U.S. Department of Energy Office of Science Office of Scientific and Technical Information

In the OSTI Collections: Microfluidics

Dr. Watson computer sleuthing scientist.

Article Acknowledgement:
Dr. William N. Watson, Physicist
DOE Office of Scientific and Technical Information

Basic microfluidics science and technology  
Applications: biology  
Application: fuel cells  
Applications: nuclear  
References  
Research and Research-Related Organizations  
Reports available through OSTI's SciTech Connect and DOepatents  
Additional Reference

 

 

 

 

 

“The concept of an ideal technological system was introduced by [Genrikh] Altshuller[Wikipedia]; it is a system whose mass, dimensions, cost, energy consumption, etc. are approaching zero, but whose capability to perform the specified function is not diminishing. 

 

The ideal system does not exist as a physical entity while its function is fully performed. 

 

Innovation on Demand, Victor Fey and Eugene Rivin, 2005 (p. 17)

To see if a system that processes fluids is functioning properly, or to restore its proper functioning, or to just understand the system’s function, one often needs to know the composition of the fluids.  One way to determine the composition is to analyze samples.  The smaller the samples one can analyze, the more efficiently one can obtain the information and the less the system’s function is disrupted by the sample extraction.  For a fluid that has a very simple composition, one might ideally not have to extract any samples at all; one could, for instance, see how the fluid affects a light shining on it since different materials affect light differently.[Wikipedia]  But if sampling is necessary, as with a more complex fluid with many different components, the ideal can be approached as one is able to extract and analyze smaller samples. 

 

Fluid systems themselves also approach an ideal if their own functions can be performed with lesser amounts of fluid and smaller processing devices. 

 

Several projects funded by the Department of Energy involve such ideal-approaching microfluidic systems[Wikipedia], which work with microliters (cubic millimeters) or even smaller amounts of fluid.  Many of the projects deal with the analysis of fluids from living organisms.  Several other projects explore microfluidic devices for monitoring nuclear fuel in reprocessing plants to ensure their safe and secure operation.  One recent project is aimed at producing a microfluidic fuel cell with high power-output density.  And still other projects, whose results we’ll look at first, represent advances in understanding the physical processes that occur in microfluidic systems and in developing technologies that make microfluidic systems possible. 

 

Basic microfluidics science and technology

 

Devices with very small features, such as microfluidic channels, can be made from polymers.  One way to do this is to take a liquid monomer[Wikipedia] solution, illuminate appropriate portions of the solution (plus a photoinitiator[Wikipedia] that decomposes into free radicals[Wikipedia] when illuminated) so the monomer molecules react to form a solid of larger polymer molecules, and then remove the still-liquid unexposed monomer.  As long as the removable monomer’s volume corresponds exactly to where the empty spaces are wanted in the resulting device, all is well.  But various byproducts of the reaction may prevent this.  For example, some of the light can reflect, diffuse, or otherwise propagate into the areas not directly exposed to it, solidifying some of the monomer there or at least making it more viscous and hard to remove.  Free-radical byproducts of the reaction may also propagate into the unexposed area and affect the microchannels’ shape and size.  A way to solve these problems is described in the Sandia Corporation patent “Method for forming polymerized microfluidic devices”[DOepatents].  The patented method involves making monomer solution flow through the device during its photopolymerization to facilitate removal of solution that hasn’t been completely polymerized. 

 

The report “Elucidating the role of interfacial materials properties in microfluidic packages”[SciTech Connect] from the Sandia National Laboratories, which are managed by Sandia Corporation, describes a chain of problems that impedes the design and use of a particular class of microfluidic sensors. 

