Microfluidic Research Research Articles

4-D dielectrophoretic handling of Janus particles in a microfluidic chip

Janus particles are dissymmetric systems with 2 faces that could present 2 different physical/chemical properties, offering new possibilities in microfluidic research fields. This work presents a novel approach of handling the rotation of Janus particles with dielectrophoresis in a determined location at the single level. We first present the manufacturing process of those particles with fluorescent PS beads coated on one side with Au. Then spectroscopic studies investigate their optical responses under fluorescence excitation as a mean to monitor their rotation angle. Finally, Janus particles are injected in an electro-microfluidic chip exerting non-uniform localized electrical fields inside the channel. The microfluidic experiment shows that not only precise 3D localization of those particles can be achieved but moreover that their rotation can be controlled by the gradient of the applied electrical field.

An Approach to Understanding Flow Friction Ignition: A Computational Fluid Dynamics (CFD) Study on Temperature Development of High-Pressure Oxygen Flow Inside Micron-Scale Seal Cracks

Abstract Flow friction ignition of non-metallic materials in oxygen is a poorly understood heat-generating mechanism thought to be caused by oxygen flow past a non-metallic sealing surface. Micron-scale fatigue cracks or channels were observed on non-metallic sealing surfaces of oxygen components and could provide a leak path for the high-pressure oxygen to flow across the seal. Literature in the field of micro-fluidics research has noted that viscous dissipation, a heat-generating mechanism, may not be negligible as the flow dimension of the channel is reduced to the micron-scale. Results of a computational fluid dynamics study are presented and used to determine if temperatures developed in high-pressure driven micro-channel oxygen flows are capable of reaching the reported autogenous ignition temperature of non-metallic materials in oxygen.

Microactuators for Fluidic Applications: Principles, Devices, and Systems

Much effort in microfluidics research has been aimed at designing microscale pumps, valves, switches, dispensers, mixers, filters, separators, and so on, which have a major role in the development of innovative systems like chemical process control, bioanalytical devices, medical drug delivery systems, environmental control, and others. Most of these microfluidic devices have one thing in common: the need for precise manipulation and control of small amounts of fluids. MEMS/NEMS research is continuously opening up new knowledge on modeling approaches, novel materials, and MEMS/NEMS processing technologies that stimulate and accelerate the development of new actuation principles and novel actuator configurations. This review paper presents research work on different actuation techniques that are used for the whole range of microfluidic applications. It covers thermomechanical and electrochemical actuation principles, as well as actuation induced with external electric or magnetic fields. It presents a brief explanation of the operating principle of each type of actuator, actuator configuration, its main characteristics, like power consumption, operational voltage, frequency range, and working fluids, and a discussion of comparisons among different actuation schemes. This study compiles and provides some basic guidelines for selection of the actuation schemes that are currently implemented in microfluidic devices.

Cover Picture: Electrophoresis 18'2009

AbstractIssue no. 18 is a special issue on “Miniaturization in Asia‐Pacific”. It has 25 contributions “covering a spectrum of topics pertaining to fundamentals, basic technologies, detection approaches and applications, and it is expected to reflect the rapid progress of up‐to‐date microfluidics research in the Asia‐Pacific region.”

