Plasmonics substrates for surface enhanced Raman scattering

Designed and fabricated plasmonic substrates for surface enhanced Raman scattering and approached improved sensitivity for detection of molecules.<br /

Manufacture and utilization of a biodegradable sensor platform from gold coated zein nanophotonic films to detect acrylamide and Ara-h1 using SERS

With the current developments in biosensor and nanotechnology, detection of analyses that are important to food industry are becoming more commonplace. One of the strong tools that nanotechnology enabled is Surface Enhanced Raman Spectroscopy (SERS). SERS is a highly sensitive and specific technique which provides molecular fingerprinting, with the enhancement effect as a result of roughened noble metal surfaces. The platform for these surfaces are generally made out of non-biodegradable, plastic materials. As the one-time use, large scale applications are needed for many fields such as medical, forensic and food industry, disposability of these sensors will pose a problem in the future. In the scope of this dissertation, we investigated the feasibility of a biodegradable sensor platform that is made of zein, a corn protein, utilized in SERS measurements of food analytes. First, the effect of parent substrate (the surface, which zein was cast on) and plasticizer, oleic acid content, on the surface hydrophilicity of resulting zein films was analyzed. It was found that the surface chemistry of the parent substrate was more important than the topography of the parent substrate. Oxygen plasma was used to make the polydimethylsilohexane (PDMS) surfaces more hydrophilic and it was found that zein film surfaces that were in contact with PDMS also had more hydrophilic surfaces, compared to regular PDMS, which is a hydrophobic material. Water contact angle (WCA) method was used to quantify the hydrophilicity of zein films. WCA reached values as low as 20 degrees with a high oleic acid content. Increase in oleic acid content in the formulation of zein films as well as the parent substrate chemistry was found to influence the water affnity of zein films. In the development of the fabrication method of nanopatterned and gold coated zein surfaces, a simultaneous three-dimensional transfer was used. Four different nanopatterns, namely positive pyramids, inverted pyramids, nano pillars and nano pores were transferred onto zein films along with either 80 or 200 nm gold coating by using solvent casting technique. Scanning microscopy images showed that the patterns were transferred onto zein films with high fidelity and success. The enhancement effect of these SERS substrates were tested by using a model molecule, Rhodamine 6G. It was found that the best enhancement effect was provided by inverse-pyramid structures coated with 200 nm gold. For the rest of the study, these structures were used. Zein-SERS substrates were utilized in two different food analyte detection purpose, acrylamide and peanut allergen protein Ara h1. Acrylamide is a potential carcinogenic compound that is formed during high temperature food processing. French fries, potato chips, bread and coffee are some of the food products that may contain high amounts of acrylamide. Since Food and Drug Administration released a draft advisory for mitigation strategies for acrylamide content in foods, there is a need for routine testing technique of acrylamide in food products. In this research, acrylamide was detected by using zein-SERS substrates as a proof of concept. Limit of detection was found to be 10 micrograms/milliliter. Calibration curve was obtained with an R2 value of 0.93 and 0.97 for log-log version. Peanut allergies are among the most common food allergies, and they can result in life-threatening reactions in allergic patients. For this reason, it is extremely important to monitor the presence or cross-contamination of peanuts into food products. There are 8 identified peanut allergen proteins and Ara h1, consists of the largest percentage of protein content, in addition to causing reactions in almost 100 % of the patients. Zein-SERS substrates were utilized in detection of Ara h1. With the use of statistical clustering technique called principal component analysis (PCA), it was possible detect and quantify Ara h1 protein. Limit of detection was found to be 0.14 mg/ml. The surface of the zein-SERS substrates were functionalized with monoclonal antibody and tested for capturing Ara h1 as a proof-of-concept. With this research, utilizing zein as a biodegradable sensor platform for SERS measurements were investigated for the first time. It was shown that detection of both acrylamide and Ara h1, peanut protein, was possible. The methods developed in this study for controlling the surface hydrophilicity of zein films and direct transfer of both micro and nano-scale patterns onto zein along with noble metals can be employed in other biosensor and biopolymer applications as well in the future. This kind of biodegradable platforms might be an alternative solution for environmentally friendly and large scale sensor applications

