Size and Shell Effects on the Photoacoustic and Luminescence Properties of Dual Modal Rare-Earth-Doped Nanoparticles for Infrared Photoacoustic Imaging

Infrared-emitting rare-earth (ytterbium and erbium) doped nanoparticles (REDNPs) have recently emerged as an excellent probe for both deep tissue luminescence and photoacoustic (PA) imaging with high resolutions and contrast. Here we report on the first study of the size and surface effects of the infrared PA imaging of dual modal REDNPs. We show that the PA signal amplitude generated by REDNPs is increased by increasing the size and coating the inorganic shell (undoped NaYF₄ or silica). We have also discovered that the choice of the coating material is critical as undoped NaYF₄ shell was able to enhance PA signal amplitude (by up to ∼30%) and infrared emission (19 times) simultaneously. The simultaneous enhancement of PA signal amplitude and infrared emission was due to increased phonon modes and reduced surface effects. The in vivo PA images obtained demonstrated that in addition to being excellent luminescent probes, the REDNPs also performed as successful PA contrast agents to visualize rodent cortical blood vessels.