Browsing by Subject "Biosensing"

Now showing 1 - 5 of 5
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    Alternative Methods and Materials for use in Plasmonics
    (2019-03) Klemme, Daniel
    Plasmonic devices are extremely useful across a wide variety of fields and have been used for ultra-high-resoulution imaging, drug detection, metamaterials, and single-molecule studies among other things. One major hurdle to achieving useful plasmonic structures is that deeply subwavelength patterns need to be generated, both for coupling the light to the device and to fabricate the device itself. Many plasmonic devices such as optical antennas used for nanofocusing are nonplanar, which vastly increases the difficulty of fabricating subwavelength structures on them. Standard lithographic processes such as photolithography and electron beam lithography are of limited use on three-dimensional substrates, which necessitates the development of novel fabrication techniques. Shadow mask lithography and conformal coating of metallic sidewalls via atomic layer deposition are two techniques that will be used to achieve subwavelength patterning of three-dimensional structures. Additionally, plasmonic materials have typically been dominated by gold and to a lesser extent silver because they exhibit good dielectric properties at optical frequencies and are reasonably robust to ambient conditions. However, these materials do come with their own fabrication limitations that other plasmonically active materials such as titanium nitride and copper do not necessarily have. In particular, atomic layer deposition recipes now exist for titanium nitride that allow sub-10 nm, continuous, and conformal metallic films to be created which opens up the door to novel ultrathin plasmonic structures. In this dissertation, plasmonic structures that were generated using nonstandard nanofabrication techniques and/or metallic materials will be explored, demonstrating the advantages that come with using such techniques and materials.
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    Engineering metallic nanogap apertures for enhanced optical transmission
    (2016-10) Yoo, Daehan
    Physics and technology of metallic nanoapertures have been of great interest in nanophotonics. In particular, enhanced optical transmission mediated by surface plasmon waves in metallic nanoapertures has been widely studied and utilized in biochemical sensing, imaging, optical trapping, nonlinear optics, metamaterials, and optoelectronics. State-of-the-art nanotechnology enables researchers to explore optical physics in complex nanostructures. However, the high cost and tedium of conventional fabrication approaches such as photolithography, electron-beam lithography, or focused-ion-beam milling have limited the utilization of metallic nanoapertures for practical applications. This dissertation explores new approaches to enable high-throughput fabrication of sub-10-nm nanogaps and apertures in metal films. In particular, we focus on a new technique called atomic layer lithography, which turns atomic layer deposition into a lithographic patterning technique and can create ultra-small coaxial nanoapertures. The resulting nanostructures allowed us to observe extraordinary optical transmission in mid-infrared regime that originates from an intriguing physical phenomenon called the epsilon-near-zero (ENZ) condition. Subsequently, we turn this nanogap structure into a high-Q-factor plasmonic resonator, called a trench nanogap resonator, by combining a nanogap and sidewall mirrors. This structure is optimized for electrical trapping of biomolecules and concurrent optical detection, which is demonstrated experimentally via dielectrophoresis-enhanced plasmonic sensing. The fabrication technique and resulting structures demonstrated in this thesis work can facilitate practical engineering of metallic nanoapertures towards harnessing the potential of plasmonics.
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    Engineering metallic nanostructures for surface plasmon resonance sensing.
    (2010-08) Lindquist, Nathan Charles
    A change in almost any characteristic of a given material can be detected by one or more beams of light. Optical sensors are extremely sensitive, non-destructive, and immune to electromagnetic interference, offering many significant advantages. Being able to harness this enormous potential within the realm of nanotechnology, however, requires manipulation and control of an optical field on scales well below its wavelength. Dielectric structures cannot achieve this due to diffraction. However, metallic nanos- tructures which support evanescent surface plasmon resonances can provide a solution. Thin gold or silver films, when patterned with nanometer-scale holes, grooves or bumps can efficiently capture incident light and launch an oscillatory motion of the electrons at the film surface, known as a surface plasmon. Using state of the art nanofabri- cation techniques, we have engineered these plasmonic structures to exhibit unusual optical properties not found in natural materials. Such novel materials are broadly ap- plicable and useful, in particular, for sensing. In this dissertation, patterned metallic nanostructures are used to demonstrate high-resolution sensing of complex biomolecu- lar interactions in a quantitative and high-throughput manner. Additionally, efficient chemical sensing via surface enhanced Raman spectroscopy, and proximity sensing with structures suitable for scanning probe microscopy are also presented. The structures are rigorously analyzed with theoretical computer simulations based on finite-difference time-domain methods. Using a newly developed high-throughput fabrication method based on template stripping of patterned metals, this work may open up avenues for the realization of practical plasmonic devices in a wide variety of disciplines.
