Researchers have developed a swallowable biosensor, called MagGel-BS, that uses engineered bacteria encapsulated in magnetic hydrogels to detect signs of gastrointestinal bleeding.
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A Gentler Way to Detect GI Disease
Current diagnostic tools for inflammatory bowel disease (IBD) and colorectal cancer often rely on colonoscopy, which is accurate, but invasive and uncomfortable.
Looking for alternatives, scientists have turned to bacterial biosensors: live, engineered microbes that react to disease biomarkers in the gut.
MagGel-BS addresses long-standing challenges that have held back these tools: bacterial survival in the digestive tract, safe containment, and reliable recovery from stool samples.
How does MagGel-BS Work?
MagGel-BS consists of engineered E. coli Nissle 1917 (strain YES601) designed to respond to heme, a key marker of gastrointestinal bleeding.
The bacteria are encapsulated in calcium cross-linked alginate hydrogel microspheres, each under 250?μm in diameter. Just small enough to transit the digestive system efficiently.
The hydrogel also contains iron oxide nanoparticles (Fe3O4), allowing for magnetic separation once the microspheres are excreted in the feces. This structure shields the bacteria from gastric acid and bile while allowing small molecules like heme to diffuse in and activate a bioluminescent genetic circuit.
In Vivo Performance in Mice
After oral administration to colitis mouse models, the microspheres passed through the GI tract and were recovered magnetically from feces within approximately 15 minutes, achieving ~75 % retrieval efficiency within eight hours. The bacteria produced a luminescent signal in response to heme, with signal intensity correlating to disease severity.
The detection limit was as low as 1 μM, well within the physiological range for gastrointestinal bleeding. The total turnaround time, from ingestion to signal readout, was approximately 25 minutes under experimental conditions.
The encapsulation method increased bacterial survival tenfold in simulated gastric fluid compared to unencapsulated bacteria. Bacterial leakage was low (<0.15 %), and the hydrogel maintained its integrity under simulated intestinal stress.
The biosensors remained active after at least 30 days of storage in freeze-dried form, and tests in healthy mice showed good biocompatibility, with no signs of immune response or toxicity.
Next Steps for MagGel-BS
While the system currently targets only heme, the researchers suggest the platform could be reprogrammed to detect a wider range of gut disease biomarkers. Still, more work is needed to optimize performance and validate safety and efficacy in humans.
MagGel-BS demonstrates how encapsulation and magnetic recovery can bring engineered microbes closer to practical, non-invasive diagnostics, especially for diseases where symptoms may be intermittent or difficult to detect early.
Journal Reference
Xu C.-Y., et al. (2025). Magnetic Hydrogel: Enhanced Bacterial Biosensor for Speedy Gut Disease Detection. ACS Sensors, 10, 8424–8434. DOI: 10.1021/acssensors.5c01813,