Printer Toner Seals The Deal

Paper-based diagnostic tests offer hope to healthcare providers with limited resources, who need cheap, rapid, and practical tests. But their open design can cause problems when the bodily fluids moving through them evaporate or get contaminated. A new study suggests a simple fix: Seal the devices with laser printer toner (Anal. Chem., DOI: 10.1021/ac202837s).

Using a store-bought printer, California Polytechnic State University, San Luis Obispo researcher Andres Martinez coated paper microfluidic devices on both sides with up to six layers of toner; he and his colleagues found that four layers made the devices watertight and protected samples from contamination. They found that liquids migrated faster through toner-encased channels than through untreated devices, an effect Martinez’s team attributed to reducing evaporation. But printing also applies heat, which inactivates up to 90% of the devices’ assay enzymes. To avoid the problem, the researchers created 1-mm-diameter reagent addition ports–that is, zones free of toner--and applied the enzymes after depositing the toner.

Sealing paper microfluidics with toner is both easy and cheap, Martinez says; he estimates it cost his lab about a penny per device. The process also enables simultaneous printing of instructions, images, and labels on the devices, which isn’t possible when researchers use other sealing approaches such as lamination. Now Martinez hopes to apply the technology to third-world healthcare needs. “The end goal,” he says, “is to be able to test and diagnose disease in the field at a very low cost”.