What if there were a technology so smart that it could detect biohazards in the air, so small that it could make cameras that fit inside of pills to swallow, so effective that it could revolutionize the production of everything from hearing aids to automobiles, and so efficient that you could make thousands of uniform components at a time, each for mere pennies. What would you do with it? Imagine the possibilities!

During the last decade, world-wide developments in micro-fabrication technologies have led to numerous Lab-On-a-Chip (LOC) micro-systems covering a wide spectrum of biotechnological applications. Although early LOC developments were driven by glass and silicon micro-fabrication techniques, in recent years polymeric-based LOC have been intensively developed. Taking advantage of each material, a hybrid device associating an active silicon chip with a passive polymeric micro-part has been developed to produce an addressable Cell-chip for individual cell manipulation and sorting. The complete hybrid micro-fluidic device fabrication is described here, including polymer structuring, hermetical sealing, biocompatibility studies, and fluidic interconnections with the sample as well as detection aspects. The cell manipulation is based on dielectrophoresis, which allows cell motion without fluid flow. First biological results will be presented.

Biological applications of micro assay devices require integrated on-chip microfluidics for separation of plasma or serum from blood. This is achieved by a new blood separation technique based on a microchannel bend structure developed within the collaborative Micro-Tele-BioChip (μTBC) project co-funded by the German Ministry For Education and Research (BMBF). Different prototype polymer chips have been manufactured with an UV-LIGA process and hot embossing technology. The separation efficiency of these chips has been determined by experimental measurements using human whole blood. Results show different separation efficiencies for cells and plasma depending on microchannel geometry and blood sample characteristics and suggest an alternative blood separation method as compared to existing micro separation technologies.

We present an approach to fabricate an array of elastomer posts in order to dynamically measure the traction forces exerted by living cells on a surface with a micrometer lateral resolution. Arrays of closely spaced vertical microposts are made in silicone elastomer [poly(dimethylsiloxane) (PDMS)] by molding a Silicon substrate that has been machined by deep Si etching after standard photolithography. The surface of the micropillars was modified to allow cell culture. Deflections of the calibrated posts were dynamically followed by direct obervation with an optical microscope. By using this set-up, we could dynamically draw up a cartography of the local traction forces exerted by the cells.

This paper focuses on the development of a custom MEMS-based array which will facilitate cell secretion studies by enabling parallel electrochemical detection of secretion events from separate cells with millisecond resolution. Initial prototypes of the microarrays have been fabricated with well-shaped gold electrodes which roughly conform to the shape of a single cell. Amperometric measurements on bovine adrenal chromaffin cells using the prototype microarrays concluded that 80% of the catecholamine secreted from the cells was captured by the well-electrodes. This was a 4-fold increase in detection efficiency over the conventional carbon fiber electrode method. To expand the applicability of this method, additional cell-lines and microarray designs are under investigation. An amphibian fibroblast cell-line (FT cell-line, American Tissue Culture Collection) is being used in our lab. FT cells can take up hormones or other biological compounds from the culture media through a non-specific uptake mechanism which is still under investigation. Microarrays of a new design have been fabricated with patterned gold electrodes on polyimide. A different testing method will be applied to these new microarrays. The FT cells will be cultured directly on top of the microarrays to cover the gold electrodes. Cells will then be loaded with norepinephrine by incubation in media containing 1mM norepinephrine. Rapid elevation of intracellular Ca²⁺ levels triggers the exocytosis of norepinephrine which then can be detected by the gold electrode. The new polyimide based microarrays have been successfully used to support confluent growth of the FT cells. Loading of the FT cells with norepinephrine and electrochemical detection tests are underway.

This work reports the micro- and nano-fabrication of substrates obtained by coupling conventional photolithography and layer-by-layer (LbL) self-assembly technologies, and the application for building in vitro cell culture scaffolds. Using photolithography, cell culture scaffolds of various shapes (circles, squares, and rectangles) and sizes (10 to 300 μm) were obtained using direct and soft lithography methods in SU-8, polydimethylsiloxane (PDMS), and Poly(methyl methacrylate) (PMMA). Using LbL technology, patterned polyelectrolyte ultrathin multilayer films, containing gelatin to promote cell adhesion, were then deposited on or between raised microstructures, depending on the intended application of the cell culture scaffolds. Fluorescent indicator dyes are integrated onto the microstructures to allow monitoring changes of pH and oxygen in the cell culture media. Thus, cell activity may be monitored by using the fluorescent film properties, enabling a high-throughput cell-based in vitro screening system. The findings indicate that combining conventional photolithography and LbL technologies is an efficient method to fabricate micro- and nanoscale patterns as substrates to modulate the surface properties of in vitro cell culture scaffolds.

