EPCAM and cancer: This “turn-on” magnetic fluorescent nanocomposite was investigated in different cultures of low- and high-EpCAM-expressing cancer cell lines (Hep G2, A549, HEK293), showing a specific ability to quickly identify CTCs (both low- and high-EpCAM-expressing cells), because of the presence of aptamers, with a linear range between 2 and 64 nM, and a LOD of 1.19 nM, thus highlighting its potential for the for early diagnosis and prognosis of cancer.