 

“Microsensors for chemical and biological detection have seen relatively little field application because the small size and low cost of the microsensor are offset by the large size, high cost, and complexity of the balance of the sensing system – principally, the required external pumps and valves. Attempts have been made to integrate these components into the sensor’s microfluidic package but success has been limited by the lack of software design tools to simulate microfluidic device performance and the high cost of design-by-intuition and trial-and-error methods. Software simulation, in turn, is limited by in part by our lack of understanding of the materials properties at the interfaces comprising the package and sensor itself. It is also limited to many researchers due to the lack of computing power for these sensors that typically apply to scales from nano to macro (approximately 10-9 m to 10-1 m). Multiscale, multiphysical, and heterogeneous (material properties) models require creative and custom approaches that can be very time intensive and expensive.”  (P. 9.) 

 

The report’s authors accordingly designed experiments to determine material properties relevant to one promising technology:  plastic laminate packaging. 

 

“… plastic laminate packaging provides an attractive combination of low capital and material cost, rapid prototyping, and complex mechanical and fluidic structures. This technology employs a variety of thin polymer and metal films bonded by adhesives, solvents, thermal fusion, and ultrasonic welding. The properties of these interfaces – thermal and electrical conductivity, mechanical deformation, adhesion strength, and chemical resistance – vary from the bulk properties of the laminate films and depend on the laminate composition and joining method employed.”  (P. 9.) 

 

“Several methods [of joining laminates of various materials] were investigated such as adhesives, solvent welding, laser welding, and ultrasonic welding. The adhesive method was the most successful and easy to implement but also one of the more difficult to understand, especially over long periods of time. Welding methods are meant to achieve a bond that is similar to bulk properties and so are easier to predict. However, methods of welding often produce defects in the bonds.”  (P. 38.) 

 

The authors also developed a mathematical model that accounts for the experimentally-discovered properties of the heterogeneous material assemblies, including those of complex adhesives and welding defects, and demonstrated the model’s capabilities by designing, fabricating, and testing a microfluidic valve. 

 

A group of researchers at Los Alamos National Laboratory, the École Normale Supérieure de Cachan in France, and Princeton University investigated a different question:  how does pressure variation along the fluid in a microchannel relate to the fluid’s rate of flow?  It’s been long known that, for a rigid microchannel, the relation is simple:  the flow rate is directly proportional to the difference in pressure between the beginning and end of the channel.  Where the pressure difference is zero (equal pressure at both ends of the channel), the fluid doesn’t flow; as the pressure increases at the beginning or decreases at the end of the channel, the fluid flows faster through it.  But if the channel is flexible—as it can be in a plastic microfluid device—it can deform in response to variations in the fluid pressure.  Furthermore, the fluid pressure and flow can themselves change in response to the channel’s deformation. 

 

So how are the pressure and flow rate related in microchannels that might not be rigid?  The researchers analyzed the problem mathematically for the case of a shallow microchannel, whose depth is much smaller than its width, and gave a slide presentation of their findings at the 66th Annual Meeting of the American Physical Society's Division of Fluid Dynamics (available as “Flow rate—pressure drop relation for deformable shallow microfluidic channels” (rev. 2)[SciTech Connect]).  They determined that once the fluid-microchannel system reaches an equilibrium, the fluid flow rate, instead of being strictly proportional to the pressure difference alone, is approximately proportional to the sum of the pressure difference and another quantity that itself is proportional to the square of the pressure difference and the inverse of the channel’s rigidity.  (For an infinitely rigid channel the second quantity would be zero, so in that special case the flow rate would be proportional to the pressure difference alone and independent of its square, as was already known.)  The group also noted plans to calculate a more refined approximation of the pressure-flow relation and include cases of non-shallow microchannels, determine the pre-equilibrium behavior of the fluid-channel system (possibly important in geophysics), and analyze channels that exhibit viscosity as well as elasticity (possibly important for biomedical uses). 

