MicroProbes for Life Science

The array shown on the left is a 36 channel FMA with electrode lengths from 2.5 to 6.5 mm and array to the right is an 18 channel FMA and has microelectrodes that are 1.25 to 1.75 mm long with 2 stabilizing electrodes used for the ground and reference electrodes that are 2.5 mm long.

The developmental concept of the Floating Microelectrode Array, or FMA, is based on the incorporation of a light-weight platform populated with rigid microelectrodes and tethered to a nano connector by a thin, flexible and light weight cable. The platform, which houses the individual electrodes, is fabricated from 125- micron thick alumina ceramic. It has been fabricated to have 18 holes evenly distributed with 400-micron separations. The overall dimension of the 18 channel FMA is 1.95 x 2.45 x 0.45 millimeters, and the 36 channel FMA is 2.2 x 4.2 x 0.45 mm. The holes are laser drilled to have a diameter of 120 microns. Due to flexibility in design, FMAs can be fabricated with varying electrode depths not typically achieved using planar silicon technology. Current fabrication techniques allow for individual electrode depths between 0.5 to 10 mm. Impedance values for individual electrodes within the array may be specified from 5.0 kilohm to 2.5 megohm. The cable is fabricated from Parylene-C insulated 25- micron diameter gold wires, which are wound in a helix for maximum flexibility and strength. The entire cable is insulated with a thin coat NuSil type MED6-6606 non-restrictive silicone elastomer for biocompatibility, flexibility and strength.

Chronic FMA Assemblies
The array shown above is tethered by eighteen fine gold wires, 0.001” (25-micron) in diameter, about 1/3 the size of a human hair. The gold wires are micro-welded to the shaft of the microelectrodes at the specified distance from the tip in order to establish the proper length below the ceramic substrate that needs to penetrate into the brain or neural tissue. The other end of the gold wire is sonically bonded to a custom Omnetics connector designed to be compatible with Omnetics’ A8141-001 model, which is used by leading suppliers including Plexon, Inc. and Alpha Omega for their headstages. These connectors have worked very well for other chronic electrode designs and are small enough to be used in mouse experiments as well. We offer optional titanium pedestals that will house a single Omnetics connector, and were currently developing pedestals that will house up to 6 connectors.

Acute FMA Assemblies
The acute FMAs are fabricated with the same design characteristics as the chronic FMA. Cables for the Omnetics FMA connectors may be purchased that will interface to headstage connectors that are not compatible with the model A8141-001. The investigators must provide a suitable method to support the FMA connector over the implant site or they may use our model VPI-002 Vacuum Inserter Tool.

Key Design Specifications

Up to 36 penetrating microelectrodes per array.
Spacing between electrodes is 400 microns (custom substrates may be specified with additional NRE costs).
Microelectrode impedance is specified by the user to be anywhere from 5 kilohm to 2.5 megohm
Un-insulated electrodes may also be specified to act as the ground or common electrode
Microelectrodes may be specified at any length between 0.5 to 10 mm including different lengths within an array.
Platinum/iridium 70/30% or pure iridium may be specified as the core conductor for the arrays.
Pure iridium is suggested for chronic stimulation studies.
Electrode tip diameter is typically 2-3 microns but maybe different depending on the application of the user.
The base diameter of the microelectrodes is typically 50 to 80 microns depending on microelectrode length.
Array size is 1.95 x 2.45 x 0.5 mm for 18 channel FMAs and 2.2 x 4.2 x 0.25 mm for 36 channel FMAs.
The cable length can be specified anywhere between 1.5 to 20 cm.
Applications in cortex, spinal cord, association areas, and peripheral nerve bundles.
Primates, rats, felines and other animal models.
Excellent long term recording stability as well as rigorous stimulation studies with activated pure iridium