Michiko Seyama

Potentiometric biosensor for urea based on electropolymerized electroinactive polypyrrole

Abstract A urea biosensor was developed by immobilizing urease into an electropolymerized electroinactive polypyrrole (PPy) on a platinum electrode. This enzyme-immobilized PPy electrode showed a stable potential response to urea based on the pH response of the electroinactive PPy film electrode. The electropolymerization conditions were optimized, and thus the biosensor showed a Nernstian response with a slope of 31.8 mV decade −1 over concentration range of 1 × 10 −4 − 0.3 mol dm −3 urea.

High-sensitivity urea sensor based on the composite film of electroinactive polypyrrole with polyion complex

Abstract A high-sensitivity urea sensor consisting of the composite film of electropolymerized electroinactive polypyrrole (PPy) with the polyion complex containing urease (Urs) was fabricated. This sensor showed potential response to urea within 20 s by detection of pH change during enzymatic reaction with a pH-sensitive electroinactive PPy. The urea response became higher with the slope of 110 mV decade −1 . This high sensitivity was attributed to the effective immobilization of the large number of Urs by electropolymerization on electrode pre-coated with polyion complex.

Flow injection analysis of potassium using an all-solid-state potassium-selective electrode as a detector

The concentration of potassium was determined by a combination of flow injection analysis (FIA) with an all-solid-state potassium sensor detection. The all-solid-state potassium-selective electrode possessing long-term potential stability was fabricated by coating an electroactive polypyrrole/poly(4-styrenesulfonate) film electrode with a plasticized poly(vinyl chloride) membrane containing valinomycin. The simple FIA system developed in this laboratory demonstrated sensitivity identical to that in the batch system and achieved considerably rapid assay (150 samples h(-1)). Analyses of soy sauce and control serum samples by this FIA system yielded results in good agreement with those obtained by conventional measurements.

Petroleum pollution sensing at ppb level using quartz crystal resonators sputtered with porous polyethylene under photo-excitation

Abstract Radio-frequency (r.f.) sputtering of a porous polyethylene (PE) disk made by sintering PE granules can be used to form hydrocarbon-polymer films applied as the chemical-sensing overlayers of quartz crystal resonator sensors that can detect petroleum hydrocarbon vapors at low parts-per-billion (ppb) levels. The vapor-sorption capabilities of these films are profoundly affected by the sputtering method used; they are enhanced by photo-excitation through irradiation using ultraviolet (UV) light, and reduced by carbonization induced by long-term processing or by water-treatment. The PE films, especially photo-excited PE film, are characterized by a smooth surface, a high atomic density with a high hydrogen content, and dangling-bond longevity. Photo-excited PE film are capable of detecting linear hydrocarbon (>C 12 ) vapors below the ppb level. Pre-sorption with water vapor at 9% relative humidity (RH) can enhance the sensing abilities of sensors for petroleum hydrocarbons. The effect of this water treatment on petroleum hydrocarbon sorption is especially prominent for d -phenylalanine-sputtered film.

Application of an array sensor based on plasma-deposited organic film coated quartz crystal resonators to monitoring indoor volatile compounds

The basic response ability of an array sensor based on plasma-deposited organic film-coated quartz crystal resonators (QCRs) was investigated with a view to their use for indoor air monitoring. The array of plasma-deposited organic film-coated QCRs was applied to detect and separate volatile organic compounds (VOCs) including alkanes, aromatic carbons, chlorocarbons, ketones, and alcohols. Continuous monitoring tests were tried in a real room environment (a refreshment area and a smoking area) with an array of plasma-deposited organic film-coated QCRs along with commercial sensors for indoor monitoring, a relative humidity/temperature sensor, a carbon dioxide sensor, and a three-dimensional micro-ultrasonic airflow meter. To provide a comparison commercial VOC detectors based on a photo-ionization detector and a semiconductor for indoor monitoring tests were used. The plasma-deposited organic film-coated QCRs exhibited fast pulse responses to volatile compounds in the room air along the baseline shift correlated with relative humidity changes and more sensitive responses compared with commercial organic gas detectors.

