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ABSTRACT Deficiencies in knowledge about water quality prevent or obscure progress on a panoply of public health problems globally. Specifically, such lack of information frustrates effective and efficient government regulation to protect the public from contaminated drinking water. In this Practical Paper, we lay out how recent scientific innovations in synthetic biology mean that rapid, at-home tests based on biosensor technology could be used to improve water quality monitoring and regulation, using the example of the U.S. Environmental Protection Agency's Lead and Copper Rule currently under revision. Biosensor tests can be used by non-scientists and the information that biosensor tests generate is relatively cheaper and faster than standard laboratory techniques. As such, they have the potential to make it possible to increase the number and frequency of samples tested. This, in turn, could facilitate more accurate compliance monitoring, justify more protective substantive standards, and more efficiently identify infrastructure priorities. Biosensors can also empower historically underrepresented communities by facilitating the visibility of inequities in lead exposure, help utilities to ensure safe water delivery, and guide policy for identifying and replacing lead-bearing water infrastructure, thereby improving public health. As the technology matures, biosensors have great potential to reveal water quality issues, thereby reducing public health burdens. 

Industrialization and failing infrastructure have led to a growing number of irreversible health conditions resulting from chronic lead exposure. While state-of- the-art analytical chemistry methods provide accurate and sensitive detection of lead, they are too slow, expensive, and centralized to be accessible to many. Cell-free biosensors based on allosteric transcription factors (aTFs) can address the need for accessible, on-demand lead detection at the point of use. However, known aTFs, such as PbrR, are unable to detect lead at concentrations regulated by the Environmental Protection Agency (24−72 nM). Here, we develop a rapid cell-free platform for engineering aTF biosensors with improved sensitivity, selectivity, and dynamic range characteristics. We apply this platform to engineer PbrR mutants for a shift in limit of detection from 10 μM to 50 nM lead and demonstrate use of PbrR as a cell-free biosensor. We envision that our workflow could be applied to engineer any aTF.