Multistage magnetic separation of microspheres enabled by temperature-responsive polymers.

A simple and rapid method for separation of cells is to functionalize magnetic particles with a receptor that selectively captures the target and then pull the magnetic particles out of the mixture upon applying a magnetic field. The separation efficiency of magnetic separation, however, is typically limited by the nonspecific interaction between the magnetic particles and nontarget species. We here present a multistage separation process that is able to effectively circumvent the problem caused by the nonspecific interactions by introducing multiple capture-and-release cycles to the magnetic separation process. The multiple capture-and-release cycles are enabled by attaching a temperature-responsive polymer to both the magnetic particles and the targets. Through temperature cycling, we demonstrate that target microspheres can be separated from nontarget microspheres in multiple separation stages. The overall enrichment factor significantly increases with the number of separation stages and reaches as high as 1.87 × 10(5) after 5 cycles.