Biocompatible phospholipid modified graphene nanocomposite for direct electrochemistry of redox enzyme

Abstract

A novel lipid based carbonaceous nanocomposite, 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (POPG) modified graphene (GP) (POPG-GP), was designed and synthesized by a non-covalent method. The nanocomposite was endowed with excellent properties of the two independent components, such as the biocompatibility of POPG and the outstanding electric properties of graphene. Fourier transform infrared (FT-IR) spectra, ultraviolet-visible (UV-vis) absorption spectra, transmission electron microscopy (TEM) were utilized to characterize the structure, morphology and surface property of the as synthesized POPG-GP. It has been found that the modification of POPG on GP could not only assist the dispersion of graphene in aqueous solution, but also endow it with negatively charged, which was favorable for the further immobilization of model enzyme via self-assembly. Based on the electrostatic interaction, the positively charged horseradish peroxide (HRP) could be immobilized onto the surface of POPG-GP to form HRP/POPG-GP/GC electrode. UV-vis and FT-IR spectroscopies were used to monitor the assembly process and demonstrated that HRP had been immobilized without denaturation. The HRP/POPG-GP/GC electrode could commendably realize the direct electron transfer (DET) between electrode and redox enzyme with good electrochemical performance. Moreover, such modified electrode also showed good electrocatalytic response toward the detection of H2O2 with high sensitivity, wide linear range, excellent stability and reproducibility. The linear response range for the HRP/POPG-GP/GC was 3.5~210 μmol/L (R=0.999). The detection limit and the sensitivity of the HRP/POPG-GP/GC electrode was calculated to be 1.17 μmol/L (S/N=3) and 356.6 mA•cm-2•M-1, respectively. The apparent Michaelis-Menten constant Km was estimated to be 0.45 mmol/L, indicating a high affinity of HRP to H2O2 on POPG-GP. The experiment results demonstrated that POPG-GP not only provided a biocompatible microenvironment for the immobilized HRP, but also supplied a necessary pathway for its direct electron transfer. Therefore, such biocompatible nanocomposite had potential applications in the field of biosensors.