFM

Established techniques for global gene expression profiling, such as microarrays, face fundamental sensitivity constraints. Due to greatly increasing interest in examining minute samples from micro-dissected tissues, including single cells, unorthodox approaches, including molecular nanotechnologies, are being explored in this application. Here, we examine the use of single molecule, ordered restriction mapping, combined with AFM, to measure gene transcription levels from very low abundance samples. We frame the problem mathematically, using coding theory, and present an analysis of the critical error sources that may serve as a guide to designing future studies. We follow with experiments detailing the construction of high density, single molecule, ordered restriction maps from plasmids and from cDNA molecules, using two different enzymes, a result not previously reported. We discuss these results in the context of our calculations.