An estimated 3.4 billion people — half of the world’s population — are at risk of malaria. Many undergo testing, providing blood samples that health workers then stain and examine under a microscope for the disease-causing parasite. It’s a simple procedure that takes minutes.

Why, then, does it often take months for people to get a diagnosis?

The same question can be asked for tuberculosis, African sleeping sickness and the 22 other infectious diseases that microscopes are used to diagnose.

It costs only 50 cents to make and can be folded together, origami-style, in less than 20 minutes.

The problem lies with microscopes themselves. “Research microscopes are not designed for field testing,” said Manu Prakash, an assistant professor of bioengineering at Stanford University. “Neither were they first designed for diagnostics at all.” They’re heavy, bulky, a hassle to maintain and cost upwards of $200, too expensive for most people in the developing countries where infectious diseases strike the hardest.

So Prakash scaled up the diagnostic ability of the microscope by scaling it down — way down. He invented the Foldscope, a microscope made of a bookmark-sized piece of folded cardstock embedded with a teensy lens. It costs only 50 cents to make and can be folded together, origami-style, in less than 20 minutes.

But don’t let its basic design fool you. Foldscope magnifies samples up to 2,000 times, allowing health workers to easily spot disease-causing microbes. And it’s durable too, as Prakash discovered after he stomped on it, hurtled it from a third-story window and tossed it into the washing machine — so it’s probably safe to say that it can weather the harsh conditions of most developing countries.

”One of the goals… is to get these instruments into the hands of health workers who do diagnostics out in the field, especially in remote locations,” Prakash said. “Most typical instruments don’t survive field conditions.”

Foldscope’s durability lies partly in the tininess of its optical components. “Imagine if you stand on a grain of salt,” Prakash said. “You can’t really do anything to destroy it because it’s just so tiny.”

During research projects in Thailand, India, Uganda and Nigeria, Prakash and his graduate students saw microscope lenses overgrown with mold and people who didn’t even know how to turn them on. Others couldn’t afford the device.

For the next two years, Prakash’s team worked to design a cheaper, simpler alternative. Since paper is inexpensive and readily accessible, they devised a way to fold a sheet of cardstock around a spherical lens as small as a grain of salt, which costs less than the precision-ground curved lenses in conventional microscopes.

One of my dreams … is to have every single kid in the world carry around microscopes in their pocket.

The components are perforated onto a sheet of cardstock, like punch-out paper doll parts, while a color-coding system indicates how to attach them to each other. To use the Foldscope, a blood or other body fluid sample is mounted on a microscope slide and inserted into a rectangular pocket. The lens is embedded in a strip of paper directly above the pocket. Grasping each end of the strip with the thumb and forefinger, the user holds the lens close enough to one eye that his or her eyebrows touch the paper. To locate the target object, the user slides the strip back and forth. Flexing the strip adjusts the focus.

Prakash is working to customize the Foldscope to diagnose specific diseases by making minor adjustments, such as adding different combinations of watch battery-powered LED lights and fluorescent filters. It can also be configured to project images on a wall.

Prakash also wants the Foldscope to democratize science education. “We have to build tools to allow everybody in the world to do science,” he said. “One of my dreams … is to truly have every single kid in the world carry around microscopes in their pocket.”

Last year, he launched the Ten Thousand Microscope project, which invited kids, teachers, tinkerers and other citizen scientists to submit ideas on how to beta-test the Foldscope. His team compiled the results from 130 different countries which may become available in a future project.

Imagine, thousands of uses on top of diagnosing infectious diseases and bringing science education to the masses. What can’t this little piece of paper do?