Magneto-capillary valve for integrated purification and enrichment of nucleic acids and proteins

Abstract

We describe the magneto-capillary valve (MCV) technology, a flexible approach for integrated biological sample preparation within the concept of stationary microfluidics. Rather than moving liquids in a microfluidic device, discrete units of liquid are present at fixed positions in the device and magnetic particles are actuated between the fluids. The MCV concept is characterized by the use of two planar surfaces at a capillary mutual distance, with specific features to confine the fluids by capillary forces, and the use of a gas or a phase-change material separating the stationary aqueous liquids. We have studied the physics of magneto-capillary valving by quantifying the magnetic force as a function of time and position, which reveals the balance of magnetic, capillary and frictional forces in the system. By purification experiments with a fluorescent tracer we have measured the amount of co-transported liquid, which is a key parameter for efficient purification. To demonstrate the versatility of the technology, several MCV device architectures were tested in a series of biological assays, showing the purification and enrichment of nucleic acids and proteins. Target recovery comparable to non-miniaturized commercial kits was observed for the extraction of DNA from human cells in buffer, using a device architecture with patterned air valves. Experiments using an enrichment module and patterned air valves demonstrate a 40-fold effective enrichment of DNA in buffer. DNA was also successfully purified from blood plasma using paraffin phase-change valves. Finally, the enrichment of a protein biomarker (prostate-specific antigen) using geometrical air valves resulted in a 7-fold increase of detection signal. The MCV technology is versatile, offers extensive freedom for the design of fully integrated systems, and is expected to be manufacturable in a cost-effective way. We conclude that the MCV technology can become an important enabling technology for point-of-care systems with sample in-result out performance.

Liquid carry-over in an injection moulded all-polymer chip system for immiscible phase magnetic bead-based solid-phase extraction

“…This is not observed and can possibly be explained by the complex nature of the total energy associated with the surfaces, as stated above. In addition, the capillary microvalve used in this system is geometrical and hence imposes a physical restriction on the movement of the MB cluster, compared to, e.g., the capillary microvalve employed by den Dulk et al, which consists of two parallel glass plates selectively modified with a hydrophobic coating [8]. In the system employed by den Dulk et al [8], the MB cluster can expand into the hydrophobic regions, since there is no physical barrier forcing the MB cluster together at the capillary microvalve.…”

“…In addition, the capillary microvalve used in this system is geometrical and hence imposes a physical restriction on the movement of the MB cluster, compared to, e.g., the capillary microvalve employed by den Dulk et al, which consists of two parallel glass plates selectively modified with a hydrophobic coating [8]. In the system employed by den Dulk et al [8], the MB cluster can expand into the hydrophobic regions, since there is no physical barrier forcing the MB cluster together at the capillary microvalve. If geometrical capillary microvalves impose a normalisation effect on the carry-over of different solution types it would be beneficial to systems, where such a variation in carry-over is undesirable.…”

“…Berry et al did not report details of their carry-over; however, they claim to be able to successfully extract 5.95 mg MBs in a 1% Triton X-100 (TX-100) PBS solution [4]. den Dulk et al reported an average water carry-over of 0.86 nL/mg using 150 mg of 2.8 mm MBs [8]. An overview of the reported characteristics is given in Table 1.…”

“…This is done by transporting the target-MB cluster through an immiscible phase, such as oil [4][5][6], wax [4,7,8], or air [8], often using an external permanent magnet. Such systems have been demonstrated for a number of applications including enzyme linked immunosorbent assays [6,9,10], nucleic acid extraction [4,7,8,[11][12][13][14], protein extraction [8], and cell extraction [15,16].…”

Stationary microfluidics: molecular diagnostic assays by moving magnetic beads through non-moving liquids

“…Berry et al [9] describe a device which contains three different wells which are filled with different immiscible reagents. Den Dulk et al [10] report on a geometrical valve solution which separates reagent-filled chambers. In our approach, we try to avoid the need of a two-phase liquid system by designing the chambers and the connecting microchannel in a way which allows on the one hand side an easy transport of the magnetic beads by an external magnet, on the other hand minimizes the carry-over of reagents from one chamber to another.…”