On the left, a microlens is in the on state and ready to detect. The right shows the microlens in the off state after it has detected its target chemical.

The system uses hydrogel microlenses so small that millions of them can fit on a 1-in.-sq plate. The technology could speed up medical testing and greatly augment how authorities respond to biological or chemical attacks.

The microlenses detect biological or chemical agents via antibody-antigen binding, the same process used by the human immune system. When antibodies on the microlenses touch the designated antigen, they swell and become less dense. The swelling changes the microlenses' focal length. So projecting an image through the tiny lenses reveals an antigen when the image goes out of focus. "They are reversible, so you can use the same lenses over and over again," says L. Andrew Lyon, associate professor at Georgia Tech School of Chemistry and Biochemistry.

The microlenses' ability to conduct rapid chemical and biological tests could significantly impact health-care costs: Many blood tests could take place in a physician's office rather than an outside lab. And authorities could rapidly detect and identify toxic chemicals after a spill or terrorist attack.

A device built with microlenses could be handheld, because there are already ways of placing microlenses in compact optical systems. "The beauty of this is that microlenses are very tunable in terms of sensitivity," says Lyon. "You can make arrays that detect multiple components on one sample, so you can multiplex your detection. Whereas in current practice, each thing that doctors look for in your blood needs a different test."

Lyon says the next step in developing the sensors is to test their performance in complex biological fluids, like blood serum.