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January 05, 2012

Photoinduced write-once read-many-times memory device based on DNA biopolymer nanocomposite

Eurekalert - In an effort to make data storage more cost-effective, a group of researchers from National Tsing Hua University in Taiwan and the Karlsruhe Institute of Technology in Germany have created a DNA-based memory device that is "write-once-read-many-times" (WORM), and that uses ultraviolet (UV) light to make it possible to encode information. The device, described in a paper accepted to the AIP's Applied Physics Letters, consists of a thin film of salmon DNA that has been embedded with silver nanoparticles and then sandwiched between two electrodes. Shining UV light on the system enables a light-triggered synthesis process that causes the silver atoms to cluster into nano-sized particles, and readies the system for data encoding. In some cases, using DNA may be less expensive to process into memory devices than using traditional, inorganic materials like silicon, the researchers say.

At first, when no voltage or low voltage is applied through the electrodes to the UV-irradiated DNA, only a low current is able to pass through the composite; this corresponds to the "off" state of the device. But the UV irradiation makes the composite unable to hold charge under a high electric field, so when the applied voltage exceeds a certain threshold, an increased amount of charge is able to pass through. This higher state of conductivity corresponds to the "on" state of the device.




The team found that this change from low conductivity ("off") to high conductivity ("on") was irreversible: once the system had been turned on, it stayed on, no matter what voltage the team applied to the system. And once information is written, the device appears to retain that information indefinitely: the researchers report that the material's conductivity did not change significantly during nearly 30 hours of tracking. The authors hope the technique will be useful in the design of optical storage devices and suggest that it may have plasmonic applications as well.


Applied Physics Letters - We demonstrate a photoinduced write-once read-many-times (WORM) organic memory device based on DNA biopolymer nanocomposite. The device consists of a single biopolymer layer sandwiched between electrodes, in which electrical bistability is activated by in situ formation of silver nanoparticles embedded in biopolymer upon light irradiation. The device exhibits a switching effect to high conductivity above a threshold of 2.6 V and a good retention property. This facile technique, taking advantage of DNA’s affinity for metals and solution processing, can optically manipulate the properties of DNA nanocomposite thin films, which holds promise for optical storage and plasmonic applications.

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