Index to 1981 NASA Tech Briefs, volume 6, 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 1981 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

Microfluidic devices interfaced to matrix-assisted laser desorption/ionization mass spectrometry for proteomics

Microfluidic interfaces were developed for off-line matrix-assisted laser desorption/ionization mass spectrometry (MALDI). Microfluidic interfaces allow samples to be manipulated on-chip and deposited onto a MALDI target plate for analysis. For this research, microfluidic culturing devices and automated digestion and deposition microfluidic chip platforms were developed for the identification of proteins. The microfluidic chip components were fabricated on a poly(methyl methacrylate), PMMA, wafer using the hot embossing method and a molding tool with structures prepared via micromilling. One of the most important components of the chip system was a trypsin microreactor. An open channel microreactor was constructed in a 100 µm wide and 100 µm deep channel with a 4 cm effective channel length. This device integrated frequently repeated steps for MALDI-based proteomics such as digestion, mixing with a matrix solution, and depositing onto a MALDI target. The microreactor provided efficient digestion of proteins at a flow rate of 1 µL/min with a residence time of approximately 24 s in the reaction channel. An electrokinetically driven microreactor was also developed using a micropost structured chip for digestion. The micropost chip had a higher digestion efficiency due to the higher surface area-to-volume ratio in the channel. Also, the electrokinetic flow eliminated the need for an external pumping system and gave a flat flow profile in the microchannel. The post microreactor consisted of a 4 cm × 200 µm × 50 µm microfluidic channel with trypsin immobilized on an array of 50 µm in diameter micropost support structures with a 50 µm edge-to-edge inter-post spacing. This micropost reactor was also used for fingerprint analysis of whole bacterial cells. The entire tryptic digestion and deposition procedure for intact bacteria took about 1 min. A contact deposition solid-phase bioreactor coupled with MALDI-TOF MS allowed for low-volume fraction deposition with a smaller spot size and a higher local concentration of the analyte. A bacterial cell-culturing chip was constructed for growing cells on-chip followed by off-line MALDI analysis. Coupling MALDI-TOF MS whole cell analysis with microfluidic culturing resulted in more consistent spectra as well as reduction of the total processing time. The microfluidic cell culturing was performed in a PMMA chip with a polydimethylsiloxane (PDMS) cover to allow gas permeation into the culture channel, which contained a 2.1 μL volume active culture chamber. After incubation of E. coli in a microfluidic culture device at 37 ℃ for 24 h, the cultured cells were analyzed with MALDI MS. Also, a microfluidic cell culture device containing continuous perfusion of culture medium was developed using a polycarbonate membrane. This microfluidic culturing format was improved with a fluidic manifold and thermostatted microheaters. Fingerprint mass spectra distinguishing E. coli strains tested were obtained after a 6 h incubation time, which was shorter compared to the 24 h incubation time using conventional culturing techniques. In addition, an enhanced identification procedure for bacteria was achieved by integrating on-chip digestion of cultured bacteria

Electrokinetically forced turbulence in microfluidic flow.

While laminar flow heat transfer and mixing in microfluidic geometries has been investigated experimentally, as has the effect of geometry-induced turbulence in microfluidic flow (it is well documented that turbulence increases convective heat transfer in macrofluidic flow), little literature exists investigating the effect of electrokinetically-induced turbulence on heat transfer at the micro scale. Successful research in this area could be invaluable in creating more efficient heat exchangers for emerging microscale electronics as well as to fields requiring greater control of mixing in microfluidic devices

Light-emitting diodes and photodiodes in the deep ultra-violet range for absorption photometry in liquid chromatography, capillary electrophoresis and gas sensing

