Shiho Tokonami

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.

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.

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.

Green Electroless Plating Method Using Gold Nanoparticles for Conducting Microbeads: Application to Anisotropic Conductive Films

We have developed a green electroless plating method, i.e., a method that ensures the saving of resources and reduction of emissions to the environment, for the formation of a conductive coating on micrometer-sized core beads. This method has great advantages in practical applications because it uses a self-assembling reaction between gold nanoparticles (AuNPs) that are synthesized by combining a nonhazardous reducing agent with a nontoxic thiol binder. Moreover, the method does not require sophisticated instruments. In our study, beads with uniform surfaces were obtained by the adsorption of AuNPs; furthermore, AuNP-growth processes were employed subsequently to increase the electrical resistance of the AuNP-fixed single microbead to a value suitable for practical applications (0.5 Ω). Various plastic cores, viz., monodisperse microbeads of acrylic resin, nylon 6, nylon 12, polylactic acid, and polystyrene, were used in this study. The prepared beads were well dispersed in an epoxy resin film. To demonstrate practical applications, they were then successfully applied to an anisotropic conductive film.

Development of a rapid bacterial counting method based on photothermal assembling

We developed a rapid bacterial counting method based on the photothermal assembling (PTA). Based on the laser-induced PTA in fluid medium, an initial bacterial concentration was estimated from the number of assembled bacteria. The measuring time of our method is 90 s, which is more rapid than the conventional cultivation method requiring several days at longest. Furthermore, the difference between the estimated concentrations by our method and by the cultivation method is less than 10%, which sufficiently guarantees the availability. The clarified principle will pave the way to a rapid and high throughput bacterial assay useful for medical care and food safety.

Submillimetre Network Formation by Light-induced Hybridization of Zeptomole-level DNA

Macroscopic unique self-assembled structures are produced via double-stranded DNA formation (hybridization) as a specific binding essential in biological systems. However, a large amount of complementary DNA molecules are usually required to form an optically observable structure via natural hybridization, and the detection of small amounts of DNA less than femtomole requires complex and time-consuming procedures. Here, we demonstrate the laser-induced acceleration of hybridization between zeptomole-level DNA and DNA-modified nanoparticles (NPs), resulting in the assembly of a submillimetre network-like structure at the desired position with a dramatic spectral modulation within several minutes. The gradual enhancement of light-induced force and convection facilitated the two-dimensional network growth near the air-liquid interface with optical and fluidic symmetry breakdown. The simultaneous microscope observation and local spectroscopy revealed that the assembling process and spectral change are sensitive to the DNA sequence. Our findings establish innovative guiding principles for facile bottom-up production via various biomolecular recognition events.

Molecularly Imprinted Overoxidized Polypyrrole Films for Sensor Applications from Enantiorecognition to Trace Analysis

This article reviews a novel approach to molecular imprinting polymer (MIP) technology using conducting polymers and related materials. Our group successfully introduced molecular recognition properties in polypyrrole by overoxidation more than two decade ago and has been applying this technique to sensor applications. In this chapter, the molecular recognition protocols developed by our group are first presented, and analytical performance of the overoxidized polypyrrole including enantiorecognition and separation are then discussed. Attempts at applying this MIP technology in practical analysis are also presented to monitor the trace concentration of ATP for the HACCP applications.

Electrochemical evaluation of poly(3,4-ethylenedioxythiophene) films doped with bacteria based on viability analysis

To immobilize viable bacteria on an electrode, we present a novel and straightforward technique that relies on the negative ζ-potentials of bacteria for insertion into conducting polymers as dopants. In the present study, we conducted an electrochemical polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with various gram-negative bacteria, including Pseudomonas aeruginosa, Escherichia coli, and Shewanella oneidensis. The PEDOT film doped with bacteria indicated a typical redox response, high conductivity, and electrochemical stability. Fluorescence microscopy confirmed that approximately 90% of the bacteria incorporated into the PEDOT film at >0.5 μm in thickness were viable.

Voltammetric detection and profiling of isoprenoid quinones hydrophobically transferred from bacterial cells.

We have developed a novel bacterial detection technique by desiccating a bacterial suspension deposited on an electrode. It was also found that the use of an indium-tin-oxide (ITO) electrode dramatically improved the resolution of the voltammogram, allowing us to observe two pairs of redox peaks, each assigned to the adsorption of isoprenoid ubiquinone (UQn) and menaquinone (MKn), which were present in the bacterial cell envelopes, giving midpeak potentials of -0.015 and -0.25 V versus Ag|AgCl|saturated KCl| at pH 7.0, respectively. Most of the microorganisms classified in both the Gram-negative and -positive bacteria gave well-defined redox peaks, demonstrating that this procedure made the detection of the quinones possible without solvent extraction. It has been demonstrated that the present technique can be used not only for the detection of bacteria, but also for profiling of the isoprenoid quinones, which play important roles in electron and proton transfer in microorganisms. In this respect, the present technique provides a much more straightforward way than the solvent extraction in that one sample can be prepared in 1 min by heat evaporation of a suspension containing the targeted bacteria, which has been applied on the ITO electrode.

Enhanced collective optical response of vast numbers of silver nanoparticles assembled on a microbead

We investigated the optical response of a huge number of silver nanoparticles (AgNPs) densely assembled on an organic microsphere, i.e., AgNP-fixed bead, under the collective phenomena of localized surface plasmons. For this purpose, various optical properties of such a AgNP-fixed bead were analyzed in aqueous solution by dark-field optical microscopy and laser Raman microscopy. In particular, in comparison with the optical spectrum of single AgNPs, significant spectral broadening and redshift were observed due to plasmonic superradiance with decreasing interparticle distance to the subnanoscale when using small binder molecules in the AgNP-fixed bead. Furthermore, we observed surface-enhanced Raman scattering and clarified the sensitivity of the signal intensity to the size of the binder molecules between the AgNPs, which can be explained based on optical response theory using a discrete integral with spherical cells. These results and discussion provide a guiding principle for broadband plasmonic light absorbers and for highly sensitive detection of small molecules and nanoscale biomaterials based on vast numbers of nanogaps produced by a bottom-up self-assembly process.