New approach for batch microfabrication of silicon-based micro fuel cells

This paper reports a novel and straightforward approach to the development of a compact micro direct methanol fuel cell. The device consists of a hybrid polymer membrane as a feasible microintegrable electrolyte to be used together with silicon current collectors. These current collectors consist in microfabricated silicon chips that incorporate a fine electrode grid. The membrane combines two polymers with different functionalities, Nafion^® as a proton conducting material and PDMS as a flexible mechanical support. The compatibility of this membrane with MEMS fabrication processes lies in the acknowledged bonding capabilities of the PDMS polymer to materials typically used in microsystems technologies—such as silicon, silicon dioxide and glass—as well as its ability to withstand variations of the Nafion^® volume. The compatibility of all the components with microfabrication processes will permit the application of batch fabrication techniques for the whole device, so contributing to a significant lowering of the fabrication costs.     

A simple and cost-effective method for fabrication of integrated electronic-microfluidic devices using a laser-patterned PDMS layer

We report a simple and cost-effective method for fabricating integrated electronic-microfluidic devices with multilayer configurations. A CO₂ laser plotter was employed to directly write patterns on a transferred polydimethylsiloxane (PDMS) layer, which served as both a bonding and a working layer. The integration of electronics in microfluidic devices was achieved by an alignment bonding of top and bottom electrode-patterned substrates fabricated with conventional lithography, sputtering and lift-off techniques. Processes of the developed fabrication method were illustrated. Major issues associated with this method as PDMS surface treatment and characterization, thickness-control of the transferred PDMS layer, and laser parameters optimization were discussed, along with the examination and testing of bonding with two representative materials (glass and silicon). The capability of this method was further demonstrated by fabricating a microfluidic chip with sputter-coated electrodes on the top and bottom substrates. The device functioning as a microparticle focusing and trapping chip was experimentally verified. It is confirmed that the proposed method has many advantages, including simple and fast fabrication process, low cost, easy integration of electronics, strong bonding strength, chemical and biological compatibility, etc.     

Chemiluminescence detection for Cu (II) based on 1,10-Phenanthroline-hydrogen peroxide reaction on a PDMS microfluidic chip

A simple, rapid and effective method for the determination of copper (II) in water on a PDMS microfluidic chip with chemiluminescence (CL) detection is presented. The CL reaction was based on oxidation of 1,10-phenanthroline by hydrogen peroxide in basic aqueous solution. Polydimethylsiloxane (PDMS) was chosen as material for fabricating the microfluidic chip with two steps lithography method. Optimized reagents conditions were found to be 6.0 × 10^?5 mol/L 1,10-phenanthroline, 1.2 × 10^?3 mol/L hydrogen peroxide, 6.5 × 10^?2 mol/L sodium hydroxide and 2.0 × 10^?3 mol/L Hexadecyl trimethyl ammonium Bromide (CTMAB). In the continuous flow injection mode the system can perform fully automated detection with a reagent consumption of only 3.4 μL each time. The linear range of the Cu (II) ions concentration was 1.0 × 10^?8 mol/L to 1.0 × 10^?4 mol/L, and the detection limit was 9.2 × 10^?9 mol/L with the S/N ratio of 3. The relative standard deviation was 2.8 % for 1.0 × 10^?6 mol/L Cu (II) ions (n = 8). The most notable features of the detection method are simple operation, rapid detection and easy fabrication of the microfluidic chip.     

Compatibility of organic solvents for electrochemical measurements in PDMS-based microfluidic devices

We have investigated the compatibility of some organic solvents commonly used in electrochemistry with microfluidic channels based on poly(dimethylsiloxane) (PDMS) and compared the stability of electrochemical measurements over several hours with how much PDMS swells when immersed in these solvents. Lee et al. (Anal Chem 75: 6544–6554. doi: 10.1021/ac0346712, 2003) have shown that there is a good correlation between swelling of PDMS and the solubility parameter (δ _H) of the various solvents and suggested that δ _H can function as an indication of PDMS compatibility. We show that solvents with a very high swelling ratio can give stable voltammetry over several hours, and thus, we do not find that swelling is a good measure for compatibility with PDMS in electrochemical experiments.     

