Near-infrared photochromic miniprotein enables photoacoustic molecular imaging of acute inflammation and intracellular antigens.

rsmiRFPnano, a compact cyanobacteriochrome-derived probe under 19 kDa, enables high-resolution photoacoustic imaging of inflammation and intracellular antigens in vivo.

• Why it matters: Current bacteriophytochrome-based probes are too large (>55 kDa), limiting their use in designing effective molecular reporters for deep-tissue photoacoustic imaging, which is crucial for studying biological processes noninvasively.
• What they did: Researchers engineered rsmiRFPnano, a small, efficient, photoswitchable probe that incorporates biliverdin and performs well in live cells, and developed reporters for NF-κB and AP-1 pathways, as well as nanobody probes for intracellular antigens.
• The result: These probes successfully visualized acute inflammation and intracellular antigens in vivo, establishing rsmiRFPnano as a versatile, ultracompact platform for molecular photoacoustic tomography.