Magnetic control of graphitic microparticles in aqueous solutions,
Significance. This paper presents the first ever magnetic transport of diamagnetic graphite microparticles in water solutions. Given the dominance of viscous drag forces at the microscale, moving a microparticle that is submerged in liquid is comparably as hard as moving a macroparticle within dense honey. While diamagnetism is a weak magnetic property, for graphite it can be exploited to generate useful transport in liquid. The contactless magnetic control of biocompatible micrographite, together with graphite’s unique physical properties, opens up new possibilities for applications in sensing, analysis, synthesis, and diagnosis in chemistry, biology, medicine, and physics.
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 for the first time. We develop a theoretical model for magnetic manipulation of graphite microflakes and demonstrate experimentally magnetic transport of such particles over distances ∼200 μm with peak velocities ∼15 μm/s 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.