title: Application of an absorption-based surface plasmon resonance principle to the development of SPR ammonium ion and enzyme sensors.
abstract: Two new types of surface plasmon resonance (SPR) sensors that can determine the concentration of ammonium cations and urea were realized based on the previously reported theory of the absorption-based SPR measurement method. The change of the dielectric constant caused by the change of the light absorption characteristics of dyes incorporated in a sensing membrane phase is utilized in these SPR sensors. The determination of ions using the SPR sensor was realized by detecting the SPR signals of the minimum reflectance related to the change of absorption spectra of the dye in the ion optode membrane consisting of an ammonium-selective ionophore (TD19C6) and a lipophilic cationic dye (KD-M11) that shows absorption spectral changes due to protonation and deprotonation. A SPR enzyme sensor that can determine the concentration of urea was prepared by the combination of this ion optode membrane and an enzyme membrane based on urease. With the newly developed SPR sensors, the intensity changes of the reflectance at the fixed SPR resonance angle are monitored, which is different from conventional SPR sensors where usually the change of the SPR resonance angles is detected. In a continuous-flow experiment using the SPR ion sensor for NH4+ ion determination, a dynamic measurement range from 10(-5) to 10(-2) M was achieved. In the case of the enzyme-based SPR urea sensor, a dynamic range from 10(-4) to 10(-1) M was observed in a stopped-flow batch arrangement. It is expected that this sensing technique can be applied for the SPR-based detection of a wide range of low molecular weight analytes.
authors.affiliation: Department of Applied Chemistry, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Fujii
authors.forename: Takashi
authors.initials: T
authors.lastname: Koike
authors.forename: Kaori
authors.initials: K
authors.lastname: Nakamura
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Sasaki
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Kurihara
authors.forename: Daniel
authors.initials: D
authors.lastname: Citterio
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Iwasaki
authors.forename: Osamu
authors.initials: O
authors.lastname: Niwa
authors.forename: Koji
authors.initials: K
authors.lastname: Suzuki
mesh_terms: D015374:Biosensing Techniques / Q000379:methods / Q000592:standards; D004800:Enzymes, Immobilized; D000644:Quaternary Ammonium Compounds / Q000032:analysis*; D012680:Sensitivity and Specificity; D020349:Surface Plasmon Resonance / Q000379:methods / Q000592:standards*; D014508:Urea / Q000032:analysis; D014510:Urease
chemical_list: D004800:Enzymes, Immobilized; D000644:Quaternary Ammonium Compounds; D014508:Urea; D014510:Urease