Sample stacking in laboratory-on-a-chip devices

Sample stacking is a very important sample concentration technique. It has been used widely in capillary electrophoresis (CE). There are many differen t stacking techniques. One of the most popular techniques is called "field- amplified sample stacking" where an electric field discontinuity is set up across a concentration boundary. Charged analytes will then automatically s tacked due to velocity changes after they cross the concentration boundary. There are several different strategies to perform sample stacking in micro fluidic laboratory-on-a-chip devices. One could simply inject a plug of low concentration buffer containing sample into a channel surrounded by high c oncentration buffer. The electric field is then applied to stack the sample and move the whole plug into the separation channel. One could also stack the sample in a side channel adjacent to the separation channel. The disadv antage of this sample stacking technique is the difficulty in control of th e precise location of stacked sample. We present a new sample stacking tech nique applied specifically to microfluidic laboratory -on -a-chip devices. Up to hundreds of fold increases in sample concentration can be achieved. W e have also combined this stacking with electrophoretic separation in the s ame device. (C) 2001 Elsevier Science BV All rights reserved.