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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Novel materials for the design of cantilever transducers

Nelson-Fitzpatrick, Nathaniel Unknown Date
No description available.
2

Specific phage based bacteria detection using microcantilever sensors

Glass, Nicholas Unknown Date
No description available.
3

Biodegradable microdevices for biological detection and smart therapy

Snelling, Diana Kathryn 01 September 2010 (has links)
Biodegradable, pH-responsive hydrogel networks composed of poly(methacrylic acid) crosslinked with varying mol percentages of polycaprolactone diacrylate were synthesized. These materials were characterized using NMR and FTIR. The equilibrium and dynamic swelling properties of these pH-responsive materials were studied. Also, the materials’ degradation was characterized using swelling studies and gel permeation chromatography. Methods were developed to incorporate these novel hydrogels as sensing components in silicon-based microsensors. Extremely thin layers of hydrogels were prepared by photopolymerizion atop silicon microcantilever arrays that served to transduce the pH-responsive volume change of the material into an optical signal. Organosilane chemistry allowed covalent adhesion of the hydrogel to the silicon beam. As the hydrogel swelled, the stress generated at the surface between the hydrogel and the silicon caused a beam deflection downward. The resulting sensor demonstrated a maximum sensitivity of 1nm/4.5E-5 pH unit. Sensors were tested in protein-rich solutions to mimic biological conditions and found to retain their high sensitivity. The existing theory was evaluated and developed to predict deflection of these composite cantilever beams. Another type of hydrogel-based microsensor was fabricated utilizing porous silicon rugate filters as transducers. Porous silicon rugate filters are garnering increased attention as components of in vivo biosensors due to their ability for remote readout through tissue. Here, the biodegradable, pH-responsive hydrogel was polymerized within the pores of a porous silicon rugate filter to generate a novel, completely degradable sensor. Silicon was electrochemically etched in hydrofluoric acid to generate the porous silicon rugate filter with its reflectance peak in the near infrared region. Poly(methacrylic acid) crosslinked with polycaprolactone diacrylate was polymerized within the pores using UV free radical photopolymerization. The reflectance peak of this sensor varied linearly with pH in the region pH 2.2 to 8.8. This work shows promise towards utilizing porous silicon rugate filters as transducers for environmentally responsive hydrogels for biosensing applications. / text
4

Specific phage based bacteria detection using microcantilever sensors

Glass, Nicholas 11 1900 (has links)
Resonant microcantilevers are promising transducers for bacteria detection because of their high sensitivities. Surface stress and mass from adsorbates affect the resonant frequency. We developed a novel method for decoupling the frequency contributions of a change in mass and surface stress on a cantilever sensor validated in theoretical, finite element and experimental framework. Bacteria capture was achieved by several different chemical immobilization of T4 phages. The most successful bacteria capturing surface produced bacterial densities of about 11 bacteria/100^m2. The developed theory is then applied to determine captured bacterial mass on the cantilevers. This provides an estimate of the bacteria mass on the cantilever. Two different functionalizations resulted in predicted bacterial densities of 5 bacteria/100^m2 and 3 bacteria/100^m2. Poor densities relative to surface capture experiments is caused by the boundary effects of the cantilever in solution. / Microelectromechanical Systems and Nanosystems
5

In-Plane, All-Photonic Transduction Method for Silicon Photonic Microcantilever Array Sensors

