Techniques to monitor functional fluorescence signal from the brain are increasingly popular in the neuroscience community. However, most implementations are based on flat cleaved optical fibers (FFs) that can only interface with shallow tissue volumes adjacent to the fiber opening. To circumvent this limitation, we exploit modal properties of tapered optical fibers (TFs) to structure light collection over the wide optically active area of the fiber taper, providing an approach to efficiently and selectively collect light from the region(s) of interest. While being less invasive than FFs, TF probes can uniformly collect light over up to 2 mm of tissue and allow for multisite photometry along the taper. Furthermore, by micro-structuring the non-planar surface of the fiber taper, collection volumes from TFs can also be engineered arbitrarily in both shape and size. Owing to the abilities offered by these probes, we envision that TFs can set a novel, powerful paradigm in optically targeting not only the deep brain, but, more in general, any biological system or organ where light collection from the deep tissues is beneficial but challenging because of tissue scattering and absorption.

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.