New Probes and Reagents for AFM Studies

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DESCRIPTION: (Applicant's Descritpion) Atomic force microscopy (AFM) is a powerful, relatively recent and rapidly expanding molecular imaging technique of broad applicability. AFM is providing for the first time images of individual biomolecules in their native state in aqueous solution. Important biological events in real time may be imaged by AFM. These include time lapse images of the assembly and deposition of amyloid fibrils, a process central to the onset of fatal diseases such as Alzheimer's disease. Nearly all type II diabetes mellitus patients have cytotoxic pancreatic amyloid, the formation of which is thought to be directly related to the development of the disease. In AFM, the sample is placed on an atomically flat surface such as freshly cleaved mica and is raster scanned by a sharp tip mounted at the end of a flexible cantilever. Resolution for biological specimens is typically 50-100 Angstroms and is limited by the sharpness of the tip. The sharpest tips available commercially for tapping mode AFM have a radius of approximately 4-50 nm. Recently, single walled carbon nanotubes were attached to AFM tips and show the best combination of' aspect ratio (tip height/base) and sharpness (approximately 3 nm) reported to date. The long term objective of this research program is to enhance the capabilities of AFM by providing a series of novel, molecularly sharp tips designed to improve the resolution of AFM images, i.e. the level of detail one can observe, without the need for highly specialized equipment. This proposal builds on the successful modular synthesis of prototype tip molecules during the first two years of the project. The synthetic tips have a broad base designed to attach chemically to a commercial tip so that only a single molecule can fit on the outermost part of the tip. The synthetic tips taper to a single atom or functional group designed to probe the sample. Prototype synthetic tip molecules prepared in our laboratory are themselves visible using conventional AFM, demonstrating the rigidity and robustness of the molecules. One aim is to synthesize new tip molecules with increased breadth of the base and height. These will be imaged by conventional AFM to determine the best synthetic building blocks to use in terms of rigidity. Another aim is to develop methodology for attaching the new tips to a conventional tip and to determine the resolution provided by the new synthetic tips. The tips are designed so that the functional group probing the sample can be changed. For example, a single biomolecule, e.g. an antibody, may be attached and used to probe the sample. The concept of an AFM label will be developed. The significance lies in the enhanced resolution that should be obtainable with the new synthetic tips.