Cellulose-Infused Carbon Nanotube Tape Simplifies Array Tomography Imaging

A new laboratory-made tape that combines natural cellulose fibrils, carbon nanotubes, and silver nanowires can support serial-section electron microscopy without the glow discharge or carbon coating steps that conventional tapes typically require. The composite tape, described in Applied Microscopy, was developed to address persistent practical problems in array tomography, a technique that allows large volumes of brain tissue to be reconstructed at nanometer resolution using scanning electron microscopy.

Array tomography with scanning electron microscopy enables nanometer-scale reconstruction of neural circuits and resolves synaptic vesicles and other ultrastructural features. When in situ destructive approaches such as serial block face SEM or focused ion beam SEM are not used, preparing hundreds or even thousands of serial thin sections remains technically demanding and depends heavily on operator expertise. Sections collected on fragile formvar film-coated single-slot EM grids are prone to breaking, which can interrupt serial imaging. Automatic tape-collecting ultramicrotomy, or ATUM, addresses this by collecting thousands of serial ultrathin sections onto tape automatically, and combined with mosaic acquisition software it allows millimeter-scale volumes to be imaged serially.

The tape itself is a critical component of this workflow. Kapton polyimide tape is currently the most widely available commercial option, offering stable supply and mechanical robustness, but it has limited electrical conductivity and insufficient surface hydrophilicity. A carbon nanotube-coated polyethylene terephthalate tape reported in 2018 improved surface conductivity and imaging stability, but glow-discharged CNT-PET tape is not commercially available. The new study set out to achieve both stable hydrophilicity and sufficient conductivity in a single material by depositing a composite of natural cellulose fibrils, carbon nanotubes, and silver nanowires onto a PET substrate.

Fabrication relied on a simple, chemical-free mechanical process. An aqueous mixture of cellulose fibrils and carbon nanotubes was subjected to high-power shaking with zirconia beads, a collision process that deagglomerates the materials and promotes the self-alignment of individual carbon nanotubes within the cellulose network, producing a homogeneous viscous dope. Silver nanowires were subsequently added for the AgNW-integrated version. The team then evaluated four tape types: Kapton, CNT tape, CNF-CNT, and CNF-CNT-AgNW, measuring water contact angle, electrical conductivity by four-point probe, and surface roughness at two magnifications.

Water contact angle measurements showed that cellulose incorporation reduced the intrinsic hydrophobicity of CNT-PET tapes without any plasma treatment. CNT-PET tape exhibited the highest contact angle at 86.68 plus or minus 2.29 degrees, while adding cellulose fibrils lowered it to 69.26 plus or minus 4.27 degrees, comparable to Kapton at 71.72 plus or minus 3.57 degrees but without requiring glow discharge. The CNF-CNT-AgNW tape maintained moderate hydrophilicity at 74.56 plus or minus 3.22 degrees, indicating that silver nanowire incorporation did not significantly compromise wettability. The authors suggest that a contact angle below roughly 75 degrees may be sufficient for stable section adhesion without plasma treatment.

Conductivity improved even more dramatically. The surface sheet resistance of Kapton exceeded the instrument’s measurement limit, while the values for CNT, CNF-CNT, and CNF-CNT-AgNW tapes were 4,419 plus or minus 1,589, 58.68 plus or minus 3.61, and 4.54 plus or minus 0.97 ohms per square, respectively. The researchers attribute this enhancement to the zirconia bead collision process, which separates bundled carbon nanotubes into individual nanotubes and aligns them along cellulose fibril chains, forming highly conductive networks. This conductivity improvement correlates with the suppression of charging artifacts during SEM imaging.

Surface roughness measurements revealed that the cellulose-containing tapes are more textured than Kapton or CNT tape. At 200-times magnification, roughness values were 0.34, 0.16, 3.39, and 1.13 for Kapton, CNT, CNF-CNT, and CNF-CNT-AgNW respectively, and at 500-times magnification the values were 0.78, 0.76, 2.12, and 2.05. The authors note that these surface features may contribute to section adhesion and imaging behavior, but that the observed charging suppression is more directly associated with the improved conductivity. Profilometry maps showed that the cellulose-containing tapes have a more heterogeneous, fibrous surface consistent with the formation of a cellulose-based network.

To test performance with real specimens, the team embedded mouse brain tissue in epoxy resin using an osmium-tetroxide-thiocarbohydrazide staining procedure and cut 50-nanometer-thick serial sections with an automatic tape ultramicrotome. Brain slices from two male mice, prepared from hippocampal CA1 stratum radiatum, were fixed, heavy-metal stained, dehydrated, and resin-infiltrated before sectioning. When sections on CNF-CNT and CNF-CNT-AgNW tapes were imaged on a Gemini 300 SEM with a backscattered electron detector at 5-kilovolt beam voltage, without plasma treatment or carbon coating, organelles including synaptic vesicles, mitochondria, and endoplasmic reticulum were visible without wrinkles or charging artifacts.

The silver nanowire version did show one drawback. In some areas of images from the CNF-CNT-AgNW tape, fiber-like signals appeared against the sample background, attributed to silver nanowire aggregates. The authors emphasize that the nanowires must be uniformly and well dispersed within the material; otherwise, aggregates can appear in acquired images and interfere with high-resolution imaging quality. The cellulose-only CNF-CNT tape did not exhibit this artifact, making it the cleaner option where maximum image fidelity is paramount, while the AgNW version offers substantially lower sheet resistance.

The researchers argue that the intrinsic, stable hydrophilicity of cellulose is a major practical advantage over plasma-treated surfaces, which gradually lose hydrophilicity over time and require re-treatment. Conventional Kapton-based ATUM workflows also require carbon coating to suppress charging, a step that introduces variability in coating thickness and consumes time in serial electron microscopy. By integrating hydrophilic nanofibers and conductive nanowires through a chemical-free collision process, the new tapes simplify the workflow and, according to the authors, enhance ultrastructural imaging fidelity for large-scale serial SEM imaging, offering an alternative to conventional Kapton-based ATUM tape.

Subject of Research: A conductive cellulose-carbon nanotube composite tape for array tomography electron microscopy

Article Title: Improved conductive carbon nanotube tape using natural cellulose fibrils for array tomography

Article References: Jung, M., Choi, H., Lee, C. K., & Mun, J. Y. (2026). Improved conductive carbon nanotube tape using natural cellulose fibrils for array tomography. Applied Microscopy, 56(1), Article 13. https://doi.org/10.1186/s42649-026-00134-w

Image Credits: AI Generated

DOI: 10.1186/s42649-026-00134-w

Keywords: array tomography, carbon nanotubes, cellulose fibrils, silver nanowires, scanning electron microscopy, ATUM, brain ultrastructure, charging artifacts, sheet resistance, Kapton tape, serial sectioning, nanomaterials