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Applications:  biology

 

A different slide presentation by a Los Alamos scientist describes “Biomedical Applications of Microfluidic Technology”[SciTech Connect].  While the slides mainly illustrate various aspects of biomedical research that uses microfluidic devices, the first few slides include an overview of the advantages such devices offer.  One advantage is low fluid consumption, which results in less waste, lower costs of reagents[Wikipedia], and smaller sample requirements for diagnostics.  Another advantage is that smaller devices permit faster analyses and respond more quickly, since processes like heating and diffusion of materials take place over shorter distances.  The faster responses of microfluidics allow better process control.  While only a tiny volume of fluid can be analyzed by a single microfluidic device at one time, high throughput can be achieved by operating large numbers of devices in parallel within a small space.  Since the small devices cost less than larger ones, they can be mass-produced.  And the integration of functions on a single device with smaller fluid volume and stored energy makes a microfluidic device safer to use for chemical, radioactive, or biological studies. 

 

Several patents have been issued for microfluidic biotechnology, among them three others assigned to Sandia Corporation. 

 

“Microfluidic devices and methods including porous polymer monoliths”[DOepatents] describes ways to make devices in which fluids flow through pores whose surfaces are treated to react with particular substances within the fluid so that those substances are captured or modified.  The fabrication methods described improve on earlier ones by being cheaper and faster, and producing pores with a narrower distribution of sizes.  Using pores instead of two-dimensional surfaces for the reaction sites may allow the captured or changed substances to reach them through shorter diffusion distances; pores may also offer a higher density of reaction sites than channel surfaces. 

 

The porous monoliths[Wikipedia] contrast with the porous gels described in “Microfluidic device having an immobilized pH gradient and PAGE gels for protein separation and analysis”[DOepatents] and illustrated at the top of Figure 1.  This invention represents the miniaturization of a laboratory process involving sample flows through several centimeters of a gel and the integration of the lab process’ two steps into a single step.  In the first step[Wikipedia] of the lab process, a biological sample is made to flow through the pores of a gel strip in which the pH has a gradient from one end to the other.  Different molecules in the sample, interacting differently with environments that have different pH, will separate along the strip as they stop flowing at different points.  In the second step[Wikipedia], the strip is transferred to a slab gel and the molecules are accelerated by an electric field to flow in a direction perpendicular to the strip.  This time the molecules are further separated in the gel pores, stopping at different points along their direction of travel according to their size and electric charge.  The inventors were able to combine both processes to be executed automatically by a single two-dimensional microfluidic device, with the separation providing significantly higher resolution than existing devices (see middle and bottom of Figure 1). 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Figure 1.  “Microfluidic device having an immobilized pH gradient and PAGE gels for protein separation and analysis”[DOepatents].  Top:  Device with an immobilized polyacrylamide gel along a central microchannel and several intersecting side microchannels, each containing a cross-linked polymerized gel having a constant pH throughout.  Middle:  Sample is introduced along one of the flanking microchannels and driven into the immobilized polyacrylamide gel for separation into molecules that interact differently with environments of different pH.  Bottom:  Molecules at different points along the central channel are accelerated by an electric field along the side channels and stop at points that depend on their size and electric charge. 

 

As Ajit Sadana said on p. ix of his 1998 work Bioseparation of Proteins, “Bioseparation stands at the very center of effective biotechnology development.”  According to “Multidimensional bioseparation with modular microfluidics”[DOepatents], which quotes this statement, “Nothing occurring since 1998 has displaced separation technology from its central place in the biotechnology industry” (column 1, lines 42-44).  This patent notes that

 

“… the separation/analysis of complex chemical mixtures, particularly mixtures arising in connection with bioseparations and/or bioanalysis, is generally a complex multi-step process, typically involving many procedures chosen from a large number of candidate procedures, which can often be carried out in numerous ways (sequencing of steps, choice of solvents, temperature, pH, among others). It is a formidable task to select from this staggering array of possibilities the proper separation/analysis protocol that enables accurate determination of chemical species of interest, for example, biological markers. For biological samples, it is frequently envisioned that the protocol will need to be performed many times on clinical samples derived from many different patients or from the same patient at different stages in the treatment or in the progression of the disease. Thus, it is clearly important to have an effective separation/analysis protocol capable of being performed reliably, rapidly and reproducibly, perhaps hundreds of times per day in a clinical environment with potentially serious consequences for inaccuracies.

