Hemoglobin immobilized in exfoliated Co2Al LDH-graphene nanocomposite film: Direct electrochemistry and electrocatalysis toward trichloroacetic acid

A sandwich-like nanocomposite of exfoliated Co2Al layered double hydroxide (ELDH) and graphene (GR) was synthesized by chemically reducing in situ the assembly of ELDH and graphene oxide (GO) nanosheets. The morphology and structure of the product were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). Then the ELDH-GR nanocomposite and chitosan (CTS) were employed for immobilization of hemoglobin (Hb) on a carbon ionic liquid electrode (CILE) to fabricate a trichloroacetic acid (TCA) biosensor. The UV-Vis, FTIR and fluorescence spectra showed that Hb kept its native structure and retained stable bioactivity in the composite material. Cyclic voltammetry (CV) displayed a pair of well-defined redox peaks with the formal peak potential (E0′) at −0.256 V (vs. SCE), in pH 4.0 Britton-Robinson solution at the scan rate of 0.1 V/s, implying the direct electron transfer of Hb-FeIII/FeII. The electron transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (ks) were calculated to be 0.492 and 1.202 s−1, respectively. The Hb-modified electrode presented excellent electro-reduction activity toward TCA in the concentration range from 5 to 360 mmol/L with the detection limit of 1.506 mmol/L (3σ) by CV. For square wave voltammetry (SWV), the concentration range and the detection limit were from 2.5 to 360 mmol/L and 0.82 mmol/L, respectively. Therefore, the ELDH-GR composite has a promising potential for construction of biosensors.