There are many efforts today trying to mimic the properties of single cells in order to design chips that are as efficient as cells. However, cells are nature’s nanotechnology engineering at the scale of atoms and molecules. Therefore, it might be better to vision a microchip that utilizes a single cell as experimentation platform. A novel, so-called Lab-in-a-Cell (LIC) concept is described, where advantage is taken of micro/nanotechnological tools to enable precise control of the biochemical cellular environment and possibility to analyze the composition of single cells. This is followed by a review on the present chip solutions for single cell handling and analysis.

This paper focuses on the development of two MEMS-based devices for lab-on-a-chip bio-applications. The first device is designed to facilitate cell secretion studies by enabling parallel electrochemical detection with millisecond resolution. Initial prototypes of micro-arrays have been fabricated with Cr/Au microelectrodes on various substrates such as polyimide, SU-8 and SiO₂. An FT cell-line (bullfrog fibroblast, American Tissue Culture Collection) has been successfully established and cultured directly on these prototype micro-arrays. It is well known that the FT cells can uptake hormones or other macromolecules from the culture media through a non-specific uptake mechanism which is still under investigation. After culturing on micro-arrays, FT cells were loaded with norepinephrine of various concentrations by incubation in the culture media supplied with norepinephrines. Rapid elevation of intracellular Ca²⁺ levels triggers the exocytosis of norepinephrine which then can be detected by the Cr/Au electrodes. Microfabrication of these prototype micro-arrays as well as cell culture and electrochemical detection results will be presented in this paper. The second device is designed for 3-dimensional transportation of living cells on chips. Initial prototypes of micro-arrays were fabricated with SU-8 buried channels on a silicon substrate. Both single-layered and double-layered SU-8 buried channels have been realized to enable 2D and 3D cell transportation. Stained solutions were used to visualize fluid transport through the channel networks. Following this, living FT cells in solution were successfully transported through single-layered SU-8 channels. Testing of 3D transportation of living FT cells is underway. Microfabrication of these prototype micro-arrays and living cell transportation on chips will also be presented in this paper.

Implantable retinal prosthetic devices consisting of microelectrode arrays are being built in attempts to restore vision. Current retinal prostheses use metal planar electrodes. We are developing a novel electro-neural interface using carbon nanotube (CNT) bundles as flexible, protruding microelectrodes. We have synthesized vertically self-assembled, multi-walled CNT bundles by thermal chemical vapor deposition. Using conventional silicon-based micro-fabrication processes, these CNT bundles were integrated onto pre-patterned circuits. CNT protruding electrodes have significant potentials in providing safer stimulation for retinal prostheses. They could also act as recording units to sense electrical and chemical activities in neural systems for fundamental neuroscience research.

The fabricated system is advantageous due to its low cost and simple structure. This is possible because it replaces many optical lenses and expensive equipment with optical fibers. We tested various optical fibers to select a suitable fiber for effective micro flow cell cytometry. In order to align between micro nozzle and optical fibers, a guide channel was fabricated by Si wafer etching with MEMS (Micro Electro-Mechanical System) technology. The micro flow cell cytometry using optical science and MEMS technology. The optical science using multi mode optical fiber and He-Ne laser (20mW, 658nm). The guide channel was fabricated by MEMS technology. The output voltage was as high as about 300 mV, so we are going to use a light source which has relatively small output power. By injecting various cells, we were able to detect cells. In addition, we can use the micro flow cell cytometry for analyzing cells (1, 2). We have no doubt that this micro flow cell cytometry can contribute to the development of biological engineering and clinical testing and it can be practically used in diagnoses of particular diseases and biological symptoms and invitro diagnostics (7, 8).

In this communication, the compatibility of porous silicon and anodic bonding technologies for the realization of sensing microcomponents in lab-on-chip applications has been demonstrated. The two techniques have been combined for the fabrication of a microsensor with biological and chemical molecules sensing capability, in view of its miniaturization and integration with smart micro-dosage systems.

