Continued development of the Utah optrode array

Devices designed to deliver light into the brain for optogenetic studies have progressed rapidly in the last 10 years [1]. Most of this work has focused on the device requirements for studies in small rodents. However, to induce a behavioral change in larger mammals requires devices that can deliver light, above the required irradiance threshold of the opsin, to a significantly larger volume. The Utah optrode array was specifically designed with these requirements in mind [2]. However, early iterations of this device required either the animal to be head fixed, to maintain optical alignment, or a bulky fiber bundle tether. Here we present a compact Utah optrode array capable of illuminating 181 individually addressable sites, suitable for optogeneic studies in the non-human primate. [3]. (fig. 1).
Optical modelling indicated that a pinhole layer is needed to ensure selective illumination of individual needles. However, optical cross-talk between adjacent sites remained at ~10%. Incorporating a Si optical interposer structure onto the Glass needle array has completely eliminated this stray light [4]. The optical modelling, fabrication and integration of the silicon interposer is discussed here. Finally, devices with custom designed micro lens are also introduced. These devices can be fabricated using a two-photon lithography system, allowing a 2 fold increase in optical efficiency.