On-Chip Testing of the Speed of Magnetic Nano- and Micro-Particles Under a Calibrated Magnetic Gradient

Abstract Magnetic drug targeting envisions the use of external magnets to manipulate magnetic particles inside the human body, to direct them to disease targets such as tumors, infections, and ear and eye targets. A key question is how good are the particles? How well do they move in media under the action of applied magnetic gradients? To address this question, we designed and implemented a simple on-chip testing and image tracking system to quantitatively assess the motion of magnetic particles in response to an applied magnetic gradient. In this system, the magnetic particles are placed in on-chip wells and then a calibrated magnetic gradient is applied to the particles. The resulting motion of the particles is monitored and quantified by a microscope, camera, and by imaging software. The system measures both particle speed and chaining. We assessed the motion of seven different commercial magnetic particle ranging in size from 10 nm to 100 μm in diameter. All seven particles displayed consistent trends: larger particles moved faster (according to a power law), particles at higher concentrations created longer chains or needle-like aggregates and moved faster, and both speed and chain or needle length increased with time yielding a final speed proportional to the square of particle diameter. The most striking finding was the consistency of all seven particles within these trends. There were no outliers. No particles performed above the trend lines (no high-performance outliers), nor were there any particles that performed below the trend line (no poor performance outliers). We hope the data collected can be used to better understand particle motion, including the physics of chaining and how it impacts the speed of particle transport in media, and will enable improved design of next-generation magnetic drug delivery systems.