Functionalized graphene oxide for clinical glucose biosensing in urine and serum samples

Abstract

A novel clinical glucose biosensor fabricated using functionalized metalloid-polymer (silver-silica coated with polyethylene glycol) hybrid nanoparticles on the surface of a graphene oxide nanosheet is reported. The cyclic voltammetric response of glucose oxidase modification on the surface of a functionalized graphene oxide electrode showed a surface-confined reaction and an effective redox potential near zero volts, with a wide linearity of 0.1-20 mM and a sensitivity of 7.66 μA mM(-1) cm(-2). The functionalized graphene oxide electrode showed a better electrocatalytic response toward oxidation of H(2)O(2) and reduction of oxygen. The practical applicability of the functionalized graphene oxide electrode was demonstrated by measuring the peak current against multiple urine and serum samples from diabetic patients. This new hybrid nanoarchitecture combining a three-dimensional metalloid-polymer hybrid and two-dimensional graphene oxide provided a thin solid laminate on the electrode surface. The easy fabrication process and retention of bioactive immobilized enzymes on the functionalized graphene oxide electrode could potentially be extended to detection of other biomolecules, and have broad applications in electrochemical biosensing.

Keywords: clinical diagnostics; cyclic voltammetry; glucose biosensor; glucose oxidase; metalloid-polymer nanoparticles.

Figure 1

Ultraviolet-visible absorbance spectrum (A) graphene oxide and (B) functionalized graphene oxide, and transmission electron microscopic images of (C) graphene oxide and (D) functionalized graphene oxide.

Figure 2

Raman spectrum of graphene oxide and functionalized graphene oxide. Abbreviations: GO, graphene oxide; FGO, functionalized graphene oxide.

Figure 3

(A) Illustration of the electrochemical setup under electrolyte solution. Dotted circle depicts the digital image of Au-PCB working electrode and the process of glucose oxidase modification at two different stages, ie, Au-PCB-GO and Au-PCB-FGO biosensor platform, respectively. (B) Enzymatic reaction at the electrode interface and its respective cyclic voltammogram. Abbreviations: Ag/AgCl, silver/silver chloride; RE, reference electrode; Pt, platinum; CE, counter electrode; Au-PCB, gold printed circuit board electrode; WE, working electrode; Au-PCB-GO, gold printed circuit board electrode modified with graphene oxide; Au-PCB-FGO, gold printed circuit board electrode modified with functionalized graphene oxide; GOx, glucose oxidase; Ag@SiO₂-PEG, silver-silica coated with polyethylene glycol; FGO, functionalized graphene oxide; GO, graphene oxide.

Figure 4

(A) CVs of GOx-modified Au-PCB (black trace), Au-PCB-GO (red trace), and Au-PCB-FGO electrode in PBS buffer (pH 7.4). (B) Focused CV curve of Figure 4A (green trace) GOx-modified Au-PCB-FGO electrode. (C) CVs of bare Au-PCB/GOx (black trace) and Au-PCB-GO/GOx (red trace) versus 20 mM D(+) glucose in PBS (pH 7.4). (D) CVs of Au-PCB-FGO-GOx versus D(+) glucose in PBS buffer at different concentration ranges from 20 mM to 0.1 mM, and the inset shows the corresponding plot of peak currents against molar concentrations of glucose. Notes: Scan rate: 50 mV/s. All the individual CV responses were measured by different electrodes prepared appropriately. Abbreviations: CVs, cyclic voltammograms; GOx, glucose oxidase; Au-PCB, gold printed circuit board electrode; Au-PCB-GO, gold printed circuit board electrode modified with graphene oxide; Au-PCB-FGO, gold printed circuit board electrode modified with functionalized graphene oxide; Au-PCB-FGO-GOx, gold printed circuit board electrode modified with functionalized graphene oxide and glucose oxidase; PBS, phosphate-buffered saline; Ag/AgCI, silver/silver chloride.

Figure 5

(A) CVs of Au-PCB-FGO-GOx against glucosuria sample (injected into supporting electrolyte) and (B) histogram of peak currents for Au-PCB-FGO/GOx electrode against glucosuria sample of different volumes from one diabetic patient, ensuring the linear relationship between the volume and peak current. Notes: Where error bars are not visible, they are smaller than the symbols. Scan rate: 50 mV/s. Abbreviations: CVs, cyclic voltammograms; Au-PCB-FGO-GOx, gold printed circuit board electrode modified with functionalized graphene oxide and glucose oxidase; Ag/AgCI, silver/silver chloride.

Figure 6

(A) CVs of Au-PCB-FGO-GOx against serum glucose samples (modified on electrode) from diabetic patients and (B) histogram of peak currents for Au-PCB-FGO/GOx electrode against serum samples from low to high concentration from different diabetic patients. Notes: Where error bars are not visible, they are smaller than the symbols. Scan rate: 50 mV/s. Abbreviations: CVs, cyclic voltammograms; Au-PCB-FGO-GOx, gold printed circuit board electrode modified with functionalized graphene oxide and glucose oxidase; Ag/AgCI, silver/silver chloride.