Microdevices for Microdialysis and Membrane Separations

Microdialysis is a commonly used technique for separating small biomolecules within a complex biological mixture for continuous biochemical monitoring. Microdialysis is based upon controlling the mass transfer rate of small biomolecules diffusing across a semipermeable membrane into a dialysis fluid while excluding larger molecules such as proteins. These small molecules are subsequently sensed using a biosensor. Since many biosensors are extremely susceptible to fouling, their stability and lifetime can be extended if metabolites are filtered through a microdialysis membrane before the dialysis fluid is moved into the sensor. Dialysis is also used commonly in biological laboratories to desalt high ionic strength protein solutions. As biochemical analysis systems become more integrated for μTAS systems there is a need to automate this process. Thus, an on-chip dialysis system is useful for biochemical reaction engineering where very tight control of ionic conditions must be maintained for effective enzymatic activity. This work demonstrates the ability to integrate polymer microdialysis membranes with microfluidic systems. Microchannels are bonded with a regenerated cellulose membrane. After microchannels are produced using standard processing techniques, they are integrated with these membranes. The cellulose is activated in an oxygen plasma followed by a lamination bond to the microchannels at moderate pressure and elevated temperature. Devices were placed in a solution of rhodamine dye, and dialysis fluid was allowed to flow through the microchannels. The outlet dye concentration was measured by fluorescence intensity as a function of flow rate and follows analytically predicted results.