A sophisticated medical test that checks for dozens of diseases at the same time can be made from little more than paper and double-sided tape, bringing the cost within reach for the developing world.
The devices, known as microfluidics chips, operate much like a home pregnancy test, in which liquid creeps up a cellulose strip toward a color-changing line. But unlike the pregnancy test, these new chips can split a single stream of liquid into dozens of channels. Each of those canals could be used to perform a different diagnosis for diseases such as HIV, dengue fever or hepatitis.
With a bit more work, the Harvard University chemists who devised the paper test could build a user-friendly, multi-layered microfluidics device with raw materials that cost roughly three cents.
"Our work was intended to bring greater capability to paper-based analytical systems, by making them three-dimensional," said Andres Martinez, a co-author on the report, which appeared in the Proceedings of the National Academy of Sciences Monday.
In the developing world, cost, durability and ease-of-use are stumbling blocks for many medical technologies. But a cheap, simple device like a paper microfluidics chip could be used in health care diagnostics, and for monitoring environmental factors, quality of water and the health of plants and animals.
The material most commonly used for microfluidics, a rubber called PDMS, is not suited for mass production, said Michelle Khine, a microfluidics expert at the University California, Merced. Plastics would be better, but it is hard to carve complicated patterns in them without expensive equipment. Even if someone could make cheap chips, hooking them up to pumps is a huge hassle.
"For microfluidic chips to become ubiquitous, I think we still need to solve a bunch of technical problems," she said.
By switching to tape and paper, the team was able to get around several of those problems. Because paper wicks moisture, they don’t need any pumps to force fluid through the system. Even better, they can slice patterns in the tape with an off-the-shelf laser cutter, instead of using a multimillion-dollar semiconductor fabrication lab.
"It’s so simple, it’s brilliant," Khine said.
Harvard chemist and lead author George Whitesides and his team have a reputation for doing amazing things with ordinary materials and making tools suitable for health-care needs in the developing world. Not long ago, several other students in the same group built a centrifuge from an egg beater.
Those experiments make them rather unusual customers at the hardware store.
"When I tried to describe what I was hoping to do with the double-sided tape, the sales reps usually looked at me as though I had completely lost it," said Martinez. "After that initial interaction, and probably more out of pity than anything else, they were very helpful in showing me the double-sided tapes that they had in stock."
That awkward shopping spree may have solved one of the biggest problems in microfluidics engineering.
Citation: "Three-dimensional microfluidic devices fabricated in layered paper and tape," by Andres W. Martinez, Scott T. Phillips, and George M. Whitesides. PNAS: doi/10.1073/pnas.0810903105
Images: Whitesides Laboratory / Top: Prototypes with four inputs on the top of the chip, they distribute the four samples into different patterns of test zones on the bottom of the device. Right: Three dimensional device with four channels in a basket weave pattern. Four dyes are wicked from the sample reservoir through the channels and cross each other multiple times without mixing.