Enhancing hydrophilicity of photoacoustic probes for effective ratiometric imaging of hydrogen peroxide

Hydrogen peroxide (H₂O₂) plays a significant role in regulating the redox balance in the living body. Compared with traditional imaging techniques, ratiometric photoacoustic imaging is no doubt a superior choice for H₂O₂ visualization. However, the difficult design of ratiometric probes with only one activatable agent that exhibits two changeable absorption peaks under H₂O₂ activation remains a big challenge. In this work, we developed a near-infrared absorbing probe, which responded to H₂O₂ selectively and permitted the ratiometric photoacoustic imaging of H₂O₂ in living mice. The probe was constructed from an Aza-BODIPY backbone attached with a benzeneboronic acid pinacol ester moiety though a quaternization reaction. Oligo(ethylene glycol) (OEG) was introduced into hydrophobic Aza-BODIPY to enhance the water-solubility of the probe. The OEG-Aza-BODIPY-BAPE probe exhibited sensitive and specific ratiometric PA signals towards H₂O₂. In vivo experiments also showed that the OEG-Aza-BODIPY-BAPE probe can be used for ratiometric PA imaging. Overall, our work illustrated a high sensitivity hydrophilic photoacoustic probe for ratiometric imaging of hydrogen peroxide in vitro and vivo.