Microfluidic chip sorts the living from the dead

Microfluidic chip sorts the living from the dead. When a cell meets its demise, so too does its fine-tuned system for regulating nutrient uptake and waste excretion. As a result, cell death is typically marked by a sharp increase in electrical conductivity, as various ions become free to pass through newly opened pores in the cell membrane. That telltale change affords a convenient way to sort live cells from dead ones: In what’s known as dielectrophoresis, electric-field gradients induce cells to migrate with a conductivity-dependent velocity. Exploiting the effect typically calls for fashioning tiny electrodes inside a microfluidic channel, but a group led by Xiangchun Xuan of Clemson University, South Carolina, has now devised a simpler alternative. The key was recognizing that a severe flow constriction is often sufficient, by itself, to distort an otherwise uniform electric field and create the strong gradients needed for dielectrophoresis. The essential component of...