26 June 2008
Liquid crystals that realign in response to DNA can reveal subtle sequence alterations, even a single base mutation, report US chemists. The finding could lead to cheap, portable alternatives to current lab-based analytical detectors, say the researchers.
Daniel Schwartz at the University of Colorado showed that liquid crystals, which naturally align themselves perpendicular to the surface of a surfactant-coated glass slide, tilt slightly following the addition of short lengths of single stranded DNA. The addition of complementary strands of DNA - with a base sequence that would bind to the strands on the slide - triggers the tilted crystals to return to their perpendicular alignment. However, adding a non-complementary DNA strand - with a sequence that differed by just one base - causes no such response. These differing responses of the liquid crystals were visible to the naked eye.
The appearance of a liquid-crystal film to which single stranded DNA has been added (left) changes following the addition of complementary single-stranded DNA
© ACS
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Fluorescence-based detection is the current state-of-the-art for DNA microarrays, but Schwartz notes that his technology does not require labelling of sample DNA with fluorescent probes, and doesn't need 'expensive, bulky' lasers or photodetectors.
Single-base mismatches are used as control experiments in conventional DNA microarray technology, so it was important for Schwartz's team to show that this was possible with their technology.
'The relevance of a one-base-pair mismatch is that it relates to the degree of precision with which this technology can identify a DNA sequence,' says Schwartz, professor of chemical and biological engineering. 'If two closely-related bacteria had similar DNA sequences in a certain gene, one might need to distinguish a single base difference in order to make a correct diagnosis,' he says, 'similarly, some genetic defects which cause genetic disease in humans are related to a single changed base.'
The study is only an initial demonstration of the technology, and more work is needed before a consumer product can be considered.
Nevertheless, says Schwartz, 'In principle, a device based on this technology could be very similar in size and cost to a digital wristwatch with an LCD display - compact, inexpensive, and battery powered. These properties make it well suited to point-of-use applications.'
Bea Perks
References
A D Price and D K Schwartz,
J. Am. Chem. Soc., 2008,
54, 391 (DOI: 10.1021/ja0774055)
Chemistry World.
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