Design of a novel electrochemical biosensor based on intramolecular G-quadruplex DNA for selective determination of lead(II) ions.

An electrochemical DNA biosensor based on a G-quadruplex (G4) for the sensitive determination of Pb2+ was reported using a carbon paste electrode (CPE) or a multi-walled carbon nanotube paste electrode (MWCNTPE) as working electrodes, ethyl green (EG) as a new G4 intercalator, and a single-stranded nucleic acid sequence rich in guanine (G) as DNA probe. Electrochemical determination of Pb2+ relied on probe structural changes from single - stranded to the stabilized intramolecular G4 in the presence of Pb2+ , which caused a change in the current of the EG reduction peak due to the intercalation of EG into the G4 structure. The change in the reduction peak of EG before and after its intercalation into the stabilized G4 (∆I) had a linear correlation to the concentration of Pb2+ ions. The linear ranges of 4.0 × 10-10 -5.0 × 10-9  M and 2 × 10-7 -1 × 1-5  M with a detection limit (LOD) of 1.04 × 10-10  M were obtained using CPE, while improved linear ranges of 4.0 × 10-11 -1.0 × 10-9  M and 2 × 10-7 -1 × 10-5  M with a lower LOD of 2.64 × 10-11  M were achieved using the MWCNTPE biosensor. The biosensors exhibited satisfactory results in terms of selectivity and practical applicability in the analysis of real samples. Graphical abstract The principle of the electrochemical sensing of Pb2+ based on intramolecular G-quadruplex using EG.