THE EFFECT OF HYDRONIUM ION-TRANSPORT ON THE TRANSIENT-BEHAVIOR OF GLUCOSE-SENSITIVE MEMBRANES

Explicit expressions for the hydronium ion transport have been added t o an existing theoretical model describing the steady-state and transi ent behavior of glucose-sensitive membranes. The glucose sensitive mem brane is a hydrogel containing pendant amine groups and immobilized gl ucose oxidase creating a membrane which swells in response to changes in glucose concentration. The extent of membrane swelling and the time required for swelling depend upon the pH within the membrane. The mem brane pH is a function of the rate of production of gluconic acid from glucose as well as the transport rate of the hydronium ion. Although the steady-state membrane [pH] was predicted by the new model to be lo wer than that predicted by the previous model, the [pH] versus glucose curves produced by the two models were similar. The predicted steady- state membrane [pH] was found by the new model to be most affected by changes in the buffer concentration and diffusivity. Contrary to findi ngs of the previous model, the steady-state [pH] was unaffected by the membrane's amine content. However, the amine content of the membrane was the most important factor affecting the transient behavior of the membrane [pH]. The time to reach steady-state with an amine content ty pically used for a glucose-sensitive membrane was in the order of hour s. To achieve response times in the range of minutes rather than hours , both the model and experimental observations show that the concentra tion of fixed titrateable groups must be minimized.