Electrodeposited Gold Nanoparticles on Glassy carbon Electrode: Correlation between Electrodeposition Time and the Amount of Immobilized Gold Nanoparticle

The glassy carbon electrode, GCE, is widely used as working electrode in different biosensors. Up to now, various methods have been developed to improve the biosensing properties of GCE.Generally, improving of electrical conductivity of this electrode is a major aim of these methods. Recently, immobilization of gold nanoparticls on the surface of glassy carbon electrode using electrodeposition technique is widely utilized for this intention. However, some aspects,particularly optimum condition of this technique are still unclear. So, the effect of eletrodepostion time on the amount of immobilized gold nanoparticle at the surface of glassycarbon electrode, is investigated and reported in this article. Chloroauric acid (HAuCl4, 3H2O) and potassium ferricyanide (K4Fe (CN)6) purchased fromSigma – Aldrich. NaNo3, potassium phosphate (KH2PO4) and dipotassium phosphate (K2HPO4)obtained from Merck Ltd. Alumina powder with 1 μM and 0.3 μM diameter obtained from Methrohm AG, Swiss. All aqueous solutions were prepared in double distilled water with a resistance of 18.0 MΩ cm−1. Double distilled, deionized water was prepared using ion exchange system (Millipore, France). Glassy carbon electrode was carefully polished by 1 μM and 0.3 μm alumina powder, respectively. Then, the electrode was rinsed with ethanol %96 using anultrasonic cleaner (Elma 530H). At the next stage, gold nanoparticles were electrodeposited indeaerated NaNo3 solution containing 0.25 mM chloroauric acid. For electrodeposition, chronoamperometery method using -0.3 V was utilized at different times (0, 10, 120, 240, 420 and 600s) at 10 ºC. In order to evaluation of electrode responses at each electrodeposition time,the voltammograms of modified glassy carbon were recorded in 65 mM ferrocyanide potassium (pH 7) by cyclic voltametry experiments (DropSens 400μ, Spain). Additionally, to evaluate the amount of gold nanoparticls immobilization at the surface of glassy carbon electrode, scanning electron microscopy images were obtained (VEGA3 TESCAN, Czech Republic) at 10s voltage exertion during eletrodepostion process.Figure 1 show the morphology and distribution of gold nanoparticles on the surface of glassy carbon electrode when 10s was selected for voltage exertion during electrodeposition. The SEM image analysis in which automatically performed by an electron microscope instrument indicatedthat only 7% of glassy carbon electrode surface was covered by gold nanoparticle with the sizes between 35 to 45 nm. At the next stage, cyclic voltametry experiments carried out. The cathodic(A) and anodic (B) peak currents obtained from cyclic voltammograms considered as the responses of modified glassy carbon electrode and presented in figure 2 (curves A and B). As shown in this figure both peak currents increased with increasing the time of voltage insertionduring electrodeposition. Also, according to this figure the response of the modified electrode reached to its maximal amount when 240s was chosen for voltage exertion during electrodeposition process. As a result, 240s can be chosen as an optimum time for electrodeposition of gold nanoparticles on the surface of glassy carbon electrode. This study showed that the further time of voltage exertion has no positive effect and it seems that the surface of the electrode is completely covered by gold nanoparticles during 240s of voltage exertion.