Design and biosensing of Mg²⁺-dependent DNAzyme-triggered ratiometric electrochemiluminescence.

A dual-potential ratiometric electrochemiluminescence (ECL) sensing approach based on Mg(2+)-dependent DNAzyme-regulated ECL signals of luminol and CdS quantum dots (QDs) is designed. The system consists of DNAzyme strand functionalized QDs as capture probes and cathode ECL emitters, luminol-reduced gold nanoparticles (Au@luminol) as anode ECL emitters, and a Mg(2+) substrate strand modified with a cyanine dye (Cy5) fluorophore as the quencher. In the absence of Mg(2+) ions, the cathode ECL of the QDs is quenched by electrochemiluminescence resonance energy transfer between CdS QDs and Cy5 molecule, while the anode ECL from Au@luminol is introduced into the system. On the other hand, in the presence of Mg(2+) ions, the DNAzyme cleaves the substrate strand, and then releases the Cy5 and Au@luminol, which results in the recovery of the cathode ECL of the QDs and the decrease of the anode ECL simultaneously. On the basis of the ratio of ECL intensities at two excitation potentials, this approach was demonstrated to yield a linear calibration range from 10 to 10,000 μM Mg(2+) before it was applied to Mg(2+) detection in Hela cell extract. DNAzyme-triggered ratiometric ECL strategy with potential resolution would provide a reliable and sensitive method in biosensing and clinical diagnosis.