Session: Current Topics in Biological Chemistry:

Visible light is used in optogenetics to modulate neural activities. Optogenetics allows us to understand the neural mechanism, to improve and fix when malfunctioning. However, this technique is limited by invasive nature and light penetration. Therefore, we are investigating tools for non-invasive, in vivo optogenetic neuron stimulation by synthesizing and functionalizing nanophosphors that emit bright visible-light when irradiated with x-ray and studying x-ray stimulated behavior of Caenorhabditis elegans that we might bypass the need of visible-light source in the future.
We are synthesizing Eu-doped NaGdF₄ nanoparticles using co-precipitate and hydrothermal processes and annealed at high temperature to increase the emission intensity. To prevent sintering during annealing and to facilitate biotin functionalization, nanoparticles are encapsulated in a silica shell. We study generating and collecting light through tissue by exciting nanophosphors using a focused X-ray source and the ability to use it as an MRI contrast agent. The nanoparticle size is ~100 nm. x-ray excited optical luminescence (XEOL) has low emission intensity at low- and high-dopant levels. Hydrothermal treatment and annealing without a silica-shell increase the emission intensity. However, the formation of silica-shell decreases the emission intensity. After annealing silica-coated NaGdF₄: Eu, there is no significant increase in intensity, the structure changed to Eu-doped sodium-gadolinium-silicate. We confirmed biotin-functionalization by attaching nanoparticles to streptavidin in vitro. Light-generating and collecting through tissue are confirmed using XEOL and x-ray excited luminescence chemical imaging. The particles are also served as MRI contrast agents. In the future, we will optimize synthesis and annealing protocols to obtain bright nanophosphors.
To study x-ray stimulated behavior, Caenorhabditis elegans are used. Wild-type and dysfunctional Lite-1, Gur-3, and both Lite-1 and Gur-3 C. elegans are used to discover the photoreceptor that responsible for x-ray stimulation and pmyo-3::Lite-1 is used for x-ray stimulated egg ejection by exposing to 1Gy/s focused x-ray radiation. The above experiments proved that C. elegans x-ray avoidance behavior is proportional to x-ray dose and Lite-1 photoreceptor is responsible for this behavior. Further, 50% of pmyo-3::Lite-1 ejected eggs after x-ray on. In the future, we will the potential of Lite-1 to control mammalian-cell neurons.

Meenakshi Ranasinghe

Clemson University

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