Three-dimensional nanostructure analysis of non-stained Nafion in fuel cell electrode by combined ADF-STEM tomography.

The polymer electrolyte fuel cell (PEFC) is one of the strongest candidates for a next-generation power source for vehicles which do not emit carbon dioxide gas (CO2) as exhaust gas. The key factor in PEFCs is the nano-scaled electrochemical reactions that take place on the catalyst material and an ionomer supported by a carbon support. However, because the nano-scaled morphological features of the key materials in the catalyst compound cannot be observed clearly by transmission electron microscopy, improvement of PEFC performance had been approached by an imaginal schematic diagram based on an electrochemical analysis. In this study, we revealed the nano-scaled morphological features of the PEFC electrode in three dimensions and performed a quantitative analysis of the nanostructure by the newly-developed "Combined ADF-STEM tomography technique." This method combines information from plural ADF detectors with different electron collection angles and can emphasize the difference of the electron scattering intensity between the ionomer and carbon in the cross-sectional image of the reconstructed three-dimensional data. Therefore, this segmentation method utilizing image contrast does not require a high electron beam current like that used in EDX analysis, and thus is suitable for electron beam damage-sensitive materials. By eliminating the process of manually determining the thresholds for obtaining classified component data from grayscale data, the obtained 3D structures have sufficient accuracy to allow quantitative analysis and specify the nano-scaled structural parameters directly related to power generation characteristics.

Delayed Increase in Near-Infrared Fluorescence in Cultured Murine Cancer Cells Labeled with Oxygen-Doped Single-Walled Carbon Nanotubes.

The labeling technique for cells with over-thousand-nanometer near-infrared (OTN-NIR) fluorescent probes has attracted much attention for in vivo deep imaging for cell tracking and cancer metastasis, because of low scattering and absorption of OTN-NIR light by biological tissues. However, the intracellular behavior following the uptake of the single-walled carbon nanotubes (SWCNTs), an OTN-NIR fluorophore, remains unknown. The aim of this study is to investigate the time-dependent change in OTN-NIR fluorescence images of cultured murine cancer cells (Colon-26) following treatment with a recently developed OTN-NIR fluorescent probe, epoxide-type oxygen-doped SWCNTs (o-SWCNTs). The o-SWCNTs were synthesized by oxygenation of SWCNTs by ozone under ultraviolet irradiation and were dispersed in an aqueous solution of N-(carbonyl-methoxypolyethyleneglycol 2000)-1,2-distearoyl- sn-glycero-3-phosphoethanolamine to prepare biocompatible o-SWCNTs (o-SWCNT-PEG). OTN-NIR fluorescent o-SWCNT-PEG showed an abnormal behavior following cellular uptake. OTN-NIR fluorescence was not observed in the cells after 24 h incubation with the o-SWCNT-PEG, but clearly increased with longer incubation time from three days after the treatment. This result was further confirmed by Raman microscopy, suggesting that OTN-NIR fluorescence intensity was associated with the cellular uptake of the o-SWCNT-PEG. These results suggest that the Colon-26 cells were successfully labeled by the o-SWCNT-PEG that emit OTN-NIR fluorescence. The o-SWCNT-PEG may aggregate in the cells over time, which could favor their internalization. This delayed concentration followed by a long retention of the o-SWCNT-PEG in cells will facilitate further biotechnological applications of the o-SWCNTs to in vivo deep OTN-NIR fluorescent imaging.

Temperature Sensing of Deep Abdominal Region in Mice by Using Over-1000 nm Near-Infrared Luminescence of Rare-Earth-Doped NaYF4 Nanothermometer.

Luminescence nanothermometry has attracted much attention as a non-contact thermal sensing technique. However, it is not widely explored for in vivo applications owing to the low transparency of tissues for the light to be used. In this study, we performed biological temperature sensing in deep tissues using ß-NaYF4 nanoparticles co-doped with Yb3+, Ho3+, and Er3+ (NaYF4: Yb3+, Ho3+, Er3+ NPs), which displayed two emission peaks at 1150 nm (Ho3+) and 1550 nm (Er3+) in the >1000 nm near-infrared wavelength region, where the scattering and absorption of light by biological tissues are at the minimum. The change in the luminescence intensity ratio of the emission peaks of Ho3+ and Er3+ (IHo/IEr) in the NaYF4: Yb3+, Ho3+, Er3+ nanothermometer differs corresponding to the thickness of the tissue. Therefore, the relationship between IHo/IEr ratio and temperature needs to be calibrated by the depth of the nanothermometer. The temperature-dependent change in the IHo/IEr was evident at the peritoneal cavity level, which is deeper than the subcutaneous tissue level. The designed experimental system for temperature imaging will open the window to novel luminescent nanothermometers for in vivo deep tissue temperature sensing.

In situ Measurement of the pH-dependent Transmission Infrared Spectra of Aqueous Lactic Acid Solutions.

The transmission infrared absorption spectra of an aqueous lactic acid solution was measured over a pH range of 2.66 - 1.59 using a cell with an optical path length of 12 µm. Absorption peaks were then identified by density functional theory (DFT) calculations. The observed pH-dependent changes in the absorbance spectra were consistent with the properties of the assigned functional groups. We therefore believe that the present method can be applied to the contactless and non-invasive quantitative evaluation of pH values in aqueous systems, such as bioprocesses and bioimaging.

Fabrication of dense two-dimensional assemblies over vast areas comprising gold(core)-silver(shell) nanoparticles and their surface-enhanced Raman scattering properties.

Fabrication of dense two-dimensional assemblies consisting of gold(core)-silver(shell) nanoparticles and the resulting peculiar surface-enhanced Raman scattering (SERS) activity are reported. The assemblies were prepared via assembly at air-toluene interfaces by drop-casting toluene solutions containing the nanoparticles protected with octadecylamine molecules onto glass plates. This simple process, which does not require special apparatus or significant fabrication time, leads to uniform assemblies over vast areas (~34 cm(2)). In the SERS measurements, the high spatial reproducibility of the SERS signals from p-aminothiophenol adsorbed on the assemblies over vast areas demonstrates that this method is useful for the quantitative investigation of SERS mechanisms. Under 532 nm laser excitation, the difference in the enhancement factors of the SERS signals at the a1 mode between assemblies consisting of gold, silver, and core-shell nanoparticles can be explained by the degree of overlap of the excitation wavelength with their plasmon coupling modes. In contrast, under 785 nm excitation, even though the plasmon band of the core-shell nanoparticle assemblies does not significantly overlap with the excitation wavelength as compared with that of gold nanoparticle assemblies, the enhancement factor from the core-shell nanoparticle assemblies was stronger than those from the gold nanoparticle assemblies. Therefore, we have demonstrated that the gold(core)-silver(shell) nanoparticle assemblies are excellent SERS active materials, which have strong electromagnetic mechanism (EM) as well as chemical mechanism (CM) effects due to the silver shells.