NanoLab offers various carbon nanotubes, which can be tailored to customer specifications. One standard material (PD15L5-20) is 15nm in diameter, and 5-20 microns in length.
Maogen Zheng, Audrey Smith, Waldemar Gorski "Carbon Nanotube-Chitosan System for Electrochemical Sensing Based on Dehydrogense Enzymes" Anal. Chem., 3, 76 (2004); 5045-5050. Sofia Sotiropoulou, Nikolas A. Chaniotakis "Carbon Nanotube Array-Based Biosensor" Anal Bioanal Chem, 375 (2003); 103-105. Kempa, K. et al. "Photonic Crystals Based on Periodic Arrays of Aligned Carbon Nanotubes" Nano Letters, 3, 1 (2003); 13-18. Lynch, M. and Patrick, D. "Organizing Carbon Nanotubes with Liquid Crystals"