Scanning single molecule force spectroscopy

Force measurements have been performed with scanning probe techniques to study protein properties and protein-surface interactions. Apart from specific recognition and specific interactions,"" single-molecule force spectroscopy,adhesion forces between ligand-receptor pairs, " and protein adsorption... 

We only mention here that the probe used in AFM is a sharp tip, which is attached to a flexible microbeam (microcantilever). In AFM various forms of interactions between the apex of the tip (with a radius between approximately 10-100 nm) and the sample surface are measured, either as a function of tip location with respect to the surface, or at a fixed (x,y) position as a function of the cantilever deflection or tip-sample distance. In most conventional instruments the cantilever-tip assembly is attached to a piezo controller, which positions the tip in the (x,y) scanned plane and adjusts the vertical position (piezo travel) to accommodate sample height, or to measure tip-sample force curves. The latest generation instruments can also be equipped with active x-y-z distance feedback control loops, which enable one to perform lithography, vertical positioning of the tip (e.g. for single molecule force spectroscopy), etc. 

SECM instruments (77,78) will undoubtedly increase the scope and power of SECM. Further improvements in the power and scope of SECM has resulted from its coupling scanning probe or optical imaging techniques, such as AFM (57,79) or single-molecule fluorescence spectroscopy (80). The combined SECM-AFM technique offers simultaneous topographic and electrochemical imaging in connection to a probe containing a force sensor and an electrode component, respectively. 

The techniques involved are single-molecule spectroscopy including optical (fluorescence) methods and single-molecule mechanical manipulation including scanning probe techniques (e.g., force measurements). 

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