Diamine Oxidase-Conjugated Multiwalled Carbon Nanotubes to Facilitate Electrode Surface Homogeneity.

M Amin,S Wylie,S J Rowley-Neale,A J Slate,B M Abdullah,C E Banks,K A Whitehead

doi:10.3390/s22020675

Abstract

Carbon nanomaterials have gained significant interest over recent years in the field of electrochemistry, and they may be limited in their use due to issues with their difficulty in dispersion. Enzymes are prime components for detecting biological molecules and enabling electrochemical interactions, but they may also enhance multiwalled carbon nanotube (MWCNT) dispersion. This study evaluated a MWCNT and diamine oxidase enzyme (DAO)-functionalised screen-printed electrode (SPE) to demonstrate improved methods of MWCNT functionalisation and dispersion. MWCNT morphology and dispersion was determined using UV-Vis spectroscopy (UV-Vis) and scanning electron microscopy (SEM). Carboxyl groups were introduced onto the MWCNT surfaces using acid etching. MWCNT functionalisation was carried out using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-Hydroxysuccinimide (NHS), followed by DAO conjugation and glutaraldehyde (GA) crosslinking. Modified C-MWNCT/EDC-NHS/DAO/GA was drop cast onto SPEs. Modified and unmodified electrodes after MWCNT functionalisation were characterised using optical profilometry (roughness), water contact angle measurements (wettability), Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX) (vibrational modes and elemental composition, respectively). The results demonstrated that the addition of the DAO improved MWCNT homogenous dispersion and the solution demonstrated enhanced stability which remained over two days. Drop casting of C-MWCNT/EDC-NHS/DAO/GA onto carbon screen-printed electrodes increased the surface roughness and wettability. UV-Vis, SEM, Raman and EDX analysis determined the presence of carboxylated MWCNT variants from their non-carboxylated counterparts. Electrochemical analysis demonstrated an efficient electron transfer rate process and a diffusion-controlled redox process. The modification of such electrodes may be utilised for the development of biosensors which could be utilised to support a range of healthcare related fields.

Highlights

The work presented demonstrated that when the enzyme diamine oxidase enzyme (DAO) was used for the facilitation of the dispersion of multiwalled carbon nanotube (MWCNT), a more uniform drop cast on the electrode surface was observed
In agreement with the results presented in this study, the relative increase in peak absorbance of the C-MWNCT in comparison to the MWCNTs was determined in other work [30,31]
This study demonstrated the successful homogenous dispersion of MWNCTs through the manipulation of the hydrophobic/hydrophilic interactions using diamine oxidase to enable a more uniformed MWCNT suspension

Summary

Introduction

The use of electrochemical analysis remains a cost effective and simple method to determine the concentration of electroactive species in solution [1]. The morphology, size of the electrode and the fabrication method utilised play a major role in determining the electrochemical response of the system [2,3]. One way to modify such systems is to use carbon nanomaterials and enzymes. Carbon nanotubes (CNTs) encompass all the requirements for fabricating an electrode surface with unique electrical, chemical, and mechanical properties which can be further modified to enable the detection of biomolecules. CNTs are an allotrope of graphitic carbon in the nanometre scale, which consists of one or more concentric tubules, each with a helically wound hexagonal honeycomb lattice structure [4]

Methods

Results

Discussion

Conclusion