Wavefront shaping by computer generated volume holograms for optogenetic applications (HoloGen)

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Optogenetics is a rapidly evolving field, which among other topics connects the fields of genetics and photonics. With the help of optogenetics it is possible to modify genetically modified cells with light-sensitive ion channels by illuminating the cells with light. The introduction of so-called opsins into a cell membrane (e.g. in neurons, heart or cochlear cells) makes it possible to activate or deactivate membrane potentials under stimulation with light of a specific wavelength. This makes it possible to selectively opening channels for positively or negatively charged ions, to induce an action potential in the cell and thereby control the electrical activity of the cell.An obstacle to the efficient use of light at the desired destination is the type of optical stimulation. Currently, this stimulation is realized by a planar illumination with optical fibers or micro-LEDs, which leads to the stimulation of cell ensembles in contrast to a desired single cell excitation. Therefore, spatial information is lost. Another currently not realizable need is the three-dimensional and simultaneous optical stimulation of different cells and cell types, especially by using multiple wavelengths. Hence, the state of the art indicates the need of a method to shape well-defined wave fronts for a flexible light delivery of three dimensionally patterned intensity distributions for the simultaneous stimulation of various optogenetically modified cells and cell types with cellular resolution for in vivo applications. These limitations can be overcome by the use of diffractive and refractive optics.Thus, the aim of this proposal is to realize an optical system on the tip of a single mode fiber. With this system various wavelength-dependent intensity patterns are displayed resulting in a three-dimensional stimulation of single optogenetically modified cells or cell ensembles with cellular resolution. The information to individually shape the wave front in order to generate these patterns is encoded in a computer-generated volume hologram (CGVH). At first, the optical system consisting of a CGVH and microlenses is numerically calculated. Then, the complete system is fabricated for the particular field of application (e.g. neuron or cochlear simulation) on the tip of an optical fiber utilizing micro- and nanofabrication methods. By this approach of wavelength dependent wavefront shaping and beam patterning, new opportunities are generated for the optogenetic micro stimulation to explore cellular networks and to deepen the understanding of cellular communication. Furthermore, this research paves the way for the development of novel therapeutic approaches of biological organisms.