Editorial: Changes to the journal and appointment of a new Co-Editor

It has been two and a half years since this journal was launched in January 2007, and the number of submissions has grown steadily. In keeping with the continued growth of the journal as well as that of the microfluidics and nanofluidics community, the editorial team is constantly thinking of ways to both improve the quality of the journal and better serve the community. It is, therefore, with great pleasure that I announce several new initiatives that will be introduced to Biomicrofluidics. First, I am delighted to announce the appointment of Dr. Leslie Yeo as the new Co-Editor of Biomicrofluidics. Dr. Yeo is considered as one of the young rising stars in the field and has a high profile among microfluidics researchers in the Pacific Rim region. His research group, the Micro∕Nanophysics Research Laboratory at Monash University, is arguably the top microfluidics research group in Australia, among the best in Asia–Pacific, and is currently the leading research group worldwide in surface acoustic wave microfluidics. Dr. Yeo is also no stranger to Biomicrofluidics, having served on the Editorial Board when the journal was launched beginning 2007 and as Associate Editor since January 2008. During this time, Dr. Yeo has tirelessly sought to promote the journal in many different ways; soliciting and handling submissions for several special issues, and introducing creative ways to enhance the visibility and quality of the journal. Second, the following three new sections are to be added to the existing Regular Articles section currently published by the journal in order for Biomicrofluidics to adapt to the rapidly evolving needs of the community. The Brief Communications section, with contributions limited to five published pages each (including figures and tables), consists of short reports of significant new research findings that constitute a complete body of work. Preliminary work or incomplete data sets, as well as publication of a series of short articles by the same research group on a particular topic, are therefore discouraged. The Perspectives and Review Articles sections consist of colloquia that serve to provide an in-depth overview or the anticipated future directions of a particular topic of importance or growth within the field. Papers in these sections are usually solicited from leading researchers in the subject area, although the editors welcome proposals from prospective authors. The Fabrication and Laboratory Methods section is intended to provide a forum for the publication of classical and novel recipes and improvements to fabrication and laboratory techniques associated with microfluidics and nanofluidics and also to those techniques that pertain to chemical and biological applications of lab-on-a-chip devices. Protocols are usually solicited from leading researchers in the field, although the editors welcome proposals from prospective authors. As with the rest of the journal articles, the protocols will carry full citation details. To kick start the section, we have commissioned a novel laboratory method protocol on the use of laser Doppler vibrometry for the spectroscopy of capillary wave vibration and a classical tried-and-tested procedure for the fabrication of polydimethylsiloxane microfluidic chips. Articles in all sections will be rigorously peer reviewed in accordance with the usual high standards of AIP journals. We hope these changes will be beneficial to you, the researcher, and we welcome your comments as these and other initiatives continue to be rolled out. Please feel free to contact us at biomf@aip.org.

Editorial: A note from the new Co-Editor

Editorial: A note from the new Co-Editor

High intensity light emitting diode array as an alternative exposure source for the fabrication of electrophoretic microfluidic devices

A commercially available array of light emitting diodes (LEDs), namely a UV Shark series LED high flux array, was evaluated as a light source for photolithographic patterning of SU-8 photoresist for the fabrication of templates suitable to make poly(dimethylsiloxane) (PDMS) microchips for electrophoresis. At a distance of 15 cm from the substrate, a relatively even intensity of 0.76 ± 0.05 mW/cm 2 was obtained over an area sufficient for patterning a 10 cm (4 in.) silicon wafer. The exposure source was evaluated using a spiral mask design covering a 10 cm wafer. PDMS replicates of this template made in a 25 μm thick layer of SU-8 3025 showed little variation in width over the surface of the substrate, with a variation of 3.2% RSD ( n = 36) and a maximum range in widths of 7.8% of the mean channel width. The use of the optional metal reflector available with the LED array provided partial collimation of the light allowing near vertical structures to be produced across the entire wafer, something which was not possible without the reflector. SU-8 masters prepared using the LED array were compared to masters made using an alternative cheap lithographic source, namely a gel crosslinker. The SU-8 features were much narrower with the LED array than the crosslinker due to the multiple light sources in the crosslinker. A PDMS microchip made using a SU-8 template created using the Shark UV LED array was used for the electrophoretic separation of three anionic fluorescent dyes, with efficiencies up to 32 000 plates. Given that the LED array can be purchased and assembled for less than US$ 500, the Shark UV LED array is a promising alternative to more expensive lithographic light sources and will have significant appeal to many researchers wishing to undertake research in microfluidics around the world.

Micro and nano electrical discharge machining in microfluidics and micro nanotechnology

Potential applications of micro and nano EDM in the research in micro nanotechnology and microfluidics are first discussed. Milling EDM, one variation of EDM, is proposed as a flexible tool for such applications. In practice EDM milling is a process rarely used because it is difficult to prepare thin electrode tools. Therefore the use of electrochemically etched Pt-Ir electrode tool for EDM machining is demonstrated. In addition a compact micro EDM machine is described. Preliminary results concerning the micromachining of silicon are also shown.

