Tapered fibertrodes for opto-electrical neural interfacing in small brain volumes with reduced artefacts

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.