Lab on a printout

THERE are quite a few paper-based diagnostic tests available in the market. These include those for diabetes, pregnancy and HIV. But the nitrocellulose paper currently used in these test kits is expensive. Researchers from University of Washington, in the United States, have developed an alternative in which regular paper, the kind used in offices, can be modified and used instead of the nitrocellulose paper.

The regular paper is modified with a cheap industrial chemical, divinyl sulfone, which is available in the market as an adhesive. The researchers diluted the chemical with water and poured it in a plastic bag. A stack of paper was also put in the bag, which was then shaken for a couple of hours. This allowed the chemical to spread evenly on the paper.

When the paper dried, it had a smooth texture. A variety of molecules of medical interest such as proteins, antibodies and DNA could stick to it. These molecules can be easily transferred to the paper using an inkjet printer where the ink had been replaced with the molecules.

To test the efficacy of their design, the researchers used a sugar called galactose. When the paper with galactose molecules printed on it was exposed to fluorescent ricin, a poison that sticks to galactose, ricin’s presence was confirmed. “We wanted to make the system as independent of the end applications as possible, something any researcher could plug into,” says Daniel Ratner, lead author of the paper recently published in Langmuir.

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