Novel Conducting Polymer Electrolyte Biosensor Based on Poly(1-vinyl imidazole) and Poly(acrylic acid) Networks Ahu Arslan, † Senem Kıralp, † Levent Toppare,* ,† and Ayhan Bozkurt ‡ Department of Chemistry, Middle East Technical UniVersity, 06531 Ankara, Turkey and Department of Chemistry, Fatih UniVersity, 34900 Buyukcekmece, Istanbul, Turkey Biosensor construction and characterization studies of poly(acrylic acid) (PAA) and poly(1-vinyl imidazole) (PVI) complex systems have been carried out. The biosensors were prepared by mixing PAA with PVI at several stoichiometric ratios, x (molar ratio of the monomer repeat units). The enzyme, invertase, was entrapped in the PAA/PVA interpenetrating polymer networks during complexation. Modifications were made on the PAA/PVI conducting polymer electrolyte matrixes to improve the stability and performance of the polymer electrolyte-based enzyme biosensor. The maximum reaction rate (V max ) and Michaelis-Menten constant (K m ) were investigated for the immobilized invertase. The temperature and pH optimization, operational stability, and shelf life of the polymer electrolyte biosensor were also examined. Introduction The discovery of polymer-salt complexes as well as the recognition of their potential application as solid electrolytes resulted in the development of numerous polymer electrolytes, including those with a protonic type of conductivity. 1-3 Entirely different classes of materials have attracted increasing attention as proton conductors including polymers, oxide ceramics, and intercalation compounds. 4-7 It is well established that proton-conducting polymer elec- trolytes can be obtained by doping polymers bearing ether, alcohol, imine, amide, or imide groups with acid. 8-12 This very simple concept is now extended to more complex systems where either an inorganic filler or a plasticizer or both are added to the binary polymer blend to improve the properties of the polymer matrix. Hydrophilic polymers such as poly(vinyl alcohol) and poly- (vinyl imidazole) can be impregnated with an acid and behave as solid proton conductors. The neutralization of polymeric bases may be a more effective way to generate various proton sources within a polymer matrix. In comparison with the usual liquid electrolytes, the polymer/ acid systems have obvious advantages in terms of reduced leakage and corrosion problems, and they represent less costly alternatives to perfluorinated polymers. The main advantage compared with conventional proton-conducting polymers is that it is relatively inexpensive. Polymer electrolytes are under extensive investiga- tion for applications in fuel cells, hydrogen sensors, and electrochromic devices. 13,14 Proton conductors can be classified according to the preparation method, chemical composition, structural dimensionality, mech- anism of conduction, and so forth. Here, a proton-conducting material is discussed according to the range of temperature in which it can be used in technological applications. Attempts to develop proton-conducting materials suitable for medium tem- perature are being made in many laboratories. 15,16 Recently, proton-conducting polymer electrolytes based on polymer het- erocycle hybrid electrolytes show improved thermal properties, and they are suitable for biosensor applications. The proton conductivity and stability of these polymer matrixes show an important dependence on temperature as x (molar ratio of the monomer repeat units) is varied. The formation of proton defects is necessary for proton conduction. Heterocycles such as imidazoles have been reported in this respect. 17 Their nitrogen sites act as strong proton acceptors that form protonic charge carriers. The protonation of PVI via doping with PAA is assumed in this direction (Figure 1). * Corresponding author. E-mail: toppare@metu.edu.tr. Tel: +90-312- 2103251. Fax: +90-312-2101280. † Middle East Technical University. ‡ Fatih University. (1) Donoso, P.; Gorecki, W.; Berthier, C.; Defendini, P.; Poinsignon, C.; Armand, M. Solid State Ionics 1988, 28-30, 969-974. (2) Petty-Weeks, S.; Zupancic, J. J.; Swedo, J. R. Solid State Ionics 1988, 31, 117-125. (3) Przyluski, J.; Wieezorek, W. Synth. Met. 1991, 45, 323-333. (4) Kreuer, K. D. Solid State Ionics 1997, 97,1-15. (5) Flint, S. D.; Slade, R. C. T. Solid State Ionics 1997, 97, 299-307. (6) Baranov, A. I.; Sinitsyn, V. V.; Vinnichenko, V. Y.; Jones, D. J.; Bonnet, B. Solid State Ionics 1997, 97, 153-160. (7) Murugaraj, P.; Kreuer, K. D.; He, T.; Schober, T.; Maier, J. Solid State Ionics 1997, 98,1-6. (8) Lasse ´gues, J. C.; Desbat, B.; Trinquet, O.; Cruege, F.; Poinsignon, C. Solid State Ionics 1989, 35, 17-25. (9) Grondin, J.; Rodriguez, D.; Lasse ´gues, J. C. Solid State Ionics 1995, 77, 70-75. (10) Polak, A.; Petty-Weaks, S.; Buehler, A. J. Sens. Actuators 1986, 9,1-7. (11) Kawahara, M.; Morita, J.; Rikukawa, M.; Sanui, K.; Ogata, N. Electrochim. Acta 2000, 45, 1395-1398. (12) Bozkurt, A.; Ise, M.; Kreuer, K. D.; Meyer, W. H.; Wegner, G. Solid State Ionics 1999, 125, 225-233. (13) Colomban, P., Ed.; Proton Conductors; Solids, Membranes and Gelss Materials and DeVices; Cambridge University Press: Cambridge, U.K., 1992. (14) Wainright, J. S.; Wang, J. T.; Weng, D.; Savinell, R. F.; Litt, M. H. J. Electrochem. Soc. 1995, 142, L121-L123. (15) Alberti, G.; Costantino, U.; Casciola, M.; Ferroni, S.; Massinelli, L.; Staiti, P. Solid State Ionics 2001, 145, 249-255. (16) Bozkurt, A.; Meyer, W. H.; Wegner, G. J. Power Sources 2003, 123, 126-131. (17) Kreuer, K. D.; Fuchs, A.; Ise, M.; Spaeth, M.; Maier, J. Electrochim. Acta 1998, 43, 1281-1288.