Cascaded amplifying circuits enable ultrasensitive cellular sensors for toxic metals

Abstract

Cell-based biosensors have great potential to detect various toxic and pathogenic contaminants in aqueous environments. However, frequently they cannot meet practical requirements due to insufficient sensing performance. To address this issue, we investigated a modular, cascaded signal amplifying methodology. We first tuned intracellular sensory receptor densities to increase sensitivity, and then engineered multi-layered transcriptional amplifiers to sequentially boost output expression level. We demonstrated these strategies by engineering ultrasensitive bacterial sensors for arsenic and mercury, and improved detection limit and output up to 5,000-fold and 750-fold, respectively. Coupled by leakage regulation approaches, we developed an encapsulated microbial sensor cell array for low-cost, portable and precise field monitoring, where the analyte can be readily quantified via displaying an easy-to-interpret volume bar-like pattern. The ultrasensitive signal amplifying methodology along with the background regulation and the sensing platform will be widely applicable to many other cell-based sensors, paving the way for their real-world applications.

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Fig. 1: Modular multilayer signal amplification for engineering ultrasensitive transcription-based cellular sensors.
Fig. 2: Amplifying arsenic sensor by tuning intracellular receptor density and employing single-layer transcriptional amplification.
Fig. 3: Sequential cascaded amplification further boosts the sensor’s sensitivity and output amplitude.
Fig. 4: Synergistic multi-layered amplification enables ultrasensitive sensors for mercury.
Fig. 5: Tuning the sensor background and output dynamic range via promoter engineering and reporter degradation regulation.
Fig. 6: Microbial sensor array display enabled by agarose hydrogel entrapment and microfluidic encapsulation for easy-to-use monitoring of arsenic contamination.

Data availability

All data and plasmids supporting the findings are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank M. Billah (Khulna University) and his colleagues for facilitating our collections of groundwater samples in Bangladesh. This work was supported by UK BBSRC project grant (no. BB/N007212/1), Leverhulme Trust research grant (no. RPG-2015-445), Wellcome Trust Seed Award in Science (no. 202078/Z/16/Z) and EPSRC/BBSRC Global Challenges Research Fund Awards. X.W. was supported by scholarships from the China Scholarship Council and Scottish Universities Life Sciences Alliance. F.V., E.P. and S.J.M. were supported by the Ecole Polytechnique Federale de Lausanne, a Swiss National Science Foundation Grant (no. CR23I2 140697) and a SystemsX.ch Special Opportunity Grant (no. 2015/325).

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B.W. conceived and led the study. X.W. designed the experiments with inputs and supervision from B.W. and C.F. X.W. performed all the experiments and data analysis excluding the microfluidics-based experiments. F.V., E.P. and S.J.M. designed and performed the microfluidics-based experiments. All authors took part in the interpretation of results and preparation of materials for the manuscript. B.W. and X.W. wrote the manuscript with comments from all authors.

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Correspondence to Baojun Wang.

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B.W. and X.W. filed a patent application based on the technology invention in this work.

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Wan, X., Volpetti, F., Petrova, E. et al. Cascaded amplifying circuits enable ultrasensitive cellular sensors for toxic metals. Nat Chem Biol 15, 540–548 (2019). https://doi.org/10.1038/s41589-019-0244-3

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