Shear-horizontal surface acoustic wave microfluidics for lab-on-chip applications

Surface acoustic wave (SAW) devices based on the piezoelectric principle have been used extensively in telecommunication applications over the last 20 years, but have recently shown promise in the area of biomedical applications due to their efficient micro-fluidic functions and highly sensitive and label-free detection of pathogens, bacteria, cells, DNA and proteins. There are two types of surface acoustic wave modes: i.e., Rayleigh SAW (R-SAW) and shear horizontal SAW (SH-SAW). R-SAW is widely used for microfluidics and sensing in dry conditions, whereas SH-SAW is mainly used for sensing in liquid conditions. This thesis firstly reviewed the current theoretical and research progress related to these devices and application within the biomedical fields to date, and then the SH-SAW was applied into a novel lab-on-chip combining both bio-sensing and micro-fluidic functions. Simulations of the SH-SAW propagation on 36o Y-cut LiTaO3 were undertaken. Results showed a weak vertical wave component, and at a 90° rotation cut, the crystal was able to support a vertical Rayleigh component showing mixed sensing and streaming possibilities on a single crystal. Experimental investigation of the SH-SAW identified the ability for the shear wave to support mixing, pumping, heating, nebulisation and ejection of sessile droplets on the surface of the crystal with a theoretical explanation for the behaviour presented. A comparison with a standard R-SAW devices made of 128o Y-cut LiNbO3 and sputtered ZnO films was performed. This novel behaviour of digital microfludics, i.e., using sessile droplet with the SH-SAW, demonstrated by this work offers the possibility to manufacture a fully integrated micro-fluidic bio-sensing platform using a single crystal to realise a range of micro-fluidic functions