Publications

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A thin flow-focusing microfluidic channel is evaluated for generating monodisperse liquid droplets. The microfluidic device is used in its native state, which is hydrophilic, or treated with OTS to make it hydrophobic. Having both hydrophilic and hydrophobic surfaces allows for creation of both oil-in-water and water-in-oil emulsions, facilitating a large parameter study of viscosity ratios (droplet fluid/continuous fluid) ranging from 0.05 to 96 and flow rate ratios (droplet fluid/continuous fluid) ranging from 0.01 to 2 in one geometry. The hydrophilic chip provides a partially-wetting surface (contact angle less than 90°) for the inner fluid. This surface, combined with the unusually thin channel height, promotes a flow regime where the inner fluid wets the top and bottom of the channel in the orifice and a stable jet is formed. Through confocal microscopy, this fluid stabilization is shown to be highly influenced by the contact angle of the liquids in the channel. Non-wetting jets undergo breakup and produce drops when the jet is comparable to or smaller than the channel thickness. In contrast, partially-wetting jets undergo breakup only when they are much smaller than the channel thickness. Drop sizes are found to scale with a modified capillary number based on the total flow rate regardless of wetting behavior. © The Royal Society of Chemistry.

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Micro-Gas-Analyzers have many applications in detecting chemical compounds present in the air. MEMS valves are used to perform sampling of gasses, as they enable control of fluid flow at the micro level. Current generation electrostatically actuated MEMS valves were tested to determine their ability to hold off a given gauge pressure with an applied voltage. Current valve designs were able to hold off 98 psi with only 82 V applied to the valves. The valves were determined to be 1.83 times more efficient than older valve designs, due to increasing the electrostatic area of the valve and trapping oxide between polysilicon layers. Newer valve designs were also proposed and modeled using ANSYS multiphysics, which should be able to hold off 100 psi with only 29 V needed. This performance would be 2.82 times more efficient than current designs, or 5.17 times more efficient than older valve designs. This will be accomplished by further increasing the valve radius and decreasing the gap between the valve boss and electrode.

A liquid metal ESD is being developed to provide electrical switching at different acceleration levels. The metal will act as both proof mass and electric contact. Mercury is chosen to comply with operation parameters. There are many challenges surrounding the deposition and containment of micro scale mercury droplets. Novel methods of micro liquid transfer are developed to deliver controllable amounts of mercury to the appropriate channels in volumes under 1 uL. Issues of hermetic sealing and avoidance of mercury contamination are also addressed.

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We present MEMS polysilicon microvalves for flow control of a rapid analytical microsystem (Micro-Gas-Analyzer, MGA). All valve components (boss, seat, springs, electrodes, and stops) are surface micromachined in the SUMMiT™ microfabrication process. The valves have been characterized at high flow rate when open (60 ml/min air), low leak rate when closed (<0.0025 ml/min Hydrogen, H2), and tunable closing pressures (1 to 35 psig). Active electrostatic valves have been shown to hold closed (voltage on) against a high pressure (>40 psig) for sample loading, open for gas chromatograph (GC) loading (voltage off), and reclose against low pressure 2-5 psig. ©2009 IEEE.

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This document is a safety analysis of a novel neutron detection technology developed by Sandia National Laboratories. This technology is comprised of devices with tiny channels containing high pressure {sup 3}He. These devices are further integrated into large scale neutron sensors. Modeling and preliminary device testing indicates that the time required to detect the presence of special nuclear materials may be reduced under optimal conditions by several orders of magnitude using this approach. Also, these devices make efficient use of our {sup 3}He supply by making individual devices more efficient and/or extending the our limited {sup 3}He supply. The safety of these high pressure devices has been a primary concern. We address these safety concerns for a flat panel configuration intended for thermal neutron detection. Ballistic impact tests using 3 g projectiles were performed on devices made from FR4, Silicon, and Parmax materials. In addition to impact testing, operational limits were determined by pressurizing the devices either to failure or until they unacceptably leaked. We found that (1) sympathetic or parasitic failure does not occur in pressurized FR4 devices (2) the Si devices exhibited benign brittle failure (sympathetic failure under pressure was not tested) and (3) the Parmax devices failed unacceptably. FR4 devices were filled to pressures up to 4000 + 100 psig, and the impacts were captured using a high speed camera. The brittle Si devices shattered, but were completely contained when wrapped in thin tape, while the ductile FR4 devices deformed only. Even at 4000 psi the energy density of the compressed gas appears to be insignificant compared to the impact caused by the incoming projectile. In conclusion, the current FR4 device design pressurized up to 4000 psi does not show evidence of sympathetic failure, and these devices are intrinsically safe.

