Optimizing the geometry of photoacoustically active gold nanoparticles for biomedical imaging

Photoacoustics is an upcoming modality for biomedical imaging, which promises minimal invasiveness at high penetration depths of several centimeters. For superior photoacoustic contrast, imaging probes with high photothermal conversion efficiency are required. Gold nanoparticles are amongst the best performing photoacoustic imaging probes. However, the geometry and size of the nanopar-ticles determine their photothermal efficiency. We present a systematic theoretical analysis to determine the optimum nanoparticle geometry with respect to photoacoustic efficiency in the near-infrared spectral range, for superior photoacoustic contrast. Theoretical predictions are illustrated by experimental results for two most promising nanoparticle geometries, namely high aspect ratio gold nanorods and gold nanostars.