Nanopore DNA strand sequencing has emerged as a competitive, portable technology. Reads exceeding 150 kilobases have been achieved, as have in-field detection and analysis of clinical pathogens. We summarize key technical features of the Oxford Nanopore MinION, the dominant platform currently available. We then discuss pioneering applications executed by the genomics community.

Single molecules of DNA or RNA can be detected as they are driven through an alpha-hemolysin channel by an applied electric field. During translocation, nucleotides within the polynucleotide must pass through the channel pore in sequential, single-file order because the limiting diameter of the pore can accommodate only one strand of DNA or RNA at a time. Here we demonstrate that this nanopore behaves as a detector that can rapidly discriminate between pyrimidine and purine segments along an RNA molecule. Nanopore detection and characterization of single molecules represent a new method for directly reading information encoded in linear polymers, and are critical first steps toward direct sequencing of individual DNA and RNA molecules.

A long-held goal in sequencing has been to use a voltage-biased nanoscale pore in a membrane to measure the passage of a linear, single-stranded (ss) DNA or RNA molecule through that pore. With the development of enzyme-based methods that ratchet polynucleotides through the nanopore, nucleobase-by-nucleobase, measurements of changes in the current through the pore can now be decoded into a DNA sequence using an algorithm. In this Historical Perspective, we describe the key steps in nanopore strand-sequencing, from its earliest conceptualization more than 25 years ago to its recent commercialization and application.

The Oxford Nanopore MinION sequences individual DNA molecules using an array of pores that read nucleotide identities based on ionic current steps. We evaluated and optimized MinION performance using M13 genomic dsDNA. Using expectation-maximization (EM) we obtained robust maximum likelihood (ML) estimates for read insertion, deletion and substitution error rates (4.9%, 7.8%, and 5.1% respectively). We found that 99% of high-quality ‘2D’ MinION reads mapped to reference at a mean identity of 85%. We present a MinION-tailored tool for single nucleotide variant (SNV) detection that uses ML parameter estimates and marginalization over many possible read alignments to achieve precision and recall of up to 99%. By pairing our high-confidence alignment strategy with long MinION reads, we resolved the copy number for a cancer/testis gene family (CT47) within an unresolved region of human chromosome Xq24.

Single-molecule techniques have been developed for commercial DNA sequencing1,2. One emerging strategy uses a nanopore to analyze DNA molecules as they are driven electrophoretically in single file order past a sensor3-5. However, uncontrolled DNA strand electrophoresis through nanopores is too fast for accurate base reads6. A proposed solution would employ processive enzymes to deliver DNA through the pore at a slower average rate7. Here, we describe forward and reverse ratcheting of DNA templates through the α–hemolysin (α-HL) nanopore controlled by wild-type phi29 DNA polymerase (phi29 DNAP). DNA strands were examined in single file order at one nucleotide spatial precision in real time. The registry error probability (either an insertion or deletion during one pass along a template strand) ranged from 10% to 24.5% absent optimization. This general strategy facilitates multiple reads of individual template strands and is transferrable to other nanopore devices for implementation of DNA sequence analysis.