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We developed prototype chemistry for nucleic acid hybridization on our bead-based diagnostics platform and we established an automatable bead handling protocol capable of 50 part-per-billion (ppb) sensitivity. We are working towards a platform capable of parallel, rapid (10 minute), raw sample testing for orthogonal (in this case nucleic acid and immunoassays) identification of biological (and other) threats in a single sensor microsystem. In this LDRD we developed the nucleic acid chemistry required for nucleic acid hybridization. Our goal is to place a non-cell associated RNA virus (Bovine Viral Diarrhea, BVD) on the beads for raw sample testing. This key pre-requisite to showing orthogonality (nucleic acid measurements can be performed in parallel with immunoassay measurements). Orthogonal detection dramatically reduces false positives. We chose BVD because our collaborators (UC-Davis) can supply samples from persistently infected animals; and because proof-of-concept field testing can be performed with modification of the current technology platform at the UC Davis research station. Since BVD is a cattle-prone disease this research dovetails with earlier immunoassay work on Botulinum toxin simulant testing in raw milk samples. Demonstration of BVD RNA detection expands the repertoire of biological macromolecules that can be adapted to our bead-based detection. The resources of this late start LDRD were adequate to partially demonstrate the conjugation of the beads to the nucleic acids. It was never expected to be adequate for a full live virus test but to motivate that additional investment. In addition, we were able to reduce the LOD (Limit of Detection) for the botulinum toxin stimulant to 50 ppb from the earlier LOD of 1 ppm. A low LOD combined with orthogonal detection provides both low false negatives and low false positives. The logical follow-on steps to this LDRD research are to perform live virus identification as well as concurrent nucleic acid and immunoassay detection.

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A variety of fabrication techniques have been used to make microfluidic microsystems: bulk etching in silicon and glass, plastic molding and machining, and PDMS (silicone) casting. Surprisingly the most widely used method of integrated circuit (IC) fabrication (surface micromachining - SMM) has not been extensively utilized in microfluidics despite its wide use in MEMS. There are economic reasons that SMM is not often used in microfluidics; high infrastructure and start-up costs and relatively long fabrication times: and there are technical reasons; packaging difficulties, dominance of surface forces, and fluid volume scaling issues. However, there are also important technical and economic advantages for SMM microfluidics relating to large-scale batch, no-assembly fabrication, and intimate integration of mechanical, electrical, microfluidic, and nano-scale sub-systems on one chip. In our work at Sandia National Laboratories MDL (Microelectronics Development Lab) we have built on the existing MEMS SMM infrastructure to produce a variety of microfluidic microsystems. These example microsystems illustrate the challenges and opportunities associated with SMM microfluidics. In this paper we briefly discuss two SMM microfluidic microsystems (made in the SUMMiT™ and SwIFT™ processes - www.mdl.sandia.gov/micromachine ) in terms of technical challenges and unique SMM microfluidics opportunities. The two example microsystems are a DEP (dielectrophoretic) trap, and a drop ejector patterning system. Copyright © 2005 by ASME.

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The objective of this LDRD was to develop microdevice strategies for dealing with samples to be examined in biological detection systems. This includes three sub-components: namely, microdevice fabrication, sample delivery to the microdevice, and sample processing within the microdevice. The first component of this work focused on utilizing Sandia's surface micromachining technology to fabricate small volume (nanoliter) fluidic systems for processing small quantities of biological samples. The next component was to develop interfaces for the surface-micromachined silicon devices. We partnered with Micronics, a commercial company, to produce fluidic manifolds for sample delivery to our silicon devices. Pressure testing was completed to examine the strength of the bond between the pressure-sensitive adhesive layer and the silicon chip. We are also pursuing several other methods, both in house and external, to develop polymer-based fluidic manifolds for packaging silicon-based microfluidic devices. The second component, sample processing, is divided into two sub-tasks: cell collection and cell lysis. Cell collection was achieved using dielectrophoresis, which employs AC fields to collect cells at energized microelectrodes, while rejecting non-cellular particles. Both live and dead Staph. aureus bacteria have been collected using RF frequency dielectrophoresis. Bacteria have been separated from polystyrene microspheres using frequency-shifting dielectrophoresis. Computational modeling was performed to optimize device separation performance, and to predict particle response to the dielectrophoretic traps. Cell lysis is continuing to be pursued using microactuators to mechanically disrupt cell membranes. Novel thermal actuators, which can generate larger forces than previously tested electrostatic actuators, have been incorporated with and tested with cell lysis devices. Significant cell membrane distortion has been observed, but more experiments need to be conducted to determine the effects of the observed distortion on membrane integrity and cell viability. Finally, we are using a commercial PCR DNA amplification system to determine the limits of detectable sample size, and to examine the amplification of DNA bound to microspheres. Our objective is to use microspheres as capture-and-carry chaperones for small molecules such as DNA and proteins, enabling the capture and concentration of the small molecules using dielectrophoresis. Current tests demonstrated amplification of DNA bound to micron-sized polystyrene microspheres using 20-50 microliter volume size reactions.