Embedding off-the-shelf filter in PDMS chip for microbe sampling

Filtration for microfluidic sample-collection devices is desirable for sample selection, concentration, preprocessing, and manipulation, but microfabricating the required sub-micrometer structures is an elaborate process. This article presents a simple method to integrate filters in polydimethylsiloxane (PDMS) devices to sample microorganisms in aqueous environments. An off-the-shelf membrane filter with 0.22-μm pores was embedded in a PDMS layer and sequentially bound with other PDMS channel layers. No leakage was observed during filtration. This device was validated by concentrating a large amount of biomass, from 15 × 10⁷ to 3 × 10⁸ cells/ml of cyanobacterium Synechocystis in simulated sample water with consistent performance across devices. The major advantages of this method are low cost, simple design, straightforward fabrication, and robust performance, enabling wide-utility of chip-based devices for field-deployable operations in environmental microbiology.     

Low-cost credit card-based microfluidic devices for magnetic bead immobilisation

We report a simple low-cost magnetic microfluidic device for magnetic bead separation and immobilisation. One dimensional arrays of localised high magnetic field gradients are constructed at the interfaces between regions magnetised with opposing polarities on the magnetic Fe₂O₃ composite stripes of credit cards. The localised high magnetic field gradients are employed to trap magnetic beads on the surface of the magnetic stripe, without the need for external magnetic components. A magnetic card writer was used to deterministically pattern the magnetic stripes of credit cards to define arrays of magnetic reversals. The fabrication of the device is based on PDMS to credit card bonding of simple flow channels. Experimental results demonstrate that magnetic beads can be captured with efficiencies of 85, 67 and 27 % at flow rates of 25, 50 and 100 μL min^?1, respectively. The results show that the credit card-based magnetic separator might offer an efficient, simple, low-cost alternative to traditional microfluidic magnetic separators for applications such as immunomagnetic cell separation.     

Fabrication of microfluidic devices for packaging CMOS MEMS impedance sensors

This work presents a polydimethylsiloxane (PDMS) microfluidic device for packaging CMOS MEMS impedance sensors. The wrinkle electrodes are fabricated on PDMS substrates to ensure a connection between the pads of the sensor and the impedance instrument. The PDMS device can tolerate an injection speed of 27.12 ml/h supplied by a pump. The corresponding pressure is 643.35 Pa. The bonding strength of the device is 32.44 g/mm². In order to demonstrate the feasibility of the device, the short circuit test and impedance measurements for air, de-ionized water, phosphate buffered saline (PBS) at four concentrations (1, 2 × 10⁻⁴, 1 × 10⁻⁴, and 6.7 × 10⁻⁵ M) were performed. The experimental results show that the developed device integrated with a sensor can differentiate various samples.     

Micromolding fabrication of microresistors with a composite of carbon nanotubes and SU-8 polymer and the application in Wilkinson power divider

This paper reports a new method to fabricate microresistors for applications in micro-electromechanical systems. The fabrication is based on ultraviolet (UV) lithography and micromolding replication. A master mold was first made using UV lithography of a negative-tune photoresist, SU-8. The SU-8 master mold was then used to produce a polydimethylsiloxane (PDMS) intermediate mold. The PDMS intermediate mold was used to replicate the microresistor using composite mixture of multi-walled carbon nanotubes (MWCNTs) and SU-8 photoresist. The replicated microresistors were thermally cured at 95 °C for 6 h. The performances of the replicated micro-resistors were then tested. The experiment had also been conducted using the micro-resistors as isolation resistance in a Wilkinson power divider to test their functionality. Because passive communication components such as Wilkinson power dividers can potentially be made with lithography/micromolding technologies and using polymer as structural material, microresistors as reported in this paper may potentially be suitable for using in such applications.     

