Optically controlled microfluidics

Abstract

Three projects are described in this thesis that combine microfabrication techniques with optical micromanipulation. The aim of these projects is to use expertise in microlithography and optical tweezing to create new tools for Lab-on-Chip devices. The first project looks at the creation of microgears that can be moved using an optical force. The microgears include one dimensional photonic crystal that creates birefringence. This allows the transfer of angular momentum from a circularly polarised light beam to the microgear, making them spin. The microgears are simulated, fabricated and tested. Possible biological applications are suggested. The second project looks at creating microchannels to perform micromanipulation experiments in. Different methods of fabricating the microfluidic channels are compared, and the resulting chambers are used to find the maximum flow rate an optical sorting experiment can be performed at. The third project involves using a thin photoconductive layer to allow the optical control of an electrical force called dielectrophoresis. This light induced dielectrophoresis (LIDEP) allows similar control to optical tweezing but requires less irradiance than optical tweezing, allowing control over a larger area with the same input optical power. A LIDEP device is created and experiments to measure the electrical trap size that is created with a given optical spot size are performed. These three projects show different microfabrication techniques, and highlight how well suited they are for use in optical manipulation and microfluidic experiments. As the size of objects that can be optically manipulated matches well with the size of objects that can be created with microfabrication, it seems likely that many more interesting applications will develop.