Next generation gold nanomaterials for photoacoustic imaging.

Photoacoustic (PA) imaging integrates ultrasound with the molecular contrast afforded by optical imaging, enabling noninvasive, real-time visualization of tissue structures and contrasts. Gold nanoparticles (GNPs) have been extensively studied as contrast agents for PA imaging due to their strong optical absorption derived from localized surface plasmon resonance, particularly when engineered to absorb in the near-infrared (NIR) region to enhance tissue penetration. However, the use of conventional anisotropic nanoparticles that absorb the NIR wavelengths is limited by their poor photostability under pulsed lasing conditions, which restricts their applicability in longitudinal in vivo imaging studies. This review first outlines the fundamental principles of PA imaging and introduces conventional GNP-based contrast agents, emphasizing their applications and inherent limitations. Subsequently, recent advances in GNP engineering are discussed, with particular focus on strategies to improve photostability, and a future perspective on the development of GNP-based PA contrast agents is provided.