Welcoming Remarks

Harnessing the high affinity, selectivity, and sensitivity of proteins for their target analyte in crowded environments for sensing applications has long been the goal of biosensors. However, living cells are dynamic, must be fed/monitored, easily killed, and difficult to control. Thus, commercial biosensors typically use just one or two proteins in an in vitro assay (e.g. antibodies in ELISA assays, glucose oxidase in glucose meter). However, recent advancements have demonstrated the robustness of Lyophilized E. coli-based cell-free protein synthesis systems to overcome many of the stability/reliability challenges of cell-based biosensors but retain complex webs of biochemical pathways that require dozens of proteins for sensing. These advancements include 1) the ability to lyophilize E. coli lysate with energy and DNA template molecules as a “single-pot”, “just-add-water or sample” system that is robustly shelf-stable for months, 2) the use of clarified E. coli lysate in small reaction volumes to reduce the cost of sensing regents to less than $1, 3) the realization that RNase Inhibitor is essential when using human samples, 4) the development of low-cost production methods for RNAse inhibitor to maintain biosensor affordability, and 5) the development of diverse reporter systems for rapid and accurate visual or electronic outputs. The field is thus rapidly growing with sensors developed to reliably detect diverse pathogens, cancers, and toxins. Here we discuss the development of cell-free systems for biosensing and its particular application in detecting glutamine, asparaginase, and endocrine disrupting chemicals.