Risk management capability model for the development of medical device software

Failure of medical device (MD) software can have potentially catastrophic effects, leading to injury of patients or even death. Therefore, regulators penalise MD manufacturers who do not demonstrate that sufficient attention is devoted to the areas of hazard analysis and risk management (RM) throughout the software lifecycle. This paper has two main objectives. The first objective is to compare how thorough current MD regulations are with relation to the Capability Maturity Model Integration (CMMI^®) in specifying what RM practices MD companies should adopt when developing software. The second objective is to present a Risk Management Capability Model (RMCM) for the MD software industry, which is geared towards improving software quality, safety and reliability. Our analysis indicates that 42 RM sub-practices would have to be performed in order to satisfy MD regulations and that only an additional 8 sub-practices would be required in order to satisfy all the CMMI^® level 1 requirements. Additionally, MD companies satisfying the CMMI^® goals of the RM process area by performing the CMMI^® RM practices will not meet the requirements of the MD software RM regulations as an additional 20 MD-specific sub-practices have to be added to meet the objectives of RMCM.     

The design and fabrication of a low-field NMR probe based on a multilayer planar microcoil

The nuclear magnetic resonance (NMR) probe has great influence on signal transmission and reception in NMR technology applications. In this paper, we present a design, fabrication, and test of an NMR probe comprised of a multilayer planar microcoil with a polydimethylsiloxane (PDMS) microchannel. First, geometric parameters of the probe are determined through theoretical analysis. Second, based on a glass substrate, the multilayer planar microcoil is manufactured using repeated photolithography and electroplating processes. During the fabrication process, the polyimide layer is used to package the coil, and the PDMS interlayer is used to adjust the distance from centerlines between the coil and the sample chamber. Third, the resistance and the quality factor of the coil are found to be 1.2158 Ω and 7.217, respectively, at a Larmor frequency of 28.1 MHz. Finally, the NMR probe is tested in an NMR experiment. The transverse relaxation time T₂ for the solid PDMS is 20.6 ± 0.4 ms, which is in agreement with 21.1 ± 0.2 ms obtained by a Bruker Minispec MQ60. Results show that the design and fabrication of this NMR probe are feasible for time-domain NMR applications.     

Rapid,simple and low cost fabrication of a microfluidic direct methanol fuel cell based on polydimethylsiloxane

In this paper a simple and rapid fabrication method for a microfluidic direct methanol fuel cell using polydimethylsiloxane (PDMS) as substrate is demonstrated. A gold layer on PDMS substrate as seed layer was obtained by chemical plating instead of conventional metal evaporation or sputtering. The morphology of the gold layer can be controlled by adjusting the ratio of curing agent to the PDMS monomer. The chemical properties of the gold films were examined. Then catalyst nanoparticles were grown on the films either by cyclic voltammetry or electrophoretic deposition. The microfluidic fuel cell was assembled by simple oxygen plasma bonding between two PDMS substrates. The cell operated at room temperature with a maximum power density around 6.28 mW cm^?2. Such a fuel cell is low-cost and easy to construct, and is convenient to be integrated with other devices because of the viscosity of the PDMS. This work will facilitate the development of miniature on-chip power sources for portable electronic devices.     

A novel technique for fabrication of micro- and nanofluidic device with embedded single carbon nanotube

This paper describes a novel technique for fabrication of micro- and nanofluidic device that consists of a carbon nanotube (CNT) and a polydimethylsiloxane (PDMS) microchannel. Single CNT was placed at desired locations using dielectrophoresis (DEP) and PDMS microchannel was constructed on the aligned CNT via photolithography and soft lithography techniques. This technique enables a CNT to be seamlessly embedded in a PDMS microchannel. Moreover, controlling the PDMS curing condition enables the construction of the device with or without a CNT (the device without CNT has a trace nanochannel in PDMS). Preliminary flow tests such as capillary effect and pressure-driven flow were performed with the fabricated devices. In the capillary effect tests, the flow stopped at the nanochannel in both devices. In the pressure-driven flow lower flow resistance was observed in the device with a CNT.     

