Development of Silicon-Based Optofluidic Sensors for Oil Sands Environmental Monitoring

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  • The oil sands industry in Alberta produces large volumes of process-affected water (PAW), which is known to contain heavy metals and organic compounds (such as naphthenic acids, naphthalene, phenanthrene, pyrene, etc.) that are toxic and hazardous to the environment. The industry has an ongoing need to improve the monitoring of concentrations and breakdown of these compounds. Currently, this is mainly accomplished by collecting samples for shipment to a laboratory for analysis. Portable and ideally distributed and real-time monitoring techniques would greatly improve efficiency and the base of knowledge with respect to these environmental concerns. The principal aim of the project was to develop a prototype lab-on-a-chip (LOC) based sensor for optical detection of target molecules in PAW using spectrally resolved fluorescence detection. The proposed sensor would offer a high level of integration between the fluidic and optical components, potentially reducing the cost and complexity of the overall system while also improving the performance (sensitivity, signal to noise ratio (SNR), alignment tolerance, etc.). In the long term, such miniaturized sensors hold promise as low-cost, highly distributed environmental monitoring devices. Most of the primary milestones of the project were successfully completed, as follows: 1. A silicon-based air-core waveguide technology was developed and optimized for the ultraviolet-visible wavelength band of interest. These waveguides employ low-loss TiO2/SiO2 Bragg reflectors deposited by sputtering deposition at the U of A nanoFab. 2. Tapered air-core waveguides were assembled and tested as visible-band micro-spectrometers. These micro-spectrometers provide resolution on the order of 1 nm over a 100 nm operational band (e.g., wavelengths in the 500 to 600 nm range), and offer compelling advantages for lab-on-a-chip and optofluidic microsystems. 3. Prototype sensing systems were developed, by combining the aforementioned micro-spectrometers with PDMS-based microfluidics. Fluorescence spectroscopy was successfully demonstrated for commercial dyes with fluorescence bands in the ~500 to 600 nm wavelength range. At the time of writing, ongoing work is aimed at translating the operational band of these sensors to the ~400 to 500 nm wavelength range. This effort has been delayed by processing difficulties, but is expected to reach a successful conclusion in summer 2013. Further work is aimed at extending the operational range of the micro-spectrometers (e.g., 400 to 650 nm), by using more sophisticated multilayer designs. We hope that this work will enable the detection of native fluorescence from hydrocarbon molecules, including the multiplexed detection of multiple species, and intend to pursue this objective in the coming months.

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    Attribution 3.0 International