Functional Conducting Polymers in the Application of SPR Biosensors

Hindawi Publishing Corporation Journal of Nanotechnology Volume 2012, Article ID 620309, 7 pages doi:10.1155/2012/620309 Review Article Functional Conducting Polymers in the Application of SPR Biosensors Rapiphun Janmanee,1, 2 Sopis Chuekachang,1, 2 Saengrawee Sriwichai,1 Akira Baba,2 and Sukon Phanichphant3 1 Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand 2 Center for Transdisciplinary Research, Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan 3 Materials Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand Correspondence should be addressed to Sukon Phanichphant, Received 20 February 2012; Accepted 21 May 2012 Academic Editor: Carlos R. Cabrera Copyright © 2012 Rapiphun Janmanee et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In recent years, conducting polymers have emerged as one of the most promising transducers for both chemical, sensors and biosensors owing to their unique electrical, electrochemical and optical properties that can be used to convert chemical information or biointeractions into electrical or optical signals, which can easily be detected by modern techniques. Different approaches to the application of conducting polymers in chemo- or biosensing applications have been extensively studied. In order to enhance the application of conducting polymers into the area of biosensors, one approach is to introduce functional groups, including carboxylic acid, amine, sulfonate, or thiol groups, into the conducting polymer chain and to form a so-called “self-doped” or by doping with negatively charged polyelectrolytes. The functional conducting polymers have been successfully utilized to immobilize enzymes for construction of biosensors. Recently, the combination of SPR and electrochemical, known as electrochemical-surface plasmon resonance (EC-SPR), spectroscopy, has been used for in situ investigation of optical and electrical properties of conducting polymer films. Moreover, EC-SPR spectroscopy has been applied for monitoring the interaction between biomolecules and electropolymerized conjugated polymer films in biosensor and immunosensor applications. In this paper, recent development and applications on EC-SPR in biosensors will be reviewed. 1. Introduction Conducting polymers (CPs) are materials discovered over 20 years ago, which have attracted considerable attention for their electronic conducting properties, optical properties, and chemical and biochemical properties [1–8]. These unique properties of CPs have been used in wide range of applications including battery technology, photovoltaic devices, light emitting diodes, electrochromic displays, and more recently in biological application [9–11]. Typical examples of conducting polymers such as polyaniline, poly(3,4ethylenedioxythiophene), polypyrrole, and their derivatives have been widely studied [12, 13]. In particular for biosensor application, conducting polymers based on polypyrrole (PPy) have been extensively investigated due to their good electrical conductivity, environmental stability to air and water, and ease of synthesis through electrochemical and chemical routes [4, 14]. Several techniques coupled to electrochemistry have been developed to study the properties of polymer films such as quartz crystal microbalance (QCM) [15], Fourier transform-infrared (FT-IR) spectroscopy [16], electron spin resonance (ESR) [17], and surface plasmon resonance (SPR) spectroscopy [18, 19]. SPR spectroscopy is the technique for monitoring the change of the refractive index at a solid-liquid interface, which has been widely used for the characterization and study of polymer films, interfaces, and kinetic processes at surfaces [20–23]. Recently, the combination of SPR and electrochemical, named electrochemicalsurface plasmon resonance (EC-SPR) spectroscopy, have been used for in situ investigation of optical and electrical properties of conducting polymer films [24–26]. Moreover, EC-SPR spectroscopy has been applied for monitoring 2 the interaction between biomolecules and electropolymerized conjugated polymer films in biosensor and immunosensor applications [27–30]. In this paper, recent development and applications on EC-SPR in biosensors will be reviewed. 2. Electrochemical SPR for Monitoring of Conducting Polymer Thin Films In 2003, the properties of poly(3,4-ethylenedioxythiophene) (PEDOT) ultrathin films investigated by the combination of surface plasmon resonance (SPR) and surface plasmon enhanced photoluminescence spectroscopy (SPPL) with electrochemical techniques, known as EC-SPPL, were reported by Baba and Knoll [21]. The electrochromic properties and the detecting of photoluminescence in PEDOT ultrathin films were observed. The photoluminescence of PEDOT was observed when the polymer was dedoped under the applied potential. The photoluminescence intensity was controlled by the potential and dependent on the angular position in an SPR reflectivity experiment. The SPR characterization of the PEDOT film is corresponding with the PEDOT bulk electrochromic properties obtained from UV-vis-NIR spectra. The EC-SPPL method can be acted as a sensitive tool for detection the photoluminescence from a conjugated polymer film and could have potentials for sensors and optoelectronic devices applications. An electroactivity of polyaniline (PANI) films in neutral pH condition and their electrocatalyzed oxidation of β-nicotinamide adenine dinucleotide (NADH) were also reported by Tian et al. [23]. Self-assembled PAIN multilayer films by forming with poly(anion) such as sulfonated polyaniline (SPANI), poly(acrylic acid) (PAA), poly(vinyl sulfonate) (PVS), and poly(styrene sulfonate) (PSS) were prepared using layer-by-layer (LBL) method. The combination of EC-SPR and quartz crystal microbalance (QCM) techniques was used to monitor the electrochemical behavior and catalytic ability for the oxidation of β-nicotinamide adenine dinucleotide (NADH) in neutral solution of PANI multilayer films. The self-assembled PANI multilayer films prepared by LBL method showed very good stability, reversible, and electroactive in neutral solution. Moreover, the results of the electrocatalytic activity of PANI multilayer films indicated that the PAIN copolymers can electrocatalyze the oxidation of NADH in neutral solution but their potential to electrocatalyze NADH oxidation was quite different under the same condition. The catalytic ability of PANI/SPANI is better than the other assemblies under the same conditions due to both PANI and SPANI monolayers of PANI/SPANI system being electroactive, while for the other systems only the PANI layer is electroactive. The investigation of the formation and effects of doping/dedoping processes (...truncated)