A constant current source for extracellular microiontophoresis.

A sophisticated constant-current source suitable for extracellular microiontophoresis of tract-tracing substances, such as Phaseolus vulgaris leucoagglutinin, Biocytin or Fluoro-Gold, is described. This design uses a flyback switched-mode power supply to generate controllable high-voltage and operational amplifier circuitry to regulate current and provide instrumentation. Design features include a fast rise time, +/- 2000 V supply (stable output in < 250 ms), simultaneous load current and voltage monitoring, and separate pumping and holding current settings. Three features of this constant-current source make it especially useful for extracellular microiontophoresis. First, the output voltage monitor permits one to follow changes in the microelectrode resistance during current injection. Second, the voltage-limit (or out-of-compliance) indicator circuitry will sound an alarm when the iontophoretic pump is unable to generate the desired current, such as when the micropipette is blocked. Third, the high-compliance voltage power supply insures up to +/- 20 microA of current through 100 M omega resistance. This device has proven itself to be a reliable constant-current source for extracellular microiontophoresis in the laboratory.

An intensity regulation system for a monochromator.

A relatively inexpensive system is described which utilizes a commercial grating monochromator and external feedback electronics to regulate the output intensity as the wavelength is varied. In this system, a sample of the output intensity is taken by a photosensor with known spectral response. The output of the photosensor is then compared electronically with that of a preprogrammed function generator which cancels nonlinearities in the photosensor. The resulting signal is used to regulate the monochromator light source. System output intensity has been observed to be constant to within 5% from 4750 A to 12000 A using two gratings.