"Off-on" electrochemiluminescence system for sensitive detection of ATP via target-induced structure switching.

An "off-on" electrochemiluminescence (ECL) strategy was constructed for highly sensitive and selective detection of adenosine 5'-triphosphate (ATP) with a quantum dots (QDs) modified electrode and a DNAzyme signal probe. The immobilized QDs were functionalized with a DNA sequence (DNA1) and then aptamer for recognition of target analyte. The signal probe was prepared by assembling another DNA sequence (DNA2) and G-quadruplex on gold nanoparticle via Au-S chemistry, which was used to bind the probe to electrode surface through a hybridization reaction with aptamer and hemin for forming G-quadruplex/hemin DNAzyme, respectively. Upon the sandwich hybridization of DNA1-aptamer-DNA2, the signal probe could be captured on the aptasensor to catalyze the reduction of dissolved oxygen, the coreactant for cathodic ECL emission of QDs, leading to a decrease of ECL intensity and thus the "off" state. In the presence of target, its recognition by aptamer led to the release of aptamer from electrode surface and decreased the amount of captured signal probe, thus the ECL emission was in its "on" state. The "off-on" strategy resulted from the target-induced structure switching could be used for specific detection of ATP with a linear range of 8-2000 nM and a detection limit of 7.6 nM. The proposed aptasensor could be successfully applied in the ECL detection of ATP in human serum. This method could resist environmental interfering agents and be extended for sensitive and reliable detection of a wide range of analytes in complex sample.