Silicon photonics for optical manipulation and separation of dielectric particles [electronic resource]
Keywords: Electrical Engineering.

Evanescent fields in waveguides can produce sufficient forces to trap, actuate, and propel particles, making them of interest for efficiently separating and manipulating large numbers of particles. Particle separation is an essential step in many biological assays, ranging from disease diagnostics and drug treatment analysis to fundamental cell studies. In this work, I explore several new techniques for separating and manipulating particles using the evanescent fields of strip waveguides. I begin by investigating strip waveguides for two complementary strategies for optical sorting of heterogeneous mixture of particles on the surface of silicon nitride waveguides. Glass particles ranging from 2 µm to 10 µm in diameter are sorted at guided powers below 40 mW. The effect of optical, viscous, and frictional forces on the particles are modeled and experimentally shown to enable sorting. Particle interactions are also investigated and shown to decrease measured particle velocity without interfering with the overall particle sorting distribution. I then move to exploring dual-core waveguides as an optical sorter that utilizes the intrinsic forces of metal-insulator-metal waveguides and their geometry to achieve particle separation by size. Experimental results show that an inner Au-Si3N4-Au waveguide is able to trap particles within the propagation distance of its dominant modes and release the particles into an outer Au-H2O-Au waveguide. The outer waveguide then propels the particles and separates them by size. The sorting results are accurately modeled by a first-principles, analytical model. After this, I leverage the fundamental understanding gained from my waveguide studies to transition into novel biological methods of the mechanics of cells. The mechanical investigation into cells leads to novel assays, disease detection, and diagnostics. I first explore and demonstrate label-free optically tunable lysis of healthy and crenate red blood cells using the evanescent field of strip waveguides. My technique uses the evanescent field of Si3N4 waveguides to induce a gradient force to trap and selectively lyse cells. The two step process of trapping and then lysing ensures that all cells are similarly situated on the waveguide when lysis is induced, leading to tight control of lysing conditions. This tight control allows me to adjust the lysing powers such that only a specific subset of cells are lysed. The characterization shows the controlled lysis of healthy and crenate red blood cells based on varying peak lysing powers. I then further the cellular investigation by extending my initial biological investigations to realize another technique in using the evanescent field of waveguides to characterize and differentiate between healthy red blood cells and malaria-infected red blood cells via their membrane properties. The optical gradient force of strip waveguides induce a force that stretch and pull cells onto the top of the waveguide surface. I quantify the deformation of cells as they interact with the evanescent field by developing a complete image processing pipeline using a random forest classifier for pixel classification and segmentation. From this pipeline, I extract cell membrane strain, eccentricity, area, and motility. From differentiating the changes in cell parameters over time, I demonstrate that infected malaria cells are on average less deformable than healthy red blood cells. In this thesis, I expand the use of evanescent fields of waveguides by investigating novel particle manipulation and separation techniques. The main contribution and key techniques I investigate for optical manipulation and separation are particle separation by size, cellular lysis, and membrane deformation. This work opens the door for future investigations and discoveries using evanescent field waveguides as a platform for various applications, especially in biological analysis.