Dielectrophoresis (DEP), the phenomenon of directed motion of electrically polarizable particles in a nonuniform electric field, is promising for applications in biochemical separation and filtration. However, quantification methods of the DEP force on individual particles with the pico-Newton resolution required for the development of theories and design of device applications are lacking. Using optical tweezers-based force transducers already developed in our laboratory, we have results that quantify the frequency-dependent DEP force and the crossover frequency of individual particles with this new experimental method.
A diagram depicting the potential well formed by OT. Under an AM DEP force the particle executes an oscillatory motion centered at the point off-set from the center of the optical trap.
The DEP force (left) and displacement phase (right) as a function of frequency for four different sizes of polystyrene particles with diameters ranging from 0.998 to 2.1 um.
The crossover frequencies of PMMA spheres (filled circles) and clusters (opened circles) are plotted as a function of the particle’s radius (r) for spheres or the effective radius (rn) for clusters. The lines show least squares fits with exponent −2.0 ± 0.1 for the spheres and −2.1 ± 0.1 for the clusters.