Chemomechanical actuation of a microcantilever beam induced by biomolecular binding such as DNA hybridization and antibody-antigen binding is an important principle useful in biosensing applications. As the magnitude of the forces involved is very small, increasing the sensitivity of the microcantilever beams involved is a priority. In this paper we are considering to achieve this by structural variation of the cantilevers. Merely decreasing the thickness of the microcantilever may improve the sensitivity, but it gives rise to the disadvantages of 'arching' and lesser reliability due to greater probability of defects during fabrication. We consider a 'ribbed' cantilever that eliminates the disadvantages while improving the sensitivity simultaneously. Simulations for validation have been performed using the finite element analysis software ANSYS 8.0. The simulations reveal that a ribbed microcantilever is almost as sensitive as a thin cantilever and has relatively very low arching effect. Simulations also reveal that higher the arching lower is the sensitivity.

This article presents a synthesis of industrial activity in polymer microcomponents and their use in biological fields. Polymer microtechnologies have emerged in the 90s as a low cost alternative technology to Si and glass micromachining. The launching of the Steag microParts company in 1990 with the FZK Research Center and Pharmacia Biosensor patents, have launched these materials in the MEMS world. Polymers are expected to be increasingly used through the development of microfluidics for bio applications.

Microfluidic devices are mainly used within the life sciences or chemical analysis. Polymers are ideally suited for these applications due to their physical and chemical properties. In this report, we describe a rapid low cost processing technology to fabricate mold inserts for microfluidic structures with high aspect ratio, as well as excellent surface quality and high hardness. These tools are used for hot embossing and as mold inserts for injection molding. They enable cost effective structuring of technical polymers like polycarbonate or cycloolefin copolymer. The main advantage of our approach is the availability of the geometry and the specific target material right from the start of the evaluation process of microfluidic devices. The process described enables a rapid prototyping for the development and evaluation of different microfluidic devices, and they can be used for a low-cost mass production of micro structured parts.

We have developed a new method for fabrication of microchannels and microcavities using only planar lithography processes. In this approach, microchannels are formed by spin-coating resist, exposure and development. Since only photoresist is used as the material and only standard lithography processes are employed in fabrication, this method is completely compatible with electronics that may have been fabricated on the same substrate. For single level microchannels, the resist is first exposed with the sidewall patterns of the channels. This is followed by another exposure with enhanced absorption to seal the channel. Enhanced absorption is achieved by mismatching the resist and the exposure wavelength. The latent channel structure is finally revealed by development. This approach can be further extended to fabricate complex multi-level microchannel system by repeating the basic approach. In this work, we fabricated single level channel up to 1.2mm long with 4μm by 2μm cross-section and demonstrated its utility by flowing water through it. We also fabricated multi-level microchannel system with unique 3D structure using the extended approach.

In this paper, we report on using polydimethylsiloxane (PDMS) tools to emboss cyclic olefin copolymer (COC). Positive photoresist AZP 4620 was used to fabricate 5 and 20 μm thick PDMS tools. The embossed microchannels were 10 μm to 100 μm in width at 10 μm to 100 μm in spacing. The COC embossing parameters, including temperature, force, and time were optimized to reduce replication errors. The optimized process was then successfully applied to fabrication of a passive microfluidic mixer designed and simulated using CFDRC ACE+.

Enzymatic digestion and peptide separation are basic steps for preparation of protein samples prior to their analysis by mass spectrometry. Micro-pillar reactors for digestion and reverse phase liquid chromatography were designed and constructed using semiconductor technologies. The performances of the micro-machined reactors were evaluated: complete Cytochrome C digestion was achieved in 6 min for a concentration up to 25 pmol.μl^-1 and the separation micro-column was seen to exhibit separation capabilities and capacity close to those obtained with a commercial column. Furthermore, a comparative study between hydrodynamic and electroosmotic driven flows was performed for each peptide of a Cytochrome C digest. It was demonstrated that parasitic electrophoretic phenomena disturbed peptide mobility but not protein identification.