“It is also important to be able to test numerous candidate protocols to arrive at one or more protocols meeting the above criteria, or at least approaching those criteria as closely as is feasible. As noted above, multidimensional separations can be enormously powerful but also enormously complex in terms of the number of different techniques that can be interconnected in numerous ways and such techniques can, separately or in cooperation, be run under many different conditions to produce many different separation protocols. As ever more complex separations and analyses are required to meet the ever more complex needs of biological, medical, environmental, chemical and other fields, the full power of multidimensional separations will be required. Developing and implementing effective protocols can be a time-consuming and complex task.

“Thus, there is a need in the art for improved systems, devices, and procedures for the separation and/or analysis of complex chemical mixtures, particularly mixtures of biological substances such as human bodily fluids.”  (column 4, lines 11-49)

 

Unlike the single-chip devices described in the aforementioned patents and articles, the solution described in this patent includes “a prototyping platform and modular microfluidic components capable of rapid and convenient assembly, alteration and disassembly of numerous candidate separation systems”[abstract, DOepatents], which can be partially or totally computer-controlled.  According to the patent’s summary of the invention, the numerous advantages of such a modular system include

 

• cost-effective assembly, optimization and/or operation

• more rapid development of effective separation protocols

• facilitated analysis and processing of complex samples

• reduced or minimized sample losses

• efficient testing and evaluation of multiple candidate sample preparation trains, with alternate trains constructible in the same platform

• simplified troubleshooting and system optimization

• facilitated sample-customized processing

 

 

 Figure 2.  Schematic and “photographic” depictions of a typical multidimensional separation using modular microfluidics on an aqueous virus sample.  (From “Multidimensional bioseparation with modular microfluidics”[DOepatents].) 

 

Another patent, assigned to the management and operating contractor for Lawrence Livermore National Laboratory (Lawrence Livermore National Security, LLC), describes a way to use ultrasound in a microfluidic (single-chip) device to separate different-size particles suspended in complex biological fluid samples (“Microfluidic ultrasonic particle separators with engineered node locations and geometries”[DOepatents]).  The particles to be separated initially flow along an input stream, but are kept to one side of the microfluid channel axis by any of various means.  This is relatively easy to accomplish in a microfluid channel, since the flow of any fluid through a narrow microchannel tends to be laminar instead of turbulent; turbulent flow in a microchannel is only possible if the fluid moves very fast, or else has a high density or low viscosity.  Under these conditions, suspended particles move away from the fluid’s lines of flow mainly by diffusion. 

 

To get the suspended particles to separate by size, the microfluid device is set to vibrating in a standing wave of very short (i.e., ultrasonic) wavelength, such that part of the microfluid, away from the initial flow line of the suspended particles, is at a node of the ultrasound wave where the vibration is zero.  The axis of fluid along which the particles initially flow is thus subject to vibration, which affects the larger particles more than the smaller ones.  The larger particles are thus more driven towards the calmer nodal region of the ultrasound wave than the smaller particles are (Figure 3).  This effectively transfers large particles to a portion of the stream that was originally empty of them, leaving smaller suspended particles behind and thus separating the two sets of particles by size.  The portions of the stream that contain different-size suspended particles can be channeled different ways.  This technique “provides high-throughput sample processing of biological material” (column 2, lines 25-26).  

 

 

Figure 3.  “The device 500 has an “H-filter” geometry in which two fluids are pumped side-by-side down a microfluidic separation channel with two inlets and two outlets.  One of the two fluids, the sample fluid 512, contains the sample and the other fluid is a “recovery” buffer 508, which is an appropriate medium (water or buffer) into which focused particles are transferred, while the unfocused components remain in the sample and continue straight through the system.  …  The two fluids enter the separation channel through separate inlets, and the separated sample fractions are collected at the two outlets.”  (From “Microfluidic ultrasonic particle separators with engineered node locations and geometries”[DOepatents].) 

