This work describes a biosensor based on magnetic resonance relaxation switching. The method leverages a large body of work involving nanoscale contrast agents employed in nuclear magnetic resonance (NMR) imaging. The aim was to develop a detection approach that mimics the human immune response to an invading pathogen, the release of 10<sup>9</sup> to 10<sup>12</sup> specific antigens to guarantee quick contact with the pathogen. The technique employs magnetic nanoparticle contrast agents conjugated with specific capture agents to achieve a similar contact goal. Detection of the species involves monitoring the average relaxation time (T2) of water protons in the solution, which is highly sensitive to the concentration and distribution of the magnetic nanoparticles present. With multiple nanoparticles attaching to each individual target species their distribution will be altered, and correspondingly, the average proton relaxation time will change
This paper describes the results of a research project to investigate magnetoelastic (ME) biosensors actuated with a pulse excitation to measure the concentration of Salmonella Typhimurium of globe fruits. The ME biosensors are based on an acoustic wave resonator platform that is a freestanding (free-free) thin ribbon of magnetostrictive material with a lengthto- width ratio of 5:1. A biorecognition probe coated on the surface of the resonator platform binds with a targeted pathogen, i.e. E2 phage that binds with S. Typhimurium. The biosensor was actuated to vibrate longitudinally such that the resonant frequency depended primarily on the length of sensor and its overall mass. A pulsed excitation and measurement system was used to actuate micron scale ME biosensors to vibrate. The biosensor responds in a ring-down manner, a damped decay of the resonance amplitude, from which the resonant frequency was measured. An increase in mass due to the binding of the target pathogen resulted in a decrease in the resonant frequency. The pulsed excitation and measurement system that was developed under this effort and the characterization of its performance on the measurement of Salmonella concentrations on globe fruits is described.
The use of cantilevered piezoelectric bimorphs under transversal excitations is an area of research well reported in literature. These devices may be tapered into triangular geometries in order to enhance axial strain over the surfaces of the device for more reliable operation. This study reports the comparison of rectangular and triangular cantilevered bimorphs of equal volume and matching resonance frequency, where it is seen that tapering geometry enhances the electromechanical coupling coefficient, which may not necessarily be the only parameter involved in enhancing power output. This is indicated in the case of a triangular cantilevered device without a proof mass, which with increased coupling is unable to outperform a rectangular device. The addition of a nominal proof mass on a rectangular and triangular device increases not only the electromechanical coupling coefficient, but also increases the damping ratio in the devices. This effect is more pronounced in the case of triangular bimorphs, and a 40% improvement in power output is seen. Therefore, these studies provides insights into the changing parameters with changing shapes, which may provide better optimization parameters for improving piezoelectric energy harvesting from cantilevered devices.
This work demonstrated the ability to transfer a nanoscale 3-D polynomial structure of arbitrary shape into Si with a single step electron-beam lithography process. The technique involved employing a proximity correction algorithm, PYRAMID, to derive the dose distribution for a given 3-D structure by accounting for the electron scattering effects of the surrounding pixels. The pattern was written into a polymethyl methacrylate (PMMA) resist and then successively transferred into Si via reactive ion etching, where a 1:1 etching ratio between PMMA and Si was achieved. The pattern transferred into Si possessed nanoscale features and matched the desired pattern with high fidelity.
The excellent tribological properties, very low friction coefficient, ~0.05, of the recently discovered carbide derived carbon (CDC) films have shown them to be excellent candidates in many applications where friction and wear are dominating issues in performance. In this work we examine the feasibility of employing a reactive ion etching process (RIE) with chlorine gas at low temperature, as opposed to the current high temperature chlorination process, in achieving the conversion of metal carbide films into amorphous carbon films. The overall goal is develop a process that is friendlier to microfabricated devices towards employing the tribological properties of CDC films in such devices. We examine this RIE processing using both bulk scale and thin film specimens. These metal-carbide specimens are subjected to a halogen containing ion plasma at reduced pressure in order to leach out the metal, resulting in an amorphous carbon film, a so-called carbide-derived carbon (CDC) process. This reactive ion etching process has been used to produce carbon layers on multiphase carbide materials containing silicon and titanium. The resulting carbon layers have been characterized using a variety of techniques. The results on the bulk scale specimens, via Raman spectrometry, indicated that RIE processing can indeed achieve conversion, while results of the thin films indicated that although conversion occurred poor adhesion of the films to the substrate resulted spallation during friction testing attempts.
Microcantilever based sensors have been being widely used for measuring or detecting various physical conditions, chemical agents and biological species. Researchers are continuing to focus on enhancing the sensitivity of these devices toward improving their performance and applicability. In this paper, a numerical study is performed to assess the influence of microcantilever geometry on sensitivity to improve these devices for better detection of hazardous biological agents in liquid environments. Modal analyses were performed on microcantilevers of different geometries and shapes using ANSYS software and compared to the basic rectangular shaped microcantilever structures employed by most researchers. These structures all possessed a 50 μm length, 0.5 μm thickness and 25 μm width where the cantilever is clamped to the substrate, and were analyzed for their basic resonance frequency as well as the frequency shift for the attachment of a 0.285 picogram of mass attached on their surfaces. These numerical results are compared for the improvement of the sensitivity for MEMS based microcantilever sensor, which is particularly promising for biosensor applications. Of the geometries studied a few were found to possess a significant increase in mass sensitivity over regular rectangular shaped cantilever beam structures of similar dimensions. In particular, it was found that geometries possessing larger clamping widths and/or reduced effective mass at the free end yielded enhanced sensitivity.
A triangular shape was found to increase mass sensitivity an order of magnitude over standard rectangular shapes.