Floating Microelectrode Arrays
Floating Microelectrode Arrays


The array shown above has microelectrodes that are 1.25 to 1.75 mm long with 2 stablizing electrodes used for the ground and reference that are 2.5 mm long.
     The concept behind the development of the Floating Microelectrode Array 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 FMA is 1.95 x 2.45 x 0.5 millimeters. The holes are laser drilled to have a diameter of 105 microns. Because of the flexibility in the way in which these arrays are designed, FMAs can be fabricated with varying electrode depths not typically achieved using planar silicon technology. Current fabrication techniques allow individual electrodes to have depths between 0.5 to 10 mm. Impedance values for individual electrodes within the array may be individually specified between 10 kilohm to 2.5 megohm. The cable is fabricated from Parylene-C insulated 25 micron diameter gold wires, which are wound in a helix and over coated with MDX4-4210 silicone elastomer for flexibility and strength.



Chronic FMA Assembly
The array shown above is tethered by eighteen fine gold wires (0.001" (25 microns) in diameter) which is about one third 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. The other end of the gold wire is sonically bonded to a custom Omnetics connector desgined to be compatible with Omnetics' A8141-001 model, which is used by several companies including Plexon 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. Micro Probe currently offers titanium pedstals that will house a single Omnetics connector but is also working on developing pedestals that will house up to 6 connectors.

Acute FMA Assembly
The acute FMAs are fabricated exactly the same as the chronic FMA designs. Connecting cables to the Omnetics FMA connectors can 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.

Key Desing Specifications
  • Up to 18 penetrating microelectrodes per array (MPI is currently working on a 36 electrode array
  • Spacing between electrodes is 400 microns
  • Array size is 1.95 x 2.45 x 0.5 mm
  • Microelectrode impedance is specified by the user
  • Microelectrodes may be spricified at any length between 0.5 to 10 mm; in addition, electode lengths can be different in the same array
  • Platinum/iridium, 70%/30%, or pure iridium may be apecified 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 length
  • The cable length can be specified by the user
  • 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 electrodes
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