A phenomenological model developed describes the steady-state sensing characteristics of a biosensor based on biooxidation of organic solutes by dissolved oxygen. The model is experimentally verified using a recently developed dopamine sensor that enzymatically oxidizes dopamine by polyphenolase in apple tissues. It adequately describes its steady-state sensing characteristics, including the effects of mass of immobilized apple fines in the biofilm, temperature, and pH of the substrate solution. The parameters provide a basis for evaluating the suitability of different bioactive materials or the same bioactive material from different sources for biosensor fabrication. At zero thickness of the membranes and biofilm, the model describes the sensing characteristics of a dissolved oxygen probe in which the oxygen diffusivity through the Teflon membrane is 9.83 × 10−11 m2/s, comparable with a previously reported value. It can also describe the sensing behavior of any nonbiocatalyzed oxidation-related sensor in a two-substrate system simply by replacing the governing faradaic equations for the dissolved oxygen probe with those appropriate to the type of probe used.