Label-free electrochemiluminescence sensor based on magnetic nanoparticles modified with G-quadruplex DNA for detecting lead ions

Developing rapid and renewable sensors to detect heavy metal lead ions is a crucial and promising area of research. Herein, we constructed a label-free electrochemiluminescence (ECL) sensor for detecting Pb2+ using magnetic nanoparticles that were modified with a G-quadruplex probe. The aptamer probe was created by immobilizing a double-stranded DNA (dsDNA) onto the surface of Fe3O4@Au magnetic nanoparticles, with Ru(phen)32+ being intercalated into the dsDNA structure. Upon introduction of Pb2+, the dsDNA structure opened up to form the Fe3O4@Au-G-quadruplex-Pb2+ structure, resulting in the dissociation of single-stranded DNA (ssDNA) and Ru(phen)32+. The dissociated Ru(phen)32+ acted as an ECL probe, allowing for the construction of a highly sensitive sensing system that quantitatively relates Pb2+ concentrations to ECL signals. In the presence of the strong chelating agent EDTA, the hybridization of the two ssDNA strands back into the dsDNA structure allowed for the re-insertion of Ru(phen)32+ into the dsDNA structure, endowing the sensor with excellent renewability. The adapter sensor was characterized using cyclic voltammetry, electrochemiluminescence, and fluorescence spectroscopy. Over the range of 50 pM to 9 nM, the Pb2+ concentration exhibited a linear relationship with its corresponding ECL signal, with a detection limit of 1.2 pM. In addition, the biosensor demonstrated outstanding selectivity, stability, reproducibility, and potential for use in real-world sample applications.