Efficient Upconverting Nanophosphors for Imaging and Photodynamic Therapy
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Efficient Upconverting Nanophosphors for Imaging and Photodynamic Therapy Brian G. Yust, Gangadharan Ajith Kumar, Lawrence C. Mimun, Dhiraj K. Sardar Dept. of Physics & Astronomy, Univ. of Texas at San Antonio, One UTSA Circle, San Antonio, Tx, 78249-1644 U.S.A. ABSTRACT Erbium-Ytterbium codoped nanophosphor systems are explored for high efficiency upconversion. The NIR to visible upconversion from 1550 nm and 980 nm excitation are of particular interest to us for biomedical applications such as imaging, sensing, and photodynamic therapy. Variations in synthesis method and rare earth concentration are carried out in sodium, potassium, and transition metal based phosphor materials. The spectroscopic properties of the material dry and in biologically appropriate solution are taken. After bioconjugation, these particles will be used in a mouse model to demonstrate that cancer imaging with a near-infrared excitation source is possible. INTRODUCTION Upconverting nanomaterials have recently become an important topic of research due to their potential applications in biomedical imaging and photodynamic therapy. In particular, nanoparticles which can be excited with near-infrared light are highly attractive for biomedical purposes because of the low absorption and scattering power of tissues in this region. Practically, this leads to better depth penetration of the excitation source through tissues which results in more useful biomarkers for imaging and greater photoactivation for photodynamic therapy. The well known and studied erbium-ytterbium and thulium-ytterbium codoped systems can be excited with 980nm or 1550nm and emit in the visible and near-infrared. While NaYF4 is known to be one of the best and most efficient hosts for these upconversion systems, the emission is primarily dual band with the brightest peaks around 550nm and 660nm for the erbium-ytterbium system [1,2]. By doping these upconversion systems into similar structures, we may retain a relatively high efficiency for the upconversion process while obtaining more singular emission profiles. Sodium and potassium transition metal fluorides of the form NaMF3, were chosen as the host structures to compare with NaYF4. The ultimate goals are 1) to provide single band upconversion emission for multiplexing and 2) to optimize these particles for dualmode infrared imaging through one excitation and emission channel and infrared photodynamic therapy (IRPDT) through another excitation channel which couples the upconversion fluorescence energy to a photosensitizer loaded onto the surface of the particles. EXPERIMENTAL DETAILS NaYF4, KMnF3, and NaMF3 (M=Mg, Mn, Fe, Co, Ni) nanoparticles doped with either erbium-ytterbium, thulium-ytterbium, or erbium-neodymium-ytterbium were synthesized using the thermal decomposition or hydrothermal synthesis methods. In a typical thermal decomposition synthesis, sodium and rare earth trifluoroacetate precursors were mixed in an
oleic acid / octadecene mixture, degased for an hour, and then heated to ~350ºC for thirty minutes [1,2].
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