Abstract
Graphite is an inexpensive material with useful electrical, magnetic, thermal, and optical properties. It is also biocompatible and used universally as a substrate. Micrometer-sized graphitic particles in solution are therefore ideal candidates for novel lab-on-a-chip and remote manipulation applications in biomedicine, biophysics, chemistry, and condensed-matter physics. However, submerged graphite is not known to be amenable to magnetic manipulation, the optimal manipulation method for such applications. Here, we exploit the diamagnetism of graphite and demonstrate contactless magnetic positioning control of graphitic microflakes in diamagnetic aqueous solutions. We develop a theoretical model for magnetic manipulation of graphite microflakes and demonstrate experimentally magnetic transport of such particles over distances [Formula: see text] with peak velocities [Formula: see text] in inhomogeneous magnetic fields. We achieve fully biocompatible transport for lipid-coated graphite in NaCl aqueous solution, paving the way for previously undiscovered biomedical applications. Our results prove that micrometer-sized graphite can be magnetically manipulated in liquid media.
Highlights
We have presented an important demonstration of label-free, contactless magnetic transport of diamagnetic graphitic microparticles in diamagnetic aqueous solutions
We have presented a theoretical model of magnetic transport of magnetically anisotropic diamagnetic microparticles in solution which captures the essential physics of the process
We have shown experimentally that transport works as described in our model by magnetically transporting and tracking the motion of submerged highly oriented pyrolytic graphite (HOPG) microflakes over distances ∼200 μm
Summary
The controlled transport of microparticles in solution is key to a broad range of microfluidic and lab-on-a-chip applications [1, 2] These include microreactors for chemical analysis and synthesis [3,4,5]; biosensing platforms for drug discovery and clinical diagnosis [6,7,8,9]; and separation and sorting of cells, bacteria, and/or viruses in mixtures for therapy and diagnosis Magnetic manipulation and actuation schemes for microparticles have been mostly limited to ferromagnetic, paramagnetic, and superparamagnetic particles [17, 19] These suffer several limitations: Attraction toward the magnetic-field source can preclude fully controlled contactless transport, particles cannot be stably trapped in 3D solely with static magnetic fields, and quantification of the magnetic moment for quantitative sensing applications can be challenging. We focus on label-free magnetic transport of diamagnetic graphite microflakes in absence of fluid flow
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