Surface Modification of Pillar Array Systems for Chromatography and Fluorescence Enhancement

Thin-layer chromatography offers many advantages in the world of chemical separations due to its ease of use, high sensitivity, range of applicability, and multiplex capability. However, this technique is succeptible to band broadening effects that limit its efficiency. Attempting to resolve these effects by decreasing particle size causes a decrease in mobile phase velocity which creates its own band broadening via longitudinal diffusion. However, pillar array systems on the micro- and nanoscale have been shown as useful analogues to thin-layer chromatography which mitigate the efficiency concerns associated with the method. The work within this dissertation is concerned with the modification of pillar array surfaces for both chromatographic and spectroscopic purposes. The first aim is to increase the surface area of the pillars for chromatography by depositing porous phases such as petal-like carbon and porous silicon oxide. The usefulness of pillar arrays as separations systems is moderated by their limited native surface area. Increasing the surface area of a stationary phase can increase the retention of analyte by the system without negatively affecting its efficiency. While we found that petal-like carbon has several properties that made it unsuitable for these pillar array systems in their current form, porous silicon oxide showed great promise as a porous phase which increased the surface area of the pillars and the retention of analytes within them. The second aim was to immobilize fluorescent molecules at the pillar surface for signal enhancement. Pillars in the nanoscale have been shown to exhibit a field effect which amplifies fluorescence signal. To this end, we developed wet chemistry methods to functionalize the pillar surface with two different immobilizing resins, one using a uranium-capturing compound, and the other a biotin-avidin complex to sequester DNA. In both cases, we created high-throughput methods which retained high sensitivity while using only minimal amounts of sample

Organic Semiconductor Lasers and Tailored Nanostructures for Raman Spectroscopy

This work presents the application of organic semiconductor distributed feedback laser as free-space excitation source in Raman spectroscopy. Surface-enhanced Raman scattering effect is exploited to improve the detection sensitivity. The SERS conditionis achiedved by using substrates consisting of gold-coated polymeric nanopillar arrays. The organic-laser-excited SERS measurements are applied to verify the concentration variation of biomolecule adenosine in aqueous solutions

Micro/Nano Structured Materials for Enhanced Device Performance and Antibacterial Applications

Micro/nanostructured materials have been used extensively for various applications due to their unique chemical, physical, and mechanical properties. In this thesis we report the fabrication and characterization of micro/nanostructured materials with antibacterial properties. Plastics are used in a wide range of medical components such as prosthetics, implants, catheters, and syringes. However, contaminating bacteria can attach to plastic surfaces and grow and form biofilms that lead to healthcare associated infections. The consequences on patients and their families are serious, as infections can extend hospital stays, create long-term disability, increase healthcare costs, and even result in unnecessary deaths. Two strategies for creating antibacterial surfaces are (1) anti-biofouling surfaces that make the bacterial attachment process difficult and (2) bactericidal surfaces that kill bacteria cells that come in proximity of or contact the surface. We demonstrate that a fluorine etch chemistry may be utilized to create lotus leaf-inspired, low surface energy, hierarchical micro-structure/nanofibrils in Polypropylene (PP). Our anti-biofouling PP surfaces exhibit a 99.6% reduction of E. coli cell adhesion compared to untreated PP. We also fabricated bactericidal surfaces consisting of uniform and regular nanostructured arrays. The interest in mechanical bactericidal effect has recently increased, as the bacteria cells grow drug resistance. Nanosphere lithography and combination of reactive ion etching and deep reactive ion etching were utilized to prepare these substrates. The pitch, diameter, taper, and height of the nanostructures are controlled. The bactericidal effect of these structures is investigated and significant enhancement in killing is observed. We also report fabrication of micro/nanostructured materials to improve device performance. Our simulation results show that absorption enhancement in vertical nanowire arrays on a perfectly electric conductor can be further improved through tilting. Tilted nanowire arrays, with the same amount of material, exhibit improved performance over vertical nanowire arrays over a broad range of tilt angles. The optimum tilt of 53° has an improvement of 8.6% over that of vertical nanowire arrays and 80.4% of the ideal double pass thin film. Incorporation of these structures could improve the efficiency of solar cells

Performance of Dye-Sensitized Solar Cell Using Size-Controlled Synthesis of TiO2 Nanostructure

Titanium dioxide (TiO2) or titania shows a great interest in solar cell application due to its morphology and crystalline structure. Moreover, it is an affordable compound that could make solar cells more cost economical than traditional silicon solar cells. In this study, one-step hydrothermal method is demonstrated to synthesis rutile TiO2 nanorods and nanoflowers morphology in nanoscale dimension on different hydrothermal reaction times for Dye-sensitized solar cells application. Increasing the reaction time could influence in formation of higher crystalline rutile phase titania nanostructure before abruptly decreases as the prolong hydrothermal process carry out. The length of the nanorods produced shows increasing behaviour and the growth of nanoflowers are become denser obviously. Band gap estimation is 2.75 eV slightly lower than bulk rutile TiO2. It shows that the growth mechanism under different reaction times has great influences on the morphologies and alignment of the nanostructure. Further, the DSSCs fabricated using 15 hours reaction time exhibited the best photovoltaic performance with highest efficiency of 3.42% and highest short-circuit photocurrent of 0.7097V

