TECHNOLOGY DIGEST - Draper Laboratory

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ionization source. Once ionized, the sample is transported by a carrier gas through an ion filter toward the detecting electrodes (Faraday plates). The electric field that is applied between the parallel ion filter electrodes can be adjusted to tune the ion filter. Two fields are applied across the parallel plates: an asymmetric waveform electric field alternating between high- and low-strength fields, and a low-strength DC compensation voltage. The asymmetric field amplitude is held constant while the compensation voltage levels are adjusted to allow a particular ion species to pass through the ion filter. Once the ion species passes through the ion filter, it is detected upon collision with the detector electrodes as an ion current. Uncompensated ions are scattered toward the ion filter electrodes, neutralized, and swept out by the carrier gas. By noting the applied field conditions (voltages) and the current level at the detector electrode, various ion species can be identified. The DMS can also be programmed to sweep through a range of compensation voltages over a specified amount of time (seconds). This is beneficial as it allows simultaneous detection of various ion species that originate from the same sample. An example of a DMS chip is shown in Figure 2(a); a development platform (Sionex Corporation, Waltham, MA) designed for proof of principle and user evaluation is shown in Figure 2b. 34 Sample Detection of Biological and Chemical Agents Using Differential Mobility Spectrometry (DMS) Technology Pyrolysis ∆H 67-keV Ionization 63Ni Figure 1. Schematic of pyrolysis-DMS operation. A solid or liquid sample is pyrolyzed, and the fragments are then ionized as they flow past a radioactive nickel source. The ions are then swept into the drift tube of the DMS where they are separated based on their mobility in the applied electric fields. Under the appropriate compensation voltage, an ion will leave the drift tube and strike a Faraday plate that detects the strike based on the charge transfer. + + Drift Tube + Compensation Electric Field Drift Tube V Detector RF Electric Field Detector (+) Figure 2. (a) Picture of a DMS chip. The drift tube region and detectors are shown with arrows. (b) Photograph of a hand-held Sionex Corporation, Inc. DMS prototype unit. Bacillus Spore Preparation B. subtilis spores were selected as a surrogate for B. anthracis to evaluate the ability of the DMS to detect these spores. B. subtilis strain SMY, a wild-type, prototrophic, Marburg strain (obtained from P. Schaeffer), [42] was pregrown overnight at 30°C on a plate of tryptose blood agar base (Difco Laboratories, Franklin Lakes, NJ) and used to inoculate 2-L of DS medium [43] in a 6-L Erlenmeyer flask. The flask was incubated with shaking (200 rpm) at 37°C for 48 hours. The cells were harvested by centrifugation at 13,000 x g for 20 min at 4°C, washed four times with 100ml sterile, deionized water, and resuspended in 20-ml sterile water. The suspension was estimated to contain 95% mature, refractile spores by phase contrast (-)
Detection of Biological and Chemical Agents Using Differential Mobility Spectrometry (DMS) Technology microscopy. The spore titer was determined by assaying colony formation on DS agar plates after heating to 80°C for 10 min. Spores were diluted in sterile water when lower concentrations were required for testing. The Effect of Pyrolysis on B. subtilis Spores as Determined by SDS-PAGE Pyrolysis was used as the sample introduction technique tested to volatilize the spores before entering the DMS. The Pyroprobe 1000 from CDS Analytical, Inc. (Oxford, PA) was used. This unit is fabricated to interface with a GC inlet port. A slurry containing spores resuspended in sterile water was loaded into a quartz tube (2.5 mm outer diameter, 1.95 mm inner diameter, 25.5 mm length) that was placed in the pyrolysis probe. The probe was then loaded into the pyrolysis unit, which has a nitrogen environment. The sample can then be pyrolyzed, and if there is gas flow, it will be carried out of the pyrolysis unit and into a GC column. For these experiments, we used a 0.5-m deactivated fused silica column only (Agilent Technologies, Palo Alto, CA). To better understand the effect of pyrolysis on B. subtilis spores, the spores were pyrolyzed using various conditions and examined using denaturing polyacrylamide gel electrophoresis (SDS-PAGE). Fifteen µg of spores (approximately 1.5e8 spores) resuspended in water were exposed initially to 110°C interface temperature and then pyrolyzed at a ramping rate of 0.01°C/ms under each of the following conditions: 250°C, 5 s; 250°C, 10 s; 350°C, 5 s; 350°C, 10 s; 450°C, 5 s; 450°C, 10 s; 550°C, 5 s; and 550°C, 10 s; 600°C, 5 s; 650°C, 5 s; 700°C, 5 s; 750°C, 5 s; 800°C, 5 s; 850°C, 5 s; and 900°C, 5 s. The pyrolyzed samples were recovered with Laemmli sample buffer (Bio-Rad), and dithiothreitol (DTT) was added to a final concentration of 300 mM to denature the proteins prior to SDS-PAGE analysis. The samples were then placed in boiling water for 5 min and run on a gradient 4-20% tris-glycine polyacrylamide gel (Bio-Rad, Hercules, CA). A sample of 1.5 µg of spores that were not pyrolyzed or exposed to the 110°C interface temperature was included as a control. As the gradient gels consist of a gradually increasing density of polyacrylamide matrix, proteins can often stain unevenly. We found that the larger proteins in the more permeable matrix in the top area of the gel are able to stain more efficiently than those