Absorbance measurement in the deep ultra-violet range (below 300 nm) has been one of the most widely used detection methods for analytical techniques as a large number of organic compounds have strong absorption bands in the deep UV region. The use of incandescent or discharge lamps coupled to a monochromator for the wavelength selection in a conventional UV detector makes it complex and costly. Light-emitting diodes (LEDs) for the deep UV range commercially available in recent years have become potential alternatives to thermal light sources. LEDs with their relatively narrow emission bandwidths (typically 20 nm) are well suited for absorption photometry in which a monochromator is not required. This dissertation, therefore, concerns the utilization LEDs and photodiodes (PDs) in the deep UV range as radiation sources and light detectors, respectively for absorption photometry in high-performance liquid chromatography (HPLC), capillary electrophoresis (CE) and gas sensing. LEDs were known to perform as light detectors. In measuring systems based on LEDs as light sources, PDs have been normally employed for detection devices. The practical reasons for the use of LEDs as alternatives to PDs, however, have not been demonstrated. Only an advantage of cost-saving was pointed out. In the first project, the performance of LEDs in the light intensity measurement was investigated and compared to that of standard silicon PDs in three different measuring configurations: current follower mode to measure to photocurrents, photovoltaic mode to determine the voltage developed across the diode on irradiation without load and discharge time mode to measure the rate to discharge the junction capacitance of diodes. LEDs as detectors were generally found to be adequate for the analytical work but PDs offered higher sensitivity and linearity as well as provided stable readings with faster settling times. Absorbance detectors for narrow-column HPLC (250 μm inner diameter) and CE (50 μm inner diameter) based on deep UV-LEDs and PDs selective for emission wavelengths were developed and evaluated in the quantification of model compounds at 255 and 280 nm. Absorbance measurements were directly obtained by the use of a beam splitter and PDs for reference signals and a logarithmic ratio amplifier-based circuitry to emulate the Lambert-Beer’s law. Narrow-column HPLC is useful for the applications in which the reduction in eluent consumption is desired or only limited amount of samples is available when utmost sensitivity is not required. In CE, the use of a capillary as the separation channel to minimize the peak broadening downscales the detection window to micrometer range which is even much narrower than that of a narrow-bore HPLC. This makes the design and construction of these LED-based detectors for narrow detection channels more challenging than for a standard HPLC as the higher efficiency for light coupling and stray light avoidance is essentially required. Additionally, high mechanical stability is needed to minimize the noise resulted from mechanical fluctuations. The performance of these optical devices at two measured wavelengths was excellent in terms of the baseline noise (low μAU range), linearity between absorbance values and concentrations (correlation coefficients > 0.999) and reproducibility of peak areas (about 1%). Not only was the potential of a deep UV-LED as a radiation source for absorption spectroscopy investigated for separation techniques but also for the detection of benzene, toluene, ethylbenzene and the xylenes compounds in the gas phase at 260 nm. In the first part of this work, its performance in the acoustic waves excitation was preliminarily investigated with some different measuring systems for the detection of the toluene vapor. It was found that the intensity of a deep UV-LED was insufficient to produce detectable acoustic signals. This was followed by the construction of an absorbance detector for the determination of these target compounds based on the combination of a deep UV-LED and PDs. This optical device was designed to use optical fibers for the light coupling from the LED to a measuring cell and a reference PD, that allows removing a beam splitter previously required for detectors of a narrow column HPLC and CE. Its performance with regard to linearity and reproducibility was satisfactory. Detection limits of about 1 ppm were determined. It could be concluded that viable absorbance detectors for narrow-column HPLC, CE and gas sensing based on deep UV-LEDs and PDs as light sources and light detectors, respectively can be constructed. The performance of these inexpensive LED-based optical devices with regard to linearity, reproducibility and baseline noise was satisfactory and found to be comparable to that of more complex and expensive commercial detectors. These detectors with features of low power consumption and small size are useful for portable battery-powered devices

Micro-mechanical logic for field produceable gate arrays

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2005.Includes bibliographical references (leaves 106-110).A paradigm of micro-mechanical gates for field produceable logic is explored. A desktop manufacturing system is sought after which is capable of printing functional logic devices in the field. A logic scheme which induces non-linearities via geometrical properties is considered. Logic devices in two-phase air-water fluid-dynamic system at micron scales are constructed. A systematic study of non-linearities and relevant force fields in fluid dynamics at low Reynolds Number is undertaken. Viscous forces dominate inertial forces at low Reynolds Number flows at low pressure. Thus devices based on non-linear inertial effects at high Reynolds numbers can not be scaled down to micron-sizes. Bubble microfluidic logic gates are invented to tackle the above problem, thus producing low Reynolds Number logic in Newtonian fluids. Various devices including AND/OR gates, NOT gate, nonvolatile bistable memory, shift registers and ON/OFF flow valves, based on this new scheme of bubble bubble interaction in microfluidic devices to induce non-linearity, are designed and characterized. On-chip bubble generators and annihilators are used for encoding and destroying information in bubble logic devices.(cont.) Applications of the above described logic devices as a flow control strategy for droplet based Lab-on-chip devices is explored. A simple to construct in-situ pressure sensor based on the principle of compressibility of an air bubble in microfluidic devices is invented. A scheme of controlled bubble/droplet movement in shift registers via pulsating pressure fields for precise temporal control of start of microfluidic reactions is proposed. Excimer laser micro-machining of boro-silicate glass is developed to direct write 3D microfluidic structures. Laser ablation process using a ArF based 193nm laser for machining is characterized using laser confocal microscopy techniques. Single bubble cavitation induced by laser pulses is developed as a process for writing micro-bubbles at precise locations in microfluidic channels.by Manu Prakash.S.M