Structural and functional imaging with carbon nanotube AFM probes

Atomic force microscopy (AFM) has great potential as a tool for structural biology, a field in which there is increasing demand to characterize larger and more complex biomolecular systems. However, the poorly characterized s ilicon and silicon nitride probe tips currently employed in AFM limit its b iological applications. Carbon nanotubes represent ideal AFM tip materials due to their small diameter, high aspect ratio, large Young's modulus, mech anical robustness, well-defined structure, and unique chemical properties. Nanotube probes were first fabricated by manual assembly, but more recent m ethods based on chemical vapor deposition provide higher resolution probes and are geared towards mass production, including recent developments that enable quantitative preparation of individual single-walled carbon nanotube tips [J. Phys. Chem. B 105 (2001) 743]. The high-resolution imaging capabi lities of these nanotube AFM probes have been demonstrated on gold nanopart icles and well-characterized biomolecules such as IgG and GroES. Using the nanotube probes, new biological structures have been investigated in the ar eas of amyloid-beta protein aggregation and chromatin remodeling, and new b iotechnologies have been developed such as AFM-based haplotyping. In additi on to measuring topography, chemically functionalized AFM probes can measur e the spatial arrangement of chemical functional groups in a sample. Howeve r, standard silicon and silicon nitride tips, once functionalized, do not y ield sufficient resolution to allow combined structural and functional imag ing of biomolecules. The unique end-group chemistry of carbon nanotubes, wh ich can be arbitrarily modified by established chemical methods, has been e xploited for chemical force microscopy, allowing single-molecule measuremen ts with well-defined functionalized tips. (C) 2001 Elsevier Science Ltd. Al l rights reserved.