/pdf/micro-total-analysis-systems-1-introduction-theory-and-27f7corp18.pdf

Micro Total Analysis Systems. 1. Introduction, Theory, and Technology

This critical review summarizes developments in microfluidic platforms that enable the miniaturization, integration, automation and parallelization of (bio-)chemical assays (see S. Haeberle and R. Zengerle, Lab Chip, 2007, 7, 1094–1110, for an earlier review). In contrast to isolated application-specific solutions, a microfluidic platform provides a set of fluidic unit operations, which are designed for easy combination within a well-defined fabrication technology. This allows the easy, fast, and cost-efficient implementation of different application-specific (bio-)chemical processes. In our review we focus on recent developments from the last decade (2000s). We start with a brief introduction into technical advances, major market segments and promising applications. We continue with a detailed characterization of different microfluidic platforms, comprising a short definition, the functional principle, microfluidic unit operations, application examples as well as strengths and limitations of every platform. The microfluidic platforms in focus are lateral flow tests, linear actuated devices, pressure driven laminar flow, microfluidic large scale integration, segmented flow microfluidics, centrifugal microfluidics, electrokinetics, electrowetting, surface acoustic waves, and dedicated systems for massively parallel analysis. This review concludes with the attempt to provide a selection scheme for microfluidic platforms which is based on their characteristics according to key requirements of different applications and market segments. Applied selection criteria comprise portability, costs of instrument and disposability, sample throughput, number of parameters per sample, reagent consumption, precision, diversity of microfluidic unit operations and the flexibility in programming different liquid handling protocols (295 references).

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Microfluidic lab-on-a-chip platforms: requirements, characteristics and applications

Polymer microfluidic devices

We review microfluidic platforms that enable the miniaturization, integration and automation of biochemical assays. Nowadays nearly an unmanageable variety of alternative approaches exists that can do this in principle. Here we focus on those kinds of platforms only that allow performance of a set of microfluidic functions—defined as microfluidic unit operations—which can be easily combined within a well defined and consistent fabrication technology to implement application specific biochemical assays in an easy, flexible and ideally monolithically way. The microfluidic platforms discussed in the following are capillary test strips, also known as lateral flow assays, the “microfluidic large scale integration” approach, centrifugal microfluidics, the electrokinetic platform, pressure driven droplet based microfluidics, electrowetting based microfluidics, SAW driven microfluidics and, last but not least, “free scalable non-contact dispensing”. The microfluidic unit operations discussed within those platforms are fluid transport, metering, mixing, switching, incubation, separation, droplet formation, droplet splitting, nL and pL dispensing, and detection.

/pdf/microfluidic-platforms-for-lab-on-a-chip-applications-2xenxmlmto.pdf

Microfluidic platforms for lab-on-a-chip applications

Conjugated polymer actuators can be operated in aqueous media, which makes them attractive for laboratories-on-a-chip and applications under physiological conditions. One of the most stable conjugated polymers under these conditions is polypyrrole, which can be patterned by means of standard photolithography. Polypyrrole-gold bilayer actuators that bend out of the plane of the wafer have been microfabricated in our laboratory. These can be used to move and position other microcomponents. Here we review the current status of these microactuators, outlining the methods used to fabricate them. We describe the devices that have been demonstrated as well as some potential future applications.

https://science.sciencemag.org/content/sci/290/5496/1540.full.pdf

Microfabricating Conjugated Polymer Actuators

A method for covering a set of open microchannel structures which are fabricated on a planar surface made of plastics and which comprise two or more part areas that have different surface characteristics. The method comprises the steps of: a) providing the surface comprising the set of microchannel structures; b) providing a lid-forming sheet having on one side an even layer of a thermoglue; c) applying the side of the sheet having the thermoglue against the surface carrying the microchannel structure; d) heating the assembly created in step (c) to selectively liquefy the hot-melt adhesive while at the same time pressing the sheet material and the planar surface of the substrate together; e) permitting the resulting laminate-covered microchannel structure to cool. An assembly comprising (a) a planar substrate, the surface of which has a set of one or more open microchannel structures each of which comprises part areas representing different functionalities, and (b) a lid-forming material covering said set of microchannel structures and having one or more openings going from a microchannel structure to ambient atmosphere. The assembly is characterized in that the joint between said surface and said sheet material is a thermoglue that possibly has been cured.

