Robert W. Crocker

High-pressure microhydraulic actuator

Electrokinetic (“EK”) pumps convert electric to mechanical work when an electric field exerts a body force on ions in the Debye layer of a fluid in a packed bed, which then viscously drags the fluid. Porous silica and polymer monoliths (2.5-mm O.D., and 6-mm to 10-mm length) having a narrow pore size distribution have been developed that are capable of large pressure gradients (250-500 psi/mm) when large electric fields (1000-1500 V/cm) are applied. Flowrates up to 200 μL/min and delivery pressures up to 1200 psi have been demonstrated. Forces up to 5 lb-force at 0.5 mm/s (12 mW) have been demonstrated with a battery-powered DC-DC converter. Hydraulic power of 17 mW (900 psi@ 180 uL/min) has been demonstrated with wall-powered high voltage supplies. The force and stroke delivered by an actuator utilizing an EK pump are shown to exceed the output of solenoids, stepper motors, and DC motors of similar size, despite the low thermodynamic efficiency.

Electrokinetically Pumped Liquid Propellant Microthrusters for Orbital Station Keeping

For most orbital maneuvers, small satellites in the sub-10 kg range require thrusters capable of spanning the micro-Newton to milli-Newton force range. At this scale, electrokinetic (EK) pumping offers precise metering of monergolic or hypergolic liquid propellants under purely electrical control at pressures and flow rates well-suited to microthruster applications. We have demonstrated direct and indirect EK pumping for delivery of anhydrous hydrazine and hydrogen peroxide monopropellants, respectively, into capillary-based microthrusters with integrated in-line catalyst beds. Catalytic decomposition generates gases which accelerate through a plasma-formed converging-diverging nozzle, producing thrust. Specific impulses up to 190 s have been shown for hydrazine in non-optimized nozzles.

Analysis of Flow-Cytometer Scattering and Fluorescence Data to Identify Particle Mixtures

As part of the U.S. Department of Homeland Security Detect-to-Protect program, a multilab [Sandia National Laboratories (SNL), Lawrence Livermore National Laboratories (LLNL), Pacific Northwest National Laboratory (PNNL), Oak Ridge National Laboratory (ORNL), and Los Alamos National Laboratory (LANL)] effort is addressing the need for useable detect-to-warn bioaerosol sensors for public facility protection. Towards this end, the SNL team is employing rapid fluorogenic staining to infer the protein content of bioaerosols. This is being implemented in a flow cytometry platform wherein each particle detected generates coincident signals of forward scatter, side scatter, and fluorescence. Several thousand such coincident signal sets are typically collected to generate a probability distribution over the scattering and fluorescence values. A linear unmixing analysis is performed to differentiate components in the mixture. After forming a library of pure component distributions from measured pure material samples, the distribution of an unknown mixture of particles is treated as a linear combination of the pure component distributions. The scattering/fluorescence probability distribution data vector a is considered the product of two vectors, the fractional profile f and the scattering/fluorescence distributions from pure components P. A least squares procedure minimizes the magnitude of the residual vector e in the expression a = fPT + e. The profile f designates a weighting fraction for each particle type included in the set of pure components, providing the composition of the unknown mixture. We discuss testing of this analysis approach and steps we have taken to evaluate the effect of interferents, both known and unknown.

Injection molded microfluidic devices for biological sample separation and detection

We are developing a variety of microsystems for the separation and detection of biological samples. At the heart of these systems, inexpensive polymer microfluidic chips carry out sample preparation and analysis. Fabrication of polymer microfluidic chips involves the creation of a master in etched silicon or glass; plating of the master to produce a nickel stamp; large lot chip replication by injection molding; precision chip sealing; and chemical modification of channel surfaces. Separation chips rely on insulator-based dielectrophoresis for the separation of biological particles. Detection chips carry out capillary electrophoresis to detect fluorescent tags that identify specific biological samples. Since the performance and reliability of these microfluidic chips are very sensitive to fluidic impedance, electromagnetic flux, and zeta potential, the microchannel dimensions, shape, and surface chemistry have to be tightly controlled during chip fabrication and use. This paper will present an overview of chip design, fabrication, and testing. Dimensional metrology data, surface chemistry characterization, and chip performance data will be discussed in detail.

