Browsing by Subject "SERS"
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Item Detection of Whey Protein in a Hot Dog Using Immunomagnetic Separation Coupled with Surface Enhanced Raman Spectroscopy(2017-04) Swanson, BenjaminWith the passing of recent legislation, most notably the Food Allergen Labeling and Consumer Protection Act in 2006 and the Food Safety Modernization Act of 2011, the focus on allergens in the food supply is a top priority for the food industry. With the consideration of unintentional allergens now being considered an adulteration, companies are trying to find detection methods that can accurately identify an unintentional allergen, but that are also rapid enough to use so as not to interrupt the production line. Immunomagnetic Separation (IMS) coupled with Surface Enhanced Raman Spectroscopy (SERS) was investigated in this research as one possible detection method. We decided to test and compare two types of IMS methods, antibody and aptamer, to see if one or the other would produce better results. The methods were based off of previous work by Dr. Lili He and were adapted to detect whey in a hot dog. During initial testing in a pure solution, both of the IMS methods appeared to show similar results, both being able to detect whey at levels of at least 125μg/mL of solution. But once we switched over testing whey in a hot dog, the antibody based IMS method proved to be the better IMS method. With a detection limit of 600μg of whey protein isolate/g of hot dog, the antibody based IMS method proved to be the more effective method. The aptamer IMS method ran into trouble with non-specific binding to the magnetic beads and was unable to detect any whey protein isolate in the hot dogs during the experiment. It is therefore concluded by the results of this experiment that the antibody based 6 IMS-SERS method is a better method to detect whey protein in a hot dog versus the aptamer method.Item Development of a surface-enhanced Raman sensor for detection in complex mixtures.(2011-12) Bantz, Kyle ChristineSurface-enhanced Raman scattering (SERS) is a powerful analytical signal transduction mechanism for the detection of analytes in aqueous environments, largely free from interfering water signals and capable of obtaining unique molecular signatures from structurally similar analytes. These characteristics make SERS ideal for the detection of analytes of interest from biological and environmental settings. To achieve the low limits of detection needed for biological and environmental analyte detection, new SERS platforms with the highest possible enhancement factors (EF) need to be developed. Traditionally, SERS has had limited analytical use because the analyte of interest must dwell on or near the Ag, Au or Cu surfaces, regardless of substrate EF. To overcome this limitation this work employs alkanethiol partition layers in combination with novel SERS platforms for the detection of environmental pollutants (eg. polychlorinated biphenyls and polycyclic aromatic hydrocarbons) and bioactive lipids. As the use of partition layers continues to increase and more SERS platforms with higher EF are developed, the use of SERS for analytical applications will increase. Overall, this work demonstrates the power of using novel SERS platforms combined with partition layers and reveals great promise for the future of environmental and biological sensing with SERS. Chapter One reviews the use of surface-enhanced Raman scattering detection in complex mixtures that have emerged in the last 10 years. SERS been employed for small molecule detection all the way to more complex systems, such as detection in living cells, and this chapter reviews the recent advancements and looks toward the future of SERS detection in biological systems. Chapter Two details the fabrication and characterization of new novel substrates for SERS sensing. In this chapter, three substrates are discussed, each with their own fabrication method and SERS sensing application. The majority of our SERS sensing schemes for non-traditional SERS analytes employ a partition layer-covered SERS substrate. In Chapter Three, I investigated what fundamental properties of an alkanethiol partition layer make it an ideal partition layer for particular analytes. I discovered both the thickness of the monolayer and the amount of disorder in the partition layer that allows for analyte partitioning and are critical for facilitating the analyte to dwell within the zone of enhancement for SERS. The last two chapters detail the implementation of partition layer-modified SERS substrates for detection in complex mixtures. Chapter Four demonstrates the use of partition layer-modified SERS substrates for the detection of environmental pollutants: polycyclic aromatic hydrocarbons, polychlorinated biphenyls and polybrominated diphenyl ethers. I was able to show that our substrate made it possible to detect and discriminate between structurally similar analytes in the presence of interfering species at environmentally relevant concentrations. The final chapter of this dissertation describes the steps I have taken towards SERS sensing in complex biological mixtures for the detection of bioactive lipids. The results of this investigation indicate that partition layer-modified AgFON substrates can facilitate the detection of phospholipids and secreted lipids at higher concentrations, but the SERS bands from the partition layer make detection of lipids at physiologically relevant concentrations challenging at this time.Item Linear Polymer Affinity Agents for the Intrinsic SERS Detection of Food Safety Targets(2018-07) Szlag, VictoriaThis dissertation explores the use of polymer affinity agents for the surface-enhanced Raman spectroscopy (SERS) detection of food safety targets. First, current molecular motifs used as affinity agents in intrinsic surface-enhanced Raman spectroscopy (SERS) sensors are reviewed. By comparing