Electrochemiluminescent lead biosensor based on GR-5 lead-dependent DNAzyme for Ru(phen)32+ intercalation and lead recognition

An electrochemiluminescent (ECL) lead biosensor was developed based on GR-5 lead-dependent DNAzyme for lead recognition and intercalated ruthenium tris(1,10-phenanthroline) (Ru(phen)32+) as the ECL probe. The thiol-modified substrate was first immobilized on the surface of the gold electrode via gold–sulfur self-assembly. Subsequently, the hybridization of DNAzyme and its substrate and the automatic intercalation of Ru(phen)32+ proceeded. Intercalated Ru(phen)32+ can transfer electrons through double-stranded DNA to the electrode and its electrochemiluminescence was excited with a potential step using tripropylamine as the coreactant. In the presence of lead, the substrate cleaves at the scissile ribo-adenine into two fragments. The dissociation of DNAzyme occurs, leading to the releasing of intercalated Ru(phen)32+ accompanied by a decrease in the intensity of electrochemiluminescence. A quantity of lead can be calculated from this decrease. The biosensor is highly sensitive and specific, along with an ultra-low limit of detection of 0.9 pM and a dynamic range from 2 to 1000 pM. It enables analysis of trace amounts of lead in serum samples. The combination of the intercalated-Ru(phen)32+ ECL probe and the cofactor-dependent DNAzyme may push the performance of cofactor-sensing tactics to the extreme.