A New Method for Dispersing Pristine Carbon Nanotubes Using Regularly Arranged S-Layer Proteins.

Andreas Breitwieser,Uwe B Sleytr,Dietmar Pum

doi:10.3390/nano11051346

Andreas Breitwieser, Uwe B Sleytr + Show 1 more

Open Access

https://doi.org/10.3390/nano11051346

Copy DOI

Abstract

Homogeneous and stable dispersions of functionalized carbon nanotubes (CNTs) in aqueous solutions are imperative for a wide range of applications, especially in life and medical sciences. Various covalent and non-covalent approaches were published to separate the bundles into individual tubes. In this context, this work demonstrates the non-covalent modification and dispersion of pristine multi-walled carbon nanotubes (MWNTs) using two S-layer proteins, namely, SbpA from Lysinibacillus sphaericus CCM2177 and SbsB from Geobacillus stearothermophilus PV72/p2. Both the S-layer proteins coated the MWNTs completely. Furthermore, it was shown that SbpA can form caps at the ends of MWNTs. Reassembly experiments involving a mixture of both S-layer proteins in the same solution showed that the MWNTs were primarily coated with SbsB, whereas SbpA formed self-assembled layers. The dispersibility of the pristine nanotubes coated with SbpA was determined by zeta potential measurements (−24.4 +/− 0.6 mV, pH = 7). Finally, the SbpA-coated MWNTs were silicified with tetramethoxysilane (TMOS) using a mild biogenic approach. As expected, the thickness of the silica layer could be controlled by the reaction time and was 6.3 +/− 1.25 nm after 5 min and 25.0 +/− 5.9 nm after 15 min. Since S-layer proteins have already demonstrated their capability to bind (bio)molecules in dense packing or to act as catalytic sites in biomineralization processes, the successful coating of pristine MWNTs has great potential in the development of new materials, such as biosensor architectures.

Highlights

In recent decades, research efforts have focused on the development of organic–inorganic hybrid nanomaterials, as they were expected to have excellent physical andchemical properties for developments in the materials and life sciences [1,2]
We introduce a new facile protocol for the non-covalent functionalization and dispersion of multi-walled carbon nanotubes (MWNTs) with two different S-layer proteins, namely, SbpA from L. sphaericus CCM2177 (Figure 1a,b) [13] and SbsB from Geobacillus stearothermophilus PV72/p2 (Figure 1c) [30]
The produced monomeric wild-type SbpA S-layer protein solution was adjusted to a final concentration of 1 mg/mL

Summary

Introduction

Research efforts have focused on the development of organic–inorganic hybrid nanomaterials, as they were expected to have excellent physical and (bio)chemical properties for developments in the materials and life sciences [1,2]. Research efforts have focused on the development of organic–. Carbon nanotubes (CNTs), fullerenes, and graphene are among the most promising candidates for such emerging technologies [3,4]. The biomedical applications of CNTs have increased tremendously in recent years, such as cellular imaging or drug-targeting and delivery in cancer therapies [5,6,7]. Further progress in all these applications is only possible when homogeneous and stable dispersions of functionalized CNTs in aqueous solutions are available. The tendency of carbon nanotubes to form bundles and, eventually, to become insoluble in water is caused by their strong hydrophobic and cohesive van der Waals interactions. In order to overcome this problem, several approaches have been developed to separate bundles into individual tubes. The covalent functionalization of surface chemical groups, such as the oxidation of carbon, and non-covalent functionalization by attaching amphiphilic

Methods

Results

Conclusion