Oops they did it again! Carbon nanotubes hoax scientists in viability assays
Abstract
New materials of emerging technological importance are single-walled carbon nanotubes (SWCNTs). Because SWCNTs will be used in commercial products in huge amounts, their effects on human health and the environment have been addressed in several studies. Inhalation studies in vivo and submerse applications in vitro have been described with diverging results. Why some indicate a strong cytotoxicity and some do not is what we report on here. Data from A549 cells incubated with carbon nanotubes fake a strong cytotoxic effect within the MTT assay after 24 h that reaches roughly 50%, whereas the same treatment with SWCNTs, but detection with WST-1, reveals no cytotoxicity. LDH, FACS-assisted mitochondrial membrane potential determination, and Annexin-V/PI staining also reveal no cytotocicity. SWCNTs appear to interact with some tetrazolium salts such as MTT but not with others (such as WST-1, INT, XTT). This interference does not seem to affect the enzymatic reaction but lies rather in the insoluble nature of MTT-formazan. Our findings strongly suggest verifying cytotoxicity data with at least two or more independent test systems for this new class of materials (nanomaterials). Moreover, we intensely recommend standardizing nanotoxicological assays with regard to the material used: there is a clear need for reference materials. MTT-formazan crystals formed in the MTT reaction are lumped with nanotubes and offer a potential mechanism to guide bioremediation and clearance for SWCNTs…
Integrity signals
Registry
Cites
Statistics
Claims the paper makes
Claims other papers make about this one
Each is checked against this paper’s own text: does it say what the citing paper says it does?
These same particle properties often interfere with experimental test systems.
“However, these same particle properties often interfere with experimental test systems (Wörle-Knirsch et al., 2006; Laurent et al., 2012; Bohmer et al., 2018).”
From In Vitro research Reproducibility: Keeping up High Standards (2019) · cites this paper as Wörle-Knirsch et al., 2006
Nanomaterials have demonstrated chemical interference in cytotoxicity assays (e.g., carbon nanotubes interfering with MTT, engineered nanoparticles producing assay-dependent toxicity estimates, nanomaterial adsorption of marker enzymes causing artefacts).
“This problem has been demonstrated particularly clearly for nanomaterials, where carbon nanotubes interfered with MTT-based viability measurements, engineered nanoparticles produced assay-dependent toxicity estimates, and nanomaterial adsorption of marker enzymes caused artefacts in cytotoxicity assays (Wohlleben et al., 2011; Wörle-Knirsch et al., 2006; Monteiro-Riviere et al., 2009).”
From Cytotoxicity across OECD methods is not a single endpoint: context-dependent roles, variability and implications for decision-making (2026) · cites this paper as Wörle-Knirsch et al., 2006
Cited by
Sorted by citations
Sharifi, S., Behzadi, S., Laurent, S., Laird Forrest, M., Stroeve, P., & Mahmoudi, M. (2012) · Chem. Soc. Rev. · doi:10.1039/c1cs15188f · Cited by 1,460 · see citing works
Direct imaging of single-walled carbon nanotubes in cells
Porter, A. E., Gass, M., Muller, K., Skepper, J. N., Midgley, P. A., & Welland, M. (2007) · Nature Nanotechnology · doi:10.1038/nnano.2007.347 · Cited by 564 · see citing works
Nanotechnology Safety Concerns Revisited
Stern, S. T., & McNeil, S. E. (2008) · Toxicological Sciences · doi:10.1093/toxsci/kfm169 · Cited by 560 · see citing works
Nanotoxicology: An Interdisciplinary Challenge
Krug, H. F., & Wick, P. (2011) · Angewandte Chemie International Edition · doi:10.1002/anie.201001037 · Cited by 556 · see citing works
Self-citationNanomaterials for Neural Interfaces
Kotov, N. A., Winter, J. O., Clements, I. P., Jan, E., Timko, B. P., Campidelli, S., Pathak, S., Mazzatenta, A., Lieber, C. M., Prato, M., et al. (2009) · Advanced Materials · doi:10.1002/adma.200801984 · Cited by 504 · see citing works
Reeves, J. F., Davies, S. J., Dodd, N. J. F., & Jha, A. N. (2008) · Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis · doi:10.1016/j.mrfmmm.2007.12.010 · Cited by 441 · see citing works
