A plasmonic-based biosensor platform that determines the biophysical properties of cells, the changes within, and their therapeutic behavior upon the molecules that cause these changes in an ex vivo and label-free manner is provided. The plasmonic-based biosensor platform includes a plasmonic chip, a light source, an inverted microscope, an incubator case, an optical read-out device, and a graphical user interface. The biosensor platform of the invention could determine the therapeutic susceptibility of cancer cells to cancer drugs in a label-free manner.