A Virus Incorporated to Nanotechnology

Oct 5, 2006 09:26 GMT  ·  By

Researchers at University of California, Los Angeles (UCLA) have created a new type of digital memory device by incorporating platinum nanoparticles into the tobacco mosaic virus (TMV) (photo), that atacks tobacco and other plant species. Recently, nano-structurated biological molecules and inorganic materials were selected for applications such as biosensing.

In the new device, this idea has gone one-step further with a hybrid biological system that can store digital information. The TMV is formed by a protein shell like a tube of 300 nm and RNA core (its genetic material). The TMV's thin, wire-like shell and RNA filament makes it suitable for attaching nanoparticles.

The UCLA team could add an average of 16 positive platinum ions per virus. "The TMV's surface makes it an ideal template for organizing the nanoparticles, which can bind to the specific carboxyl or hydroxyl sites on the surface," said Yang Yang, researcher at UCLA.

The device works by transferring charge, under a high electric field, from the RNA core to the Pt nanoparticles with the TMV's surface shell proteins acting as an energy barrier to the charge transferring process. Applying a voltage to the transistor, each platinum nanoparticles donates one electron to proteins on the surface of the virus, moving the device to an ON state. When the voltage dips below a certain limit, the electrons jump back to the nanoparticle, switching the transistor to an OFF state. The team built a transistor by embedding the coated virus strips in a polymer matrix, sandwiched between two electrodes much like a standard transistor.

Millions of such transistors could be used in a memory chip to replace flash memory in mp3 players and digital cameras, for example. "This device can be operated as an electrically bistable memory device whose conductance states can be controlled by a bias voltage." said Yang.

This process takes just 100 microseconds because the charge only has to travel 10 nanometres between each nanoparticle and the surface of the virus. "A camera fitted with a virus chip would take a few microseconds to display an image, compared with the milliseconds taken by existing devices," says Yang.

This is comparable to today's flash memory. In flash memory chips, a capacitor is used as a control gate, building up charge to a certain level before current is able to flow to a second gate. In addition, "the states are non-volatile and can be digitally recognized", which means that data is retained once the computer's power is turned off.

The device still needs to be belittled to increase storage density and to include more circuitry. "There will be issues involving retention time, power consumption, and integration of drivers required to write and read each bit, which we need to consider in order to optimize the system," said Yang.

The device is still some way from practical use in a memory chip. "Now we need to figure out how to wire up the viruses," says Yang.

The first device with practical use in a memory chip will be built within four years. These devices could one day be integrated in biological tissues for applications in therapeutics or biocompatible electronics.