Carbon Nanotubes Demonstrate Antibacterial Activity

CARBON nanotubes synthesised using ferrocene have demonstrated antibacterial activity against Escherichia coli in laboratory experiments, suggesting potential applications for nanomaterials in antimicrobial research.

Researchers found that multi-walled carbon nanotubes (MWCNTs) inhibited bacterial growth in a concentration-dependent manner, with both minimum inhibitory and bactericidal concentrations of 256 µg/mL. The findings highlight the antibacterial properties of the experimental preparation, although further research is needed to determine the mechanisms responsible and whether these effects could translate into practical applications.

Exploring Nanomaterials as Antibacterial Agents

The development of novel antibacterial materials remains an important area of research, particularly as antimicrobial resistance continues to challenge the treatment and prevention of bacterial infections.

Carbon nanotubes have attracted interest because of their distinctive structural and physicochemical properties, which may support applications in antimicrobial surfaces, filtration systems, and other technologies.

To investigate their antibacterial potential, researchers synthesised MWCNTs using chemical vapour deposition (CVD), with ferrocene serving as the carbon and iron-catalyst precursor.

The resulting material was characterised using X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy.

These analyses confirmed the formation of graphitised multi-walled nanotube structures and identified iron-containing residues originating from the synthesis process.

Researchers subsequently evaluated antibacterial activity against the reference strain E. coli ATCC 25922 using agar well diffusion, broth microdilution, and viable-count plating.

Carbon Nanotubes Inhibit E. coli Growth

The experimental preparation demonstrated concentration-dependent antibacterial activity across the tested range of 1–512 µg/mL.

Broth microdilution testing identified a minimum inhibitory concentration (MIC) of 256 µg/mL, defined by the absence of visible bacterial growth.

Blank-corrected quantitative measurements provided additional support for this inhibitory endpoint.

Viable-count analysis further demonstrated that no bacterial colonies could be recovered on drug-free Mueller–Hinton agar at concentrations of 256 and 512 µg/mL.

These findings supported a minimum bactericidal concentration (MBC) of 256 µg/mL under the experimental conditions, indicating that the preparation demonstrated bactericidal activity at the same concentration required to inhibit visible growth.

The results suggest that the ferrocene-derived nanotube preparation was capable of both inhibiting bacterial proliferation and preventing recovery of viable E. coli colonies at sufficiently high concentrations.

Antibacterial Effects Increase With Concentration

Agar well-diffusion testing provided further evidence of concentration-dependent antibacterial activity.

The largest inhibition zone, measuring 26 mm, was observed at a concentration of 512 µg/mL.

At 256 µg/mL, the inhibition zone measured 21 mm, decreasing to 19 mm at 128 µg/mL.

Smaller inhibition zones were recorded at lower concentrations, measuring 9 mm at 64 µg/mL and 7 mm at 32 µg/mL.

No inhibition was observed in the negative control.

These findings demonstrate that higher concentrations of the experimental material were associated with larger zones of bacterial growth inhibition.

However, inhibition-zone measurements can also be influenced by how materials disperse and diffuse through agar, meaning they should be interpreted alongside the broth microdilution and viable-count findings.

Potential Applications Require Further Investigation

The researchers concluded that ferrocene-derived MWCNTs demonstrated measurable antibacterial activity against E. coli under laboratory conditions.

However, an important limitation was that the nanotubes were evaluated without post-synthesis purification.

Consequently, the observed antibacterial effects cannot be attributed exclusively to the carbon nanotube structures, as residual iron-containing compounds and other synthesis-derived components may also have contributed.

The study was also limited to laboratory testing against a single reference strain of E. coli, and did not establish effectiveness against other bacterial species, resistant clinical isolates, or infections in living organisms.

Further studies using purified nanotubes and appropriate synthesis-residue controls are needed to clarify the mechanisms responsible for antibacterial activity.

Additional research will also be necessary to assess toxicity, biocompatibility, and practical performance before any potential clinical or environmental applications can be considered.

The findings provide preliminary evidence supporting further investigation of ferrocene-derived carbon nanotube preparations as antibacterial materials, while emphasising the importance of distinguishing nanotube-specific effects from those of residual synthesis components.

Reference

Ahmed, S.K., Taay, Y.M., Ahmed, A.J. et al. Antibacterial activity of ferrocene-derived multi-walled carbon nanotubes synthesized by chemical vapor deposition against Escherichia coli. Sci Rep (2026). https://doi.org/10.1038/s41598-026-70564-9