Sensors and Actuators B 136 (2009) 484–488 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb A new amperometric cholesterol biosensor based on poly(3,4-ethylenedioxypyrrole) Özlem Türkarslan, Senem Kıralp Kayahan, Levent Toppare ∗ Middle East Technical University, Department of Chemistry, 06531 Ankara, Turkey article info Article history: Received 4 August 2008 Received in revised form 8 October 2008 Accepted 18 October 2008 Available online 30 October 2008 Keywords: Amperometric biosensor Enzyme electrodes Cholesterol Cholesterol oxidase Conducting polymers PEDOP abstract Cholesterol oxidase (ChOx) was physically entrapped in poly(3,4-ethylenedioxypyrrole) (PEDOP) to con- struct an amperometric cholesterol biosensor. The responses of the enzyme electrodes were measured via monitoring oxidation current of H 2 O 2 at +0.7V in the absence of a mediator. Kinetic parameters, operational and storage stabilities, pH and temperature dependencies were determined. K m , I max and sensitivity (I max /K m ) were calculated as 3.4 mM, 34 A cm -2 and 10 A mM -1 cm -2 , respectively. The min- imum detectable substrate concentration was 0.4mM and for a period of 20 days the biosensor showed the maximum relative activity. © 2008 Elsevier B.V. All rights reserved. 1. Introduction A biosensor is defined as a device consisting of a biological recognition system, often called a bioreceptor, and a transducer. A bioreceptor can be a biological molecular species or a living bio- logical system that use a biological mechanism for recognition [1]. Since selective determination of glucose [2,3], urea [4,5], lactate [6,7] and cholesterol [8,9] present in blood is important in medical diagnosis, most of the research is carried out on developing fast and sensitive biosensors for the determination of these analytes present in the blood. The bioreceptor part can be constructed via immobilizing the biomolecule on a substrate such as a synthetic polymer [10], natural polymer [11], hydro gel [12], Langmuir–Blodgett film [13], and self-assembled monolayer [14]. Conducting polymers [15–17] are suitable matrices for biomolecule immobilization since biomolecules can be entrapped in one step in polymer films dur- ing their electro generation on the electrode surface of any size and geometry. In addition, this method enables exact control of the thickness of the polymer layer based on the measurement of elec- trical charge passing during the electrochemical polymerization [18]. ∗ Corresponding author. Tel.: +90 312 2103251; fax: +90 312 2103200. E-mail address: toppare@metu.edu.tr (L. Toppare). The transducer, which is in close contact with the bioreceptor, should be highly specific for the analyte of interest. Furthermore, it should be able to respond in the appropriate concentration range and have a moderately fast response time. The signal may be transduced by optical, thermal, electrical, or electronic ele- ments [19]. The electrochemical conversion occurs at a conducting polymer/solution interface when the overall rate of both the bio- chemical reaction and charge transport exceed considerably the rate of mass transport of species to the electrode. This diffusion- controlled electro catalytic process is used for the amperometric detection [15]. In the work cholesterol oxidase (ChOx) was immobilized for the first time in poly(3,4-ethylenedioxypyrrole) (PEDOP) matrix in order to construct an amperometric biosensor. The aim of the study is to show that there exists a third water compatible polymer, which can be used as a matrix for enzyme immobilization. In addition, this polymer allows the use of a very small potential (0.6V compare to the other matrices 1 V (polypyrrole), 0.9 V (PEDOT)), which helps to prevent the denaturation of the enzyme partly. The use of this polymer also enables the immobilization procedure in a single step. Conducting polymers constitute a new generation of poly- mers exhibiting the electrical in addition to optical properties of metals and semiconductors while retaining the attractive mechanical properties and processing advantages of polymers [20]. Aqueous-compatible conducting polymers are polymers that are able to undergo electrochemical switching in aqueous media [21]. They may be considered as the member of another class 0925-4005/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2008.10.016