Analytical Methods High catalytic activity of electrochemically reduced graphene composite toward electrochemical sensing of Orange II Mira Yun a , Ju Eun Choe a , Jung-Min You a , Mohammad Shamsuddin Ahmed a , Kyungmi Lee a , Zafer Üstündag ˘ b,⇑ , Seungwon Jeon a,⇑ a Department of Chemistry and Institute of Basic Science, Chonnam National University, Gwangju 500-757, Republic of Korea b Department of Chemistry, Faculty of Arts and Science, Dumlupınar University, 43100 Kutahya, Turkey article info Article history: Received 13 January 2014 Received in revised form 5 June 2014 Accepted 30 July 2014 Available online 7 August 2014 Keywords: Azo dye Electrochemically reduced GO Electrochemical sensor Orange II Platinum nanoparticles abstract Orange II, an azo dye, is sometimes illegally used as a red dye in food products despite its adverse health effects if consumed. Therefore, the determination of low concentrations of Orange II is an important target. An Orange II sensor was prepared using electrochemically reduced graphene oxide grafted with 5-amino-1,3,4-thiadiazole-2-thiol-Pt nanoparticles (denoted as ERGO-ATDT-Pt) onto a glassy carbon electrode (GCE) and investigated for Orange II detection in 0.1 M acetate buffer solution (ABS at pH 4.5) with prominent reversible redox peaks. A wide linear range of 1  10 8 –6  10 7 M with a low detection limit of 3.4  10 10 M(s/n = 3) was found for Orange II detection. This developed ERGO- ATDT-Pt/GCE sensor showed good selectivity, excellent stability and better response to the real sample analysis with excellent recovery. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Orange II (sodium 4-[2-(2-oxonaphthalen-1-ylidene)hydrazi- nyl]benzenesulfonate) is an azo dye containing one or more azo groups (R 1 –N = N–R 2 ) tinged with colour through visible-light absorption. It is used in many industries, such as for organic light- emitting diodes (OLEDs), inks, soaps, wood preservatives, textiles, hair dyes, leather materials, shoe polishes, cosmetics, wood stains, and foodstuffs (Yadav, Kumar, Dwivedi, Tripathi, & Das, 2012). Many countries, however, have regulated the use of Orange II in foodstuffs because it poses a risk to human health as carcinogenic (Guo, Pan, & Jing, 2004; Pourreza & Zareian, 2009), and reduces the number of red blood cells, accompanied by the lowering of hemoglobin and packed cell volume (Gan, Sun, Lin, & Li, 2013). Hence, the determination of low concentrations of Orange II is an important target. Methods of determining the concentration of Orange II were recently reported, including photocatalysis (Cetinkaya, Neuwirthová, Kutláková, Tomášek, & Akbulut, 2013; Divya, Bansal, & Jana, 2013), capillary electrophoresis (Pérez- Urquiza, Ferrer, & Beltrán, 2000; Takeda et al., 1999), spectroscopy (Pourreza & Zareian, 2009), HPLC–MS (Fang et al., 2013; Zou, He, Yasen, & Li, 2013), and polarography (Guo et al., 2004). Although these techniques, they are time-consuming and require complex instrumentation (You et al., 2011). The electrochemical (i.e. voltam- metric) method, on the other hand, has high sensitivity, fast response speed, short analysis time, excellent selectivity, low cost, and handling convenience (Wang et al., 2013; You et al., 2011). Graphene oxide (GO), a single layer of graphite oxide, has abundant functional groups, such as epoxy and hydroxyl group. Therefore, a reaction between the functional groups of GO and the amine groups of an amine-terminated ionic liquid should easily occur (Yang et al., 2009). The introduction of a heterocyclic com- pound in the graphene sheets yielded a large surface-active groups-to-volume ratio, superb thermal stability, good electrical and mechanical properties (Ahmed, Han, & Jeon, 2013; Yang, Li, Rana, & Zhu, 2013). On the other hand, noble metals, such as Au, Pd, and Pt nanoparticles (NPs), have been used for electrocatalysis (Ahmed & Jeon, 2013; You et al., 2013). Among them, the Pt NPs have attracted much attention owing to its unique effects in electrocatalysis and in the enhancement of the electron transfer (Xu, He, Sun, & Wang, 2013). The loading of Pt NPs on the hetero- cycle-doped GO layers showed the synergy effects of a narrower particle size distribution and improved catalytic performance (Zhao, Zhou, Xiong, Wang, Chen, O’Hayre, & Shao, 2013; Zhang, Liang, Song, & Wu, 2010). In this work, we synthesise an electrochemical sensor for orange II detection with better selectivity, sensitivity and low detection limit. The synthesis of GO with 5-amino-1,3,4-thiadiazole-2-thiol http://dx.doi.org/10.1016/j.foodchem.2014.07.143 0308-8146/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding authors. E-mail addresses: zustundag@gmail.com (Z. Üstündag ˘), swjeon3380@naver.com (S. Jeon). Food Chemistry 169 (2015) 114–119 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem