Electrochemiluminescence ratiometry: a new approach to DNA biosensing.

Inspired by dual-wavelength fluorescence ratiometric method which could reduce the influence from the environmental change, here, we present a novel dual-potential electrochemiluminescence (ECL) ratiometric sensing approach. CdS nanocrystal (NC) and luminol as two different ECL emitters are employed. ECL from CdS NCs coated on glassy carbon electrode at -1.25 V (vs SCE) could be quenched by closely contacted Pt nanoparticles (NPs) via a biological binding event, while ECL from luminol at +0.45 V (vs SCE) could be enhanced by the same Pt NPs, in the presence of their common coreactant of H₂O₂. Thus, the quenching of ECL from CdS NCs and the enhancement of ECL from luminol could indicate the same biological binding event. With the mp53 oncogene as a model DNA molecule, a molecular beacon (MB) containing a 20-base loop, which is complementary with the mp53 oncogene, is immobilized on CdS NCs/GCE first; Pt NPs are then captured on CdS NCs surface by DNA hybridization between the MB and mp53 oncogene labeled on Pt NPs. By measuring the ratio of ECL intensities at two excitation potentials, this approach could sensitively detect the concentration of target DNA in a wide range from 5.0 fM to 1.0 pM. The sensing scheme is general and can be utilized for many other biological binding events.