Credit: © 2008 RSC

Microfluidic, or lab-on-a-chip, techniques for automated handling of minute volumes of liquid have various applications in medical diagnostics, but for these to be of use in the developing world, simple and cheap methods are needed. Paper-based microfluidic devices show promise for this purpose and a group from Harvard University led by George Whitesides has devised a technique for making prototypes of them without any specialized equipment1.

The FLASH (fast lithographic activation of sheets) technique patterns microsized channels that extend through the thickness of a small piece of paper. The paper is impregnated with a photoresist, which is then selectively polymerized by exposure to ultraviolet light and temperatures of around 130 °C. Sunlight can be used as the light source, although an ultraviolet lamp gives more control over intensity. Photomasks can be printed simply with an inkjet printer or photocopier, or simply drawn by hand with a waterproof black pen, and the unexposed photoresist can be removed by washing. This process leaves hydrophilic channels bounded by hydrophobic barriers of polymerized photoresist that can distribute fluids by capillary action.

This technique may prove useful for rapidly creating prototypes of devices for medical applications in regions where facilities for conventional photolithography, such as clean rooms, are not available, as well as for applications such as environmental monitoring.