Biomedical subjects

Yuzuru Iwasaki

Publications and source records attributed to Yuzuru Iwasaki.

6 recordsLinked to original sources

PubMed2005

Selective detection of a catecholamine against electroactive interferents using an interdigitated heteroarray electrode consisting of a metal oxide electrode and a metal band electrode.

We developed an interdigitated array electrode (IDAE) consisting of a metal oxide electrode and a metal band heteroelectrode and employed it for the selective detection of catecholamines. We used an indium-tin oxide (ITO) film as the oxidation electrode of the IDAE because the ITO was able to suppress response currents from L-ascorbic acid (AA) and uric acid (UA), which are major electroactive interferents in biological fluids. However, the ITO film also suppresses the reduction of quinones including oxidized catecholamines. We developed a simple technique for fabricating our hetero IDAE, which also preserves the electrochemical properties of the ITO. When we compared hetero ITO-gold, homo ITO-ITO, and carbon-carbon IDAEs, we found that the hetero IDAE provided both high sensitivity and selectivity for DA detection. We achieved high selectivities for DA against AA and UA. The ratios of the response currents of AA and UA to DA were calculated as 6 and 5%, respectively.

Catecholamines↗

PubMed2005

Discriminative detection of volatile sulfur compound mixtures with a plasma-polymerized film-based sensor array installed in a humidity-control system.

We demonstrated the discrimination of volatile sulfur compound mixtures with different mixing ratios by using an array of the plasma-polymerized film (PPF)-coated quartz crystal resonators. The PPF sensor array, which contains PPFs prepared from amino acids and synthetic polymers, exhibited different response patterns to mono or mixed volatile sulfur compounds (VSCs) (hydrogen sulfide and methanethiol) under a dry environment. The sensor array was installed in a desktop-size relative humidity controller. The relative humidity and temperature conditions of the sample flow to the sensor cell were equalized to those of the inner atmosphere of the sensor cell based on the concept of the two-separate-temperatures method. In this way, the baseline drift of PPF sensor response caused by the introduction of a highly humid sample was successfully suppressed. We compared the sensor array responses under the controlled humidity conditions. Presorption of water molecules by PPFs caused a decrease of sensor sensitivity, but the films still had the ability to discriminate sub-ppmv VSC mixtures having 6:1, 1:1, and 1:6 mixture ratios of hydrogen sulfide and methanethiol.

Journal Article↗

PubMed2004

Biocompatible glucose sensor prepared by modifying protein and vinylferrocene monomer composite membrane.

This paper proposes a very simple procedure for preparing a biocompatible sensor based on a protein (bovine serum albumin, BSA), enzyme and vinylferrocene (VF) composite membrane modified electrode. The membrane was prepared simply by first casting vinylferrocene and then coating it with BSA and glucose oxidase immobilised with glutaraldehyde. The sensor response was independent of dissolved oxygen concentration from 3 to 10 ppm and showed good stability for serum sample measurement, unlike the commonly used BSA/enzyme modified electrode. The sensor response was almost unchanged over the measurement time (>10 h) whereas the responses of a BSA and glucose oxidase modified platinum electrode and an osmium-polyvinylpyridine wired horseradish peroxidase modified electrode (Ohara et al., 1993) fell to 68% of their initial value in a serum sample containing 10mM glucose.

Biocompatible Materials↗

PubMed2002

Application of an absorption-based surface plasmon resonance principle to the development of SPR ammonium ion and enzyme sensors.

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.

Biosensing Techniques↗

PubMed2002

Preparation of refractive index matching polymer film alternative to oil for use in a portable surface-plasmon resonance phenomenon-based chemical sensor method.

In order to simplify the procedure for assembling a surface-plasmon resonance (SPR) sensor, a refractive index matching polymer film was prepared as an alternative to the conventionally used matching oil. The refractive index matching polymer film, the refractive index of which was nearly equal to the prism and sensor chip material (a cover glass) of the SPR sensor, was prepared by casting a tetrahydrofuran solution of poly (vinyl chloride) (PVC) containing equal weights of dioctyl phthalate and tricresyl phosphate. The refractive index matching polymer film was found to have a refractive index of 1.516, which is identical to that of the prism and the cover glass used for the present SPR sensor. The utility of the matching polymer film for the SPR sensor was confirmed by the detection of anti-human albumin, based on an antigen-antibody reaction.

Antibodies↗

PubMed2002

Imaging of electrochemical enzyme sensor on gold electrode using surface plasmon resonance.

Three types of imaging, namely layer structure, electrochemical reaction, and enzyme sensor response, were achieved by applying surface plasmon resonance (SPR) measurement to an electrochemical biosensor. We constructed glucose oxidase based mediator type sensors on a gold electrode by spotting the mediator that contained horseradish peroxidase and spin coating the glucose oxidase film. The layer structure of the sensor was imaged by means of angle scanning SPR measurement. The single sensor spot (about 1 mm in diameter) consisted of about 100 x 100 pixels and its spatial structure was imaged. The multilayer structure of the enzyme sensor had a complex reflectance-incident angle curve and this required us to choose a suitable incident angle for mapping the redox state. We chose an incident angle that provided the most significant reflection intensity difference by using data obtained from two angle scanning SPR measurements at different electrode potentials. At this incident angle, we controlled the electrochemical states of the spotted mediator in cyclic voltammetry and imaged the degree to which the charged site density changed. Finally, we mapped the enzymatic activity around the mediator spot by the enzymatic reoxidation of pre-reduced mediator in the presence of glucose.

Biosensing Techniques↗