University of Bihac, Biotechnical faculty Bihac, Luke Marjanovica bb 77 000 Bihac, Bosnia and Herzegovina b. University of Sarajevo, Faculty of Science, ...
Development of a New Amperometric Sensor for Dopamine Based on the Carbon Electrode Modified with Ru(III) Complex a
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Safeta Redžić , Emira Kahrović , Emir Turkušić
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University of Bihac, Biotechnical faculty Bihac, Luke Marjanovica bb 77 000 Bihac, Bosnia and Herzegovina b
University of Sarajevo, Faculty of Science, Department of Chemistry, Zmaja od Bosne 33-35, Sarajevo, Bosnia and Herzegovina Abstract The electrode is scanned by Differential Pulse Voltammetry (DPV) and Cyclic Voltammetry (CV) in the range of -0.3 V to + 0.4 V vs. Ag/AgCl electrode in the phosphate buffer, pH 7.42. The modified electrode shows a fast electric current response, i.e. an excellent electro-catalytic activity for the oxidation of dopamine. Hydrodynamic (HA) and Flow injection (FIA) amperograms were also recorded. Amperometric measurements were performed at an applied potential of 0.0; 0.1 and 0.15 V. An impact from numerous interferences being present in real samples will be reduced by low working potential of this sensor.
Dopamine is one of the most important neurotransmitters controlling the motor activity, autonomic and endocrine functions as well as the mental and emotional health of the human being. On the one side, the reduced dopaminergic activity leads to Parkinson's disease, while on the other side, the increased dopaminergic activity is associated with the emergence of psychosis and schizophrenia. Considering the wide range of physiological and pathophysiological effects, the development of a new sensor for specific and selective measurement of dopamine at low levels of concentration can make a major contribution to the disease diagnosis. With the aim of developing a new dopamine amperometric sensor, a glassy-carbon electrode was modified. The electrode was modified with waterinsoluble redox mediator Sodium bis [N-2-oxyphenyl-5-bromo-salicylideneiminatoONO] ruthenate(III) complex using carbon ink.
Keywords: Ru(III) complexes, Schiff Bases, Dopamine, Modified electrode, Carbon ink, Amperometry.
Introduction Dopamine (DA) with IUPAC nomenclature 4-(2-aminoethyl)- benzene-1,2-diol, structure given in Fig. 1, is one of the most important catecholamine neurotransmitters in the mammalian central nervous system in the brain from where dopamine functions as a neurotransmitter that is a chemical released by the nerve cells to send signals to other nerve cells, thus acting as a chemical messenger and in such a way plays a key role in the functioning of the renal, hormonal, and cardiovascular systems (Staden et al., 2012).
Because of its electrochemical activity, DA can be determined with electrochemical methods. Electrochemical techniques have attracted great interest in many cases, and these techniques can be fast in detections, low in cost, and with merits of low detection limit and high accuracy (Chang et al., 2006). Kahrović et al. (Kahrović et al., 2012; Turkusic and Kahrović, 2012) have prepared the complexes of Ru (III) with Schiff's bases that have been shown to act as electron transfer mediators being able to be used for the amperometric determination of ascorbic acid and L-cysteine. This group of authors have also prepared and published synthesis of Ru complexes Sodium bis [N-2-oxyphenyl-5-bromo-salicylideneiminato-ONO] ruthenate (III), being presented by formula Na[Ru(N-Ph-O-5-Br-salim)2] hereinafter referred to as SB5 (Kahrović et al., 2014). The aim of this paper is to investigate the application of SB5 complex as the electron transfer mediator in order to develop a new sensor for dopamine.
Fig.1 Structure of dopamine
Materials and methods Apparatus. Cyclovoltametry (CV), Hydrodynamic amperometry (HA) and Flow injection analyses (FIA) were performed with an electrochemical workstation Autolab potentiostat/galvanostat (PGSTAT 12). The convective transport in HA was provided by magnetic stirrer and a Teflon-coated stirring bar (approx. 300 rpm). As a counter electrode a platinum wire was used and an Ag/AgCl electrode (Model 6.0733.100; Metrohm, Switzerland) as a reference electrode.