Fabrication and characterization of polymer microfluidic devices for bio-agent detection

Sandia and Lawrence Livermore National Laboratories are developing a briefcase-sized, broad-spectrum bioagent detection system. This autonomous instrument, the BioBriefcase, will monitor the environment and warn against bacterium, virus, and toxin based biological attacks. At the heart of this device, inexpensive polymer microfluidic chips will carry out sample preparation and analysis. Fabrication of polymer microfluidic chips involves the creation of a master in etched glass; plating of the master to produce a nickel stamp; large lot chip replication by injection molding; and thermal chip sealing. Since the performance and reliability of microfluidic chips are very sensitive to fluidic impedance and to electromagnetic fluxes, the microchannel dimensions and shape have to be tightly controlled during chip fabrication. In this talk, we will present an overview of chip design and fabrication. Metrology data collected at different fabrication steps and the dimensional deviations of the polymer chip from the original design will be discussed.

Confirmatory measurement channels for LIF-based bioaerosol instrumentation

As part of the U.S. Department of Homeland Security Detect-to-Protect (DTP) program, a multilab [Sandia National Laboratories (SNL), Lawrence Livermore National Laboratories (LLNL), Pacific Northwest National Laboratory (PNNL), Oak Ridge National Laboratory (ORNL), and Los Alamos National Laboratory (LANL)] effort is addressing the need for useable detect-to-warn bioaerosol sensors for public facility protection. Towards this end, the SNL team is investigating the use of rapid fluorogenic staining to infer the protein content of bioaerosols. This is being implemented in a flow cytometer wherein each particle detected generates coincident signals of correlated forward scatter, side scatter, and fluorescence. Several thousand such coincident signal sets are typically collected to generate a distribution describing the probability of observing a particle with certain scattering and fluorescence values. These data are collected for sample particles in both a stained and unstained state. A linear unmixing analysis is performed to differentiate components in the mixture. In this paper, we discuss the implementation of the staining process and the cytometric measurement, the results of their application to the analysis of known and blind samples, and a potential instrumental implementations that would use staining.

Application of Microseparation Arrays to the Detection of Biotoxins in Aerosol Backgrounds

We are investigating the use of parallel separation channels that utilize orthogonal separation techniques as a platform for a biosensor to accurately identify protein biotoxins. Two separation techniques were initially chosen for proof of concept demonstration—capillary zone electrophoresis (CZE) and capillary gel electrophoresis (CGE)—and have been implemented in our compact “µChemLab™” device. This device integrates automated high-voltage control of microchip-based separations with laser-induced fluorescence (LIF) detection and on-board data analysis. The effectiveness of this two-channel approach was evaluated using biotoxin-spiked aerosol samples.

EDS Containment Vessel Explosive Test and Analysis

This report documents the results of two of tests that were performed on an explosive containment vessel at Sandia National Laboratories in Albuquerque, New Mexico in July 2013 to provide some deeper understanding of the effects of charge geometry on the vessel response [1]. The vessel was fabricated under Code Case 2564 of the ASME Boiler and Pressure Vessel Code, which provides rules for the design of impulsively loaded vessels [2]. The explosive rating for the vessel, based on the Code Case, is nine (9) pounds TNT-equivalent. One explosive test consisted of a single, centrally located, 7.2 pound bare charge of Composition C-4 (equivalent to 9 pounds TNT). The other test used six each 1.2 pound charges of Composition C-4 (7.2 pounds total) distributed in two bays of three.Copyright

Engineered Improvement of the Generation-2 μChemlab™ Biotoxin Detector

The μChemLab™ program is developing hand-portable systems for detecting a broad range of chemical, biological, and viral agents in both gas and liquid samples. The μChem Lab liquid sample analyzer employs electrokinetic sample injection, chip-based electrophoretic microseparations and laser-induced florescence detection to analyze liquid samples. A second-generation liquid phase prototype is described. The device incorporates improvements from technological advances and applied research experience. New features include a modular design that readily accommodates on-chip preconcentration and additional separation techniques. The redesign reduces hardware failures, minimizes downtime during component replacement, improves usability, and provides increased sensitivity. Improvements have been made without compromising previous system performance.