Environmental uranium (U) concentrations are monitored in order to minimize human exposure, motivate environmental cleanup efforts, and enhance nonproliferation efforts. Current methods are not satisfactory to allow sensitive, selective, in situ detection in a robust, cost-effective, manner. Furthermore, sensing technologies which provide detection of bioavailable U are the most useful.
Current spectroscopy methods (e.g., ICP, AES, MS) are extremely sensitive and selective, but they are equipment-intensive, costly, require skillful operation, are not robust and thus cannot be easily used for in situ monitoring. This greatly limits sample throughput. A more recent approach is the use of antibodies and DNA enzymes with high specificity and selectivity for U. However, both systems require sample preparation and costly synthesis or purification steps. In addition, these methods cannot distinguish the amount of bioavailable U (i.e., that can transverse the cell membrane and exert toxicity). Another recent approach has been a whole-cell uranyl biosensor developed in the bacterium Caulobacter crescentus using a promoter that is activated in the presence of uranium. However, this promoter is not specific to U and is also activated by zinc, copper, and lead.
Using native bacterial regulatory systems, LLNL researchers have developed whole-cell biosensors that can be used in aqueous samples for sensitive and selective in situ detection of the uranyl oxycation (UO22+), the most toxic and stable form of U in oxygenated environments. Specifically, two functionally independent, native U-responsive regulatory systems, UzcRS and UrpRS, were integrated within an AND gate circuit in the bacterium Caulobacter crescentus, creating a synthetic U sensing pathway. By leveraging the distinct, but imperfect, selectivity profiles of both two component systems (TCS)s this pathway enabled high U selectivity. No cross-reactivity was observed with most common environmental metals (e.g, Fe, As, Cu, Ca, Mg, Cd, Cr, Al) or the U decay–chain product. The functionality of the sensor in an environmental context was confirmed by detection of U concentrations as low as 1 μM in ground water samples.
LLNL’s whole-cell U biosensors provides detection of bioavailable U which is:
- cost effective
- potentially autonomous
- for a wide range of aqueous environments
Government and commercial monitoring of uranyl contamination in regions surrounding known or suspected uranium mining, processing, and enrichment operations. This technology could also be incorporated into bioremediation operations and the study of uranium toxicity and resistance of organisms.