Development of a New Amperometric Sensor for Dopamine Based on the

Carbon Electrode Modified with Ru(III) Complex

Safeta Redžića, Emira Kahrovićb, Emir Turkušićb

aUniversity of Bihac, Biotechnical faculty Bihac, Luke Marjanovica bb 77 000 Bihac, Bosnia and Herzegovina

bUniversity of Sarajevo, Faculty of Science, Department of Chemistry, Zmaja od Bosne 33-35, Sarajevo,

Bosnia and Herzegovina

Fig.1 Structure of dopamine

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 water-

insoluble redox mediator Sodium bis [N-2-oxyphenyl-5-bromo-salicylideneiminato-

ONO] ruthenate(III) complex using carbon ink.

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.

Keywords: Ru(III) complexes, Schiff Bases, Dopamine, Modified electrode, Carbon

ink, Amperometry.

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.

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.

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.

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).

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).

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.

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-5-

hlorosalicylideniminato- 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-salicylideniminato-

N,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.

Abstract

Introduction

Materials and methods

Results and conclusions

References