Nano-Photonic Waveguides for Chemical and Biomedical Sensing

In this dissertation, advances in the fields of Photonics, and Plasmonics, and specifically, single cell analysis and waveguide sensing will be addressed. The first part of the dissertation is on Finite Difference Time Domain (FDTD) optimization and experimental demonstration of a nano-scale instrument that allows sensing at the cellular and subcellular levels. A new design of plasmonic coupler into a nanoscale waveguide is proposed and optimized using FDTD simulations. Following this, a subcellular nanoendoscope that can locally excite fluorescence in labelled cell organelles and collect the emitted fluorescent light for detailed spectrum analysis is fabricated and tested. The nanoendoscope has a sharp tapered tip of diameter ~ 50 nm that permits safe insertion into the cell that was confirmed by a number of viability experiments. FDTD analysis demonstrated that, with an optimized nanoendoscope taper profile, light emission and collection was very local. Thus, signal detection could be used for nano-photonic sensing of proximity of fluorophores. In further experiments, fluorescent signals were collected from individual organelles of living cells including: the nucleus of Acridine orange labelled human fibroblast cells, the nucleus of Hoechst stained live liver cells and the mitochondria of MitoTracker Red labelled MDA-MB-231 cells. In addition, this endoscope was inserted into a live organism, the nematode Caenorhabditis elegans, and in- vivo fluorescence signal was collected. Second, an innovative single step fabrication method of low loss polysilicon waveguides was developed as a potential platform for a number of photonic sensors. Optimization of a capacitively coupled plasma etching for the fabrication of a polysilicon waveguide with smooth sidewalls and low optical loss was demonstrated. A detailed experimental study on the influences of RF plasma power and chamber pressure on the roughness of the sidewalls of waveguides was conducted and waveguides were characterized using a scanning electron microscope. It was demonstrated that optimal combination of pressure (30 mTorr) and power (150 W) resulted in the smoothest sidewalls. The optical losses of the optimized waveguide were 4.1± 0.6 dB/ cm. Finally, an on-chip nanophotonic sensor for continuous blood coagulation analysis was proposed. The system was simulated using three-dimensional FDTD software. At first, the noise due to the presence of cells was calculated. Next, the design of a waveguide cladding-based filtering structure for elimination of the noise from cells was proposed and significantly decreased noise level was theoretically demonstrated

The effect of catalyst properties on the synthesis of carbon nanotubes by plasma enhanced chemical vapor deposition

A study of the effect of catalyst properties on the synthesis of carbon nanotubes (CNTs) is done in this thesis. Three different metal alloy catalysts, Fe/Ti, Ni/Ti, Co/Ti, have been studied. Various atomic concentrations and thicknesses were cosputter deposited on clean Si wafers using AJA Orion 4 RF Magnetron sputter deposition tool at 5mtorr and 17°C, and the films were characterized using a scanning electron microscope, Energy-dispersive X-ray spectroscopy. All the alloys have been annealed at 650°C and 3 torr in an argon atmosphere at 100 SCCM, followed by ammonia gas plasma etch at different powers at 3 torr and 50 SCCM NH₃ flow in a modified parallel plate RF chemical vapor deposition tool for 1 minute. The influence of plasma power, thickness of catalyst and concentration of Ti the secondary metal in the alloy composition, on the surface morphology of the catalyst are investigated by characterizing them with atomic force microscopy. The study has shown that the surface roughness is affected by Ti concentration, thickness and plasma power. The 35 W power NH₃ plasma produced rougher surfaces when compared to the 75 W NH₃ plasma. The result is interpreted as follows: ion bombardment leads to greater etching of the catalyst surface. Thus, plasma power must be optimized for catalyst thin film and etch time. The study has provided an in depth analysis and understanding of the various factors that influence catalyst surface morphology which can be applied into further study for optimizing parameters for synthesis of single walled CNTs. Following this, a study on catalysts for CNT synthesis was performed using Plasma enhanced chemical vapor deposition and characterized by scanning electron microscope. CNTs were synthesized on Ni, Ni-Ti, Co, Co-Ti and Fe catalyst. Ni, Ni-Ti catalyst produced forest like vertically aligned CNTs whereas Co, Co-Ti produced vertically aligned free standing CNTs. The growth was dense and uniform across the substrate. Initial growth runs on Fe, Fe-Ti alloy did not produce any CNTs until catalyst was restructured with a thicker Ti under layer after an investigation using Secondary ion mass spectrometry of suspected Fe catalyst poisoning due to reaction with Si substrate. A room temperature run was carried out on annealed and plasma etched Ni catalyst and no CNTs were produced indicating the importance of substrate temperature of CNTs. A deeper understanding of factors of influence on CNTs such as catalyst types, structure/morphology, and substrate temperature has been achieved with this study

