Electrochemiluminescence sensor using quantum dots based on a G-quadruplex aptamer for the detection of Pb2+

A layer of aptamer probes with hairpin structures was modified on the surface of Fe3O4–Au magnetic nanoparticles (Fe3O4–Au-Aptamer). The "stem-loop" structure of the hairpin aptamer was opened when adding Pb2+. Then a G-quadruplex was formed, exposing 3′-NH2, which bound to CdTe quantum dots. Thus the magnetic nanoparticles were separated and enriched on the surface of the magnetic controlled gold electrode (MCGE). By this method, a "turn-on" electrochemiluminescence (ECL) sensor for Pb2+ detection using quantum dots was constructed. The changes to the structure of the aptamer were characterized by cyclic voltammetry, AC impedance measurements, transmission electron microscopy and UV-Vis absorption spectroscopy. Pb2+ concentration and ECL signal presented a linear relationship in the range 2.0 × 10−10–1.0 × 10−8 M. The detection limit was 1.08 × 10−11 M. In addition, the biosensor showed good selectivity, stability and reproducibility.