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. Author manuscript; available in PMC: 2013 Jun 5.
Published in final edited form as: Anal Chem. 2012 May 15;84(11):4907–4914. doi: 10.1021/ac3001622

Figure 1.

Figure 1

Representation of a force profile for a probe (microsphere) approaching a surface. To bind to the DNA molecule, the probe must interact with the amine terminal group by passing into the area represented by the blue-gray shaded box. If the probe comes in contact with the surface, it will most likely adhere strongly, so it must not pass completely through the region indicated by a shaded box. The graph shows three representative force-distance profiles as the probe approaches the surface. The repulsive electrostatic force can be too strong and prevent the probe from approaching the target molecule. Conversely, the van der Waals attractive forces can be too strong and cause the probe to stick irreversibly to the surface. If the forces become balanced, the probe will be attracted to the point where it may bind to the DNA, but is repelled at a very close proximity to the surface.