A novel PDMS microfluidic spotter system has been developed for the patterning of surface microarrays that require individually addressing each spot area and high probe density. Microfluidic channels are used to address each spot region and large spot arrays can be addressed in parallel. Fluorescence intensity measurement of dye-spotted samples compared to control and pipetted drops demonstrated a minimum of a three-fold increase in dye surface density. Surface plasmon resonance measurement of protein-spotted samples as compared to pin-spotted samples demonstrated an 86-fold increase in protein surface density. This novel spotter system can be applied to the production of high-throughput arrays in the fields of genomics, proteomics, immunoassays and fluorescence or luminescence assays.

This work presents a novel design for a micromachined, capacitively sensed hydrophone. The design consists of a fluid-filled chamber constrained by two sets of membranes. The "input" membranes are arrayed around the outside of the circular chamber. Incoming sound generates a trapped cylindrical wave, creating mechanically amplified motion of the 1 mm diameter central "sensing" membrane. The membrane material is a LPCVD nitride/oxide/nitride triple-stack with respective film thickness 0.1/0.65/0.1 micron. The chamber is filled with 200 cSt viscosity silicone oil. Fluid-filling eases design constraints associated with submerging the sensor, especially with respect to exterior mass loading. Both silicon-glass anodic bonding and tin-gold solder bonding are used to form the structure, including the 5 micron sensing gap. The fluid-structure system is computationally modeled using both approximate analytic and numerical techniques. Model results indicate a 28 dB displacement gain between the motion of the "input" membranes and the "sensing" membranes. An off-chip charge amplifier, with a 10 pF integrating capacitor, is used to convert membrane motion into an electrical signal. Mean measured system sensitivity is 0.8 mV/Pa (-180 dB re 1 V/microPa) from 300 Hz-15 kHz with a 1.5 volt applied bias and a 26 dB preamplifier gain. The predicted low frequency sensitivity is 0.3 mV/Pa. The measured sensitivity exhibits considerable scatter below 7 kHz, with a standard deviation of 80%. Laser vibrometry measurements indicate that this scatter may be caused by compliance of the chip mounting scheme. Above 10 kHz, the quiescent noise is -100 dB re 1 V/rtHz. Noise characteristics exhibit a 1/f character below 10 kHz, rising to a maximum of -50 dB re 1 V/rtHz at 100 Hz.

We report on the progress of a novel nanofluidic device for detecting and manipulating single molecules in solution. This paper discusses the development of an earlier proposed molecule separation method, where electrokinetic forces separate different molecules based on their masses and charges. Optical imaging using confocal microscopy is applied to perform the detection of the single molecules. Potential applications of this device will be assessed. This research aims for the high spatial and spectral resolutions, both in manipulation and detection, which can lead to molecular identification.

Self-assembly is a commonly used strategy in synthesis and fabrication. One of the most economic routes for the fabrication of large ensembles of functional nanosystem is to utilize self-assembly to assemble building blocks such as colloids, nanotubes and nanowires. However, if the functional nanostructures are to be assembled across many length scales within the integrated system, it is necessary to develop new tools for large-scale assembly of nanostructures and manipulation of individual components. Here we report a simple approach to actively control the formation of the self-assembled colloidal crystals in the two-dimensional microfluidic networks. Utilizing a combination of electrocapillary forces and evaporation induced self-assembly, it is possible to actively control the self-assembly process of the colloidal nanoparticles to form colloidal crystals inside the two-dimensional microchannel networks. Using this approach, we can not only selectively fabricate the colloidal crystals in the desired channels, but we can also build colloidal crystals with different optical properties in different channels or in the same channel. This method is not limited to the fabrication of colloidal crystals. In general, it can be configured to produce other novel functional materials using self-assembly process when it is integrated with more sophisticated microfluidic system.

Microbead immunoassay with electrochemical detection has been developed as a sensitive and selective technique for rapid and small volume analyses. In this assay, applications of paramagnetic microbeads in a microfluidic system have aided the automation of all assay steps to enable near-continuous monitoring. These mobile microbeads can be transported through microchannels, captured and held at specific points by a magnet. Hence, by performing immunoassay on microbeads, they can be dispersed throughout a small sample of water, where they provide a large surface area to sample volume ratio that enhances the capture of the target antigen by minimizing diffusional distances. They can then be collected magnetically and manipulated to accomplish all the assay steps to determine if any target was captured. In addition, the microbeads can be accommodated in small volumes, which reduces the dilution of the enzyme product in the detection step thus maximizing sensitivity. Further, electrochemical detection coupled with enzyme-labeled immunoassay has led to the development of a sensitive analytical technique. In this area, interdigitated array electrodes are particularly suited to microfluidics. Improved sensitivity is obtained by redox cycling of the species being detected. In this work, the microbead immunoassays is demonstrated for the virus MS2 bacteriophage.