Noh, Jong Wook 23 November 2009 (has links)
We have invented an in-plane all-photonic transduction method for photonic microcantilever arrays that is scalable to large arrays for sensing applications in both bio- and nanotechnology. Our photonic transduction method utilizes a microcantilever forming a single mode rib waveguide and a differential splitter consisting of an asymmetric multimode waveguide and a Y-branch waveguide splitter. The differential splitter's outputs are used to form a differential signal that has a monotonic response to microcantilever deflection. A differential splitter using an amorphous silicon strip-loaded multimode rib waveguide is designed and fabricated to demonstrate the feasibility of the in-plane photonic transduction method. Our initial implementation shows that the sensitivity of the device is 0.135×10^-3 nm^-1 which is comparable to that of other readout methods currently employed for static-deflection based sensors. Through further analysis of the optical characteristics of the differential splitter, a new asymmetric double-step multimode rib waveguide has been devised for the differential splitter. The new differential splitter not only improves sensitivity and reduces size, but also eliminates several fabrication issues. Furthermore, photonic microcantilever arrays are integrated with the differential splitters and a waveguide splitter network in order to demonstrate scalability. We have achieved a measured sensitivity of 0.32×10^-3 nm^-1, which is 2.4 times greater than our initial result while the waveguide length is 6 times shorter. Analytical examination of the relationship between sensitivity and structure of the asymmetric double-step rib waveguide shows a way to further improve performance of the photonic microcantilever sensor. We have demonstrated experimentally that greater sensitivity is achieved when increasing the step height of the double-step rib waveguide. Moreover, the improved sensitivity of the photonic microcantilever system, 0.77×10^-3 nm^-1, is close to the best reported sensitivities of other transduction methods (~10^-3 nm^-1).
6

A piezoresistive microcantilever array for chemical sensing applications

Choudhury, Arnab 14 November 2007 (has links)
Numerous applications in the present day ranging from testing humidity in air to detecting miniscule quantities of potentially hazardous chemical and biological agents in the air or water supplies require the development of chemical sensors capable of analyte detection with high sensitivity and selectively. Further, it has become desirable to create lab-on-chip systems that can detect multiple chemical agents and allow for sampling and testing of environments at locations distant from conventional laboratory facilities. Current challenges in this area include design, development and characterization of low detection limit sensors, development of low-noise readout methods, positive identification of analytes and, identification and reduction of the effect of various noise sources - both intrinsic and extrinsic to the sensor. The current work examines the performance limits of a 10-cantilever piezoresistive microcantilever array (PµCA) sensor. The microcantilevers measure analyte concentration in terms of the surface stress associated with analyte binding to the functionalized cantilever surface. The design, fabrication, characterization and testing of this measurement platform is presented. A novel aspect of the sensors developed is the use of n-type doping which increases the sensitivity of the device by one order of magnitude. In addition, design rules for surface stress-based chemical sensors have been developed. Extensive thermal characterization of the piezoresistive microcantilevers has been performed for DC and AC electrical excitation and values of heat transfer coefficient for the associated microscale phenomena are reported. Further, a method of low-noise measurement of cantilever resistance has been developed based on phase-sensitive detection techniques and this has been integrated with a multiplexing circuit to measure piezoresistance change in multiple cantilevers. Finally, the two novel techniques of chemical sensing- double-sided sensing and thermal array-based sensing have been investigated. These methods are presented as a means of extending the applicability and functionality of piezoresistive microcantilever sensors for chemical sensing.
7

Nanomechanical measurements of fluctuations in biological, turbulent, and confined flows

