Graphene versus Multi-Walled Carbon Nanotubes for Electrochemical Glucose Biosensing

Abstract

: A simple procedure was developed for the fabrication of electrochemical glucose biosensors using glucose oxidase (GOx), with graphene or multi-walled carbon nanotubes (MWCNTs). Graphene and MWCNTs were dispersed in 0.25% 3-aminopropyltriethoxysilane (APTES) and drop cast on 1% KOH-pre-treated glassy carbon electrodes (GCEs). The EDC (1-ethyl-(3-dimethylaminopropyl) carbodiimide)-activated GOx was then bound covalently on the graphene- or MWCNT-modified GCE. Both the graphene- and MWCNT-based biosensors detected the entire pathophysiological range of blood glucose in humans, 1.4-27.9 mM. However, the direct electron transfer (DET) between GOx and the modified GCE's surface was only observed for the MWCNT-based biosensor. The MWCNT-based glucose biosensor also provided over a four-fold higher current signal than its graphene counterpart. Several interfering substances, including drug metabolites, provoked negligible interference at pathological levels for both the MWCNT- and graphene-based biosensors. However, the former was more prone to interfering substances and drug metabolites at extremely pathological concentrations than its graphene counterpart.

Keywords: electrochemical glucose sensor; glucose oxidase; graphene; multi-walled carbon nanotubes.

Scheme 1

The preparation of graphene- and multi-walled carbon nanotube (MWCNT)-based glucose biosensors.

Figure 1

High resolution images of (a) grapheme-glucose oxidase (GOx); (b) Nafion/graphene-GOx; (c) MWCNT-GOx and (d) Nafion/MWCNT-GOx modified glassy carbon substrates using a helium ion microscope from Carl Zeiss, Germany. The scale bars for (a)/(b) and (c)/(d) are 10 μm and 200 nm, respectively.

Figure 2

(a) CVs of Nafion/GOx/glassy carbon electrodes (GCE) (blue), Nafion/graphene/GCE (yellow), Nafion/MWCNT/GCE (red), Nafion/graphene-GOx/GCE (green) and Nafion/MWCNT-GOx/GCE (black) in N₂-saturated PBS at 100 mV s⁻¹; (b) The effect of scan rate (20, 50, 100, 150 and 200 mV s⁻¹) on the DET of GOx on Nafion/MWCNT-GOx/GCE in N₂-saturated PBS. Inlet: the linear relation between i_pc (or i_pa) and v; (c) The relation between the formal potential (observed on Nafion/MWCNT-GOx/GCE) and different pH values: 5.65, 6.36, 7.2, 7.72, 8.29. Scan rate = 100 mV s⁻¹; (d) Plot of E_p (of the Nafion/MWCNT-GOx/GCE) vs. log v, v = 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9 V s⁻¹. Inlet: the relation between E_pa (or E_pc) and log v.

Figure 3

CVs of (a,c) Nafion/graphene-GOx/GCE and (b,d) Nafion/MWCNT-GOx/GCE in (a,b) nitrogen and (c,d) air-saturated PBS containing (i) 0 mM; (ii) 1 mM and (iii) 8 mM glucose. Scan rate: 100 mV s⁻¹.

Figure 4

(a) The amperometric response of Nafion/MWCNT-GOx/GCE for the detection of 0.5 to 32 mM glucose at −0.45 V in the presence of O₂; (b) Assay curves for the detection of commercial glucose by the graphene- and MWCNT-based electrodes. The error bars represent standard deviation (SD); (c) Assay curves for the detection of Sugar-Chex whole blood glucose linearity standards by both electrodes. The error bars represent the SD; (d) The effect of interfering substances on the electrochemical detection of 6.8 mM blood glucose standard by both electrodes.