Separation of superparamagnetic particles through ratcheted Brownian motion and periodically switching magnetic fields

Abstract

Brownian ratchet based particle separation systems for application in lab on chip devices have drawn interest and are subject to ongoing theoretical and experimental investigations. We demonstrate a compact microfluidic particle separation chip, which implements an extended on-off Brownian ratchet scheme that actively separates and sorts particles using periodically switching magnetic fields, asymmetric sawtooth channel sidewalls, and Brownian motion. The microfluidic chip was made with Polydimethylsiloxane (PDMS) soft lithography of SU-8 molds, which in turn was fabricated using Proton Beam Writing. After bonding of the PDMS chip to a glass substrate through surface activation by oxygen plasma treatment, embedded electromagnets were cofabricated by the injection of InSn metal into electrode channels. This fabrication process enables rapid production of high resolution and high aspect ratio features, which results in parallel electrodes accurately aligned with respect to the separation channel. The PDMS devices were tested with mixtures of 1.51 lm, 2.47 lm, and 2.60 lm superparamagnetic particles suspended in water. Experimental results show that the current device design has potential for separating particles with a size difference around 130 nm. Based on the promising results, we will be working towards extending this design for the separation of cells or biomolecules.Published by AIP Publishing. [http://dx

Controlling the preferential motion of chiral molecular walkers on a surface

“…[13][14][15] The behaviours of many other molecules have also been investigated in terms of their ability to walk or rotate preferentially in a particular direction either driven by a laser pulse, 16 chemical reactions, [17][18][19][20] electric eld, [21][22][23][24] temperature, 25 or a combination of different stimuli. 26 A ratchet-like behaviour has been observed in colloidal particles, 27 an articial motor system designed to replicate a realistic motor protein, 28 cold atoms in optical lattices, [29][30][31] nanoparticles in solution, 32,33 SQUIDs, 34 soliton transport, 35 nanopores in polymer lms, 36 polarons in diatomic molecular chains, 37 superparamagnetic particles, 38 and many other cases.…”

Polymeric fully inertial lab-on-a-chip with enhanced-throughput sorting capabilities

“…To determine which fabrication technology is the best suited, it is important to take into account the choice of the material substrate, the production costs and manufacturing time, as well as the chip design and the desired functions to integrate (Becker and Gärtner 2008). The microfluidic sorting techniques can be classified into two categories: passive methods in which the functionality is established by exploiting geometrical effects and/or hydrodynamic forces in the microchannel (Karimi et al 2013); active methods, such as dielectrophoresis (Chan et al 2018), magnetophoresis (Liu et al 2016), and acoustophoresis (Simon et al 2017), which are based on the application of external force fields. Active microfluidic systems ensure high separation efficiency but require sophisticated external controls.…”

Transport and diffusion of paramagnetic ellipsoidal particles in a rotating magnetic field

“…However, there exit few natural particles which have the perfect spherical symmetry. In contrast to isotropic particles, anisotropic magnetic colloids are characterized by an induced or spontaneous magnetization which has a dependence on a particular direction, feature the advantages of being easily torqued by an external field, and attract considerable interest in theoretical [26][27][28][29][30] and experimental studies [31][32][33][34][35][36][37][38]. Martin [26] studied a vortex magnetic field that can induce strong mixing in a magnetic particle suspension theoretically.…”

“…Liu and their coworkers [31] experimentally showed separating superparamagnetic particles with a size difference around 130 nm by using periodically switching magnetic fields and asymmetric sawtooth channel sidewalls. Gao et al [32].…”