Investigations of acoustic sorting for large microobjects

Abstract

Microsorting and separation methods are of great importance to medical diagnostic, environmental science and life science. In recent years, lab on a chip (LOC) technology enabled performing microsorting operations using miniature devices. Among the LOC sorting methods, acoustic sorting is an emerging technology that does not require labeling, is non invasive, and can work on almost any type of microscale objects regardless of their charge or optical characteristics. For this reason, acoustic sorting became an active research field and every now and then new techniques are been investigated and introduced. This thesis introduces a study of new acoustic sorting and separation techniques that are suitable for processing large particles, which might not be possible in devices with narrow channel designs. This thesis presents investigations of acoustic sorting and separation techniques in wide scale devices (4.4 mm - 2.2 cm). The first device used a sorting technique that employs orthogonal acoustic rotating fields to arrange targeted particles in specific locations in a stagnant fluid. Sorting with this technique was done based on size difference using (10, 6, 4 and 3 µm ) polystyrene particles and based on density difference using 10 µm particles made of polystyrene and iron oxide with a density difference of (0.45 g/cm3). The highest efficiency and purity of sorting achieved was 96.8±3.1% and 83.9±2.5 % respectively for sorting 10 and 3 µm particles. The second device integrated the rotating acoustic fields sorting technique in a microfluidic device with a fluid flow to separate particles by size. The device gave purities of 67.1±4.6% and 77.5±6.3% for separating (14.5 and 6 µm) and (14.5 and 3 µm) polystyrene particles respectively. The third device was designed to test two separation techniques that separate particles in the vertical direction named the acoustic levitation fractionation and the acoustic sedimentation fractionation. High purities were achieved using this device with (96.2±4.4%) purity for separation by size (14.5 and 10 µm polystyrene particles) and (96.5±3.7%) purity for separation by density (10 µm polystyrene and iron oxide particles). As a contribution to the fabrication of microfluidic devices, one chapter of this thesis is devoted to explaining the difficulties and best approaches to be taken when fabricating a layered resonator by testing previously reported techniques. A new rapid, easy and cost effective microfluidic device bonding method is also presented using xylene as a solvent. By exploring the new methods the thesis adds new knowledge to the area of multi node sorting. Also, the exploration of sedimentation for sorting has shown that there is still room to investigate last century technology and combine it with new technologies to develop new sorting mechanisms and solve emerging sorting issues. Potential applications for the devices include detection and quantification of large parasites in the environment such as E.histolytica in water and isolation of neurospheres for toxicity studies.