Penciling In Reagents

Researchers have developed a simple method for loading chemical reagents onto paper-based microfluidic devices: Just draw them on. Andres W. Martinez and coworkers at California Polytechnic State University, San Luis Obispo, developed reagent pencils as a solvent-free way to deposit the chemicals needed for paper assays (Lab Chip 2015, DOI: 10.1039/c5lc00297d). The Cal Poly team makes the pencils by dispersing reagents in a matrix of 75% poly(ethylene glycol) methyl ether and 25% graphite powder. The researchers then press the mixture into pellets, which they load into mechanical pencils. They use the pencils to draw the reagents on premarked channels on paper microfluidic devices. During an assay, water in the sample wicks reagents into a test zone. The researchers ran colorimetric glucose assays using the enzymes glucose oxidase and horseradish peroxidase. They found that the assays performed with pencil-deposited reagents had comparable accuracy and precision as ones performed with solvent-deposited reagents. The enzymes remain stable in the reagent pencils for weeks to months.