There is disclosed a method for selectively detecting epithelial to mesenchymal transition (EMT) phenotypic cells but not noncancerous/normal epithelial cells and breast fibroblasts in a biological sample or a patient. The compositions comprise novel binding peptides that specifically bind to EMT cancer cells. EMT phenotypic cells can be identified using the specific peptides and quantitatively measured by detection of a complex of the peptide and a detectable marker. Further, nanodevices incorporating specific EMT phage ligand may be used to identify EMT cancer cells in vivo. Also disclosed are the novel binding phage peptides, and compositions and nanodevices containing the phage ligand for carrying out methods of the invention.