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The new technology has changed that. Nanoparticles are tiny clusters of atoms created by scientists, so small that it would take thousands of them to equal the dimensions of a human red-blood cell. The unique qualities that nano-sizing gives to substances are the subject of intense study in a number of fields, and many of the particles are already used in consumer products ranging from scratch-resistant eyeglasses to better-gripping car tires.

When silver is turned into nano-sized bits, it seems to become more effective at combating bacteria and viruses, said Dr. Xiaojian Yao, lead author of the study. “At such nanoscale, the extremely small size of silver particles exhibits remarkable, unusual physio-chemical properties and biolgical activity,” he said.

At the end of the day, if they stay in the pocket, it’s not going to do the job

Their tiny dimensions also mean they can be plastered on something like a polyurethane condom without changing its size or shape.

Yet how, exactly, the silver nanoparticles neutralize HIV and other viruses is still a bit of mystery. It could be the particles or the silver ions they release attach to the virus and prevent it from binding to cell “receptors” in the host’s body, said Dr. Yao, a medical microbiologist. Or they could actually change a key protein on the virus’s surface, and in that way stop it from sticking to host cells. Some condoms are now treated with an anti-microbial substance, called Nonoxynol-9. Recent studies, though, have shown that N-9 can trigger inflammation and ulceration in the genitals, actually making infection more likely.