1. 2National Institute of Standards and Technology, Boulder, CO 80305
Magneto-Optical Properties of Iron Oxide Nanoparticles for Use in Medical Imaging
Kathleen B. Oolman1, Subash Kattel1, Katherine P. Rice2, William D. Rice1
1Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071
2National Institute of Standards and Technology, Boulder, CO 80305
Outline
Nanoparticle properties and applications in medical imaging
Optical characterization of iron oxide nanoparticles

2. Diameter Nanoparticles (NP)
Small particles made out of semiconductor material
<100nm in diameter
Absorb light and re-emit light based on the material and size of particle
Semiconductor nanoparticles increasing in diameter

3. Semiconductor band structure
Band gap energy (Eg)
Absorption
Photon is absorbed and electron jumps to conduction band
Optically creates electron- hole pair called exciton
Photoluminescence (PL)
Electron relaxes to valence band producing photon
Radiative relaxation
Cadmium selenide (CdSe) nanocrystals absorption and photoluminescence
WD Rice et al., Nature Nanotechnology, 11, (2016)

4. Iron Oxide Nanoparticles
Magnetite iron oxide nanoparticles (Fe3O4)
Rare earth metal dopants should add interesting optical properties
Terbium (Tb3+) and Europium (Eu3+) replace Fe3+ in octahedral lattice sites
Oxygen
Iron (tetrahedral Fe3+)
Iron (octahedral Fe3+ and Fe2+)
M Setvín et al., Chem. Soc. Rev., 46, (2017)

5. doped Iron oxide nanoparticles
Approximately 5nm in diameter
Dopants cluster on outside of NP due to atomic size
1:6 ratio of Tb3+ to Fe3+ in lattice
Similar characteristics for Eu-doped NPs
High-angle annular dark-field (HAADF) image of Tb-doped nanoparticles taken with a transmission electron microscope
K.P. Rice, et al. Applied Physics Letters; 106, (2015)

6. Nanoparticles for medical imaging
Magnetite iron oxide nanoparticles could be used as a contrasting agent for magnetic resonance imaging (MRI)
Magnetic
Non-toxic and biocompatible
Small
MnO nanoparticle contrasting agents MR image in tissue cells
Hyon Bin Nam et al. Angewandte Chemie International; 46, 5397–5401 (2007)
K.P. Rice, et al. Applied Physics Letters; 106, (2015)

7. Optical imaging Magnetite has poorly defined optical properties
Doped iron oxide NPs could also be used for optical medical imaging
Rare earth metal dopants could enhance optical behaviors
Large spin and optical moments
Nature of magnetic iron oxide and optically active rare earth metal dopants could allow for dual MRI and optical imaging for non-invasive soft tissue imaging.
Optical image of a blue blood vessel with amyloid deposits in a mouse.

8. purpose
Investigate optical and magnetic properties of doped and undoped magnetite iron oxide nanoparticles

9. Absorption Measurements of Fe3o4 solution
Excitonic absorption seen around 2.6eV for undoped iron oxide in solution.
Excitonic Absorption

10. Photoluminescence Experimental set up
λ=405nm
Excitation wavelength of 405nm (3.06eV)
Power of 1.3mW at sample
Cut off filter at 440 nm (2.82eV) used to remove excitation light
Spectrometer and CCD camera

11. Pl Measurements of Fe3o4 solution
Weak photoluminescence around 2.5eV
10nm - 5µm
5nm
Excitation energy
M.E. Sadat, et al. Applied Physics Letters; 105, (2014)

12. Measurements of Fe3o4 solution

13. Thin film preparation
Thin films desired for low-temperature and magnetic field measurements
Nanoparticles initially in hexanes
Pipetted and dropped onto glass cover slips
Lightly stirred while drying
Solution pipetted onto glass cover slips
Thin films set to dry after stirring
Undoped
Tb-doped
Eu-doped

14. Thin film absorption Thin Film absorption matches solution absorption
Shows optical properties of NPs did not change in thin film creation

15. Thin film photoluminescence
Thin film shows loss of PL peak
Glass cover slip could dominate Fe3O4 PL peak
Non-radiative relaxation pathways may dominate

16. Low-temperature experimental set up
𝐴𝑏𝑠𝑜𝑟𝑝𝑡𝑖𝑜𝑛=−log⁡( 𝑇𝑟 𝑠𝑎𝑚𝑝𝑙𝑒 𝑇𝑟 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 )
Tr is transmittance

17. Low-temperature absorption
Varshni Shift
Expected band gap energy shift with temperature
𝐸 𝑔 𝑇 = 𝐸 𝑔 − 𝛼 𝑇 2 𝑇+𝛽
Eg(T) band gap as function of temperature (T)
Eg band gap at 0K
α, β parameters of the material
Varshni shift seen in GaN semiconductor material
A. Najar, et al. Royal Society of Chemistry Advances; 7, (2017)

18. Low-temperature absorption results
Peak shift as a function of temperature expected
Shift may not be seen due to unresolved plasma lines of Xenon lamp light source

19. Xenon light source Xenon Arc Lamp Spectrum

20. Summary Future Research Acknowledgements
Optically characterized undoped magnetite iron oxide nanoparticles
Absorption, PL, Low-temperature absorption
Future Research
Acknowledgements
Remake thin films for low-temperature photoluminescence
Measurements of Tb- and Eu-doped iron oxide samples
Optical properties in magnetic field
Katherine P. Rice at NIST for providing the iron oxide samples
Prof. Bill Rice and members of RiceLab for their guidance and assistance with this project

21. Double Monochromator Joshua Walker, Joseph R. Murphy, Samuel Pasco

22. Double Monochromator
Further characterize optical properties of materials
Two Czerny-Turner monochromators
Narrow frequency selection
Outdated software but hardware is still functional
New system is expensive

23. electronics Replace old electronics and computer with modern equipment
Arduino microcontroller
2 slit motors
Czerny-Turner monochromator motor
Photo gate
Reflector sensor
Still need to calibrate slit width and monochromator