Detection of petroleum hydrocarbons at low ppb levels using quartz resonator sensors and instrumentation of a smart environmental monitoring system

Petroleum hydrocarbon vapors at low ppb levels can be detected using a thickness shear mode resonator (TSMR) coated with a chemical-sensing overlayer, prepared by radiofrequency sputtering of porous sintered-polyethylene (PS-PE). The sensing capabilities of PS-PE sensors were profoundly affected by the sputtering methods; they were enhanced by the photo-excitation effect, and were reduced by carbonization and water treatment. The photo-assisted PS-PE sensor was extremely sensitive and could detect linear hydrocarbon (> C12) vapors below the ppb level. The time constant of the sorption curve, however, was large, indicating a slow sensing speed. Toward creating instrumentation for a smart environmental monitoring system, the TSMR sensors were arrayed on a circuit board equipped with a serial interface and signal processing chips of the oscillation drive and frequency counter. Co-sorption with water vapor at a relative humidity of about 10% has almost no effect on the sensing ability of PS-PE sensors for 1,2,4-trimethylbenzene. Conversely, it enhances the sensitivity of the TSMR sensor coated with a D-phenylalanine film. Upward shifts in the baseline are evident with elapsed time. However, a rigorous ten-cycle iteration test for 100 ppm toluene vapor demonstrated good reproducibility of the sensors signals.

Cooperative suction by vertical capillary array pump for controlling flow profiles of microfluidic sensor chips.

A passive pump consisting of integrated vertical capillaries has been developed for a microfluidic chip as an useful component with an excellent flow volume and flow rate. A fluidic chip built into a passive pump was used by connecting the bottoms of all the capillaries to a top surface consisting of a thin layer channel in the microfluidic chip where the thin layer channel depth was smaller than the capillary radius. As a result the vertical capillaries drew fluid cooperatively rather than independently, thus exerting the maximum suction efficiency at every instance. This meant that a flow rate was realized that exhibited little variation and without any external power or operation. A microfluidic chip built into this passive pump had the ability to achieve a quasi-steady rather than a rapidly decreasing flow rate, which is a universal flow characteristic in an ordinary capillary.

Chiral-discriminative amino acid films prepared by vacuum vaporization and/or plasma processing

D-Phenylalanine (D-Phe) films capable of discriminating optical isomers were prepared by dry processing: radiofrequency sputtering or vacuum vaporization with and without the assistance of an inductively coupled plasma (ICP). Chemical and spectroscopic analyses revealed that the majority of the constituents of the vaporized film are D-Phe molecules. However, the film prepared by ICP-assisted vaporization contains scarcely any D-Phe. The chiral-sensing properties of these D-Phe films were confirmed by sorption measurements on cyclic monoterpenes. Quartz crystal resonators coated with these films respond to the (−)-forms of limonene and α-pinene preferentially to their (+)-forms at the ppm level. This chiral preference was not observed for carvone, which induced comparable frequency shifts to limonene and α-pinene even at sub-ppm levels. The strong electrostatic interactions of the carbonyl group in carvone probably overcome the weak interactions of the discriminative optical isomers.

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.

Effects of surface water on gas sorption capacities of gravimetric sensing layers analyzed by molecular descriptors of organic adsorbates

The gas sorption capacities of sputtered carbonaceous films are evaluated with quartz crystal resonators. These films are sensitive to 20 ppm organic vapors and exhibit structure-dependent responses. Films derived from synthetic polymers are hydrophobic, whereas films derived from biomaterials are amphiphilic or hydrophilic. Polyethylene (PE) film has an extremely high sorption capacity for a wide range of vapors. Transient sorption responses are investigated using a humidified carrier by employing carboxylic acid esters, whose aliphatic groups are systematically changed. Small esters with a higher affinity to water induce negative U-shaped responses from amphiphilic films derived from biomaterials. On the other hand, polymeric films exhibit positive exponential response curves. Even if the concentrations are decreased, the response intensities are enhanced with the incremental expansion of carbon chains of aliphatic groups. Only fluoropolymer film shows the opposite tendency. The modeling of quantitative structure property relationships has indicated that the sorption capacities of the PE film to the carboxylic acid esters are fundamentally governed by electrostatic interactions. The intermolecular attractive forces are basically attributable to interactions between the positively polarized sites in esters and the negatively polarized/charged sites in PE film.