Multiplexed neural recording along a single optical fiber via optical reflectometry

Abstract

Abstract. We introduce the design and theoretical analysis of a fiber-optic architecture for neural recording without contrast agents, which transduces neural electrical signals into a multiplexed optical readout. Our sensor design is inspired by electro-optic modulators, which modulate the refractive index of a waveguide by applying a voltage across an electro-optic core material. We estimate that this design would allow recording of the activities of individual neurons located at points along a 10-cm length of optical fiber with 40-μm axial resolution and sensitivity down to 100 μV using commercially available optical reflectometers as readout devices. Neural recording sites detect a potential difference against a reference and apply this potential to a capacitor. The waveguide serves as one of the plates of the capacitor, so charge accumulation across the capacitor results in an optical effect. A key concept of the design is that the sensitivity can be improved by increasing the capacitance.To maximize the capacitance, we utilize a microscopic layer of material with high relative permittivity. If suitable materials can be found-possessing high capacitance per unit area as well as favorable properties with respect to toxicity, optical attenuation, ohmic junctions, and surface capacitance-then such sensing fibers could, in principle, be scaled down to few-micron cross-sections for minimally invasive neural interfacing. We study these material requirements and propose potential material choices. Custom-designed multimaterial optical fibers, probed using a reflectometric readout, may, therefore, provide a powerful platform for neural sensing.

Liquid crystal electro-optical transducers for electrophysiology sensing applications

“…Using optics to observe changes in cell refractive index and birefringence during electrical excitation [34] has failed to materialise as mainstream techniques. Theoretical studies have explored the feasibility of optical fibre refractometry [35] and surface plasmon resonance has been reported for neural recording in chamber [36] and fibre tip [37] configurations, but several issues remain unaddressed, including refractometry sensor characterisation, poor signal resolution, and a means of calibrating the outputted signal to biopotentials. Here, we present a practical implementation and experimental validation of a sensing fluorophore-free optrode with properties suitable for electrophysiology and brain-machine interface applications based on photonic techniques.…”

Developing Next-Generation Brain Sensing Technologies—A Review

“…Recently, preliminary designs have been proposed to allow fiber-based electro-optic neural activity sensing [115]. The design is similar to that of free carrier effect based electrooptic modulators.…”

“…Improved designs using resonant enhancement of the electro-optic effects via optical cavities, or improved capacitor materials, could allow the still-hypothetical system to operate at lower light powers, reducing heat dissipation from the fiber. With such improvements, as well as improvements in the reflectometry or multiplexing scheme, e.g., wavelength multiplexing, it may be possible to engineer ultra-long (e.g., centimeters), ultramultiplexed, low-power neural activity sensors for deployment into the brain tissue or via the cerebral vasculature [115]. Achieving this will require creative designs from nanophotonics experts via a cross-disciplinary collaboration with neurophysiologists, materials scientists and experts on optical detection methods.…”