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    Mechanistic Understanding and Optimization of Printed Floating Gate Transistors for Chemical Sensing Applications
    (2020-11) Thomas, Mathew
    Monitoring of human environments, food and health for toxin, carcinogen, allergen and pathogen detection motivates the development of chemical and biosensing platforms that can be deployed in portable field applications. Transistors are suitable transducers for such devices due to their direct electronic response, compact size, and multiplexing capabilities. Electrolyte-gated transistors (EGTs) can provide additional advantages including low voltage operation and the use of fast and simple fabrication methods such as printing. The Floating Gate EGT (FGT) is a sensing derivative of the EGT that utilizes a floating gate to physically separate yet still electronically couple the active sensing area with the transistor. Previous work has shown that FGTs can provide fast and reliable detection of DNA, ricin, and gluten. The aim of this thesis is to investigate fundamental operating mechanisms of the device, improve its sensing capabilities and characterize its design space. The first study, detailed in chapter 3, implemented well-established acid-terminated self-assembled monolayer (SAM) chemistry on the sensing area to characterize the role of interfacial charge in generating device responses. The shifts observed are further compared with Grahame’s equation, derived from Guoy-Chapman double layer theory, and is found to match closely with the experimentally observed shifts. This represents the first quantification of the charge response of floating gate transistor sensors. Chapter 4 focuses on the detection of capacitance, an important physical quantity for the detection of charge-neutral targets, which has proved to be a challenge for transistor-based sensing devices. In this study, alkylthiol chains of increasing lengths are used to alter the capacitance of the sensing surface. A simple amplification circuit called an inverter is used to amplify the change in output when the capacitance is perturbed. The FGT platform was found to respond to the capacitive change in a manner distinguishable from the charge-based sensing. This represents the first demonstration of quasi-static capacitance detection in the FGT platform as an alternative to charge detection, a critical issue in transistor-based sensing for neutral targets or in high electrolyte concentrations. In chapter 5, a theoretical model is derived for the device response and it is utilized to predict the performance and sensitivity of floating gate devices using well-known transistor current equations. The derivation yields 5 parameters, which are combinations of physically understood variables that can effectively tune the response of the device. To validate the model experimentally, SAMs are utilized to generate capacitive and charge-based signals, and the area of the sensing surface is systematically reduced. The model is found to match experimental performance and sensitivities well for higher sensing area capacitances (>1 nF). The model predictions are further extended across large ranges of the relevant parameters to provide general design rules for sensing using thin film organic electronic devices that can be utilized regardless of materials choice. The overall contribution of this project is to understand quantitatively the mechanisms behind transistor-based detection, specifically charge and capacitance, and provide guidelines for device sizing and materials choice, in order to make transistor-based sensors more accessible and move closer to the overarching goal of a rapid, portable, general purpose sensor for chemical and biosensing in distributed field applications.
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    Metallic Nanostructures and Plasmonic Devices for Surface Plasmon Resonance Biosensing
    (2011-08) Im, Hyungsoon
    High-throughput real-time sensing of molecular binding kinetics is important for drug discovery, basic biology, and the emerging field of proteomics. In particular, label-free surface plasmon resonance (SPR) sensing, which harnesses electromagnetic surface waves excited on metallic nanostructures, has been widely used in pharmaceutical development. Despite successful commercialization, the reflection-based configuration of traditional SPR instruments suffer from high cost, low sensing throughput, and incompatibility of studying molecules in cell membranes. In this dissertation, a new SPR biosensor based on plasmonic nanohole arrays made in metallic films is demonstrated. These biosensors are used for multiplexed sensing of molecular interactions in a quantitative manner. The nanohole-based SPR devices measure transmission of normally-incident light and the co-linear optical transmission setup offers simple optical setup and high-resolution imaging capability, leading to high-throughput multiplex kinetic assays for protein microarray applications. Additionally, the nanoholes can readily incorporate lipid membranes to study antibody binding to lipids and membrane-bound proteins. Newly developed nanofabrication methods enable production of large-area nanohole- and nanogap arrays in an inexpensive and high-throughput fashion. These methods may facilitate wide dissemination of nanohole SPR sensing as well as chemical sensing via surface-enhanced Raman spectroscopy