Chapter II-Abstract Electrochemical co-deposition of ZnO and MB hybrid films were carried out onto glassy carbon, gold and ITO electrodes and their electrochemical properties were investigated using CV. The surface morphology and deposition kinetics of MB/ZnO hybrid films were studied by means of SEM, AFM and EQCM techniques, respectively. The MB/ZnO/GCE acted as a sensor and displayed an excellent specific electrocatalytic response to the oxidation of NADH. The linear response range between 50 – 300 μM NADH concentration at pH 6.9 was observed with a detection limit of 10 μM (S/N=3). The electrode was stable during the time it was used for the full study (about 1 month) without a notable decrease in current. Indeed, DA, AA, AP and UA did not show any interference during the detection of NADH at this modified electrode.

Chapter III-Abstract
Thin TBO and ZnO hybrid films have been grown on GCE and ITO electrodes by using CV. The SEM images revealed spherical and beads-like shape of highly oriented TBO/ZnO hybrid films. The EDS results declared that the films composed mainly of Zn and O. Moreover, TBO/ZnO hybrid films modified electrode is electrochemically active, dye molecules were not easily leached out from the ZnO matrix and the hybrid films can be considered as sensor for amperometric determination of NADH at 0.0 V. A linear correlation between electrocatalytic current and NADH concentration was found to be in the range between 25 and 100 μM in 0.1 M phosphate buffer solution.

Chapter IV-Abstract
The ZnO and FAD molecules were deposited onto the GCE, gold and ITO by using CV from the bath solution containing aqueous 0.1M Zn(NO3)2, 0.1M NaNO3 and 1×10-4 M FAD. It was called as ZnO/FAD modified electrodes. Second type of modified electrode was prepared by electropolymerization method. Electrochemical polymerization of FAD was carried out from the acidic solution containing 1×10-4 M FAD monomers onto electrode surfaces. This poly(FAD) modified electrode yields a new redox couple in addition to monomer redox couple. The electrochemical and electrocatalytic properties of ZnO/FAD and poly(FAD) modified electrodes are investigated. In addition, the EQCM technique has been employed to follow the deposition process of both kind of modified. The electrocatalytic activity of poly(FAD) modified electrode towards the reduction of H2O2, oxidation of DA and AA has also been explored. The important electrocatalytic properties of poly(FAD) modified electrode was observed for simultaneous separation of DA and AA in (pH 6.0) buffer solution.

Chapter V-Abstract
Electrochemical synthesis and characterization of PABS films doped with flavins (FAD, FMN, RF) were investigated. In this study, the conducting polymer, PABS served as a matrix during the electropolymerization to synthesize PABS/flavin composite films. The synthetic, morphological and electrochemical properties of PABS/flavin films and PABS films were compared. Characterization was performed by CV, AFM, SEM and UV–vis spectroscopy. UV–vis spectroscopy confirmed the presence of flavins within composite films. PABS/FAD composite modified GCE (PABS/FAD/GCE) is used to electrochemically detect NADH and NAD+. PABS/FAD/GCE showed excellent electrocatalytic activity for the oxidation of NADH and for the reduction of NAD+. At optimum conditions, the sensor has a fast response to NADH and a good linear response to NADH in the range from 10 to 300 μM.

Chapter VI-Abstract
The electrocatalytic ability of the modified electrodes for the reduction of dioxygen to hydrogen peroxide was investigated by using CV and chronocoulometry techniques at PABS modified GCE. The electrochemical reduction of O2 has been studied in pH 7.0 buffer solution by using PABS modified glassy carbon rotating ring disk electrode (RRDE). The PABS-modified GCE (GCE/PABS) showed excellent electrocatalytic activity for O2 and H2O2 reduction reactions. The RRDE data indicated that the reduction of O2 on GCE/PABS electrodes proceed by a two-electron (n=2) pathway in aqueous buffer solution (pH 7.0). In addition, PABS/GCE was successfully utilized as an enzyme-less amperometric sensor for the detection of H2O2 in the range from 50 – 550 µM with detection limit of (S/N) 10 µM.

Chapter VII-Abstract
We have investigated electrochemical polymerization of 4-amino-1-1'-azobenzene-3,4'disulfonic acid (AY) was carried out onto the surface of GCE and ITO from acidic solution containing AY monomers. The redox response of the poly(AY) film on the GCE showed a couple of redox peak in 0.1 M sulfuric acid solution and the pH dependent peak potential was -58 mV/pH which was close to the Nernst behavior. The poly(AY) film-coated GCE (GCE/PAY) exhibited excellent electrocatalytic activity towards the oxidations of DA in 0.1M PBS (pH 7.0. However, in contrast to other polymer modified electrode, due to the strong negatively charged back bone of poly(AY) film modified electrode highly repelled the important interference of DA such as AA, UA and NADH in 0.1 M PBS (pH 7.0). This behavior makes the GCE/PAY for selective detection of DA in the presence of higher concentrations of AA, UA and NADH. Using differential pulse volatmmetry the calibration curves for DA were obtained over the range of 1 – 100 μM with good selectivity and sensitivity.

