Magnetic actuator for the control and mixing of magnetic bead-based reactions on-chip

Abstract

While magnetic bead (MB)-based bioassays have been implemented in integrated devices, their handling on-chip is normally either not optimal--i.e. only trapping is achieved, with aggregation of the beads--or requires complex actuator systems. Herein, we describe a simple and low-cost magnetic actuator to trap and move MBs within a microfluidic chamber in order to enhance the mixing of a MB-based reaction. The magnetic actuator consists of a CD-shaped plastic unit with an arrangement of embedded magnets which, when rotating, generate the mixing. The magnetic actuator has been used to enhance the amplification reaction of an enzyme-linked fluorescence immunoassay to detect Escherichia coli O157:H7 whole cells, an enterohemorrhagic strain, which have caused several outbreaks in food and water samples. A 2.7-fold sensitivity enhancement was attained with a detection limit of 603 colony-forming units (CFU) /mL, when employing the magnetic actuator.

Predicting the Self‐Assembly of Superparamagnetic Colloids under Magnetic Fields

“…The models described so far consider only static fields. In certain applications, the direction of the magnetic field rotates and depending on the frequency of the rotating field, self‐assembled structures may be able or not to follow the magnetic field and new phenomena may appear. Also, it is relevant to include other typical colloidal interactions in the models, such as electrostatic interactions since there are interesting experimental examples in which self‐assembled structures are influenced by the addition of salt .…”

“…Typical commercial superparamagnetic colloids for use in magnetophoretic separation have very large values of (of the order of several μm) due to values of the magnetic coupling parameter of the order of Γ ≈ 10 3 (see refs. ) or even larger . According to Equation the self‐assembly process will be dominated by deterministic magnetic interactions for volume fractions larger than 10 −4 .…”

“…This highly tunable behavior makes these materials highly attractive for many applications . These applications are extremely diverse and include: ferrofluids used as sealants or lubricants; multifunctional materials such as reconfigurable coatings or magnetically controllable photonic colloidal crystals; materials for biological and biomedical applications such as immunoassays, drug delivery or hyperthermia treatments; adsorbent materials for magnetic separation or magnetic actuators for microfluidics. Many of these applications employ superparamagnetic particles in the form of composite superparamagnetic colloids.…”

Mixing in microfluidic devices and enhancement methods

“…Bynum and Gordon utilized a dual-axis centrifuge to produce a constantly changing meniscus within a microfluidic device, which enhances the mixing properties even for a very thin channel [92]. Berenguel-Alonso et al also successfully created a simple magnetic bead actuator that can be used for microfluidic devices to enhance mixing [93], and Zhu and Nguyen have studied mixing enhancement using ferrofluids and uniform magnetic fields [94]. Overall, the possibilities for active microfluidic mixing enhancement are endless, and the field is still an area of active research.…”

A 3D mixing-based portable magnetic device for fully automatic immunofluorescence staining of γ-H2AX in UVC-irradiated CD4+ cells

“…26,27 Researches on MB-based on-chip IF staining have shown the possibilities of magnetic POC IF assays. 11,[28][29][30][31] As for MB-based on-chip IF staining, a front-end MBs mixing step allows efficient capture of target cells, 31 which is determined by the extent of interactions between MBs and cells. These kind of interactions are not controlled by diffusion because of the large size of cells.…”