4M Knowledge base - papers

Severin Dahms, Frederik Bundgaard and Oliver Geschke
MIC - Department of Micro and Nanotechnology, Technical University of Denmark (DTU), Building 345 East, 2800 Kgs. Lyngby, Denmark

Abstract

Waveguides are an excellent means of integrating sensor components in single use microfluidic polymer systems. However, most processes for producing on-chip waveguides require several process steps, some of which are not suited for mass production. We report a simple procedure in which two different grades of the cyclic olefin copolymer (COC) Topas® are used as substrate and core layer. In a spin coating process a Topas® grade with high refractive index is spin coated onto the injection moulded substrate with lower refractive index, thereby generating a core layer. A simple hot embossing process enables simultaneous structuring of waveguides and microfluidic channels in the core layer. In a final step the microfluidic structures can be closed with a lid, either by thermal bonding or by laser transmission welding.

The refractive index and glass transition temperature Tg can be altered by changing the ratio between the two copolymers of Topas®. The low optical transmission loss of the material, along with its chemical resistance and low water absorption, makes Topas® a good choice for making integrated optics in microfluidic systems.

S. G. Serra(a), A. Schneider(a), K. Malecki(b), S. E. Huq(a), W. Brenner(b)
a: Science and Technology Facilities Council, Rutherford Appleton Laboratory,Technology – Central Microstructure Facility, Harwell Science and Innovation Campus, Didcot, OX11 0QX, UK
b: Institute of Sensor and Actuator Systems Vienna University of Technology, Floragasse Str./E366 MST, Vienna 1040, Austria

Abstract

This paper describes a simple process of adhesive bonding between a glass lid and a SU-8 microfluidic device. The bonding is made by applying pressure, between 1.24 MPa – 3.72 MPa, and heat, above the SU-8 glass transition temperature (Tg). The advantages of this process are low cost, simplicity and no need of extra adhesive material, which could block microchannels and inlets. The SU-8 microchannels are fabricated on a glass substrate by UV photolithography. The resist thickness is 30 μm and the smallest channels are 5 μm in width. The bonding process was performed using a simple uniaxial press, a torque wrench and a convection oven as an alternative to the complex and expensive bonding machines with a vacuum chamber and alignment tools. To identify a suitable bonding temperature, a Tg of 175°C for the patterned SU-8 was obtained by Dynamic Mechanical Analysis (DMA). The bonding strength was 1.15MPa, measured by a pull-out test, and a bonding area of 90% was achieved, which was observed by visual inspection. It was also investigated the effect of an O2 plasma cleaning process on the bonding quality.

S. Valkai, H. I. Kirei, L. Oroszi and P. Ormos
Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, H-6726 Szeged, Hungary

Abstract

A fully integrated microfluidic sorter is introduced. It is able to count, characterize and sort micrometer sized articles and cells. All functions of the device are performed by light. The objects to be sorted are counted optically, they are characterized by measuring their fluorescence. Even the sorting itself, directing the particles into different channels is performed by the pressure of light. The device is built by photopolymerization, from a light cured optically clear resin upon a glass plate support. The whole structure is created in a single photolithography step. The microfluidic channels and optical waveguides that carry the illuminating, detecting and sorting light form a single integrated structure. The supporting units, like sample reservoirs, pumps, light sources, light detectors are easily connected to the device from the outside. The device is optimized for simplicity. It is a proof-of-concept instrument, it demonstrates that it is possible to build simple optically driven microfluidic systems that perform complicated functions.

B. Ahmed-Omera (b), D. Barrow (b), T. Wirth (a)

(a) Cardiff School of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK
(b) Laboratory for Applied Microsystems, Cardiff School of Engineering, Cardiff University, Cardiff, CF24 3TF, UK

Abstract

The contact between immiscible liquids in a microfluidic system creating segmented flow offers great potential in the study of biphasic reactions in organic chemistry with significant advantages with respect to conventional flask techniques. As organic solvents play a key role in many chemical processes within the pharmaceutical and chemical industry, there are many applications of biphasic reactions in different areas of chemistry. For a simple biphasic reactions, we show that the application of various reaction conditions in microreactors using segmented flow can dramatically increase the reaction rate, especially when microwave irradiation, sonication or phase transfer catalysis
are combined with segmentation.

T. Brenner, C. Müller, H. Reinecke, R. Zengerle, and J. Ducrée
IMTEK – University of Freiburg, Georges-Koehler-Allee 106, D-79110 Freiburg, Germany

Abstract

We established an integrated prototyping chain for rapid fabrication of microfluidic chips in polymers comprising fabrication of masters made from elastomers, replication into polymers by soft embossing, surface modification and thermal sealing. Our techniques enable rapid and precise fabrication of fully functionalized microfluidic chips featuring typical minimum lateral dimensions of 50 μm and aspect ratios smaller than one.