A dielectrophoresis-based in-droplet cell concentrator is disclosed herein. The concentrator can include a concentration microchannel having an input port and two or more outlet ports. The input port introduces cell-encapsulated droplets or particle-encapsulated droplets into the microchannel; a first outlet port receives droplets including most of the cells or particles and a second output port receives droplets including few cells or particles. The concentrator also can include a pair of electrodes. When voltage is applied, the electrodes will create an electric field across the microchannel. The concentrator adds new capabilities to droplet microfluidics operations, such as adjusting concentrations of cells in droplets, separating cells of different properties from inside droplets, and solution exchange.