Carbon nanotube-hydroxyapatite-hemoglobin nanocomposites with high bioelectrocatalytic activity

In this paper, carbon nanotubes-hydroxyapatite (MWCNTs-HA) composite were synthesized by self-assembling technique, and investigated by X-ray diffraction, scanning electron microscopy (SEM) and FT-IR spectroscopy. Hemoglobin (Hb) immobilized in MWCNTs-HA film not only retained its similarly native conformations, but also achieved the direct electron transfer. The apparent heterogeneous electron transfer rate constant (k_s) was evaluated as (5.05 ± 0.41) s^{- 1} according to Laviron's equation, and the surface coverage (Γ*) was estimated as (9.25 ± 0.69) × 10^{- 10} mol cm^{- 2}. Moreover, the Hb immobilized in MWCNTs-HA film exhibited remarkable bioelectrocatalytic activity for the electrochemical reduction of H₂O₂. The amperometric response of the biosensor varied linearly with the H₂O₂ concentration ranging from 0.5 μM to 2 μM, and the results showed a detection limit of 0.09 μM. Furthermore, the Hb-immobilized MWCNTs-HA film exhibited the excellent catalytic reactivity toward trichloroacetic acid (TCA).