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This is the latest in a series of LDRD's that we have been conducting with Florida State University/Florida A&M University (FSU/FAMU) under the campus executive program. This research builds on the earlier projects; ''Development of Highly Integrated Magnetically and Electrostatically Actuated Micropumps'' (SAND2003-4674) and ''Development of Magnetically and Electrostatically Driven Surface Micromachined Pumps'' (SAND2002-0704P). In this year's LDRD we designed 2nd generation of surface micromachined (SMM) gear and viscous pumps. Two SUMMiT{trademark} modules full of design variations of these pumps were fabricated and one SwIFT{trademark} module is still in fabrication. The SwIFT{trademark} fabrication process results in a transparent pump housing cover that will enable visualization inside the pumps. Since the SwIFT{trademark} pumps have not been tested as they are still in fabrication, this report will focus on the 2nd generation SUMMiT{trademark} designs. Pump testing (pressure vs. flow) was conducted on several of the SUMMiT{trademark} designs resulting in the first pump curve for this class of SMM pumps. A pump curve was generated for the higher torque 2nd generation gear pump designed by Jason Hendrix of FSU. The pump maximum flow rate at zero head was 6.5 nl/s for a 30V, 30 Hz square wave signal. This level of flow rate would be more than adequate for our typical SMM SUMMiT{trademark} or SwIFT{trademark} channels which have typical volumes on the order of 50 pl.

The objective of this LDRD was to develop a uniquely capable, novel droplet solution based manufacturing system built around a new MEMS drop ejector. The development all the working subsystems required was completed, leaving the integration of these subsystems into a working prototype still left to accomplish. This LDRD report will focus on the three main subsystems: (1) MEMS drop ejector--the MEMS ''sideshooter'' effectively ejected 0.25 pl drops at 10 m/s, (2) packaging--a compact ejector package based on a modified EMDIP (Electro-Microfluidic Dual In-line Package--SAND2002-1941) was fabricated, and (3) a vision/stage system allowing precise ejector package positioning in 3 dimensions above a target was developed.

The pump and actuator systems designed and built in the SUMMiT{trademark} process, Sandia's surface micromachining polysilicon MEMS (Micro-Electro-Mechanical Systems) fabrication technology, on the previous campus executive program LDRD (SAND2002-0704P) with FSU/FAMU (Florida State University/Florida Agricultural and Mechanical University) were characterized in this LDRD. These results demonstrated that the device would pump liquid against the flow resistance of a microfabricated channel, but the devices were determined to be underpowered for reliable pumping. As a result a new set of SUMMiT{trademark} pumps with actuators that generate greater torque will be designed and submitted for fabrication. In this document we will report details of dry actuator/pump assembly testing, wet actuator/pump testing, channel resistance characterization, and new pump/actuator design recommendations.

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Electro-microfluidics is experiencing explosive growth in new product developments. There are many commercial applications for electro-microfluidic devices such as chemical sensors, biological sensors, and drop ejectors for both printing and chemical analysis. The number of silicon surface micromachined electro-microfluidic products is likely to increase. Manufacturing efficiency and integration of microfluidics with electronics will become important. Surface micromachined microfluidic devices are manufactured with the same tools as IC's (integrated circuits) and their fabrication can be incorporated into the IC fabrication process. In order to realize applications for devices must be developed. An Electro-Microfluidic Dual In-line Package (EMDIP{trademark}) was developed surface micromachined electro-microfluidic devices, a practical method for getting fluid into these to be a standard solution that allows for both the electrical and the fluidic connections needed to operate a great variety of electro-microfluidic devices. The EMDIP{trademark} includes a fan-out manifold that, on one side, mates directly with the 200 micron diameter Bosch etched holes found on the device, and, on the other side, mates to lager 1 mm diameter holes. To minimize cost the EMDIP{trademark} can be injection molded in a great variety of thermoplastics which also serve to optimize fluid compatibility. The EMDIP{trademark} plugs directly into a fluidic printed wiring board using a standard dual in-line package pattern for the electrical connections and having a grid of multiple 1 mm diameter fluidic connections to mate to the underside of the EMDIP{trademark}.

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Microfluidic devices have applications in chemical analysis, biomedical devices and ink-jets. An integrated microfluidic system incorporates electrical signals on-chip. Such electro-microfluidic devices require fluidic and electrical connection to larger packages. Therefore electrical and fluidic packaging of electro-microfluidic devices is key to the development of integrated microfluidic systems. Packaging is more challenging for surface micromachined devices than for larger bulk micromachined devices. However, because surface micromachining allows incorporation of electrical traces during microfluidic channel fabrication, a monolithic device results. A new architecture for packaging surface micromachined electro-microfluidic devices is presented. This architecture relies on two scales of packaging to bring fluid to the device scale (picoliters) from the macro-scale (microliters). The architecture emulates and utilizes electronics packaging technology. The larger package consists of a circuit board with embedded fluidic channels and standard fluidic connectors. The embedded channels connect to the smaller package, an Electro-Microfluidic Dual-Inline-Package (EMDIP) that takes fluid to the microfluidic integrated circuit (MIC). The fluidic connection is made to the back of the MIC through Bosch etched holes that take fluid to surface micromachined channels on the front of the MIC. Electrical connection is made to bond pads on the front of the MIC.