Fusion Probes: Double-Sided Microelectrodes
Fusion probes have sites on both faces of one shank — twice the sites in the same cross-section. What it buys and costs, which experiments, how to order.
4 min read
Updated October 12, 2026
A Fusion probe has recording sites on both faces of the shank rather than one. The trade is the reason the family exists: two faces double the sites without doubling the tissue the shank displaces, and the packaging is what makes both faces reach a single headstage. The family is explained once in Fusion Series ↗.
Research use only. NeuroNexus products and the procedures described here are for non-clinical research use, and must not be used in human or veterinary medical procedures.
What the catalog contains#
Eight catalog Fusion packages at 32, 64 and 128 channels, in standard (F) and
headstage-mating (FH) variants, plus wide (W) forms at 32 channels.
Per-design site count, shank length and site geometry are catalog data; read them from the product catalog rather than from this document.
What double-sided buys, and what it costs#
It buys site density per unit of displaced tissue. For a given shank cross-section you record from twice as many sites, which matters most where the structure is small enough that a second penetration is not an option.
It costs you a known orientation. With sites on both faces, which face looks at what is set by the rotation of the shank at insertion. That is a protocol step, not a probe property: orientation has to be fixed and recorded at surgery, and it cannot be recovered afterwards from the data alone.
It also costs routing. Both faces reach one connector, which is what the package does, and it is why Fusion designs are specified as a probe-and-package pair rather than a probe alone.
Which experiments a Fusion probe is for#
A Fusion probe is chosen where the target is small enough that a second penetration is not an option and the question needs more units than one face can give: a nucleus a few hundred micrometers across, a thin structure that a multi-shank design would straddle, or a chronic implant where every additional track is a cost the animal pays. Because sites face in two directions, a single shank samples its whole surrounding cylinder rather than a half of it, and a spike sorter ↗ sees a neuron on the near face at high amplitude and on the far face at low, which separates units that a one-sided layout would merge. The same doubling applies to stimulation: a site on each face can be driven independently for a 360° field.
It is not the choice where reach matters more than density. The doubled site count arrives as more channels in the same site span ↗, not a longer one; a study that needs a 3 mm depth profile is better served by a linear layout on one face at 100 µm pitch than by two faces at 50 µm, and a study that needs lateral coverage is better served by shanks than by faces.
How a Fusion probe is ordered and read#
Fusion is a build on the catalog families rather than a family of its own: 63 catalog silicon designs are tagged double-sided, across the A-Series, Buzsaki, polytrode and Vector lines, and the Fusion package ↗ is what routes both faces to a headstage. The doubled channel count comes out as several 16- or 32-pin Omnetics connectors rather than one larger connector, so a 64-site Fusion probe presents as two 32-channel connectors and needs a headstage or adapter pair to match; the FH builds mate a headstage directly. Confirm the channel map at setup — each face has its own map and the two are folded together through the package — and record the shank's rotation at insertion in the surgical log, because it is the only record of which face looked at what. The package is chosen with Choosing a Probe Package; the design against the target with Choosing an Electrode for Your Experiment.