Single-Walled Carbon Nanotubes Exhibit Strong Antimicrobial Activity

Abstract

We provide the first direct evidence that highly purified single-walled carbon nanotubes (SWNTs) exhibit strong antimicrobial activity. By using a pristine SWNT with a narrow diameter distribution, we demonstrate that cell membrane damage resulting from direct contact with SWNT aggregates is the likely mechanism leading to bacterial cell death. This finding may be useful in the application of SWNTs as building blocks for antimicrobial materials.Carbon-based nanomaterials, such as fullerene and carbon nanotubes (CNTs), exhibit unique size-and structure-dependent optical, electronic, magnetic, thermal, chemical, and mechanical properties. 1 As a result, it is not surprising that these nanomaterials have been considered for use in numerous applications, including the fabrication of superconductors, optical devices, sensors, energy storage devices, fuel cells, and catalysts. 2 However, such extraordinary physical and chemical properties are accompanied by concerns about possible adverse effects of these materials on biological systems. In particular, applications that use singlewalled carbon nanotubes (SWNTs) for biosensors, 3 drug and vaccine delivery transporters, 4,5 and novel biomaterials 6 increase the potential for encounters between SWNTs and humans and the ecosystem. Future commercial development of nanotechnology may also lead to the discharge of SWNTs into the environment.Information concerning the potential toxicity from exposure to SWNTs and their environmental impact is scarce, often debated, 7 and focused on human cells. [8][9][10][11] The toxicity of SWNTs to human cells has been observed to vary with SWNT functionalization and the concentration of the solubilizing agent (i.e., surfactants), 12,13 as well as with SWNT physicochemical properties such as structure, diameter, cleanliness (e.g., % metal), and defect level. 14 In these studies, however, commercial SWNTs were used, and characterization was not well defined. Furthermore, for these SWNTs, factors such as mean diameter, diameter distribution, metal content, and defect level cannot be independently varied because of limitations of the SWNT synthesis, cleaning, and separation processes. Commercial SWNTs have generally been treated with strong acids and contain on average 4.5-15% metal and other impurities. 15 Only a handful of groups can produce SWNTs with a narrow diameter distribution. 16 The above studies with human cells may suggest that SWNTs can also interact with microbes and exhibit antimicrobial

Capture of bacteria by flexible carbon nanotubes

“…The adhesive activities of the CNTs were assessed by a bacterial precipitation assay using S. mutans adhesion to CNTs are in agreement with the previously reported results regarding bacterial adhesion to CNTs in the case of E. coli [7][8][9][10]. Among the carbon samples, the precipitation efficiency of 30-MWCNTs was the highest; 30-MWCNTs at 0.17 mg/mL concentration had the highest efficiency.…”

“…This observation contradicts the previous result that flattened cells are inactivated on SWCNTs, which was reported by Kang et al [9,10] and Brady-Estévez et al [14]. The differences in morphology could be depend on the differences between gram-positive bacteria, which have a thick cell wall (such as S. mutans) and gram-negative bacteria, which have a thin cell wall (such as E. coli) or on the purity of SWCNTs.…”

“…In recent investigations for biological applications, CNTs have been utilized as adsorbents to eliminate dyes [5]. In addition, CNTs can adsorb bacteria [6][7][8]; single-walled carbon nanotubes (SWCNTs) exhibit strong antimicrobial activity toward Escherichia coli [9,10]. However, bacterial adhesion, particularly, oral bacterial adhesion, to CNTs has not yet been sufficiently investigated.…”

Fe3+-saturated montmorillonite effectively deactivates bacteria in wastewater

“…No significant bacterial deactivation (−9.3 ± 3.9%) was observed within 2 h incubation in the FeCl 3 -added secondary wastewater. Previous studies have suggested that direct contact between microbial cells and surface of antimicrobial materials is necessary for microbial deactivation (Kang et al, 2007). It was shown that microbial cell deactivation was mainly localized on the Cu 2+ -montmorillonite surface and was not due to the limited amount of Cu 2+ desorbed from the mineral (1.2-2.3% of overall exchanged Cu 2+ ) into solution (Hu et al, 2005).…”

“…It was reported that single-walled carbon nanotubes (50 mg/L) and graphene oxide (80 mg/L) could deactivate E. coli (~10 6 to 10 7 CFU/mL) after 4 h in aqueous environment at average efficiency of 88% and 92%, respectively (Kang et al, 2007;Liu et al, 2011). After immersion of silver nanoparticles-coated silicon wafers into E. coli and S. aureus inoculated growth medium for 12 h, 99% and 98% of E. coli and S. aureus (~2 × 10 5 CFU/mL) were deactivated, respectively (Zhou et al, 2014).…”