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The next step in miniaturization of analytical devices involves the use of MEMS and Lab-on-a-Chip applications, where many biological or chemical reactions are carried out on the device in real time. Since detection mechanisms occur almost immediately after the reactions, inefficient mixing of reagents could cause a decrease in sensing capability, especially on micro- and nano-scaled devices. Thus a microfluidic mixer has become a crucial component in these applications. Here we propose a new design of a passive microfluidic mixer that utilizes the theories of chaotic advection to enhance mixing. The micro-channels for the mixer have dimensions with width ranging from 10µm to 40µm, depth 40µm, and a total length of 280µm. First the designs are simulated using CFD-ACE+ for computational analysis. After the device geometry has been decided, the actual devices are fabricated using traditional UV photolithography on silicon and bonded with pyrex glass by anodic bonding. To test the actual device mixing efficiency, we used a fluorescent dye rhodamine B solution to mix with DI water and put the devices under fluorescent microscope observations for real-time analysis. Images of fluorescent light intensities are taken at different flow rates during the analysis and are later used to study the experimental results calculated using a published mixing efficiency formula for comparison.

In this thesis, planar photonic crystals for optofluidic biosensing applications are analyzed. Planar photonic crystals are optically resonant structures which possess modal characteristics which can be exploited for biosensing applications. Sensing is achieved by detecting changes in refractive index due to analyte interactions in a sampled fluid. This work describes a broad study of photonic crystal slab sensors, with special consideration to biosensing. Outlined are considerations pertaining to sensing figures of merit, device fabrication, and performance. Results of simulations and device characterization indicate that planar photonic crystals possess sensing attributes similar or better than existing optically resonant refractive index sensors, such as surface plasmon resonance, grating, and interferometric waveguide sensors. Additionally, these photonic crystals can be patterned in large-areas which enable a simple light coupling scheme. All considered, their appeal as a biosensing solution is justified in the area of in vitro diagnostics.

In this thesis, planar photonic crystals for optofluidic biosensing applications are analyzed. Planar photonic crystals are optically resonant structures which possess modal characteristics which can be exploited for biosensing applications. Sensing is achieved by detecting changes in refractive index due to analyte interactions in a sampled fluid. This work describes a broad study of photonic crystal slab sensors, with special consideration to biosensing. Outlined are considerations pertaining to sensing figures of merit, device fabrication, and performance. Results of simulations and device characterization indicate that planar photonic crystals possess sensing attributes similar or better than existing optically resonant refractive index sensors, such as surface plasmon resonance, grating, and interferometric waveguide sensors. Additionally, these photonic crystals can be patterned in large-areas which enable a simple light coupling scheme. All considered, their appeal as a biosensing solution is justified in the area of in vitro diagnostics.

The next step in miniaturization of analytical devices involves the use of MEMS and Lab-on-a-Chip applications, where many biological or chemical reactions are carried out on the device in real time. Since detection mechanisms occur almost immediately after the reactions, inefficient mixing of reagents could cause a decrease in sensing capability, especially on micro- and nano-scaled devices. Thus a microfluidic mixer has become a crucial component in these applications. Here we propose a new design of a passive microfluidic mixer that utilizes the theories of chaotic advection to enhance mixing. The micro-channels for the mixer have dimensions with width ranging from 10µm to 40µm, depth 40µm, and a total length of 280µm. First the designs are simulated using CFD-ACE+ for computational analysis. After the device geometry has been decided, the actual devices are fabricated using traditional UV photolithography on silicon and bonded with pyrex glass by anodic bonding. To test the actual device mixing efficiency, we used a fluorescent dye rhodamine B solution to mix with DI water and put the devices under fluorescent microscope observations for real-time analysis. Images of fluorescent light intensities are taken at different flow rates during the analysis and are later used to study the experimental results calculated using a published mixing efficiency formula for comparison.

Photonic crystal slabs (PCS) are explored in the context of optofluidic refractive index (RI) sensing for portable, label-free, biosensing applications. The accuracy of RI sensors is limited by noise signals that cause a change in RI that cannot be differentiated from the signal of interest. For this reason self-referencing schemes that provide rejection of common mode signals, and an inherent temperature stabilization approach, are explored. A novel referencing method that allows for frequency shifts to be read out in the transmission power spectrum is proposed and characterized. In terms of improving sensing metrics the relevant characteristics of various PCS architectures are explored numerically. In addition, a novel suspended \emph{air-substrate} device that offers greatly improved sensitivity is proposed and characterized. An experimental measurement near the theoretical detection limit for a PCS is demonstrated. In understanding measurement errors the crossed-polarization effect and its practical limitations are explored numerically.

Photonic crystal slabs (PCS) are explored in the context of optofluidic refractive index (RI) sensing for portable, label-free, biosensing applications. The accuracy of RI sensors is limited by noise signals that cause a change in RI that cannot be differentiated from the signal of interest. For this reason self-referencing schemes that provide rejection of common mode signals, and an inherent temperature stabilization approach, are explored. A novel referencing method that allows for frequency shifts to be read out in the transmission power spectrum is proposed and characterized. In terms of improving sensing metrics the relevant characteristics of various PCS architectures are explored numerically. In addition, a novel suspended \emph{air-substrate} device that offers greatly improved sensitivity is proposed and characterized. An experimental measurement near the theoretical detection limit for a PCS is demonstrated. In understanding measurement errors the crossed-polarization effect and its practical limitations are explored numerically.

Thesis (doctoral)--Lund University, 1998. / Thesis statement on t.p. verso. Includes bibliographical references.

Thesis (doctoral)--Lund University, 1998. / Thesis statement on t.p. verso. Includes bibliographical references.

Thesis (doctoral)--Lund University, 1994.