Polydopamine-Coated Solid Silica Nanoparticles Encapsulating IR-783 Dyes: Synthesis and NIR Fluorescent Cell Imaging.

We report a simple and efficient synthetic method for polydopamine (PDA)-coated solid silica nanoparticles (s-SiO2@PDA NPs) encapsulating anionic near-infrared (NIR) fluorescent dyes through physical adsorption. Despite the use of anionic NIR fluorescent dyes indocyanine green (ICG) and 2-[2-[2-chloro-3-[2-[1,3-dihydro-3,3-dimethyl-1-(4-sulfobutyl)-2H-indol-2-ylidene]-ethylidene]-1-cyclohexen-1-yl]-ethenyl]-3,3-dimethyl-1-(4-sulfobutyl)-3H-indolium (IR-783), they were successfully immobilized on anionic s-SiO2@PDA NP surfaces under acidic aqueous conditions. After embedding in the s-SiO2@PDA NPs, the fluorescence of ICG was almost quenched, while a diminished IR-783 fluorescence remained observable. The fluorescence intensity of IR-783 embedded in s-SiO2@PDA NPs remained almost constant over 2 weeks in a pseudobiological solution, with a slight reduction due to dye degradation and dye leakage from the s-SiO2@PDA NPs. Finally, the s-SiO2@PDA NPs encapsulating IR-783 were successfully used for NIR fluorescent imaging of African green monkey kidney cells.

Room-temperature coalescence of Pd nanoparticles with sacrificial templates and sintering agents, and their catalytic activities in the Suzuki coupling reaction.

Porous metal structures are very useful for heterogeneous catalysts in organic syntheses. This study reports a novel method to fabricate porous Pd structures by room-temperature (RT) coalescence of Pd nanoparticles (Pd NPs). First, oleylamine-capped Pd NPs were synthesized, and then Pd NP pastes were fabricated by mixing with tri-n-octylphosphine oxide as a sacrificial template. Finally, the Pd NP paste was dipped into methanol containing a sintering agent. When KOH was used as the sintering agent, porous Pd structures could be successfully obtained at RT. The catalytic activities of porous Pd structures were investigated in the Suzuki coupling reaction and they increased with the increase of the KOH concentration in the sintering process. These results indicate that pre-activation of porous Pd structures by KOH increased the catalytic activities.

Synthesis of Silica Nanoparticles with Physical Encapsulation of Near-Infrared Fluorescent Dyes and Their Tannic Acid Coating.

This study reports a novel method for the synthesis of silica nanoparticles (NPs) encapsulating near-infrared (NIR) fluorescent dyes through physical adsorption. Although a NIR cationic fluorescent dye, oxazine 725 (OXA), has no chemical bonding moiety toward silica NPs such as the triethoxysilyl group, the dyes were successfully incorporated into silica NPs without denaturation under the mild reaction conditions. Next, tannic acid (TA) molecules were coated in the presence of Fe3+ on the particle surface for the functionalization of silica NPs encapsulating OXA (OXA@SiO2 NPs). The TA coating on the surface of OXA@SiO2 NPs was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy. The TA coating significantly contributed to the resistance improvement against photobleaching and leakage of the dyes in the NPs. Furthermore, the obtained TA-coated silica NPs encapsulating OXAs (OXA@SiO2@TA NPs) were used for the fluorescence imaging of African green monkey kidney (COS-7) cells, and it was shown that the fluorescence originated from OXA@SiO2@TA NPs was clearly observed in the COS-7 cells.

Effects of Polypropylene Glycol at Very Low Concentrations on Rheological Properties at the Air-Water Interface and Foam Stability of Sodium Bis(2-ethylhexyl)sulfosuccinate Aqueous Solutions.

The present study investigates the effects of very low concentrations of polypropylene glycol (PPG) on the rheological properties of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) aqueous solutions at the surface for the precise control of foam properties. Langmuir trough experiments and Brewster angle microscopy (BAM) of the AOT monolayer on the surfaces of PPG aqueous solutions indicated that a very low concentration of PPG increased the number of AOT molecules at the surface. Viscoelastic behaviors at the surface and surface tension isotherms in mixed aqueous solutions of AOT and PPG revealed that AOT interacted with PPG in the surface and bulk phase. A modified Ross-Miles method was performed to assess the foam stabilities of AOT aqueous solutions with and without PPG. The stabilization of foam by PPG was attributed to the rheological properties of AOT aqueous solutions at the surface.

Crystallite Size Increase of Silver Nanoparticles by Ligand Exchange and Subsequent Washing Process with Antisolvent.

