(24a) Plasmonic Semiconductor Nanoparticles for Photoacoustic Imaging and Photothermal Therapy

The creation and study of non-metallic nanomaterials that exhibit localized surface plasmon resonance (LSPR) interactions with light has been a rapidly growing field of research over the past few years. In particular self-doped copper chalcogenide semiconductor nanocrystals have extremely high concentrations of free charge carriers, which allows them to exhibit LSPR at near infrared (NIR) wavelengths. In this presentation, we will discuss recent progress in developing and synthesizing doped semiconductor nanocrystals with LSPR, studying and controlling the optical properties of these plasmonic nanocrystals, and applying them as contrast agents for photoacoustic imaging, as sensitizers for photothermal therapy, and in sensing applications. A key advantage of these materials is the ability to produce strong LSPR absorbance at wavelengths where tissue is relatively transparent, using small (<10 nm) quasi-spherical particles.  Reaching these IR wavelengths using conventional plasmonic materials (silver and gold) requires engineering larger nanorods, nanoshells, nanocages, etc. The smaller semiconductor naoparticles can potentially have improved biodistribution and clearance profiles compared to those larger structures. We have synthesized several binary and ternary allow nanoparticles with tunable LSPR wavelength, and have also reported a new type of heterogeneous nanoparticles composed of a heavily-doped semiconductor domain (Cu_2-xSe) and a metal domain (Au). These heterodimers exhibit a broad localized surface plasmon resonance (LSPR) across visible and near infrared (NIR) wavelengths, arising from interactions between the two nanocrystal domains. We demonstrate both in vivo photoacoustic imaging and in vitro dark field imaging, using the broad LSPR in Cu_2-xSe-Au hybrid NPs to achieve contrast at different wavelengths. The high photoacoustic imaging depth achieved, up to 17 mm, shows that these novel contrast agents could be clinically relevant. We have seen similarly promising results with pure copper chalcogenide alloy nanoparticles, and are also investigating use of these particles for photothermal therapy and sensing applications.