Here we report that a novel zinc(II) complex with an intramolecular ‘push–pull’ structure was synthesized and fully characterized. For the zinc(II) complex, the photoluminescence (PL) emission wavelength is at 460 nm and the excitation wavelength is at 380 nm. The two-photon absorption cross-section (σ) of the zinc(II) complex reached 140 GM (1 GM = 1 × 10⁻⁵⁰ cm⁴ s photon⁻¹). An electrochemiluminescence (ECL) sensor could be built with a glass carbon disk electrode (GCE, Φ 4 mm) modified with the zinc(II) complex, and this exhibited an enhanced ECL intensity, good biocompatibility and long-term stability to detect ctDNA. Meanwhile, the reliability of the extracted signal was demonstrated in solutions of different pH values.