10.1021/acsbiomaterials.6b00012.s001 Yang Sheng Yang Sheng Lun-De Liao Lun-De Liao Aishwarya Bandla Aishwarya Bandla Yu-Hang Liu Yu-Hang Liu Nitish Thakor Nitish Thakor Mei Chee Tan Mei Chee Tan Size and Shell Effects on the Photoacoustic and Luminescence Properties of Dual Modal Rare-Earth-Doped Nanoparticles for Infrared Photoacoustic Imaging American Chemical Society 2016 surface effects undoped NaYF 4 shell vivo PA images REDNP PA signal amplitude undoped NaYF 4 PA contrast agents 2016-03-29 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Size_and_Shell_Effects_on_the_Photoacoustic_and_Luminescence_Properties_of_Dual_Modal_Rare_Earth_Doped_Nanoparticles_for_Infrared_Photoacoustic_Imaging/3167269 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 NaYF<sub>4</sub> or silica). We have also discovered that the choice of the coating material is critical as undoped NaYF<sub>4</sub> 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.