In the present manuscript, mouse breast tumor cells (4T1), human breast tumor cells (MCF7), and human cervical cancer cells (HeLa), all of which overexpress nucleolin on their surface, were incubated in the presence of control human foreskin fibroblast cells (HFFF-PI6) and CDs-AS1411 aptamer probes to investigated the sensitivity and selectivity of our signal-on spectrofluorometric assay for the targeted detection of cancer cells. The gene discussed is NUCLEOLIN; the disease is cancer.