10 December 2008—Harvard researchers have made a device from just paper and double-sided sticky tape that could be used to test for diseases at just a fraction of the cost of today’s diagnostic devices. George Whitesides, a professor of chemistry and chemical biology, and his colleagues built the three-dimensional microfluidic device using photolithography techniques similar to those used in the semiconductor industry. The study was published this week in the Proceedings of the National Academy of Sciences .
”It’s very creative and also potentially very useful,” says Sam Sia, assistant professor of molecular and microscale bioengineering at Columbia University. ”It has use for diagnostics in resource-poor settings.”
Like microchips, microfluidic diagnostic devices are made using etching or photolithography techniques to create channels on silicon, glass, or plastic substrates. Fluids flow through the chip’s microchannels, where they go through chemical reactions that indicate the presence or absence of disease. Depending on their complexity and materials, they typically cost between US $10 and $1000. The Harvard device is simply a stack of papers. Tiny channels lead from eight single wells on top and branch out through the stack to an array of microwells on the bottom.
To construct the device, the researchers first soaked the paper in a photoresist and then exposed the paper to ultraviolet light through a negative of the channel pattern. The portions of the paper that were exposed to the light hardened, creating a pattern of solid, water-repellent regions. The remaining unexposed photoresist was washed away, leaving the pattern of microchannels in the paper. Then alternating layers of patterned paper and double-sided tape with precisely placed perforations were stacked atop each other to create a 3-D device through which fluids can flow both horizontally, through the paper microchannels, and vertically, through the perforations in the tape.
Unlike devices made from plastic or glass, the paper device does not require a pump to transport the fluid. The paper itself transports the fluid laterally because of its wicking properties.
The materials to build one device cost just three cents, says Andres Martinez, a graduate student in Whitesides’s Harvard laboratory. However, while the aim is to produce a low-cost device, three cents will not likely be the final cost, because the device will probably need to incorporate analytic chemicals and other items. ”The philosophy behind the whole project is to make it as cheap as possible, so the cost of the device is not a limiting factor,” Martinez says.
The goal is to use it to diagnose diseases that are endemic in developing countries. But before it can be useful, Columbia’s Sia says researchers will have to make sure it works on clinically relevant samples like blood.
Whitesides also acknowledges that being able to perform more-complex functions is a critical step. ”If you’re trying to analyze a sample of blood for AIDS, the test is more difficult biologically,” he says. ”It’s much different than analyzing a urine sample for the presence of glucose.”
Martinez says the next step is working with immunological assays and HIV. He also wants to take advantage of the unique properties of paper, like its ability to filter, which he says could be used to filter out red blood cells.