Three Dimensional Imaging of Structure and Flow—Critical to Advances in Microfluidics

Abstract Microfluidics, the study of fluid flow through structures with micrometer scale dimensions, is an increasingly important discipline within a number of commercial and industrial applications. One focus of active microfluidic research at the Stanford University Microscale Heat Transfer Laboratories (MHTL) is mass and heat transport in two-phase flows, which has applications in the cooling of integrated circuits and the management of water created in PEM fuel cells. At its core, two-phase microfluidics is the study of interactions between moving liquids and/or gases and/or solids (though not necessarily stationary) structures. Advanced confocal microscopy, with its ability to visualize and measure both flow and structure on a single instrumental platform, will certainly play a key role in the continuing development of microfluidic devices.

Aquacore

Advances in microfluidic research has enabled lab-on-a-chip (LoC) technology to achieve miniaturization and integration of biological and chemical analyses to a single chip comprising channels, valves, mixers, heaters, separators, and sensors. These miniature instruments appear to offer the rare combination of faster, cheaper, and higher-precision analyses in comparison to conventional bench-scale methods. LoCs have been applied to diverse domains such as proteomics, genomics, biochemistry, virology, cell biology, and chemical synthesis. However, to date LoCs have been designed as application-specific chips which incurs significant design effort, turn-around time, and cost, and degrades designer and user productivity. To address these limitations, we envision a programmable LoC (PLoC) and propose a comprehensive fluidic instruction set, called AquaCore Instruction Set (AIS), and a fluidic microarchitecture, called AquaCore, to implement AIS. We present four key design aspects in which the AIS and AquaCore differ from their computer counterparts, and our design decisions made on the basis of the implications of these differences. We demonstrate the use of the PLoC in a range of domains by hand-compiling real-world microfluidic assays in AIS, and show a detailed breakdown of the execution times for the assays and an estimate of the chip area.

Editorial: A brief welcome to this new electronic journal on microfluidic applications to biology and medicine

Spurred by breakthroughs in molecular characterization and microcircuit fabrication techniques, the last decade has seen significant growth in the fields of biophysics and biomedical engineering. Quantum dots, PCR amplification, optical tweezers, AFM, nanocolloids, electrosprays, etc., have catalyzed a myriad of new ways to detect antigens, assay proteins, diagnose diseases, and decipher the genome. Nanomedicine based on immunocolloids is no longer a dream. The time is ripe to bring these diagnostic and drug delivery techniques out of the laboratory and into miniature chips that can be used in the field. Glucose detection kits, DNA hybridization microarrays for genetic identification, insulin inhalers, etc., are just the first of such products that can drive a major biotechnology industry in the near future. This extension from the lab to field requires, however, a robust microfluidic platform that is the focus of our new journal, Biomicrofluidics. These microfluidic techniques allow us to transport fluids and manipulate colloid∕cells∕molecules in small devices. Cellular and molecular level operations, like electroporation and chip-scale optical spectroscopy of molecules, all require specific microfluidic designs that are not yet available. Indeed, the same microfluidic know-how can be used to assemble biological materials (membranes and bones) via directed assembly. The large Editorial Board of Biomicrofluidics is interdisciplinary and multinational, which reflects the composition of this new community. With rapid turnaround and wide circulation, we hope to promote interaction among the large but scattered research communities over the globe. The open-access format and full-media capability are designed to allow rapid dissemination of new techniques and information to the biotechnology industry. The Blog page on the journal website is intended to be a bulletin and sounding board for the community to announce conferences and to solicit responses to new ideas∕technological challenges. We anticipate a major growth in the biotechnology industry and a corresponding increase in microfluidic research. It is our hope that Biomicrofluidics will serve this growing community by offering a common link and a communication conduit among the various scientific and engineering disciplines that participate in this exciting new field. We welcome your submissions; visit the journal’s submission and peer review website at http://bmf.peerx-press.org.

