Transport of biological materials in microfluidic channels on-chip has gained increasing popularity over the past decade. Many efforts aim at building integrated microfluidic devices that combine several functions such as sample preparation, separation and detection on a single chip, to form a so-called “labon-a-chip”. Highly integrated lab-on-a-chip devices are also known as micro total analysis systems (microTAS). These systems can manipulate sample volumes of less than picoliters, reducing the amount of required sample and analyte that are of ten difficult and expensive to acquire. By integrating conventional lab bench analysis methods on-chip, cost for laboratory equipment can be significantly reduced, and automatic sample handling between the different lab processes requires less

human intervention and reduces the risk of sample loss. Another advantage of the compactness of mocro TAS is faster completion of a sequence of laboratory processes. In addition, the time required for many analytical steps and chemical reactions scale favorably at small length scales, as will be described in more detail further below. The small size and reduced power consumption ofmicroTASmakes them attractive for portable analytical instruments for the biomedical field or for environmental monitoring and control.