Lissandrello, Charles Andrew 08 April 2016 (has links)
The microcantilever has become a ubiquitous tool for surface science, chemical sensing, biosensing, imaging, and energy harvesting, among many others. It is a device of relatively simple geometry with a static and dynamic response that is well understood. Further, because of it's small size, it is extremely sensitive to small external perturbations. These characteristics make the microcantilever an ideal candidate for a multitude of sensing applications. In this thesis dissertation we use the microcantilever to conduct numerous physical measurements and to study fundamental phenomena in the areas of fluid dynamics, turbulence, and biology. In each area we use the cantilever as a sensitive transducer in order to probe fluctuating forces. In micro and nanometer scale flows the characteristic length scale of the flow approaches and is even exceeded by the fluid mean free path. This limit is beyond the applicability of the Navier-Stokes equations, requiring a rigorous treatment using kinetic theory. In our first study, we conduct a series of experiments in which we use a microcantilever to measure gas dissipation in a nanoscopically confined system. Here, the distance between the gas molecules is of the same order as the separation between the cantilever and the walls of its container. As the cantilever is brought towards the wall, the flow becomes confined in the gap between the cantilever and the wall, affecting the resonant frequency and dissipation of the cantilever. By carefully tuning the separation distance, the gas pressure, and the cantilever oscillation frequency, we study the flow over a broad range of dimensionless parameters. Using these measurements, we provide an in-depth characterization of confinement effects in oscillating nanoflows. In addition, we propose a scaling function which describes the flow in the entire parameter space and which unifies previous theories based on the slip boundary condition and effective viscosity. In our next study, we seek to gain a better understanding of the transition to turbulence in a channel flow. We use a cantilever embedded in the channel wall to perform two sets of experiments: first, we study transition to turbulence triggered by the natural imperfections of the channel walls and second, we study transition under artificially added inlet noise. Our results point to two very different paths to turbulence. In the first case, wall effects lead to an extremely intermittent transitional flow and in the second case, broadband fluctuations originating at the inlet lead to less intermittent flow that is more reminiscent of homogeneous turbulence. The two experiments result in random flows in which high-order moments of near-wall fluctuations differ by orders of magnitude. Surprisingly however, the lowest order statistics in both cases appear qualitatively similar and can be described by a proposed noisy Landau equation. The noise, regardless of its origin, regularizes the Landau singularity of the relaxation time and makes transitions driven by different noise sources appear similar. Our results provide evidence of the existence of a finite turbulent relaxation time in transitional flows due to the persistent nature of noise in the system. In our last study, we turn to biologically-driven fluctuations from bacterial motion. Recent studies suggest that the motion of living bacteria could serve as a good indicator of bacteria species and resistance to antibiotics. To gain a better understanding of these fluctuations, we measure the nanomechanical motion of bacteria adhered to a chemically functionalized silicon microcantilever. A non-specific binding agent is used to attach E. coli to the surface of the device. The motion of the bacteria couples efficiently to the cantilever well below its resonance frequency, causing a measurable increase in its mechanical fluctuations. We vary the bacterial concentration over two orders of magnitude and are able to observe a corresponding change in the amplitude of fluctuations. Additionally, we administer antibiotics (Streptomycin) to kill the bacteria and observe a decrease in the fluctuations. A basic physical model is used to explain the observed spectral distribution of the mechanical fluctuations. These results lay the groundwork for understanding the motion of microorganisms adhered to surfaces and for developing micromechanical sensors for rapid bacterial identification and antibiotic resistance testing.
8

Effect of Surface Stress on Micromechanical Cantilevers for Sensing Applications

Liangruksa, Monrudee 21 July 2008 (has links)
Three models for surface stress loading effect on a micromechanical cantilever are proposed as concentrated moment acting at the free end (Model I), concentrated moment plus axial force acting at the free end (Model II), and uniformly distributed surface force acting along the microcantilever (Model III). Solution to Model I loading is based on the Stoney formula, assuming that the microcantilever is subjected to pure bending and deformed with a constant curvature. Model II takes into account the clamping effect in such a way that an additional axial force is introduced. The deflections resulting from Models I and II surface stress loading effect are solved by Euler-Bernoulli beam theory. In Model III, the effect of surface stress is modeled as uniformly distributed surface force that causes both uniformly distributed bending moment and axial force acting along the axis of the microcantilever. The energy method is then used to obtain the governing equation and boundary conditions for Model III displacement. Comparison of the results obtained by the three models with those by the finite element method and experiment indicates that Model III is the most realistic model for surface stress loading effect to obtain the deflection of a microcantilever. <p> Model III for surface stress loading effect is then used to demonstrate the applications of a microcantilever in sensor technology through the measurement of tip deflection under an atomic adsorption as the source of surface stress. Dual attractive or repulsive characteristics of interactions between a pair of mercury atoms are described in terms of Lennard-Jones potential. The force per unit atomic spacing induced by the adjacent free surface atoms of a monolayer is then computed using the potential. The sensitivities of atomic spacing and monolayer thickness to the tip-deflection of a microcantilever are studied in this research. / Master of Science
9

