Multitip scanning bio-Kelvin probe

We have developed a novel multitip scanning Kelvin probe which can measure changes in biological surface potential Delta V-s to within 2 mV and, quasisimultaneously monitor displacement to 1 mm. The control and measurement subcomponents are PC based and incorporate a flexible user interface permitting software control of each individual tip, measurement, and scan parameters. We review the mode of operation and design features of the scanning bio-Kelvin probe including tip steering, signal processing, tip calibration, and novel tip tracking/dithering routines. This system uniquely offers both tip-to-sample spacing control (which is essential to avoid spurious changes in Delta V-s due to variations in mean spacing) and a dithering routine to maintain tip orientation to the biological specimen, irrespective of the latter's movement. These features permit long term (>.48 h) "active'' tracking of the displacement and biopotentials developed along and around a plant shoot in response to an environmental stimulus, e.g., differential illumination (phototropism) or changes in orientation (gravitropism). (C) 1999 American Institute of Physics. [S0034-6748(99)04703-6].