Rare-earth doped phosphors have interesting optical properties depending on their size, crystal structure and type of dopant. They are being used in bioimaging, chemical sensing and radiology imaging screens. We are interested in synthesizing x-ray excited nanophosphors for a non-invasive, in vivo optogenetic neuron simulation method. However, it is challenging to synthesize monodisperse nano-size particles that emit bright visible light photons when irradiated with X-ray. We are synthesizing Eu-doped NaGdF4 nanoparticles using a citrate method which involves lanthanides-citrate complex formation followed by nucleation and growth upon the addition of NaF. Then, the nanoparticles are annealed at high temperature to increase the emission intensity by removing defect sites that can quench luminescence. To prevent nanoparticle sintering during annealing we encapsulated NaGdF4: Eu nanoparticle in a silica shell. The synthesized NaGdF4: Eu nanoparticles are characterized using dynamic light scattering, powder x-ray diffraction, transmission electron microscopy and x-ray luminescence spectroscopy. The TEM images confirm that the size of the nanoparticles is around 100 nm. According to the x-ray luminescence spectroscopy measurements, at low and high dopant levels, they show low emission intensity, likely due to lack of luminescent centers and self-quenching, respectively. Hydrothermal treatment increased the emission intensity by a factor of 2-3 and annealing without a silica-shell increased the emission intensity by another factor of 5 which resulted in sintered particles, negating their bio-application. However, this may have potential to form thin films to use in solar cells and fluorescence screens. Formation of silica-shell resulted in a decrease in emission intensity due to boundary defects and small molecules trap in the shell. After annealing silica-coated NaGdF4: Eu there is no large increase in intensity compared to pristine nanoparticles. Annealing at 350-450 °C resulted in porous NaGdF4: Eu coated with silica which may have potential drug delivery applications. At high temperatures silica-coated NaGdF4: Eu changes its structure to a mixture of sodium-gadolinium-silicate nanoparticles. In the future, we will optimize synthesis, annealing, and surface passivation protocols to obtain bright monodisperse nanophosphors. We will functionalize them and test their application as in situ light sources for sensing and actuating in vivo.

Study of radio-luminescence nanoparticles for non-invasive, in vivo optogenetic neuron stimulation

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.