Nanobiosensor is the simple and powerful device for sensing biological species. This kind of sensors responds to analytes not only sensitively, but also selectively. Sensitivity and selectivity are two important merit figures in the evaluation of analytical instrument. Using nanoparticle such as nanographene (NG) causes the better electron transfer and higher sensitivity. In the other hand, utilizing the biological agent like BSA leads to the better selectivity. The NG describes a group of nanomaterial made up entirely of carbon atom. Because of their excellent electrical conductivity, NG is of special interest for the electrocatalyst and will be the subject of this research. Therefore, it can be employed as an electron transfer catalyst in the construction of the sensors. Adding NG into agar powder at low weight fractions can improve electrical properties of the resulting sensor. Bovine serum albumin (BSA) is a serum albumin protein isolated from cows. Because of its negative charge, BSA binds water, salts, fatty acids, vitamins and hormones and carries these bound components between tissues and cells. Temperature is the critical factor affecting the BSA structure. By heating to 50°C or above, BSA quite rapidly forms hydrophobic aggregates which do not revert to monomers upon cooling. Aggregation is also expected to occur at somewhat lower temperatures but at a relatively slower rate. Rizatriptan benzoate (RB) belongs to a family of medicines known as serotonin agonists. It is chemically described as: N, N dimethyl-5-(1H-1,2,4-triazol-1-ylmethyl)-1H-indole-3-ethanamine mono benzoate. It is used in the treatment of migraines. Despite many investigations about RB determination such as high-performance liquid choromatography (HPLC), reverse phase ultra-performance liquid chromatography (UPLC), reverse phase liquid chromatography, liquid chromatography/tandem mass spectrometry, spectrophotometry, UV spectroscopy, only few articles regarding voltammetric measurement of RB in the literature are present [1-4]. Therefore, The main target of this study is to develop a new sensitive and selective RB nanobiosensor using BSA as highly selective biological modifier and NG as electrocatalyst. Evaluation of kinetic and thermodynamic parameters of RB is another novel aspect of this research, to the best of our knowledge.

   The CV and EIS measurements were performed with µAutolab FRA2 Potentiostat-Galvanostat (Autolab comp.). A three-electrode system was used with the BSA-NG/APE (3mm/ 60mm) as working, glassy carbon electrode (GC ROD 2mm/ 76mm) as the counter and an Ag/AgCl as the reference electrode (Autolab comp.). A digital pH meter (Jenway 370) was applied for pH adjustment. Measurement cell was used to immerse in a water-circulating bath in order to provide and hold a constant temperature.

   In this effort, nanographene (NG), bovine serum albumin (BSA) and agar powder were used as electrocatalyst, selective biological agent and supporting material in construction of novel Rizatriptan benzoate (RB) nanobiosensor, respectively. The important experimental factors for RB quantitation, such as BSA/NG ratio, potential scan rate, pH and supporting electrolyte have been optimized. This optimized nanobiosensor (BSA-NG/APE) was applied for electrochemical assay of RB in HCl solution (pH = 3.0) using cyclic voltammetry (CV). Under the optimum condition, RB could be linearly detected in the acceptable concentration range of 0.10-1.0 mM (R² = 0.9934). The detection limit was down to around 0.027 mM (k=3). The Kinetic and thermodynamic parameters such as standard rate constant (ks), apparent activation energy (Ea), enthalpy (DH), entropy (DS) and Gibbs free energy (DG) for RB reduction were evaluated. BSA-NG/APE exhibits a very good performance for detection of RB in hand-making and real samples.

   To sum up, this research reveals the key factors in construction of RB nanobiosensor. BSA and NG act as a selective biological agent and an electrocatalyst, respectively. Presence of NG in electrode composition leads to lower charge transfer resistance. The pH of solution is an important parameter and acidic medium exhibits better response. Proposed sensor has a good linear dynamic range and detection limit. Analysis of real samples was successfully done by BSA-NG/APE. The suggested mechanism has three steps with final electrochemical one. Thermodynamic and kinetic evaluation showed exothermic nature of reaction with less ordered product. The principal advantages of the proposed method are its simplicity, selectivity and rapidity. 

Keywords: Nanobiosensor, Voltammetry, Nanographene, Bovine Serum Albumin, Rizatriptan benzoate

References:

1. S. Iijima, Nature., 354, 56 (1991).

2. J. Kong, N.R. Franklin, C. Zhou, M.G. Chapline, S. Peng, K. Cho, H. Dai, Science., 287, 622 (2002).

3. R. Jain, D.C. Tiwari, P.Pandey, Electroanalysis., 25, 1363 (2013).

4. N.L. Teradal, P.S. Narayan, A.K. Satpati, J. Seetharamappa, Sensor. Actuat. B., 196, 596 (2014).