Desorption performance of ligands from silver nanoparticles extremely affects a sintering process of nanoinks for their writing fine pattern. In this study, we investigated desorption behaviors of ligands on the surface of silver nanoparticle through ligand exchange and subsequent washing process with antisolvent. Ligand exchange reactions from oleic acid to tri-n-octylphosphine oxide (TOPO), octanoic acid (OA), and 1-dodecanethiol (DDT) were carried out on the surface of silver nanoparticle. After the washing process with methanol as an antisolvent, their crystallite sizes and the amounts of ligands existing on the particle surface were evaluated by powder X-ray diffraction and thermogravimetric analysis, respectively. In the case of ligand exchange with TOPO, the crystallite size dramatically increased and the amount of ligands existing on the particle surface significantly decreased. This result shows that TOPO is easy to desorb from the silver surface in the washing process with methanol, which resulted in the efficient coalescence of silver. In contrast, the coalescence of silver nanoparticles capped with OA and DDT was less efficient. Moreover, the effect of the antisolvent in the washing process on the coalescence of silver was demonstrated in detail.

Effect of Protective Agents on Silver Nanoparticle Preparation by Vacuum Evaporation on Running Hydrocarbon Solution.

In order to simply compare the performance of protective agents in the preparation of metal nanoparticles, a systematic investigation based on the same synthetic conditions is necessary. We successfully achieved this objective using improved vacuum evaporation on running oil substrate (VEROS) method. The efficient synthesis of nanoparticles with the improved VEROS method enabled us to characterize them by various analytical methods. In this study, five types of protective agents with different functional groups were employed to clarify their effect on the preparation of silver nanoparticles. They are sorbitan monooleate, oleylamine, oleic acid, oleyl alcohol, and methyl oleate. Particles synthesized by the improved VEROS method were evaluated by transmission electron microscope (TEM) and UV-vis spectrophotometer. These results indicate that sorbitan monooleate and oleic acid effectively protect the aggregation between particles. It is also evident from the evaluation of powdered nanoparticles isolated from the trap solution by thermogravimetric analysis (TGA) that these protective agents adsorb on the surface of the particles. On the other hand, the aggregates of silver nanoparticles were formed in the cases using oleic alcohol and methyl oleate. Silver nanoparticles were obtained in the case of oleylamine but the material efficiency of silver was extremely low. As a result, our systematic investigation using the improved VEROS method disclosed suitable protective agents in the preparation of silver nanoparticles with the physical method.

Remarkable potassium selectivity of ion sensors based on supramolecular gel membranes made from low-molecular-weight gelators without any ionophore.

Supramolecular gels formed by low-molecular-weight gelators bearing diamide groups were used as ion-sensing membranes for the first time. Even though no special ionophore was added to the membranes, excellent ion selectivities for K(+) over alkali metal ions were realized with the sensor systems.

Drastic selectivity reversal on crown-ether based ion-sensing membranes made of ordered mesoporous silica and conventional sol-gel derived one.

A crown-ether based ion sensor, in which ordered mesoporous silica was used as a membrane material, was fabricated for the first time, and drastic selectivity reversal was attained in comparison with conventional sol-gel derived membrane based on the same crown ether.

Selectivity enhancement in neutral-carrier-type ion sensors based on a liquid-crystalline polymer.

A liquid-crystalline polymer was applied to a neutral-carrier-type ion sensor as a membrane material for enhancement of ion selectivity. An ion-sensitive field-effect transistor (ISFET) based on the membranes containing the polymer showed high sensitivity and selectivity for K+ by adding a low-molecular-weight liquid crystal as the plasticizer. The ion-sensor properties of the ISFETs based on the membranes containing a liquid-crystalline polymer were similar to those of the corresponding ion-selective electrodes (ISEs) based on the same polymer. The ion sensor with a liquid-crystalline polymer was more durable than that without any liquid-crystalline polymer. The use of liquid-crystalline polymer as the membrane material improves not only the ion-sensor properties but also the durability.

Strong molecular aggregation of neutral carriers bearing perfluoroalkyl chains in liquid-crystalline ion-sensor membranes.

A liquid-crystalline benzocrown ether, 4'-[(4''-1,1,2,2-tetrahydroperfluorooctyloxy)biphenyloxycarbonyl]benzo-15-crown-5, was used as a neutral carrier of ion-selective electrodes (ISEs) to elucidate the effect of highly ordered assembling of the neutral carrier on the sensor properties through fluorophilic interactions. The properties for the membrane and the resulting ISEs based on a benzocrown ether bearing a perfluoroalkyl chain were compared with those based on the corresponding crown ether bearing an alkyl chain. Atomic force microscopy and fluorescence measurements suggested that the neutral carrier bearing a perfluoroalkyl chain formed highly aggregational states in the membranes of ISEs.

Silver-ion redox sensing based on colloid formation by gallate ester derivatives.

