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A simple and low-cost method of fabricating an optical fiber for a surface plasmon resonance (SPR) sensor was proposed. The method is based on the electroless nickel plating and subsequent displacement gold plating of the core of the optical fiber. The thickness of the nickel and gold thin films deposited on the core of the optical fiber could be controlled by measuring the reflected light intensity from the tip of the optical fiber during the plating processes. The sensitivity and resolution of the SPR sensor with the fabricated optical fiber in the refractive index range from 1.333 to 1.348 were 1324.3 nm/RIU and 7.6 × 10

Anthropogenic CO2 emissions are contributing to global warming and ocean acidification. Rapid and accurate measurements of seawater carbonate chemistry are critical to understand current changes in the ocean and to predict future effects of such changes on marine organisms and ecosystems. Total alkalinity (AT) measurements can be used to directly determine the calcification rate, but they are time-consuming and require large sample volumes. Herein, we describe an automated and transportable flow-through system that can conduct continuous AT measurement using an ion sensitive field effect transistor (ISFET) – Ag/AgCl sensor and three different reference materials. The response time, stability, and uncertainty of our system were evaluated by comparing AT values of calibrated reference materials to those calculated by our system. Our system requires only small amounts of seawater (

We developed a small fluorescence microplate reader with an organic photodiode (OPD) array. The OPD array has nine OPDs that have a large light receiving area (9.62 mm2 per one OPD). Since the OPD array is fabricated on a flat glass plate, it can be placed just below microwells and can detect fluorescence emitted through the entire surface of the microwell bottom. The analytical performance of the developed plate reader was evaluated by measuring an aqueous solution of resorufin. The limit of detection (LOD) for resorufin (0.01–0.05 μM) was lower than that obtained with a plate reader equipped with nine inorganic photodiodes developed in a previous study (0.30 μM) and a commercially available microplate reader (0.16 μM). These results indicate that the large light receiving area improves the detection performance of the system. In addition, the developed reader was successfully used to quantify immunoglobulin A (IgA) in human saliva. The LOD for IgA was estimated to be 1.2 ng/mL, which is low enough to objectively evaluate human stress.

A portable-type surface plasmon resonance (SPR) sensor, composed from a new optical system for multi-sensing, has been developed to apply to environment analysis, clinical diagnosis etc., where many samples are desired to be analyzed at high throughput. The optical system of the sensor consists of a light-emitting diode, a pair of cylindrical lenses, a pair of collimator lenses, a correction lens, a prism, a polarizer and a linear CCD sensor with 2048 pixels. Reflected light from a sensor chip of the width of 6 mm at a certain incident angle was detected by ca. 618 pixels of the linear CCD sensor as an SPR sensor signal. An SPR sensor signal at a specified incident angle is controllable for optimization by adjusting the position of the CCD sensor. A sensor chip having a 30-stripe linear pattern (100 μm width/stripe) was prepared. The spatial resolution as well as the performance of the sensor were evaluated by using sucrose solutions. As a result, the acquisition of SPR sensor signals from 30 sensing points was successfully achieved with a spatial resolution of 100 μm (distance between 2 sensing points). A lower detection limit of ca. 3.2 - 5.5 × 10(-5) RIU with a standard deviation of ±4.5% was obtained by averaging the signals from 6 - 7 pixels of the CCD sensor per one sensing stripe.

A novel thin-layer electrolysis flow cell based on the ion transfer at the liquid|liquid interface was proposed for the absolute determination of a sub-nanomole ionic species. By using the conducting polymer-coated electrode as an electrode in organic phase, the flow cell was developed as a laminate structure with a thin aqueous layer and a thin organic layer, which were set between an Ag/AgCl electrode and the conducting polymer-coated electrode. Its simple structure made it possible to miniaturize the flow cell, and the required sample volume was reduced to only 1 μl. In the present electrolysis cell, both quantitative extraction and quantitative back-extraction of total amount of the ionic species were achieved. This advantage was applied to two methods for absolute determination. One is that by flow injection method, and the other is that by pre-concentration into the thin organic phase followed by back-extraction of the species from the thin Org to the thin aqueous phase (i.e., the stripping technique). In these methods, coulometrical determination of sub-nanomol ionic species was realized without a calibration curve.

A novel two dimensional surface plasmon resonance (SPR) sensor system with a multi-point sensing region is described. The use of multiplied beam splitting optics, as a core technology, permitted multi-point sensing to be achieved. This system was capable of simultaneously measuring nine sensing points. Calibration curves for sucrose obtained on nine sensing points were linear in the range of 0–10% with a correlation factor of 0.996–0.998 with a relative standard deviation of 0.090–4.0%. The detection limits defined as S/N = 3 were 1.98 × 10−6–3.91 × 10−5 RIU. This sensitivity is comparable to that of conventional SPR sensors.

