Development of novel chip-based integrated optics for miniaturized analytical systems
Abstract
Most detection schemes for chip-based electrophoresis employ off-chip optics with external sources and detectors that are bulky for microscale analysis. As a step towards a total analysis system, a novel approach for integrating chip-based optics has been developed which uses hollow waveguides. Hollow waveguides simply operate by guiding light in an air core, which is surrounded by a transparent dielectric medium. These waveguides are lossy because they do not work on the principle of total internal reflection. However, we have used theory, experiment, and model simulations to evaluate light losses due to propagation within and insertion into the waveguide. According to our near-field diffraction model, light inserted with a profile of a half-wave cosine significantly enhances reflectivity, thus reducing light losses. A transmission efficiency of 87% over a distance of 10 cm was achieved with a 100 x 100 μm square glass capillary, which was used as a surrogate hollow waveguide. As an application, we have constructed a microchip device that uses square hollow waveguides to integrate measurements of absorption with chip-based electrophoresis. A 50 x 50 μm liquid channel and transverse 50 x 50 μm waveguide are etched as a negative pattern into a silicon master and replicated as a positive in polydimethylsiloxane (PDMS). The integrated waveguide has a 60% transmission efficiency over a distance of 3.2 cm. Separation of fluorescein and the dye BODIPY is demonstrated. A detection limit (S/N = 3) of 200 μM fluorescein is obtained using a 50 μm pathlength and a simple photocell detector. The ultimate goal of miniaturized analytical systems is to perform multiple analyses simultaneously and for high throughput purposes. Novel chip-based beam splitters and bends were integrated on-chip to construct multiplex devices. According to theory we should be able to integrate 26 absorption channels on a 10 cm diameter chip.
Degree
Ph.D.
Advisors
Lytle, Purdue University.
Subject Area
Analytical chemistry
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