A simple and highly sensitive electrochemical method, based on a gold nanoparticle (GNP)-modified indium tin oxide (ITO) electrode (ITO/GNP), was developed for the detection of melamine (MLM). The modified electrode surface was characterized by scanning electron microscope (SEM) and cyclic voltammetry (CV). MLM was detected based on the adsorption of MLM onto ITO/GNP electrode causing suppression in the cathodic peak current of ferricyanide. A wide linear concentration range from 5 to 500 nM with a lower detection limit of 1.0 nM (i.e. 0.13 ppb) for MLM was obtained. The proposed method was successfully applied to detect MLM in milk samples. It has been illegally added to dairy products by unethical manufacturers to artificially increase the apparent protein content. 2 High concentration of MLM can induce acute kidney failure, serious renal problems and even death. 3 Therefore, a highly sensitive analytical method is necessary for the determination of MLM in dairy products.Various methods, such as high performance liquid chromatography, capillary electrophoresis, chemiluminescence, and electrochemical techniques have been reported for the determination of MLM. 4 Electrochemical methods are more advantageous than the others mostly due to fast response, low cost, simple operation, and high sensitivity. 5,6 However, the problem with this method is the electrochemical inactivity of the MLM. Therefore, MLM can be detected indirectly by applying electrochemical method. Few reports are available regarding the indirect electrochemical detection of MLM. Cao et al. applied the interactions between oligonucleotides and MLM lead to the increase in the peak currents of ferricyanide at an oligonucleotide-modified gold electrode for electrochemical sensing of MLM. 4 The same group further reported an electrochemical sensor for MLM with 3,4-dihydroxyphenylacetic acid as the recognition element. 7 In this study, we have used ferricyanide as the recognition element and gold nanoparticle (GNP) modified indium tin oxide (ITO) electrode as base materials. MLM was attached with the ITO/GNP electrode through strong interaction between the -NH 2 group of MLM and GNP. After the attachment of MLM, the cathodic peak current of ferricyanide was found to suppress, which is directly related with the concentration of MLM and can be used to build up an electrochemical detection scheme for the determination of MLM. ExperimentalAll reagents were obtained as analytical grade and used without further purification. Double distilled water was used throughout the experiments. Melamine, gold chloride trihydrate, potassium ferricyanide, sodium phosphate dibasic and sodium phosphate monobasic were purchased from Sigma-Aldrich (Germany).ITO/GNP electrode was prepared as previously reported. 8 Briefly, the cleaned ITO was subjected to the electrochemical deposition of GNPs (around 50 nm in diameter) through the cyclic sweeping of the potential from −0.2 to −1.3 V for 20 cycles at 50 mV/s in 0.1M PBS (pH 7.0) containing 0.1 mM HAuCl 4 . The prepared ITO/GNP...
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