| My thesis research has focused on means of integrating optical systems into microfluidic chips, specifically for the creation of lab-on-a-chip flow cytometers. The benefits of microfluidics are perhaps most often applied to biological assays, which frequently employ optical readout of fluorescence or light scatter. By integrating the optical system onto the microfluidic chip, we can facilitate chip interfacing while ensuring optical alignment to a tiny sample. Integrated optical systems also offer the ability to collect light from a localized area, allowing for the collection of true angular light scatter (which carries much information about cells) and can furthermore significantly improve the signal to noise ratio (SNR) relative to simple fiber or waveguide based approaches to integrated light collection. This work explores both the unique challenges and advantages encountered when creating optical systems integrated with mold-replicated microfluidic devices.;The first contribution presented is the demonstration of fluid-filled lenses integrated alongside microfluidic channels using a slab waveguiding structure. The use of fluid represents an important tradeoff between lens power and Fresnel reflections. The creation of a slab waveguiding structure is critically important to control light losses when utilizing lens systems for light collection.;The second contribution in this work is the demonstration of a microfluidic chip emplying a number of lenses to perform both localized excitation of the samples as well as light collection from localized areas defined by a specific angular range. Sample coefficients of variation (CVs) ranged from 9-16% for a single bead population, far exceeding previously-published CVs of 25-35%.;The last contribution is an atypical approach to optical systems based on the unique advantages offered by microfabricated architectures, namely small sizes and close proximities to the sample. Using only custom-shaped total internal reflection (TIR) based components and light blocking elements, we create a device that can achieve forward light scatter CVs of 8-28%. The device is able to clearly distinguish 5 mum, 10 mum, and 15mum beads based on forward and side scatter. The results from this vastly simplified optical system show great promise towards reaching the performance metrics of the commercial cytometer. |