SU-8 microchannels for live cell dielectrophoresis improvements

In this work a novel highly precise SU-8 fabrication technology is employed to construct microfluidic devices for sensitive dielectrophoretic (DEP) manipulation of budding yeast cells. A benchmark microfluidic live cell sorting system is presented, and the effect of microchannel misalignment above electrode topologies on live cell DEP is discussed in detail. Simplified model of budding Saccharomyces cerevisiae yeast cell is presented and validated experimentally in fabricated microfluidic devices. A novel fabrication process enabling rapid prototyping of microfluidic devices with well-aligned integrated electrodes is presented and the process flow is described. Identical devices were produced with standard soft-lithography processes. In comparison to standard PDMS based soft-lithography, an SU-8 layer was used to construct the microchannel walls sealed by a flat sheet of PDMS to obtain the microfluidic channels. Direct bonding of PDMS to SU-8 surface was achieved by efficient wet chemical silanization combined with oxygen plasma treatment of the contact surface. The presented fabrication process significantly improved the alignment of the microstructures. While, according to the benchmark study, the standard PDMS procedure fell well outside the range required for reasonable cell sorting efficiency. In addition, PDMS delamination above electrode topologies was significantly decreased over standard soft-lithography devices. The fabrication time and costs of the proposed methodology were found to be roughly the same.

     

Rapid and low cost replication of complex microfluidic structures with PDMS double casting technology

In this paper, a new method for fast and precise replication of high-aspect-ratio microfluidic structures is reported. First, SU-8 microfluidic structures on the master mold were replicated into Polydimethylsiloxane (PDMS), which served as an intermediate, negative mold, by a conventional soft lithography process. The PDMS negative mold was then treated by wetting its surface with a diluted aqueous solution of a hydrophilic polymer, hydroxypropylmethylcellulose and rinsed with deionized water. Last, the negative mold was used in yet another PDMS molding process to produce a PDMS replica of the microfluidic structures (the hydrofocusing unit for a micro-cytometer) with the same structures as the master mold. Experimental results showed that microstructures with high-aspect-ratio could be consistently replicated with high fidelity. This technique can not only greatly simplify the design and fabrication of master molds, but also protect the expensive and fragile original master mold. The process does not require sophisticated equipment and is well suited for the replication of precision master structures in bulk quantities at low cost.     

3D-printed peristaltic microfluidic systems fabricated from thermoplastic elastomer

Recent advancements in 3D printing technology have provided a potential low-cost and time-saving alternative to conventional PDMS (polydimethylsiloxane)-based microfabrication for microfluidic systems. In addition to reducing the complexity of the fabrication procedure by eliminating such intermediate steps as molding and bonding, 3D printing also offers more flexibility in terms of structural design than the PDMS micromolding process. At present, 3D-printed microfluidic systems typically utilize a relatively ‘stiff’ printing material such as ABS (acrylonitrile butadiene styrene copolymers), which limits the implementation of large mechanical actuation for active pumping and mixing as routinely carried out in a PDMS system. In this paper, we report the development of an active 3D-printed microfluidic system with moving parts fabricated from a flexible thermoplastic elastomer (TPE). The 3D-printed microfluidic system consists of two pneumatically actuated micropumps and one micromixer. The completed system was successfully applied to the detection of low-level insulin concentration using a chemiluminescence immunoassay, and the test result compares favorably with a similarly designed PDMS microfluidic system. Prior to system fabrication and testing, the material properties of TPE were extensively evaluated. The result indicated that TPE is compatible with biological materials and its 3D-printed surface is hydrophilic as opposed to hydrophobic for a molded PDMS surface. The Young’s modulus of TPE is measured to be 16 MPa, which is approximately eight times higher than that of PDMS, but over one hundred times lower than that of ABS.     

Fast and inexpensive method for the fabrication of transparent pressure-resistant microfluidic chips

The recent rise of high-pressure applications in microfluidics has led to the development of different types of pressure-resistant microfluidic chips. For the most part, however, the fabrication methods require clean room facilities, as well as specific equipment and expertise. Furthermore, the resulting microfluidic chips are not always well suited to flow visualization and optical measurements. Herein, we present a method that allows rapid and inexpensive prototyping of optically transparent microfluidic chips that resist pressures of at least 200 bar. The fabrication method is based on UV-curable off-stoichiometry thiol-ene epoxy (OSTE+) polymer, which is chemically bonded to glass. The reliability of the device was verified by pressure tests using CO₂, showing resistance without failure up to at least 200 bar at ambient temperature. The microchips also resisted operation at high pressure for several hours at a temperature of 40 °C. These results show that the polymer structure and the chemical bond with the glass are not affected by high-pressure CO₂. Opportunities for flow visualization are illustrated by high-pressure two-phase flow shadowgraphy experiments. These microfluidic chips are of specific interest for use with supercritical CO₂ and for optical characterization of phase transitions and multiphase flow under near-critical and critical CO₂ conditions.     

