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Making an Extracellular Suction Electrode

  • Obtain the following items to make your own suction electrode : a soldering iron; solder; a wire stripper; a wooden-handled dissecting pin; an alcohol burner; a can or tube of contact or plastic cement; a fine flat file; emery cloth; electrical tape; a popsicle stick; two pieces of chlorided silver wire (0.005” dia, 5” long); three feet of shielded, two-conductor, insulated cable; three color-coded connectors that will mate to the connectors on the input cable for the amplifier; three feet of flexible plastic tubing (20 gauge Tygon or PE 100); an 18-gauge needle,
    a 3-way stop cock, a 3cc syringe, a 1cc tuberculin syringe; glass micropipette tip.
  • Connectors and electrodes need to be attached to the ends of the shielded, two-conductor cable. Take one end of the cable and carefully strip 5 inches of insulation off the end. Minimize the number of strands of
    braided shielding cut during the removal of the insulation. Avoid cutting the conductor wires under the braided shielding.
  • Unbraid the 5 inches of exposed shielding. Pull the conductor wires aside. Gather all the strands of the shielding in a bundle and twist them together. Solder a small alligator clip to the end of the twisted shielding.
  • Strip a quarter of an inch of insulation off the end of each conductor wire. Solder a piece of the chlorided silver wire to the end of each wire.
  • Take the other end of the cable and carefully strip 3 inches of insulation off the end. Again, minimize the number of strands of braided shielding cut during the removal of the insulation. Avoid cutting the conductor wires
    under the braided shielding.
  • Unbraid the 3 inches of exposed shielding. Pull the conductor wires aside. Gather all the strands of the shielding in a bundle and twist them together. Solder a color-coded connector, that mates with the connector on the
    input cable of the amplifier, to the end of the twisted shielding. Since the shielding is the ground wire, the connector is usually color-coded green.
  • Strip a quarter of an inch of insulation off the end of each conductor wire at this end of the cable. Solder a color-coded connector to the end of the each conductor wire. A red connector is usually put on the wire
    conducting the signal from the recording electrode. On this suction electrode assembly, the recording electrode will be the silver wire that is inside the lumen of the suction tubing. A black connector is usually put on
    the wire connected to the indifferent or reference electrode, which is a silver wire wrapped around the outside of the electrode tip.
  • Heat the tip of the dissecting pin in the flame of the alcohol burner. Use the heated tip to poke a small hole in the side of the plastic tubing that is about 3 inches from the end of the tubing and angled toward the end at 45
    degrees. 
  • Remove the plunger from the 1cc tuberculin syringe. Find the end of the plastic tubing without the hole. Push this end of the tubing through the hole in the front end of the 1cc syringe barrel until the tube exits the rear
    of the syringe barrel. Push and pull the tubing through the syringe barrel until the small angled hole in the side of the tube is about half of an inch from the front of the syringe barrel.
  • Find the silver electrode that is designated as the recording electrode by being color-coded to the red conductor wire or connector. Push the tip of this electrode wire through the hole in the side of the plastic tubing. Keep
    the solder joint of the electrode to the conductor wire about a quarter of an inch away from the hole in the tubing.
  • Mix up the contact or plastic cement. Use the popsicle stick to place a drop of cement over the hole in the tubing to create an air-tight seal around the silver electrode wire going through the hole. Make sure the
    cement does not drip into the lumen of the tubing and block it. Contact and plastic cement usually dries to the touch in 10 to 15 minutes.
  • Once the hole is sealed, cut the end of the silver recording electrode so that a quarter of an inch of the wire is sticking out of the end of the tubing.
  • Use the flat file and emery cloth to remove the point and smooth the tip of the 18-gauge needle. Once smoothed, push the tip of the needle into the other end of the plastic tubing.
  • Attach the 3-way stopcock to the 18 gauge needle, and the 3cc syringe to the 3-way stopcock.
  • When the nerve has been isolated, determine the diameter of the tip of the glass micropipette needed to fit the nerve. Snap the tip of the micropipette at the correct diameter, and fire-polish the tip to remove and jagged
    edges.
  • Place the glass micropipette over the wire sticking out the end of the plastic tubing. Push the micropipette into the plastic tubing to make a tight seal. The silver wire should be sticking a short distance into the glass
    micropipette.
  • The silver wire that is the indifferent or reference electrode is wrapped around the outside of glass micropipette and part of the plastic tubing supporting the micropipette. The tip of the indifferent electrode should be
    as close as possible to the tip of the glass micropipette, but, the positive and negative electrodes and their connectors must not touch each other!
applications - making-suction-electrode
Updated on April 16, 2021

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