Micromixing Within Microfluidic Devices

A passive microfluidic device using SU-8 photoresist has been developed for detection and analysis of viruses. Due to its high aspect ratio with almost vertical sidewalls and its chemical stability, SU-8 offers a wide variety of applications in the fabrication of microfluidic systems. This photoresist is transparent allowing optical detection and thus, identification of biomolecules. Additionally, SU-8 shows a good biocompatibility offering the possibility to develop assay on the surface that allows the specific binding of biomolecules for analytical applications. In this work, the performance of the microfluidic device has been successfully demonstrated by detection of specific contaminants in test solutions. The microfluidic chip is composed of SU-8 microstructures which have been fabricated by means of photolithography, using glass and silicon as substrate materials. Beside the fabrication of microchannels by means of SU8, we have also used SU-8 as adhesive layer. Introduction Microfluidic chips are nowadays a concept widely used in different fields like biology, pharmacy, medicine and other biotechnologies. Microfluidic or lab-on-a-chip technology promises significant advantages for carrying out rapid, efficient and specific analysis of microorganisms, which could be found in chemical substances. The cost and reagent consumption required for analysis will be reduced by using microfluidic devices due to their small size that is very useful for μTAS (Micro Total Analysis Systems) [1]. Furthermore, analysis time is reduced diffusion paths are shorter and reactions occur with higher efficiency. Depending on the design and complexity of the microstructures, such fluidic systems can provide all necessary functions as well as to identify or quantify specific pathogens. These functions include cell handling, sample mixing [2], sorting [3], transport and measurement of biomolecules [4]. IMSAS develops multichannel microfluidic systems (see figure 1) by using the negative photoresist SU-8. With this photoresist, microstructures up to 2mm of thickness and aspect ratios up to 20 can be constructed [5]. Besides, the SU-8 is a favourable material for fabrication of microchannels because of its excellent chemical stability against several acids and bases and its thermal stability. These properties make SU-8 a very attractive material for a wide range of applications like micro optics, micro machining, packaging and analytical microfluidic applications, as described in this paper. Figure 1: Picture showing one of several microfluidic devices which have been developed and fabricated at IMSAS. It is a microchannel with integrated columns. This paper presents a method for the fabrication of microchannels, which are composed completely of SU-8 for biological applications. The microstructures were fabricated by using a soft lithography process, which involves the negative resist and utilizes SU-8 itself as adhesive bonding, under low temperatures. B3.3 SENSOR+TEST Conference 2009 SENSOR 2009 Proceedings I 193 Borosilicate glass and silicon were selected as substrate material, because processing techniques of the silicon are well developed and SU-8 provides good adhesion to both materials.

Optical trapping allows manipulating very small objects – varying from Angstoms to micron size particles – without physical contact by taking advantage of laser light. This technique, relying on light momentum transfer, allows manipulating biological matter (such as cells, organelles, vesicles or chemically functionalized artificial particles, etc.) and offers promising potentialities for research in biotechnology and biochemistry. Individually confining a large number of microscopic objects opens new ways for the downscaling of analysis tools for drug screening, particles sorting and the assessment of statistical data. In particular, the combination of optical trapping with microfluidics greatly enlarges the possibilities offered by both techniques. This PhD work takes place in a research aiming at developing novel bio-analytical instrumentation relying on large arrays of optical traps compatible with microfluidic systems. The dissertation focuses on the use of micro-optics for generating extended matrices of three-dimensional optical traps capable of capturing a large number of particles within microfluidic environments. The stability of optical traps is first studied with special emphasis on the conditions present in microfluidic flows, both from a theoretical and an experimental point of view, and trapping forces achievable on biological cells are investigated. A multiple optical trapping system relying on microlens arrays, adapted to work on commercial microscopes, is shown to be capable of generating arrays of more than 500 three-dimensional traps. Simultaneously trapping in multiple planes is also evidenced using matrices of microlenses, thanks to a self-imaging effect of the array of traps. Furthermore, possibilities offered by multiple optical trapping within microfluidic environments are explored. Polystyrene spheres as well as biological particles, such as native vesicles, can be trapped in arrays, manipulated inside microfluidic devices and analyzed in parallel through fluorescence microscopy while extremely small quantities of chemical reagents are flown past the array. Finally, for the sake of system miniaturization and further extension of the number of traps, multiple three-dimensional optical trapping based on arrays of miniaturized high numerical aperture parabolic mirrors is proposed, allowing the optics necessary for optical trapping, fluorescence excitation and collection to be integrated at the level of a microfluidic chip. Such miniaturized mirror matrices did not even exist before this thesis; their fabrication and characterization are detailed in this dissertation.

We present a novel microfluidic system in which an aqueous two-phase laminar flow is stably formed, and the continuous partitioning of relatively large cells can be performed, eliminating the influence of gravity. In this study, plant cell aggregates whose diameters were 37-96 microm were used as model particles. We first performed cell partitioning using a simple straight microchannel having two inlets and two outlets and examined the effects of the flow rate and the phase width on partitioning efficiency. Second, by using a microchannel with a pinched segment, the partitioning efficiency was successfully improved. This microscale aqueous two-phase flow system can further be incorporated into micro total analysis systems (microTAS) or lab-on-a-chip technology, owing to its simplicity, applicability, and biocompatibility.

