Yuzuru Iwasaki

Detection of odorants using an array of piezoelectric crystals and neural-network pattern recognition

Abstract AT-cut quartz crystals were applied as chemical vapour sensors. The responses of such crystals operating at 9 MHz and coated with phosphatidylglycerol, phosphatidylinositol, phosphatidylethanolamine, phosphatidylserine and lipid A were determined for amyl acetate, acetoin, menthone and other organic vapours which showed different affinities for each lipid. The identification of odorants depending on the species of lipid used for coating is discussed in terms of the normalized resonant frequency shift pattern. Using a number of different lipid-coated quartz crystals, odorants could be identified by a neural-network pattern recognition with a back-propagation algorithm.

Analysis of electrochemical processes using surface plasmon resonance

Abstract We simultaneously employed voltammetry and surface plasmon resonance (SPR) measurements and monitored electrochemical processes on gold electrode. SPR is sensitive not only to the adsorbed layer on the gold electrode, but also to the dielectric properties of the solution phase. Therefore, an electrochemically modulated diffusion layer can be detected by SPR. We tested the relationship between the time differential SPR data and the electrode current for two electrochemical processes and confirmed the possibility of using electrochemical SPR measurement.

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.

Electrochemical reaction of Fe(CN)3−/4−6 on gold electrodes analyzed by surface plasmon resonance

Abstract Surface plasmon resonance (SPR) measurements were combined with cyclic voltammetry (CV) to analyze the electrochemical reactions of Fe(CN) 3−/4− 6 on gold electrodes in the phosphate electrolyte. The time differential of the SPR signal was correlated with the current. When a low concentration of Fe(CN) 3−/4− 6 was introduced, the replacement of adsorbed phosphate ions with Fe(CN) 3−/4− 6 was observed in SPR. At higher concentrations, the SPR signal reflected the refractive index difference of the redox state of Fe(CN) 3−/4− 6 . After continuous potential scanning, the potential dependence of the SPR signal changed completely. However, the cyclic voltammogram was almost identical to that for the first cycle. The change in the SPR signal reflected the formation of a surface film, but electrochemical data showed that this film did not affect the electron transfer reaction in the experimental time window.

Development of Nanoscale Interdigitated Array Electrode as Electrochemical Sensor Platform for Highly Sensitive Detection of Biomolecules

We studied nanoscale interdigitated array electrodes (nano-IDAEs) to create a detector platform for highly sensitive biosensing devices. We successfully fabricated a gold nano-IDAE with 1000 pairs of electrodes (width and gap both 250 nm) and a 1 mm band length. We also fabricated a series of IDAEs whose widths and gaps ranged from 250 nm to 2 μm, and performed cyclic voltammetry with the IDAEs using 100 μm of ferrocenylmethyl trimethyl ammonium bromide solution to evaluate their characteristics. As the width and gap (line and space) of the IDAEs decreased, the difference between the experimental and theoretical limiting currents became larger, and when the line and space were 250 nm, the limiting currents were 20% higher than the theoretical value. We also employed the nano-IDAEs for measuring adrenaline. We demonstrated that the collection efficiency of 0% obtained when using a 2 μm IDAE could be improved to more than 60% when using a 250 nm IDAE.

Characterization of a microfluidic device fabricated using a photosensitive sheet

We investigated the characteristics of microfluidic devices fabricated using photosensitive sheets adhered to substrates. We evaluated them in regard to practical criteria, namely chemical resistance, pressure sealing, electrical resistance and elution of ions. No samples exhibited peeling after postbaking when we investigated the adhesion characteristics by dicing. The sheet swelled dramatically on exposure to an alkaline solution. The microfluidic devices consisting of photosensitive sheet sandwiched by two Pyrex substrates and a photosensitive sheet sandwiched by two PMMA substrates had a pressure sealing of 0.6 MPa, were capable of withstanding a pressure of 0.2 MPa for 1 h when ultrapure water was injected. The sheets had a high volume resistivity (9.7 ? 1012 ? cm) and a high surface resistivity (2.3 ? 1011 ?) after postbaking. Sodium ions were adsorbed onto the photosensitive sheet and then gradually desorbed. The total amount of sodium ion elution per unit area over 24 h was 8.3 ? 10?9 mol mm?2 as measured by ion exchange chromatography. These results confirm that microfluidic devices fabricated using photosensitive sheets are suitable for use as disposable devices for certain applications.

A novel biosensor using electrochemical surface plasmon resonance measurements

Surface plasmon resonance measurements have been conducted to construct a unique electrochemical enzyme sensor which detected the reversible change in the refractive index of a redox film containing an enzyme.

Selective electrochemical detection using a split disk array electrode in a thin-layer radial flow system.

An eight-sector array (split disk) electrode was designed for a low flow rate (<100 μL/min) amperometric detector. This electrode was fabricated photolithographically for dimensional accuracy and reproducibility. This array of a pie-shaped electrode was combined with a thin-layer radial flow cell, and a conversion efficiency of 94% was achieved at the lowest flow rate tested (0.01 mL/min). Each electrode worked free from the effects of electrochemical reactions of the other electrodes. A coulometric hydrodynamic voltammogram of reversible redox species obtained using this system exhibited a Nernstian curve. These properties enabled this electrochemical detector to be used for determining the ratio of two redox species (redox potential difference ≈ 100 mV) with small injection volume (5 μL).

Imaging of flow pattern in micro flow channel using surface plasmon resonance

We describe the visualization of the mixing and control of flow patterns in micro fluidic devices using a surface plasmon resonance (SPR) imaging sensor. We employed Kretschmann-type prism coupling SPR optics and an expanded laser diode light source via a single mode optical fibre. The reflected light was focused on a CCD camera. Two types of micro fluidic device were fabricated using photolithography and polymer imprinting a 2 mm wide, 100 µm high channel flow cell for the mixing and a slab channel device for flow control. We were able to observe mixing in the flow channel in real time with SPR imaging as the local refractive index change. Because the sensitivity of this system was limited within wavelength long distance from the gold surface, we could image the flow condition very near the channel wall. We also succeed in delivering the flow to a part of 4 × 4-array sensing area in a slab flow channel. These results will assist the development of integrated biosensors.

Passive fluidic chip composed of integrated vertical capillary tubes developed for on-site SPR immunoassay analysis targeting real samples.

We have successfully developed a surface plasmon resonance (SPR) measurement system for the on-site immunoassay of real samples. The system is composed of a portable SPR instrument (290 mm(W) × 160 mm(D) × 120 mm(H)) and a microfluidic immunoassay chip (16 mm(W) × 16 mm(D) × 4 mm(H)) that needs no external pump system. An integrated vertical capillary tube functions as a large volume (150 μL) passive pump and a waste reservoir that has sufficient capacity for several refill operations. An immunoassay was carried out that employed the direct injection of a buffer and a test sample in sequence into a microfluidic chip that included 9 antibody bands and 10 reference reagent bands immobilized in the flow channel. By subtracting a reliable averaged reference sensorgram from the antibody, we effectively reduced the influence of the non-specific binding, and then our chip successfully detected the specific binding of spiked IgG in non-homogeneous milk. IgG is a model antigen that is certain not to be present in non-homogeneous milk, and non-homogeneous milk is a model of real sample that includes many interfering foreign substances that induce non-specific binding. The direct injection of a real sample with no pretreatment enabled us to complete the entire immunoassay in several minutes. This ease of operation and short measuring time are acceptable for on-site agricultural, environmental and medical testing.