Chapter VIII-Abstract
Anodic polymerization of the azo dye DB71 on GCE in 0.1 M H2SO4 acidic medium was found to yield thin and stable polymeric films. The poly(DB71) films were electroactive in wide pH range (1 - 13). One pair of symmetrical redox peaks at a formal redox potential, E0’ = -0.02 V vs. Ag/AgCl (pH 7.0) was observed with a Nernstian slope -0.058 V, is attributed to a 1:1 proton + electron involving polymer redox reactions at the modified electrode. SEM, AFM and EIS measurements were used for surface studies of polymer modified electrode. Poly(DB71) modified GCE showed excellent electrocatalytic activity towards ascorbic acid in neutral buffer solution. Using amperometric method, linear range (1×10-6 M to 2×10-3 M), dynamic range (1×10-6 M to 0.01 M) and detection limit (1×10-6 M, S/N=3) were estimated for measurement of ascorbic acid in pH 7.0 buffer solution. Major interferences such as DA and UA were tested at this modified electrode and found that selective detection of AA could be achieved.

Chapter IX-Abstract
The adsorption processes and electrochemical behavior of 4-NA and 2-NA adsorbed onto GCE have been investigated in aqueous 0.1M HNO3 electrolyte solutions using CV. 4NA and 2-NA adsorbs onto GCE surfaces and upon potential cycling between 0.5 and -0.55 V is transformed into the ArHA which exhibits a well-behaved pH dependent redox couple centered at 0.32V (pH 1.5). This modified electrode can be readily used as an immobilization matrix to entrap proteins and enzymes. In our studies, Mb was chosen as a model protein for investigation. A pair of well-defined reversible redox peaks for Mb(Fe(III)–Fe(II)) was obtained at the Mb/ArHA modified GCE (Mb/ArHA/GCE) by direct electron transfer between the protein and the GCE. E0’, Γ and ks were calculated as -0.317 V, 4.15±0.5×10-11 mol/cm2 and 51±5 s-1, respectively. Dramatically enhanced biocatalytic activity was exemplified at the Mb/ArHA/GCE for the reduction of H2O2, TCA and O2.

Contents
Contents…………… (i)
Dedication………… (iii)
Acknowledgement……(iv)
Certificate of Originality…… (vi)
List of Abbreviations…… (vii)
Abstract………… (ix)

Chapter I Introduction 1
Chapter II Fabrication and Characterization of ZnO/Meldola’s blue Hybrid
Electrode for Efficient Detection of NADH at Low Potential 35
Chapter III Electrochemical Deposition of ZnO/Toluidine Blue Hybrid Film: Characterization and its use as NADH sensor 66
Chapter IV Electrochemical Preparation of ZnO/FAD and Poly(FAD)
Film Coated Electrodes: Characterization and Electrocatalytic Properties 86
Chapter V Electrochemically Polymerized Films of Poly(p-aminobenzene sulfonic acid)/Flavins and Their Use as Electrochemical Sensors 122
Chapter VI Electrocatalytic Reduction of Oxygen and H2O2 at Poly(p-aminobenzene sulfonic acid)-modified Glassy
Carbon Electrode 155
Chapter VII Poly(acid yellow 9) Coated Electrode for Selective
Detection of DA from its Interferences 174
Chapter VIII Electrochemical Selective Determination of Ascorbic Acid at Redox Active Polymer Modified Electrode Derived from Direct Blue 71 191
Chapter IX Direct Electrochemistry and Electrocatalytic Properties of Myoglobin on Redox-active self-assembling Monolayers
Derived from Nitroaniline Modified electrode 211
Chapter X Conclusions and Future Prospects 239
List of Publications 245

[1] J. Koryta, W. Dvorak, L. Kavan, Principles of Electrochemistry, Second Edition, 1993, John Wiley & Sons Ltd.

[2] A. J. Bard, L. R. Faulkner, Electrochemical Methods: Fundamentals and Applications, 2nd ed., 2001, Wiley-VCH, New York, 2001.

[3] J. Wang, Anaytical Electrochemistry, 2nd ed., 2001, Wiley-VCH. New York.

[4] V. S. Bagotsky, Fundamentals of Electrochemistry, John Wiley & Sons, 2006, New Jersey.

[5] C. M. A. Brett, A. M. Oliveira Brett, Electrochemistry (Principles, Methods and Applications), 1994, Oxford University Press Inc., New York.

[6] C. G. Zoski, Handbook of Electrochemistry, Elsevier, 2007.

