title: Determination of biodistribution of ultrasmall, near-infrared emitting gold nanoparticles by photoacoustic and fluorescence imaging.
abstract: This study compares fluorescence and photoacoustic (PA) imaging of ex vivo tumors and organs from tumor-bearing mice injected intravenously with ultrasmall (<3  nm ) tiopronin-capped Au nanoparticles and compares the data with inductively coupled plasma mass spectrometry (ICP-MS). Good agreement is seen in particle distributions and concentrations at the organ level. The spatial resolution from the imaging techniques allows for localization of the particles within organ structures. Although the particles do not have a plasmon peak, their absorbance in the near-infrared (NIR) is sufficient for PA excitation. PA imaging shows an increase of signal as particle concentrations increase, with changes in spectrum if particles aggregate. Fluorescence imaging using the particles’ native NIR emission shows agreement in general intensity in each organ, though quenching of emission can be seen at very high concentrations. Both of these imaging techniques are noninvasive and labor-saving alternatives to organ digestion and ICP-MS and may provide insight into cellular distribution of particles. The simple construct avoids the use of toxic semiconductor materials or dyes, relying upon the gold itself for both the fluorescence and PA signal. This provides a useful alternative to more complex approaches to multimodal imaging and one that is readily translatable to the clinic.
authors.affiliation: McGill University, Department of Biomedical Engineering, 3775 University Street, Montréal, Quebec H3A 2B4, CanadabUniversity of Toronto, Institute of Biomaterials and Biomedical Engineering, 160 College Street, Toronto, Ontario M5S 3E1, Canada.
authors.forename: Wilson
authors.initials: W
authors.lastname: Poon
authors.affiliation: VisualSonics Inc., 6100-3080 Yonge Street, Toronto, Ontario M4N 3N1, Canada.
authors.forename: Andrew
authors.initials: A
authors.lastname: Heinmiller
authors.affiliation: McGill University, Department of Biomedical Engineering, 3775 University Street, Montréal, Quebec H3A 2B4, Canada.
authors.forename: Xuan
authors.initials: X
authors.lastname: Zhang
authors.affiliation: McGill University, Department of Biomedical Engineering, 3775 University Street, Montréal, Quebec H3A 2B4, Canada.
authors.forename: Jay L
authors.initials: JL
authors.lastname: Nadeau
mesh_terms: D000818:Animals; D002645:Chickens; D006046:Gold / Q000737:chemistry* / Q000493:pharmacokinetics; D053768:Metal Nanoparticles / Q000737:chemistry*; D051379:Mice; D057054:Molecular Imaging; D009369:Neoplasms / Q000473:pathology*; D061848:Optical Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D061088:Photoacoustic Techniques / Q000379:methods*; D008625:Tiopronin; D014018:Tissue Distribution
chemical_list: D006046:Gold; D008625:Tiopronin