Target-triggered assembly of engineered bacteria enables dual-mode detection of microRNA

Engineered bacteria offer unique opportunities for biosensing because they combine genetically programmable biological activity with tunable surface interfaces. However, constructing living sensing systems that enable programmable recognition, reliable signal output, and robust performance in complex samples remains challenging. Here, we report an interfacially engineered bacterial sensing platform for dual-mode microRNA detection. Engineered Escherichia coli expressing enhanced green fluorescent protein (eGFP) were used as living signal carriers, and a polyphenol coating was deposited to create a stable, functionalizable interface. This coating preserved bacterial fluorescence while enabling immobilization of nucleic acid hairpin probes. Upon target recognition, catalytic hairpin assembly (CHA) was triggered, driving the programmable bridging and aggregation between bacteria and magnetic beads. This process converts molecular recognition into a magnetically separable assembly event, enabling target enrichment and background reduction. Meanwhile, enriched bacteria provide fluorescence output via intracellular eGFP, while Fe³⁺ released from the coating under acidic conditions generates a Prussian blue colorimetric signal. Together, these processes establish a fluorescence-colorimetric dual-mode sensing platform with limits of detection of 5.33 pM for the fluorescence mode and 14.1 pM for the colorimetric mode. In serum samples from glioma patients, the platform effectively distinguished patients from healthy controls, with dual-mode analysis showing improved discrimination performance compared to single-mode detection. This work demonstrates that interfacial engineering transforms engineered bacteria into multifunctional living sensing units and provides a practical strategy for developing reliable biosensing systems for liquid biopsy applications.