Showing papers on "Microfluidics published in 1995"

Development of a PCR-Microreactor

Abstract: The application of microfabrication technology to the development of miniaturized analytical and clinical instrumentation is an area of active interest and research. As a part of this effort, we are developing miniaturized devices and instrument components including reaction chambers, microfluidic devices (i.e. pumps, valves, and flow systems) and detection systems for biomedical applications. Specifically, a microfabricated thermal cycling instrument for application to the polymerase chain reaction (PCR) is being developed. The miniaturization of a PCR thermal cycler and associated analytical system will allow for a portable, low-power, rapid, and highly efficient bioanalytical instrument. We have successfully amplified several DNA targets from different biological systems in silicon-based microfabricated reaction chambers. These include human immunodeficiency virus (HIV) and β-globin DNA targets. Verification of the amplified target has been provided by standard agarose gel electrophoresis. Thermal modeling and infrared imaging have helped delineate optimal designs leading to efficient multiple-heater reaction chambers. Instrument efficiencies and PCR amplification results from the micro devices compare favorably to the commercial benchtop PCR systems. In the present report, we will discuss the most recent micro-PCR DNA amplification results, reaction chamber and thermal cycler optimization, fluidic manipulation and detection strategies, and the overall direction and advantages of the application of microfabrication to DNA-based microinstruments.

Integrated micro devices for small scale gaseous flow study

Abstract: Microfluidics has been an active research field for several years. Numerous micro devices such as pumps, valves, flow sensors and integrated systems for chemical analysis and medical applications have been developed. However, experimental studies of fluid flow in those micro devices are rare to find. As a result, design and analysis of microfluidic devices are mostly based upon continuous flow theory which is subjected to serious suspection as dimensions of the device become smaller and smaller. Several experimental studies have actually shown their results can not be explained with continuous flow model. So far, almost all the experimental studies of microflow are limited to the two-point pressure (inlet and outlet) and flow rate measurements using either conventional capillaries or micromachined channels. In order to measure the microflow with more details, several integrated microflow systems are presented in the thesis. These systems include microchannels (with either uniform or non-uniform cross-sections) and pressure sensors (which are distributed along the channels). Using the integrated microflow systems, some preliminary gas flow experiments have been conducted. For the first time, the gaseous pressure distribution inside microchannels are measured experimentally. The pressure distribution inside a microchannel with uniform cross-sectional area is found to be nonlinear. The experimental results can be explained with an isothermal viscous flow model with slip-flow boundary conditions. Furthermore, it is found that a channel with non-uniform cross-sections can cause a non-trivial pressure change. During the developments of the integrated microflow systems, several related problems has been studied and solved, for example, a universal model has been found which can be used to simulate PSG or oxide sacrificial layer etching process in HF based solutions, a surface micromachined pressure sensor has been designed and modeled. Many technical difficulties such as, thin film stress, etching and sealing of the microchannels and chambers, process integration for microchannels and pressure sensors, etc., have been overcome. All the details related to the design and fabrication have been discussed in the thesis.

Fluid modelling in micro flow channels

Abstract: Over the last few years there has been an increased level of interest in the development of miniaturised systems which require liquids to flow through narrow channels, often only a few microns across. Whilst much has been written on the design and fabrication of pumps, valves, flow channels and on their integration into useful systems, relatively little work has been done on modelling fluid flow behaviour on this scale. As micro-fluidic systems become more complex, the ability to model such flows will be seen as increasingly valuable. This paper begins by reviewing the limited amount of previous fluid modelling work which has been done on the micro-scale. The approach to Computational Fluid Dynamics modelling adopted by the authors and their use of the CFDS-FLOW3D package for this work are then described. Important assumptions and boundary conditions adopted in the analysis are outlined and a comparison given between code predictions and experimental results for fluid flows through a number of different channels of the order of tens of microns in width, showing good agreement. A more complex example in the use of CFDS-FLOW3D as a design tool for a micro-fluidic manifold structure is then given which, when compared with experimental observations, again shows that the methods employed give a valuable insight into flow behaviours on this scale. Finally, areas where future work is needed to improve microfluidic modelling are summarised.