We report a new bioMEMs nanolaser technique for measuring characteristics of small organelles. We have initially applied the method to study mitochondria, a very small (500nm to 1um) organelle containing the respiration apparatus for animal cells. Because the mitochondria are so tiny, it has been difficult to study them using standard light microscope or flow cytometry techniques. We employ a recently discovered a nano-optical transduction method for high-speed analysis of submicron organelles. This ultrasensitive detection of submicron particles uses nano-squeezing of light into photon modes imposed by the ultrasmall organelle dimensions in a submicron laser cavity. In this paper, we report measurements of mitochondria spectra under normal conditions and under high calcium ion gradient conditions that upset membrane homeostasis and lead to organelle swelling and lysis, similar to that observed in the diseased state. The measured spectra are compared with our calculations of the electromagnetic modes in normal and distended mitochondria using multiphysics finite element methods.

With the goal of a portable diagnostic system in mind, we have designed a disposable platform for DNA detection. Surface micromachining using the SwIFT process at Sandia National Laboratories was used to make the new device, combining a waveguide, grating optics, heating structures, on-chip pumping, and microfluidics in a disposable package. PDMS microfluidic channels are integrated with the surface micromachined device to enable higher flow rates and added fluid complexity. Work on DNA hybridization under flow is presented, as applies to the function of the sensor. A description of the platform covering heating of the waveguide surface, laser coupling into the waveguide using grating optics, attachment chemistry for the sensor surface, and sealing of the PDMS microfluidic system to the device is given.

In this paper, we describe the development of a culture-based biochip for detecting mycobacteria in environmental samples. The biochips use the paraffinophilic nature of mycobacteria to rapidly detect and differentiate them from non-target micro-organisms. New methods of depositing and patterning paraffin were developed to fabricate prototype biochips. Biochips were experimentally tested to demonstrate rapid detection of mycobacteria in environmental samples collected from a municipal sewage treatment plant. Our successful demonstration of the culture-based biochip technology presents an alternative approach for developing new technology to track microorganisms in complex environmental samples.

The objective was to design and manufacture a microscale Ligase Detection Reaction (LDR) device for detection of cancer-associated rare gene mutations. The LDR module will be incorporated with other devices such as a Continuous Flow Polymerase Chain Reaction (CFRCR) unit and a Capillary Electrophoresis (CE) chip in a modular lab-on-a-chip technology. During LDR, devloped by Francis Barany, several primers are mixed with the analyte, exposed to a thermal cycle consisting of two steps of 95°C and 65°C for 20 cycles, and cooled to 0°C. The first step in the design was to determine if the baseline time for the LDR reaction could be reduced from the 2½ hours required for the orignal reaction. Experiments have shown that it is posssible to obtain useable product from the LDR after 40 minutes, a 75% reduction, before going to the microscale, which should allow further improvements. Due to the extensive mixing needed prior to the reaction a set of alternative diffusion mixers was identified and microfabricated to determine which geometry was the most effective. Simulations of the thermal response of the device were done using finite element analysis (FEA) to compare to experimental results. The required temperature profile will be obtained by using resistive heaters and thermoelectric modules. A prototype LDR device was laid out based on the results of the studies.

We are investigating the development of a rapid and highly sensitive detection method for immunoreactive substances combining MEMS (Micro Electro Mechanical Systems) technology and the appropriate immune stimulant or response factors. Cantilevers of micrometer scale can be used for trace detection of mass change. When a layer of an antigenic substance is covalently deposited, the cantilever is capable of capturing antibodies from samples with high affinity and specificity. The antigen/antibody binding causes multiple physical changes in the cantilever device, including a shift of effective mass and a change in surface tension. The change of effective mass consequently induces a shift in the cantilever’s natural resonant frequency. By monitoring these changes with an optical readout mechanism, the presence of immunoreactive targets in the sample can be detected. This detection method can be used for various types of targets with immunoreactivity and therefore is potentially applicable in hazardous substance monitoring and disease diagnosis. In our effort, phoS1, an antigen shed by Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is utilized for rapid and economic TB detection.

This paper describes the design and fabrication of an integrated optical glucose sensing system using the combination of the oxygen sensitive dye tris(2,2’-bipyridyl) dichlororuthenium(II) hexahydrate and glucose oxidase. Layer-by-layer self-assembly is used to immobilize the dye/enzyme system onto the surface of the waveguides. Changes in the enzyme/dye system as it interacts with the surrounding environment are monitored using end-face interaction with light injected into waveguides. The waveguides are thermally-defined monolithic polydimethlysiloxane (PDMS) waveguide system, fabricated on a PDMS substrate. The method of waveguide fabrication is a radical departure from conventional microscale waveguide systems, and offers unique opportunities for integration of this sensor into existing microfluidic systems.

Molding of micro components from thermoplastic polymers has become a routinely used industrial production process. Besides the famous injection molding technology hot embossing is nearly unknown to most people in micro technology. Initially developed for first feasibility tests with microstructured moldinserts hot embossing has been developed during the last ten years to a flexible and successful replication technology for polymer MEMS: Material screening, rapid prototyping but even small series with far more than 10.000 components has lead to a first commercialization of the related machinery. But also high end applications, difficult to realize with other technologies, are requested to replicate complex microstructures. This paper gives an overview about the development of this technique and presents some new developments.

An important activity is developed today in the field of biosensors and biochips. These sensors are used essentially in the detection and/or characterization of biological or chemical entities in complex media. The aim of this paper is the development of a new type of biosensors combining microfluidic components and millimeter or sub-millimeter wave (or THz or FIR) spectroscopy tools. Today, many different microsystems in the field of biology are realized in all polymers or in silicon with a bounding of silicon or glass. We have selected to deposit a Plasma Polymerized TetraMethylDiSiloxane (PPTMDS) on a silicon wafer. A new technological process based on cold remote nitrogen plasma allows us to obtain 50-80μm thick layers with a rigid texture and a very good link with silicon. This technological process is now well defined and is compatible with a classical microelectronic process for the deposition of the metallic planar waveguides. For the first time, measurements using an-in-house vectorial network analyzer (VNA) 140-220GHz are reported. Fairly good results have been obtained from impedance and propagation characteristics. These measurements allow us to determine the PPTMDS permittivity in this bandwidth. Thanks to this knowledge, we have designed a matched coplanar waveguide where a water droplet is deposited. An inversion model has been developed to retrieve the water permittivity and will be broadened to biological entities.

Using biodegradable polymers for implantable drug delivery purposes has been a very important research area and industry for many years. Polymers, such as PLGA, have been the most attractive one because it does not require removal after the drug has been released. We report a research effort to microfabricate high aspect ratio microstructures of PLGA and its potential applications in implantable drug delivery. The prototypes of packaged cells with dyes have also been made and currently under test for linear release of sample dyes.

The need for disposable diagnostic sensors in the health care industry has been a major driver in the development of low-cost polymer microfluidic devices. Of crucial importance to many of these devices is the incorporation of sieves and filters for the pretreatment of biological samples. Much of the previous work on integrating filtration systems in microdevices has focused on silicon and glass technologies. Of more difficulty, due to the different manufacturing methodology and lower mechanical strength, is the integration of filtration systems in polymer microfluidic chips. This paper presents a design and construction methodology to fabricate such integrated devices in polyethylene terepthalate (PET) and describes their characterization for particle filtration. To demonstrate the application of these systems, DNA extraction from whole blood was investigated. This currently represents a major stumbling block for point-of-care diagnostics. To this end two approaches were taken; the isolation of leucocytes for subsequent DNA extraction, and the trapping of silica microspheres for DNA adsorption. The polymer surfaces of the fluidic chips were modified by UV exposure and chemical etching to increase their surface energy for improved non-specific binding and electroosmotic flow characteristics. Integrated filtration devices were successfully fabricated with excimer laser machined membranes having pore dimensions down to 1μm, and contact angles from 75° down to less than 25° were achieved using UV modification, and from 75° down to 16° by chemical modification of PET. White blood cells were filtered from whole blood and silica particle retention was demonstrated successfully.

