Reversibly photoswitchable protein assemblies with collagen affinity for in vivo photoacoustic imaging of tumors.

Recent advancements in photoacoustic (PA) imaging have leveraged reversibly photoswitchable chromophores, known for their dual absorbance states, to enhance imaging sensitivity through differential techniques. Yet, their deployment in tumor imaging has faced obstacles in achieving targeted delivery with high efficiency and specificity. Addressing this challenge, we introduce innovative protein assemblies, DrBphP-CBD, by genetically fusing a photosensory module from bacterial phytochrome (DrBphP) with a collagen-binding domain (CBD). These protein assemblies form sub-100-nanometer structures composed of 24 DrBphP dimers and 12 CBD trimers, presenting 24 protein subunits. Their affinity for collagens, combined with impressive photoswitching contrast, markedly improves PA imaging precision. In various tumor models, intravenous administration of DrBphP-CBD has demonstrated enhanced tumor targeting and retention, augmenting contrast in PA imaging by minimizing background noise. This strategy underscores the clinical potential of DrBphP-CBD as PA contrast agents, propelling photoswitchable chromoproteins to the forefront of precise cancer diagnosis.