An ionic-complementary peptide, EFK16-II, was used to modify a highly ordered pyrolytic graphite (HOPG) electrode surface. The nanofiber structure of the self-assembling peptide on the electrode surface was characterized by atomic force microscopy (AFM). Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) spectra showed that, upon addition of 1-etllyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), EFK16-II molecules Lend to be cross-linked among themselves. Cross-linking of the peptide diminishes the number of carboxyl groups available for immobilizing a sensing enzyme, which is glucose oxidase (GOx) in the present case. A simple method based on premixing of the carbodiimide and GOx was developed; it inhibited peptide cross-linking and significantly improved enzyme immobilization. Biosensors Constructed in this way showed increased overall signal intensity and a much higher sensitivity at 4.94 mA M-1 cm(-2), a 6-fold increase compared to the previously reported peptide-modified electrodes. The results presented here demonstrate significant potential for ionic-complementary peptides for constructing electrochemical biosensors.