We describe a number of microfluidic components that have been formed by laer micromachining and incorporated in a picoliter droplet dispenser. The laser micromachined structures include an adhesive interface between macrofluidic and microfluidic regions, a particle filter, a fluid manifold, channels, and nozzles. Both excimer laser and C0₂ laser processes are used.

After more than a decade of activities in the field of microfluidics, an increasing need for standardized modules and off-the-shelf components can be observed. In particular the compatibility with existing laboratory equipment o procedures greatly helps the acceptance of miniaturized systems, as in practice, miniaturized systems are very likely to be used in parallel with existing equipment and are not totally replacing this. In this paper we present the basic concept of a microfluidic toolbox with interchangeable components where the external dimensions are adopted from existing standards. Furthermore the fluidic interfaces were selected for compatibility to established systems.

This paper presents the dry actuation testing procedures and results for novel viscous drag micropumping systems. To overcome the limitations of previously developed mechanical pumps, we have developed pumps that are surface micromachined for efficient mass production which utilize viscous drag (dominant at low Reynolds numbers typical of microfluidics) to move fluid. The SUMMiT (www.sandia.gov/micromachine) fabricated pumps, presented first by Kilani et al., are being experimentally and computationally analyzed. In this paper we will describe the development of optimal waveforms to drive the electrostatic pumping mechanism while dry. While wet actuation will be significantly different, dry testing provides insight into how to optimally move the mechanism and differences between dry and wet actuation can be used to isolate fluid effects. Characterization began with an analysis of the driving voltage waveforms for the torsional ratcheting actuator (TRA), a micro-motor that drove the gear transmission for the pump, actuated with SAMA (Sandia’s Arbitrary waveform MEMS Actuator), a new waveform generating computer program with the ability to generate and output arbitrary voltage signals. Based upon previous research, a 50% duty cycle half-sine wave was initially selected for actuation of the TRA. However, due to the geometry of the half-sine waveform, the loaded micromotor could not transmit the motion required to pump the tested liquids. Six waveforms were then conceived, constructed, and selected for device actuation testing. Dry actuation tests included high voltage, low voltage, high frequency, and endurance/reliability testing of the TRA, gear transmission and pump assembly. In the SUMMiT process, all of the components of the system are fabricated together on one silicon chip already assembled in a monolithic microfabrication process. A 40% duty cycle quarter-sine waveform with a 20% DC at 60V has currently proved to be the most reliable, allowing for an 825Hz continuous TRA operating frequency for the micropumps. This novel waveform allowed for higher TRA actuation frequencies than those obtained in prior research of the pumps.

With macroscopic chemical analysis devices, it is usually possible during the development phase to mount flow sensors, temperature probes, and optical detectors at various positions along the instrument pathway to experimentally determine the optimum operational parameters for the device. This approach usually fails for microdevices as standard sensors and probes are typically of the same scale as the microdevice. These relatively large sensors interfere so much with the experiments that any results generated do not represent the actual performance of the system. Fortunately, modeling of microscale processes provides a uniquely useful tool to develop microanalytical devices and optimize their operational parameters, since the chemical and physical processes in the microscale generally follow deterministic physical laws that can be accurately represented in mathematical models. We will discuss some of the methods used to model and design microanalytical assays based on these principles, as well as several ongoing development projects that MicroPlumbers is currently involved in (including a clinical microsensor, a microvolume blood collection device, and a novel clinical assay), and show how modeling and rational design is used during the development processes and yield devices with optimized performance.

Passive (diffusional) mixing has been used in designing high-aspect-ratio micro-mixers for the purpose of performing Liagase Detection Reaction (LDR). The types of mixers considered are simple, cheap, and durable and can perform over a broad range of volumetric flow rates at reasonably modest pressure drops. The fluids to be mixed have a very low typical diffusion coefficient of=1.2x10^-10m²/s and diffusional mixing is only effective in high-aspect-ratio micro-channels. A very modestly high aspect ratio of 6 has been considered initially because it is easily releasable using the LIGA technique. Numerical simulations of a few basic diffusional mixer configurations are going to be presented in this paper. Two variants of a Y-type mixer with contraction and several variants of a mixer employing jets in cross-flow have been simulated. The various mixers have been evaluated in terms of volumetric mixing efficiencies and maximum pressure drops. One of the mixers with jets-in-cross-flow was found to perform best.

