An electrokinetic sensor for studying immersed surfaces, using focused ultrasound

A novel method for obtaining information on the charge density of an immers ed surface is presented. The technique uses focused ultrasound to excite os cillatory fluid motion in the plane of the solid-liquid interface, over a l ocalised area. The displacement current (resulting from the motion of fluid -borne ions in the outer double-layer) is detected by electrodes in the liq uid. The method is demonstrated as a means for monitoring protein adsorptio n, and for monitoring interactions between two different proteins. A second electrokinetic effect at the interface is identified, isolated from the fi rst, and shown to provide additional information on the compressibility and charge density of the double-layer. (C) 2001 Elsevier Science B.V. All rig hts reserved.