By virtue of the overlaid red fluorescence from both QDs’ recovered emissions and the Ru(II) complexes’ emerged emissions, the as-prepared fluorescent “turn-on” clutch probe could be effectively applied to selectively recognize cancer-specific cfDNA with EGFR gene mutation from the blood plasma of lung cancer patients, showing great promise for rapid, sensitive, practicable identification of circulating tumor nucleic acids and further early cancer diagnosis. The gene discussed is EGFR; the disease is lung carcinoma.