Vertically-aligned carbon nanofiber arrays provide densely clustered, microscopic spikes that penetrate leaf tissue.

(a) Scanning electron micrograph (SEM) of a small region of a VACNF array chip. Nanofibers are arrayed across this chip at a 10 μm pitch. Individual nanofiber heights were 20–25 μm. In the image, the chip is tilted 30° from perpendicular to the beam to show the aspect ratio of each nanofiber. (b) Application of a carbon nanofiber chip onto the adaxial surface of a Populus leaf. (c) SEM of a leaf impaled with a VACNF chip (20-μm pitch), showing fibers embedded in the epidermal cells of the adaxial surface as indicated by the arrows. The position of a minor vein adjacent to the site of impalement is marked by (*), and a region of unimpaled tissue is marked by (**). (d) A close-up view of the impalement site, showing individual carbon nanofibers that have broken off of the VACNF chip and remain embedded in the leaf epidermal cells, as indicated by arrows. The image was taken ~15 min after VACNF impalement. Excised leaf tissue was placed directly in the electron microscope, where it was dried in vacuo prior to imaging. Results shown are from single, typical experiments.