Plasmon absorption of silver colloid, which was formed by reduction of silver ion with compounds bearing gallate ester groups in ethanol, was observed by absorption spectroscopy. The time-dependent absorption of silver colloid was found, which shows that the silver colloid is unstable and easy to aggregate. It seemed that a calixarene derivative bearing two gallate ester groups was the most suitable for determining silver ion. In order to prevent the silver colloid aggregation, poly(N-vinylpyrrolidone) (PVP) was added into the solution at a constant time after the preparation of sample solutions. In the calibration graph, the absorbance increased with increasing silver ion concentration, especially in the concentration range of 2.00 x 10(-6) to 1.00 x 10(-5) M. It is possible to determine silver ion concentrations using this method.

Photocontrol of ion-sensor performances in neutral-carrier-type ion sensors based on liquid-crystalline membranes.

Neutral-carrier-type ion-selective electrodes based on liquid-crystalline ion-sensing membranes containing an azobenzene derivative as the photosensitive chromophore show remarkable changes in their ion selectivity on photoirradiation, which is induced by the phase transition of the membranes.

Neutral-carrier-type potassium ion-selective electrodes based on polymer-supported liquid-crystal membranes for practical use.

Polymer-supported liquid-crystal membranes have been designed for neutral-carrier-type potassium ion-selective electrodes, aiming for practical applications of high-performance liquid-crystalline membrane ion sensors. Two types of polymer-supported liquid-crystal membranes were tested for their usefulness; one is microporous poly(tetra fluoroethylene) (PTFE) membranes impregnated by thermotropic liquid-crystalline compounds, and another is poly(methyl methacrylate) (PMMA) membrane dispersing the same liquid-crystalline compounds. Both of the polymer-supported liquid-crystal membranes containing a liquid-crystalline benzo-15-crown-5 neutral carrier as well as a lipophilic anion excluder work well as ion-sensing membranes for potassium ion-selective electrodes, the ion selectivities of which can be switched by the measurement temperatures. Specifically, PTFE-impregnated liquid-crystal membranes are better than the PMMA-dispersed ones in the sensitivity and selectivity of the resulting ion electrodes. A potassium ion assay in blood sera has proved that neutral-carrier-type ion-selective electrodes based on the polymer-supported liquid-crystal membranes are reliable for practical uses.

Dependence of ion selectivity on ordered orientation of neutral carriers in ion-sensing membranes based on thermotropic liquid crystals.

Thermotropic liquid-crystalline compounds were applied as membrane materials (membrane solvent and neutral carrier) for neutral carrier-type ion sensors to investigate how the ordered arrangement of neutral carriers affects the property of the resulting ion sensors. Nematic, smectic, and cholesteric liquid-crystalline compounds were used as the membrane solvents and crown ether derivatives with a molecular structure similar to the liquid-crystalline solvent as the K+ neutral carriers. Polarized IR spectroscopy and X-ray diffraction experiments confirmed that the highly ordered arrangement of membrane components was retained in the liquid-crystal-based ion-sensing membranes containing a neutral carrier and a lipophilic salt. The ordered arrangement of neutral carriers in the liquid-crystalline membranes enhanced the ion selectivity significantly, probably due to the efficient cooperation of two adjacent crown ether moieties in the highly ordered and aggregated state.

Synthesis and photochromism of spirobenzopyrans and spirobenzothiapyran derivatives bearing monoazathiacrown ethers and noncyclic analogues in the presence of metal ions.

Spirobenzopyrans bearing monoazathiacrown ethers and noncyclic analogues were synthesized, and their ion-responsive photochromism depending on the dual metal ion interaction with the crown ether and the phenolate anion moieties was examined using alkali and alkaline-earth metal ions, Ag(+), Tl(+), Pb(2+), Hg(2+), and Zn(2+). The prepared spirobenzopyrans showed a selective binding ability to Mg(2+) and Ag(+) with negative and positive photochromism, respectively. Among the metal ions, only Ag(+) facilitated photoisomerization to the corresponding merocyanine form. Depending on the ring size of the monoazathiacrown ether moieties, soft metal ions such as Hg(2+) and Ag(+) showed significant shifts in the UV-vis absorption spectra, while hard metal ions such as Mg(2+), Zn(2+), and Pb(2+) did not afford any meaningful shift. This result reflects that the monoazathiacrown ether and phenolate anion moieties prefer soft and hard metal ions, respectively. Therefore, the Mg(2+) and Ag(+) selectivities are mainly derived from the phenolate anion and monoazathiacrown ether moieties, respectively. On the other hand, a spirobenzothiapyran bearing 3,9-dithia-6-monoazaundecane showed a remarkable selectivity to Ag(+).