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Application:  fuel cells[Note]

 

Microfluidic systems can also produce chemical reactions on usefully small scales, as shown by the project report from Cornell University, “Transport Phenomena and Interfacial Kinetics in Planar Microfluidic Membraneless Fuel Cells”[SciTech Connect].  While the chemical reactions here involve small amounts of fluid, the power they produce is meant to be relatively large—in this case, “the highest power density yet recorded for a non-H2 fuel cell.”  The report describes an extensive range of experiments with borohydride ions ().  Borohydride, “most commonly used as its sodium salt, NaBH4”, has “many attractive features as a fuel”, but these are negated by its hydrolysis into hydrogen and boric acid.  However, using a platinum catalyst, this hydrolysis is avoided.  The investigators compared numerous alternatives to oxygen as an oxidant, and found that cerium ammonium nitrate (Ce(NH4)2(NO3)6) was powerful.  They used borohydride with cerium ammonium nitrate in a membraneless, room-temperature, laminar-flow fuel cell, with micromixers to provide chaotic-convective flow to enhance the fuel cell’s power output and efficiency.  The investigators have been involved in the design of a scaled-up version of this cell intended to provide a 10-watt output. 

 

Applications:  nuclear fuel

 

Different ways of applying microfluidics to the analysis of used nuclear fuel and nuclear waste are explored in other recent reports. 

 

“Preliminary Study of Microfluidic Chip as Sample Containment for Quantitative hiRX Measurements”[SciTech Connect] from Los Alamos National Laboratory describes experiments with devices to hold microfluid samples of spent nuclear fuel for high-resolution measurements with x-rays (hiRX measurements).  Two criteria to be met by the sample holder were transparency to the x-rays used and resistance to the main component of spent-fuel solutions, nitric acid (HNO3).  Polycarbonate and silicone resisted 25% and 75% nitric-acid solutions, while Kapton sample covers were also resistive and barely degraded the x-ray signals from the spent-fuel samples (Figure 4, right).  Handmade prototype sample holders made of these materials worked well (Figure 4, left), particularly for detecting concentrations of strontium between 50 and 1,000 micrograms per milliliter:  the intensity of characteristic x-rays[Wikipedia] from strontium[Wikipedia] at these concentrations was almost directly proportional to the strontium concentration in this range.  For strontium concentrations between 5,000 and 10,000 micrograms/milliliter, the x-ray intensity was a nonlinear function of concentration, “most likely an indication of saturation” whose cause the report authors expect can be found from further development work.  The authors also expect that commercial production’s greater control over removal of material to make the microfluid channels and sample volume should yield more reproducible sample wells and significantly better precision than the handmade prototypes had.  

 

 Figure 4.  Left:  prototype microfluidic sample cell for high-resolution x-ray measurements.  Cell has two ports for fluid input and output, 2 channels to transport the fluid into and out of the sample volume, and a central sample volume of about 1 microliter (1 mm3).  Right:  sample cell’s Kapton cover layer has little effect on the intensities of various-frequency x-rays emitted by strontium in the sample volume.  (From “Preliminary Study of Microfluidic Chip as Sample Containment for Quantitative hiRX Measurements”[SciTech Connect].) 

