Thanks to a team of researchers from California Polytechnic State University, chemicals formed into pencils can be used to react with each other by simply drawing with them on a piece of paper. The work, published recently in the journal Lab on a Chip, is based on a well-known technique called paper-based microfluidics, which uses the capillary effect of paper to mix chemicals, indicating the presence or absence of a substance. The channels on the paper are made using waxy ink, and the chemicals are deposited in the channels by drawing between the lines. When water is added to the channels, it forces the chemicals to move due to capillary action and react with one other. As a proof-of-concept, the team tested pencils loaded with chemicals such as horseradish peroxidase (HRP) for monitoring blood glucose levels, and the results were identical to that using the traditional approach of finger pricking with a chemical solution.
Additionally, the reagents used for the test are stable for two months in the pencil form, whereas as liquids they degrade within a few days, making transport and storage easier and less expensive. From the abstract of the paper, “Reagent pencils offer a new option for preparing and customizing diagnostic tests at the point of care without the need for specialized equipment.”