Development of Single-Chip Silicon Photonic Microcantilever Arrays for Sensing Applications

Hu, Weisheng 17 March 2011 (has links)
Microcantilever arrays have been shown to be promising label-free nanomechanical sensing devices with high sensitivity. Two factors that affect the usefulness of microcantilevers in sensing scenarios are the sensitivity of the transduction method for measuring changes in microcantilever properties and the ability to create large compact arrays of microcantilevers. In this dissertation, we demonstrate that microcantilevers with an in-plane photonic transduction method are attractive because they maintain the sensitivity of the traditional laser beam reflection method while being scalable to simultaneous readout of large microcantilever arrays. First I demonstrate the integration of a compact waveguide splitter network with in-plane photonic microcantilevers which have amorphous silicon strip loading differential splitter and simultaneous microcantilever readout with an InGaAs line scan camera. A 16-microcantilever array is fabricated and measured. Use of a scaled differential signal yields reasonable correspondence of the signals from 7 surviving released microcantilevers in the array. The average sensitivity is 0.23 µm-1. To improve the sensitivity and consistency, and reduce fabrication difficulties, a new differential splitter design with 4 µm long double-step multimode rib waveguide is introduced. Furthermore, a modified fabrication process is employed to enhance the performance of the device. A new 16-microcanitiler array is designed and fabricated. The sensitivity of a measured 16-microcantilever array is improved to approximately 1 µm-1, which is comparable to the best reported for the laser reflection read out method. Moreover, most of the microcantilevers show excellent uniformity. To demonstrate large scale microcantilever arrays with simultaneous readout using the in-plane photonic transduction method, a 64-microcantilver array is designed, fabricated and measured. Measurement results show that excellent signal uniformiy is obtained for the scaled differential signal of 56 measured microcantilevers in a 64-array. The average sensitivity of the microcantilevers is 0.7 µm-1, and matches simulation results very well.
10

Characterization and Preliminary Demonstration of Microcantilever Array Integrated Sensors

Anderson, Ryan R. 07 July 2012 (has links)
I characterize the behavior of microcantilever arrays which utilize the in-plane photonic transduction that I've previously developed and evaluate the performance of the microcantilever arrays in simple sensing scenarios with integrated microfluidics. First the thermal responses of microcantilevers with a variety of patterns of deposited gold films are compared. Using a scanning electron microscope, I observe the deflection thermal sensitivities of 300 µm long microcantilevers to be -170.82 nm/K for a full gold coating and -1.93 nm/K for no gold coating. Using the photonic transduction method I measure a thermal sensitivity of -1.46 nm/K for a microcantilever array with no gold. A microcantilever array integrated with microfluidics is exposed to a solution of bovine serum albumin (BSA) followed by solutions of various pH's. In all cases I observe a previously unreported transient deflection response. We find that the transient response is due to temporary nonuniform concentration distributions. In response to nonspecific binding of BSA, I observe a transient surface stress of -0.23 mN/m that agrees well with the -0.225 mN/m predicted by simulations. We hypothesize that the deflection response to pH changes is due to stress generated by conformational changes of bound BSA.The deflection response of an integrated microcantilever array to different types of flow and different flow rates is observed. Simulations of the deflection response match well with experimental results but disagree at higher flow rates. For flow rates greater than 200 µL/min, the limitation of the differential signal's dynamic range becomes apparent. We then investigate flow driven by an on-chip reciprocating reservoir pump. We demonstrate that it is possible to use the reciprocating pump to achieve high flow rates while making deflection measurements in-between reservoir actuations. Investigations of the microcantilever array noise show that flicker noise dominates below 10 Hz, while above 10 Hz, readout noise dominates. A minimum deflection noise density of 15 pW/√Hz is achieved. To improve the signal-to-noise ratio I develop algorithms for a digital lock-in amplifier with a digital phase-lock loop. In simulation the lock-in amplifier is able to improve the SNR by up to a factor of 6000, and self-lock to a noisy carrier signal without an external reference signal.

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