Ionic-complementary peptide-modified highly ordered pyrolytic graphite electrode for biosensor application

Ionic-complementary peptides are promising new biomaterials with potential applications in bionanotechnology. In the present investigation, a typical ionic-complementary peptide, EFK16-II, was used to modify a highly ordered pyrolytic graphite (HOPG) electrode. Upon modification, peptide nanofibers, parallel or oriented 60 degrees or 120 degrees to each other, were formed on the surface of HOPG electrode. Surface wettability of the electrode was improved as indicated by a significant decrease in the water contact angle. The electrochemical response of the EFK16-II nanofiber-modified HOPG electrode for the ferricyanide/ferrocyanide redox couple was characterized. Cyclic voltammograms indicated that the presence of peptide nanofibers on the HOPG electrode did not block electron transfer at slow scan rates ( approximately 2 mV/s), but did so at high scan rates ( approximately 100 mV/s). A model enzyme glucose oxidase (GOx) was covalently immobilized onto this nanofiber-modified electrode, and its potential as an enzyme-based biosensor for glucose was examined. At an applied potential of +0.45 V (vs. Ag/AgCl), the current increased linearly with glucose concentration up to 7.5 mM and a relative high sensitivity was obtained at 11.3 +/- 1.0 nA/(mM mm(2)). The immobilized GOx showed high affinity for glucose, with a Michaelis-Menten constant K(m) of 6.8 +/- 0.9 mM. It also exhibited relatively good storage and operational stabilities, and reflected in only a small decrease (13%) in the current response after 1 month storage and negligible changes upon 50 cyclic voltammetric scans. The results presented here demonstrate an excellent potential of the use of ionic-complementary peptides to modify electrode surfaces for biomolecular sensing and diagnostics.