Saengrawee Sriwichai

Nanostructured ultrathin films of alternating sexithiophenes and electropolymerizable polycarbazole precursor layers investigated by electrochemical surface plasmon resonance (EC-SPR) spectroscopy.

Nanostructured ultrathin films of linear and dendrimeric cationic sexithiophenes, 6TNL and 6TND, respectively, alternated with anionic polycarbazole precursor, poly(2-( N-carbazolyl) ethyl methacrylate- co-methacrylic acid) or PCEMMA32, were successfully fabricated using the layer-by-layer self-assembly deposition technique. The two electro-optically active oligomers exhibited distinct optical properties and aggregation behavior in solution and films as studied by UV-vis and fluorescence spectroscopy. The stepwise increase of the 6TNL/PCEMMA32 and 6TND/PCEMMA32 layers was confirmed by UV-vis spectroscopy and in situ surface plasmon resonance (SPR) spectroscopy. The intralayer electrochemical polymerization and cross-linking behavior of the carbazole functionalized PCEMMA32 layers were then investigated using cyclic voltammetry (CV) and electrochemical surface plasmon resonance (EC-SPR) spectroscopy. The increase in current with each cycle confirmed intralayer cross-linking followed by the doping-dedoping process within these films. The two types of films differed with respect to dielectric constant and thickness changes before and after electropolymerization, indicating the influence of the oligothiophene layers. This demonstrated for the first time the preparation of highly ordered organic semiconductors alternated with in situ electropolymerizable layers in ultrathin films.

In situ Electrochemical-Transmission Surface Plasmon Resonance Spectroscopy for Poly(pyrrole-3-carboxylic acid) Thin-Film-Based Biosensor Applications

In this study, we describe the combination of transmission surface plasmon resonance (TSPR) and electrochemical techniques for the application to biosensors with conducting polymers. Electropolymerization was employed to construct poly(pyrrole-3-carboxylic acid) (PP3C) film on a gold-coated grating substrate using pyrrole-3-carboxylic acid (P3C) monomer solution in 0.5 M H(2)SO(4). In situ electrochemical-transmission surface plasmon resonance (EC-TSPR) measurements were carried out to study the kinetic and electroactivity properties of PP3C film. Immobilization of antihuman IgG on the activated surface and the binding process of human IgG and antihuman IgG in neutral solution could be detected in situ by EC-TSPR measurement. The surface modification steps on the PP3C layer led to an increase in intensity of the transmission peak. The performance, sensitivity, and utility of EC-TSPR spectroscopy showed obvious advantages for the detection of binding process with the simple experimental setup, and could be applied to the study of biomolecular interactions in various systems.

Detection of Human IgG on Poly(pyrrole-3-carboxylic acid) Thin Film by Electrochemical-Surface Plasmon Resonance Spectroscopy

An electrochemically controlled surface plasmon resonance (SPR) immunosensor for the detection of human immunoglobulin G (IgG) has been developed using poly(pyrrole-3-carboxylic acid) (PP3C) film. In this work, a pyrrole-3-carboxylic acid monomer was used for electropolymerization of a PP3C film on a gold-coated high-refractive-index glass slide. In situ electrochemical (EC)-SPR spectroscopy was performed to study the kinetic property and electroactivity property of the PP3C film. Moreover, ultraviolet–visible (UV–vis) spectroscopy was performed to characterize the PP3C film. Finally, the immunosensor-based PP3C film was constructed. The carboxylic acid surface of the PP3C film was activated for the immobilization of anti-human IgG. The immunosensor electrode was used for probing the binding reaction of anti-human IgG/human IgG with several concentrations of human IgG at different constant applied potentials. The probe immobilization and immunosensing process were in situ monitored by EC-SPR technique. The sensitivity of the sensor was improved by controlling the morphology of the PP3C film by applying the potential. # 2011 The Japan Society of Applied Physics

Functional Conducting Polymers in the Application of SPR Biosensors

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.

In Situ Study of Electropolymerized Poly(3-aminobenzoic acid) Thin Film on BD-R and DVD-R Grating Substrates by Electrochemical-Transmission Surface Plasmon Resonance Spectroscopy

The electropolymerization process and doping/dedoping properties of poly(3-aminobenzoic acid) (PABA) thin films on gold-coated commercial BD-R and DVD-R grating substrates were simultaneously studied by the combination of electrochemical technique and transmission surface plasmon resonance (TSPR) spectroscopy. The optical property as a function of the applied potentials and time dependence during electropolymerization were studied. The obtained TSPR wavelength scan spectra after electropolymerization showed that the maximum wavelength slightly shifted to longer wavelength indicating the increase of film thickness. In addition, the change during construction of PABA-based immunosensor for label-free detection of human immunoglobulin G can be observed.

