Surface acoustic wave microfluidic pumps for on-chip diagnostics

Most of point-of-care diagnostics and lab-on-chip devices that do on-chip sample preparation require active fluid actuation. In a laboratory setting, this is done via bulky benchtop equipment such as syringe pumps, peristaltic pumps and pressure systems. However, integration of a pumping unit onto the device allows for increased portability and decreased footprint of the device. Although there are multiple examples of realised micropumps based on different technologies, no one solution offers a combination of small footprint, low costs, scalable manufacturing and high performance required for point-of-care devices. Surface acoustic wave (SAW)-based micropumps are an exciting alternative to the current micropump systems due their small footprint and simplicity of manufacturing, yet many of the SAW micropumps presented to date suffer from poor performance and/or utilisation of open channels, which can be a problem regarding contamination. The SAW micropump demonstrated here uses a novel planar design and SAW scattering effects to significantly improve the pump performance and maintain closed channels, which is a pre-requisite for point-of-care applications. This thesis evaluates the fabrication of SAW devices and microfluidic channels using soft lithography. After evaluating the SAW device design concerning electrical characteristics both experimentally and theoretically, the first iteration of SAW micropumps utilising SAW momentum along the piezoelectric substrate is presented and characterised in terms of fluid flow velocity profiles and volume flow rates produced. Subsequently, a concept of a more efficient SAW micropump is presented based on out of the plane interaction between SAW and liquid. To fully utilise this interaction a protocol on the development of 3D microfluidic channels is introduced followed by a discussion on SAW-liquid coupling setting the scene for a demonstration of efficient and closed-loop SAW micropump that delivers pressure gradients up to an order of magnitude higher than the best to-date reported values at a similar input power levels. Finally, the newly developed pump is utilised in an on-chip flow cytometer to showcase the advanced flow manipulations, showing the potential applications of the SAW micropump beyond simple fluid actuation.