Sensors and Actuators B 190 (2014) 149–156 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal h om epage: www.elsevier.com/locat e/snb Sensitivity enhancement of a “bananatrode” biosensor for dopamine based on SECM studies inside its reaction layer Zsuzsanna ˝ Ori a , András Kiss a , Anton Alexandru Ciucu b,∗ , Constantin Mihailciuc c,∗ , Cristian Dragos Stefanescu d , Livia Nagy e , Géza Nagy a a University of Pécs, Faculty of Sciences, Department of General and Physical Chemistry Pécs, Ifjúság útja 6. 7624 Pécs, Hungary b University of Bucharest, Faculty of Chemistry, Department of Analytical Chemistry, 90-92 Panduri Avenue, 050663 Bucharest, Romania c University of Bucharest, Faculty of Chemistry, Department of Physical Chemistry, 4-12 Regina Elisabeta, 030018 Bucharest, Romania d National Institute of Aerospace Medicine, 88 Mircea Vulcanescu Street, Bucharest, Romania e University of Pécs, Szentagothai Research Center Pécs, Ifjúság útja 34. 7624 Pécs, Hungary a r t i c l e i n f o Article history: Received 22 May 2013 Received in revised form 16 August 2013 Accepted 20 August 2013 Available online 2 September 2013 Keywords: Banana tissue biosensor Dynamic voltammetry Scanning electrochemical microscopy Periodically interrupted amperometry Dopamine a b s t r a c t A model biosensor based on a reaction layer containing banana pulp was constructed and dopamine (DA) has been selected as analyte for the investigations. On the basis of dynamic voltammograms it was found that the optimal potential for DA detection should be -0.2 V vs. SCE, potential where the oxygen interference was avoided. Based on vertical scanning electrochemical microscopy (SECM) the optimal width of the reaction layer for the model biosensor was determined to be in between 130 and 160 m. Optimal resting potential in periodically interrupted amperometry (PIA) detection mode was determined to be in the range from -0.02 V to -0.03 V vs. SCE. The resting time used in PIA experiments was 0.5 s. A detection limit of 2 × 10 -6 M was obtained for DA by using PIA detection mode. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Following the pioneering steps of Clark Jr. [1], the research in the field of developing and application of biosensors has been an intensive cultivated area of analytical chemistry. The function of the earliest developed group of biosensors is based on catalytic action of different enzymes used in immobilized form. The stability of enzymes in their natural environments is usually much higher than in extracted preparations or in immobilized form. It was obvi- ous to prepare enzyme sensors by using native biological tissue as catalytic layer. High number of original papers [2–5] and reviews [6] has been reported about enzyme sensors prepared in this way. Several plant tissue based biosensors were made for measurements of phenolic compounds like cathecols [7–10]. One of them is the dopamine (DA) measuring biosensor that uses the catalytic action of banana pulp that was nicknamed “banana- trode” [11]. In case of this biosensor, the banana pulp was used as a very thin slice (membrane form) mechanically attached to ∗ Corresponding authors. Tel.: +40 722470324; fax: +40 214102279. E-mail addresses: anton ciucu@yahoo.com (A.A. Ciucu), cmpaul@gw-chimie.math.unibuc.ro (C. Mihailciuc), g-nagy@gamma.ttk.pte.hu (G. Nagy). the active surface of an electrode [12] or was incorporated, by a well-known procedure, into carbon paste [4]. For the first case, the reaction layer is banana pulp, located between the working electrode and the sample, where catechol oxidase or o-diphenol- oxygen oxidoreductase (EC 1.10.3.2) is the acting biocatalyst. The sample diffuses into the reaction layer, and any substrate of catechol oxidase undergoes enzymatic oxidation consuming the dissolved oxygen, resulting in quinone product. There are two ways for obtaining amperometric signal. One is following the oxygen concentration with a Clark oxygen cell [12]. The other one is recording the concentration dependent reduc- tion current of the quinone formed in catalytic oxidation [13]. In the first case the analytical signal of the sensor is influenced by the dissolved oxygen concentration in the sample. Furthermore, small analyte concentration introduced in the sample results in small local change of oxygen concentration, and therefore small analytical signal will be generated. It is obvious that using ampero- metric current of quinone reduction is the more advantageous way of detection. In the biocatalytic reaction the oxygen concentration decreases, while the quinone concentration increases. Special care must be taken in selecting the electrode potential. It has to be reduc- tive enough for the quinone reduction, but should not facilitate electrode reaction of oxygen. The response time of the “banana- trode” was very much affected by the structure of the catalytic layer. 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.08.063