23.1. INTRODUCTION

The study of fluidic motion at small size scales has always been a part of several engineering areas. For example, water or oil transport through porous material (e.g., rocks and soil) has been important in petroleum engineering for a long while. The introduction of the 'lab-on-a-chip' or the 'micro total analysis system ( TAS)' concept has generated a renewed interest in micro/nanofluidic technologies among engineers and biologists over the last decade. Most chemical and biological analyses are currently done in 'wet' laboratories, and require bulky and expensive analysis tools as well as skilled labor. In addition, these analysis methods require large amount of sample because of the sample loss during the complicated sample preparation/purification steps they entail. These problems would be greatly alleviated if a molecular analysis system could be scaled down to very small dimensions. Also the scaling laws of molecular separation processes generally favor miniaturization in terms of speed and separation resolution.1 Such concept was first introduced by Terry et al.2 ^, 3 when they devised a gas chromatography system micromachined on a silicon wafer. However, it was only in 1990 when the advantages of micromachined chemical analysis system were fully appreciated by Manz et al.1 Micro total analysis systems have many advantages, such as lower power consumption, smaller reagent consumption, smaller overall size, lower cost, portability and disposability. Such prospects became of specifically high...