that are smaller and found in the thicker polyacrylamide matrix at the bottom of the gel. To minimize the disproportionate staining, we found that it was best to prestain the gel initially with Coomassie Blue, destain the gel, and then stain with silver to produce uniform results. Other groups have used the technique of consecutive Coomassie Blue and silver staining in the examination of proteins separated by electrophoresis in gradient gels, [44] and silver staining reveals proteins at lower concentration levels than other analytical methods. The gels were stained in a 40% methanol/10% acetic acid/ 0.01% Coomassie Blue R-250 solution for 1 h, and then destained in a 40% methanol/10% acetic acid solution overnight. The gels were then prepared for silver staining by washing twice in deionized water for 30 min. The Silver Stain Plus Kit (Bio-Rad) was used to silver stain the gels for 20 min, with the silver stain solution made per manufacturer instructions. The staining reaction was stopped by exposing the gel to a 5% acetic acid solution for 20 min, and the gels were then washed with deionized water for an additional 20 min before recording the results by digital photography. Bacillus Spore Analysis Using DMS Pyrolysis was the sample introduction method for DMS analysis of spores. The pyrolysis unit was attached to an inlet port of an HP 5890 GC. The sample was pyrolyzed and swept into 0.5 m of a fused silica guard column with the carrier gas, helium (He), at 150 ml/min flow. This flow exited the GC oven and joined 50 ml/min nitrogen (N2) flow to enter the DMS. Mass flow controllers (MKS Instruments, Andover, MA) were used to ensure constant volumetric flow of the carrier gases. The GC oven temperature was set to a 250°C constant temperature. The DMS was programmed so that the compensation electric field swept through a range of voltages from -40 to 10 V every 1.6125 s. The RF field was set to 1200 V. The detection of ions at the various compensation voltages over time is recorded on a laptop computer that is connected to the DMS unit. Ten 4-µl sterile water samples were pyrolyzed and their spectra from the DMS recorded. These spectra give the background signal of the water in which the spores were resuspended. Next, 10 samples of 120,000 spores (3 x 108 spores/ml slurry) were pyrolyzed and the DMS spectra recorded. Finally, 10 samples of 40,000 spores (1 x 107 spores/ml slurry) were pyrolyzed. The pyrolysis unit was held at a 150°C interface temperature, and the samples were pyrolyzed at 550°C for 100 s, with a 20°C/ms ramping rate. The spectra were analyzed using OriginPro 7.0 and the data graphed as the signal intensity vs. the compensation voltage. Each plotted line is the signal average of 25 voltage sweeps after spore pyrolysis in a single experiment. The baseline of all data signals was shifted to zero, and the maximum absolute value across each scan was calculated. Each spectral sweep was then normalized at the highest peak. Simulant Nerve and Blister Agent DMS Detection Solutions of methyl salycilate (MS) (Kintek, La Marque, TX), a simulant nerve agent, were made at the following concentrations: 344 parts-per-billion (ppb), 57 ppb, 9.5 ppb, 1.6 ppb, 0.27 ppb, and 0.045 ppb. These solutions were analyzed with the DMS. The intensity of the signal was examined as a function of concentration. Next, solutions of MS and dimethyl methyl phosphonate (DMMP) (Kintek, La 35
Page 1 and 2: THE DRAPER TECHNOLOGY DIGEST 2006 V
Page 3 and 4: Introduction by Vice President, Eng
Page 5 and 6: niversary N O L O G Y D I G E S T e
Page 7 and 8: Bias Table 1. Typical SOA Performan
Page 9 and 10: A series expansion of Eq. (3) can b
Page 11 and 12: photo-maskset needed to fabricate t
Page 13 and 14: SF (ppm) & Bias (µg) 2.0 1.5 1.0 0
Page 15 and 16: The Silicon Oscillating Acceleromet
Page 17 and 18: The Flight Hardware Configuration A
Page 19 and 20: integrated and validation tested, f
Page 21 and 22: about a 25% base deflection. The la
Page 23 and 24: FalconView graphical map interface
Page 25 and 26: Table 1. Initial GN&C-Related Drago
Page 27 and 28: Autonomous Guidance, Navigation, an
Page 29 and 30: opposite side of the cell back to a
Page 31 and 32: Heat loss due to gas conduction was
Page 33 and 34: REFERENCES [1] X-72 Data Sheet, htt
Page 35: Detection of Biological and Chemica
Page 39 and 40: Intensity (a.u.) Detection of Biolo
Page 41 and 42: shown here, we could move toward a
Page 43 and 44: Detection of Biological and Chemica
Page 45 and 46: Autonomous Mission Management for S
Page 47 and 48: capable of instantiating the agent
Page 53 and 54: Error (m) RESULTS Autonomous Missio
Page 59 and 60: A micromechanical tuning-fork gyros
Page 61 and 62: where σ is the squeeze number, [3]
Page 63 and 64: y 1 0.8 0.6 0.4 0.2 0 0 0.2 0.4 0.6
Page 65 and 66: Solving for the pressure nodes simu
Page 67 and 68: Output Voltage (V) 1 0.8 0.6 0.4 0.
Page 69 and 70: (49) where µ is 1.9e-5 N-s/m2 for
Page 71 and 72: Fluid Effects in Vibrating Micromac
Page 73 and 74: Barton, G.; Marinis, T.; Pryputniew
Page 75 and 76: Gustafson, D.; Dowdle, J.; Monopoli
Page 77 and 78: Sawyer, W.; Prince, M.; Brown, G. S
Page 79 and 80: Low-Cost, Low-Power Geolocation Sys
Page 81 and 82: The Optically Rebalanced Accelerome
Page 83 and 84: Anderson, R.; Connelly, J.; Hanson,
Page 85 and 86: The 2006 Charles Stark Draper Prize
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The Howard Musoff Student Mentoring
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MacLellan, S.; Supervisor: Staugler
Page 91 and 92:
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