  The interaction of proteins with small molecules is fundamental to their
function in living organisms and it is widely studied in drug development. Here
we compare optical trapping dynamics of streptavidin and biotinylated
streptavidin using a double nanohole optical trap in a metal film. Consistent
and clearly distinct behavior is seen between the protein with and without the
small molecule binding. The real-time dynamics at the single protein level are
accessible with this technique, which also has advantages of not requiring
tethering to a surface or the need for exogeneous markers.
