Investigations of acoustic sorting for large microobjects
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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.