Particle and Bacteria Sorting in Viscoelastic Fluids Using an Elasto-Inertia-Magnetic Fractionation Method

Detection of harmful biological substances in food at the Point of Use (PoU) is very important for the prevention of foodborne diseases. Sample and reagent preparation at the PoU, as a necessary step before detection, is urgently needed. Portable and field-deployable sample preparation microfluidic devices for manipulating particles and biological substances in water have been widely studied. During the recent years, more attention has been given to particles separation in non-Newtonian fluids due to their rheological similarity to the prominent fluids such as food (e.g. milk) and bodily fluids (e.g. blood). However, the mechanism of particle focusing and separation in non-Newtonian fluids is less understood, mainly due to the dominance of elastic forces in such flows. Accordingly, we developed a microfluidic device to investigate the effect of elastic, inertial, and magnetic forces on the focusing of magnetic (9 and 15 m) and non-magnetic (15 m) particles in synthetic viscoelastic fluids with various viscosities. The device included a square microchannel with a side permanent magnet, expanding symmetrically downstream to a wider channel to drop the particles velocity for on-chip imaging. We investigated the effect of multiple parameters on the focusing of each particle experimentally and analytically, in order to obtain physical understanding and the best recipe in which multiplex particle or bacteria separation could be achieved with high efficiency. The studied parameters included the microchannel cross-sectional size, flow rate, fluid viscoelasticity, and magnetic field strength and exposure time. We then used the results of the parametric study to perform Triplex-Inertia-Magneto-Elastic (TIME) sorting of magnetic and non-magnetic particles with >92% purity and efficiency. To demonstrate the potential use of this method in biological applications, we immunologically conjugated two types of bacteria to magnetic and non-magnetic particles and separated them from each other in the microfluidic device with a purity and efficiency of >99%. This study provides the foundation for development of devices for separation of bio-substances in viscoelastic fluids, immunologically attached to microparticles. Our device has the potential to be used for on-site sample preparation along with a variety of biosensors to render biodetection possible at the PoU.