Biodegradable plasmonic nanoclusters as contrast agent for photoacoustic imaging

Metallic nanoparticles have been widely used in a variety of imaging and therapeutic applications due to their unique optical properties in the visible and near-infrared (NIR) regions - for example, various plasmonic nanoparticles are used for molecular photoacoustic imaging and photothermal therapy. However, there are concerns that these agents may not be safe under physiological conditions, because these nanoparticles are not biodegradable, could accumulate and, therefore, could be toxic long-term. We investigate the feasibility of using biodegradable gold nanoclusters as a contrast agent for highly sensitive photoacoustic imaging. The size of these biodegradable nanoclusters, consisting of sub-5 nm primary gold particles and a biodegradable polymer binder, is less than 100 nm. Due to plasmon coupling, these nanoclusters are characterized by a broad extinction spectrum that extends to the near infrared (NIR) spectral range. Photoacoustic imaging of tissue models containing inclusions with different concentrations of nanoparticles was performed using a tunable pulsed laser system. The results indicate that the biodegradable nanoclusters, comprised of small gold nanoparticles, can be used as contrast agents in photoacoustic imaging.