Exploring Nanopore Sequencing: A New Era in DNA Analysis

DNA sequencing has come a long way since the early days of Sanger sequencing in the 1970s. But one technology is pushing boundaries in ways that older methods simply cannot – nanopore sequencing. Instead of relying on chemical labelling or amplification, nanopore sequencing reads individual strands of DNA, RNA, or even proteins by threading them through a tiny pore just a few nanometers wide. The result? Real-time data, longer reads, portable devices, and significantly lower costs. Whether it’s tracking a viral outbreak in a remote village or assembling a complete human genome, nanopore sequencing is reshaping how we understand biological information.

What is nanopore sequencing? 🔗

At its core, nanopore sequencing works by passing a single strand of a biological molecule – DNA, RNA, or a protein – through a nanoscale pore embedded in a membrane. An electrical voltage is applied across the membrane, creating an ionic current through the pore. As each molecule passes through, it disrupts this current in a pattern that is characteristic of the sequence of bases (or amino acids) in the strand. Sensitive electronics record these current fluctuations thousands of times per second, and software algorithms translate them into a readable sequence.

Unlike earlier sequencing generations that required DNA to be chopped into small fragments and amplified using PCR, nanopore sequencing is a label-free and amplification-free method. It reads molecules directly at the single-molecule level. This gives it several built-in advantages: there is no amplification bias, the reads can be extremely long (over 100 kilobases), and the data streams in real time as sequencing occurs.

A brief history of nanopore sequencing 🔗

The concept of using nanopores for molecular detection dates back to the 1980s, when researchers including David Deamer, George Church, and Hagan Bayley independently explored the idea. The foundational proof-of-concept came in 1996, when Kasianowicz and colleagues demonstrated that individual polynucleotide strands could be driven through an alpha-hemolysin protein channel using an applied voltage. This landmark experiment showed that the ionic current was measurably disrupted during translocation – opening the door to sequence-level detection.

Over the following two decades, extensive work went into slowing the DNA translocation speed (molecules naturally pass through too quickly for accurate reading), improving base-calling algorithms, and engineering better pore proteins. Oxford Nanopore Technologies (ONT) released its first portable sequencing device, the MinION, in 2014, bringing nanopore sequencing from the research lab to the field. Since then, the technology has been used in diverse environments – from sequencing Ebola virus genomes during the West African outbreak to contributing roughly a quarter of the world’s SARS-CoV-2 genome data during the COVID-19 pandemic.

Types of nanopore sequencing 🔗

Not all nanopores are built the same. Depending on the material and design, nanopore sequencing systems can be broadly classified into three categories: biological (protein-based), solid-state, and hybrid nanopores. Each type has distinct characteristics, strengths, and trade-offs.

Biological (protein-based) nanopores 🔗

These are the most widely used nanopores in commercial sequencing today. Biological nanopores are formed by protein channels – such as alpha-hemolysin, MspA, CsgG, or aerolysin – that are embedded in a lipid bilayer membrane. Because these proteins are produced using standard molecular biology techniques, they are highly reproducible at the atomic level from batch to batch. Their pore geometry is naturally suited to single-molecule detection, and they can be precisely modified through site-directed mutagenesis to improve sensitivity or selectivity.

ONT’s commercial sequencing platforms use a mutant CsgG pore paired with a motor protein that controls the speed of DNA translocation. The main limitation of biological nanopores is their dependence on a fragile lipid membrane, which reduces the device’s operational lifespan and makes them sensitive to environmental conditions like pH and temperature.

Solid-state nanopores 🔗

Solid-state nanopores are fabricated in synthetic membranes made from materials like silicon nitride (Si₃N₄), aluminium oxide (Al₂O₃), titanium dioxide (TiO₂), or graphene. These pores are created using techniques such as focused ion beam drilling or electron beam sculpting. The key advantages of solid-state nanopores are their mechanical robustness, tunable pore size, and compatibility with semiconductor manufacturing processes, which opens the door to mass production and integration into chip-based devices.

However, solid-state nanopores currently face challenges related to controlling DNA translocation speed and achieving the base-level resolution that biological pores offer. Pore size also cannot yet be reproduced with the same atomic-level precision as protein channels, although advances in graphene-based nanopores are closing this gap.

Hybrid nanopores 🔗

Hybrid nanopores combine a biological protein pore with a solid-state support structure, aiming to capture the best of both worlds. The solid-state membrane provides mechanical stability and durability, while the biological component offers the precise pore geometry needed for accurate molecular sensing. Research groups have demonstrated hybrid designs by inserting alpha-hemolysin pores into silicon nitride nanopores, successfully detecting DNA translocation events through the combined structure. While still largely in the research phase, hybrid nanopores represent a promising direction for future commercial devices.

Advantages of nanopore sequencing 🔗

Nanopore sequencing has several features that set it apart from both short-read (Illumina) and other long-read (PacBio) platforms.

Real-time data generation: Unlike batch-based sequencing methods, nanopore devices stream sequence data as molecules pass through the pore. This means researchers can begin analysing results within minutes of starting a run and can stop sequencing as soon as enough data has been collected – saving both time and reagent costs.

Ultra-long read lengths: Nanopore sequencing routinely produces reads exceeding 10 kilobases, with some reads stretching beyond 100 kilobases. These long reads are invaluable for resolving repetitive regions, structural variants, and complex genomic architectures that short-read technologies often fragment or misassemble.

Direct detection of base modifications: Nanopore sequencing can natively detect epigenetic modifications – such as DNA methylation – without the need for chemical treatment like bisulphite conversion. This is because modified bases produce distinct current signatures as they pass through the pore, providing an additional layer of biological information in a single sequencing run.

