Transparent indium-tin oxide electrode patterns for extracellular, multisite recording in neuronal cultures.

Glass plates coated with transparent thin film conductors of indium-tin oxide (ITO), 100 nm thick and 10 microns wide, have been successfully used to record spike potentials from neuronal monolayer cultures. The material is non-toxic to mammalian spinal neurons and is stable under warm culture medium. Laser-deinsulated recording craters that expose 100 mu m2 of ITO yield impedances of 8-10 M omega at 1 kHz with noise levels of 40 muV. Conventional gold plating of the craters reduces these impedances to below 3 M omega. The material is easily etchable and sputtered glass plates of high quality are commercially available at relatively low cost. The high light transmittance of ITO makes the conductors essentially invisible and allows unobstructed observation of circuit components in monolayer cultures. The introduction of ITO as a thin film microelectrode material should accelerate the construction of high density recording patterns that could exceed 400 microelectrodes per mm2.