Understanding Diffusion in a Single-Metal Organic Framework Crystal Used for Sensing Applications

Metal–organic frameworks (MOFs) stand out as remarkable materials renowned for their exceptionally high surface area and large number of pores, making them invaluable for diverse sensing applications including gas, biomedical, chemical, and optical sensing. Traditional methods of molecule infusion and release often involve a large number of crystals with varying shapes and sizes, leading to averaged outcomes across a heterogeneous crystal population. In this study, we present continuous monitoring of the infusion and release dynamics of model drug molecules, specifically vitamin B12, within individual Tb-mesoMOF crystals. Our findings underscore the critical influence of crystal size and shape on the infusion and diffusion processes and corresponding color change, underscoring the necessity to account for these factors in the design of large-scale systems. Leveraging optical microscopy, we employed a histogram-based algorithm for image processing, enabling automated tracking of diffusion phenomena. This investigation offers crucial insights into the dynamics of these processes, laying the groundwork for optimizing parameters in future sensing systems

Plasmono-magnetic Material for Precise Photothermal Heating

Noble metal nanoparticles have been extensively studied as photo-sensitive agents for photothermal cancer therapy. Precise control over the size and shape of the nanoparticles allowed strong optical absorption and efficient heat generation necessary for destroying a tumor to be achieved. However, one of the fundamental challenges of application of the nanoparticles towards photothermal cancer therapy is low specificity in the targeting tumor tissue in comparison with the healthy tissue and the resulting unfavorable biodistribution of the nanoparticles. Additional levels of control over particle distribution can be achieved by making the particles magnetic and using external magnets to control their accumulation in a tumor. Since the direct synthesis of particles with a magnetic core and a metallic shell limits the options for design and fine-tuning of plasmonic properties, the alternative approaches to the design of such materials have to be investigated. Here we propose and demonstrate a new design of a hybrid plasmono-magnetic material for photothermal heating created by grafting Au nanocages onto a surface of magnetic micro-beads. Next, we confirm its dual functionality in in vitro studies and show that individual hybrid particles can be magnetically controlled with a precision of a few micrometers and precisely destroy individual cells using plasmonic heating

Plasmono-magnetic Material for Precise Photothermal Heating

Noble metal nanoparticles have been extensively studied as photo-sensitive agents for photothermal cancer therapy. Precise control over the size and shape of the nanoparticles allowed strong optical absorption and efficient heat generation necessary for destroying a tumor to be achieved. However, one of the fundamental challenges of application of the nanoparticles towards photothermal cancer therapy is low specificity in the targeting tumor tissue in comparison with the healthy tissue and the resulting unfavorable biodistribution of the nanoparticles. Additional levels of control over particle distribution can be achieved by making the particles magnetic and using external magnets to control their accumulation in a tumor. Since the direct synthesis of particles with a magnetic core and a metallic shell limits the options for design and fine-tuning of plasmonic properties, the alternative approaches to the design of such materials have to be investigated. Here we propose and demonstrate a new design of a hybrid plasmono-magnetic material for photothermal heating created by grafting Au nanocages onto a surface of magnetic micro-beads. Next, we confirm its dual functionality in in vitro studies and show that individual hybrid particles can be magnetically controlled with a precision of a few micrometers and precisely destroy individual cells using plasmonic heating