Index to 1985 NASA Tech Briefs, volume 10, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1985 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Micro- and nano-electrode arrays for electroanalytical sensing

A systematic investigation of the electrochemical behaviour of two sets of microelectrode arrays, fabricated by standard photolithographic and reactive-ion etching techniques, is presented. The first set of microelectrode arrays had a constant relative centre-centre spacing of 10r (where r is the electrode radius). As a value of r was decreased, the cyclic voltammograms recorded from the array became increasingly peak-shaped, due to merging of the diffusion fields of the individual electrodes. Furthermore, it was shown that the peak current densities obtained were largest for the arrays with the smallest individual electrodes, as were the signal-to-noise ratios (SNRs). Electroplating the individuals electrodes with platinum black was also shown to increase the peak currents and the SNRs, due to an increase in the effective surface area. Sigmoidal voltammograms, which are indicative of radial diffusion, were obtained for an individual electrode radius of 25 mm but not for arrays with smaller electrodes. To obtain radial diffusion for an array of 2.5 mm electrodes, it was shown (using a second set of microelectrode arrays) that a minimum relative centre-centre spacing of 40r is required. Further enhancement of the peak current densities were obtained by decreasing the size of the individual electrodes. A series of nanoelectrode arrays were fabricated using electron-beam lithography (EBL). The voltammograms obtained from these arrays exhibited a continual increase in the recorded peak current as the individual electrodes radius was decreased to a value of 110 nm. Since EBL is a slow and costly technique, nanoimprint lithography (NIL) was investigated as an alternative method of fabricating nanoelectrode arrays and comparable results were obtained from arrays produced by EBL and NIL. A dissolved oxygen and temperature sensor incorporating a working microelectrode array was also designed and fabricated. The sector comprised a densely packed array of 2.5 mm radius electrodes and a micro-reference electrode, both of which were covered with an agarose electrolyte gel enclosed in an SU8 chamber. A thermal resistor was included for temperature compensation of the dissolved oxygen measurements. The Ag|AgCl micro-reference electrode was found to be stable for approximately 80 hours in 0.1 M KCl, with 100 nA of current passing through it. Linear calibration curves were obtained from both temperature and dissolved oxygen measurement

Fabrication of High-Performance Probes for Atomic Force Microscope (AFM)

Atomic force microscope (AFM) is widely used for topographical structure characterization. However, one serious issue with AFM imaging is the intrinsic artifact in the AFM image when mapping a none-flat surface (e.g. a deep and narrow hole/trench) where the tip cannot fully follow the sample surface. The natural solution to overcome this issue is by using thin and high aspect ratio (HAR) tips that can follow the sample surface more precisely. This thesis focuses on the fabrication of HAR AFM probes. The HAR tips are obtained by modifying regular AFM tips having a pyramid shape. The high aspect ratio structure in silicon, sitting on top of a pyramid base, is created by a dry plasma etching process, so the key is to form a hard metal dot right on top of the pyramid tip apex to act as the mask for silicon etching. Three approaches were developed to form the hard mask metal nano-dot on the tip apex. The first method (Chapter 3) employed metal deposition steps with the regular tip mounted on a tilted surface, and its etching back to leave behind metal only at the tip apex (the metal on the sidewall of the pyramid was etched away). Since both metal film deposition and its etching, as well as the subsequent dry plasma etching of silicon using the metal as mask to form the HAR structure, can be carried out on an entire wafer of regular AFM tips, this process is a low-cost and high throughput batch process. The second method (Chapter 6) utilized focused ion beam (FIB). FIB has been extensively used to fabricate HAR tips by milling away the silicon surrounding the tip axis, leaving behind a thin pillar or sharp cone of silicon at the pyramid axis. However, the FIB milling time for each tip is long, leading to high cost. Our method used FIB to mill away only a very thin layer of metal film to leave behind a metal dot at tip apex, thus the expensive FIB machine time is greatly reduced. The third method (Chapter 6) also utilized Ga-ion FIB, but instead of milling a metal dot mask pattern, the Ga ions were implanted to the tip apex area to act as a mask since Ga metal is resistant to fluorine-based plasma etching. For the above three approaches, silicon etching is very critical, so Chapter 5 covers our effort in developing silicon etching recipes using a non-switching pseudo-Bosch process with C4F8-SF6 gas, with a goal of obtaining vertical sidewall profile needed for HAR, high selectivity to mask, and high etching rate. As well, the etched silicon structures must be further sharpened to reduce its apex radius to below 10nm. So, Chapter 4 covers the process optimization of the oxidation sharpening process that involves thermal oxidation and subsequent oxide etching by HF. It was found that 950°C is a suitable oxidation temperature, and the oxidation sharpening can be carried out more than once to improve tip sharpness. Lastly, inspired by the first approach described above, we also developed the fabrication process for “edge probe”, for which the tip apex sits right at the end of the cantilever, and thus the tip location can be precisely determined in the view of the integrated optical microscope in an AFM system. Our method involves angle evaporation of a hard mask layer onto the AFM probe, followed by silicon dry etching that etches away the area not covered by the metal layer, i.e., the shadow area of the pyramid-shaped tip