 

A project further beyond the preliminary stage is described in the Idaho National Laboratory report “Recent Results of the Investigation of a Microfluidic Sampling Chip and Sampling System for Hot Cell Aqueous Processing Streams”[SciTech Connect].  Here, the motivation for investigating the use of microfluidics in radiation containment chambers (hot cells[Wikipedia]) is made more explicit: 

 

“Sampling and analysis of nuclear fuel recycling plant processes are required to both monitor process efficiency while ensuring Safeguards and Security goals are met. In addition, environmental regulations lead to additional sampling and analysis to meet licensing requirements. The volume of samples taken by conventional means can restrain productivity while samples are analyzed, require process holding tanks that are sized to meet analytical issues rather than process issues (creating a larger facility footprint), or, in some cases, overwhelm analytical laboratory capabilities. These volumes can also provide a significant radiation dose to analytical personnel and equipment. These issues only grow when process flow sheets propose new separations systems and new byproduct material for transmutation[Wikipedia] purposes. A novel means of streamlining sampling and analysis was evaluated to increase efficiency while meeting all process information requirements.”  (P. 2 of 7)

 

The work reported has had time to go beyond the preliminary stage to the construction and testing of a robotic sampling system based on microfluidics, with the overall goal being “to significantly reduce sample volume thus reducing the sample waste streams and at the same time reducing radiation exposure to humans and analytical instrumentation” (p. 6 of 7).  Whereas the more preliminary Los Alamos study concentrated on just designing a sample holder for x-ray analysis, this project aimed at a complete analysis process, which not only included a microfluidic-chip design, but methods of getting samples into and out of the chips, robotically handling them, and performing tests on the samples.  Accordingly, intermediate test results informed several adjustments to the process during testing (e.g., in flowrates to reduce pressure on the sample lines, and in tubing lengths and positions at the unloading station to decrease leaks).  The findings also led to several observations and recommendations for the future (e.g., minimizing sample evaporation from chips requires minimizing the time between chip loading and unloading; developing a chip that would fill by pumping instead of capillary action would allow sample volumes of enough microliters to minimize fill-volume errors). 

 

 

Figure 5.  The robotic system for taking microfluidic samples shown in the Idaho National Laboratory report “Recent Results of the Investigation of a Microfluidic Sampling Chip and Sampling System for Hot Cell Aqueous Processing Streams”[SciTech Connect]. 

 

To support the development of material balance, control, and accountability (MC&A) systems at treatment facilities for used nuclear fuel was the reason for “Testing of a Microfluidic Sampling System for High Temperature Electrochemical MC&A”[SciTech Connect], as reported by Argonne National Laboratory.  Here, the system was designed to sample molten electrochemical process salts. 

 

“Tracking the composition of salt as it moves through an electrochemical reprocessing facility is a difficult task because electrochemical material processing is done continuously at elevated temperatures while transfers involve discrete batches of used fuel or solids with adhered salts. Salt is recycled at several points within the process, making it difficult to relate changes in composition to specific processing operations. Particularly over long time steps, small differences or inhomogeneities may result in quantifiable changes in product output compositions. It is desirable to obtain an accurate and timely measure of the chemical and isotopic composition of the salt within the electrorefiner and through other operations in the facility to fully close the material mass balance.

 

“The goal of this project is to develop a sampling system that will enable the accurate determination of the chemical and isotopic composition of the molten salt in an electrorefiner or adhering to cathode products or cladding wastes within a electrochemical facility. The system will ideally allow the combination of the best aspects of destructive analysis (high sensitivity, low measurement uncertainty, and high quantitative resolution) with the best aspect of non-destructive analysis (low sample loss, low processing impact, and rapid turnaround).

 

“Practical safeguard difficulties associated with electrochemical processing include the absence of an input accountancy tank, high temperature processing, and batch-wise fuel addition and product harvesting coupled with synchronous dissolution and cathode deposition within the electrorefiner. In addition, salt is collected and recycled at several points within the cathode processing cycle, making it challenging to fully close the mass balance after the initial batch of fuel is dissolved. In addition, salt collected from processed cathodes may differ in composition from the balance of salt in the electrorefiner. Finally, minor inhomogeneity may exist in the salt or metal compositions in the electrorefiner.”  (“Introduction”, p. 5.)

 

Initial tests show the concept is viable for high-temperature sampling but further development is required to optimize the system. 