[7] R. A. Durst, A. J. Bäumner, R. W. Murray, R. P. Buck, C. P. Andrieux, Pure Appl. Chem. 69 (1997) 1317.

[8] W. Kutner, J. Wang, M. L’Her, R. P. Buck, Pure Appl. Chem. 70 (1998) 1301.

[9] C. R. Martin, C. A. Foss, Jr., “Chemically Modified Electrodes”, in Laboratory Techniques in Electroanalytical Chemistry, 2nd ed., P. T. Kissinger, W. R. Heineman, Eds., Marcel Dekker, Inc.: New York, 1996.

[10]
R. W. Murray, “Molecular Design of Electrodes Surfaces”, in Techniques of Chemistry, J.William H. Saunders, A. Weissberger, Eds., John Wiley and Sons, Inc.: New York, 1992, Vol. 22.

[11] R. W. Murray, “Chemically Modified Electrodes”, in Electroanalytical Chemistry, A. J. Bard, Ed., Marcel Dekker, Inc.: New York, 1984, Vol. 13, pp. 191–368.

[12] A. Ulman, An Introduction to Ultrathin Organic Films From Langmuir-Blodgett to Self- Assembly, Academic Press: San Diego, 1991.

[13] A. Walcarius, “Implication of Zeolite Chemistry in Electrochemical Science and Applications of Zeolite-Modified Electrodes”, in Handbook of Zeolite Science and Technology, S. M. Auerbach, K. A. Carrado, P. K. Dutta, Eds., Marcel Dekker, Inc.: New York, 2003, pp. 721–783.

[14] M. C. Petty, Langmuir-Blodgett Films: An Introduction, Press Syndicate of the University of Cambridge: New York, 1996.

[15] D. H. Karweik, C. W. Miller, M. D. Porter, T. Kuwana, “Prospects in the Analysis of Chemically Modified Electrodes”, Surface Analysis, 1982, 89–119, American Chemical Society Conference Proceedings.

[16] J. A. Cox, M. E. Tess, T. E. Cummings, Rev. Anal. Chem. 15 (1996) 173.

[17] H. O. Finklea, “Electrochemistry of Organized Monolayers of Thiols and Related Molecules on Electrodes”, in Electroanalytical Chemistry: A Series of Advances, A. J. Bard, I. Rubinstein, Eds., Marcel Dekker, Inc.: New York, 1996, Vol. 19, pp. 109–335.

[18] R. L. McCreery, K. K. Cline, “Carbon Electrodes”, in Laboratory Techniques in Electroanalytical Chemistry, 2nd ed., P. T. Kissinger, W. R. Heineman, Eds., Marcel Dekker, Inc.: New York, 1996.

[19] R. L. McCreery, “Carbon Electrodes: Structural Effects on Electron Transfer Kinetics”, in Electroanalytical Chemistry, A. J. Bard, Ed., Marcel Dekker, Inc.: New York, 1984, Vol. 17, pp. 191–368.

[20] K. B. Blodgett, J. Am. Chem. Soc. 56 (1934) 495.

[21] K. B. Blodgett, J. Am. Chem. Soc. 57 (1935) 1007.

[22] A. Mälkiä, P. Liljeroth, K. Kontturi, Anal. Sci. 17 (2001) i345.

[23] J. Gong, X. Lin, Electrochim. Acta 49 (2004) 4351.

[24] M. Ferreira, L. R. Dinelli, K. Wohnrath, A. A. Batista, O. N. Oliveira, Jr., Thin Solid Films 446 (2004) 301.

[25] T. Miyahara, K. Kurihara, J. Am. Chem. Soc. 126 (2004) 5684.

[26] G. G. Roberts, Adv. Phys. 34 (1985) 475.

[27] L. M. Goldenberg, M. C. Petty, A. P. Monkman, J. Electrochem. Soc. 141 (1994) 1573.

[28] L. M. Goldenburg, J. Electroanal. Chem. 379 (1994) 3.

[29] A. T. Hubbard, Chem. Rev. 88 (1988) 633.

[30] A. J. Downard, Electroanalysis 12 (2000) 1085.

[31] A. Fitch, Clays and Clay Minerals 38 (1990) 391.

[32] S. M. Macha, A. Fitch, Mikrochim. Acta 128 (1998) 1.

[33] A. J. Bard, T. Mallouk, Electrodes Modifed with Clays, Zeolites, and Related Microporous olids, in Molecular Design of Electrode Surfaces, R. W. Murray, Ed., John Wiley & Sons, Inc.:New York, (1992) Vol. XXII, pp. 271–312.

[34] Z. Navrátilová, P. Kula, Electroanalysis 15 (2003) 837.

[35] J.-M. Zen, A. S. Kumar, Anal. Chem. 76 (2004) 205A.

[36] M. D. Baker, C. Senaratne, Anal. Chem. 64 (1992) 697.

