Fig. 1.

Three simple models of an instrumented bioreactor or microphysiometer. a Bare sensing electrode, e.g., pH or O₂. b Enzymatic electrode, e.g., lactate. c Enzyme electrode with a polymer layer, e.g., glucose. Concentrations of the substrate c_s (Glu, Lac) and the peroxide c_h have a superscript index e in the enzyme, p in the second polymer layer, and 0 in the liquid. R_s is the cellular flux, D is the diffusion constant, A is the area of the electrode, i is the current, n is the number of donated electrons, and F is the Faraday constant