A simple and pump-free chemiluminescence immunoassay based on a compact disc (CD)-type microfluidic platform for the determination of alkylphenol polyethoxylates (APnEOs) is described. The method is based on a competitive immunoreaction of the anti-APnEOs antibody immobilized on the magnetic microbeads between APnEOs and horseradish peroxidase (HRP)-labeled APnEOs in the sample solution. The luminol solution containing H2O2 and enhancer is caused to flow from one reservoir in the platform to another by appropriate adjustment of the speed of the rotation of the disc. The detection limit was similar to that reported in our previous paper, i.e., 10 ppb according to IC80.

A surface plasmon resonance (SPR) sensor on a compact disk (CD)-type microfluidic device was developed to miniaturize the elements of a complete analytical system, pump and valves. The CD-type microfluidic device was fabricated by attaching a polydimethylsiloxane disk plate that contained microchannels and reservoirs to a flat polycarbonate disk plate that contained grating films with a thin layer of Au. The optical system of the SPR sensor and the theory for its operation are based on the principle of a grating coupled-type SPR. The sample and reagent solutions in the reservoirs on the CD-type microfluidic device were sequentially introduced into the detection chamber by centrifugal force generated by the rotation of the microfluidic device. The variation of resonance wavelength was dependent on the refractive index of the sample solution. This CD-type SPR sensor was successfully used in an immunoassay of immunoglobulin A (IgA). The anti-IgA, blocking reagent, sample and washing solution in the reservoirs were sequentially introduced into the detection chamber by changing the frequency of rotation of the microfluidic device. IgA in the sample solution was adsorbed to the anti-IgA immobilized on the Au thin layer in the detection chamber and was then detected by the SPR sensor.

A fluorescence detection system for a microfluidic device using an organic light-emitting diode (OLED) as the excitation light source and a charge-coupled device (CCD) as the photo detector was developed. The OLED was fabricated on a glass plate by photolithography and a vacuum deposition technique. The OLED produced a green luminescence with a peak emission at 512 nm and a half bandwidth of 55 nm. The maximum external quantum efficiency of the OLED was 7.2%. The emission intensity of the OLED at 10 mA/cm(2) was 13 μW (1.7 mW/cm(2)). The fluorescence detection system consisted of the OLED device, two band-pass filters, a five microchannel poly(dimethylsiloxane) (PDMS) microfluidic device and a linear CCD. The fluorescence detection system was successfully used in a flow-based enzyme-linked immunosorbent assay on a PDMS microfluidic device for the rapid determination of immunoglobulin A (IgA), a marker for human stress. The detection limit (S/N=3) for IgA was 16.5 ng/mL, and the sensitivity was sufficient for evaluating stress. Compared with the conventional 96-well microtiter plate assay, the analysis time and the amounts of reagent and sample solutions could all be reduced.

Enzyme-linked immunosorbent assays (ELISAs) are considered the gold standard for the detection of various immunological reactions and can be used for the detection of infectious diseases during outbreaks or in the care of individual patients. To be useful in the timely implementation of prevention and control measures against infectious diseases, a diagnostic modality should be rapid, accurate, and affordable. In the current study, we demonstrate the efficiency (90% less time and volume consumption compared with those of a standard 96-well ELISA), detection capability, and ease of operation of a field-portable, battery-operated ELISA system, approximately the size of a cellular phone (12 × 6 × 5.5 cm), in the serological diagnosis of measles and rubella viruses that has the potential for onsite testing such as during disease outbreaks.

A surface plasmon resonance (SPR) immunosensor based on a competitive immunoreaction for the determination of trinitrophenol (TNP) is described. A goat anti-mouse IgG (1st antibody), which recognizes an Fc moiety of an antibody, was immobilized on a gold film of an SPR sensor chip by physical adsorption. A TNP solution containing a fixed concentration of a mouse anti-TNP monoclonal antibody (2nd antibody) and a TNP-keyhole limpet hemocyanin (KLH) conjugate was incubated in one-pot and introduced into the sensor chip. The TNP-KLH conjugate competes with TNP for binding with the 2nd antibody. The resulting complex of the 2nd antibody with the TNP-KLH conjugate was bound to the 1st antibody, which is immobilized on the sensor chip. The SPR sensor signal based on resonance angle shift is dependent on the concentration of TNP in the incubation solution in the range from 25 ppt to 25 ppb, and the coefficient of variation of the SPR signals for the 25 ppb TNP solution was determined to be 13% (n = 4). The experimental results for the adsorption constant of the 1st antibody on the sensor chip and the binding constant of the 1st antibody complex with the 2nd antibody are discussed, together with theoretical considerations.

