Microfluidic devices background

The substrate for the microfluidic device should be selected with consideration of the end application. Substrates used to fabricate the microchip device should not interact with target analytes, and must be compatible with the detection method employed (i.e., should not exhibit background fluorescence, BGF.). For the analysis of nonpolar compounds, it should be kept in mind that substrates such as poly(dimethyl)siloxane (PDMS) can adsorb hydrophobic analytes such as peptides and proteins. Plasma oxidation or treatment of the surface can sometimes be useful to minimize these interactions [34,35]. For perfusates containing organic solvents, compatibility with polymer substrates can also be an issue. Substrates to be used for the fabrication of electrophoresis-based separation devices should be capable of supporting a stable electroomostic flow (EOF). The use of a low cost material and standard processing procedures can permit mass fabrication of devices. 

Cell responses to physical or chemical cues are measured in microfluidic devices primarily via optical or electrochemical means. Huorescence is the most widely used optical detection technique, because absorbance detection (commonly used for macroscale assays) is of limited value in microchannels because of the short path lengths. Fluorescence detection, characterized by its unparalleled sensitivity, is easy to implement in microfluidic systems. Chemiluminescence and bioluminescence also offer low detection limits and have less background noise than fluorescence [8]. Electrochemical detectors are even more easily integrated with microfluidic devices and often are much less expensive than optical systems. However, fabrication of electrodes in microchannel devices is a technical challenge, and the electrical fields used in detection can interfere with on-chip processes such as electrophoresis. Electrochemical techniques include potentiometry, amperometry, and... 

Enhanced Microfluidic Separation by Pressure-Driven Flow, Fig. 5 (a) Effect of the depth of the shallow region in segment D of the CZE device shown in Fig. 1 on its resolving power. The electropherograms presented here were obtained using 1 mM sodium tetraborate solution as the background electrolyte and an... 

---