Short communication A novel electrochemical sensor based on metal-organic framework for electro-catalytic oxidation of L-cysteine Hadi Hosseini a , Hamid Ahmar a , Ali Dehghani b , Akbar Bagheri a,n , Azadeh Tadjarodi b , Ali Reza Fakhari a a Department of Chemistry, Shahid Beheshti University, G.C., P. O. Box 19396-4716, Tehran, Iran b Department of Chemistry, Iran University of Science and Technology, Tehran, Iran article info Article history: Received 25 July 2012 Received in revised form 25 September 2012 Accepted 26 September 2012 Available online 22 October 2012 Keywords: Metal-organic frameworks Gold nanoparticles Electrochemistry Electrochemical sensors L-cysteine abstract A novel electrochemical sensor based on Au-SH-SiO 2 nanoparticles supported on metal-organic framework (Au-SH-SiO 2 @Cu-MOF) has been developed for electrocatalytic oxidation and determination of L-cysteine. The Au-SH-SiO 2 @Cu-MOF was characterized by scanning electron microscopy, transmis- sion electron microscopy, x-ray diffraction and cyclic voltammetry. The electrochemical behavior of L-cysteine at the Au-SH-SiO 2 @Cu-MOF was investigated by cyclic voltammetry. The Au-SH-SiO 2 @Cu-MOF showed a very efficient electrocatalytic activity for the oxidation of L-cysteine in 0.1 M phosphate buffer solution (pH 5.0). The oxidation overpotentials of L-cysteine decreased significantly and their oxidation peak currents increased dramatically at Au-SH-SiO 2 @Cu-MOF. The potential utility of the sensor was demonstrated by applying it to the analytical determination of L-cysteine concentration. The results showed that the electrocatalytic current increased linearly with the L-cysteine concentration in the range of 0.02–300 mM and the detection limit was 0.008 mM. Finally, the sensor was applied to determine L-cysteine in water and biological samples. & 2012 Elsevier B.V. All rights reserved. 1. Introduction There have been continuous researches for fabricating new electrode materials in order to develop sensitive and selective electroanalytical methods which can detect trace amounts of biologically and environmentally important compounds (Zen et al., 2003). Among the wide range of electrode modifiers, metal nanoparticles (NPs) have received an increasing attention in recent years due to their good performance to enhance the electron transfer rate and reduce the overpotential in both oxidation and reduction processes (Zen et al., 2003). Regarding this, gold NPs (AuNPs) have been used to fabricate various types of modified electrodes because of their large surface area, good biocompatibility, high conductivity, renewable surface, and electrocatalytic activities. Also, a variety of electrocatalytic systems have recently been developed based on different meth- odologies for the stabilization of Au film or AuNPs on the surface of solid supports. Supported AuNPs on conducting polymer (Chandra et al., 2011), carbon nanotube (Lin et al., 2008), graphene (Zheng et al., 2011), ordered mesoporous carbon (Wang et al., 2011), SiO 2 (Zhou and Zhang, 2011), TiO 2 nanotubes (Wang et al., 2010), and Fe 3 O 4 (Liu et al., 2011) have been recently studied as electrocatalysts. However, controlling the size and shape of NPs is very important in the electrocatalytic properties of NPs. A great number of the new methods for preparing high performance catalytic and/or electro-catalytic systems are based on immobili- zation of metal NPs on the surface of solid support materials. The main advantages of using solid supports are good accessibility of catalyst NPs, controlled particle sizes and morphologies, high dispersion, high loading level and high stability of NPs (Schlogl and Hamid, 2004; Zhang and Zhao, 2009). Metal-organic frameworks (MOFs) are a new class of crystal- line porous materials consisted of metal ions coordinated to organic ligands in order to form rigid three dimensional frame- works with unique properties including high surface area, high pore volume, and chemical tenability. MOFs have shown great potential in gas storage, separation, chemical sensing, drug delivery and heterogeneous catalysis applications (An et al., 2009; Dinca and Long, 2008; Fujita et al., 1994; Jiang and Xu, 2011; Meek et al., 2011; Murray et al., 2009; Seo et al., 2000; Shekhah et al., 2011; Zacher et al., 2009). In general, the flexible and highly porous structure of MOFs allow guest molecules such as metals to diffuse into the bulk structure; and the shape and size of the pores lead to shape- and size-selectivity over the guests which may be incorporated. These features make an ideal candidate out of them for preparing solid-phase electro-catalysts based on metal NPs. However, there is only limited information available about the electrochemistry of MOF systems (Babu et al., 2010; Domenech et al., 2007; Yang et al., 2010) and the study and Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/bios Biosensors and Bioelectronics 0956-5663/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.bios.2012.09.062 n Corresponding author. Tel.: þ98 21 29903251; fax: þ98 21 22431661. E-mail address: akbr_bagheri@yahoo.com (A. Bagheri). Biosensors and Bioelectronics 42 (2013) 426–429