The journal Science describes recent advances in sequencing technology. Stuart Lindsay, director of the Biodesign Institute's Center forSingle Molecule Biophysics has just successfully addressed acentral stumbling block in nanopore sequencing -- reading singlenucleotide bases in a DNA chain. Lindsay's latest experimentalresults, which demonstrate critical improvements in DNA reads, havejust appeared in the journal Nanotechnology. Once accurate sequencing falls below the threshold of $1000 pergenome, the technology should become ubiquitous, according to many.As the current Science overview suggests, that day may be drawing near as both the speedand cost of whole genome sequencing advances at a pace outstrippingMoore's famous Law, (which dictates a doubling of computing power-- and halving of the expense -- every 18 months). The latest technological competition involves the idea of threadinga single strand of DNA through a tiny, molecular-scale eyelet knownas a nanopore. This strategy may soon allow the entire DNA sequenceto be read in one go, rather than cut apart, deciphered in brieffragments and painstakingly re-assembled. While the first sequencing of the human genome took researchers 13years and $3 billion to achieve, under the auspicies of the HumanGenome Project , the feat may soon be accomplished at the blindingrate of 6 billion nucleotide bases every 6 hours at a cost of $900.At least that is the extravagant claim being made by OxfordNanopore Technologies, one of the pioneering companies driving newsequencing developments. Since the seemingly quixotic idea of nanopore sequencing was firstthought up in the mid 1990s, enormous advances have been made. Thebasic idea is that when a nanopore is immersed in a conductingfluid and a voltage is applied across it, conduction of ionsthrough the nanopore will produce a measurable electric current.This current is highly sensitive to the size and shape of thenanopore and in theory, each nucleotide base in the DNA thread willobstruct the nanopore as it migrates, altering the ionic current ina recognizable and reproducible way. The DNA "thread" is tricky material to manipulate however-- so fine that it would take about 5000 DNA strands laid side byside to equal the width of a human hair.Just finding a suitableeyelet at this scale proved a challenge. At first, porous,transmembrane proteins were explored. Alpha hemolysin (αHL),a bacterium that causes lysis of red blood cells, seemed aparticularly promising candidate, given the nanopore diameterrequired for sequencing DNA. Since then, other protein-based portals for DNA have been tinkeredwith and more recently, various "solid state" nanoporesof silicon or graphene have been investigated. These can be moreeasily fabricated and their properties, more precisely controlled. According to Science's review of the present state of the art,nanopore sequencing "seems poised to leave the lab," andthe dream of a $1000 genome may be close at hand, though challengesremain. A persistent problem in sequencing individual bases hasbeen that they tend to stream through the nanopore too rapidly topinpoint each base independently. Instead, the measured current inearly experiments reflected the average produced by a group ofbases wending their way through the tunnel. Lindsay's technique relies on reading electrical current in a tinycircuit composed of a DNA nucleotide trapped between a pair of goldelectrodes, which span a nanopore. The electrodes are made byfunctionalizing the tip of a scanning tunneling microscope (STM),with molecules that can bind individual DNA bases as they poketheir heads through the nanopore. Recognition Tunneling, the name Lindsay applies to his sequencingmethod, relies on outfitting one of two electrodes with sensingchemicals, the other with the nucleotide target to be sensed. Asignal is produced when the junction between sensing chemical andtarget self-assembles, closing the circuit. In this type of junction, where lengths separating electrodes aredown to a molecular scale, electrons can exhibit odd behaviorassociated with the quantum subatomic world, "tunneling"through barriers under conditions prohibited by classical physics.In such a scenario, each of the 4 nucleotides should produce asignature tunneling current, which can be used to sequence DNAbase-by-base as it feeds its way through the nanopore. Trappingeach base momentarily allows time for an accurate identification,before it is released and the DNA thread continues itstransmigration through the nanopore. Replacing ionic current flow with tunneling current can potentiallyimprove sequencing resolution considerably and in their latestwork, Lindsay's group demonstrates that multiparameter analysis ofthe current spikes produced by tunneling can indeed identify eachDNA base as it is temporarily pinned by hydrogen bonding betweenthe functionalized electrodes. There's more. In addition to pinpointing nucleotide identity with greater than 90percent accuracy, the technique also permits environmental genemodifications to be identified, for example,methylation. Thisrepresents a major advance for sequencing, as such epigeneticalterations to the genome have profound implications for the studyof human health and disease, including embryonic and post-nataldevelopment, and cancer. The Nanotechnology paper describes a new approach to analyzing thetunneling signals.The Lindsay group used machine learning (theprocess used by IBM's Watson to win at Jeopardy) to train acomputer to recognize the DNA bases.The machine called all fourbases (A,T,C and G) as well as the "fifth base" -- methyl-- that carries the epigenetic code, with 96 percent accurarcy on asingle molecule read. "Oxford Nanopore have a made a tremendous breakthrough innanopore sequencing using ion current, as highlighted in theNEWSFOCUS story [in the journal Science ]," Lindsay says."But we think we can bring even more tothe table with the supersensitivity and chemical resolution ofRecognition Tunneling." Roche Pharmaceuticals has recently licensed the technology. The high stakes race for rapid sequencing appears to be enteringthe home stretch, though new surprises are likely before the finishline. Once it is crossed, the era of personalized medicine willhave arrived. 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