Simultaneous diamagnetic and magnetic particle trapping in ferrofluid microflows via a single permanent magnet

Abstract

Trapping and preconcentrating particles and cells for enhanced detection and analysis are often essential in many chemical and biological applications. Existing methods for diamagnetic particle trapping require the placement of one or multiple pairs of magnets nearby the particle flowing channel. The strong attractive or repulsive force between the magnets makes it difficult to align and place them close enough to the channel, which not only complicates the device fabrication but also restricts the particle trapping performance. This work demonstrates for the first time the use of a single permanent magnet to simultaneously trap diamagnetic and magnetic particles in ferrofluid flows through a T-shaped microchannel. The two types of particles are preconcentrated to distinct locations of the T-junction due to the induced negative and positive magnetophoretic motions, respectively. Moreover, they can be sequentially released from their respective trapping spots by simply increasing the ferrofluid flow rate. In addition, a three-dimensional numerical model is developed, which predicts with a reasonable agreement the trajectories of diamagnetic and magnetic particles as well as the buildup of ferrofluid nanoparticles.

Microfluidics Based Magnetophoresis: A Review

“…Although electromagnets produce a high magnetic gradient, they yield a low magnetic induction – 100 times smaller than that reported by the permanent magnets ,,. In addition, the design and fabrication processes of the circuitry is complex …”

“…Figure b shows both magnetic and diamagnetic microparticles carried by a diamagnetic fluid through a T‐shaped microchannel towards a single permanent magnet. The magnetic microparticles are attracted to the magnet while the diamagnetic microparticles are repelled away from the magnet and trapped within the microchannel as a result of the negative magnetophoresis . Figure c and 3d show a simple concentration method that can achieve simultaneous trapping of diamagnetic and magnetic microparticles in a capillary using a pair of permanent magnets positioned symmetrically on either side of a microchannel (i. e., opposite poles facing each other).…”

Continuous-flow sheathless diamagnetic particle separation in ferrofluids

“…In order to predict and understand the diamagnetic particle separation in ferrofluid flows, a 3D numerical model was developed to simulate the magnetophoretic particle transport in the Ushaped microchannel. Similar to our earlier work [59], this model considers only the one-way actions that the flow field (via the drag force) and the magnetic field (via the magnetic force) have on the suspended particles. The re-actions of these particles on the flow and magnetic fields, as well as the dipole-dipole interactions between themselves, are, however, neglected considering the low particle concentration in our experiments [60,61].…”

“…Moreover, the grid size is set to decrease from the microchannel center to each of the four walls at a constant ratio (see insets II and III). With this approach, no additional boundary layer meshes, which were employed in the 3D model in our earlier work [59] are needed because the meshes near channel walls are fine enough to trace the particle position accurately.…”

Label‐Free Microfluidic Manipulation of Particles and Cells in Magnetic Liquids

“…With such a configuration, they achieved a stronger magnetic force and thus higher ferrofluid flow rate for continuous particle trapping. Zhou et al [75] used a single permanent magnet and a T-junction microchannel to trap simultaneously and pre-concentrate diamagnetic and magnetic particles in EMG 408 ferrofluids, as shown in Figure 6(e). Diamagnetic particles experienced negative magnetophoresis and were trapped in the main channel (T-junction region).…”