**2.1 Conducting films prepared by electropolymerization method**

Conducting polymers have the polyconjugated structures with electronic properties similar to metals, but retaining the properties of conventional organic polymers. They have gained much attention in sensor areas [2,3] in recent years because of their unique characters [4]. A wide variety of organic molecules have been used as the monomers for the preparation of conducting polymers, such as polycyclic benzenoid, nonbenzenoid hydrocarbons, acetylene, polyaromatic and heterocyclic compounds. **Fig. 1** gives some examples of the conductive

**2. Classification of films obtained by electrochemical polymerization method**  Polymerization is a reaction in which large molecules are created from many small monomers. Normally it is a process which must be controlled carefully under strict conditions. Recently electropolymerization method has been successfully used for the controllable preparation of films because of the advantages we referred in the introduction section. Three types of electrochemical methods are generally employed for the polymerization of different monomers: (1) a constant current (galvanostatic); (b) a constant potential (potentiostatic) and (3) a potential scanning/cycling or sweeping. Different types of polymer films were applied for the construction of sensors. They are classified as

Conducting polymers have the polyconjugated structures with electronic properties similar to metals, but retaining the properties of conventional organic polymers. They have gained much attention in sensor areas [2,3] in recent years because of their unique characters [4]. A wide variety of organic molecules have been used as the monomers for the preparation of conducting polymers, such as polycyclic benzenoid, nonbenzenoid hydrocarbons, acetylene, polyaromatic and heterocyclic compounds. **Fig. 1** gives some examples of the conductive

N

H

<sup>S</sup> \* \*

n

\* \*

\*

\* n

n

n

conductive and nonconductive films.

**2.1 Conducting films prepared by electropolymerization method** 

N H

<sup>N</sup> n

Poly(paraphenylene) Poly(paraphenylenevinylene)

n

Poly(paraphenyleneethynylene) Polyfluorene

\*

Polypyrrole Polythiophene

\* n

\* \*

\*

Polyacetylene Polyaniline

Fig. 1. Main chasses of conductive polymers

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 present will be reviewed.

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

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].

Electrochemical Sensors Based on Electropolymerized Films 191

Electrochemical sensors in clinical assay was developed from 1962 by Clark and Lyons who used the glucose oxidase (GOx) enzyme to construct an amperometric electrode for dissolved oxygen detection [14]. From that time, the application of electrochemical sensors to determine the concentration of substances and other parameters of biological interest has represented a rapidly expanding field of instrument. The electrochemical sensors have been widely used in clinical analysis because of their high sensitivity and selectivity, portable field-based size, rapid response time and low-cost. Some of these sensor devices have been routinely used in clinical, industrial, environmental, and agricultural areas. Many works and reviews related on this area have been reported. Lakshmi D et al has reviewed the application of electrochemical sensors for uric acid detection in mixed and clinical samples[15]. Ronkainen et al reviewed the application of electrochemical biosensors from

Since the original work reported by Diaz et al. [17], the films prepared by electropolymreization method have attracted considerable interest due to their versatility. Polymers have gain considerable interest in the clinical analysis area because of their unique and biochemical properties. In 1992, Davies et al have extensively reviewed the application of the polymer membranes in clinical sensor application [18]. In this work, the authors were concerned with the relationship between the polymer design and the proposed application. They highlighted the permeability, permselectivity and transmembrane potential of the polymer membranes and the role of polymer membranes as matrices for the immobilization of reactive chemical and biological agents. Cosnier reviewed the application of the electropolymerized films on the construction of affinity sensor[19]. He compared the different strategies for the immobilization of biomolecules on electropolymerized films to construct affinity sensors which can be used as clinical sensors. Table 1 [20-52] summarized the numerous of recent applications in clinical areas based on the electropolymerized films. The information on the analytes, the polymer films, and the characters of the sensors has

Non-conductive polymer from polyphenylenediamines has been used as a matrix for the entrapment of enzymes. Glucose oxidase has been caged into the microtubule structures of polycarbonate membrane by using poly (1, 3- phenylenediamine) to fill the pores. The sensitivity of the sensor increased 60 times [23]. Different techniques for the electropolymerization of 1,2-, 1,3- and 1,4-phenylenediamine, such as cyclic voltammetry and chronoamperometry, were compared by Currulli et al [53]. When heparin was coimmobilized with glucose oxidase during the electropolymerization of a non-conductive poly (1,2- phenylenediamine) film, an implantable glucose biosensor could be constructed [54]. This sensor could prevent the fibrin formation and clotting when the glucose sensor

Phenol and its derivative have also been widely used for clinical analysis. The electropolymerization of phenol derivatives is similar to that of phenol. We reported the polymerization of the acid chrome blue K on a glassy carbon electrode by cyclic viltammetric method in 0.05 M pH 7.0 phosphate buffer solution in the potential range from -0.4 V to 1.5 V at the scan range of 100 mV/s by 25 cycles [28]. This film can be used to separate the electrochemical response of dopamine (DA), ascorbic acid (AA) and uric acid (UA). Under the optimum conditions, the calibration curves for DA, AA and UA were obtained in the range of 1.0–200.0, 50.0–1000.0 and 1.0–120.0μM, respectively. Both poly

**3.1 Electropolymerized films for clinical monitoring** 

two points: biocatalyst and affinity [16].

been listed**.** 

was exposed to blood.

Non-conductive polymers obtained from amino acid or their derivates have also obtained particular interest because they bears specific groups which can interact with some electroactive species through the formation of covalent bonds between either the amino and aldehyde or amino and carboxyl groups. We have used cyclic voltammetric method to form the L-cysteine modified electrode for the detection of sinomenine [10] , dopamine [11], terbinafine [12] and adenine [13]. Cystein was electropolymerized on a glassy carbon electrode in 0.04 M HCl solution in the scan range from -1.20 to 2.60 V at the scan rate of 100 mV/s [13].

Fig. 2. The process for the preparing of the Phenol film by electrochemical method.

Fig. 3 illustrated the structures of some of the non-conductive films obtained by electropolymerization method. They included the already discussed polyphenol, polymers of phenylendiamines and the overoxidized polypyrrole (PPy). These polymers can be used as a novel support matrix for the immobilization of biomolecules to construct different electrochemical sensors. We would discuss the preparation and application of these films in the following section.

Fig. 3. Structures of some non-conductive polymerfilms