Portability and accessibility: ONT’s MinION device weighs under 100 grams and connects via USB to a laptop. This portability makes it transformative for on-site diagnostics in resource-limited settings, field research, and outbreak surveillance – environments where traditional sequencing infrastructure is unavailable.

Low cost per run: While the cost per base may vary depending on the application, nanopore sequencing has notably lower upfront capital costs compared to Illumina or PacBio platforms. The starter kits and flow cells are relatively affordable, making the technology accessible to smaller laboratories and individual researchers.

Limitations and challenges 🔗

Despite its many strengths, nanopore sequencing has notable limitations that researchers must consider.

Higher error rates: Compared to Illumina’s short-read sequencing, nanopore sequencing has historically exhibited higher per-read error rates, particularly with homopolymer stretches (repeats of the same base). Recent improvements have brought the raw read accuracy to around Q28 (roughly one error in 630 bases) with the latest ONT chemistry, but this still lags behind the Q30-Q40 accuracy levels achieved by some short-read platforms.

Background noise: The ionic current signals detected during nanopore sequencing can be affected by electrical noise from the membrane and surrounding electronics. This noise complicates the task of base-calling algorithms, especially when distinguishing between chemically similar bases or modified bases. Advances in nanopore design – such as reducing membrane area and optimising electrolyte conditions – are helping to address this issue.

Pore lifespan and degradation: Biological nanopores embedded in lipid membranes have a limited operational window. The membranes can degrade during long sequencing runs, reducing data output. Solid-state alternatives offer more durability but have not yet matched the resolution of their biological counterparts.

Translocation speed control: Getting molecules to pass through the pore at the right speed remains a fundamental challenge. If translocation is too fast, the electronics cannot resolve individual bases. Motor proteins are used to slow this process in biological systems, but further refinement is needed for consistent performance across different sample types.

Applications in genomics and diagnostics 🔗

Nanopore sequencing’s combination of long reads, real-time data, and portability has made it a powerful tool across multiple areas of biology and medicine.

Pathogen identification and outbreak surveillance 🔗

One of the most impactful applications of nanopore sequencing is in infectious disease diagnostics. Traditional methods for identifying pathogens – culture, PCR, serological tests – can be slow and have limited scope. Nanopore-based metagenomic sequencing can identify bacteria, viruses, and fungi directly from clinical samples within hours, without needing to know what pathogen to look for in advance.

During viral outbreaks, this technology has proven especially valuable. Portable nanopore devices were deployed in Guinea during the 2014-2016 Ebola outbreak for real-time genomic surveillance. During the COVID-19 pandemic, nanopore sequencing contributed significantly to global SARS-CoV-2 genome tracking, helping scientists monitor variants and transmission patterns. The technology has also been used to detect antimicrobial resistance genes directly from patient samples, potentially cutting turnaround time for resistance profiling to under four hours.

Genome assembly and structural variant detection 🔗

The ultra-long reads generated by nanopore sequencing make it particularly well-suited for de novo genome assembly – building a genome sequence from scratch without a reference. Long reads can span repetitive regions and structural variants (such as large insertions, deletions, or inversions) that short-read technologies struggle with. This has proven valuable in assembling complete bacterial genomes, resolving complex plant genomes, and contributing to projects like the Telomere-to-Telomere (T2T) consortium, which produced the first truly complete human genome sequence.

Cancer research and liquid biopsy 🔗

Nanopore sequencing is increasingly being explored for analysing cell-free DNA (cfDNA) in cancer diagnostics. cfDNA fragments released by tumour cells into the bloodstream carry genetic and epigenetic signatures that can reveal tumour type, stage, and treatment response. Because nanopore sequencing can simultaneously detect mutations and methylation patterns in a single run, it offers a potentially comprehensive approach to liquid biopsy – a minimally invasive alternative to traditional tissue biopsy. Researchers are working on integrating multiple cfDNA features to improve diagnostic accuracy for various cancer types.

Personal genomics and rare disease diagnosis 🔗

Nanopore sequencing’s ability to detect structural variants and epigenetic modifications has made it a valuable tool for diagnosing rare genetic conditions that conventional sequencing may miss. In clinical settings, targeted nanopore sequencing has been used to rapidly identify pathogenic mutations in patients with suspected genetic disorders. The ability to produce results within a day – rather than the weeks required by some traditional workflows – can be critical for conditions where early diagnosis influences treatment decisions.

Environmental monitoring 🔗

Beyond clinical applications, nanopore sequencing has found a role in environmental monitoring and biodiversity assessment. Its portability allows researchers to conduct metagenomic surveys in the field – analysing soil microbiomes, water quality, or wildlife biodiversity in remote locations without shipping samples to a centralised laboratory. This real-time capability is particularly useful for detecting pathogens in water sources, monitoring agricultural pests, and assessing ecosystem health.

The road ahead 🔗

Nanopore sequencing technology continues to evolve rapidly. Recent years have seen the introduction of improved pore chemistries (like ONT’s R10.4.1), better base-calling algorithms powered by deep learning, and new platforms from companies in China such as Qitan Technology, BGI (CycloneSEQ), and others. Research is also advancing toward nanopore-based protein sequencing, which could eventually enable single-molecule analysis of the proteome – a goal that would complement existing genomic and transcriptomic capabilities.

The integration of nanopore sensing with machine learning, microfluidics, and surface chemistry is expected to further improve accuracy, throughput, and the range of detectable molecules. As these developments converge, nanopore sequencing is well positioned to become an even more central tool in precision medicine, public health, and environmental science.

What do you think? As nanopore sequencing becomes cheaper, faster, and more portable, could it eventually replace traditional sequencing methods entirely – or will it remain best suited as a complementary tool for specific applications? How might widespread access to real-time sequencing change the way we respond to disease outbreaks in resource-limited regions?

References

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