Novel Ternary System for Electrochemiluminescence Biosensor and Application toward Pb²⁺ Assay

This study constructed an electrochemiluminescence (ECL) biosensor for ultrasensitive detection of Pb²⁺ in a ternary system by employing DNAzyme. The ternary system is composed of a potassium-neutralized perylene derivative (K₄PTC) as the ECL emitter, K₂S₂O₈ as the coreactant, and neodymium metal-organic frameworks (Nd-MOFs) as the coreaction accelerators. Nd-MOFs immobilize DNAzymes and enhance the luminescence intensity of the K₄PTC/K₂S₂O₈ system. As part of this system, K₄PTC enhances the ECL signal in solution and supports Pb²⁺ detection. The sequence of ferrocene (Fc)-linked DNA (DNA-Fc) is catalytically cleaved by DNAzymes in the presence of Pb²⁺. This causes the removal of DNA1-Fc from the electrode surface to recover the ECL signal. As a result, the as-prepared ECL biosensor can quantify Pb²⁺ with a detection limit (LOD) of 4.1 fM in the range of 1 μM to 10 fM. The ECL biosensor displays high specificity, good stability, excellent reproducibility, and desirable practicality for Pb²⁺ detection in tap water. Moreover, by simply changing the sequence of the DNAzyme, new biosensors can be designed for ultrasensitive detection of different heavy metal ions, offering an excellent approach for monitoring water quality safety.