Investigation of a microfluidic free-flow electrophoresis chip of glass substrate with integrated indium tin oxide electrodes

Free-flow electrophoresis (FFE) is a unique form of electrophoresis that allows continuous electrophoresis separation. Small scale FFE is very practical for processing of limited amounts of samples for analytical purposes. In this work, glass substrate was designed as a chip FFE and its performance was visually demonstrated and characterized using fluorescent probes. The chip consisted of two pieces of glass substrate. One of them was patterned with a planar indium tin oxide (ITO) electrodes, and the other glass was designed with inlets for sample infusion and electrolyte transfer. The depth of the separation channel (15 x 60 mm) is defined by a tape spacer of 85 mu m. Since the integrated ITO electrodes in direct contact with the working solution in the separation channel, a voltage as high as 600 V can be applied without bubbling problems. The main operation factors such as buffer concentration, pH, voltage, and flow rate were optimized to separate the probes, and the results were compared with capillary electrophoresis. The role of EOF and electrolysis was also discussed. Compared to photolithographic wet etching, this design is easier to implement, and it enables effective FFE operation. This chip FFE system has potential application in processing and cell sorting.