antibody, aptamer, small molecule, and polymer affinity agents, the largely unresearched potential of polymer affinity agents (chemical customization, tunable length, ease of production, opportunity for multiplexing) is highlighted. The first proof of concept work of this dissertation targets the detection of the bioterror agent, ricin B-chain (RBC) in water and liquid food matrices. An N-acetyl-galactosamine glycopolymer capture layer was designed and applied to create a SERS sensor. The sensing scheme’s detection limit (20 ng/mL) is well below that of the predicted oral exposure limit. The RBC was detected in two types of juice, and a computed normal Raman spectrum of the glycomonomer supports polymer–RBC intermolecular interactions at the functional group level. Subsequent work focuses on the translation of this sensing scheme from the detection of proteins to the detection of small molecules relevant to food safety. Because interactions between a small molecule target and a polymer affinity agent are less specific than those that were leveraged in the RBC work, the development of a rapid affinity agent screening method was deemed necessary. A potent carcinogenic metabolite of a fungal pathogen that can infect food and feedstocks, aflatoxin B1 (AFB1), was used as a model target. Seven homopolymers of nitrogen-inclusive poly(N-(2-aminoethyl) methacrylamide) (pAEMA) and their oxygen analogs, poly(2-yydroxyethyl methacrylate) (pHEMA) were synthesized to be evaluated as AFB1 affinity agents based on hypothetical hydrogen bonding interactions and optimal polymer length. An isothermal titration calorimetry (ITC) method was development for rapid affinity agent screening and good agreement was observed between the ITC results and follow-on SERS sensing experiments. A final polymer series (poly(N-acryloyl glycinamide), pNAGA) was designed for the capture of AFB1 and was used to explore the influence of polymer molecular weight (2.0 – 5.2 kDa), attachment chemistry (thiol vs. trithiocarbonate), and order of addition (pre- vs. post- functionalization of the substrate) on the sensitivity of AFB1 detection. The best polymer chain length (pNAGA22), anchoring chemistry (thiol), and polymer/toxin assembly scheme (in-solution) allowed detection of 10 ppb AFB1 in water (below the FDA regulatory limit of 20 ppb), a hundred-fold improvement over SERS sensing without the pNAGA affinity agent. This dissertation concludes with the advantages, disadvantages, and future perspectives of polymers used as analytical affinity agents. Adjustment of surface attachment moieties, the use of crosslinkers with target affinity, and application to other signal transduction mechanisms are emphasized a potential areas for continuing work.Item Localized Programmable Gas Phase Electrodeposition and Its Applications in Functional Nanomaterials and Devices(2016-04) Fang, JunThis thesis focuses on development and application of a gas phase nanomaterial integration concept. We developed and demonstrated a novel gas phase electrodeposition method to control material flux transported and deposited at desired points on a patterned biased substrate based on the Coulomb force. The thesis is divided into two sections: (A) a corona based analyte charging method and an electrodynamic nanolens based analyte concentration concept to effectively transport airborne analytes to sensing points to improve the response time of existing gas sensor designs, and (B) a gas phase electrodeposition process to grow free-standing point-to-point electrical nanowire connections spanning a distance of up to 10 µm. Section A introduces a new general approach which uses a corona based charging method in combination with an electrodynamic lens based collection concept to transport particles to precise points on a surface. We discovered that the transport is faster than diffusion based transport commonly used. The faster transport and speed was then applied to the field of nanosensors of airborne particles. Specifically, we were able to reduce the response time of existing airborne sensor designs by several orders of magnitude. The process, referred to as “corona/lens-based-collection”, enables us to transport nanomaterials and airborne analytes from a space that is centimeters away to specific sensing points on a surface with a minimal spot size approaching 100 nm. We find that the collection rate is several orders of magnitudes higher than the case where the corona/lens-based-collection is turned off and collection is driven by diffusion only. The collection scheme is integrated on an existing SERS based sensor that is sensitive to the adsorption of small molecules. We compare the results with and without corona/lens-based-collection and find that SERS signal is enhanced by three orders of magnitudes as a result of increased collection efficiency. In terms of response time, the process is able to detect analytes at 9 ppm (parts per million) within 1 second. As a comparison, 1 hour is required to approach the same signal intensity in the case where diffusion-only-transport is used. Section B presents a gas phase electrodeposition process to grow free-standing point-to-point electrical nanowire connections spanning a distance of up to 10 µm. The gas phase electrodeposition process uses a patterned resist with openings to a conductor to guide the deposition of charged nanoparticles. Nanowire growth occurs at charge dissipating contacts which are accessible due to the openings in the resist. The formation of interconnects between contacts or bridges across a trench is possible through nearest neighbor interaction. The growing nanowires are composed of metallic nanoparticles. We discovered that a reduction of the primary nanoparticles size to the 1-5 nm range is required to achieve electrical conductive and mechanically stable bondwires. The annealing temperature has been reduced to 250°C due to the small particle size. The diameter of the