Hiroshi Shiigi

Review: micro- and nanosized molecularly imprinted polymers for high-throughput analytical applications.

This review covers the analytical properties and applications of micro- and nanostructured molecularly imprinted polymers. The first two parts focused on their intrinsic and receptor properties specific to 0-1 dimensional MIP nanoobjects. The third part reviews the recent publication regarding the 2-3D patterned MIP structures mainly focusing on their sensor and microarray applications. Several patterning techniques that can be used for the fabrication of MIP microsensors/arrays are explained. Finally, a recent publication on some other nanomaterials (metal and semiconductor nanoparticles), which are compatible with MIP receptors to enhance the sensitivity, is discussed.

A New Humidity Sensor Using the Composite Film Derived from Poly(o‐phenylenediamine) and Poly(vinyl alcohol)

A composite film consisting of conducting poly(o-phenylenediamine) (PoPD) and insulating poly(vinyl alcohol) (PVA) has been prepared in a proportion which possesses satisfactory mechanical strength and characteristics favorable for a humidity senor. The electrical conductivity and PoPD content curves were measured, and it was found that the conductivity of the composite film rose sharply at about 0.1 volume percent (v/o) of the PoPD content, reaching a value of ∼10 -2 S cm -1 corresponding to that of PoPD itself. The change in conductivity was as large as four orders of magnitude, which was attributed to the formation of networks that ena le the insulating composite to reveal the electrical conduction. The conductivity of the composite film was linearly related to the humidity, extending from 2.5 x 10 -5 to 1.5 x 10 -1 S cm -1 between the dry and wet states. Measurements of the conductivity were not attended with hysteresis in the moistening or desiccating runs. The change in conductivity was caused by a shift of the equilibrium between the conducting and the insulating PoPD depending on the atmospheric humidity in which, e.g., in the drying process the reaction of the protonated and conjugated PoPD with the OH group of PVA occurred to form the insulating PoPD and a water molecule resulting in the decrease of the conductivity of the composite film.

The humidity dependence of the electrical conductivity of a solublepolyaniline–poly(vinyl alcohol) composite film

A humidity-sensitive composite film has been synthesized that consists of soluble polyaniline (PAn) and poly(vinyl alcohol) (PVA). PAn gave a percolation threshold where the electrical conductivity rose sharply at a volume fraction of 0.1%. This value is very small compared with that (about 5 vol%) reported in general for composite films consisting of conducting and non-conducting polymers, indicating that the two polymers used in this study were mixing completely. The conductivity of the PAn–PVA composite was proportional to the relative humidity, and the linearity was valid from 3×10–5 to 1.5×10–1 S cm–1 . The response time of the composite for the humidity change was 45 s and 9 min for moistening and desiccating steps, respectively. The conductivity of the composite film varied depending on the doping level of PAn, which was affected by the concentration of water molecules surrounding the conducting polymer. At high humidity, the PAn was in the form of an emeraldine salt, and transformed into a non-conducting base with decreasing environmental humidity.

Thermogravimetric/Mass and Infrared Spectroscopic Properties and Humidity Sensitivity of Polyaniline Derivatives/Polyvinyl Alcohol Composites

Humidity-sensitive polyaniline derivatives/polyvinyl alcohol (PVA) composites have been studied using thermogravimetric (TG)/mass (MS) and in situ Fourier transform infrared spectroscopy. The electrical conductivity of the poly(o-phenylenediamine) (PoPD)/PVA and poly(o-aminophenol) (PoAP)/PVA composites were linearly related with the atmospheric humidity, but there was no such linear relationship for the poly(m-phenylenediamine) (PmPD)/PVA and poly(o-toluidine) (PoTd)/PVA composites. The FTIR intensity at 3600 and 3200 cm -1 for the PoPD/PVA and PoAP/PVA composites decreased with a decrease of humidity, indicating a removal of water molecules from the composite. For the PmPD and PoTd composites, however, the involvement of water molecules in the drying and wetting stages was not pronounced. The TG/MS analyses suggested that the PoPD/PVA and PoAP/PVA composites have two types of water: one is weakly bound to the composite and equilibriates with the atmospheric moisture, and the other is strongly bound to the composite at the PVA unit and stays there even in a dry state (<130°C). Emphasis is laid on the role of these different types of water for the linear dependence of the conductivity on the atmospheric humidity

Synthesis and bioanalytical applications of specific-shaped metallic nanostructures: a review.

Many successful synthesis routes for producing different shapes of metallic nanostructures, including sphere, rod, cube, and hollow shapes, have been developed in the past few decades. Many applications using these nanostructures have been studied because the outstanding properties of the nanostructures are not exhibited by their bulk-state counterparts. This review paper reports some recent developments in clinical and biosensor applications. The first part focused on the synthesis methods of metallic nanostructures having various shapes along with their optical properties. The second and third part is an introduction of the gold nanoparticle assemblies and arrays, explaining the conjugation methods of metallic nanostructures with biological entities. The final part reviews on the recent bioanalytical applications using various shapes of metallic nanostructures.