Clastogenic and aneugenic effects of multi-wall carbon nanotubes in epithelial cells
Muller, J., Decordier, I., Hoet, P. H., Lombaert, N., Thomassen, L., Huaux, F., Lison, D., & Kirsch-Volders, M. (2008) · Carcinogenesis · doi:10.1093/carcin/bgm243 · Cited by 298 · see citing works
Muller, J., Huaux, F., Fonseca, A., Nagy, J. B., Moreau, N., Delos, M., Raymundo-Piñero, E., Béguin, F., Kirsch-Volders, M., Fenoglio, I., et al. (2008) · Chemical Research in Toxicology · doi:10.1021/tx800101p · Cited by 261 · see citing works
Sanchez, V. C., Pietruska, J. R., Miselis, N. R., Hurt, R. H., & Kane, A. B. (2009) · WIREs Nanomedicine and Nanobiotechnology · doi:10.1002/wnan.41 · Cited by 186 · see citing works
Boyles, M. S. P., Young, L., Brown, D. M., MacCalman, L., Cowie, H., Moisala, A., Smail, F., Smith, P. J. W., Proudfoot, L., Windle, A. H., et al. (2015) · Toxicology in Vitro · doi:10.1016/j.tiv.2015.06.012 · Cited by 182 · see citing works
Bioavailability of Nickel in Single‐Wall Carbon Nanotubes
Liu, X., Gurel, V., Morris, D., Murray, D. W., Zhitkovich, A., Kane, A. B., & Hurt, R. H. (2007) · Advanced Materials · doi:10.1002/adma.200602696 · Cited by 169 · see citing works
In Vitro research Reproducibility: Keeping up High Standards
Hirsch, C., & Schildknecht, S. (2019) · Frontiers in Pharmacology · doi:10.3389/fphar.2019.01484 · Cited by 161 · see citing works
Mandal, A. K., Wu, X., Ferreira, J. S., Kim, M., Powell, L. R., Kwon, H., Groc, L., Wang, Y., & Cognet, L. (2020) · Scientific Reports · doi:10.1038/s41598-020-62201-w · Cited by 85 · see citing works
Behan, B. L., DeWitt, D. G., Bogdanowicz, D. R., Koppes, A. N., Bale, S. S., & Thompson, D. M. (2011) · Journal of Biomedical Materials Research Part A · doi:10.1002/jbm.a.32939 · Cited by 56 · see citing works
Potential Uses of Carbon Nanotubes in The Medical Field: How Worried Should Patients Be?
Boczkowski, J., & Lanone, S. (2007) · Nanomedicine · doi:10.2217/17435889.2.4.407 · Cited by 39 · see citing works
Pedata, P., Boccellino, M., La Porta, R., Napolitano, M., Minutolo, P., Sgro, L. A., Zei, F., Sannolo, N., & Quagliuolo, L. (2012) · Nanotoxicology · doi:10.3109/17435390.2011.579630 · Cited by 31 · see citing works
Thoma, T., Löhr, L., Demuth, P., Hambruch, N., Oesch, F., & Landsiedel, R. (2026) · NAM Journal · doi:10.1016/j.namjnl.2026.100126
- Authors
- Wörle-Knirsch, J. M., Pulskamp, K., & Krug, H. F.
- Affiliations
- Forschungszentrum Karlsruhe, Institute of Toxicology and Genetics, Department of Molecular and Environmental Toxicology, P.O. Box 3640, D-76021 Karlsruhe, Germany
- Corresponding author
- Krug, H. F.
- ORCID
- Krug, H. F.
- Venue
- Nano Letters
- Publisher
- American Chemical Society (ACS)
- Published
- 2006-04-27
- Volume
- 6
- Issue
- 6
- Pages
- 1261-1268
- ISSN
- 1530-6984 (ISSN-L)
- 1530-6992
- OpenAlex
- W2074947593
- Cited by
- 994
- References
- 0
- Citations by year
- 2026: 14 · 2025: 9 · 2024: 10 · 2023: 18 · 2022: 32 · 2021: 32 · 2020: 19 · 2019: 26 · 2018: 44 · 2017: 31 · 2016: 53 · 2015: 68 · 2014: 76 · 2013: 87 · 2012: 83
- FWCI
- 50.12
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Nano Letters (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Physical Sciences › Engineering › Biomedical Engineering › Graphene and Nanomaterials Applications
- Physical Sciences › Materials Science › Materials Chemistry › Nanoparticles: synthesis and applications
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Cancer Research › Carcinogens and Genotoxicity Assessment
- Keywords
- single-walled carbon nanotubes, cytotoxicity, tetrazolium salts, formazan, A549 cells, reference materials, mitochondrial membrane potential, Annexin V/PI staining, LDH, tissue engineering scaffolds
- MeSH terms
- Cell Survival, Fraud, Lethal Dose 50, Risk Factors, Sensitivity and Specificity, Reproducibility of Results, Artifacts, Risk Assessment, Toxicity Tests, Evidence-Based Medicine, Nanotubes, Carbon
About these checks
Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.
Statistics and arithmetic are recomputed, not judged.
Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.
What counts as a claim ›How we measure confidence ›How we check this ›
Are you an author, or do you see a problem with this page? Request a review
