A challenging topic of the lab-on-a-chip research is to implement sorting mechanisms on low cost disposable chips. In
many applications, surface acoustic waves (SAW) have recently proven to be a versatile and efficient technique for
microfluidic actuation. A SAW is excited by applying a high frequency signal to a piezoelectric substrate. When the
wave hits the solid/liquid interface it transmits its acoustic energy into the liquid and a local pressure gradient emerges,
leading to surface acoustic streaming. Experiments can be performed directly on the piezoelectric substrate or on a
separate glass slide positioned on top of the SAW source. We developed a technique for the accumulation of solid and
soft objects in SAW generated microvortices in microfluidic channels. For this purpose, the corner of a rectangular
microchannel is irradiated by a wide SAW beam. There, the SAW excites sound waves in the fluid producing a typical
acoustic streaming flow pattern which typically exhibits two vortices. Particles injected into the flow are accumulated
and dynamically trapped in one of these vortices. After the flow is stopped, the collected particles stay in the position of
the vortex. In our experiments, we use open microfluidic channels with functionalized hydrophilic-hydrophobic surfaces
on glass substrates as well as closed channels build with the elastomer PDMS via soft lithography. We find that the
accumulation efficiency for particles is strongly size dependent. Below a critical radius of 500 nm, particles tend to flow
through the vortex and are not captured in the corner. Generally, larger particles can be collected at more moderate SAW
power levels compared to smaller particles. Therefore, by adjusting the SAW power level, one is able to collect particles
above a designated size. This concept is not limited to solid particles but can also be applied to soft objects like cells.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.