According to Fletcher, fluorescence is increasingly preferred by the World Health Organization as a TB detection tool, because it's easier for the untrained eye to spot something green than to pick out a colored stain against a bright-field background. However, with traditional fluorescence equipment, health workers still have to count spots on a microscope slide by eye, which can be unreliable. The Berkeley group developed software that counts the green spots automatically; when installed on the smart phone, it could make the process easier and faster.

The cell-phone microscope could also be useful for TB therapy, Lam says. TB patients must be directly observed taking their medication over several weeks, to prevent drug resistance buildup. The phone can store images for comparison, and it provides immediate feedback, so patients could go to their local health worker and see their progress each week, rather than waiting a month for samples to come back from a centralized processing location, or seeing complications of the disease show up three or four months later.

That ability to transmit microscope images makes the Cellscope a new tool for telemedicine, says Lam. And because the images can have GPS tags associated with them, they could provide early warning for disease outbreaks.

Digitizing medical records is another problem for health workers in the field. Fletcher's group ran into the issue while demonstrating their technology in Bangladesh and the Democratic Republic of Congo. Pen-and-paper records are easily lost--a problem that the cell-phone microscope could solve by attaching patient-identification information to each digital image. Records could then be called up for easy reference when a patient returns to the health clinic.

The researchers' key innovation, Lam says, was not inventing a new medical test, but rather taking a standard test and presenting it in a new way. Their technology "just happens to be smaller, cheaper, and attached to a cell phone," he says.

In a world with four billion cell phones, many in developing countries, Ozcan says, the cell-phone microscope could take advantage of existing infrastructure to fight disease on a new, more mobile front.