سید مجید هاشمی

Silver nanoparticles were synthesized through reduction of silver nitrate by i) NaBH4 as reducing agent and sodium dodecyl sulfate as stabilizing agent; ii) hydrazine as reducing agent andpolyvinylpyrolidine as stabilizing agent. The prepared silver nanoparticles were characterized using UV-Vis spectroscopy, Dynamic light scattering (DLS) and scanning electron microscopy (SEM). The results show that the average size of silver nanoparticles obtained through reducing by NaBH4 is smaller than the average size of silver nanoparticles obtained through reducing by hydrazine. The "protein corona" of catalase as a model enzyme around the silver nanoparticles was created by two different methods, electrostatic adsorption in the case of silver nanoparticles prepared through reduction by NaBH4, and bioconjugation in the case of silver nanoparticles prepared through reduction by hydrazine. The Michaelis- menten model was used for the kinetic study of the effect of binding of silver nanoparticles on the enzymatic activity of catalase and show changes in Vmax and Km values. The effect of binding silver nanoparticles on the tendency of the enzyme for the interaction with a cationic surfactane, dodecyl trimethyl ammonium bromide (DTAB), and an anionic surfactant, sodium dodecyl sulfate (SDS) was also studied. The results show that the adsorption and bioconjugation of catalase to silver nanoparticles decreases its tendency for the electrostatic interaction to these surfactants. The electrochemical response of catalase-silver nanoparticles was investigated using a carbon paste electrode modified with a film of catalase-silver nanoparticles via surface adsorption. The resultant film exhibited a pair of well-defined quasi-reversible cyclic voltammetric peaks corresponding to the catalas(ox)/catalse (red) redox with a formal potential (E??) = -0.407 V vs. Ag/AgCl, in 50mM phosphate buffer solution at pH 7.0.The results showed that the modified electrode in aqueous solution can be applie