Structuring unbreakable and autoclavable hydrophobic barriers in paper via direct printing and mask-based photolithography

Microfluidic paper-based analytical devices (µPADs) have gained a lot of attention in recent years because they enable the production of diagnostic devices in a simple and cost-efficient way. To control the fluidic flow, hydrophobic barriers are generated that reach into the fibrous structure of the paper. Popular methods for creating such barriers are wax printing or polymer deposition. These barriers are however very stiff: bending or folding leads to the destruction of the barriers. Another problem is the low resistance of common barrier materials against different solvents, which makes it impossible to execute chemical tests on paper. Destruction of the barriers leads to leakage and causes assay failure. Here we present a method that produces bendable hydrophobic barriers on paper by photolithography. These barriers are based on silanes and withstand solvents such as DMSO. We show that these barriers can also be autoclaved, which is important for conducting biological assays using bacteria or cells on μPADs.