Self-Contained Handheld Magnetic Platform for Point of Care Cytometry in Biological Samples

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (1 of 10) 1600144 wileyonlinelibrary.com based on their refractive index and size.[4] Label-free approaches eliminate the need for cell markers and allow separation based on intrinsic cell properties. Magnetic levitation enables label-free, sensitive, and specific density measurements of particles which are suspended in a paramagnetic medium and placed in a magnetic field.[5–8] A diamagnetic object or immiscible liquid droplet which is suspended in a paramagnetic medium, such as a gadolinium (Gd) ion solution, and placed in a magnetic field will experience two opposing forces: (i) the buoyancy of the object due to its density relative to the medium and (ii) a magnetic force due to its magnetic susceptibility relative to the suspending medium. At equilibrium between these two forces, the object will levitate at a height which is proportional to its volumetric mass density. Magnetic levitation has been proposed for a wide range of applications, including self-assembly and arrangement of objects,[9–12] monitoring of chemical reactions and substrate binding,[13–17] material characterization,[17–19] bottom-up tissue engineering,[10,20] and quality control based on the volumetric mass density of the levitated object.[21,22] This method allows measurements of the intrinsic cell densities and, compared to other label-free approaches, active sorting using a magnetic field formed by two permanent magnets and does not require peripheral equipment to generate the field, reducing the overall cost. A small-scale magnetic levitation setup compatible with a microscope has previously been developed to separate different types of cells within a blood sample, estimate the age of red blood cells (RBCs), and identify circulating tumor cells.[5] More recently, a compact, portable, and inexpensive smartphonecompatible magnetic levitation device was proposed to levitate micro-objects, measure the equilibrium levitation height of the object using a smartphone camera and a magnifying lens, and analyze the height to estimate the density of the microobject.[23,24] This device was also presented for sickle cell disease diagnostics based on increased density of RBCs in the presence of sodium metabisulfite.[25] Here, we develop a self-contained magnetic levitation platform fully independent from a dedicated microscope and a smartphone for density-based microparticle separation from heterogeneous groups of particles, and an algorithm running on the same platform for on-board image analysis and quantification of the levitation height of the particles in order to estimate particle densities. Using this Self-Contained Handheld Magnetic Platform for Point of Care Cytometry in Biological Samples