The tip profile is another subtle specification which will determine the ultimate success of your recording or stimulation paradigm. It is however, a microprobe parameter for which there is some debate. Many first time users will want to experiment with different tip profiles in order to see which one works best for their recording or stimulation protocols.
Use microprobes are the most widely used tip profile. It works best for most recording situations and is recommended for stimulation.
Treated tapered configuration should be used mainly by those investigators who must penetrate their microprobes through tough membranes such as the dura mater of larger mammals. By applying a small local heat source near the electrode tip under a microscope we are able to provide a microprobe that has a more gradual tip profile than the "A" type. The heat treatment also will have the effect of toughening the insulation near the tip making it less likely to push back when penetrating tougher membranes.
This tip profile is available in 3 inch (76mm) in both the 0.003" and 0.005" (75 and 125 micron) diameter tungsten microprobes. The TM31AXX series is intended for generally shallow penetrations where one requires extremely good isolation. For penetrations greater than 3 mm in which the tip impedance is greater than 1.5 megohms the addition of polyimide tubing, TM31CXXKT series is recommended to reduce capacitive shunting.
By making the tip bullet shaped the electrode's exposed length is less than it would be if it was sharp for the same impedance. Isolation can therefore be improved in some situations since the exposed tip looks more like a point source. Many investigators feel that this provides greater selectivity than the conventional sharper tip profiles and that they hold up better for heavy stimulation protocols. Some investigators have also reported that they feel there is less puncturing of cells with the blunted tips. Many first time users will want to experiment with different tip profiles in order to see which one works best for their recording or stimulation protocols.