Ultrasonic-trap-enhanced selectivity in capillary electrophoresis.

We combine ultrasonic trapping and capillary electrophoresis (CE) with the goal to detect ultra-low concentrations of proteins via size-selective separation and enrichment of antibody-coated latex spheres. An 8.5 MHz standing ultrasonic wave is longitudinally coupled into the sub-100- micro m diam capillary of the CE system. Competition between acoustic and viscous forces result in in-flow separation of micro m-diam spheres according to their size. Experiments separating 2.8- and 2.1- micro m-diam fluorescent latex particles, which model a protein-specific immunocomplex/free particle mixture, indicate a potential improvement of the concentration limit of detection of 10(4) compared to current CE systems. Theoretical calculations show room for further improvement.