An electrochemical DNA biosensor based on G-quadruplex (G4) for sensitive determination of Pb2+ was reported using carbon paste electrode (CPE) or multi-walled carbon nanotubes paste electrode (MWCNTPE) as working electrodes, ethyl green (EG) as a new G4 intercalator and single stranded nucleic acid sequence rich in guanine (G) as DNA probe. Electrochemical determination of Pb2+ relied on the probe structural changes from a single-stranded to the stabilized intramolecular G4 in the presence of Pb2+, which caused a change in the current of EG reduction peak due to the intercalation of EG into the G4 structure. The change in 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 the 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 analysis of real samples.
