Proteins can be rapidly prototyped with cell-free expression (CFE) but in most cases there is a lack of probes or assays to measure their function directly in the cell lysate, thereby limiting the throughput of these screens. Increased throughput is needed to build standardized, sequence to function data sets to feed machine learning guided protein optimization. Herein, we describe the use of fluorescent single-walled carbon nanotubes (SWCNT) as effective probes for measuring protease activity directly in cell-free lysate. Substrate proteins were conjugated to carboxymethyl cellulose-wrapped SWCNT, yielding stable and sensitive probes for protease detection with a detection limit of 6.4 ng/mL for bacterial protease from