This paper presents the development of a giant magnetoresistive (GMR) sensor array for the in-line monitoring of magnetic microparticles in microfluidic systems. The GMR sensors employ Ni₈₀Fe₂₀/Cu multilayers with the thickness of each layer controlled between 1 nm to 3 nm, achieving a maximum magnetoresistance (MR) value of 16%. The multilayer films exhibit specific magnetoresistive properties that can be employed for the in-line detection of particular biological molecules bound to magnetic microparticles. The electrical current variations in the developed GMR sensor array in the presence of magnetic microparticles show that the GMR sensor array can be used for real-time monitoring of magnetic microparticles in microfluidic systems.

Fluorescently labeled beads may be utilized in transparent microfluidic devices to facilitate a variety of immunoassay based chemical measurements. We investigate the ability to visualize, quantitate, and reduce undesirable adsorption of beads within a polydimethylsiloxane (PDMS) microchannel device. These methods are prerequisites to the design of practical bead-based microfluidic sensing devices. The PDMS microchannels were shown to be transparent enough to make accurate quantitative optical measurements, although significant adsorption was observed. Epifluorescence microscopy was employed in an attempt to quantitatively evaluate microbead adsorption to PDMS microchannel walls and bulk surfaces after different agitation, solution, and surface treatments. This microscopy method provides reproducible imaging of individual beads and allows for characterization of adsorption to PDMS microchannel walls. Solution composition seemed to play a more important role in the ability to reduce the number of adsorbed beads to the PDMS surface than agitation. The most significant reduction in bead adsorption was seen in surface treatment. The most effective surface treatment examined in this study was Teflon AF.

We report the development of miniature fluorescence detection systems that employ miniature prism, mirrors and low cost CCD camera to detect the fluorescence emitted from 40 fluorescently-labeled protein patterns without scanner. This kind of miniature fluorescence detection systems can be used in point of care. We introduce two systems, one uses prism + mirror block and the other uses prism and two mirrors. A large NA microscope eyepiece and low cost CCD camera are used. We fabricated protein chip containing multi-pattern BSA labeled with Cy5, using MEMS technology and modified the surface chemically to clean and to immobilize proteins. The measurements show that the combination of prism and mirrors can homogenize elliptical excitation light over the sample with higher optical efficiency, and increase the separation between excitation and fluorescence light at the CCD to give higher signal intensity and higher signal to noise ratio. The measurements also show that protein concentrations ranging from 10 ng/ml to 1000 ng/ml can be assayed with very small error. We believe that the proposed fluorescence detection system can be refined to build a commercially valuable hand-held or miniature detection device.

A new passive micromixer has been developed with a low dependence on Reynolds number. The mixer design contains obstructions inside the mixing microchannels to breakup the flow resulting in chaotic mixing. Using CFDRC ACE+ software the mixer was modeled and was shown to completely mix water and glycerin in less than 1 cm. The micromixer was fabricated in cyclic olefin copolymer (COC) using hot embossing with polydimethylsiloxane (PDMS) tools and evaluated using epifluorescence microcopy.

A series of polymer-based Polydimethylsiloxanes (PDMS) ball valves with different opening pressures have been developed for biomedical applications. By tuning different weight ratios of the two components (the base and the curing agent) of PDMS, the valves will have different opening pressures because of different stiffness of the PDMS materials. The curing conditions and mechanical properties of the PDMS material with different ratios have been thoroughly studied. The compressive Young's modulus of the material can be tuned from 310 KPa to 2.0 MPa. Such kind valves can be fabricated by injection molding, one of the cheapest fabrication techniques. Also such kind valve has no dead volume and easily to be integrated into micro-total analysis systems (μTAS).

