Smart-phone attachable, flow-assisted magnetic focusing device

Detection and sorting of particles and cells in a continuous flow stream is of great importance to downstream biological studies and high-throughput screening. Many particle separation techniques require peripheral devices, complex channel designs or setups that can limit the process and its applications. Here, we present a smart-phone attachable continuous flow magnetic focusing device as an inexpensive and portable tool for reproducible, real-time detection and sorting of particles in highvolume samples based on their volumetric mass density. Diamagnetic particles were suspended in a paramagnetic medium and pumped through a microcapillary located between two permanent magnets. Appropriate flow rate allows each particle to be confined at a vertical equilibrium height. A magnifying lens is placed between the smart-phone camera and capillary to capture images of microobjects illuminated by an LED. A custom-developed Android application is used for adjusting the focal plane and other imaging parameters, and communicating with a microcontroller to control the pump and LED intensity. The effects of magnet length and flow rate on the particle sorting performance of the setup have been investigated. This device offers a portable, low-cost, digital, and versatile method for identifying, sorting, and quantifying particles on the basis of their volumetric mass densities.