Assessment of Colorimetric Reporter Enzymes in the PURE System

Colorimetric reporter enzymes are useful for generating eye-readable biosensor readouts that do not require a device to interpret, an attractive property for applications in remote or developing parts of the world. The use of cell-free gene expression further facilitates such applications via amenability to lyophilization and incorporation into materials like paper. Currently, detection of multiple analytes simultaneously with these systems requires multiple reactions or a device. Here we evaluate seven enzymes and 15 corresponding substrates for functionality in a particular cell-free expression system known as PURE. We report eight enzyme/substrate pairs spanning four enzymes that are compatible with PURE. Of the four enzymes, three pairings exhibit no cross-reactivity. We finally show that at least one pairing can be used to create a third color when both are present, highlighting the potential use of these reporters for multiplex sensing.