Now they have succeeded in carrying out both sticky acts simultaneously. It’s a simple process. First the researchers coat a sheet of paper with DVS, giving it lots of “hooks” on which biomolecules like proteins and DNA can be hung. Next, they use an Epson inkjet printer to create patches of biomolecule, filling empty refill ink cartridges with the appropriate reagent. In alkaline solution, the molecules spontaneously form chemical bonds with the sole remaining ‘sticky end’ of the DVS linkers. The position and shape of these patches can be controlled with an accuracy of less than a millimetre.
When a sample meets the coated paper, its ingredients will stick to the respective patches tailored to capture them and, depending on the design, change colour or become fluorescent. The paper bioassays still work after being stored for at least 30 days in dry air.
One of the next steps will be to combine the printing of patches with the printing of flow channels that can convey particular samples to specific parts of the assay. If this is successful, it would allow complex diagnoses to be made quickly and cheaply on a single sheet of paper. As throwaway ideas go, paper-based diagnostic tests could be one of our most valuable ones yet.