Use of laser interferometry for evaluation of static characteristics of a microelectrode-positioning system

In an already published work (M. Asfour et al., "Single cell volume measurement using a computer controlled patch-clamp electrode displacement", in the l8th Annual international conference of the IEEE Engng. in Med. and Biol. Soc., 31 Oct.-3 Nov. 1996, Amsterdam, The Netherlands.), the authors described a motor-driven hydraulic micromanipulator for patch-electrode positioning control with a theoretical resolution of 0.16 /spl mu/m. That was the first stage aimed to do noninvasive measurements of modulation in a single endothelial cell volume using the patch-clamp equipment. In this paper, which can be considered a continuation of the first one, the authors specially examined static performances of this system using a Michelson interferometer. They determined the experimental value of the resolution (0.142/spl plusmn/0.01 /spl mu/m) and showed the existence of repeatable hysteresis characteristics and a nonlinear portion in the real position of the electrode. The relationship between the position of the electrode and the resistance of the liquid interface cell-micropipette can give changes in the cell height.