This Engineering Seminar Topic deals with the following:
Ultrasonic Trapping In Capillaries For Trace-Amount Biomedical Analalysis
Non-intrusive manipulation by standing-wave acoustics has been widely used for levitation and trapping of macroscopic objects.
1 The standing-wave field creates an acoustic radiation force on the object that depends on its size and acoustic parameters.
2 In the present article we demonstrate size-selective separation and retention of latex spheres inside a small-diameter flow-through capillary by use of an ultrasonic radiation trap. The work aims at rapid in-flow detection and separation of specific molecules via antibody-coated latex spheres. Acoustic radiation forces have been used for non intrusive manipulation of macroscopic as well as microscopic objects. Basically, objects with higher acoustic impedance than the surrounding medium are trapped in the velocity antinodes of the standing-wave acoustic field. The theory of acoustic levitation and trapping is well understood.
3 In aqueous solutions the method has been applied for studies of mechanical properties of mm- to mm-sized liquid droplets and biological cells.
4,5 These experiments typically operate at low frequencies ~kHz up to a few 100 kHz! using a closed cylinder levitation vial. Similar systems have been used for cell concentration,
6 cell filtering,
7 and for enhanced rate and sensitivity of latex agglutination tests by increasing particle collision rates.
8 Here few-mm-diam tubes or chambers are combined with a transverse acoustic field ~propagation perpendicular to the length of the tube!, resulting in a higher cell concentration in several velocity antinodes parallel with the tube. In-flow separation and fractionation of suspended particles are performed on the basis of size and/or acoustic properties with a liquid flow in combination with flow splitters.
9,10 Electric fields have been employed in a similar arrangement to transversely separate charged particles by exploiting the competition between acoustic radiation forces and electrostatic forces.
11 At higher ultrasonic frequencies ~.10 MHz! acoustic traps based on a standing-wave confocal ultrasonic cavity have demonstrated that longitudinal forces of similar magnitude or higher than those of optical traps can be achieved.
12 Finally, it should be noted that low frequency airborne acoustic traps have been used for improved biomedical analysis.
13 In biomedical analysis, great effort is made to develop detection techniques of trace amounts of specific proteins and other biomolecules. Very small sample volumes (pl-nl) may be analyzed with narrow-bore sub-100 mm capillaries in