nanowires depends on the growth duration and the size of the openings. The adjustable range is 50 nm-1 µm. Mechanically stable bondwires have a typical diameter of 250 nm. A 5 µm long interconnects with a radius of 250 nm had a resistance of 85 Ω.Item Localized programmable gas phase electrodeposition yielding functional nanostructured materials and molecular arrays(2013-04) Lin, En-ChiangThis thesis focuses on nanomanufacturing processes for the heterogeneous integration of nanomaterials and molecules. We demonstrate and discovered a novel gas phase method to control material flux at specific points on a surface which is based on the interplay of high mobility gas ions and lower mobility nanoparticles and molecules in the presence of a patterned substrate. The thesis is divided into two parts describing applications of the discovered process for the localized deposition of (A) metallic and semiconducting particles producing functional nanostructured deposits including multimaterial sensor arrays and nanostructured electrodes for photovoltaic applications and, (B) molecules for gas sensor application demonstrating improved collection efficiencies and sensitivity over previously methods. Section (A) begins with the description of an arc discharge based method to produce a flux of charged nanoparticles (<5nm particles Au, Ag, Pt, W, TiO2, ZnO and Ge) which are characterized using various methods. It then describes a process to locally deposit the charged particles into extended two and three dimensional metallic and semiconducting nanostructured deposits. The thesis describes the use externally-biased electrodes to achieve an electronic shutter to turn ON/OFF the deposition in selected domains. Subsequently it explores and describes the use of patterned dielectrics whereby the patterned dielectrics are charged to define arrays of electrodynamic lenses. Incorporation of these lensing structures was found to enable nanostructured deposits with sub 100nm lateral resolution. The utility of the discovered processes are demonstrated in two areas. For the first application, semiconducting nanomaterial are sequentially deposited on the same substrate to fabricate a multi-material / multi-functional sensor array on a single substrate in a single deposition process. The process eliminates critical alignment and masking steps and has a higher material efficiency when compared with traditional vapor deposition methods. In the second application, we demonstrate the fabrication of 3D nanostructured electrodes for photovoltaic application. The second application adjusts the material flux in selected domains to identify nanostructures and device metrics in a combinatorial way. Section (B) applies the process to the localized collection of airborne molecules. The goal was to determine if the process can be scaled to particles with molecular dimensions. This turned out to be the case. As an application we demonstrate enhanced collection efficiencies of molecular species in gas sensor applications. The research recognizes that various nanostructured sensor designs currently aim to achieve or claim single molecular detection by a reduction of the active sensor size. However, a reduction of the sensor size has the negative effect of reducing the capture probability considering the diffusion based analyte transport commonly used. Specifically, we applied the discovered localized programmable electrodynamic precipitation concept to collect, spot, and detect airborne species in an active-matrix array-like fashion. The method is tested using surface enhanced Raman spectroscopy (SERS). The process can produce hybrid molecular arrays on a single chip over a broad range of molecular weights including small molecules or large macromolecules. From a gas sensor system point of view it was possible to improved collection efficiencies and sensitivity over previously method.Item Rapid detection of ricin in liquid foods using surface-enhanced Raman spectroscopy(2013-06) Rodda, Thomas CaseyThe potential for bioterror agents to be distributed using existing supply chains for food with the purpose of causing mass casualty, terror, and/or economic damage is a hazard to homeland security. Therefore, it is necessary that bioterror agent detection procedures be developed which are appropriate and can serve as tools for food companies and other security personnel to monitor the U.S. food supply. The present research develops an appropriate assay which could be used to detect the toxin ricin in fresh liquid foods, specifically milk and orange juice. Ricin toxin is a category B bioterror agent as defined by the Centers for Disease Control and Prevention due to its potent toxicity and relative ease of access. For this application, an appropriate detection assay was rapid, inexpensive, easy to conduct, and sensitive enough to detect ricin at concentrations below toxic doses if consumed. These criteria were important since food surveillance requires frequent monitoring by personnel who do not necessarily have backgrounds in chemistry nor laboratory techniques. Additionally, tested foods should not proceed through the processing/distribution chain until a negative result was received; therefore the assay must be very rapid. Research was conducted and procedure developed using an immuno-based separation technique to capture dilute concentrations of ricin, (or a surrogate), from foods spiked with the toxin. Two separation techniques were utilized and evaluated for speed, ease, and final sensitivity. The first separation technique utilized a commercially available polyclonal ricin antibody conjugated to magnetic beads in order to concentrate and separate ricin from a sample. The second separation technique used a single-stranded DNA aptamer to perform the capture step. Following either separation technique, surface-enhanced Raman spectroscopy (SERS) was used to directly detect the target. Raman is a mode of vibrational