Viruses vanquished with a burst from a laser

04 November 2007
Posted by Chris Smith.

Scientists in the US have developed a laser technique to selectively wipe out viruses and bacteria whilst leaving human cells unharmed. The approach could be used to improve the safety of blood transfusions and other blood-derived products butwithout the risk of harming the cells present. Kong-Thon Tsen and his colleagues at Arizona State University made the discovery when they exposed solutions of viruses including bacteriophages and TMV, a plant virus, to a train of very short (femtosecond duration) bursts from a near infrared (850nm) laser. After an hour the viruses were completely inactivated. The team then repeated the experiment using E. coli bacteria and, again, after one hour the bacteria were all destroyed. But when they exposed solutions of human cells to the same treatment, the cells remained viable and healthy. The researchers think that the laser pulses rip apart the outer coats of the microbes in the same way that it's possible to smash a glass with sound waves. The bursts of laser light cause a phenomenon called impulsive stimulated Raman scattering (ISRS), which sets up patterns of lethal vibrations amongst the proteins on the outsides of the micro-organisms, breaking them open. But mammalian cells, possibly because they are much larger, require between 20 and 100 times more energy totrigger the same process, so they're relatively invulnerable to the effect. As a result the team are confident that the technique, which should also be immune to bugs becoming resistant to its effects, could play a major role in the clinical setting. "Although it is not clear at the moment why there is a large difference in laser intensity for inactivation between human cells and micro-organisms such as bacteria and viruses, the research so far suggests that ISRS will be ready for use in disinfection and could provide treatments against the worst, often drug-resistant, bacterial and viral pathogens," says Tsen.

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