A palm-sized differential surface plasmon resonance (SPR) meter, which consisted of a single light source, a prism, a divided mirror, and a single linear CCD element, was developed aiming at the miniaturization of an SPR instrument for use in field analysis of endocrine disrupting chemicals. The size and weight of the meter were 160 cm ( W ) × 10 cm ( H ) × 6 cm ( D ) and 770 g, respectively. The SPR meter composed of an Sprode with the sample and reference sensor-cells was found to be very effective for compensating drift and fluctuation of sensor signals as well as temperature variation at the same time without time lag. The effectiveness was due to a subtraction function of reference signal from the sample signal. The basic performance of the meter was a drift of within 0.001° in SPR measurement over 4300 s and a angle stability of within 0.0004° at a 10° incident LED light beam. Also, the SPR meter was applied to the immunoassay of 2,4-dichlorophenol (2,4-DCP) using a solid extraction technique. A good linear relationship between the concentration of 2,4-DCP and the SPR signal was obtained with the present meter. It was possible to determine 10 ppb of 2,4-DCP with the developed meter. A new concept of a divided mirror and the Sprode was thought to be useful for miniaturization of the SPR instrument aimed at on-site analysis.

A simple immunosensor based on a conductivity method was developed for determination of methamphetamine (MA, a stimulant drug) in urine. Anti-MA antibody was immobilized onto the surface of a pair of platinum electrodes. The reaction of MA with the antibody causes a decrease in the conductivity of the anti-MA immobilized layer between the electrodes. A linear relationship was obtained between the conductivity and MA concentration in the range of 1–10 μg/ml. The method requires the sample to be rinsed with water on the electrodes after the immunoreaction. This detection system was applied to the determination of MA in urine and proved to be a useful and a simple detection technique of MA in forensic science in comparison with a gas chromatography-mass spectrometry method.

A low cost chemiluminescence detector with a photodiode for flow-injection analysis (FIA) of l-lactate in food was developed for quality control in food industry. In this system, l-lactate is oxidized by the enzymatic reaction with l-lactate oxidase immobilized on the column to produce hydrogen peroxide. Then chemiluminescence caused by mixing hydrogen peroxide with the chemiluminescence reagent was detected by the photodiode. This light intensity was proportional to l-lactate concentration. For detecting weak chemiluminescence efficiently a flow-through cell of the detector was specially designed. A photodiode was used for the purpose of reducing the costs of FIA systems instead of a photomultiplier tube. As a result, a linear working curve was obtained from 10−7to 10−3 mol l−1l-lactate concentration. We applied the present system with a photodiode detector for food samples and compared the results with those obtained by the conventional HPLC method. The data obtained by the present FIA method were fairly in good agreement with those obtained by the conventional HPLC method. The correlation factor and regression line between both methods were 0.992 and Y = 1.07X-0.15, respectively. The present FIA system with the photodiode detector is available as a simple, easy-handling instrument for quality control in food industry.

We have investigated the possibility of utilizng a semiconductor gas sensor for quality control of meat freshness in the food industry. A semiconductor gas sensor based on In 2 O 3 is exploited for detecting ethyl acetate, a typical flavour volatile component produced in the initial bacterial putrefaction of meat. Of the sensor elements examined, Rh-La 2 O 3 -In 2 O 3 is found to show excellent sensitivity and selectivity to ethyl acetate at 300 °C. The sensor response signal increases with increasing meat-storage time and reflects rather well the increase of bacteria determined by a conventional colony-counting method. The multiple correlation factor between both methods is 0.8.