[37] D. R. Rolison, Chem. Rev. 90 (1990) 867.

[38] D. R. Rolison, C. A. Bessel, Acc. Chem. Res. 33 (2000) 737.

[39] D. R. Rolison, R. J. Nowak, T. A. Welsh, C. G. Murray, Talanta 38 (1991) 27.

[40] A. Walcarius, Electroanalysis 8 (1996) 971.

[41] A. Walcarius, Anal. Chim. Acta 384 (1999) 1.

[42] O. Lev, Z. Wu, S. Bharathi, V. Glezer, A. Modestov, J. Gun, L. Rabinovich, S. Sampath, Chem. Mater. 9 (1997) 2354.

[43] M. M. Collinson, A. R. Howells, Anal. Chem. 72 (2000) 702A.

[44] A. Walcarius, Electroanalysis 10 (1998) 1217.

[45] B. Adhikari, S. Majumdar, Prog. Polym. Sci. 29 (2004) 699.

[46] M. Yuqing, C. Jianrong, W. Xiaohua, Trends Biotechnol. 22 (2004) 227.

[47] J.-K. Park, P. H. Tran, J. K. T. Chao, R. Ghodadra, R. Rangarajan, N. V. Thakor, Biosens. Bioelectron. 13 (1998) 1187.

[48] A. Ciszewski, G. Milczarek, Talanta 61 (2003) 11.

[49] M. Kavanoz, H. Gülce, A. Yildiz, Turk. J. Chem. 28 (2004) 287.

[50] C. E. D. Chidsey, R. W. Murray, Science 231 (1986) 25.

[51] L. R. Faulkner, Chem. Eng. News 62 (1984) 28.

[53] N. D. Popovich, H. H. Thorp, Electrochem. Soc. Interface 11 (2002) 30.

[54] M. E. Napier, C. R. Loomis, M. F. Sistare, J. Kim, A. E. Eckhardt, H. H. Thorp, Bioconjugate Chem. 8 (1997) 906.

[55] M. Mascini, I. Palchetti, G. Marrazza, Fresenius J. Anal. Chem. 369 (2001) 15.

[56] T. G. Drummond, M. G. Hill, J. K. Barton, Nat. Biotechnol. 21 (2003) 1192.

[57] M. Fojta, Electroanalysis 14 (2002) 1449.

[58] J. J. Gooding, Electroanalysis 14 (2002) 1149.

[59] E. Katz, I. Willner, J. Wang, Electroanalysis 16 (2004) 19.

[60] F. Lucarelli, G. Marrazza, A. P. F. Turner, M. Mascini, Biosens. Bioelectron. 19 (2004) 515.

[61] E. Palacek, M. Fojta, M. Tomschik, J. Wang, Biosens. Bioelectron. 13 (1998) 621.

[62] H. H. Thorp, Trends Biotechnol. 21 (2003) 522.

[63] J. Wang, G. Rivas, X. Cai, E. Palecek, P. Nielsen, H. Shiraishi, N. Dontha, D. Luo, C. Parrado, M. Chicharro, P. A. M. Farias, F. S. Valera, D. H. Grant, M. Ozsoz, M. N. Flair, Anal. Chim. Acta 347 (1997) 1.

[64] P.-H. Lo, S. A. Kumar, S. –M. Chen, Colloids and Surfaces B: Biointerfaces 66 (2008) 266.

[65] A.P.F. Turner, I. Karube, G.S. Wilson, (ed.), Biosensors-Fundamentals and Applications. Oxford University Press 1987, 21.

[66] S. A. Kumar, S.-M. Chen, Biosens. Bioelectron. 22 (2007) 3042.

[67] S. A. Kumar, S. –M. Chen, J. Molecular Catalysis A: Chemical 278 (2007) 244.

[68] S. A. Kumar, S. –M. Chen, Talanta 72 (2007) 831.

[69] S. A. Kumar, P. –H. Lo, S. –M. Chen, Nanotechnology 19 (2008) 255501.

[70] S. A. Kumar, S. –M. Chen, Analytical Letters, 41 (2008) 141.

[71] S. A. Kumar, S. –M. Chen , Sensors 8 (2008) 739.

[72] A. Malinauskas, J. Malinauskien˙e, A. Ramanaviˇcius, Nanotechnology 16 (2005) R51.

[73] G. Kossmehl, G. Engelmann, in: D. Fichou, (Ed.), Handbook of Oligo and Polythiophenes, Wiley–VCH, New York, 1999 (Chapter 10).

[74] C. Lamy, J.M. Leger, F. Garnier, in: H.S. Nalwa, (Ed.), Handbook of Organic Conductive Molecules and Polymers, vol. 3, JohnWiley&Sons, NewYork, 1997 (Chapter 10).

[75] S. Cosnier, Anal. Bioanal. Chem. 377 (2003) 507.