ORIGINAL PAPER Simultaneous voltammetric determination of ascorbic acid and dopamine at the surface of electrodes modified with self-assembled gold nanoparticle films Jahan Bakhsh Raoof & Abolfazl Kiani & Reza Ojani & Roudabeh Valiollahi & Sahar Rashid-Nadimi Received: 21 April 2009 / Revised: 7 July 2009 / Accepted: 3 August 2009 / Published online: 3 September 2009 # Springer-Verlag 2009 Abstract Gold nanoparticles (GNs) could be efficiently immobilized on binary mixed self-assembled monolayers (SAMs) on a gold surface composed of 1,6-hexanedithiol and 1-octanethiol (nano-Au/SAMs gold electrode). This GN chemically modified electrode was used for electro- chemical determination of ascorbic acid (AA) and dopa- mine (DA) in aqueous media. The result showed that the GN-modified electrode could clearly resolve the oxidation peaks of AA and DA, with a peak-to-peak separation (∆E p ) of 110 mV enabling determination of AA and DA in the presence of each other. The linear analytical curves were obtained in the ranges of 0.3–1.4 mM for AA and 0.2– 1.2 mM for DA concentrations using differential pulse voltammetry. The detection limits (3σ) were 9.0×10 −5 M for AA and 9.0×10 −5 M for DA. Keywords Gold nanoparticles . Self-assembled monolayers . Ascorbic acid . Dopamine . Voltammetric determination Introduction The design of new nanoscale materials has acquired ever greater importance in recent years due to their wide-ranging applications in various fields. Among these materials, metallic nanoparticles are of great interest due to their important properties and their numerous possible applications [1, 2]. The metal nano- particles have size-dependent unique chemical, electrical, and optical properties and are very promising for practical applications in diverse fields such as multifunctional reagent and biosensors [3–9]. The nanoparticles are very different from bulk materials and their electronic, optical, and catalytic properties originate from their quantum scale dimensions (<2 nm) [10]. The electrocatalytic activity of metal nanoparticles is strongly dependent on their com- position, size, surface area, and surface morphology [11]. Noble metal nanoparticles have been extensively utilized in recent years, owing to their extraordinarily catalytic activities for both oxidation and reduction reactions. To obtain high surface area, metal nanoparticle catalysts were usually dispersed in an organic polymer such as nafion [12, 13], colloids [14], surfactants [15], and porous substrates, which enable metal particles to be highly dispersed and stable. Due to the unique properties of gold nanoparticles (GNs), such as good conductivity, useful electrocatalytic ability, and biocompatibility, several researchers have been attracted to fabricate electrochemical sensors and biosensors [16–19]. The GNs dispersed on various substrates such as carbon paste electrode; conducting and non-conducting polymers and self-assembled monolayer have been reported. The fabrication of sensors based on self-assembly GNs nanostructure is of recent technologi- cal interest [20–23]. Arrays of GNs have been utilized for electrochemical sensors as they exhibit excellent catalytic activity towards various reactions [24]. In these, the GNs function as an “electron antennae”, efficiently tunneling electrons between the electrode and electrolyte [25]. J. B. Raoof (*) : R. Ojani : R. Valiollahi : S. Rashid-Nadimi Chemistry Research Laboratory, Department of Analytical Chemistry, Faculty of Chemistry, Mazandaran University, Babolsar, Iran e-mail: j.raoof@umz.ac.ir A. Kiani Department of Chemistry, Faculty of Science, University of Isfahane, Isfahane, Iran J Solid State Electrochem (2010) 14:1171–1176 DOI 10.1007/s10008-009-0917-z