The silk fibroin protein membrane is an amphoteric ion-exchange membrane composed of both weak acidic and weak basic groups. Its isoelectric point is pH 4.5 and the charge thereof is dependent on pH of the solution. This characteristics of the membrane was exploited in a chemical modified electrode in this paper. Silk fibroin protein membrane was modified on a graphite electrode, the pH- responsive function of the modified electrode was investigated. The apparent diffusion coefficient of DA in the fibroin membrane was 2.65×10^-7 cm^2/s. The rate constant of the heterogeneous electron transfer was calculated to be 8.9×10^-6 cm/s by computer fitting. When the modified electrode was applied to detect neurotransmitters, some metabolites and ascorbic acid did not interfere with the measurement.

Key words: FIBROIN, DOPAMINE, NEUROTRANSMITTER, GRAPHITE ELECTRODE, ELECTRON TRANSFER REACTION, MODIFICATION, MEMBRANE ELECTRODES, PH, ELECTROCHEMICAL ANALYSIS