To demonstrate the new microfluidic concept, paper strips containing arrays of dots dipped in luminol were created. Blood was then sprayed on the strips, showing the presence of hemoglobin. (Photo courtesy of Purdue University)

Researchers at Purdue University (West Lafayette, IN) have invented a technique for making microfluidic devices out of paper. The patented technique could enhance commercially available diagnostic devices that use paper-strip assays such as those used to test for diabetes and pregnancy.

"With current systems that use paper test strips you can measure things like pH or blood sugar, but you can't perform more complex chemical assays," remarks Babak Ziaie, professor of electrical and computer engineering and biomedical engineering. "This new approach offers the potential to extend the inexpensive paper-based systems so that they are able to do more complicated multiple analyses on the same piece of paper. It's a generic platform that can be used for a variety of applications.”

As detailed in the journal Lab on a Chip, current lab-on-a-chip technology is relatively expensive because chips must be specifically designed to perform certain types of chemical analyses, with channels created in glass or plastic and tiny pumps and valves directing the flow of fluids for testing. In contrast, the new technique is simpler because the testing platform is contained on a disposable paper strip containing patterns created using a laser.

Colored water shows how liquid wicks along tiny channels formed in paper using a laser. Silica microparticles were deposited on patterned areas, allowing liquid to diffuse from one end of a channel to the other. (Photo courtesy of Purdue University)

The researchers start with paper having a hydrophobic coating, such as parchment paper or wax paper used for cooking. A laser is used to burn off the hydrophobic coating, forming lines, dots, and patterns. The removal of the hydrophobic agent in select areas creates islands of hydrophilic patterns, Ziaie explains. "This modified surface has a highly porous structure, which helps to trap and localize chemical and biological aqueous reagents for analysis. Furthermore, we've selectively deposited silica microparticles on patterned areas to allow diffusion from one end of a channel to the other." These microparticles help to wick liquid to a location where it can combine with another chemical, called a reactant, causing it to change colors and indicating a positive or negative test result.

To demonstrate the new concept, the researchers created paper strips containing arrays of dots dipped in luminol, a chemical that turns fluorescent blue when exposed to blood. Then they sprayed blood on the strips, showing the presence of hemoglobin. "This is just a proof of concept," Ziaie remarks.

The scientists say that their process is easier than others because they simply use a laser to create patterns on commercially available paper impregnated with hydrophobic material. "It's a one-step process that could be used to manufacture an inexpensive diagnostic tool for the developing world, where people can't afford more-expensive analytical technologies," Ziaie says.

For more information on this technology, visit the Purdue newsroom article "New Lab-on-Chip Advance Uses Low-Cost, Disposable Paper Strips."

Interested in microfluidics? For a small sampling of MPMN articles on microfluidic technologies, peruse "Channeling Microfluidic Devices into Point-of-Care Diagnostics," "Scientists Put Microfluidic Devices in Stitches," and "Movable Microchannels Could Revolutionize Microfluidics."