Tapered fibertrodes for optoelectrical neural interfacing in small brain volumes with reduced artefacts

Abstract

Deciphering neural patterns underlying brain functions is essential to understand how neurons are organized into networks. This has been greatly facilitated by optogenetics and its combination with optoelectronic devices to control neural activity with millisecond temporal resolution and cell-type specificity. However, targeting small brain volumes causes photoelectric artefacts, in particular when light emission and recording sites are close to each other. We take advantage of the photonic properties of tapered fibers to develop integrated “fibertrodes” able to optically activate small brain volumes with abated photoelectric noise. Electrodes are positioned very close to light-emitting points by non-planar microfabrication, with angled light emission allowing simultaneous optogenetic manipulation and electrical readout of one to three neurons, with no photoelectric artefacts in vivo. The unconventional implementation of two-photon polymerization on the curved taper edge enables the fabrication of recoding sites all-around the implant, making fibertrodes a promising complement to planar microimplants.

Novel technologies to micro and nanostructure highly nonplanar optical fibers: from the micro to the sub-50 nm regime

“…In Ref. 31 , two different approaches are proposed to address this challenge. The first approach (depicted in Figure 2.a) utilizes a combination of conformal depositions of dielectric and metallic materials around a µTOF on which the optical sites are previously defined, followed by Focused Ion Beam Milling (FIBM) to mill the dielectric encapsulation layer from a defined region down to the underlying conformal metallic layer.…”

“…Interestingly, Ref. 31 proposes a similar approach also to fabricate µTOFs. This approach involves using Two-Photon Polymerization (TPP) to create a lift-off mask that covers the silica during metal deposition.…”

Toward the Next Generation of Neural Iontronic Interfaces

“…The new generation of neural interfaces should therefore not only record and stimulate neural activity, but also be able to monitor and influence neurochemical properties such as local pH or neurotransmitter levels, and measure the release of neurotransmitters, via the use of substrate‐integrated optical and spectroscopic techniques. [ 110 ] This would yield a multi‐dimensional picture of the state of the neural network that goes far beyond the current state in electrophysiology, which is largely focused on information coding in action potential discharge.…”

Toward Plasmonic Neural Probes: SERS Detection of Neurotransmitters through Gold‐Nanoislands‐Decorated Tapered Optical Fibers with Sub‐10 nm Gaps

“…Optical-fiber-based neural probes are indeed widely employed to optically access brain tissue, and they have been extensively used to reveal neural activity by collecting fluorescence of GEI in a fiber photo metry configuration. [22][23][24][25]33,34] Among these, tapered optical fibers (TFs) are particularly attractive to develop this technology for two reasons: i) the tapered shape can minimize the damage to the tissue, enabling extensive use in vivo; [35][36][37] and ii) the photonic properties of the taper give access to mode-division de-multiplexing strategies to deliver and collect light over a large optically active area on the square millimeter scale. [38] Therefore, integrating TFs with plasmonic structures represents an important path to explore a novel generation of neural implants for studying chemical signalling in the brain.…”