Lab-on-a-chip devices work by directing small samples of liquid through tiny “microchannels” embedded in a small platform, and are used for analyzing liquids in medical and scientific settings. Earlier this week, we reported on a high school teacher who has invented a way of creating such devices using transparency film and a photocopier. Now, scientists from Indiana’s Purdue University have announced a new method of making them using paper. While previous approaches have involved laying down lines of wax or other hydrophobic (water-repelling) material on hydrophilic (water-absorbing) paper, this method uses store-bought hydrophobic paper, and creates the microchannels by burning away the waterproof coating with a laser.
Currently, lab-on-a-chip devices are made by using photolithography or etching techniques to create microchannels on small glass or plastic platforms. The liquid being analyzed must then be pumped through those channels using tiny pumps and valves.
The Purdue process starts with a strip of ordinary wax or parchment paper, such as that used for cooking. Once the laser burns away the wax in precise lines, dots and patterns, the underlying base hydrophilic paper is exposed. Silica microparticles are also placed in key locations, to help draw the liquid through the channels. As with conventional paper strip tests, the liquid is ultimately drawn to a reagent, which will cause the paper to change color if a specific chemical is present in the liquid. Utilizing the microchannels, different parts of the paper strip could be used to test for different chemicals within the same sample.
As a proof-of-concept exercise, the scientists treated some of the paper with luminol, which is used to detect the presence of hemoglobin in blood. When blood was introduced to the paper, the luminol fluoresced blue.
The field of paper microfluidics is not brand new, but this particular approach is claimed to be considerably simpler than what has preceded it. “Our process is much easier because we just use a laser to create patterns on paper you can purchase commercially and it is already impregnated with hydrophobic material,” said Babak Ziaie, a Purdue professor of electrical and computer engineering and biomedical engineering. “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.”
Researchers from Pennsylvania State University announced something similar last November – paper test strips that indicate when they’re ready to be read, via a color-changing dot that the liquid reaches through microchannels within a wax coating.
The Purdue research was recently published in the journal Lab on a Chip.