This paper reports a research effort to design, microfabricate, and test a uniquely designed waveguide technology with integrated micro-lenses in vertical orientations. The waveguide and integrated focusing lenses were microfabricated using thick photo-resist such as SU-8 with UV-light lithography. The waveguide can be used in various biological and biomedical systems.

A micro bubble separator capable of multi-directional bubble exhaustion is designed, fabricated, and tested. The bubble separator fabricated by MEMS fabrication process includes a flat region and a microchannel region. In the flat region, there are a matrix of micro holes with hydrophobic inner surface. The microchannel region contains a set of alternating gas and liquid microchannels. Within the gas microchannels, microholes are further made. The liquid microchannels are hydrophilic, while the gas microchannels, and the micro holes therein are hydrophobic. This bubble separator was experimentally demonstrated to exhale bubbles in multiple directions successfully with fuel recycling capability. Such bubble separators are suitable to deal with the CO₂ bubbles generated at the anode of a micro direct methanol fuel cell (μDMFC).

Laser processing of glass is of significant commercial interest for microfabrication of "lab-on-a-chip" microfluidic devices. High repetition rate pulsed lasers have been investigated and provide adequate processing speeds but suffer from the inherent risk of laser-induced microcracking and other collateral damage induced in the glass. In this paper we present a comparative study between nanosecond deep UV (255nm) frequency doubled copper laser and femtosecond Ti:Sapphire (800nm) regenerative amplifier laser machining of borosilicate glass. Microchannel scribing and high aspect ratio hole drilling is demonstrated in thick glass using direct writing and mask projection techniques. The resulting material structure geometries have been examined using SEM microscopy and white light interferometry. The feasibility of glass laser machining and the significance of each laser type for this application are discussed.

We have developed a microchannel device and a technique for automated microinjection, through which DNA molecules can be delivered to living cells. Microinjection is a reliable way of introducing DNA and various compounds for new drugs into many kinds of cells. However, it is tedious because all the operations, such as holding each cell with a micropipette, positioning it, and injecting the materials, have to be done manually. This is why we have developed the microchannel device and use it in conjunction with the cell manipulation and trapping techniques. Cells flow in a suspension liquid and are trapped when suctioned through a microhole at the bottom of the microchannel. We can automatically trap cells and inject individual DNA molecules. The microchannel device is made of a 100 x 50 mm cross section of silicon rubber. A micro hole is drilled to a minimum diameter of 3mm by excimer laser ablation on a polycarbonate plate. A glass capillary filled with DNA is inserted in the trapped cell from the upper side of the microchannel. We verified the basic operation of the microchannel device in an experiment using white blood corpuscles (K562 cell line) of about 15mm in diameter.

To successfully design and operate the micro fluidics system, it is essential to understand the fundamental fluid flow phenomena when channel sizes are shrink to micron or even nano dimensions. One important phenomenon is the electro kinetic effect in micro/nano channels due to the existence of the electrical double layer (EDL) near a solid-liquid interface. Modeling and simulation of electro-kinetic effects on micro flows poses significant numerical challenge due to the fact that the sizes of the double layer (10 nm up to microns) are very "thin" compared to channel width (can be up to 100's of mm). To fully resolve the double layer, tremendous computational cells are required in a typical finite volume method. It is impractical for designing purpose on typical lab-on-chip platform, in which the length of the microchannel can be orders of magnitude greater than the width and the flow geometries are three dimensional and complicated. In this study, a novel sub-grid integration method to properly account for the electro-viscous effect is developed. This integration approach can be used on simple or complicated flow geometries. Resolution of the double layer is not needed in this approach, and the effects of the double layer can be accurately accounted for at the same time. With this approach, the numeric grid size can be much larger than the thickness of double layer. Presented in this paper are a description of the approach, model development, implementation, and several validation and demonstration simulations of pressure-driven Lab-on-Chip micro flows with electro-viscous effects.

