Stimuli-Responsive Organic Near-Infrared Photoacoustic Probes

Photoacoustic (PA) imaging is an emerging biomedical imaging technique with the features of non-invasiveness and non-ionization. It takes advantage of the photothermal effect of PA probes to convert absorbed photon energy into heat and subsequent transient thermoelastic tissue expansion for ultrasonic waves for PA images. Thus, PA imaging exhibits the combined superiority of high-contrast optical imaging and deep tissue penetration of acoustic imaging, which furnishes high-resolution and high-contrast tissue images. Stimuli-responsive organic PA agents in the near-infrared (NIR) biological window have attracted increasing attention because of their low biological toxicity and response characteristics. This review focuses on the recent research progress of stimuli-responsive organic NIR probes for PA imaging, including the temperature response, pH response, redox response, metal ion response, and enzyme response. And the stimuli-responsive mechanisms are highlighted in detail. Moreover, their perspectives and challenges are discussed. It will be of great help for the further development of organic NIR PA probes with stimuli-response.