The vision for this PhD research project was born out of a desire to study the in situ behaviour of suspended nano-materials; specifically, implementing a Raman microscopy system for investigating suspended materials in the microfluidic environment. The author developed a set of innovative research goals to achieve this vision, which include: (1) forming a suitable microfluidic system which can apply controlled forces onto the suspended materials on demand, (2) implementing Raman microscopy to study the behaviour of particles under the influence of such forces while inside the microfluidic system and (3) incorporating the developed microfluidic system for investigating suspended materials of low concentration, including biological cells and surface-enhanced Raman scattering studies. The author implemented the research in three distinct stages such that the work in earlier stages could provide the platform for the future work. In the first stage, the author designed a microfluidic dielectrophoresis platform consisting of curved microelectrodes. This platform was integrated with a Raman microscopy system for creating a novel system capable of detecting suspended particles of various types and spatial concentrations. The system was benchmarked using polystyrene and tungsten trioxide suspended particles, and the outcomes of this novel integrated system showed its strong potential for the determination of suspended particles types and their direct mapping, with several unique advantages over conventional optical systems. In the second stage of this research, the author developed a novel microfluidic-DEP system that could manipulate suspended silver nanoparticles’ spacing in three dimensions. Silver nanoparticles are capable of producing strong surface enhanced Raman scattering (SERS) signals, allowing the Raman system to detect very low concentrations of suspended analytes. DEP provided facile control of the positions and spacings of the suspended silver nanoparticles, and allowed for the creation of SERS hot-spots. The system was studied to determine the optimum DEP and microfluidic flow parameters for generating SERS, and the author was able to demonstrate this as a reversible process. This stage of the research used dipicolinic acid as the target analyte, and the system was demonstrated to have detection limits as small as ~1 ppm concentration levels. In the third stage, the microfluidic-DEP platform was used for trapping and isolating yeast cells. Silver nanoparticles were again used for SERS applications. The trapped cells were interrogated by the Raman system in order to obtain deeper understandings of cells functionalities and their communications under various physical conditions: live vs. dead and isolated vs. grouped. Live vs. dead experiments were conducted as a benchmark, to observe whether SERS is capable of differentiating cells based on the life condition. The research was expanded to study cells that were isolated from one another, and compared those Raman signatures to those from cells in grouped clusters. The author was able to extract unique information from such studies, including the importance of glycine, or proteins with glycine subunits, in the proliferation of yeast cells. The developed system showed great potential as a universal platform for the in situ study of cells, their communications and functionalities