 

“Tests were run with a LiI-CsI [lithium iodide – cesium iodide] low-melting eutectic salt [a salt mixture that melts at lower temperature than the individual salts do separately[Wikipedia]] and a thermal transfer fluid as the carrier. Several additional candidate thermal transfer fluids will be tested to determine their suitability as material transfer media. The initial tests were intended to optimize operating conditions for each liquid-liquid system in order to characterize their properties and behavior under process conditions. The microchip imaging set-up was found to be capable of imaging the high temperature chip from a safe distance. However, due to poor contrast between the fluids, further effort to examine contrasting agents that can be added to a liquid component and a refining the imaging techniques is required. Additional testing of the chip and holder set-up at near-process temperatures is required to obtain the data necessary to better tailor future iterations of microchips to the LiI-CsI and LiCl-KCl systems. Although a number of flow types were observed, including the desired slug flow, the establishment of stable flow and consistent droplets must be verified, while the contrast between phases and in-channel freezing of salt should be improved. As testing proceeds, the chip design will be refined and procedures developed for cooling and heating microchips.

 

“Once the concept is more fully developed for a single temperature zone, the approach can be used in designs with multiple temperature zones, which will likely be required in the deployed design. Any necessary refinements will be made once a gauge of the performance is attained. In the longer term, it will be necessary to develop an interface with on-line/at-line analysis equipment to assess temperature and timing requirements, as well as purification requirements. All multi-zone modifications will require detailed design specification for fabrication and eventual testing. Integration of purification with thermal transfer requirements and stability in high-radiation, high-temperature environments must all be demonstrated.”  (“Conclusion”, p. 19.)

 

Fast and easy detection and separation of plutonium in aqueous solutions, as well as monitoring nuclear waste storage facilities for radionuclide leaching and migration, is the focus of an investigation by scientists at the Savannah River National Laboratory, the University of South Carolina, the Savannah River Ecology Laboratory, and the Medical College of Georgia.  Their brief report “Nanofluidics Revolution:  Protecting the World One Drop at a Time”[SciTech Connect] is more preliminary than the ones described above.  “Nanofluidics” here refers to devices that operate on microliter or picoliter[Wikipedia] fluid volumes confined to nanoscale structures[Note]

 

The report describes shortcomings of existing methods of tracking radioactive materials that don’t incorporate nanofluidics, and an advantage that nanofluidic systems might offer: 

 

“Currently, the most reliable analytical method to aid in [special nuclear material, or] SNM control and accountancy is isotope dilution mass spectrometry (IDMS). This technique involves tedious procedures and requires highly skilled operators to separate the analyte from complicated matrices such as INF [irradiated nuclear fuel] solutions. The process is also large-scale and costly. Another method to measure SNM is radiation detection, which is limited due to high background noise level in the presence of an amalgam of other radioisotopes, such as actinides and fission products, in the INF solutions. This complication leads to difficulties in lower level detection, noise discrimination, and self-shielding attenuation in the solutions due to process configurations, such as pipe volumes and distances.

 

“Spectroscopic analysis for the detection of analytes within a liquid has been popular for decades and can provide high selectivity (to isolate detection signals of desired analytes) for lab-on-a-chip devices. Typical spectroscopic systems have large footprints which are not readily portable. Implementing a method for portable detection with a very small sample volume would be a significant advantage for nuclear safeguards, where detection procedures must be performed in the field. Furthermore, the spectroscopic system must be aligned to reduce interfering signals – a procedure which requires rigorous discipline and is time consuming.”  (P. 2.) 

 

The authors specifically advocate integrating optical waveguides into the detector chips along with the nanofluidic channels, in order to facilitate delivery of the photon beam that probes the liquid sample, which “increases the device’s detection efficiency and eliminates the need for system alignment”. 

 

The report closes with the authors’ expectations for how the project’s results may be eventually used, not only for monitoring nuclear facilities, but for other purposes (pp. 2-3). 

