Position correlation microscopy: probing single particle dynamics in colloidal suspensions

A novel optical tweezer based microscope is described which probes the dynamics of an individual pair of colloidal particles over many decades of time, with nanometer position resolution. The potential of the technique is demonstrated by probing the distance dependence of the hydrodynamic forces between two polymer-coated poly(methyl methacrylate) spheres suspended in cyclohexane.