Researchers at the University of California, San Diego (UCSD) have developed dust-sized chips of silicon that allow them to rapidly and remotely detect a variety of biological and chemical agents.
According to a statement from UCSD, the development is likely to have wider commercial use in research and medical laboratories – in performing rapid biochemical assays, screening chemicals for potential new drugs and testing samples for toxic materials. But because the technique permits rapid detection of the biological and chemical substances remotely, using a laser, it also could be employed as an advanced warning system for biological and chemical attacks.
‘The idea is that you can have something that’s as small as a piece of dust with some intelligence built into it so that it could be inconspicuously stuck to paint on a wall or to the side of a truck or dispersed into cloud of gas to detect toxic chemicals or biological materials,’ said Michael J. Sailor, a professor of chemistry and biochemistry at UCSD.
‘When the dust recognises what kinds of chemicals or biological agents are present, that information can be read like a series of bar codes by a laser that’s similar to a grocery store scanner to tell us if the cloud that’s coming toward us is filled with anthrax bacteria,’ added Sailor.
The ‘bar code’ on the silicon dust particles is a specific wavelength of light, or colour, reflected from their surfaces after thin films layered on the silicon chip chemically react to a specific chemical or biological agent.
The scientists start with silicon wafers similar to those used in the manufacture of computer chips, then encode them by generating layers of nanometre-thick porous films on the wafers using an electrochemical etch.
This layered structure on the dust-sized particles, which are created by breaking apart the wafer using ultrasound, imparts unusual optical properties to the particles. Referred to as photonic crystals, these micron-sized particles are able to reflect light of very precise colours.
‘When you’re looking for chemical or biological warfare agents, you’re going to want to search for thousands of different chemicals,’ says Sailor. ‘Since the particles can be encoded for millions of possible reactions, it’s possible to test for the presence of thousands of chemicals at the same time.’
The encoding that takes place in these particles provides colours that are so sharp from the visible to the infrared that a laser can read thousands of distinct colours corresponding to separate chemicals. In this way, the UCSD researchers say these coded particles can perform thousands of biochemical assays in a small receptacle.
Because the smart-dust chips are fabricated from silicon, they can be easily made from existing computer chip technology. And the compatibility of porous silicon with living cells and the long-term stability and non-toxicity of this material makes them especially useful in biomedical applications.
Sailor and his group have been able to get their laser to detect the colour changes in the smart dust 20 meters away. With a more powerful laser, he adds, ‘we’re planning to take this outside and see how far we can go. Our goal is one kilometre.’