Surface Treatments for Microfluidic Biocompatibility

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.

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.

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.

Micromixing is a crucial process within microfluidic systems such as micro total analysis systems (μTAS). A state-of-art review on microstructured mixing devices and their mixing phenomena is given. The review first presents an overview of the characteristics of fluidic behavior at the microscale and their implications in microfluidic mixing processes. According to the two basic principles exploited to induce mixing at the microscale, micromixers are generally classified as being passive or active. Passive mixers solely rely on pumping energy, whereas active mixers rely on an external energy source to achieve mixing. Typical types of passive micromixers are discussed, including T- or Y-shaped, parallel lamination, sequential, focusing enhanced mixers, and droplet micromixers. Examples of active mixers using external forces such as pressure field, electrokinetic, dielectrophoretic, electrowetting, magneto-hydrodynamic, and ultrasound to assist mixing are presented. Finally, the advantages and disadvantages of mixing in a microfluidic environment are discussed.

Microfluidic approaches to malaria detection

Lab-on-a-chip or Micro total analysis systems (μTAS) technologies offer a lot of potential applications for biosensing and biomedical detections. This paper presents the design, fabrication and characterization of a fully integrated siliconpolymer based biophotonic Micro-Total Analysis System for the real-time detection of enzymes and antigens. This device uses optical detection methods i.e, optical absorption, Laser induced fluorescence and evanescence measurement technique to detect the presence, concentration and the activity of biomolecules. The main components of the proposed system are microfluidic unit and micromechanical fluid actuation system, integrated with the optical detection systems. An Echelle grating based Spectrometer-on-Chip on Silica-on-Silicon (SOS) is integrated with the opto-microfluidic assembly for fluorescence detection. On-Chip fabrication and integration of valveless micropump has been carried out in order to facilitate the transportation of fluid within the system. The important advantages of the proposed μTAS are functional independence of each module of the system, simultaneous multi-analyte detection, rapid, precise and discriminating results, low background/high signal-to-noise ratio, lack of moving parts, robust, portability, and feasibility of bulk fabrication.

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.

ADVERTISEMENT RETURN TO ISSUEPREVNewsNEXTNews from Micro Total Analysis Systems (µTAS) 2000: Driven by shear force.Elizabeth Zubritsky reports from Enschede, The Netherlands.Elizabeth ZubritskyCite this: Anal. Chem. 2000, 72, 15, 518 APublication Date (Web):August 1, 2000Publication History Published online1 August 2000Published inissue 1 August 2000https://doi.org/10.1021/ac002898gRIGHTS & PERMISSIONSArticle Views70Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (48 KB) Get e-Alerts Get e-Alerts

Rapid prototyping of glass and PDMS microstructures for micro total analytical systems and micro chemical reactors by microfabrication in the general laboratory

In this work, micro particle imaging velocimetry (micro-PIV) was performed on the fundamental components of a micro total analysis system. Specifically, high aspect ratio passive valves and mixers were designed, fabricated, and characterized. The components were built using Micralyne Protolyne technology on a glass substrate and operated at reasonably achievable pressures. The flows through the components were analyzed both qualitatively and quantitatively with the goal of developing a more complete understanding of internal device performance. Using the results of the micro-PIV developed velocity fields it was found that the high aspect ratio passive valves are able to perform at reasonably achievable pressures. However, it was determined that the high aspect ratio passive mixers offer limited performance enhancements because of the low Reynolds number flows. The results of this work contribute to the understanding of passive component operation and address some of the challenges associated with developing completely integrated micro total analysis systems that use passive devices.

Over the past decades microfluidics has proved its game-changing potential where biomedical diagnostics are performed (Manz et al. 1990; Whitesides 2006). The field of research focuses on so-called ‘Lab-on-a-Chip’ or ‘Micro Total Analysis Systems’ (μTAS) that manipulate and analyse fluid on the microscale. These devices integrate the labour intensive operations of a specific laboratory diagnostic exam onto a chip of the typical size of a credit card. The method offers significant reduction of reagent volumes, reaction times and human intervention through on-chip automation [1]. Since the adaptation of microfluidics towards the biological sciences there has been a surge of interest in the evolution of these two complimentary fields; leading to the adaptation of a huge array of bioanalytical assays onto microfluidic platforms. One of the most promising areas of research in the field of microfluidics is the development of Point of Care (POC) diagnostic devices that are simple to use, cost efficient, fast and effective. By now different modes of operation such as continuous flow, batch-wise discrete volumes and droplet-based liquid handling have been implemented. A range of integrated microfluidic platforms have been developed including passively driven systems propelled by capillary action and paper imbibition, alongside pneumatically, peristaltically, and electrokinetically actuated platforms. This chapter introduces the centrifugal microfluidic “Lab on a Disc” platform [2].

In order to realize a medical micro total analysis system in practical use, a partly disposable 3-way microvalve was developed. The separate channel structure and pneumatic actuation are employed considering the problems of whole blood handling. It has the advantages of easy assembly, large on/off flow ratio (about 10/sup 4/), no bubble problem, low cost due to the partly disposable structure and perfect process matching to micro chemical sensors (amperometric sensors or ISFETs).

Micropumps are one of the most important microfluidic components in Micro Total Analysis System (μTAS). The authors have developed a traveling wave micropump that demonstrates high energy efficiency and does not require valves. A prototype valveless micropump was fabricated using microfabrication techniques to validate the pumping principle. The micropump uses piezoelectric bimorph cantilevers to deform a flexible microchannel wall. Traveling waves are induced on the surface of the microchannel by applying properly phased sinusoidal voltage to the piezoelectric cantilevers. The resulting peristaltic motion of the channel wall transports the fluid. The fluid flow in the micropump was numerically simulated with the computational fluid dynamics code, FLUENT. Comparing the experimental and numerical results confirmed that the proposed modeling method can accurately evaluate the performances of the traveling wave micropump. Based on the flow obtained in numerical analysis, an improvement in the pump efficiency is expected with optimization of the shape of the moving wall.

In this paper, the authors described an extended gate field effect transistor (EGFET)-based biosensor for the detection of streptavidin-biotin protein complexes in a silicon micro-fluidic channel. The connection between EGFET and micro-fluidic system could be achieved with the proposed device, offering merits of isolation between the device and solution, compatibility with the integrated circuit (IC) technology and applicability in the micro total analysis system (/spl mu/-TAS). The device was fabricated on the basis of the semiconductor IC fabrication and micro-electro mechanical system (MEMS) technology. Au was used as the extended gate metal to form a self-assembled monolayer (SAM) with thiol. The bindings of SAM, streptavidin and biotin were detected by measuring the electrical characteristics of the FET device.

A combined circuit/device model for the analysis of integrated microfluidic systems is presented. The complete model of an integrated microfluidic device incorporates modeling of fluidic transport, chemical reaction, reagent mixing, and separation. The fluidic flow is generated by an applied electrical field or by a combined electrical field and pressure gradient. In the proposed circuit/device model, the fluidic network has been represented by a circuit model and the functional units of the /spl mu/-TAS (micro Total Analysis System) have been represented by appropriate device models. We demonstrate the integration of the circuit and the device models by using an example, where the output from the fluidic transport module serves as the input for the other modules such as mixing, chemical reaction and separation. The combined circuit/device model can be used for analysis and design of entire microfluidic systems with very little computational expense, while maintaining the desired level of accuracy.