Microfluidic batch process platforms for lab on a chip applications using acoustofluidics

The inception of microfluidics, utilising borrowed technology from the microelectronics industry, has enabled a wide range of applications in various fields ranging from engineering to biochemistry. Advancements in terms of microfabrication and micro-scale fluid control has led to the rise of Lab on a Chip. These systems aim to replicate the results of conventional laboratory procedures in miniaturised systems. Lab on a Chip systems, offer immense potential for a wide range of diagnostic and therapeutic tools. Furthermore, when sample volumes are extremely scarce, rendering conventional diagnostic methods and continuous flow micro fluidic techniques impractical, other methods need to be established. To this end, microfluidic batch process systems offers a solution, although relatively underdeveloped. Batch process systems are a single or multi-stage process in which a certain quantity of inputs are processed to achieve the desired outcome one sample set at a time. It should be noted, as these systems operate at a much smaller scale, some conventional forcing techniques, such as centrifugation are no longer practical. Therefore, different actuation mechanisms need to be developed to replicate the results of their larger scale conventional laboratory and continuous flow counterparts. Acoustic excitation is a potential actuation mechanism which enables the handling of micron-sized particles and cells. Here, we look at different acoustic excitation methods and the underlying principles that allow acoustofluidic systems to manipulate particles for sample preparation and as point- of-care diagnostic tools. In this thesis, three systems are developed to perform particle manipulation both in liquid and air based batch process systems. Firstly, an open bulk acoustic wave system, allowing the ease of external gripping mechanisms is developed to perform size-deterministic separation of 3 μm and 10 μm particles. The task of particle separation is further explored using a different underlying principle and actuation method, and separation of 3.1 μm and 5.1 μm is achieved utilising surface acoustic waves, a different excitation mechanism that enables operation at relatively higher frequencies. Finally, optimisation of an acoustic resonator in air is carried out and serves as a building block for a complete 3-dimensional (3D) acoustic trapping microgripper to be used for individualised particle transport and inspection. Throughout this thesis, a case is made for acoustic based methods to be utilised in developing essential batch process systems for sample preparation and diagnostics.