Optical stimulation is a novel method for controlling biological systems. Optical stimulation is applied to influence specific functions of a cell, for example neurons can be fired or silenced. The tissue is sensitive to specific wavelengths and can be sensitised to others. The effect of the stimulation can be verified by measuring local electric potentials. The realization of a microelectrode system where optical stimulation electrical recording are both available simultaneously would enable high precision, repeatable in vivo measurements.
In my work, a silicon-based deep-brain microprobe was improved to be suitable for optical stimulation applications. The probe was developed in the MEMS Laboratory of the Institute for Technical and Material Science, RCNS, HAS. In my paper, two phenomena are investigated: visible light and infrared optogenetics. These phenomena require the fabrication of different optical waveguide structures on the silicon probe shaft. To optimize the optical parameters, wave optics and ray optics simulations were carried out. The probes were manufactured, and measured with a custom-made optical setup. The simulation results were verified by the experimental results. In the first part of the paper, a description of the biological background based on literature data, helps to understand underlying phenomena. The physics behind waveguide operation is also discussed. In the second part, the finite-element and ray tracing models are presented, which are used to simulate the light propagation. The technological processes and used materials during the device fabrication are also detailed. Waveguide sidewall smoothing is investigated in detail with respect to optical transmission. Finally, fabricated and measured samples as well the experimental setup are described.
If the optimized stimulation device works reliably, the system is ready to the investigation of optical stimulation phenomena in live animal as well.