Evaluation of an electrochemical biosensor based on carbon nanotubes, hydroxyapatite and horseradish peroxidase for the detection of hydrogen peroxide

Evaluation of an electrochemical biosensor based on glassy carbon (GC) electrode that was modified with multiwall carbon nanotubes (MWCNTs), which in turn were modified with hydroxyapatite (HAp) and horseradish peroxidase (HRP), for the detection of hydrogen peroxide (H₂O₂), is reported. Hydroxyapatite nanoparticles namely HAp5 and HAp20, that respectively correspond to five- and twenty-days aging times, were in situ synthesised on functionalized carbon nanotubes (fCNTs) walls by a biomimetic procedure using a solution mimicking the inorganic composition of human blood plasma (simulated body fluid (SBF)). HRP was introduced dropwise to the electrode surface. The materials were characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetry and electrochemical techniques. The Michaelis-Menten apparent constant obtained for both sensors were 0.37 mmol L⁻¹ for HAp5-fCNT/GC and 2.93 mmol L⁻¹ for HAp20-fCNT/GC, indicating that the HRP keeps its enzymatic activity on both electrodes H₂O₂ detection was performed by chronoamperometry. The linear range obtained for the HRP/HAp5-fCNT/GC electrode and the HRP/HAp20-fCNT/GC electrode was from 1.0 × 10⁻⁵ M to 2.34 × 10⁻⁴ M, with a detection limit of 1.91 μmol L⁻¹ for the HRP/Hap5-fCNT/GC electrode and 4.45 μmol L⁻¹ for the HRP/HAp20-fCNT/GC electrode. H₂O₂ was quantified using real-life raw and pasteurized milk samples using the electrode that showed the better performance parameters, the HRP/HAp5-fCNT/GC electrode. The obtained recovery percentage (R%) indicate that the proposed method has a good accuracy.