A paper-based microfluidic device that can be programmed on the spot using a ball-point pen has been developed by US scientists. 

Microfluidic devices are increasingly being used to detect and analyse chemicals, particularly in areas such as medicine and water purity. Devices made from simple materials such as paper have great potential in developing countries, as they are cheap and easy to use. George Whitesides and colleagues at Harvard University in Cambridge have now developed a paper-based microfluidic device that can be programmed to carry out any test the user wants. 

Paper is not an obvious choice for handling fluids, but by soaking it in a polymer solution, and then curing it using light where you want the paper to be impermeable, you can create a network of channels in a piece of paper through which liquid can travel by capillary action. Whitesides' advance lies in stacking sheets of paper to give a programmable 3D device, which, he says 'brings another layer of sophistication to microfluidic devices.' 

The new device works by separating two sheets of treated paper with a layer of double-sided sticky tape. Tiny holes are made in this tape, aligned with the channels in the paper, act as buttons that are activated by pressing the two layers of paper together using a ball-point pen. Once the layers of paper are in contact, liquid flows from one to the other.

These single-use buttons make the device as universal as possible, allowing the user to adapt the microchannel system for a specific application on the spot. It could be programmed to test a wide variety of samples, such as blood, water, urine or saliva, for a wide range of analytes. The programmability decreases the cost for each application, as a different test kit is not needed each time.

John McDevitt, an expert in lab on a chip technologies at Rice University, Houston, US, says that this is exciting research, and that 'using these inexpensive materials is key for the medical micro-device field, which has to date been dominated by silicon, glass and polydimethlysiloxane (PDMS) materials.' 

David Barden

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