An analysis of the liquid filling processes in an oval disk-shaped micro chamber is demonstrated while associated with the micro systems at various widths of inlet and outlet which are fabricated using MEMS technology. The results are presented in terms of the movement of the gas-liquid interface. During the filling processes the front shape results from the competition among the inertia, adhesion and surface tension. The influences of non-dimensional parameters such as the Reynolds number and Weber number, both based on the inlet velocity, as well as the wall adhesive conditions on flow characteristics are investigated. The effects of the change in channel widths of a circle chamber as well as the change in lengths of semimajor axis and the semiminor axis of an oval chamber on the filling process are also studied. The above-mentioned geometric changes result in a change in the angle between the microchannels and micro chamber at intersection and significantly affect the filling phenomenon of liquid in the micro chamber. It is evident that the air entrapment appears while the strong inertia is imposed and hydrophobic property inside the chamber wall occurs. The numerical results are also compared with experimental measurements and show similar filling processes.

A 3D model of a piezoelectrically actuated microjet was built to characterize acoustic wave propagation in liquid produced by the vibration of a piezoelectric transducer. The model considered the coupling between the piezoelectric transducer, the liquid and the nozzle film. Modal analysis was carried out based on numerical simulation to study the field of pressure wave. The contours of amplitude of pressure wave on the liquid-solid interface at the nozzles inlet were obtained under different resonant frequency. The results demonstrated that the transducer dominated vibration mode with an axis-symmetric distribution is more efficient for the device operation than others. The results also indicated that pressure distribution in the liquid chamber is related to driven frequencies in a different way from that of displacement of structure. The impedance analyzer was used to measure the resonant frequencies of the microjet system and validate the simulation results experimentally. The experimental results agreed well with the predicted. The microjet we developed has the optimum frequency of about 36.5KHz, which corresponds to the first axis-symmetric vibration mode dominated by the transducer, as is predicted well by the simulation result. According to comparison of pressure wave field with nozzle layout of present design under different resonant frequencies, the phenomena that the microjet behaves differently under different orders of resonant vibration are explained, and a frequency design for nozzles layout are presented according to the simulation result.

Microcantilever based biosensors are increasingly used for several bio-applications. In this paper a model based on electrostatic interactions between bio-molecules is proposed to explain the cantilever deflection in biosensor. This modeling, at molecular level, is difficult due to large number of molecules and large simulation times involved. This problem is overcome by evaluating the electrostatic interactions between the groups of molecules rather than the individual molecules. The analysis shows that for sufficiently fine grids (small groups of molecules), the results don't vary much even if the grid is made finer. Simulations carried out verify the analytical results. Simulations carried out also show that the cantilever biosensor deflections match fairly with the experimental data obtained for myoglobin marker for myocardial infarction (MI) published recently. The discrepancies are attributed to surface irregularities which are not considered in the model. It is also observed that the deflection obtained for non-uniform distribution of biomolecules on the cantilever surface (more close to the actual case) doesn't vary much from a uniform distribution. Though the model is validated using results for myoglobin markers used in detection of MI, the modeling and simulation methodology is fairly general and will be valid for other biosensors.

This paper presents the design, fabrication, and testing of a multi-channel microfluidic system specifically designed for use with porous microbeads that can serve as both reagent sources and detectors. The system contains anisotropically etched reservoirs in which reagent source and detector beads are located, and microchannels that are fabricated on both side of the wafer to connect the each reservoir. Fluids are transported from reagent source bead reservoirs to "downstream" reservoirs containing detector beads. The system employs airflow channels to control liquid flow. Finally, the system is completed with PDMS covers on the top and bottom of the device to seal the channels. We have tested the complete system with sample fluid, showing control of liquid flow using the air channels. The result indicates that this system may be useful in biochemical applications where both reagent sources and receptor sites are combined.

Fluorescence calibration is usually done by preparing bio-samples with a series of concentrations and measuring their corresponding fluorescence intensities. A simplified approach is studied by using a microfluidic chip and microspheres. The fluorescence calibration can be carried out on the chip with only one concentration of the microspheres. Microspheres with the diameter of 1~5μm are very useful in bio-detection research. These microspheres are manufactured using high-quality, ultraclean polystyrene microspheres and loaded with a variety of proprietary dyes. They can be labeled with biotin-, NeutrAvdin-, streptavidin- and protein, which can be used as tracers for bio-detections. A microfluidic chip was successfully fabricated for the experiment, and preliminary experimental results have proved the feasibility of the approach for fluorescence calibration.

