Enhanced particle focusing in microfluidic channels with standing surface acoustic waves

We demonstrated an enhanced particle focusing in microfluidic channels by using standing surface acoustic waves (SAWs) generated on a piezoelectric substrate. Interdigitized microelectrode arrays patterned by standard photolithography and lift-off techniques are used for both excitation and detection of SAWs. Bragg reflectors (BR) are also integrated to enhance the standing SAW formation. Furthermore, air cavities are introduced in both sides of microfluidic channels made of polydimethylsiloxane (PDMS). Whereas the system without PDMS cover layer showed a loss less than 2 db, the absorption loss after adding PDMS structures was also limited to a few db. Consequently, enhanced particle focusing could be easily observed, showing clear advantages of the use of BR and minimized PDMS wall thicknesses. (C) 2009 Elsevier B.V. All rights reserved.