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Current nanotechnology based on top-down nanofabrication may encounter a variety of drawbacks in the near future so that development of alternative methods, including the so-called bottom-up approach, has attracted considerable attention. However, the bottom-up strategy, which often relies on spontaneous self-assembly, might be inefficient in the development of the requisite functional materials and systems. Therefore, assembly processes controlled by external stimuli might be a plausible strategy for the development of bottom-up nanotechnology. In this review, we demonstrate a paradigm shift from self-assembly to commanded assembly by describing several examples of assemblies of typical functional molecules, i.e. porphyrins and fullerenes. In the first section, we describe recent progress in the design and study of self-assembled and co-assembled supramolecular architectures of porphyrins and fullerenes. Then, we show examples of assembly induced by external stimuli. We emphasize the paradigm shift from self-assembly to commanded assembly by describing the recently developed electrochemical-coupling layer-by-layer (ECC-LbL) methodology.

Large amounts of radioactive material were released from the Fukushima Daiichi nuclear plant in Japan, contaminating the local environment. During the early stages of such nuclear accidents, iodine I-131 (half-life 8.02 d) is usually detectable in the surrounding atmosphere and bodies of water. On the other hand, in the long-term, soil and water contamination by Cs-137, which has a half-life of 30.17 years, is a serious problem. In Japan, the government is planning and carrying out radioactive decontamination operations not only with public agencies but also non-governmental organizations, making radiation measurements within Japan. If caesium (also radiocaesium) could be detected by the naked eye then its environmental remediation would be facilitated. Supramolecular material approaches, such as host–guest chemistry, are useful in the design of high-resolution molecular sensors and can be used to convert molecular-recognition processes into optical signals. In this work, we have developed molecular materials (here, phenols) as an optical probe for caesium cation-containing particles with implementation based on simple spray-on reagents and a commonly available fluorescent lamp for naked-eye detection in the solid state. This chemical optical probe provides a higher spatial resolution than existing radioscopes and gamma-ray cameras.

We introduce a novel strategy of fabricating nanoporous carbons loaded with different amounts of CuO nanoparticles via a hard templating approach, using copper-containing mesoporous silica as the template and sucrose as the carbon source. The nature and dispersion of the CuO nanoparticles on the surface of the nanoporous carbons were investigated by x-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM) and high-resolution transmission electron microscopy (HRTEM). XRD results reveal that nanoporous carbons with embedded CuO nanoparticles exhibit a well-ordered mesoporous structure, whereas the nitrogen adsorption measurements indicate the presence of excellent textural characteristics such as high surface area, large pore volume and uniform pore size distribution. The amount of CuO nanoparticles in the nanochannels of the nanoporous carbon could be controlled by simply varying the Si/Cu molar ratio of the mesoporous silica template. Morphological characterization by SEM and TEM reveals that high-quality CuO nanoparticles are distributed homogeneously within the nanoporous carbon framework. The supercapacitance behavior of the CuO-loaded nanoporous carbons was investigated. The material with a small amount of CuO in the mesochannels and high surface area affords a maximum specific capacitance of 300 F g^-1 at a 20 mV s^-1 scan rate in an aqueous electrolyte solution. A supercapacitor containing the CuO-loaded nanoporous carbon is highly stable and exhibits a long cycle life with 91% specific capacitance retained after 1000 cycles.

Mesoporous materials have been paid much attention in both scientific researches and practical applications. In this review, we focus on recent developments on preparation and functionalization of new families of mesoporous materials, especially non-siliceous mesoporous materials invented in our research group. Replica synthesis is known as the method to synthesize mesoporous materials composed of various elements using originally prepared mesoporous replica. This strategy has been applied for the syntheses of novel mesoporous materials such as carbon nanocage and mesoporous carbon nitride. Carbon nanocage has a cage-type structure with huge surface area and pore volume, which exhibits superior capabilities for biomolecular adsorption. Mesoporous carbon nitride was synthesized, for first time, by using mixed material source of carbon and nitrogen simultaneously. As a totally new strategy for synthesis of mesoporous materials, the elemental substitution method has been recently proposed by us. Direct substitution of component elements in original mesoporous materials, with maintaining structural regularity, provided novel mesoporous materials. According to this synthetic strategy, mesoporous boron nitride and mesoporous boron carbon nitride have been successfully prepared, for first time. In addition to these material inventions, hybridization of high functional materials, such as biomaterials, to mesoporous structure has been also developed. Especially, immobilization of proteins in mesopores was systematically researched, and preparation of peptide-hybridized mesoporous silica was demonstrated. These new families of mesoporous materials introduced in this review would have high potentials in future practical applications in wide ranges from electronics and photonics to environmental and medical uses.

