Nanoporous Membranes for Microfluidic Concentration Prior to Electrophoretic Separation of Proteins in Urine

Abstract

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.

Label-free time- and space-resolved exometabolite sampling of growing plant roots through nanoporous interfaces

“…For example, previous efforts described the use of multilayer microfluidic layers for sample pre-concentration and separation applications that employed polycarbonate track etched (PCTE) membranes and plasma treatment to facilitate bonding between the layers 17 . Plasma treatment is as effective as PDMS layers and can also irreversibly bond other substrates such as glass, silicon and oxide layers 17,18 . However, plasma treatment causes oxidative damage to certain commercial membranes, irreversibly changing chemical properties.…”

“…This is likely due to increased molecular interactions of dextran with the membrane compared to FITC. Surface fouling, clogging and adsorption to the membrane and PDMS surfaces are expected to increase for large molecules 16,17 .

Figure 2Effect of pixel size on the rate of diffusion of ( A ) FITC, a small fluorescent molecule and ( B ) labelled dextran, a large fluorescent molecule. Diffused fraction (%C/C 0 ) with respect to sampling time in stopped-flow mode.

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Recent advances in microfluidic sample preparation and separation techniques for molecular biomarker analysis: A critical review

“…To provide analyte selectivity a PDMS microfluidic device was developed with integrated polycarbonate track etched membranes having different sized nanopores [45]. This double-membrane microfluidic device processed a urine sample, with the 100 nm pore membrane excluding particles and cells in human urine, but passing proteins, small molecules and ions.…”

Recent advances in protein analysis by capillary and microchip electrophoresis

“…138 Recently, a microfluidic device featuring two nanoporous membranes with different sizes was employed for preconcentration of albumin in urine samples. 139 The upper membrane containing larger (100 nm) nanopores acted as a size-selective filter passing out particles, cells and larger proteins, ensuring high robustness and reliability for analyzing untreated samples. The lower, smaller pore sized membrane (10 nm) permitted the transport of inorganic ions and small organic ones but not proteins allowing them to be concentrated.…”