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The atomic force microscopy (AFM) or scanning force microscopy (SFM) is a high-resolution type of scanning probe microscopy, with a resolution of sub-nanometer. The precursor to the AFM, the scanning tunneling microscope, was developed by Gerd Binnig and Heinrich Rohrer in the early 1980s, for which they were awarded the Nobel Prize for Physics in 1986. The AFM is one of the foremost tools for imaging, measuring and manipulating matter at the nanoscale. The information is gathered by "feeling" the surface with a mechanical probe or tip. The movement of the probe is detected through a laser beam reflected off the tip as it “feels” and scans the surface. The precise and accurate movement is electronically controlled by Piezoelectric elements.

Diagram of the Principle of Atomic Force Microscopy, (From Wikipedia)

AFM has attracted keen attentions for life science research, because it is compatible with non-conductive materials, does not require labeling, and can be operated under the physiological condition, while allowing single molecular level analysis. Therefore, AFM has become an important tool for nano-biotechnology. Also, imaging surfaces with the nanoscale resolution, probing local mechanical properties, and measuring a variety of interaction forces from nano-Newton (nN) to pico-Newton (pN) are possible with the instrument. In particular, the microscopy measuring the force of a pN range has been utilized for a variety of single molecule measurements, and the examples include protein unfolding process, DNA-DNA, protein-protein, and ligand-receptor interaction. At the same time, a significant growth of the genomic and proteomic studies for drug discovery, as well as for disease diagnosis and prevention, has placed a strong demand for advanced biomolecular recognition probes with high sensitivity and enhanced specificity. It is therefore clear that this type of approach finds important applications not only within basic life science research, but also within emerging areas for the analysis of larger biomolecular libraries.

When the force measurement between individual biomolecules is carried out with AFM, the accuracy and the resolution of the force value is a critical factor for the reliability. In order to enhance the reliability, it is necessary to control density and orientation of the immobilized biomolecules on surface. It used to be hard to control small scale variations due to spatial differences in surface topography and chemistry, and such factor is some of the remaining bottle-necks to the future progress of such force-based approaches. To resolve such issues, Nanogea has developed NE-AFM, or NanoCone-Enabled AFM, to use nanocone coated AFM tips and substrates for measuring specific biomolecular interaction forces reliably (J. Am. Chem. Soc. 2007, 9349; Adv. Mater. doi:10.1002/adma.200801323). The dendron-modification of the surfaces can optimize the density of immobilized biomolecules, remove steric hindrance between interacting biomolecules, and avoid unwanted nonspecific binding and/or the formation of multiple biomolecular complexes. Therefore, dendron modified-AFM tip of Nanogea provides a superb option to the existing biomolecular surface immobilization methods. We believe that thus-modified AFM tips are ideal for studying the interactions between DNA and DNA/RNA, ligand and protein, protein and protein, as well as receptor on cell surface and ligand.

A schematic drawing of the experimental setup employing the dendron-modified AFM tip and substrate.
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