Scientists have developed a method for detecting DNA that is 10 times more sensitive than conventional methods and can distinguish a mismatch based on only one incorrect base pair, according to a report published today in Science. Once refined, the new technique could form the basis for handheld devices, making DNA tests cheaper, faster and portable.

Current DNA testing methods rely on polymerase chain reaction (PCR) and fluorescence measurements that require multiple experimental steps and specialized instruments. Moreover, it typically takes days to acquire the results. So-Jung Park and her colleagues at Northwestern University developed and tested their detection system using a synthetic sequence of DNA (modeled after anthrax lethal factor) as the target molecule.

The team first placed so-called capture DNA--short sequences of nucleotides synthesized to have a sequence of bases complementary to one end of the target DNA--between a pair of electrodes. They next placed the setup, which fits on a glass slide, in a test solution containing target DNA. Gold nanoparticle probes covered with snippets of DNA complementary to the other end of the target molecule were also present in the solution. Target DNA molecules then bind to both the capture DNA strands and the gold probes. When the slide is washed with modified photographic developing solution, silver ions cover the gold nanoparticles, causing them to grow and close the gap between the two electrodes. A measurable change in electrical current signifies the presence of target DNA.

The most important step in any DNA test is to distinguish between a close match and a perfect one. According to the report, the new technique can distinguish a mismatch that contains only one incorrect base pair match, an improvement over currently available tests. Another advantage to the new system is the possibility of testing for multiple biological targets simultaneously, a benefit that could be put to use in portable field sensors designed to detect biological weapons.