Nanoporous membranes for microfluidic concentration prior to electrophoretic separation of proteins in urine

A microfluidic device with two nanoporous membranes was developed to seamlessly integrate sample preparation and electrophoretic separation of proteins. The device was fabricated by sandwiching two nanoporous polycarbonate track etched (PCTE) membranes with differently sized nanopores between PDMS slabs containing embedded microchannels. The first membrane contained larger (100 nm) pores and served as an initial filter to screen out particles, cells and larger proteins. The second membrane contained smaller pores (10 nm) which facilitated transport of inorganic ions and small organic molecules, but not proteins. The sequential combination of these two membranes allows proteins to be concentrated and purified simultaneously. The device was used for the sample-in/answer-out quantification of albumin in human urine within 2.5 min with an improvement in sensitivity of 500 fold compared to a normal pinched injection using fluorescence detection. The linear range of was 0–100 μg mL^–1, with a LOD of 1.5 μg mL^–1 covering the diagnostic level of microalbuminuria of 30 μg mL^–1. The presented device, which is simple to make and use, provides a quantitative alternative for point-of-care detection of proteins, as demonstrated through its application to albumin in urine for the diagnoisis of (micro)albuminuria.