A longitudinal hemispherical standing-wave ultrasonic trap for size-selective separation of microspheres in capillaries is utilized for biomedical trace element analysis. The trap utilizes the competition between acoustic radiation forces and viscous drag forces on spheres suspended in a liquid inside 20-75 μm diam fused silica capillaries. Experiments performed on 3.0 and 4.7 μm diam latex spheres demonstrate the principles of trapping and verify the theoretically calculated size-dependent forces on the spheres. The spheres are detected by the use of laser-induced fluorescence (LIF). The goal is to use the trap for separation and ultra-high-sensitivity detection of trace amounts of proteins and other macromolecules containing two antigenic sites, by binding the target molecule with high specificity to antibody-coated latex spheres.
Acoustics, Chemical analysis, Ultrasound