Bioelectrochemical Properties of Enzyme-Containing Multilayer Polyelectrolyte Microcapsules Modified with Multiwalled Carbon Nanotubes

Abstract

This work investigated changes in the biochemical parameters of multilayer membrane structures, emerging at their modification with multiwalled carbon nanotubes (MWCNTs). The structures were represented by polyelectrolyte microcapsules (PMCs) containing glucose oxidase (GOx). PMCs were made using sodium polystyrene sulfonate (polyanion) and poly(allylamine hydrochloride) (polycation). Three compositions were considered: with MWCNTs incorporated between polyelectrolyte layers; with MWCNTs inserted into the hollow of the microcapsule; and with MWCNTs incorporated simultaneously into the hollow and between polyelectrolyte layers. The impedance spectra showed modifications using MWCNTs to cause a significant decrease in the PMC active resistance from 2560 to 25 kOhm. The cyclic current-voltage curves featured a current rise at modifications of multilayer MWCNT structures. A PMC-based composition was the basis of a receptor element of an amperometric biosensor. The sensitivity of glucose detection by the biosensor was 0.30 and 0.05 μA/mM for PMCs/MWCNTs/GOx and PMCs/GOx compositions, respectively. The biosensor was insensitive to the presence of ethanol or citric acid in the sample. Polyelectrolyte microcapsules based on a multilayer membrane incorporating the enzyme and MWCNTs can be efficient in developing biosensors and microbial fuel cells.

Keywords: PMC impedance decrease; glucose oxidase; modification with multiwalled carbon nanotubes; multilayer membrane structures; polyelectrolyte microcapsules (PMCs).

Figure 1

Formation of polyelectrolyte microcapsules with the enzyme and nanotubes.

Figure 2

Atomic force microscopy (AFM) images of microcapsules. An AFM micrograph of a layer of aggregated and single polyelectrolyte microcapsules (PMCs) (a); a histogram of 100 microcapsules (b); and the geometric size of a single microcapsule (c).

Figure 3

PMC micrographs obtained by phase-contrast microscopy (a) and scanning electron microscopy ((b) intact capsules and (c) open capsules). Scale bars are 10 μm (a) or 1 μm (b,c).

Figure 4

Impedance spectra for electrodes with various surface modifications: 1, a nonmodified electrode; 2, with PMCs; 3, glucose oxidase (GOx); 4, PMCs containing multiwalled carbon nanotubes (MWCNTs) in the hollow and between polyelectrolyte layers; 5, PMCs containing MWCNTs between polyelectrolyte layers; 6, PMCs containing MWCNTs in the hollow; 7, PMCs with GOx; 8, MWCNTs; and 9, PMCs with GOx and MWCNTs in the hollow. Inset shows the equivalent electric circuits used for electrodes without MWCNTs (A) and for electrodes with MWCNTs (B).

Figure 5

Cyclic voltammograms of modified electrodes: 1, a nonmodified electrode; 2, with PMCs, 3, GOx; 4, PMCs containing MWCNTs in the hollow and between polyelectrolyte layers; 5, PMCs containing MWCNTs between polyelectrolyte layers; 6, PMCs containing MWCNTs in the hollow; 7, PMCs with GOx; 8, MWCNTs; and 9, PMCs with GOx and MWCNTs in the hollow. Measurements were carried out with the addition of 5 mM HCF. For comparison, a shows all types of dependences, while b represents the zoom of curves 1–6.

Figure 6

Calibration dependences of biosensor signals vs. glucose concentrations at various modifications of the electrode: 1, PMCs/GOx/MWCNTs in the hollow; 2, PMCs/GOx; 3, GOx; and 4, PMCs/GOx/MWCNTs in the hollow plus an additional modification of the electrode with MWCNTs (see explanations in the text).

Figure 7

Amperometric signals of a PMCs/GOx/MWCNTs-modified biosensor upon addition of citric acid, ethanol, or glucose.