**1. Introduction**

186 Electropolymerization

Hoshino, D., Morita, T., Chida, Y., Duan, Z., Ogihara, S., Suzuki, Y., & Nishioka, Y. (2011).

Hutchison, A. S., Lewis, T. W., Moulton, S. E., Spinks G. M., & Wallace, G. G. (2000).

Ogasawara, M., Funahashi, K., Demura, T., Hagiwara T., & Iwata, K. (1986). *Synth. Met., 14,*

Jager, E. W. H., Smela, E., Inganas O., & Lundstrom, I. (1999). *Synthetic Metals 102,* 1309. Morita, T., Chida, Y., Hoshino, D., Fujiya, T., & Nishioka, Y. (2010). *Mol. Cryst. Liq. Cryst.* 

Sendai, T., Suematsu, H., & Kaneto, K. (2009). *Jpn. J. Appl. Phys., 48,* 51506.

Zama, T., Hara, S., Takashima, W., & Kaneto, K. (2005). *Bull. Chem. Soc. Jpn., 78,* 506. Zama, T., Hara, S., Takashima, W. & Kaneto, K. (2005). *Jpn. J. Appl. Phys., 44,* 8153. Zama, T., Hara, S., Takashima, W., & Kaneto, K. (2005). *Synth. Met., 149,* 199.

*Jpn. J. Appl. Phys. 50 (2011)* 01BG10 .

*Synthetic Metals 113,* 121.

*519,* 121.

61.

Chemical sensors are the devices that provide a certain type of responses related to the quantity of a specific species. All chemical sensors consist of a transducer and a chemically selective layer. The transducers transform the response into a detectable signal on modern instrumentation, and the chemically selective layer isolates the response of the analyte from its immediate environment. According to the properties to be determined, chemical sensors can be classified as electrical, optical, mass or thermal sensors. Among all of them electrochemical sensors obtained more attention because they are sensitive and selective, fast and accurate, portable and in expensive.

The modification of electrodes surfaces by some special layers has been the major growth area in electrochemical sensors in recent years. Compared to conventional electrodes, greater control of electrode characteristics and reactivity is achieved by surface modification, since the immobilization transfers the physicochemical properties of the modifier to the electrode surface. This process could impart a high degree of selectivity or sensitivity to the electrochemical transducers. Different procedures such as chemical reaction, chemisorption, composite formation or polymer coating have been used to modify electrodes. Several papers have reviewed the application of the modified electrodes in electrochemical sensors areas [1]

Electrochemical polymerization (ECP) refers to the application of electrochemical methods in the cathode or anode during the polymerization reaction process. The polymerization method provides a new current or potential control factor, so some important advantages were recognized at the beginning of its development such as: short process and low cost. The film thickness and composition can be achieved easily by controlling the electrochemical parameters during the electrochemical process. In addition, electrochemical polymerization can make raw monomer aggregate directly on the substrate film to avoid the use of a large number of volatile organic solvents to achieve the aim of clean production. Because of these excellent features, electropolymerization method holds a promising future for construct simple design, high stable, rapid response and enhanced selectivity sensors. This review will briefly present the development and application of the sensors prepared by electropolymerization method in the recent ten years. The main goal of this contribution is not to collect all papers published recently, but to discuss the development and advantages of the electropolymerized films for analytical purpose. For application, we specifically focused on the most recent and promising applications of those sensors in environmental and clinical monitoring.

Electrochemical Sensors Based on Electropolymerized Films 189

polymer films. Their unusual electrochemical properties are caused by the conjugated electron backbones. A large number of reviews devoted to the fabrication and description of the properties of conducting polymers have been published. Numbers of reviews focus on their use as electrochemical sensors. However there is still considerable interest in the development of new conductive polymers by the electropolymerization method, and new application of the films continually appear. Novel work in the literature from 2000 up to

Non-conducting films prepared by electropolymerization method are also important. The resulting non-conducting film usually has a small thickness and is self-controlled by the increase in electrical resistance during its growth on the electrode. Because non-conducting polymers are always thin (10-100 nm), substrates and products can diffuse rapidly to and from the film modified electrodes. Therefore, fast response time and high selectivity could be expected for non-conducting polymer based electrochemical sensors. In most cases, phenol and its derivates are always used for the synthesis of non-conductive films by electrochemical methods [5]. **Fig. 2** illustrated the process for the preparing of the phenol related films. Phenylate will be oxidized to generate phenolate radicals which would couple together by ortho- or para- coupling way. Subsequent reactions produce oligomers and, finally, poly(phenylene oxide) films are polymerized on the surface of the electrode. Mahmoudian MR et al prepared poly (pyrrole-co-phenol) (co-PyPh) film by using cyclic voltammetry in the mixture electrolytes of dodecyl benzene sulphonic acid (DBSA) and oxalic acid solution on steel electrodes [6] . It can be used to protect the corrosion of steel. Tahar NB and Savall A[7] have studied the electrochemical oxidation of phenol at different temperatures in basic aqueous solution on a vitreous carbon electrode at different temperatures by cyclic voltammetry and chronoamperometry techniques. Other phenol derivatives have also been prepared by the electropolymerization method. Matsushita et al reported the electropolymerization of coniferyl alcohol in an aqueous system (0.2 M NaOH) and in an organic solvent system [CH2Cl2/methanol (4:1 v/v) in the presence of 0.2 M LiClO4][8]. Ciriello R et al. investigated the electrosynthesis mechanism of 2-naphthol (2- NAP) in phosphate buffer at pH 7 on Pt electrodes. The voltammetric behavior suggested the formation of a non-conducting polymer (poly(2-NAP)) through an irreversible electrochemical process complicated by 2-NAP adsorption and fast electrode passivation [9].

N H

\*

N H

\*

n

N H

Fig. 1. Main chasses of conductive polymers

present will be reviewed.

Polycarbazole Polyindole

**2.2 Non-conducting films prepared by electropolymerization method** 
