Neural Signal Recording with Optical Fiber-based Surface Plasmon Resonance Sensor

Abstract

Surface plasmon is the surface electromagnetic wave which propagates in a direction parallel to the metal and the dielectric interface. Surface Plasmon Resonance (SPR) is induced by excitation of surface plasmon, and SPR sensor has been widely used as an optical sensor to detect biochemical reactions because of its high sensitivity. In the previous research, it was reported that a conventional prism-based SPR sensor is suitable for detecting neural signal with ex vivo rat sciatic nerve. Neural signal recording technique is very important to interpret neural behaviors. Electrophysiological approaches using microelectrodes of various shapes have been commonly used, but these approaches involves stimulation artifact. Optical neural signal recording using voltage-sensitive dyes have been studied to solve this problem, but these methods also have some shortcomings such as photo-bleaching effect. Neural recording with SPR sensor can be useful method because it is label-free and stimulation artifact-free. In this study, optical fiber-based SPR sensor system was developed to detect in vivo neural signal. The 50nm gold film was deposited on the optical fiber tip to induce SPR, and the reflectance change which means the change of the refractive index was measured. The SPR responses and electrical responses were recorded simultaneously on rat somatosensory cortex while the forepaw was electrically stimulated. Both responses were removed when the lidocaine which can temporarily block neuronal activation was applied. Also, preliminary SPR response was measured in the in-vitro single dorsal root ganglion cell with patch clamp system. To attach the optical fiber core precisely and safely to the single neuron, the optical fiber tip was tapered until the tip size becomes about 1μm by wet etching method. Optical neural signal recording with the SPR sensor can be applied in many areas in the future because they are label-free and stimulation artifact free.