(179c) Acoustically-Driven Microcentrifugation

The Lab-on-a-CD concept has opened up the powerful possibility of carrying out a wide range of microfluidic operations simply by using a compact disk (CD) player to spin a disk on which microfluidic channels and components are fabricated . Nevertheless, the bulk rotation of the entire CD structure is relatively cumbersome, expensive and unreliable, quite the antithesis of microfluidic philosophy. Interconnectivity, i.e., fluid transfer on and off the chip, is also difficult with these devices. Moreover, the rotation of the entire structure is non-specific (i.e., all components on the CD are rotated), which places severe limitations on upstream or downstream components, e.g., the dispensing or detection components, for which rotation may produce undesirable effects. Here, we demonstrate a novel microcentrifugation technique in which symmetry breaking of a planar surface acoustic wave (SAW) propagating along a piezoelectric substrate can generate a rotational acoustic streaming flow in a sessile nanoliter drop (which is several orders of magnitude smaller than the CD) placed atop the substrate. The azimuthal flow is rapid, with linear velocities of several cm/s giving rise to Reynolds numbers between 10 and 100. Such fast azimuthal streaming flows, shown to be chaotic beyond a threshold power, can be used to generate intense micromixing within the drop. Indeed, we show that the rate and yield of a variety of distinct chemical and biochemical reaction classes far exceed that obtained using ultrasonic or microwave-assisted mixing, and with considerably lower power. As an example, in-gel protein sample processing and tryptic digestion can be carried out on-chip in under 30 mins. Further, samples can be atomised from a cheap paper-based microfluidic system, thus demonstrating the potential for direct interfacing with mass spectrometry following chemical synthesis. The microcentrifugation effect can also be exploited for particle manipulation and sorting. We demonstrate this for bioparticle concentration for rapid and sensitive pathogen detection or the separation of red blood cells from plasma for miniaturized diagnostic applications. It is also possible to separate two different particle species by size by exploiting the unique size-dependent scaling between the acoustic and drag forces acting on the particle. Finally, we show the ability of the device to drive the rotation of tiny thin disks made from SU-8 or Mylar down to 100 micron in diameter at speeds close to several thousand rpm.