The controlled fabrication of nanometer-scale objects is without doubt one of the central issues in current science and technology. However, existing fabrication techniques suffer from several disadvantages including size-restrictions and a general paucity of applicable materials. Because of this, the development of alternative approaches based on supramolecular self-assembly processes is anticipated as a breakthrough methodology. This review article aims to comprehensively summarize the salient aspects of self-assembly through the introduction of the recent challenges and breakthroughs in three categories: (i) types of self-assembly in bulk media; (ii) types of components for self-assembly in bulk media; and (iii) self-assembly at interfaces.

Through layer-by-layer adsorption (LBL) technique, multilayer film was prepared from enzymes, diaphorase (DI) and glucose-6-phosphate dehydrogenase (G6PDH) and polyelectrolytes. The adsorption interface morphology was directly observed by atomic force microscopy, and the immobilization amount and layer thickness were characterized from quartz crystal microbalance which showed formation of nanoscale multilayer structure and linear mass increase which depended on alternate adsorption cycles. In order to construct a new mediated bi-enzyme biosensor system, polymerized mediator, DI and G6PDH were immobilized on carbon electrode surface by using LBL method. Electrochemical experiments indicated highly efficient electron transfer by the polymerized mediator. Two enzymes kept their activities after immobilization, and the electrode immobilized by mediator and enzymes showed sensitive response to glucose-6-phosphate in the presence of free NAD⁺, and high stability during long period of storage.

Gold clusters modified with first, second and third generation dendritic polyphenylazomethines (DPA) were synthesized by an exchanged reaction of corresponding DPA dendron thiols. Measurements by high performance perfect sizer (HPPS) and TEM reveal that their diameters increase with a change in the chain length of the modifying molecules from the first to third generation. These gold clusters with DPA dendrons exhibit coordination quantitatively to metal ions such as Fe³⁺, Sn²⁺, etc., because of their imine groups; this then resulted in self-aggregation to form a large sphere.

L-Proline sensor has been fabricated through multilayer assembly of recombinant dye-linked L-proline dehydrogenase (L-proDH) originally from hyperthermophilic archaeon (Therococcus profundus) and polymerized mediator, poly(allylamine) ferrocene (PAA-Fc), on a gold electrode by electrostatic layer-by-layer alternate adsorption method. The characteristic redox peaks of ferrocene groups were obvious exhibited in cyclic voltammograms, and both anodic and cathodic peaks increased with PAA-Fc/L-proDH bilayer number which confirmed the formation of a multilayer structure. Further experiments showed that an electrode fabricated in this way catalyzed the oxidation of L-proline. It suggested that polymerized mediator could transfer electrons between electrode surface and immobilized L-proDH. Ampeormetric experiments showed that the current response to L-proline increased with PAA-Fc/L-proDH bilayer number. The stability of the sensor was measured, and it kept a 40% relative response after 30 days storage in buffer under 4 °C.

A hybrid nanomaterial was prepared by human serum albumin (HSA) and vitamin B₁₂ derivatives. The incorporation of hydrophobic vitamin B₁₂ derivatives, which have ester groups in place of the peripheral amide moieties of the natural cobalamin, into HSA is primarily controlled by the hydrophobicity of the peripheral ester groups. Microenvironmental property around the hydrophobic vitamin B₁₂ in HSA was examined by fluorescence and fluorescence polarization measurements. The hydrophobic vitamin B₁₂ itself in HSA is in a microenvironment equivalent in medium polarity to dichloromethane. The molecular motion of hydrophobic vitamin B₁₂ in HSA was markedly suppressed under such microenvironmental conditions. Carbon-skeleton rearrangement reaction of an alkyl radical derived from an alkyl ligand bound to the hydrophobic vitamin B₁₂ was markedly favored in HSA aqueous solution, relative to the reactions in methanol and benzene. The 1,2-migration of the electron-withdrawing group arises from both the suppression of molecular motion and desolvation effects on the alkylated hydrophobic vitamin B₁₂ in HSA.