spectroscopy where a sample is exposed to a monochromatic laser and a spectrum of Raman-active vibration modes is obtained. These spectra contain a large amount of information about the sample's molecular structure, and therefore act as `fingerprints' for a sample. Surface-enhanced Raman exploits cutting edge nanotechnology to significantly increase the sensitivity of Raman analyses by placing a sample on or near noble metal nanostructures. Immunomagnetic separation (IMS), the first of the separation techniques, produced limits of detection of 4 micrograms/mL in milk, in less than 20 minutes. According to current toxicological data, these limits of detection are sufficient for providing proper protection in the case of a ricin-related attack. Additionally, the procedure was conducted with a portable, hand-held Raman instrument to validate its compatibility with technology that could be used in a harsh environment. The second separation technique used an aptamer which had been covalently bound to the nano-enhancing substrate to capture ricin from food. Aptamers are oligomers of single-stranded DNA which can be used like antibodies to selectively concentrate antigens from complex solutions. This separation protocol delivered a final detection limit of 25 ng/mL, 100 ng/mL, and 100 ng/mL, in buffer, milk, and orange juice, respectively. This assay could also be completed in less than 20 minutes. This project has developed novel procedures for the rapid detection of ricin in liquid foods. These procedures were designed to be easily integrated into existing food quality monitoring programs within food plants or at other sensitive locations, such as national borders or international shipping ports. Additionally, these methods serve as a proof-of-concept since their flexibility allows for easy adaptation to provide detection of other targets as well by replacing the capture molecule.Item Surface-Enhanced Raman Spectroscopy as a Probe to Understand Plasmon-Mediated Photochemistry(2019-09) Brooks, JamesThe development of plasmonic nanostructures as light-activated photocatalysts has proven to be a promising research avenue due to their ability to access and drive unfavorable chemical reactions. Theses chemical reactions are fueled by the presence of surface plasmons, which are the collective oscillation of the free electron density on the material’s surface. Once a surface plasmon is photoexcited, their initial energy rapidly decays into multiple different pathways, such as enhanced electromagnetic fields, an abundance of hot carriers, and dramatically elevated local thermal environments. To better understand the various chemistries that are enabled by plasmonic materials and the associated mechanisms driving these processes, we have employed surface-enhanced Raman spectroscopy to interrogate a plethora of plasmon-molecule coupled systems. Our initial studies investigated the relationship between the plasmonic local fields and a well-established plasmon-driven photochemical reaction. We found that there were no observable correlations between the two in our studies and identified a competing degradation pathway for the studied analytes. In addition to exploring well-studied plasmon-induced chemical photoreactions, we have highlighted two new reactions that were accessed on the gold film-over-nanosphere substrates. First, we were able to induce and subsequently monitor a selective intramolecular methyl migration on N-methylpyridinium using surface-enhanced Raman spectroscopy. This work emphasizes the growing potential of initiating highly-selective chemistries with plasmonic materials for synthetic or redox purposes. The second previously unreported plasmon-driven reaction involves the double cleavage of the C-N bond on a pair of viologen derivatives. While these viologens have traditionally been employed as robust redox species, the unique and highly-powerful plasmonic local fields allowed the viologens to access an entirely new reaction pathway to transform into 4,4’-bipyridine. Lastly, we discuss our experimental approaches towards transiently studying the mechanism behind plasmon-mediated hot electron transfer. Using ultrafast surface-enhanced Raman spectroscopy, we interrogated the transient dynamics that occurred between surface plasmons and a bevy of electron accepting chemical adsorbates. Ultimately, the primary goal of this work is to provide a quantitative description of the transient interactions, which will assist in increasing the reported efficiencies and yields of plasmon-mediated chemical reaction and inspire the rational design of plasmonically-powered devices.Item Theoretic investigation on plasmonics of noble metallic nanoparticles(2013-08) Qian, XiaohuIn this thesis, we report our theoretic investigation on the surface plasmon polaritons of noble metallic nanoparticles and its applications. By means of numerical experiments, we studied the general far-field and near-field optical properties of the promising hollow metallic nanoparticles, the pattern of far-field extinction efficiency and the near-field surface-enhanced Raman scattering. We demonstrated the distribution of plasmon resonance wavelength as functions of the geometrical factor of hollow spherical gold and silver nanostructures. In addition, we utilized a novel mechanism of harnessing the mechanical strain to controllably tailor the plasmon-based optical spectra of single metallic nanospheres and the array of metallic nanoparticle of spheres and circular discs. The second goal of this thesis is to utilize a novel mechanical-strain-induced effect to enhance the light-trapping performance of plasmonic solar cells. This multi-physical scheme has the potential of considerably reducing the thickness of semiconductor layer and hence save the cost of production of the solar cells. Corresponding simulation results demonstrated this strategy is promising to decrease the fabrication budget of solar industry.