The solubilities of lanthanum fluoride (LaF3) powder and single crystals were measured in various aqueous electrolyte solutions. In contrast with the classical assumption of the stoichiometric dissolution of LaF3, it was found that the dissolution of the component cation La3+ was undetectable and the fluoride ion dissolved preferentially: cF−> 3cLa3+ where c is the ion concentration. X-ray photoelectron spectroscopy (XPS) of the LaF3 surface treated with electrolyte solutions corroborated this observation. As a result of the preferential fluoride dissolution, charge separation was expected to occur in such a way that the LaF3 surface would have positively charged “fluoride-vacancies”. This was confirmed by changes in membrane potential as a function of the fluoride dissolution the adsorption of an anionic adsorption marker (eosin Y) on the solid surface. It was also found that the preferential dissolution of fluoride ions was accompanied by simultaneous adsorption of almost the same amount of electrolyte anions (e.g. NO 3−) onto the LaF3 surface. This was confirmed by both solution measurements and surface analysis by diffuse reflectance IR Fourier transform (DRIFT) spectrometry. The result of this anion adsorption was explained in terms of ion exchange to ensure electroneutrality in the bulk of the adjacent electrolyte solution, which would otherwise be violated by the preferential fluoride dissolution. The anionic adsorption marker and DRIFT measurements were used to characterize further the above-mentioned ion exchange and selective uptake of fluoride ions into the “fluoride vacancies”. Release of the adsorbed eosin Y or electrolyte anions, such as NO3−, from the LaF3 surface was found to be induced by F− or OH− ions only. On the basis of this observation, the response mechanism of the fluoride ion-selective electrodes was discussed.

The performance of an organic thin film photodiode (OPD), fabricated from a hetero-junction comprised of two layers of C60 and a phthalocyanine-Cu(II) complex was evaluated by detecting the chemiluminescence generated from the reaction of luminol with horseradish peroxidase in the presence of H2O2, and the fluorescence from resorufin, as an optical detector. The photocurrent of the OPD was linear with respect to the power of light from a commercial LED. The sensitivity of the OPD was sufficient for detecting chemiluminescence with a power 0.1 μW/cm2. The OPD was successfully used in a flow-immunoassay for IgA, a marker of human stress, in which a sandwich immunoassay was carried out on the microchip and the fluorescence from resorufin, produced by the enzymatic reaction, was detected. The detection limits for resorufin and IgA were 5.0 μM and 16 ng/mL, respectively. The photosensitivity of the OPD remained relatively constant for a minimum of one year.

A surface plasmon resonance (SPR) sensor on a compact disk (CD)-type microfluidic device was developed to miniaturize the elements of a complete analytical system, pump and valves. The CD-type microfluidic device was fabricated by attaching a polydimethylsiloxane disk plate that contained microchannels and reservoirs to a flat polycarbonate disk plate that contained grating films with a thin layer of Au. The optical system of the SPR sensor and the theory for its operation are based on the principle of a grating coupled-type SPR. The sample and reagent solutions in the reservoirs on the CD-type microfluidic device were sequentially introduced into the detection chamber by centrifugal force generated by the rotation of the microfluidic device. The variation of resonance wavelength was dependent on the refractive index of the sample solution. This CD-type SPR sensor was successfully used in an immunoassay of immunoglobulin A (IgA). The anti-IgA, blocking reagent, sample and washing solution in the reservoirs were sequentially introduced into the detection chamber by changing the frequency of rotation of the microfluidic device. IgA in the sample solution was adsorbed to the anti-IgA immobilized on the Au thin layer in the detection chamber and was then detected by the SPR sensor.

The solubilities of lanthanum fluoride (LaF3) powder and single crystals were measured in various aqueous electrolyte solutions. In contrast with the classical assumption of the stoichiometric dissolution of LaF3, it was found that the dissolution of the component cation La3+ was undetectable and the fluoride ion dissolved preferentially: cF−> 3cLa3+ where c is the ion concentration. X-ray photoelectron spectroscopy (XPS) of the LaF3 surface treated with electrolyte solutions corroborated this observation. As a result of the preferential fluoride dissolution, charge separation was expected to occur in such a way that the LaF3 surface would have positively charged “fluoride-vacancies”. This was confirmed by changes in membrane potential as a function of the fluoride dissolution the adsorption of an anionic adsorption marker (eosin Y) on the solid surface. It was also found that the preferential dissolution of fluoride ions was accompanied by simultaneous adsorption of almost the same amount of electrolyte anions (e.g. NO 3−) onto the LaF3 surface. This was confirmed by both solution measurements and surface analysis by diffuse reflectance IR Fourier transform (DRIFT) spectrometry. The result of this anion adsorption was explained in terms of ion exchange to ensure electroneutrality in the bulk of the adjacent electrolyte solution, which would otherwise be violated by the preferential fluoride dissolution. The anionic adsorption marker and DRIFT measurements were used to characterize further the above-mentioned ion exchange and selective uptake of fluoride ions into the “fluoride vacancies”. Release of the adsorbed eosin Y or electrolyte anions, such as NO3−, from the LaF3 surface was found to be induced by F− or OH− ions only. On the basis of this observation, the response mechanism of the fluoride ion-selective electrodes was discussed.

