Terahertz Spectroscopy and Spectral Imaging
Over recent years, terahertz wavelengths (over 0.1-10 THz frequencies) have contributed strongly to spectroscopy and imaging in Biomedical Engineering. Terahertz radiation is sensitive to the vibrational and rotational modes of biomolecules, making it ideal for identifying chemical signatures. Additionally, terahertz radiation is non-ionizing and safer than other frequencies (e.g., x-rays). Given these motivations, there is significant interest in the generation and detection of terahertz radiation. However, current emission techniques have challenges related to Joule heating.
Dr. Collier's research has produced novel photoconductive terahertz emitters whereby Joule heating is reduced. This work looked investigated the transient mobility effects in a GaP material. The results were very favourable with the GaP photoconductive terahertz emitter having high mobility for terahertz generation with low mobility for subsequent residual current consumption for enhanced performance.
A related spectral imaging technology is hyperspectral imaging, whereby wavelength information (over the visible spectrum) for a line of pixels is stored on a two-dimensional sensor. An image is then scanned line-by-line. The Collier Research Group has made advancements in snapshot hyperspectral imaging, whereby the full image can be stored instantly. Such advancements come about through strategic implementation of Fourier analyses.
Digital Microfluidic Systems
Lab-on-a-chip systems have revolutionized the biomedical device industry and Biomedical Engineering. These microsystems allow high throughput analyses of biofluids for diagnostics and scientific pursuits. Traditionally, these systems are continuous-flow-based and make use of micropumps, microvalves, and other components. However, a reconfigurable form of microfluidics has emerged whereby microdroplets are actuated on a two-dimensional planar structure using electric fields. These systems are Digital Microfluidic systems.
The Collier Research Group investigated such Digital Microfluidic devices and produced multiplexed systems whereby individual microdroplets are actuated with a trinary activation algorithms and sensed through integration of fibre-optic cables. This multiplexed system has been integrated with optical and terahertz spectroscopy techniques for investigations of full lab-on-a-chip systems. Additionally, work has focused on development of digital microfluidic platforms for polymerase chain reaction. Here, enhanced infrared annealing is achieved through total internal reflection of an optical beam.
Microfluidic Devices for Antibiotic Detection in the Dairy Industry
Microfluidic devices have well-studied implementations as biomedical lab-on-a-chip systems. However, these microfluidic devices but can also be applied in Biological Engineering applications. These highly-miniaturized and sensitive detection systems can be used in food quality assessment. Continuous flow systems can be actuated through application of high electric fields in the technique microchip capillary electrophoresis (MCE). Careful application of electric fields in MCE devices can contribution to isolation, detection, and quantification of an analyte within a sample mixture.
The Collier Research Group has developed such an MCE device to isolate antibiotics within milk, and detect and quantify antibiotics using fluorescence spectroscopy. This device is being developed through collaboration with the dairy industry.
There is great potential for Engineering Systems and Computing through development of optofluidic lenses. Such lenses use the refractive properties of fluid for focusing and magnification of light. A liquid lens has advantages over a fixed lens in that it can its optical properties (e.g., focal length) can be adapted in real-time. Therefore, adaptive optofluidic lenses are sought after in beam steering applications and on-chip integration. Further applications include free-space optical communication devices and remote sensing requiring high field-of-view.
The Collier Research Group has developed optofluidic lenses. These lenses are able to create subunit aspect ratio lenses and have been implemented in closed systems with mechanical tuning for in-plane focusing and low-voltage operation.