Acetaminophen Powder

All electrochemical measurements were performed with an Autolab potentiostat/galvanostat (PGSTAT 101, Eco Chemie, The Netherlands) interfaced with a Nova 1.11 software. A three-electrode system was used in this work consisting of a platinum wire as the auxiliary electrode, an Ag/AgCl/KCl (saturated) as the reference electrode, and a modified carbon paste electrode as the working electrode. A metrohm 827 pH lab (Herisau, Switzerland) supplied with a combination glass-reference electrode was used for pH measurements.

2.2. Materials

Acetaminophen powder and TiO2 nanoparticles were purchased from Sigma-Aldrich (Taufkirchen, Germany). A 5.0 mM stock solution of acetaminophen was prepared by dissolving an appropriate amount of the powder in a small

Paraffin oil was then added to the mixture and mixed until a uniformly wet paste was achieved and then the resulting paste was placed in the bottom of a glass tube.The electrical connection was established via a copper wire to the paste. The resulting electrode was designated as chitosan/TiO2 nanoparticles-carbon paste electrode (ChiTNP-CPE).The surface of the electrode was gently flattened by rubbing it on a piece of filter paper until it is completely uniform, smooth,and shiny. Finally, it was rinsed with double distilled water. An unmodified carbon paste electrode (CPE) without any contain chitosan and TiO2 nanoparticles was made in a similar way for use in comparative

Next, while stirring the solution for 400 sec, a 0.50 V voltage was applied to the electrode. The electrode was then washed thoroughly with sodium acetate-acetic acid buffer solution. The obtained electrode is called ChiTNP-CPE/DNA.To evaluate the DNA immobilization on the electrode surface,the study of cyclic voltammetry[Fe(CN)6]3-/4- redox couple was performed at the presence and absence of DNA.The work is based on the large electrostatic repulsion between this redox couple and the negatively charged DNA [22]. For this purpose, cyclic voltammograms (CVs) of 20 mL of a solution containing 0.05 M [Fe(CN)6]4− and 0.5 M KClwere performed on the surface of bare CPE, ChiTNP-CPE, and ChiTNP-CPE/DNA at a scan rate of 100 mV/s (Fig. 1). As can be seen, a pair of reduction and oxidation peaks is found for the [Fe(CN)6]3-/4- redox couple at CPE surface.At the surface of ChiTNP-CPE, the currents of both peaks increase along with an improvement in the redox reversibility due to electrostatic adsorption of negative species of [Fe(CN)6]3-/4- and cationic polymer in chitosan. As can be seen, immobilization of DNA on the surface of ChiTNP-CPE noticeably decreases the peak currents and redox reversibility of the indicator. This observation suggests that the negatively charged phosphate groups of DNA lead to the electrostatic repulsion of the redox couple on the