Glassy carbon electrodes modified with hemin-carbon nanomaterial films for amperometric H2O2 and NO2− detection

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(III)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 μM), a lower detection limit (L.O.D. = 3σ) of 2.0 × 10−6 M, a higher sensitivity of 2.2 × 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 × 10−3 to 2.5 × 10−1 M), a lower detection limit (L.O.D. = 3σ) of 3.18 × 10−4 M, a higher sensitivity of 1.2 × 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.