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This thesis summarizes the development of a microfabricated system, which uses a new handling method to manipulate very small particles in fluids. The idea of a channel network with integrated mechanical valves as described here is unique. Such a mechanical system is ideally suited for the preparation of sampies containing particles, e.g. body fluids, and for the manipulation of cells or bacteria contained therein. The system has means for both manipulation and detection of particles with sizes of up to two micrometers. During the work on the system, models were developed to predict the system performance. These models showed excellent agreement with the experimental data. The first discrete microfluidic components such as valves or pumps were presented in the 1970's. Following these first developments, monolithically integrated fluidic microsystems were proposed in the 1980's. This development can be compared to the miniaturization of bulk electronic components. Today (2001), a big market potential for microfluidic systems is forecast. Clinical diagnostic testing is considered to be the most interesting application by the author, especially "point of care" testing. The benefit of having immediate test results at every patient's bed is obvious. Nowadays, only a few such tests are available and they are all based on a simple chemistry. The goal is to perform the more complex processes as in the large centralized labs of today in a "Iab on a chip". These micro-Iabs will thus have to work with bodyfluids, i. e. particles in fluid suspension. The particle sizes can be anything from a few hundred nm to a few micrometers. The Suspension Handling System evolved in three stages. A first prototype was used to give proof of the working principle and to develop the basic micromachining process for the actuators. The device consists of a silicon chip encapsulated by two glass chips. Small freestanding silicone rubber membranes with a thickness of only three micrometers are used to reduce the cross section of the channels. By heating air confined in a small cavity underneath the membrane, the pressure is increased and the membrane is bent into the channel. The channel cross-section is 25x7 um in the open state of a valve. It was shown that the flow of the particles in the channels can be controlled by actuating the valves. The density of valves in this prototype is 90 valves/crrr'. It was also shown that these particles can be monitored with a video microscope. With the first tests it became clear that thermal crosstalk between the valves in such high-density arrays is an important issue. The second prototype was used to show that water-cooling can eliminate this problem. Finite element simulations were used to predict device performance and the simulation results could be confirmed with

Suspension handling system, a micromachined channel network with integrated actuators and sensors