Developing integrated optical structures, with special respect to applications in medical diagnostics

In my dissertation, I described two label-free optical biosensors based on integrated optical (IO) structures for the sensitive, rapid detection of pathogens - bacterial cells, viral proteins - from fluid samples, which can serve as a basis for rapid clinical tests. These types of devices provide a specific, cost-effective, user-friendly and portable way of detection with sufficient sensitivity by changing the optical signal. Thus, in practice, they could potentially be used as point-of-care (POC) or home rapid diagnostic tests, offering a promising alternative to traditional laboratory assays. Their realization is supported by their integration with microfluidic channels in a lab-on-a-chip (LOC) device, for handling small volumes of fluid. Based on these aspects, biosensors were designed as waveguides, integrated in a microfluidic channel on a glass substrate, performing evanescent-field sensing. The detection method is based on the fact that the light, propagating in the waveguide with total internal reflections, penetrates into the surrounding media at a limited extent, which is called the evanescent field. Material can enter this space and become bound to the surface, which can change the phase of the light, propagating in the structure, or even scatter it into the surrounding medium. These phenomena offer the possibility of specific detection of pathogens, adhering to the surface, pre-coated with a biological recognition element, such as an antibody. As a first application, an electro-optical biosensor was developed with an evanescent field-based detection concept, aiming at label-free, rapid, selective and sensitive detection of bacteria from body fluids. The usability of the measurement principle, based on the processing of light-scattering patterns, caused by evanescent waves, scattered on target cells, was demonstrated by quantitative detection of Escherichia coli bacterial cells from their suspensions. One of the keys to the applicability of biosensors is their sensitivity. To increase it in case of this device, I applied the phenomenon of dielectrophoresis using the polarizability of the target cells. It provides the possibility to selectively collect cells on the surface of electrodes placed close to the waveguide and then detect them based on the evanescent field. To test this, I wanted to sense bacteria in an artificial urine sample containing somatic cells, in this case endothelial cells, mimicking urine in an inflammatory state. By optimizing the parameters of the measurements, a rapid, sensitive bacterial detection of about 10 minutes was achieved. The detection limit of the biosensor was comparable to the characteristic pathogen concentration in body fluids. Furthermore, selective bacterial detection was also achieved from a fluid sample containing somatic cells, mimicking inflammatory urine. In my dissertation, a second application is also presented, in this case a miniature IO Mach-Zehnder interferometer-based biosensor was developed for the specific quantitative detection of viral proteins. Thanks to the interferometric measurement principle, a fast and accurate detection of target proteins can be achieved. With this device, the aim was to investigate the potential neuroinvasion of coronavirus (SARS-CoV-2) infection, from which point of view the pathological effects of viral surface spike proteins on the blood-brain barrier are of great importance in the case of severe symptoms. Furthermore, infection may also cause adverse effects in the intestinal tract. Thus, the specific aim of this application was to evaluate the ability of the S1 subunit of the coronavirus surface spike protein to cross the human in vitro blood-brain barrier and intestinal epithelial biological barrier system models using the biosensor. Experiments were designed to use the sensor for specific, quantitative detection of spike proteins, that may have been passed through permeability assays on biological barrier models prepared by our collaborators. To reach the specific sensing of the target protein, the waveguide surface of the interferometer’s measuring arm was functionalized with specific S1 protein antibody. To achieve optimal, stable measurement conditions, the operating point of the interferometer was adjusted thermo-optically. The results of the experiments with the biosensor were in agreement with the ones of the conventional immunological tests (ELISA) carried out in parallel. It was possible to determine that S1 protein could pass through the two types of barriers in different amounts. The findings of the experiments with the integrated optical Mach-Zehnder interferometer biosensor demonstrate that this detection approach can be used for similar medical diagnostic purposes, and thus can contribute to the investigation of the adverse effects of SARS-CoV-2 on the human body

