Henning Klank

CO2-laser micromachining and back-end processing for rapid production of PMMA-based microfluidic systems

In this article, we focus on the enormous potential of a CO(2)-laser system for rapidly producing polymer microfluidic structures. The dependence was assessed of the depth and width of laser-cut channels on the laser beam power and on the number of passes of the beam along the same channel. In the experiments the laser beam power was varied between 0 and 40 W and the passes were varied in the range of 1 to 7 times. Typical channel depths were between 100 and 300 microm, while the channels were typically 250 microm wide. The narrowest produced channel was 85 microm wide. Several bonding methods for microstructured PMMA [poly(methyl methacrylate)] parts were investigated, such as solvent-assisted glueing, melting, laminating and surface activation using a plasma asher. A solvent-assisted thermal bonding method proved to be the most time-efficient one. Using laser micromachining together with bonding, a three-layer polymer microstructure with included optical fibers was fabricated within two days. The use of CO(2)-laser systems to produce microfluidic systems has not been published before. These systems provide a cost effective alternative to UV-laser systems and they are especially useful in microfluidic prototyping due to the very short cycle time of production.

Microsystem engineering of lab-on-a-chip devices

Introduction Clean rooms Microfluidics - theoretical aspects Microfluidics - components Simulations in microfluidics Silicon and cleanroom processing Glass micromachining Polymer micromachining Packaging of microsystems Analytical chemistry on microsystems Index

Microstructure fabrication with a CO2 laser system

In this paper, we investigate the use of a commercial CO2 laser system for fabrication of microfluidic systems in polymers. We discuss the cutting process with the laser system and present a straightforward model for the channel depth of microchannels dependent on the fabrication parameters. In particular, we examine the influence of the cutting sequence, the number of cut passes, the laser beam velocity and the laser radiant flux. The model allows the prediction of microchannel depths within a maximum deviation of 8 µm for channels that are up to 210 µm in depths. It was shown that, at constant channel depth, the channel width could be varied by 27% by using different cutting parameters. The optimum cutting sequence for the production of a channel -junction is also presented in the paper. The laser system is shown to be a flexible and rapid tool for the production of polymer microfluidic prototypes.

PIV measurements in a microfluidic 3D-sheathing structure with three-dimensional flow behaviour

The design and production time for complex microfluidic systems is considerable, often up to several months. It is therefore important to be able to understand and predict the flow phenomena prior to design and fabrication of the microdevice in order to save costly fabrication resources. The structures are often of complex geometry and include strongly three-dimensional flow behaviour, which poses a challenge for the micro particle image velocimetry (micro-PIV) technique. The flow in a microfluidic 3D-sheathing structure has been measured throughout the volume using micro-PIV. In addition, a stereoscopic principle was applied to obtain all three velocity components, showing the feasibility of obtaining full volume mapping (x, y, z, U, V, W) from micro-PIV measurements. The results are compared with computational fluid dynamics (CFD) simulations.

Direct milling and casting of polymer-based optical waveguides for improved transparency in the visible range

Polymer waveguides fabricated from photoresist have an inherent high propagation loss in the short visible wavelength range caused by absorption due to the added photosensitizers. We have addressed this problem by development of two novel methods for the fabrication of microfluidic systems with integrated optical waveguides. Polymethylmethacrylate (PMMA) is dissolved in anisole and doped with styrene-arcylonitrile copolymer to vary the refractive index. The doped PMMA with a higher refractive index is then spin coated onto a PMMA substrate with a lower refractive index to provide waveguide properties. Direct micromilling enabled us to fabricate 100 µm wide optical waveguides. Propagation losses of less than 1 dB cm−1 could be achieved throughout the entire visual range down to a wavelength of 400 nm. A casting process amenable to high number production of such devices was furthermore developed.

Multi-Layer PMMA Microfluidic Systems for Ammonia Detection

Bio/chemical microsystems are often aimed at the determination of biological or chemical compounds in fluids. An example of such an application is the quantification of ammonia in water samples. Currently, there are several efforts in the scientific community to make it possible to inexpensively, robustly and reliably measure ammonia in environmental samples using a microanalytical system [1, 2]. It is possible to envision a network of several mass-produced ammonia sensors that monitor water quality. In addition to stationary placed ammonia measuring units, light-weight portable measurement systems are also of interest, especially to environmental monitor officers and field scientists.

Optimization of the optical detection in a polymer-fabricated microfluidic manifold for the determination of phosphorus

Many microfluidic systems have been designed, fabricated and applied to a variety of different analyses in silicon. In recent years attention has turned to polymer fabrication for a number well-documented reasons. The three major advantages of polymer fabrication that have sparked this trend include rapid prototyping, the availability of cheap starting materials and the abundance of polymers with different chemical, physical, electrical and mechanical properties to suit every application. Laser micro machining was chosen for the fabrication of the microfluidic components in this prototype system presented here and polymethyl methacrylate, PMMA as the polymer substrate. The three-layered microfluidic chip was bonded with an applied force at elevated temperatures and leak-free fluidic interconnects were designed. The chosen application for this device is a simple stopped flow measurement in the determination of phosphorus in natural waters. The colorimetric method chosen was based in the formation of the yellow vanadomolybdophosphoric heteropoly acid complex in the presence of inorganic orthophosphate ion in water. Optical detection below 400 nm was achieved with a UV-LED as light source. The optical alignment of the UV-LED through the microfluidic chip at the optical cuvette and the overall integration of the optical components into the manifold were described here.