A CO 2 Sensor with Polymer Composites Operating at Ordinary Temperature

Many sensors proposed to date require high operation temperature (e.g., 400°C for solid electrolytes) to detect with a high sensitivity, which restricts the wide application of sensors. We have found that composites consisting of the emeraldine base‐polyaniline (EB‐PAn) and poly(vinyl alcohol) (PVA) serve as a promising sensor operating at room temperature with a high sensitivity. The logarithm of electrical conductivity of the EB‐PAn/PVA composite is proportional to the log of concentration. For the composite with 13 wt % EB‐PAn and 87 wt % PVA, the linear relationship holds in the concentration range from 50 ppm to 5% at 30% relative humidity. This composite is insulating in a moist atmosphere without . With the addition of , however, carbonate ions are formed by the hydrolysis of , and these ions equilibrate with the atmospheric . The carbonic acid is reversibly incorporated to and ejected from the EB‐PAn depending on the concentration of atmospheric , and the conductivity varies between conducting and insulating levels.

Label-Free and Selective Bacteria Detection Using a Film with Transferred Bacterial Configuration

Specific identification of bacteria has been achieved through precisely transferred bacterial structure on the surface of overoxidized polypyrrole (OPPy) film. The recognition of target bacteria was successfully carried out in real time using OPPy film in combination with dielectrophoresis. The unique combination of both techniques made the specific detection of template bacilli possible at concentrations as low as 10(3) CFU/mL within 3 min, without any bacterial pretreatment. The observation of the movement of bacteria by using a fluorescent microscope revealed that living bacteria were being trapped vertically in the cavity created in the OPPy film. Further, the bacterial cavities had high selectivity and were able to discriminate particular target bacteria, Pseudomonas aeruginosa, out of bacterial mixtures containing Acinetobacter calcoaceticus, Escherichia coli, and Serratia marcescens, which are known to have a similar shape. This simple method can be used for a wide variety of applications in which rapid bacterial detection is required, such as food safety risk assessment, clinical point-of-care testing, and continuous environmental monitoring.

Open bridge-structured gold nanoparticle array for label-free DNA detection.

We focused on changes in the electrical property of the open bridge-structured gold nanoparticles array consisting of 46-nm parent and 12-nm son gold nanoparticles by hybridization and applied it for a simple electrical DNA detection. Since a target DNA of a 24-mer oligonucleotide was added to the probe DNA modified 12-nm Au nanoparticles, which was arranged on the gap between the 46-nm Au particles, the response was read by an electrical readout system. Even in a simple measuring method, we obtained a rapid response to the cDNA with a high S/N ratio of 30 over a wide concentration range and a detection limit of 5.0 fmol. Moreover, the array discriminated 1-base mismatches, regardless of their location in the DNA sequence, which enabled us to detect single-nucleotide polymorphism, which is one of the important diagnoses, without any polymerase chain reaction amplification, sophisticated instrumentation, or fluorescent labeling through an easy-to-handle electrical readout system.

An Electroless Plating Method for Conducting Microbeads Using Gold Nanoparticles

Gold nanoparticles interlinked with alkanethiols were deposited on 6 μm acrylic resin microbeads as a 30 nm thickness layer, and it was found that the electroconductance of the deposited nanoparticle film can be controlled by the concentration of binder thiol and that replating of the bead dramatically reduced the single-bead resistance. This new synthetic strategy for the metallization of plastic micro-objects with a gold nanoparticle provides a way to form a homogeneous conducting layer. This technique also has the advantage of producing metallized plastic materials with environment-friendly protocols as an alternative pathway to the conventional electroless plating techniques.

AC Impedance Spectroscopy of Humidity Sensor Using Poly(o-phenylenediamine)/Poly(vinyl alcohol) Composite Film

Logarithm of electrical conductivity of poly(o-phenylenediamine)/poly(vinyl alcohol) composite is known to be proportional to relative humidity covering more than five orders of magnitude. Such a humidity-sensing system has been analyzed by ac impedance spectroscopy. Two different equivalent circuits for the humidity-sensing process are proposed in the humidity region lower and higher than 70% RH. In the former, the film impedance (R film , C film ) and the interfacial impedance (R ct , C dl ) are combined in series. The first semicircle on the Nyquist plot corresponds to the impedance of the composite film, and the start of the second semicircle is related to the interface impedance. In the latter, the Warburg diffusion is involved, which is attributed to the diffusion of the protonic acid from the insulating polymer unit to the whole composite. The logarithmic value of R film changes linearly over more than eight orders upon the variation of relative humidity from 20 to 95% RH, and the capacitive contribution (C dl ) at the film/electrode interface becomes appreciable for the composite films with larger thickness (>50 nm) and/or with larger weight ratio of PoPD to PVA (>0.25).