 

“Potentially, these portable optofluidic chips can be deployed easily to nuclear facilities around the world, and the analysis of the samples can be achieved rapidly to meet the safeguards requirements.

 

“The experiments being conducted at SRNL will lead to innovative analytical techniques for rapid and simple confirmation of plutonium and other radioisotopes in aqueous solutions. The project goals are aimed at furthering nanofluidics development to produce portable and sensitive nanofluidic lab-on-a-chip instruments for the detection of nuclear materials in a wide variety of situations. Not only is this technology of paramount interest in the nuclear and anti-proliferation fields, but it also can be applied to many other fields, such as in the medical sciences, where a minute amount of substances in small liquid samples needs to be measured. As a resent discussion with the researchers at the Institute for Regenerative and Reparative Medicine at Georgia Health Sciences University [sic], the fluid-structure interaction may be considered in fluidics to explain the Whole Body Vibration (WBV) test results with the murine samples, in which the serum glucose and inflammatory markers may be reduced. This treatment has a tremendous impact on the war against obesity worldwide. Meanwhile, fluidics technology may be used in soft tissue modification to prevent and cure pressure ulceration, which also has a major economic impact in caring the elderly and paralyzed patients. In deep space exploration, the U.S. National Aeronautics and Space Administration (NASA) has initiated research in electrokinetic pumping in near weightless environments using micro/nano fluidics principles to eliminate the mechanical parts and the fluid transfer momentum. This emerging technology will lead to endless opportunities in Nuclear Energy, Environmental Management, National Security, Nuclear Waste Management, Medical Applications, and Advanced Engineering.”

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References

 

Notes

Wikipedia

Research and Research-Related Organizations

Reports Available through OSTI’s SciTech Connect and DOepatents

  • “Method for forming polymerized microfluidic devices” [Metadata and full text available from DOepatents] 12 pp. 
  • “Elucidating the role of interfacial materials properties in microfluidic packages” [Metadata and full text available from DoE’s SciTech Connect] 62 pp. 
  • “Flow rate--pressure drop relation for deformable shallow microfluidic channels” (rev. 2) [Metadata and full text available from DoE’s SciTech Connect] 26 pp. 
  • “Biomedical Applications of Microfluidic Technology” [Metadata and full text available from DoE’s SciTech Connect] 7 pp. 
  • “Microfluidic devices and methods including porous polymer monoliths” [Metadata and full text available from DOepatents] 18 pp. 
  • “Microfluidic device having an immobilized pH gradient and page gels for protein separation and analysis” [Metadata and full text available from DOepatents] 24 pp. 
  • “Multidimensional bioseparation with modular microfluidics” [Metadata and full text available from DOepatents] 13 pp. 
  • “Microfluidic ultrasonic particle separators with engineered node locations and geometries” [Metadata and full text available from DOepatents] 12 pp.
  • “Transport Phenomena and Interfacial Kinetics in Planar Microfluidic Membraneless Fuel Cells” [Metadata and full text available from DoE’s SciTech Connect] 20 pp. 
  • “Preliminary Study of Microfluidic Chip as Sample Containment for Quantitative hiRX Measurements” [Metadata and full text available from DoE’s SciTech Connect] 6 pp. 
  • “Recent Results of the Investigation of a Microfluidic Sampling Chip and Sampling System for Hot Cell Aqueous Processing Streams” [Metadata and full text available from DoE’s SciTech Connect] 7 pp. 
  • “Testing of a Microfluidic Sampling System for High Temperature Electrochemical MC&A” [Metadata and full text available from DoE’s SciTech Connect] 22 pp. 
  • “Nanofluidics Revolution:  Protecting the World One Drop at a Time” [Metadata and full text available from DoE’s SciTech Connect] 4 pp

Additional Reference

  • Innovation on Demand by Victor Fey and Eugene Rivin (Cambridge University Press, 2005). 

 

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Last updated on Monday 11 August 2014