Microfluidic chips, devices for testing water quality and identifying pathogens, now can be made using paper, ink, and sunlight. Conventional microfluidic chips are blocks of glass or plastic containing labyrinths of tiny channels no more than a few hundred micrometers wide. These channels manipulate fluids with great precision because capillary forces draw liquid through them without turbulence. The chips offer a way to shrink and streamline lab procedures such as, a test for spotting the DNA of bacterial diseases. The task previously took a few steps. Several solutions can be loaded into one chip, and the results read soon after.

Researchers at Harvard University have developed a way to make the devices out of paper instead of casting chips out of plastic, which calls for a costly copper mold for each design. The method could help developing countries access the latest lab techniques.

Researchers realized that the natural pores in paper carry liquids in a way similar to that of standard microfluidic chips. The process uses a polymer liquid or photoresist that hardens when exposed to UV light to make impermeable "walls" to confine the fluids into narrow channels.

To make the paper processors, researchers soak a piece of normal office paper in a photoresist. They then cover one side with a transparency and on it draw with a pen the needed pattern of channels.

Exposing the paper to sunlight hardens the photoresist, except the lines or channels beneath the inked-on pattern. The transparency is peeled off, and the paper washed to remove any still-liquid photoresist. Once dried, the final product is a sheet of impermeable paper with a tiny network of embedded permeable channels.