Electrooxidation of insulin at silicon carbide nanoparticles modified glassy carbon electrode Abdollah Salimi a,b, * , Loghman Mohamadi a , Rahman Hallaj a , Saied Soltanian b a Department of Chemistry, University of Kurdistan, P.O. Box 416, Sanandaj, Iran b Research Center for Nanotechnology, University of Kurdistan, P.O. Box 416, Sanandaj, Iran article info Article history: Received 26 February 2009 Received in revised form 10 March 2009 Accepted 17 March 2009 Available online 27 March 2009 Keywords: Silicon carbide Nanoparticles Insulin Flow injection analysis abstract For the first time silicon carbide nanoparticles (SiC) was used for electrode modification and electrocat- alytic oxidation of insulin. In comparison to bare glassy carbon (GC) electrode, the oxidation of insulin at GC electrode modified with SiC nanoparticles occurred at reduced overpotentials. The modified electrode was applied for insulin detection using cyclic voltammetry, differential pulse voltammetry (DPV) and flow injection analysis (FIA). Flow injection amperometric determination of insulin at this modified elec- trode yielded a calibration curve with the following characteristics; linear dynamic range up to 600 pM, sensitivity of 710 pA pM À1 cm À2 and detection limit of 3.3 pM. In addition interference effect of the elec- troactive existing species (uric acid, glucose, lactic acid, L-cysteine and cholesterol) was diminished and for ascorbic acid eliminated by covering the surface of modified electrode with nafion film. This electrode shows many advantages as an insulin sensor such as simple preparation method without using any spe- cific electron transfer mediator or specific reagent, high sensitivity, excellent catalytic activity, short response time, long term stability and remarkable antifouling property toward insulin and its oxidation product. Sensitivity, detection limit and antifouling properties of this insulin sensor are better than all of the reports in the literature for insulin detection at physiological pH solutions. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Direct electrooxidation of insulin is important for the develop- ment of fast and sensitive amperometric detectors coupled to flow systems or chromatographic instruments for this hormone. Low sensitivity, stability and reproducibility, slow kinetics, surface foul- ing, and high overpotential at which the insulin oxidation process occurred are limitations of unmodified electrodes. Various electron transfer mediators have been used for electrooxidation and deter- mination of insulin [1–13]. Although the modified electrodes have been successfully employed for monitoring insulin, they usually have many disadvantages such as reduced stability under physio- logical condition, high detection limit, poor long term stability, and complicated multi-step preparation methods. Silicon carbide is a wide band gap semiconductor with a range of excellent physical, chemical, mechanical and electronic proper- ties [14]. It is a good candidate for many applications such as, catalysis supports, substrate material and heating elements, rein- forcement materials, next generation high temperature and high frequency electronic devices [15–17]. The application of SiC slurry for the electrolyte matrix of phosphoric acid fuel cell and metal oxide gas sensors have been reported [18,19]. SiC–C composite film has been used for sensing of dopamine and ascorbic acid [20]. Furthermore, SiC electrode has been used as an ordinary oxi- dation–reduction indicator electrode in potentiometric titrations [21]. The stability and optical properties of SiC quantum dots, luminescence behavior of amorphous silicon carbide film and electrochemical properties of SiC nanoparticles have been investi- gated [22–24]. Here we have described the application of SiC nanoparticles as electrocatalysts for oxidation of insulin at physi- ological pH. Due to chemical stability and antifouling properties of SiC modified GC-electrode, it has been successfully used for insu- lin detection using voltammetry or amperometric techniques. Fi- nally, analytical performance of modified electrode has been described as an amperometric detector for picomolar concentra- tion of insulin in flow system. This sensor applied for insulin determinations without interference effect of co-oxidized compounds. 2. Experimental 2.1. Chemicals Bovine insulin (5800, >27 USP units mg À1 ) was from Sigma. SiC powders with average particle size of 15 nm, supplied by MTI Cor- poration, USA have been used in this work. 1388-2481/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2009.03.024 * Corresponding author. Address: Department of Chemistry, University of Kurd- istan, P.O. Box 416, Iran. Tel./fax: +98 871 6624001. E-mail addresses: absalimi@uok.ac.ir, absalimi@yahoo.com (A. Salimi). Electrochemistry Communications 11 (2009) 1116–1119 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom