Fabrication of a modified electrode based on Fe(3)O(4)NPs/MWCNT nanocomposite: application to simultaneous determination of guanine and adenine in DNA.

Multi-walled carbon nanotubes decorated with Fe(3)O(4) nanoparticles (Fe(3)O(4)NPs/MWCNT) were prepared and used to construct a novel biosensor for the simultaneous detection of adenine and guanine. The direct electro-oxidation of adenine and guanine on the modified electrode were investigated by linear sweep voltammetry. The results indicate a remarkable increase in the oxidation peak currents together with negative shift in the oxidation peak potentials for both adenine and guanine, in comparison to the bare glassy carbon electrode (GCE). The surface morphology and nature of the composite film deposited on GCE were characterized by transmission electron microscopy, atomic force microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The Fe(3)O(4)NPs/MWCNT based electrochemical biosensor exhibits linear ranges of 0.01-10 μM and 0.05-8 μM with detection limits of 1 nM and 5 nM for adenine and guanine, respectively. The proposed method was successfully applied for a highly sensitive simultaneous determination of trace amounts of adenine and guanine in DNA of fish sperm samples with satisfactory results. The experimental detection limit was found to be equal to 3 ng mL(-1) DNA. The value of (G+C)/(A+T) in DNA was calculated to be 0.81. The fabricated electrode showed excellent reproducibility, repeatability and stability.