Results and conclusions
Figure 2. Cyclic voltamograms (CV) in phosphate buffer pH 7.5 with SB5 modified electrode (A) dopamine with unmodified electrode (B) and dopamine with SB5 modified electrode (C) (PMF Sarajevo).
Figure 3. Hydrodynamic amperogram of dopamine with SB5 modified carbon pasta electrode; operating potential 0.15 V vs Ag/AgCl; 0.1 M phosphate buffer pH 7.42. The arrows indicate additions of dopamine (the first addition was 25 µL, while other four per 1 mL of 200 ppm dopamine) (PMF Sarajevo).
Reagents and solutions. All chemical of analytical grade were purchased from commercial sources and used without further purification. Various concentrations of dopamine were prepared in phosphate buffer (pH 7.42) immediately before the measurement. Fabrication of the electrodes. SB 5 carbon-modified electrode was prepared by dissolving SB5 complex in ethanol and mixing with carbon ink (Electrodag 421SS PTF ink, UN1210 PSN Printing ink) for amperometric measurements in the FIA system. The electrode was dried for 10 minutes at 60°C. The surface modification of electrode SB 5 complex was carried out for cyclovoltammetric (CV) and hydrodynamic (HA) measurements.
Figure 4. FIA current responses SB5 modified carbon pasta electrode with the addition of various concentrations of dopamine (a = 200 ppm: b = 100 ppm; c = 50 ppm; d = 25 ppm); operating potential 0.1 V vs. Ag/AgCl; flow rate 0.4 mL/min; injection volume 100 µL; 0.1 M phosphate buffer, pH 7.42 (PMF Sarajevo).
Figure 5. FIA current responses SB5 modified carbon pasta electrode with the addition of various concentrations of dopamine (a = 200 ppm: b = 100 ppm; c = 50 ppm); operating potential 0 V vs. Ag/AgCl; flow rate 0.4 mL/min; injection volume 100 µL; 0.1 M phosphate buffer pH 7.42 (PMF Sarajevo).
References Staden J, F., Stefan van Staden. (2012) Flow- injection analysis systems with different detection devices and other related techniques for the in vitro and in vivo determination of dopamine as neurotransmitter. Areview. Talanta. Wang C.Y., Wang Z.X., Zhu A.P., Hu X.Y. (2006) Voltammetric Determination of Dopamine in Human Serum with Amphiphilic Chitosan Modified Glassy Carbon Electrode. Sensors 6, 1523-1536. Kahrović, E., Turkušić, E., Ljubijankić, N., Dehari, S., Dehari, D., Bajsman A. (2012) New Ruthenium Complexes with Schiff Bases as Mediators for the Low Potential Amperometric Determination of Ascorbic Acid, Part I: Voltametric and Amperometric evidence of mediation with Tetraethylamonium dichloro-bis[N-phenyl-5hlorosalicylideniminato- N,O]ruthenat (III). HealthMED - Volume 6 / Number 2.699-702. Turkušić, E., Kahrović, E. (2012) Development of new low potential amperometric sensor for L-cysteine based on carbon ink modification by Tetraethylamonium dichloro-bis[N-phenyl-5- bromo-salicylideniminatoN,O]ruthenat (III).Volume 7/Number 3. Technics technologies education management-TTEM.699-702. Kahrović, E., Zahirović, A., Turkušić, E. (2014) Calf Thymus DNA Intercalation by Anionic Ru(III) Complexes Containing Tridentate Schiff Bases Derived from 5-X-Substituted Salicyladehyde and 2-Aminophenol. J. Chem. Chem. Eng. 8, 335-343.
Quasi-reversible cyclic voltammogram of dopamine at SB 5 modified electrode shows a significant increase of dopamine oxidation followed by the reduction of Ru(III) in Ru(II), confirming the role of the mediator compound Ru(III)/Ru(II) of redox couple. The oxidation starts at about 0.1 V and by potential enhancement it is stepped up. Carbon paste SB 5 modified electrode demonstrates clearly visible reproductive and reversible responses to dynamic changes in the concentration of dopamine in the applied potential of 0 and 0.1 V (Figure 4 and 5). In order to develop a new sensor for dopamine specified studies have confirmed the thesis of applicability Ru(III) complexes SB5 as the electron transfer mediators.
