(714e) Synthesis and Optical Characterization of Gadolinium-Containing Scintillating Nanoparticles to Enable Neural Stimulation

Optogenetics is a method that combines optics and genetics, the two fields from which it is named, in order to monitor and control living tissue. This technique currently uses an invasive and potentially harmful process to control neuronal activity by implanting LEDs into brain tissue. These implantations are labor intensive, can lead to brain tissue damage, and some areas of the brain just are not accessible. It would be safer and potentially more versatile to improve this technique by systematically synthesizing and characterizing nano-scintillators that could be inserted into brain tissue via injection. These particles would serve as the visible light source to stimulate neuronal activity. These particles need to meet a number of strict requirements that would allow them to serve as local light sources to stimulate neuronal activity.

In order to achieve an inoffensive means to manipulating specific neurons, our particles will contain a scintillating inorganic crystalline material. The scintillating core must be able to effectively absorb X-ray radiation and emit photons with the desired energy required to activate the conformational switch in the chosen opsins. The particles have a stringent size restriction to be smaller than 100 nm to allow them access to the brain tissue.

We have been able to produce, through a core-shell synthetic approach, a number of species that are alluring candidates for such an application. Ce:Gd_4.67(SiO₄)₃O, Ce:Gd₂SiO₅, Ce:Gd₂Si₂O_7, and mixed Ce:GLSO core-shell nanophosphors were synthesized by the successful deposition of rare earth shells onto silica cores via sol-gel processing followed by the induction of a solid state reaction between the core and shell domains. SiO₂ nanoparticles were used as the templating core component to produce dispersible, spherical particles as well as providing the silicon source for the gadolinium silicate species. Careful monitoring of the resulting particles characteristics’ were accomplished by using powder X-ray diffraction (PXRD) to identify the reaction pathway, crystallinity, phase purity, and crystal domain size, scanning electron microscopy (SEM) to monitor particle size and morphology, and photoluminescence (PL) and radioluminescence (RL) measurements to assess optical behavior. PXRD results suggested that clean conversion of crystalline silicate phases occurred at 1000°C and increasing temperatures produced larger crystallite sizes. The final silicate phase of the rare earth shell was manipulated by varying the silicon to rare earth ratio and dopant concentration. The synthesized silicate particles were uniform spheres with an average diameter of 70nm.