Fabrication and Characterization of laser-patterned Polymer Membranes for Protein Concentration and Dialysis in Microchips

Abstract

The advent of microfluidic chips has enabled miniaturization of many biochemical techniques resulting in faster and cheaper analysis using much smaller amounts of sample and reagents. While many analysis methods such as separations, immunoassays, cell sorting etc. have been successfully adapted to microchips, in most cases sample pretreatment is performed off-chip. Towards the goals of ease of automation, improvement in speed of analysis, and reduction in sample loss, many of the sample preparation steps need to be integrated with analysis at the chip level. Numerous approaches have been developed to incorporate functions such as sample cleanup, sample concentration, mixing, reaction prior to analysis in microchips over the past decade (1). Sample pretreatment can include many steps such as sample clean-up, labeling, mixing, and preconcentration (2). This presentation discusses on-chip sample pretreatment techniques developed using nanoporous polymer membranes in-situ laser-patterned in microfluidic chips.

A unique technique was developed to laser-pattern nanoporous polymer membranes in a microfluidic chip using a projection lithography and phase separation polymerization. The membranes are used for microdialysis (3) and preconcentration of proteins (4), controlling the membrane size, shape and the pore size. For microdialysis, a mass exchanger is fabricated in a fused silica chip. About 35 m thick membranes are polymerized along the microchannel centerline of the mass exchanger. Results indicate that the mass exchanger can be used for desalting protein solutions or separating cytosolic proteins from cell lysates. On the other hand, a 50 m thick membrane is fabricated at the junction of a simple cross channel for electrophoretic sample preconcentration. Results show that the protein concentration increases at least by two orders of magnitude and that the increase is linearly proportional to the concentration time and electric field strength applied.