A Simplified Production Method for Multimode Multisite Neuroprobes

Unified electro-optical microprobes for co-localized optical and electrical recordings within a rats brain have been recently introduced (Krapohl, Bonin et al. 2008). In this work, we show a simplified production method for these multimodal multisite neuroprobes. The electro-optical neuroprobe has an outer diameter of 255µm and is composed of eight NiChrome wires (Ø 25µm) fixed to the surface of a mono-mode glass fiber (Ø 125µm). Where the former method elaborately braids the wires around the fiber, the new method uses the property of a PTFE tube to shrink at higher temperature (≫300°C). Thus the microwires are pressed to the fiber. The probe tip is than hand polished and is such ready to be used in rat brain navigation experiments, featuring both functions electrical as well as anatomical, optical look-ahead properties. The latter is achieved by using the glassfiber as working probe for an Optical Coherence Tomography (OCT) system. Hence these electrooptical probes are called OCTrodes. We determined the impedance of the OCTrodes by impedance spectroscopy to lie in the range of 500kΩ at 1kHz frequency. This range enables them to record both single and multi unit activity. OCT experiments have shown promising results in detecting transversal boundaries between structures of different density in phantoms and cadaver brain. Ongoing experiments aim at co-localized optical and electrical recordings in living animals.