| Rod-shaped metallic particles with 300 nm diameters and lengths of 1 to 12 microns can be electroplated with stripes of gold and silver that provide an identifiable code. These commercially available particles have been utilized as tags in hybridization reactions and immunoassays. Current assay protocols use bench top sample preparation to bind relevant target and reporter molecules to the particle surface. Currently, particles are placed in well plate chambers and interrogated using a CCD camera after they settle to the bottom of each well. This approach is time and labor intensive and leads to particle agglomeration and loss of assay information.; This thesis presents a fundamental study of the basic physical phenomena contributing to rod-shaped particle motion, and provides useful tools for the design of particle control and detection systems. We explore the effects of electric and magnetic fields on the transport and manipulation of these particles in microchannels. Electric and magnetic fields cause alignment of the particles parallel to the field and translational motion of the particles if the current is direct. We developed analytical models to describe the translation and rotation of homogenous and striped metallic particles in these fields. The electric field analysis is further extended to consider secondary flows generated around the particle due to the motion of the charge at the particle surface. These flows lead to significant particle-particle interactions even at low particle concentrations (<0.01% by volume). We quantified these effects at both high and low particle concentrations using custom particle tracking methods. We demonstrate two proof-of-principle microfluidic systems for particle-based assays. The first system uses the alignment and transport characteristics of the particles in an electric field to produce a flow-based detection platform with reduced effects of particle agglomeration compared to existing technology. The second system uses magnetic fields to extract the particles to the surface of a microchannel for washing and mixing steps of an immunoassay. The particles are detected on a unique microfabricated substrate with grooved patterns to enhance particle alignment and spacing. |