In this paper we present and demonstrate a technique for mapping fluid flow rates in microfluidic systems with sub-micron resolution using confocal microscopy in conjunction with fluorescence correlation spectroscopy. Velocity profiles and velocity images of the fluid within poly(dimethylsiloxane)-glass microchannels are presented and analyzed. Flow velocities ranging from a few μm/s to a few cm/s can be recorded using nanometer-scale fluorescent polymer spheres as fluid motion tracers. The method is applied to mapping the hydrodynamic flow velocity in complex geometries. This is, to our knowledge, the first report of FCS for producing 2-dimensional velocity maps.

We present the design of two efficient micromixers, a 3-D serpentine micromixer and a vortex mixer. Light and confocal microscopy and image analysis programs were used to study mixing efficiency in these two micromixers and a Y-shape straight channel. By utilizing Optical Coherence Tomography (OCT), an emerging high-resolution medical and biological imaging technology, we obtained 3-D structural data and mixing dynamics for the 3-D serpentine mixer and the vortex mixer. The results indicate that mixing efficiency characterized with OCT is more accurate.

Phase-resolved Optical Doppler Tomography (ODT), an imaging technique based on low coherence interferometry, is presented as a tool to quantify the micro flow in microfluidic channel. Experiments using phase-resolved ODT to image and quantify Electroosmotic Flow (EOF) within a single microchannel are described demonstrating its utility in determining EOF in microchannels. Since it provides cross-sectional imaging of flow velocity, complex flow dynamics caused by microscale effects, such as electrokinetic flow, can be investigated and quantified using this tool.

This paper presents a novel micro injector, by which microfluidic delivery, transport and control can be digitally realized in femtoliter scale. The microinjection is based on a new principle that the micropipette is actuated by an actuator, which is located outside the micropipette and may have macro scale dimensions, moving in such a manner that its acceleration changes. When the acceleration is small, the liquid moves along with the pipette; while, when the acceleration becomes large enough, the liquid flows relative to the micropipette. The validity of the presented principle is verified by experiment. Digital microinjection has been realized, particularly under conditions that neither micro moving parts nor embedded micro electric circuits are necessary, hence greatly simplifying the structure and reducing the cost. The microfluidic system can work normally over a rather wide range, even though where very large resistance to flow exists. The amount of injected fluid material may reach an ultra high resolution of the order of femtoliters. The kinds of the fluid materials that can be injected include conventional liquids as well as solid powders, pastes, and other substances of similar characteristics. Furthermore, the digital femtoliter microinjector can be expected for making nano particles.

This work demonstrates the design optimization, fabrication process development, process optimization and testing of a microfluidic ink delivery apparatus (called "Inkwells") for simultaneously coating an array of DPN pens with different inks. The objective of this work is to deliver between 4 and 10 different inks from reservoirs into appropriately spacd microwell array. A tips of the multi-pen array are coated with different inks by dipping them into the microwell array. The reservoirs, microwells and their connecting micro-channels were etched in silicon wafers using Deep Reactive Ion Etching (DRIE). Fluid actuation was achieved by capillary wicking. The optimum layouts for different applications were selected with respect to the volume requirement of inks, the efficacy of ink-well filling, to obviate the problem of bubble formation, and to test the operations of dipping and writing with a parallel array of pens.

The effect of the electric double layer (EDL) on the linear stability of Poiseuille planar channel flow is reported. It is shown that the EDL destabilizes the linear modes, and that the critical Reynolds number decreases significantly when the thickness of the double layer becomes comparable with the height of the channel. The planar macro scale Poiseuille flow is metastable, and the inflexional EDL instability may further decrease the macro-transitional Reynolds number. There is a good correspondence between the estimated transitional Reynolds numbers and some experiments, showing that early transition is plausible in microchannels under some conditions.

This paper describes a simple packaging method to fabricate microfluidic channels and obtain an optical detection interface for micro analysis systems. Specifically, this work reports on efforts to develop new methods for simple, fast and reliable design and fabrication of microscale field flow fractionation (FFF) based biological analysis systems. This modular detector interface results in a 38 nl detection region. Detector characterization is carried out to evaluate important figures of merit such as sensitivity, S/N ratio, and limit of detection. Plate height, a primary performance criterion for field flow fractionation is determined and compared with an on-chip detector. The developed system allow for a plug-and-play approach to the optical interface has resulted in flexibility in operation and increased robustness of the micro device.