Nanophotonic Waveguides For Biomolecular Transport And Particle Control

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Current separation and fractionation technologies developed for lab-on-a-chip platforms are often unable to differentiate single particles or objects from those with similar properties (eg. size or charge). One potential solution to this dilemma uses focused optical fields for remote and precise control of discrete microscale objects. While optical tweezers and similar technologies are useful tools for microparticle or cellular manipulation, these methods are fundamentally limited by light diffraction. The consequences of these limitations are: (1) it is extremely difficult to optically manipulate nanoscale (below 100 nm in size) particles and (2) movement of trapped particles are generally restricted to two dimensions. Previous work by the author (Master‟s thesis) has shown that optical waveguides integrated into microfluidic channels can use the evanescent field to trap and manipulate particles using gradient and radiation pressure forces. This dissertation extends the previous work and focuses on methods for nanoparticle trapping by using nanophotonic devices which can exert greater optical forces. Slotted waveguides confine light within a nanoscale slot cut into a silicon waveguide that provides access to more optical energy and increases the strength of the optical trapping force. Microring resonators use an optical resonance effect to amplify the optical field within the ring structure which can be used to exert precise control over trapped particles. This study contains the following key results: (1) controlled trapping and release of dielectric nanoparticles and single biomolecules in silicon slot waveguides, (2) a comprehensive analytical and numerical study of particle trapping on nanometer length scales in slot waveguides, and the (3) integration of microring resonators and microfluidics to enable optically controlled switched for particles trapped on waveguides. The nanophotonic architectures for optofluidic transport demonstrated in this work can be integrated into lab-on-a-chip platforms using existing manufacturing techniques. They allow for the discrete optical manipulation and transport of nanoscopic objects with greater precision and control than is available with existing approaches. Future potential applications include integrated sensor/trapping capabilities for lab-on-a-chip devices and sophisticated particle manipulation in microfluidic environments. This fusion of nanofluidics and optical manipulation could lead to new methods for biomedical diagnostics and biochemical processing.

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