The Role Of Photonics In Energy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)In celebration of the 2015 International Year of Light, we highlight major breakthroughs in photonics for energy conversion and conservation. The section on energy conversion discusses the role of light in solar light harvesting for electrical and thermal power generation; chemical energy conversion and fuel generation; as well as photonic sensors for energy applications. The section on energy conservation focuses on solid-state lighting, flat-panel displays, and optical communications and interconnects. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.5Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)U.S. National Science Foundation [DMR-1309459, ECCS 1408051, DMR 1505122]U.S. Office of Naval ResearchEngineering and Physical Sciences Research Council of the UK [EP/K00042X, EP/L012294]European Research Council of the European Union [321305]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Advances in Plasmonic Technologies for Point of Care Applications

Demand for accessible and affordable healthcare for infectious and chronic diseases present significant challenges for providing high-value and effective healthcare. Traditional approaches are expanding to include point-of-care (POC) diagnostics, bedside testing, and community-based approaches to respond to these challenges. Innovative solutions utilizing recent advances in mobile technologies, nanotechnology, imaging systems, and microfluidic technologies are envisioned to assist this transformation.National Institutes of Health (U.S.) (RO1 AI093282)National Institutes of Health (U.S.) (RO1 AI081534)National Institutes of Health (U.S.) (U54EB15408)National Institutes of Health (U.S.) (R21 AI087107

Two-Dimensional and High-Throughput Electrophoretic Separation of Proteins Using Polymeric Microchips

A major task in proteomics is to identify proteins from a biological sample using two-dimensional (2-D) separation prior to mass spectrometry of peptides generated via proteolytic digestion of the proteins. For 2-D separations, microfluidic devices are superior to bench top and capillary-based systems since they potentially provide higher separation efficiencies due to the minimal dead volumes produced during peak transfer between the two separation dimensions. In addition, fast separations can be envisioned because the column lengths are typically shorter in microfluidic platforms without scarifying peak capacity. High-throughput capabilities are extremely desirable for many types of bio-analytical analyses, such as understanding molecular interactions and the role they play in cellular functioning and drug discovery. Polymeric microchips possess a variety of physiochemical properties to match the intended application and their ease of fabrication increases the accessibility of technology to a large research base. In this dissertation, a comprehensive 2-D separation platform for proteins using a polymeric microchip with the ability to perform high performance separations within a few minutes was established. The system combined sodium dodecyl sulfate micro-capillary gel electrophoresis (SDS µ-CGE) with micellar electrokinetic chromatography (MEKC) in a poly(methyl methacrylate), PMMA, microchip and was reported with a programmed pulse injection/separation protocol with laser-induced fluorescence for detection. A novel sixteen-channel polycarbonate (PC) microfluidic device for high-throughput separations of proteins was also presented using a process to pattern gold features as microelectrode array for sixteen parallel channels on microchips. The system was able to simultaneously analyze sixteen different samples in parallel consisting of native proteins, amino acids, peptides, and oligonucleotides with conductivity. Finally, due to the diverse nature of polymer properties and the large number of potential applications for microfluidic chips, the physiochemical properties of various polymers were investigated to guide researchers in selecting the best material for a given application including protein analysis

Heterojunctions and Schottky Diodes on Semiconductor Nanowires for Solar Cell Applications

Photovoltaic devices are receiving growing interest in both industry and research institutions due to the great demand for clean and renewable energy. Among all types of solar cells, cadmium sulfide (CdS) – cadmium telluride (CdTe) and cadmium sulfide (CdS) - copper indium diselenide (CuInSe2 or CIS) heterojunctions based thin film solar cells are of great interest due to their high efficiency and low cost. Further improvement in power conversion efficiency over the traditional device structure can be achieved by tuning the optical and electric properties of the light absorption layer as well as the window layer, utilizing nano template-assisted patterning and fabrication. In this dissertation, simulation and calculation of photocurrent generation in nanowires (NW) based heterojunction structure indicated that an estimated 25% improvement in power conversion efficiency can be expected in nano CdS – CdTe solar cells. Two novel device configurations for CdTe solar cells were developed where the traditional thin film CdS window layer was replaced by nanowires of CdS, embedded in aluminum oxide matrix or free standing. Nanostructured devices of the two designs were fabricated and a power conversion efficiency value of 6.5% was achieved. Porous anodic aluminum oxide (AAO) was used as the template for device fabrication. A technology for removing the residual aluminum oxide barrier layer between indium tin oxide (ITO) substrate and AAO pores was developed. Causes and remedies for the non-uniform barrier layer were investigated, and barrier-free AAO on ITO substrate were obtained. Also, vertically aligned nanowire arrays of CIS of controllable diameter and length were produced by simultaneously electrodepositing Cu, In and Se from an acid bath into the AAO pores formed on top of an aluminum sheet. Ohmic contact to CIS was formed by depositing a 100 nm thick gold layer on top and thus a Schottky diode device of the Au/CIS nanowires/Al configuration was obtained. Material properties of all these nanowires were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), absorption measurement. Current-voltage (I-V), capacitance-voltage (C-V) and low-temperature measurements were performed for all types of devices and the results were analyzed to advance the understanding of electron transport in these nano-structured devices

