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The development of deployable biosensors that monitor the cumulative dose of toxic pesticides is essential to enable monitoring of soil and water exposure in populated areas. Liquid crystal elastomers (LCEs) offer unique potential as cumulative dose biosensors due to their ability to store chemical information within the polymer network that can later be decoded in the form of quantifiable shape changes. Here, we present an LCE-based biosensor for the detection of the organophosphorus pesticide malathion through the immobilization of the hydrolytic enzyme pig liver esterase (PLE). Exposure to malathion was detected via shape change of the LCE from a flat ribbon to a helical structure. Quantification of the helical pitch provided a label free readout that correlated directly with the cumulative dose of malathion and enabled detection of successive doses independent of dosage timing or dilution. The cumulative dose was chemically encoded in the LCE and could be decoded by hydration, even after successive drying and rehydration steps. Importantly, the signal from the LCE was largely insensitive to sensing conditions and to interference from various chemicals. The combined results illustrate the utility of biocatalytic LCEs for monitoring harmful pollutants while allowing continuous and cumulative dose sensing in real-world conditions. [Display omitted] • LCE-based biosensor for malathion detection using pig liver esterase. • Label-free shape-change readout by measuring the ribbon helical pitch. • Malathion cumulative dose is chemically encoded in LCE. • Output can be rapidly encoded/decoded by drying/hydration of LCE. [ABSTRACT FROM AUTHOR]