Calibration-free photoacoustic thermal imaging of nanoparticle-labeled immune cells

Accurate temperature monitoring is essential for safe and effective application of mild hyperthermia (39–43 °C) in immunotherapy. We present a calibration-free photoacoustic (PA) thermometry approach using macrophages labeled with gold nanospheres (AuNSs). The labeled cells were embedded in tissue-mimicking phantoms containing varying fat content in the background. Ultrasound (US) imaging and PA imaging were performed during controlled heating. While US thermal strain (TS) varied significantly with fat content of the background tissue, PA signal from labeled cells showed consistent temperature dependence across all backgrounds. This stability arises from a water-stabilized interfacial layer around the NPs, decoupling the PA thermal response from bulk surrounding tissue properties. In addition to enabling robust, tissue-independent thermometry, these labeled immune cells retain their therapeutic functions, such as tumor homing and immunomodulation. This dual functionality supports image-guided immunotherapy with localized, controllable heating in complex biological environments.