A novel PCR based DNA microanalyzer system for detection of viral genome

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file viewed on (April 25, 2007)Vita.Thesis (Ph.D.) University of Missouri-Columbia 2006.A micro-fluidic assay to quickly analyze microscopic samples of DNA is being developed for field applications. It consists of a micro-PCR chamber, micropumps, and micro-heaters. Additional components of the device include gel electrophoresis microchannels and solid core waveguide fluorescence collectors. The intended analyzer is a micro-fluidic platform that is principally based on the three-step polymerase chain reaction (PCR) mechanism. Currently, all off chip control is executed using a labview code. The micro-pumps, PCR chamber and capillary electrophoresis system have been designed fabricated and tested. For fabrication of the device, a regime has been developed for bonding PDMS surfaces to a variety of substrates (silicon in the present case). We have successfully achieved a compression in the cycle time by a factor of ten in our on chip PCR reactor as compared to the conventional PCR system and also amplify samples with pico-gram concentration. Fluorescent studies indicate negligible non-specific binding to our chip which has been a major problem in earlier assays. A working electrophoretic capillary and new biphasic gel material with extremely low background and high signal to noise ratio have been developed. We have further achieved low voltage capillary electrophoresis by doping different gel materials with conducting nano-particles. We envision this assay as a highly sensitive field deployable analyzer tool.Includes bibliographical reference

Tin Catalyst preparation for Silicon Nanowire synthesis

>Magister Scientiae - MScSolar cells offer SA an additional energy source. While Si cells are abundantly available they are not at an optimal efficiency and the cost is still high. One technology that can enhance their performance is SiNW. However, material properties such as the diameter, porosity and length determine their effectiveness during application to solar cell technology. One method of growing SiNW uses Sn catalysts on a Si substrate. As the properties of the Sn nanoparticle govern the properties of the SiNW, this thesis investigates their formation and properties by depositing a Sn layer on a Si wafer and then subjecting it to different temperatures, during process the layer forms into nanoparticles. At each temperature the morphology, composition and crystallinity will be determined using XPS, SEM, TEM and EDS. Thus, in Chapter 1 there is an overview, Chapter 2 deals with techniques used in this study, Chapter 3 will give the quantitative and qualitative results on the XPS analysis and Chapter 4 will illustrate the structural behaviour of the annealed Sn film samples

Polymer Processing and Surfaces

This book focuses on fundamental and applied research on polymer processing and its effect on the final surface as the optimization of polymer surface properties results in the unique applicability of these over other materials. The development and testing of the next generation of polymeric and composite materials is of particular interest. Special attention is given to polymer surface modification, external stimuli-responsive surfaces, coatings, adhesion, polymer and composites fatigue analysis, evaluation of the surface quality and microhardness, processing parameter optimization, characterization techniques, among others

Index to 1986 NASA Tech Briefs, volume 11, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1986 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Flexible ZnO thin film-based surface acoustic wave devices for environmental and biomedical sensing applications

Flexible ZnO thin film on aluminium foil-based SAW devices have been investigated for the first time as sensors for temperature, UV light, and humidity as well as breath and apnoea detection, and these devices were performing sensing while they were placed in flat and bending (curved) positions. Flexible SAW devices offer a promising technology of low cost, highly sensitive and bendable sensors. They also exhibit high potential for wearable, point of care and microfluidics and lab-on-chips applications. The ZnO thin film was deposited on the aluminium foil and ZnO nanorods were grown on the surface of selected samples. The SAW sensors were fabricated by patterning Au/Cr IDTs with various wavelengths. Film and nanorods possessed the preferred structure and piezoelectric properties. Lamb modes were identified, and they were in a good agreement with the FEA results. The maximum value of TCF was -773 ppm/K which is among the highest values mentioned in the literature. The sensors showed excellent linearity and repeatability during temperature cycling test. The maximum value of sensitivity to UV light was 63 ppm (mW/cm2)-1. ZnO nanorods enhanced the sensitivity by 1.76 times. The sensors showed excellent repeatability and reliability during UV light cycling in flat, bent-up and bent-down positions. The maximum values of sensitivity to humidity were 47.7 kHz at 90%RH for nanorodenhanced device and the maximum frequency shift was -57 kHz. The sensors exhibited good repeatability in response to humidity cycling. Besides, the devices exhibited an excellent response, sensitivity, and reliability for various breath patterns (e.g., healthy breathing, apnoea, slow and fast breathing)