A simple method of constructing microfluidic solid-state quantum dot molecular beacon array for label-free DNA detection

Solid-state molecular beacons show great potential for label-free biomarker detection, however, it is challenging to construct robust and homogenous quantum dot molecular beacon microarrays in a microfluidic platform. Here, we report a simple and cost-effective method of constructing a mercaptopropionic acid quantum dot (MPA-QD) microarray in a microfluidic platform using a PDMS through-hole structure. This method combines soft lithography and surface functionalization to achieve uniform QD immobilization in a microfluidic network. With the simple fabricated quantum dot microarray sensor integrated in the microfluidic device, label-free biomarker detection was performed with high efficiency, specificity and sensitivity. We performed cardiovascular biomarker detection, and our microfluidic QD molecular beacon platform achieved target DNA sequence identification at a low concentration of 1 nM/L.     

Low cost transparent SU-8 membrane mask for deep X-ray lithography

Deep X-ray lithography masks require good transparency and mechanical resistance to the intense synchrotron X-ray beam, large active areas (cm)² and compatibility with the standard fabrication processes (optical lithography and gold electroforming). Moreover higher resolution can be achieved with low roughness flat membrane. Furthermore multiple aligned exposures require an optically transparent material. Diamond like Carbon membranes fulfill those requirements but have a prohibitive cost. Our approach consists in using an SU-8 epoxy resin layer as membrane material. In this communication the different steps of the fabrication process will be presented, as well as the results obtained using the mask for particular applications.     

Direct imprinting of organic–inorganic hybrid materials into high aspect ratio sub-100 nm structures

The challenging fabrication of sub-100-nm structures with high aspect ratio by UV-nanoimprint lithography (NIL) is addressed in this work. Thermal shrinkage is induced by cooling the structures below room temperature to avoid the issues commonly arising during the release of the polymeric nanostructures from the master. The UV-NIL has been performed to obtain OrmoComp^® nanostructures using OrmoStamp^® working stamps copied from Si masters. Nanoridges and nanopillars with 45 nm width and 380 nm thickness have been fabricated with a corresponding aspect ratio of 8.5. This is, to the best of our knowledge, the highest aspect ratio achieved using organic–inorganic hybrid materials at the sub-100-nm scale.     

In-situ fabrication of an out-of-plane microlens with pre-definable focal length

Out-of-plane microlenses are an important component for integrated optics. Unlike their in-plane counterparts, the fabrication of out-of-plane microlenses is more complicated, which limits their applications. In this paper, a new technique that is capable of fabricating out-of-plane microlenses is described. The resulting lenses have pre-definable focal length and can focus light beams not only in the horizontal plane, but also in the vertical plane. The fabrication process is completely compatible with the soft lithography technique. The lens chamber with two thin polydimethylsiloxane (PDMS) membranes was designed and fabricated together with microfluidic or other components using the same UV lithography mask. The lens was then formed in an in-situ fashion. Curable polymers were injected into the lens chamber and cured while pneumatic pressure was applied to keep the PDMS membranes deformed in a quasi-spherical profile. Pneumatic pressure and membrane thickness can be adjusted to control the resulting lens focal length. With a group of lens chambers with different membrane thickness, a single pressure line can be used to fabricate microlenses with different focal lengths. Since cured polymer was used as the lens filling material, the resulting lens can be used without a pressure source. Different polymers can be selected for desirable optical properties. The simulation and experimental results have proved the feasibility of this technique and resulting lens showed good focusing ability for a divergent light beam from an on-chip multi-mode optical fiber. The small design footprint, total compatibility with soft lithography and technical versatility of this technique make it particularly useful for intergrating out-of-plane microlens into microfluidic chips, which may open new possibilities for the development of on-chip optical detection system.