A small-sized surface plasmon resonance (SPR) sensor with a microchip flow cell has been developed for the purpose of enhancing the sensitivity of the SPR detector for low molecular weight compounds. This portable differential SPR detector consisted of an LED, two cylindrical lenses, a round prism, a divided mirror, a CCD, electronics, and a polydimethylsiloxane/gold microchip with two flow paths (10 mm long, 1 mm wide, 20–100 μm deep). 3-Mercaptopropyltrimethoxysilane was used for sealing the microchip. The performance of the on-site orientated SPR detector was estimated using sucrose and IgA. A drastic change in the SPR intensity appeared. The depth of the flow cell was in inverse proportion to the SPR intensity. Compared to a conventional flow cell having the size of 10 mm (L) × 1 mm (W) × 1 mm (D), its sensitivity to 10% sucrose and 0.9 nM IgA increased about 11 and 39 times, respectively. This phenomenon seemed to be due to the increase in the substance on the SPR sensor based on its size effect. These results showed that the application of the microchip sensor for SPR measurement has the possibility for improvement of the SPR intensity for low molecular substances.

Indirect conductimetric detection of cyclodextrins (CDs) was investigated in liquid chromatography (LC). The mobile phase contained an electrolytic substance which maintained high background, and CDs were indirectly detected owing to a depression of the background signal due to dilution of the mobile phase by the analyte molecules. The dynamic reserve, defined as the ratio of the background to its noise level, was (1–2) × 105, and the detection limits at S/N = 3 were 23–40 ng for CDs when a microcolumn LC system was employed.

A divalent cation-selective electrode, which utilizes a lipophilic resin as a matrix for the sensing membrane, and which has long-term stability has been developed. The sensing membrane is a lipophilic acrylate resin which is impregnated with a solution of 1-decylalcohol and the calcium salt of bis[4-(1,1,3,3-tetramethylbutyl) phenyl] phosphate at concentrations of 0.08 g ml(-1) each. The electrode exhibited nearly equal selectivity to Ca(2+) and Mg(2+) ions and could be used as a water hardness sensor. The electrode shows a Nernstian response with a slope of 29 mV decade(-1) to both Ca(2+) and Mg(2+) ions in the concentration range from 10(-5) M to 10(-1) M and could be used in the pH range from 3 to 10 for the determination of 10(-3) M Ca(2+) and Mg(2+) solutions. The initial performance of the electrode could be maintained for 1 year, since the lifetime test of the electrode was conducted in tapwater at a continuous flow rate of 4 ml min(-1). The hardnesses of tapwater and upland soil extracts were determined using the developed electrode and the analytical results were in good agreement with those obtained by chelatometric titration using an EDTA solution as the titrant. A coefficient factor of correlation 0.998 was obtained between the electrode method and titrimetry. The long-term stability of the electrode was found to be due to strong affinity of 1-decylalcohol to the lipophilic acrylate resin.

A simple flow injection analysis (FIA) system for residual chlorine in tap water has been developed by using a Pb(II) ion-selective electrode (ISE) detector. The method is based on a specific response of the Pb(II)-ISE to residual chlorine. The FIA system consists of a millivolt meter, a peristaltic pump, a Pb(II)-ISE detector and a recorder. A linear working curve between peak height and concentration of residual chlorine was obtained from 0.1 to 1 mg l −1 for the developed FIA system. The relative standard deviation for repeated injections of a 0.2 mg l −1 residual chlorine sample was 2%. The regression line and its correlation factor between the conventional o -tolidine colorimetric method and the present method were Y =0.75 X +0.17 and 0.967, respectively, for this determination.

This chapter discusses the development of conductivity-based immunosensor for sensitive detection of methamphetamine in human urine. There has been increasing needs for a simple, sensitive and selective method for determination of the stimulant drug of methamphetamine (C 10 H 15 N, abbreviated as MA) in drug abuser's urine. A method based on gas chromatography–mass spectrometry has been used as a conventional method so far. This method is accruable, but it needs an expensive instrument and time-consuming procedures. Method based on the chemical reactivity of secondary amino groups of MA have also been used for screening MA in human urine, but the MA selectivities of these methods is not so high. Recently immunoassay of MA employing polychronal or monochronal antibodies against MA, such as enzyme linked immunosorbent assay and latex aggulutination assay have been reported. To establish a practically applicable measuring system constructed from a portable immunosensor, a novel immuno assay method is developed that is based on conductivity detection using an antibody-immobilized electrode. Anti-MA antibody was immobilized onto the surface of a pair of platinum electrodes. The reaction of MA with the antibody causes an increase in conductivity of the immobilized antibody. The conductivity of the electrode increased with the increment of MA concentration.