Think small

Think small

Microfluidics meets MEMS

The use of planar fluidic devices for performing small-volume chemistry was first proposed by analytical chemists, who coined the term "miniaturized total chemical analysis systems" (μTAS) for this concept. More recently, the μTAS field has begun to encompass other areas of chemistry and biology. To reflect this expanded scope, the broader terms "microfluidics" and "lab-on-a-chip" are now often used in addition to μTAS. Most microfluidics researchers rely on micromachining technologies at least to some extent to produce microflow systems based on interconnected micrometer-dimensioned channels. As members of the microelectromechanical systems (MEMS) community know, however, one can do more with these techniques. It is possible to impart higher levels of functionality by making features in different materials and at different levels within a microfluidic device. Increasingly, researchers have considered how to integrate electrical or electrochemical function into chips for purposes as diverse as heating, temperature sensing, electrochemical detection, and pumping. MEMS processes applied to new materials have also resulted in new approaches for fabrication of microchannels. This review paper explores these and other developments that have emerged from the increasing interaction between the MEMS and microfluidics worlds.

MEMBRANELESS DIALYSIS IN A MICROFLUIDIC CONFIGURATION

It has been shown to be possible to bring two miscible fluids together, allow diffusional interchange of species between them, and separate the fluids with little or no mixing. This procedure, visualized to occur on small ‘microfluidic’ chips, has been under development for analytical purposes but has recently been proposed as a means of blood purification. Such a system might: (i) enhance biocompatibility; (ii) allow much longer operating times without performance decrement, because there is no membrane to foul (iii) allow multi-step, on-chip processing that is unattractive to realize at macro-scale. These systems raise, however, serious questions: (i) how to achieve volume transport, (ii) how to keep flows in balance over longer times (to avoid mixing), (iii) how to approximate countercurrent flow, (iv) how to avoid excessive protein leakage, and (v) how to design well-behaved inlets and outlets. We report, here, that useful liquid-liquid contact areas behave stably and exchange marker molecules, on prototypes assembled in our laboratory. We show how these prototypes follow predictions of flow and diffusion theory. We describe functional inlets and outlets. We describe photolithographic and silicone casting methods for forming prototypes and demonstrate a ‘flowing sandwich’ (dialysate-blood surrogate-dialysate, see figure) that would eliminate all contact of blood with anything other than dialysate in the transport region of an exchange device.FigureThe challenge of scaling these systems to a level of clinical utility has no precedent in microfluidic research. We thus discuss a smaller system that would support in vitro organogenesis, without transport decrement, as a step toward a wearable clinical dialyzer. Finally, we describe how the technology might be configured to support an adult ESRD patient who uses the device 85% of the time (143 hr/wk).

Shear-induced molecular precession in a hexatic Langmuir monolayer

Liquid crystalline behaviour is generally limited to a select group of specially designed bulk substances. By contrast, it is a common feature of simple molecular monolayers and other quasi-two-dimensional systems, which often possess a type of in-plane ordering that results from unbinding of dislocations-a 'hexatic' liquid crystalline phase. The flow of monolayers is closely related to molecular transport in biological membranes, affects foam and emulsion stability and is relevant to microfluidics research. For liquid crystalline phases, it is important to understand the coupling of the molecular orientation to the flow. Orientationally ordered (nematic) phases in bulk liquid crystals exhibit 'shear aligning' or 'tumbling' behaviour under shear, and are described quantitatively by Leslie-Ericksen theory. For hexatic monolayers, the effects of flow have been inferred from textures of Langmuir-Blodgett films and directly observed at the macroscopic level. However, there is no accepted model of hexatic flow at the molecular level. Here we report observations of a hexatic Langmuir monolayer that reveal continuous, shear-induced molecular precession, interrupted by occasional jump discontinuities. Although superficially similar to tumbling in a bulk nematic phase, the kinematic details are quite different and provide a possible mechanism for domain coarsening and eventual molecular alignment in monolayers. We explain the precession and jumps within a quantitative framework that involves coupling of molecular orientation to the local molecular hexatic 'lattice', which is continuously deformed by shear.