Nanostructured Materials for Energy Storage and Conversion

The conversion and storage of renewable energy sources is key to the transition from a fossil-fuel-based economy to a low-carbon society. Many new game-changing materials have already impacted our lives and contributed to a reduction in carbon dioxide emissions, such as high-efficiency photovoltaic cells, blue light-emitting diodes, and cathodes for Li-ion batteries. However, new breakthroughs in materials science and technology are required to boost the clean energy transition. All success stories in materials science are built upon a tailored control of the interconnected processes that take place at the nanoscale, such as charge excitation, charge transport and recombination, ionic diffusion, intercalation, and the interfacial transfer of matter and charge. Nanostructured materials, thanks to their ultra-small building blocks and the high interface-to-volume ratio, offer a rich toolbox to scientists that aspire to improve the energy conversion efficiency or the power and energy density of a material. Furthermore, new phenomena arise in nanoparticles, such as surface plasmon resonance, superparamegntism, and exciton confinement. The ten articles published in this Special Issue showcase the different applications of nanomaterials in the field of energy storage and conversion, including electrodes for Li-ion batteries and beyond, photovoltaic materials, pyroelectric energy harvesting, and (photo)catalytic processes

Advances in High-Throughput Analysis: Automated Radiochemical Separations and Nanopillar based Separations and Field Enhanced Spectroscopy

Often the need to analyze a large number of samples coincide with critical time consternates. At such times, the implementation of high-throughput technologies is paramount. In this work we explore some viable pathways for high-throughput analysis and develop advancements in novel forms of detection of materials that are vital in the environmental, biological as well as national security arenas. Through the use of new protocols with high sensitivity and specificity as well as simplified chemical processing and sample preparation we aim to allow for improved throughput, fieldable detection, and rapid data acquisition of extensive sample sets. The methods developed in this work focus on unique platforms of the collection and analysis and combine them with automation and portability. Foremost, analytes of interest must be selectively isolated and concentrated by chemical and/or mechanical processes. Secondly, spectroscopic and physical properties are exploited and enhanced by employing viable detection platforms. Finally, automation and field portability are implemented through a combination of optimized robotics, minimized chemical preparation and/or unique lab on a chip type platforms. Presented are two sub areas of research. One focuses on the automation of a time consuming solid phase extraction process that is coupled to inductively coupled plasma mass spectrometry increasing sample throughput by orders of magnitude. The second focused on the fabrication and use of silicon nanopillars as a platform for separations and enhanced optical analysis. Each section of work focuses on the development of a practical, accessible, and deployable methods of analysis

Engineering of plasmonic excitations for hand-held and ultra-sensitive biosensors

Thesis (Ph.D.)--Boston UniversityEarly detection and effective diagnosis are important for disease screening and preventing epidemics. Recently, optical biosensors have attracted significant attention, as they are very powerful detection and analysis tools that have variety of applications in homeland security, public and global healthcare, biomedical research and pharmacology. However, most of these biosensors are time-consuming, require costly chemical procedures and bulky instrumentation, and need advanced medical infrastructures with trained laboratory professionals. In order to address these needs, recently lensfree computational on-chip imaging techniques have been introduced to eliminate the need for bulky and costly optical components. However, this technology is limited by the size of the analytes as it uses a lensfree computational technique insufficient for detecting biomolecules down to nm-scale. In order to provide highly sensitive and massively multiplexed detection of biomolecular binding events, fluorescent imaging and surface plasmon resonance (SPR) based platforms are the most favored. However, SPR sensors are limited due to the alignment sensitive prism coupling scheme and bulky instrumentation while the fluorescence imaging suffers from quantitative and qualitative drawbacks of the labeling steps. This thesis focuses on the unique integration of lensfree telemedicine technology and nanostructured plasmonic chip technology to realize ultra-sensitive and label-free biosensing in a high-throughput and massively multiplexed manner for field-settings. Toward this aim, we introduce a handheld on-chip biosensing technology that employs plasmonic microarrays coupled with a lensfree computational imaging system. Employing a sensitive plasmonic array design that is combined with lensfree computational imaging, we demonstrate label-free and quantitative detection of biomolecules with a protein layer thickness down to 3 nm. Integrating large-scale plasmonic microarrays, our platform enables the simultaneous detection of protein mono- and bilayers on the same platform over a wide range of biomolecule concentrations. In this plasmonic device, we also monitor binding dynamics of protein complexes as a function of time by integrating it with microfluidics. Plasmonic antennas utilized in our lensfree platform, supporting very sharp and sensitive spectral feature as well as easily accessible large local electromagnetic fields, are highly advantageous for biosensing applications as they enable stronger interaction between surface waves and biological molecules on the sensing chip

Nanocoax Arrays for Sensing Devices

Thesis advisor: Michael J. NaughtonWe have adapted a nanocoax array architecture for high sensitivity, all-electronic, chemical and biological sensing. Arrays of nanocoaxes with various dielectric annuli were developed using polymer replicas of Si nanopillars made via soft lithography. These arrays were implemented in the development of two different kinds of chemical detectors. First, arrays of nanocoaxes constructed with different porosity dielectric annuli were employed to make capacitive detectors for gaseous molecules and to investigate the role of dielectric porosity in the sensitivity of the device. Second, arrays of nanocoaxes with partially hollowed annuli were used to fabricate three-dimensional electrochemical biosensors within which we studied the role of nanoscale gap between electrodes on device sensitivity. In addition, we have employed a molecular imprint technique to develop a non-conducting molecularly imprinted polymer thin film of thickness comparable to size of biomolecules as an "artificial antibody" architecture for the detection of biomolecules.Thesis (PhD) — Boston College, 2014.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Physics

FABRICATION AND PATTERNING OF METAL AND METAL OXIDE NANOSTRUCTURES FOR ELECTRONIC APPLICATIONS

Ph.DDOCTOR OF PHILOSOPH