A system for detecting rare cells in a fluid is disclosed. The system includes a substrate and a mixture disposed on the substrate and including a carrier and a thermo-responsive polymer for capture and release of the rare cells. Also disclosed is a method for detecting rare cells in a fluid using a system including a substrate and a mixture that is disposed on the substrate. The mixture includes a carrier and a thermo-responsive polymer. The method includes providing the system and introducing a sample of fluid containing the rare cells into the system such that the sample interacts with the carrier for capturing the rare cells.