The application of micro total analysis systems has grown exponentially over the past few years, particularly diversifying in disciplines related to bioassays. The primary focus of this review is to detail recent new approaches to sample preparation, nucleic acid amplification and detection within microfluidic devices or at the microscale level. We also introduce some applications that have as yet to be explored in a miniaturised environment, but should benefit from improvements in analytical efficiency and functionality when transferred to planar-chip formats. The studies described in this review were published in commonly available journals as well as in the proceedings of three major conferences relevant to microfluidics (Micro Total Analysis Systems, Transducers and The Nanotechnology Conference and Trade Show). Although an emphasis has been placed on papers published since 2002, pertinent articles preceding this publication year have also been included.

Chapter 2 - Critical factors affecting cells behavior in microfluidic chips

The feasibility of micro total analysis systems (μTAS) on microchips based on the concept of a monolithic instrument is demonstrated. In such a device a microfluidic layer system is deposited in a backend process on a conventional CMOS integrated circuit with the aim to achieve cost and performance enhancements through integration and miniaturization. Experimental results on elementary functional components of a μTAS are presented including a narrow channel electroosmotic micropump, a micro mass flow meter using the thermal anemometric principle, a micro cytometer with integrated optical detection, and elementary structures for on-chip micro-capillary electrophoresis.

Automation Highlights from the Literature

Rapid, sensitive, and selective detection of live pathogens remains a key priority for quality control and risk assessment. While conventional methods often require complicated workflows, costly reagents, lab equipment, and are time‐consuming, rendering them inadequate for field testing and low‐resource settings. Increased attention has been drawn to developing alternative low‐cost and rapid methods to detect on‐site live pathogens in different environmental matrices. Among them, microfluidic devices that integrate various laboratory functions in a miniaturized manner have proven to be a promising tool for the rapid and sensitive detection of pathogens. Herein, the development of microfluidic devices specifically designed for the detection of live pathogens is discussed along a concise summary of novel microfluidics systems recently developed, contrasted to conventional methods regarding assay time, the limit of detection, and target organisms. These include a variety of micro total analysis systems (µTAS) and microfluidic paper‐based analytical devices (µPADs) in combination with molecular methods and traditional live cell detection techniques, such as cell culture, DNA intercalating dyes, resazurin, and immobilized bioreceptors (e.g., aptamers and capture antibodies). Furthermore, insights on the future perspectives of microfluidics for live pathogen detection with a highlight on the rapid and low‐cost method development for field testing are provided.

Sensing of inorganic ions in microfluidic devices

Microfluidic systems allow small volumes of liquids to be manipulated, either by being passed through channels or moved around as liquid droplets. Such systems have been developed to separate, purify, analyze, and deliver molecules to reaction zones. Although volumes are small, reaction rates, catalysis, mixing, and heat transfer can be high, enabling the accurate sensing of tiny quantities of agents and the synthesis of novel products. The incorporation of multiple components, such as pumps, valves, mixers, and heaters, onto a single microfluidic platform has brought about the field of lab-on-a-chip devices or micro total analysis systems (μTAS). Although used in the research laboratory for numerous years, few of these devices have made it into the commercial market, due to their complexity of fabrication and limited choice of material. As the dimensions of these systems become smaller, interfacial interactions begin to dominate in terms of device performance. Appropriate selection of bulk materials, or the application of surface coatings, can allow control over surface properties, such as the adsorption of (bio)molecules. Here we review current microfluidic technology in terms of biocompatibility issues, examining the use of modification strategies to improve device longevity and performance.

Microfluidic approaches to malaria detection

Recently, micro-electro-mechanical-systems (MEMS) technology and micromachining techniques have enabled miniaturization of biomedical devices and systems. Not only do these techniques facilitate the development of miniaturized instrumentation for biomedical analysis, but they also open a new era for integration of microdevices for performing accurate and sensitive diagnostic assays. A so-called “micro-total-analysis-system”, which integrates sample pretreatment, transport, reaction, and detection on a small chip in an automatic format, can be realized by combining functional microfluidic components manufactured by specific MEMS technologies. Among the promising applications using microfluidic technologies, nucleic acid-based detection has shown considerable potential recently. For instance, micro-polymerase chain reaction chips for rapid DNA amplification have attracted considerable interest. In addition, microfluidic devices for rapid sample pretreatment prior to nucleic acid-based detection have also achieved significant progress in the recent years. In this review paper, microfluidic systems for sample preparation, nucleic acid amplification and detection for fast diagnosis will be reviewed. These microfluidic devices and systems have several advantages over their large-scale counterparts, including lower sample/reagent consumption, lower power consumption, compact size, faster analysis, and lower per unit cost. The development of these microfluidic devices and systems may provide a revolutionary platform technology for fast sample pretreatment and accurate, sensitive diagnosis.

