Nanopores for DNA Diagnostics?
Sequencing DNA without gels seems pretty far-fetched. But Stefan Howorka and colleagues have shown that this may be possible code (Nature Biotechnology, Vol. 19, No. 7, 01 July 2001). They have exploited the electrical conductivity properties of a nanopore-membrane-embedded proteins that form a channel-to detect single nucleotide changes in a sequence of DNA.
As a molecule moves through a nanopore, there are characteristic electrical conductivity changes that can be measured. Such conductivity profiles correspond with the size (and other characteristics) of the molecule moving through the pore.
The authors engineered a nanopore, tethering a short sequence of DNA at the entrance of the pore. Then they distinguished the DNA molecules drawn into the pore by examining the changes in current flow through the pore: Those DNA sequences that complemented the tethered DNA likely formed a duplex with the tethered molecule before passing through the membrane, producing a current reduction that was of longer duration than that generated by sequences containing mismatches. The researchers also determined the partial sequence of a DNA strand tethered to a nanopore by applying a series of DNA molecules of known sequence to the pore.
However, before nanopores can be used for routine DNA analysis and sequencing, further work needs to be done to engineer more robust and reproducible nanopores and, for sequencing, their fabrication into arrays.
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