Density-Based Diamagnetic Separation:  Devices for Detecting Binding Events and for Collecting Unlabeled Diamagnetic Particles in Paramagnetic Solutions

Abstract

This paper describes the fabrication of a fluidic device for detecting and separating diamagnetic materials that differ in density. The basis for the separation is the balance of the magnetic and gravitational forces on diamagnetic materials suspended in a paramagnetic medium. The paper demonstrates two applications of separations involving particles suspended in static fluids for detecting the following: (i) the binding of streptavidin to solid-supported biotin and (ii) the binding of citrate-capped gold nanoparticles to amine-modified polystyrene spheres. The paper also demonstrates a microfluidic device in which polystyrene particles that differ in their content of CH2Cl groups are continuously separated and collected in a flowing stream of an aqueous solution of GdCl3. The procedures for separation and detection described in this paper require only gadolinium salts, two NdFeB magnets, and simple microfluidic devices fabricated from poly(dimethylsiloxane). This device requires no power, has no moving parts, and may be suitable for use in resource-poor environments.

Separation and enrichment of enantiopure from racemic compounds using magnetic levitation

“…Winkleman et al used a microfluidic device combined with magnets to continuously separate and collect polystyrene particles of different densities in a flowing stream of aqueous GdCl 3 solution. 16,17 Although the diameters of these polystyrene particles (75 ~ 150 μm) are larger than the crystals used here, our experiments here showed that ~ 80% of particles (volumetric percentage by visual inspection) reached their equilibrium positions within 5 minutes while it takes ~12h for the other ~20% of particles to separate. We therefore believe that it is reasonable to achieve a high degree of separation in a continuous system as long as some considerations are taken into the process design regarding particle size and separation time.…”

“…The theory of MagLev is described in details elsewhere. 10,11,12 Briefly, under the influence of an external magnetic field, diamagnetic materials of different densities (suspended in a paramagnetic medium) can be levitated to different heights by the balance of magnetic and gravitational forces (Figure 1). Since most materials (especially most organic compounds) are diamagnetic, 2 | J.…”

Combining Step Gradients and Linear Gradients in Density

“…We have, however, previously demonstrated methods to remove objects separated by MagLev including the use of syringes and tubing with a modified container 49 and the use of a continuous flow system. 50 These methods could be applied to a system that combines MagLev and AMPS, but a low flow rate may be required to maintain a stable interface between phases in a continuous flow method.…”

Continuous-flow ferrohydrodynamic sorting of particles and cells in microfluidic devices

“…Many groups have been working on adapting this principle to particles and cells sorting. For example, Whitesides' group separated synthetic particles according to their densities' difference using paramagnetic salt solutions (Winkleman et al 2007;Mirica et al 2009). Pamme's group demonstrated continuous particle and cell manipulation using paramagnetic salt solution in microfluidic devices (Peyman et al 2009;Rodriguez-Villarreal et al 2011).…”