Method for covering a microfluidic assembly

A radiofrequency air plasma has been used to incorporate new functionalities at the surface of cycloolefin polymers (Zeonex® and Topas®), polymethyl methacrylate (PMMA), styrene–acrylonitrile copolymer (SAN), and polystyrene (PS). The main goals with the plasma treatment of the different plastics were to hydrophilize the surfaces and to provide good cell culture properties. Surfaces treated at high RF power/gas flow ratios (50 to 100 W/sccm) became highly hydrophilic (water contact angles of about 5 degrees) and stable towards washing in 70% (v/v) ethanol. Those treated at lower power/gas flow ratios (3 to 10 W/sccm) were less hydrophilic and not wash-stable. Cell growth properties of HeLa cervix carcinoma cells as good as on commercial tissue-culture polystyrene could be obtained for Zeonex, SAN, and PS, treated at relatively low RF power/gas flow ratios. However, no untreated plastics were suitable for culturing these cells. XPS spectra features show that ester, ether/alcohol, and ester/carboxyl groups are formed during the plasma treatments of the different plastics. Measurable amounts of carboxylic acid carbon after plasma treatment were only observed for PS and Topas. Furthermore, at high RF power/gas flow ratios fluorine, aluminium and silicon were incorporated in all investigated plastics surfaces due to ablation–deposition processes in the reaction chamber. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2618–2625, 2002

Characterization of air plasma‐treated polymer surfaces by ESCA and contact angle measurements for optimization of surface stability and cell growth

A general drawback observed with plasma treatment is the limited stability of the hydrophilic-treated surfaces toward washing, storage, or heating. It has recently been found that oxygen, air, or argon radiofrequency plasmas with higher intensities than normally used can give hydrophilic surfaces having good wash stability. High intensity oxygen plasma treatment of polystyrene and polycarbonate surfaces was therefore carried out using two different capacitively coupled RF reactors with internal shelf electrodes. The obtained surface characteristics and stability were evaluated using contact angle measurements, XPS, AFM, and nanoindentation. For both materials, low water contact angles were found to correlate with high surface oxygen content. Only the surfaces exposed to relatively intense treatments, with self-bias voltages above 140 V (polystyrene) or 240 V (polycarbonate), could withstand washing in ethanol and remain highly hydrophilic. Substantial amounts of nonsoluble material were observed on the plastic substrates after treatment. Furthermore, for polycarbonate Young's modulus of the surface was found to increase with increasing intensity of the plasma. These observations were taken as an indication that extensive cross-linking of the surface layer took place. After more than 6 months of storage, the samples treated with the most intense plasmas (self-bias voltages in the range of 480–600 V) still had water contact angles around 20°.

Stability of polycarbonate and polystyrene surfaces after hydrophilization with high intensity oxygen RF plasma.

A method for rendering a surface covered by a polymer material (plastics) more hydrophilic by treatment in a gas plasma of a non-polymerizable gas. The method is characterized in that the intensity of the plasma is selected so that the surface becomes permanently more hydrophilic. A naked plasma treated surface of plastics having an immediate water-contact angle ≤ 30°, such as ≤ 20°, said water-contact angle being changed less than ± 20 % and/or less than ± 5° upon washing with ethanol/water mixture (70 % w/w). A kit comprising (a) a microfabricated device comprising a surface (i) which is manufactured from a synthetic polymer material (plastics) and (ii) on which there are at least one chamber and/or at least one channel, and (b) a fluorescent substance to be detected in the device. The kit is characterized in that the plastics has a fluorescence that is non-significant with respect to the fluorescence of the substance at the wavelength at which the substance fluoresces. A microfabricated device having a liquid transportation system which is formed in/on a polymer material (plastics) that is a polymerised aliphatic monomer containing unsaturation.

Surface and its manufacture and uses

In this work we present microfluidics on a CD platform. Using this approach multiple samples can be analysed simultaneously without any tubing connected to the chip. Valving techniques based on surface tension and surface energy is presented together with a passive valving technique that allow liquids with low surface tension. To better understand the motion of discrete liquid plugs in the nanolitre range in the chip, we have compared experimental results on the hysteresis influence on microfluidic resistance with those from theoretical calculations.

Anders Larsson

Papers

Method for covering a microfluidic assembly

Characterization of air plasma‐treated polymer surfaces by ESCA and contact angle measurements for optimization of surface stability and cell growth

Stability of polycarbonate and polystyrene surfaces after hydrophilization with high intensity oxygen RF plasma.

Surface and its manufacture and uses

Microfluidics in a Rotating CD