Conventional DNA separation procedures involve large sizes, high voltages and are unfit for large molecules. Proposed set-up constitutes two fold separation techniques, porous filter for fractionating strands on size and final run through microchannels (agarose, buffer solution) viscous enough for DNA electrophoresis. For arriving at the final set-up all the physical contradictions like voltage, viscosity of the fluid, length of the channel were analyzed. The physical set up consists around 20 microchannels (varying diameters) positioned at 500um (centre-to-centre spacing) assembling entire device within 1cm. Polymerase Chain Reaction (PCR) treated DNA assays, are fed to microchannel entrances. Mixture of DNA strands are then passed through magnetic filters. Filtering property of the filters is adjusted by regulating corresponding magnetic field strengths. Smallest strands pass through small pored filter, owing to high velocity (in electrophoresis), thus categorization being done. Proposal replaces conventional apparatus by miniaturized equipment, in ideal case disposable. Miniaturization reduced voltages requirement, solving high-voltage handling problems. Proposed apparatus can fractionate large (>200kbp) molecules and even organic molecules.

Micro gas pump is one of the important micro fluidic components, which can be used for gas analysis in chemical, air supply of micro fuel cell and micro fluid cooling systems. Pumping gases requires a strong compression ratio inside the pump chamber for gas could be compressed. This paper presents a micro diaphragm air pump actuated by PZT bimorphs, which characterizes thin structure, large air flow and low power consumption. The diaphragm air pump is made up of a cavity and an actuating structure. The actuating structure consists of two PZT bimorphs and a diaphragm with check valves, which could produce large volumetric change ratio. Then, a prototype of the pump whose cavity's dimension is 60×16×2mm was fabricated by precise manufacture. The mathematical models were established and simulation had been carried out, in which the parameters, such as flow rate, diaphragm's vibrating amplitude and resonant frequency are calculated and analyzed. Furthermore, experiments on the pump were carried out. The experimental data are basically agreement with the simulation results. With a voltage of 20V, the air pump's flow is 85.3ml/min in resonance and its power consumption is only 3.18mW. Simulations and experiments show that the diaphragm air pump has high efficiency and good performance. It also shows good application prospects in air supply for micro fuel cell and micro electronic devices' cooling.

This paper describes a novel fabrication method for the manufacture of multi-level microfluidic structures using SU-8. The fabrication method is based on wafer bonding of SU-8 layers and multilayer lithography in SU-8 to form microchannels and other structures at different levels. In our method, non-UV-exposed SU-8 layers are transferred to SU-8 structured wafers at desirably low temperatures. This technique is particularly useful for building multi-level fluidic structures, because non-UV-exposed SU-8 can be used as cover for microchannels and the cover can then be lithographically structured, i.e., to form interconnects, after which subsequent transferring of non-UV-exposed SU-8 onto the wafer allows for the fabrication of interconnected multi-level channels and other structures. Examples of interconnected multi-level microchannels were realized using this newly developed method. Liquid has been introduced into the microchannels at different levels to reveal the desirable functionality of the interconnected multi-level channels. The method described here is easily implementable using standard photolithography and requires no expensive bonding equipment. More importantly, the fabrication procedure is CMOS compatible, offering the potential to integrate electronic devices and MEMS sensors into microfluidic systems.

The assembly of plastic microfluidic devices, MOEMS and microarrays requiring high positioning and welding accuracy in the micrometer range, has been successfully achieved using a new technology based on laser transmission welding combined with a photolithographic mask technique. This paper reviews a laser assembly platform for the joining of microfluidic plastic parts with its main related process characteristics and its potential for low-cost and high volume manufacturing. The system consists of a of diode laser with a mask and an automated alignment function to generate micro welding seams with freely definable geometries. A fully automated mask alignment system with a resolution of < 2 &mu;m and a precise, noncontact energy input allows a fast welding of micro structured plastic parts with high reproducibility and excellent welding quality.