Nanoparticle Regrowth Enhances Photoacoustic Signals of Semiconducting Macromolecular Probe for In Vivo Imaging

Smart molecular probes that emit deep‐tissue penetrating photoacoustic (PA) signals responsive to the target of interest are imperative to understand disease pathology and develop innovative therapeutics. This study reports a self‐assembly approach to develop semiconducting macromolecular activatable probe for in vivo imaging of reactive oxygen species (ROS). This probe comprises a near‐infrared absorbing phthalocyanine core and four poly(ethylene glycol) (PEG) arms linked by ROS‐responsive self‐immolative segments. Such an amphiphilic macromolecular structure allows it to undergo an ROS‐specific cleavage process to release hydrophilic PEG and enhance the hydrophobicity of the nanosystem. Consequently, the residual phthalocyanine component self‐assembles and regrows into large nanoparticles, leading to ROS‐enhanced PA signals. The small size of the intact macromolecular probe is beneficial to penetrate into the tumor tissue of living mice, while the ROS‐activated regrowth of nanoparticles prolongs the retention along with enhanced PA signals, permitting imaging of ROS during chemotherapy. This study thus capitalizes on stimuli‐controlled self‐assembly of macromolecules in conjunction with enhanced heat transfer in large nanoparticles for the development of smart molecular probes for PA imaging.