Multi wall carbon nanotubes (MWCNTs) and titanume oxide nano particles (TiO₂NPs) are widely used in the fabrication of immunosensors because of their high electrical conductivity, high chemical stability, and extremely high mechanical strength. DNA is an important biological polymer, which is classified as a natural, negatively charged polyelectrolyte due to its phosphate groups. It can be immobilized onto carbon nanotubes via covalent and noncovalent interactions. In this study, firstly, using a positively charged polyelectrolyte (PDDA) as dispersant of MWCNTs, a method for immobilization of DNA on the MWCNTs and pencil graphite electrode (PGE) was developed. The MWCNTs not only display unique electron transfer properties that induce the conductivity of PDDA and improve electron transfer characteristics, they also increase the amount of positively charged polyelectrolyte deposited on the electrode. Then, using constructed DNA biosensor and different electrochemical methods (cyclic voltammetry, differential pulse voltammetry, electrochemical impedance, etc.), the interaction of several drugs with DNA was studied. The decrease in intensity of the guanine and adenine oxidation signals and the change in intensity and position of the oxidation signals of riboflavin, codeine and morphine was used as an indicator for the sensitive determination of these drugs. Under optimized conditions, the detection limits of the above compounds are 0.34, 0.41 and 0.43 µg mL^-1, respectively. The biosensor was applied to validate its capability for the analysis of riboflavin, codeine and morphine in real samples.

In continuing, an electrocatalytic voltammetric method to assess total antioxidant capacity (TAC) using DNA-modified PGE was developed. studied. The biosensor developed was applied to the determination of TAC in several beverages and the results were compared with those attained using other methodologies to obtain an overall picture of the antioxidant profile. Then, A DNA-based biosensor was fabricated for the first time for the electrochemical study of transition metal-catalyzed oxidation of sulfite. At the final section, a simple electrochemical method was used to directly assess the drug-release profile from therapeutic nanoparticles. The method is based on the multiple pulse amperometric (MPA) measurement of the oxidation and reduction of doxorubicin released from liposome at a multiwalled carbon nanotube modified glassy carbon electrode (MWCNT-GCE).

Keywords: DNA-based biosensor; DNA damage; Drug relese; Antioxidant capacity; Electrochemical impedance spectroscopy; Voltammetry