| Microfluidic devices are advantageous to the field of analytical chemistry because of their small volumes, high throughput, fast analysis and inline coupling to other lab-on-a-chip devices. A separation technique called micro-free flow electrophoresis (muFFE) has been developed as a continuous analytical separation technique. muFFE continuously introduces a thin sample stream at the top of the separation channel. Pressure driven flow moves the analyte toward the bottom of the channel and an electric field is applied perpendicular to the direction of flow. As the sample flows through the separation channel, analytes in the sample are separated based on size and charge differences. muFFE for analytical separations holds many advantages over other micro fluidic devices due to the continuous flow and detection of sample. Signal averaging can be used to improve signal to average by 10-fold in under two minutes of data collection. Limits of detection as low as 10 picomolar have been reported. Continuous flow and detection in muFFE allows the fast analysis of samples with changing concentrations. For example, a receptor can be titrated with a gradient of increasing ligand concentration to measure binding. Upon binding, the ligand-receptor complex assumes a larger size than the remaining unbound receptor. The bound complex and free receptor were continuously separated and detected using muFFE. Binding constants were determined from ligand, receptor and complex concentrations. Gradient muFFE was shown to collect more data and in a shorter time than other binding affinity methods. In addition, muFFE was demonstrated as a technique for high speed monitoring of in vivo neurotransmitter concentrations. The muFFE instrument allowed observation of concentration changes on the second time scale. Unlike discrete sampling techniques, temporal resolution was not limited by sampling rate. |
