THE ability of electrons to whizz along a strand of DNA lies behind an idea for a new type of biosensor. Hand-held devices that exploit this phenomenon could one day be used in a wide range of situations, including testing food and water for microbial contaminants, fingerprinting human DNA found at the scene of a crime, and screening blood for viruses.
DNA diagnostics is used increasingly to tackle legal, medical and environmental questions, such as whose DNA or what virus is present in a drop of blood or water. 快猫短视频s are working hard to miniaturise the key steps in DNA analysis. The aim is to create tiny 鈥渃hips鈥� that can separate pieces of DNA and match them with genetic material from known sources.
Thomas Meade, a chemist at the California Institute of Technology, has a new approach that he thinks could be even more convenient. It relies on his team鈥檚 discovery that electrons can race from one end of a DNA strand to the other, provided that the two strands of the molecule are securely zipped together. When two perfectly matched strands of DNA are zipped up, a series of 鈥減i鈥� electron orbitals are neatly stacked on top of each other, creating a 鈥減i-way鈥� for the electrons to travel.
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When a single-stranded, unzipped piece of DNA is used, the group calculates that the pi orbitals are no longer stacked on top of each other. As a result, the electrons have to travel by a more circuitous route, and their movement is much slower.
Meade and his colleague, Jon Faiz Kayyem, first took a short length of DNA and modified it at each end by adding the element ruthenium and various aromatic side-groups. This modification meant that when laser light was shone on the DNA, it excited the electrons at one end of the strand. These electron then travelled to the other end. The researchers tracked this movement via changes in the optical properties of the molecule.
A large portion of DNA diagnostics relies on zipping a 鈥渒nown鈥� strand of DNA (for instance, from a virus) to a matching piece of DNA in the sample being tested. In Meade and Kayyem鈥檚 proposed device, many copies of a short piece of modified DNA would be fastened onto the tip of an electrode. Each sensor will be custom-built for a particular purpose: a device to detect HIV, for instance, will contain DNA strands unique to the virus. The electrode will be dipped into samples of DNA prepared from the blood to be tested. If DNA in the sample matches the DNA in the sensor, the two strands will zip together and an electron will race down the double-stranded molecule. If no match is made, then movement of electrons down the unzipped, single strands will be much slower. Sensors will distinguish between the two.
Caltech has already filed a patent for Meade鈥檚 technology, which he presented last week at the annual meeting of the American Association for the Advancement of Science. Kayyem is president of a new company, Clinical Micro Sensors, which is developing the applications further.