Electrochemically Fabricated Pyrrole Copolymer Thin Films and Their Electroactivity in Neutral Aqueous Solution

The functionalized pyrrole copolymers were fabricated by electropolymerization of pyrrole (Py) and functionalized pyrrole monomers, pyrrole-3-carboxylic acid (P3C) and 4-(3-pyrrole) butyric acid (PBA). The electrochemical behavior and doping/dedoping properties of the obtained copolymer thin films were investigated by cyclic voltammetry (CV) in neutral phosphate-buffered saline (PBS) solution. Moreover, the functionalized pyrrole copolymer films were characterized by UV-vis absorption spectroscopy and atomic force microscopy (AFM). The obtained copolymer thin films showed good stability and electroactivity in neutral PBS solution. The presented functionalized pyrrole copolymer thin films may possess potential applications to study in various systems of the biosensors.

Fabrication of Thin Film from Conducting Polymer/Single Wall Carbon Nanotube Composites for the Detection of Uric Acid

Poly(2–aminobenzylamine)/single wall carbon nanotube (P2ABA/SWNTS) thin films were fabricated for the detection of UA by using electrochemical surface plasmon resonance spectroscopy (EC–SPR) technique. The suspension of 0.01% wt of carboxylated SWNTSs was assembled on the polymer film because of the electrostatic and van der Waals interactions between the ‒COOH and ‒NH2. The P2ABA/SWNTS thin film formation on gold electrode was studied by EC–SPR technique. In this work, uric acid was detected by EC–SPR in PBS buffer comparing with the interference response with ascorbic acid. EC–SPR uric acid sensor using P2ABA/SWNTS thin film can be applied for the detection of uric acid in urine.

Fabrication of Carboxylated Conducting Polymer/CNTs Composites Thin Films for Immunosensor Application

Electropolymerization of carboxylated conducting polymer/carbon nanotubes (CNTs) composites thin films has been studied by in situ electrochemical-surface plasmon resonance (EC-SPR) spectroscopy. Two derivatives of benzothiophene, thianaphthene-2-carboxylic acid and benzothiophene-2-propionic acid, composited with CNTs were electropolymerized in an acetonitrile with the potential range between 0 and 1.2 V at scan rate of 20 mV/s. The obtained films were characterized by in situ EC-SPR spectroscopy, UV-vis absorption spectroscopy, and atomic force microscopy. It was found that CNTs can improve properties of polymer/CNT composites films. Moreover, the obtained thianaphthene-2-carboxylic acid film can be further used for construction of immunosensor for detection of human IgG.

Fabrication and Characterization of Cytochrome C Modified Poly(3-Aminobenzoic Acid) Thin Film

The electropolymerized poly(3-aminobenzoic acid) (PABA) film on indium tin oxide electrode was used for fabrication of cytochrome c (Cyt c) modified PABA thin film upon immobilization of Cyt c onto the PABA surface. The obtained Cyt c modified PABA thin film was characterized by UV-vis spectroscopy, XPS, AFM, and SEM-EDX techniques. Shifts of the UV-vis absorption peaks were observed from Cyt c modified PABA thin film compared with Cyt c solution and PABA thin film. The formation of the covalent amide bond between the carboxylic groups of PABA and amine groups in Cyt c was observed from XPS results.

Flame-made Pt-loaded TiO 2 thin films and their application as H 2 gas sensors

The hydrogen gas sensors were developed successfully using flame-made platinum-loaded titanium dioxide (Pt-loaded TiO2) nanoparticles as the sensing materials. Pt-loaded TiO2 thin films were prepared by spin-coating technique onto Al2O3 substrates interdigitated with Au electrodes. Structural and gas-sensing characteristics were examined by using scanning electron microscopy (SEM) and showed surface morphology of the deposited film. X-ray diffraction (XRD) patterns can be confirmed to be the anatase and rutile phases of TiO2. High-resolution transmission electron microscopy (HRTEM) showed that Pt nanoparticles deposited on larger TiO2 nanoparticles. TiO2 films loaded with Pt nanoparticles were used as conductometric sensors for the detection of H2. The gas sensing of H2 was studied at the operating temperatures of 300, 350, and 400°C in dry air. It was found that 2.00 mol% Pt-loaded TiO2 sensing films showed higher response towards H2 gas than the unloaded film. In addition, the responses of Pt-loaded TiO2 films at all operating temperatures were higher than that of unloaded TiO2 film. The response increased and the response time decreased with increasing of H2 concentrations.