DETECTION OF MYCOTOXINS USING SURFACE-ENHANCED RAMAN SPECTROSCOPY

Mycotoxins are toxic metabolites produced by fungus that can be parasites or saprophytes of crops or livestock forage. Consumer demand for plant-based foods and interest in animal-based foods originating from animals fed plant-based feed has been on the rise. Therefore, monitoring mycotoxins occurring in the food supply is more critical than ever. The goal of this project is to improve surface-enhanced Raman spectroscopy’s (SERS) ability to identify and detect mycotoxins using label-free SERS substrates. Two simple approaches were designed to enhance the detection of mycotoxins produced by the Aspergillus and Penicillium genera, ochratoxin A and aflatoxin B1. Ochratoxin A was successfully detected in wine samples spiked with the mycotoxin in a range of 0.01 to 1 ppm using a facile solvent-mediated extraction that showed the key role that the food matrix can play on the SERS substrate performance. The detection of aflatoxin B1’ SERS signals using bare gold nanoparticles was enhanced with the addition of human serum albumin (HSA) as a mediating molecule. A combination of the HSA-mediated protocol and a liquid-liquid extraction (LLE) method allows the detection of up to 2 ppb of AFB1 in compound feedstuff samples. Additionally, a simple SERS protocol applied to Aspergillus flavus grown in liquid and solid medium showed the technique’s capacity to classify between aflatoxigenic and non-aflatoxigenic species. Raman spectroscopy, SERS, Infrared Spectroscopy (IR) and surface-enhanced infrared absorption spectroscopy (SEIRAS) showed differences yet potential complementarity in their ability to identify mycotoxins produced by the Fusarium genus, deoxynivalenol and fumonisin B1

Fabrication and Study of Graphene-Based Nanocomposites for Sensing and Energy Storage

Graphite is an allotrope of carbon made up of atomically thin sheets, each covalently bound together, forming a π-conjugated network. An individual layer, called graphene, has extraordinary electrical, thermal and physical properties that provide the opportunity for innovating new functional composites. Graphene can be produced directly on a metallic substrate by chemical vapor deposition or by chemical oxidation of graphite, forming a stable aqueous suspension of graphene oxide (GO), which allows for convenient solution processing techniques. For the latter, after thermal or chemical reduction, much of the properties of the starting graphene re-emerge due to the reestablishment of π-conjugation. The ?-conjugated basal plane of graphene has been shown to influence the crystallization of ?-conjugated polymers, providing thermodynamically strong nucleation sites through the relatively strong π-π interactions. These polymers can homocrystallize into 1-D filaments, but when nucleated from graphene, the orientation and geometry can be controlled producing hierarchical structures containing an electrical conductor decorated with wires of semi-conducting polymer. The resulting structures and crystallization kinetics of the conjugated polymer, poly(3-hexylthiophene-2,5-diyl) (P3HT) nucleated by graphene was studied. Further, field-effect transistors were developed using graphene as both the electrodes and the polymer crystallization surface to directly grow P3HT nanowires as the active material. This direct crystallization technique lead to higher charge mobility and higher on-off ratios, and this result was interpreted in terms of the morphology and polymer-graphene interface. Besides these thin-film technologies, neat GO suspensions can be lyophilized to produce monolithic, free-standing aerogels and then reduced to produce an electrically conductive porous material with a surface area greater than 1000 m2/g. The present research focuses on functionalizing the aerogel surfaces with metal nanoparticles to increase electrical conductivity and to impart functionality. Functionalization was carried out by adding a metal salt as a precursor and a chelating agent to inhibit GO flocculation. The GO and metal salt were simultaneously reduced to form rGO aerogels homogeneously loaded with metal nanoparticles. The size and distribution of these nanoparticles was controlled by concentration and chelating agent identity and abundance. Optimum aerogel formulations were used as a functioning and reversible conductometric hydrogen gas sensor and as an anode in an asymmetric supercapacitor with excellent properties