There is increasing interest in the development of simple analytical systems enabling the fast screening of target components in complex samples. A number of newly invented protocols are based on quasi separation techniques involving microfluidic paper-based analytical devices and/or micro total analysis systems. Under such conditions, the quantification of target components can be performed mainly due to selective detection. The main goal of this paper is to demonstrate that miniaturized planar chromatography has the capability to work as an efficient separation and quantification tool for the analysis of multiple targets within complex environmental samples isolated and concentrated using an optimized SPE method. In particular, we analyzed various samples collected from surface water ecosystems (lakes, rivers, and the Baltic Sea of Middle Pomerania in the northern part of Poland) in different seasons, as well as samples collected during key wastewater technological processes (originating from the "Jamno" wastewater treatment plant in Koszalin, Poland). We documented that the multiple detection of chromatographic spots on RP-18W microplates-under visible light, fluorescence, and fluorescence quenching conditions, and using the visualization reagent phosphomolybdic acid-enables fast and robust sample classification. The presented data reveal that the proposed micro-TLC system is useful, inexpensive, and can be considered as a complementary method for the fast control of treated sewage water discharged by a municipal wastewater treatment plant, particularly for the detection of low-molecular mass micropollutants with polarity ranging from estetrol to progesterone, as well as chlorophyll-related dyes. Due to the low consumption of mobile phases composed of water-alcohol binary mixtures (less than 1 mL/run for the simultaneous separation of up to nine samples), this method can be considered an environmentally friendly and green chemistry analytical tool. The described analytical protocol can be complementary to those involving classical column chromatography (HPLC) or various planar microfluidic devices.

Pneumatically controlled multi-level microchannel for separation and extraction of microparticles

It has been more than 20 years since the first micro total analysis systems (μTAS) papers were published. Initial reports of these devices, which are also commonly referred to as Labs-on-a-Chip (LOC), LabChips, microchips or microfluidic devices, generally focused on separations and the development of a variety of functional elements for sample manipulation and handling. One of the greatest potentials of μTAS, however, has always been in the integration of multiple functional elements to produce truly sample-in/answer-out systems. In the last decade, the march toward developing such integrated devices has accelerated significantly. Many μTAS reported now are quite sophisticated with multiple sample handling and processing steps that are highly integrated and often automated. While most of these devices are not yet strictly sample-in/answer-out several come quite close. There are, however, some significant hurdles still facing the development of true sample-in/answer-out systems especially in the areas of sample preparation, chip-to-real-world interfacing and detection. Additionally, further progress is needed in the miniaturization or elimination of external fluidic control elements. μTAS have found a major niche in the areas of biological and biomedical analyses, especially cellular and nucleic acid analysis. This focus on biological applications reflects the capabilities of these devices to precisely and accurately handle picoliter volumes of materials and to integrate cell transport, culturing or trapping with reagent delivery, and on-chip detection. Significant progress has been made in the development of a variety of cellular analysis systems; this field, however, is still rapidly growing and many papers focused on the expansion of such capabilities continue to be seen. Areas of focus remain the development of substrate materials and culturing conditions that do not unnaturally perturb or stress cells and that allow for extended culturing so that changes in cell physiology over time can be monitored. In addition, a significant amount of work has been directed to developing cell co-cultures on μTAS to mimic tissues, organs, and organ systems. μTAS can create unique, controlled environments to study cell-cell interactions that can not be replicated in any other way. For cellular assays substantial increases in throughput are also a focus. While significant development toward completely integrated cell assays has occurred and even some clinical demonstrations of such assays have been reported, the availability of commercial, fully integrated devices, however, has lagged. In addition to biological assays, the creative expansion of the basic μTAS toolkit with centrifugal platforms, digital microfluidics, and paper-based devices has substantially expanded its potential application base. Interest in these devices is generally more clinical in nature and again focused on generating sample-in/answer-out analyses. Significant work, however, is still needed for most of these platforms in terms of substrate materials, fluid control, sample handling, integration and throughput. Finally, the development of label-free detection technologies remains of interest. This review focuses on recent advances in μTAS technology in the areas of integrated biological assays and diagnostics with an analytical focus. We have also tried to highlight some material, fabrication, coating, separation, and detection advances with more general applicability. We have not included, for the most part, papers on synthesis, biosensors, theory, simulations or reviews. The papers included in this review were published between September 2012 and September 2013. The material was compiled using several strategies including extensive searches using Scifinder, Web of Science, PubMed, and Google Scholar. The contents of high impact journals were also scanned, including Analytical Chemistry, Lab-on-a-Chip, Nature, PNS, Appl. Phys., Letters, and Langmuir. Almost 2000 papers relating in some way to microfluidics were examined. We have done our best to try to identify some of the most interesting and promising papers and to report on them in this review. Without a doubt we have missed a few excellent papers and had to eliminate others based on space constraints and readability. For those papers that we have failed to include, we apologize in advance and welcome comments regarding any oversight that we have made.