Acoustophoresis in open fluidic films

Acoustic particle manipulation (acoustophoresis) is a rapidly developing technology in the field of microfluidics, which uses small fluid samples for the purposes of biological or chemical based testing. Microfluidics is often aimed at producing Lab-on-a-Chip based systems, particularly useful for testing in remote locations where standard laboratory techniques are not available. Acoustophoresis holds advantages over many other particle manipulation methods as it only alters the fluid pressure to displace the non-homogeneous elements within the fluid. Other methods typically require application of a potential difference to the fluid, which may damage sensitive biological cells; or direct contact with the particles, which may also cause damage or cross-contamination with repeated trials. Common uses for acoustophoresis are the filtering of particles from fluid by displacing them to a location and then splitting the fluid flow (an acoustic filter), or creating arrays of particle clumps for drug testing purposes (bioassays). The actuating mechanism for these devices is typically a piezoelectric transducer (PZT), which vibrates upon application of an alternating current, attached to a carrier which is in turn coupled with the particulate fluid. This work seeks to adapt established acoustophoresis devices for novel uses. The key to the setup presented is the vertical offset between the PZT and carrier glass, which allows the carrier to be partially submerged while under actuation. The device then utilises two novel methods of acoustophoresis, the first has the fluid bounded by the edge of the glass carrier during actuation. The second method is for a partially submerged carrier that applies standing waves to an open and stationary fluid volume many times the size of the carrier itself. The advantage of the device itself is that the two piece system allows for ease of use, repetition and easily adjustable spatial parameters. The first method presented has the advantage of requiring only a small fluid volume and no external mechanisms. For a known fluid volume the actuating frequency is varied and the horizontal wavelength (determined by the distance between the lines the particles relocate to), is calculated and compared to theoretical expectations. The frequency against horizontal wavelength analysis is conducted for the open fluid method as well, in addition to recording the effect of variation in the fluid thickness layer on the acoustic wave. The open fluid setup has the advantage of the particle arrays being highly accessible and is examined compared to other acoustic methods using enclosed chambers. Both methods presented have experimental techniques adapted to exploit the advantages of the novel setup, as well as 2 dimensional COMSOL finite element models. The work produced succeeds in utilising the device presented for two alternate modes of particle manipulation, both of which present advantages over current methods of acoustophoresis.