A Novel Sampling and Analytical Framework for Airborne Carbon Nanotubes

Our plain-English summary of A Novel Sampling and Analytical Framework for Airborne Carbon Nanotubes, by H.A. Davey, S. Pradeep, Y.H. Chen, et al (Analytical Chemistry, 2026).

The study

• Authors: H.A. Davey, S. Pradeep, Y.H. Chen, J. Su, C.S. Tsai
• Journal: Analytical Chemistry
• Published: 2026;98(27):19992-20004
• Read it: PubMed · Publisher · Free full text

Abstract

Airborne carbon nanotubes (CNTs) present growing environmental and occupational health concerns. Like asbestos, CNT can deposit deep in the lungs and induce toxic effects, underscoring the need for accurate exposure metrics amid increasing global production. Current exposure assessment methods by the National Institute for Occupational Safety and Health (NIOSH) rely on mass-based measurements and indirect transmission electron microscopy (TEM), which often underestimate exposure, particularly for nanoscale fibers. To overcome these limitations, the objectives of this study were to develop a CNT-specific sampling and analysis method to improve fiber detection and characterization and validate its performance by comparing the novel diffusion-based sampler, Tsai Diffusion Sampler (TDS), with conventional approaches. Samplers were operated side-by-side under controlled conditions to ensure comparability. Furthermore, polycarbonate (PC) and mixed cellulose ester (MCE) filters were evaluated for all of the sampling configurations. CNTs collected onto filters and TEM grids were examined for their corresponding direct or indirect analysis. An automated image segmentation algorithm was applied to CNT images to ensure consistent fiber sizing and to support a count-based exposure metric. Results demonstrated that the TDS (which utilizes low flow rate) paired with PC filters most effectively captured individualized nanoscale fibers, enabling recovery of CNT structures of less than 100 nm that were underrepresented in compared methods. Aerosolized hydrophilic CNTs exhibited higher number concentrations than hydrophobic CNTs, while open-face samplers with MCE filters produced the highest mass concentrations. Importantly, these findings establish a reproducible, integrated sampling, and analytical framework that enhances CNT exposure assessment and supports refinement of occupational health guidelines.

In plain English

This laboratory study tested ways to sample and measure airborne multiwalled carbon nanotubes (MWCNTs). It did not study people or asbestos. Inside a sealed glovebox, the authors stirred hydrophobic and hydrophilic MWCNT powders. They collected the airborne material with three samplers: open-face cassettes, closed-face cassettes with cyclones, and the low-flow Tsai Diffusion Sampler (TDS). Each ran on polycarbonate or mixed cellulose ester filters, for 36 samples in total. They compared direct electron microscopy with indirect analysis by NIOSH method 7402, a method originally developed for asbestos fibers, and used an automated image program to size particles. Mixed cellulose ester filters collected more mass than polycarbonate filters (p = 0.02). Sampler type and nanotube type were not statistically significant for mass. For hydrophilic MWCNTs, the TDS yielded 279 sized particles and was the only sampler with particles under 100 nm (approximately 8%). The authors concluded that current gravimetric and asbestos-adapted methods do not adequately represent airborne CNT exposure. They noted that image-based sizes are not aerodynamic sizes and that other CNT types still need testing.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment comparing air samplers, filter types and electron microscopy methods for collecting and measuring aerosolized carbon nanotubes
• Who was studied: No human subjects. Hydrophobic and OH-functionalized hydrophilic multiwalled carbon nanotube powders were aerosolized in a glovebox. Six sampler and filter configurations were run with 3 replicates for each of the 2 MWCNT types, giving 36 samples.
• Exposure: Airborne MWCNTs generated by stirring bulk powder. They were sampled for 120 min with open-face and closed-face (cyclone) cassettes at 2.0 L/min and with the Tsai Diffusion Sampler at 0.3 L/min, on polycarbonate (0.22 μm pore) or mixed cellulose ester (0.45 μm pore) filters.
• Main results:
  • In the 10 to 420 nm range measured by the SMPS instrument, aerosolized hydrophilic CNTs peaked at 3032 particles/cm3. This was about double the peak for hydrophobic CNTs, 1510 particles/cm3.
  • In the gravimetric (mass) analysis, the TDS with mixed cellulose ester filters gave the highest mass concentrations, particularly for hydrophobic CNTs (2.3 mg/m3).
  • In the three-way analysis of variance, filter type had a statistically significant effect on mass concentration (p = 0.02), with mixed cellulose ester filters collecting more than polycarbonate filters. Sampler type (p = 0.12) and CNT type (p = 0.81) were not statistically significant.
  • Closed-face samplers with mixed cellulose ester filters collected significantly less mass than the reference configuration, open face with mixed cellulose ester filters (mean 1.88 mg/m3).
  • For hydrophilic MWCNTs sized by the image algorithm, the TDS yielded the most particles (n = 279), with a mean diameter of 4.2 μm. It was the only sampler to detect particles under 100 nm, approximately 8% of its particles.
  • For hydrophilic MWCNTs, the open-face sampler yielded 186 particles and the closed-face sampler 127 particles. Both had a mean diameter of 1.8 μm, and neither had particles under 100 nm.
  • In transmission electron microscopy of TDS samples, direct analysis showed fibers on grids placed on either filter type. Indirect analysis (filter-to-grid transfer) mostly showed an agglomerate.
• The authors' conclusion: The authors concluded that current gravimetric and asbestos-adapted methods do not adequately represent airborne CNT exposure, particularly for submicron structures and nanosized fibers.
• Limitations the authors state:
  • Electron microscopy measures two-dimensional projected size, which does not directly represent how particles behave in air.
  • The method needs validation with additional CNT types and in relevant environments.
  • Loose agglomerates on open-face filters were often lost during handling, so open-face size distributions underrepresent larger particles.
  • Microscope imaging has an inherent bias toward smaller particles.

Topics

Medical terms in this study, explained in our Lexicon: NIOSH, Transmission Electron Microscopy (TEM).

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