In this work a new chemical sensor for the H2O2 and nitrite amperometric detection was assembled, using a glassy carbon (GC) bare electrode modified by two different nanocomposite materials. The nanocomposite films were prepared by casting a functionalised carbon nanofiber (CNF-COOH) and single-walled carbon nanotubes (SWCNT-OH, for comparison) on the glassy carbon electrode surface; then an iron(III) protoporphyrin IX (Fe(111)P) was adsorbed on these modified surfaces. A morphological investigation of the nanocomposite layers was also carried out, using the Scanning Electron Microscopy (SEM). The electrochemical characterization, performed optimising several electro-analytical parameters (such as different medium, pH. temperature, scan rate, and potential window), demonstrated that the direct electrochemistry of the Fe(III)P/Fe(II)P redox couple involves 1e(-)/1H(+) process. A kinetic evaluation of the electron-transfer reaction mechanism was also carried out, demonstrating that the heterogeneous electron transfer rate constant resulted higher at CNF/hemin/GC biosensor than that evaluated at SWCNT/hemin/GC modified electrode. Finally, the electrocatalytic activity toward the H2O2 reduction was also demonstrated for both sensors but better results were observed working at CNF/hemin/GC modified electrode, especially in terms of an extended linearity (ranging from 50 to 1000 mu M), a lower detection limit (LO.D. = 3 sigma) of 2.0 x 10(-6) M, a higher sensitivity of 2.2 x 10(-3) A M-1 cm(-2), a fast response time (9 s), a good reproducibility (RSD% < 1, n =3) and operational stability. In addition, a nitrite electrocatalytic effect was also demonstrated only at CNF/hemin/GC modified electrode, showing an extended linearity (ranging from 5.0 x 10(-3) to 2.5 x 10(-1) M), a lower detection limit (LO.D. = 3 sigma) of 3.18 x 10(-4) M, a higher sensitivity of 1.2 x 10(-2) A M-1 cm(-2), a fast response time of 10 s. a good reproducibility (RSD% <1, n = 3) and finally a good operational stability. (C) 2011 Elsevier Ltd. All rights reserved.