Magnetic Nanorobots, Generating Vortexes Inside Nanoliter Droplets for Effective Mixing

Abstract

Magnetic nanorobots are used as nanometer‐size stir bars for rapid stirring inside ultrasmall volumes of fluids. Because of their small size and rapid stirring, they can generate many vortexes inside confined small droplets. It is shown that these vortexes can vigorously churn up large microparticles without destabilizing or moving the droplets. The vortex formation can be easily controlled by tuning the stirring rate of nano stir bars using a simple magnetic stirrer.

On‐Chip Generation of Vortical Flows for Microfluidic Centrifugation

“…Moreover, these have been the subject of a number of extensive reviews. [13][14][15][16][17] In addition, we also omit from the scope of this review technology that has been developed to date that allows rotation to be induced directly on particles and cells themselves (for example, that driven magnetically, [18] which, can also, in turn, be employed to drive vortical flows), as opposed to indirectly due to hydrodynamic rotation. Table 1 shows the different actuation mechanisms by which centrifugal flows can be generated in a microfluidic device.…”

Effects of magnetic nanoparticles on mixing in droplet-based microfluidics

“…Therefore, various experimental and numerical studies have been conducted to improve the mixing performance of droplet-based microfluidics, using either passive or active techniques. 17,26,27 In passive mixers, chaotic advection inside the droplet is introduced by passing the droplet through serpentine, sinusoidal and meandering microchannels. A droplet traveling in a curved microchannel establishes asymmetric recirculation, which allows for convective mass transfer enhancement in both axial and radial directions.…”

“…29 Exploiting magnetic force is a convenient technique because of advantages such as convenient bio-functionalizing of magnetic particles, remote control and straightforward design. 24,26 Combining magnetism and fluid flow in the microscale for actuation and sensing applications led to the field of micro magnetofluidics. 30 Several studies devoted to mixing within microdroplets using magnetic particles.…”

“…Magnetic stirring inside a droplet is an alternative strategy for mixing enhancement. Magnetic polymer beads, 32 polymer structures containing magnetic nanoparticles, 26 and magnetic bars have been used for stirring inside droplets. In this technique, the dipole-dipole interaction between magnetic particles in the presence of a magnetic field causes the formation of a particle chain forming the stirrer.…”

“…Sedimentation of large magnetic stirrers and the need for a very strong magnetic field for smaller stirrers are the main problems of this approach. 26 Despite the above experimental works, there is a lack of detailed study that numerically investigates magnetofluidic mixing process of ferrofluid and its efficiency.…”