Abdollah Yari - Department of Chemistry, Faculty of Science, Lorestan University, Khorramabad, Iran
Somayeh Derki - Department of Chemistry, Faculty of Science, Lorestan University, Khorramabad, Iran

Recently, using of self-polymerization of dopamine (DA) in various Nanocomposites has been prevalent as multifunctional coating material onto many surfaces [1]. CNTs also have been usedwidely as electrode modifier materials because they enhanced electronic properties and rapidelectrode kinetics [2]. Herein, we report the preparation of multiwall carbon nanotube-Fe3O4 nanoparticles@polydopamine-Ag nanoparticle (MWCNT-Fe3O4@PDA-Ag) nanocomposite whichwas characterized with FT-IR, FE-SEM, EDS and TEM. The characterization results showed thatAgNPs were well anchored onto the surface of the MWCNT-Fe3O4@PDA nanocomposite. Changes in the concentration of DNA bases affect the activities of catabolic and anabolic, and cause various diseases so the prepared nanocomposite, was used as a novel electrochemicalsensor for simultaneous determination of guanine (G) and adenine (A). The modified electrode shows an excellent electrocatalytical function towards determination of G and A. The oxidationpeak currents were linear with the concentration of G and A on the range of 8‒130 and 10‒120μM, respectively. The lower detection limit of the sensor was estimated to be 1.47 μM for G and 5.66 μM for A. The MWCNT-Fe3O4@PDA-Ag nanocomposite based sensor was successfully applied to detect G and A in some real sample.We synthesized MWCNT-Fe3O4 [3], MWCNTFe3O4@ PDA [4] and incorporated Ag-nanoparticles (AgNPs) into MWCNT-Fe3O4@PDA nanocomposite by simple stirring of MWCNT-Fe3O4@PDA and Ag+ ion in a basic medium followed by NaBH4 reduction. The procedures used for preparation of the MWCNTFe3O4@ PDA-Ag nanocoposite are demonstrated pictorially in Scheme 1. The morphology of Fe3O4-MWCNTs and MWCNT-Fe3O4@PDA-Ag nanocomposite were investigated by SEM andTEM respectively (Fig. 1a&b). Fig. 2a presents the results obtained from EIS. As shown in Fig. 2b we investigate the electrochemical behavior of G or A at various pH (from 3.0 to 9.0, in 0.1 M ABS) on the surface of MWCNT-Fe3O4@PDA-Ag/CPE. We used DPV technique for individual and simul taneous determinations of the purine seen, the responses show two separated anodic peaks for G and A. The repeatability, selectivity, reproducibility and stability of the sensor were also investigated. These results demonstrate that The proposed system provides a simple, economical, robust and a rapid measuring tool for monitoring guanine and adenine in real sample

Adenine, Guanine, Nanocomposite, Polydopamine, Silver-nanoparticle