A Portable Arsenic Sensor Integrating Bacillus megaterium with CMOS Technology

Hu, Chelsea Y.; McManus, John; Aghlmand, Fatemeh; Mei, Tracy; Larsson, Elin; Emami, Azita; Murray, Richard M.

doi:10.1021/acssynbio.4c00895

Published May 16, 2025 | Version Published

Journal Article Open

A Portable Arsenic Sensor Integrating Bacillus megaterium with CMOS Technology

1. California Institute of Technology
2. Texas A&M University

Bacteria innately monitor their environment by dynamically regulating gene expression to respond to fluctuating conditions. Through synthetic biology, we can harness this natural capability to design cell-based sensors. Bacillus megaterium, a soil bacterium, stands out due to its remarkable heavy metal tolerance and sporulation ability, making it an ideal candidate for heavy metal detection with low transportation costs. However, challenges persist: the synthetic biology toolkit for this strain is underdeveloped, and conventional whole-cell sensors necessitate specialized laboratory equipment to read the output. In our study, we have genetically modified B. megaterium for arsenic detection and established a detection threshold below the EPA’s recommendation of 10 ppb for drinking water in both vegetative and spore forms. Additionally, we have integrated both engineered B. megaterium living cells and spores with a complementary metal-oxide-semiconductor (CMOS) chip, providing a proof-of-concept for field-deployable arsenic detection. We show that the limit of detection (LOD) of our integrated sensor is within the range to test arsenic levels in soil and food. As a proof of concept, this work paves the way for the deployment of our sensor in resource-limited settings, ensuring real-time arsenic detection in challenging environments.

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Acknowledgement

This research is partially supported by the Institute for Collaborative Biotechnologies (ICB) through contract W911NF-19-D-0001 from the U.S. Army Research Office. In addition to the support from ICB, the study also received support from the Caltech Center for Sensing to Intelligence (S2I) and the Heritage Medical Research Institute. The content of the information does not necessarily reflect the position or policy of the government, and no official endorsement should be inferred.

Funding

This research is partially supported by the Institute for Collaborative Biotechnologies (ICB) through contract W911NF-19-D-0001 from the U.S. Army Research Office. In addition to the support from ICB, the study also received support from the Caltech Center for Sensing to Intelligence (S2I) and the Heritage Medical Research Institute. The content of the information does not necessarily reflect the position or policy of the government, and no official endorsement should be inferred.

Contributions

R.M.M., A.E., J.M., and C.Y.H. conceptualized the project; C.Y.H. and J.M. designed the experiments; C.Y.H., J.M., F.A., T.M., and E.L. conducted the experiments; C.Y.H. performed data analysis; C.Y.H. wrote the manuscript with assistance from T.M.

Conflict of Interest

The authors declare no competing financial interest.

Supplemental Material

Additional experimental results including promoter characterization, growth curves in different media, GFP expression dynamics, and arsenic tolerance assays with microscopy images (Figure S1); characterization of the arsenic sensor using fresh spores is detailed, including sporulation under arsenic exposure, dose–response curves, and determination of the limit of detection (Figure S2); a full protocol for protoplast transformation of Bacillus megaterium is included, along with recipes for all required media and buffers; finally, DNA sequences for all plasmid constructs and sensor components used in this study are listed, including the pMM1522 backbone, arsenic-responsive elements (pArs, pArs-ArsR), sfGFP, and alternative promoters (PDF)

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