Akifumi Ikehata - Academia.edu (original) (raw)

Papers by Akifumi Ikehata

Nanoplasmonics - From Fundamentals to Applications, Proceedings of the 2nd International Nanophotonics Symposium Handai

This chapter discusses the novel surface-enhanced Raman scattering (SERS) mechanism that has been... more This chapter discusses the novel surface-enhanced Raman scattering (SERS) mechanism that has been recently proposed. The main point of this chapter lies in the description about new findings on the strong optical correlations among the localized surface plasmon (LSP) resonance, SERS, and the continuum. It is found that (1) the continuum has clear a luminescence band structure; (2) the polarization-angle dependences of the LSP resonance, SERS and luminescence are the same as each other; (3) the changes in the band energy positions of the LSP resonance induce the same band changes in the luminescence; and (4) the LSP resonance having a higher quality factor yields stronger intensities of both SERS and luminescence. By combination of these new findings, one could succeed in the direct demonstration of the SERS mechanism: SERS is computed tomography (CT) resonance Raman scattering coupling to radiative decay of the LSP. The chapter demonstrates the mechanism of both the luminescence band variations and the temporal changes in the luminescence, LSP resonance, and SERS for isolated Ag nano-aggregates during the SERS active-to-inactive processes.

Nondestructive measurement of sugar content (Brix or soluble solids content) of fruit is known as... more Nondestructive measurement of sugar content (Brix or soluble solids content) of fruit is known as a widely-spread near-infrared (NIR) application. However, the mechanism of the prediction model is not necessarily understood (black box) because of the deficient band assignment. To reveal the molecules contributing the NIR prediction model, we are working with NMR based metabolomics. Metabolomics is an authorized comprehensive study of metabolites (small organic molecules) based on quantitative measurement of the dynamic multiparametric metabolic response of living systems. For this purpose, chromatographymass spectrometry and NMR spectroscopy are used as the primary techniques. High separation performance and well assigned spectra of these techniques are helpful to understand the contribution of metabolites in the NIR prediction model. However, it is also known that some important NIR wavelengths are embedded in absorption bands of water and they are not assigned to absorptions of an...

npj Microgravity, 2021

To elucidate a mechanism for enhancing mung bean seedlings’ growth under microgravity conditions,... more To elucidate a mechanism for enhancing mung bean seedlings’ growth under microgravity conditions, we measured growth, gene expression, and enzyme activity under clinorotation (20 rpm), and compared data obtained to those grown under normal gravity conditions (control). An increase in fresh weight, water content, and lengths were observed in the clinostat seedlings, compared to those of the control seedlings. Real-time PCR showed that aquaporin expression and the amylase gene were upregulated under clinorotation. Additionally, seedlings under clinorotation exhibited a significantly higher amylase activity. Near-infrared image showed that there was no restriction of water evaporation from the seedlings under clinorotation. Therefore, these results indicate that simulated microgravity could induce water uptake, resulting in enhanced amylase activity and seedling growth. Upregulated aquaporin expression could be the first trigger for enhanced growth under clinorotation. We speculated th...

Heliyon, 2018

Evaluating the maturity of peach fruit is desirable during both the preharvest and postharvest pe... more Evaluating the maturity of peach fruit is desirable during both the preharvest and postharvest periods, and flesh firmness (FF) is a representative maturity index. Although a non-destructive FF measurement technique using visible (VIS) and near-infrared (NIR) spectroscopy has been developed, the principle has been unclear. This study was conducted to examine the structure of the FF prediction model by comparing with that of the model for measuring water-soluble pectin (WSP) content. Those two prediction models have the same information regions related to the colors of pericarp and mesocarp (chlorophyll) and to a water band in the NIR region. Moreover, a statistical heterospectroscopy analysis between NIR and 1 H nuclear magnetic resonance (NMR) spectra suggests the possibility that absorptions of methanol and succinate as well as galacturonic acid embedded in a water band play important roles in predicting FF. This approach would enhance the reliability of nondestructive VIS-NIR prediction models in many practical situations.

Japan Journal of Food Engineering, 2019

Nippon Shokuhin Kagaku Kogaku Kaishi, 2016

Food Science and Technology Research, 2017

The severity of internal browning in apple cultivars is often evaluated subjectively, making it p... more The severity of internal browning in apple cultivars is often evaluated subjectively, making it potentially unreliable, and a method for automatic evaluation is necessary in order to process many samples efficiently. The objective of this study was to propose a model for estimating subjective browning severity ratings (SBSRs) in scanned images of sliced apples that mimics mean expert judgments. We assessed SBSRs made by three expert observers for images of sliced apples. The results indicated that the experts' evaluations of internal browning were qualitatively similar, but not quantitatively equivalent. The proposed model estimates the mean SBSRs of experts as a percentage of the browning region of the total flesh. The browning regions were qualified using CIELAB color difference from the standard color. The model estimations were consistent with increasing browning during longer storage periods.

2008 International Symposium on Semiconductor Manufacturing, 2008

Far-ultraviolet (FUV) spectroscopy combined with attenuated total reflection (ATR) is employed fo... more Far-ultraviolet (FUV) spectroscopy combined with attenuated total reflection (ATR) is employed for direct measurement of the concentrations of semiconductor wafer cleaning fluids such as SC-1 and SC-2. FUV absorption spectra of these aqueous solutions in the 170 – 200 nm region are highly sensitive to changes in both hydrogen bonding and hydration. We adopt quartz as an internal reflection element (IRE) for ATR measurement. We created calibration models for predicting both NH<inf>3</inf> and H<inf>2</inf>O<inf>2</inf> in the concentration ranges of 1 – 10 % in SC-1 using multiple linear regression (MLR). The standard deviations of the models were 0.033 % and 0.265 % for NH<inf>3</inf> and H<inf>2</inf>O<inf>2</inf>, respectively. The same procedure was repeated under the same conditions for HCl and H<inf>2</inf>O<inf>2</inf> in SC-2, yielding corresponding values of 0.018 % for HCl and 0.178 % for H<inf>2</inf>O<inf>2</inf>.

Applied Microbiology and Biotechnology, 2015

Aflatoxins (AFs) are carcinogenic and toxic secondary metabolites produced mainly by Aspergillus ... more Aflatoxins (AFs) are carcinogenic and toxic secondary metabolites produced mainly by Aspergillus flavus and Aspergillus parasiticus. To monitor and regulate the AF contamination of crops, a sensitive and precise detection method for these toxigenic fungi in environments is necessary. We herein developed a novel visual detection method, the dichlorvos-ammonia (DV-AM) method, for identifying AF-producing fungi using DV and AM vapor on agar culture plates, in which DV inhibits the esterase in AF biosynthesis, causing the accumulation of anthraquinone precursors (versiconal hemiacetal acetate and versiconol acetate) of AFs in mycelia on the agar plate, followed by a change in the color of the colonies from light yellow to brilliant purple-red by the AM vapor treatment. We also investigated the appropriate culture conditions to increase the color intensity. It should be noted that other species producing the same precursors of AFs such as Aspergillus nidulans and Aspergillus versicolor could be discriminated from the Aspergillus section Flavi based on the differences of their phenotypes. The DV-AM method was also useful for the isolation of nonaflatoxigenic fungi showing no color change, for screening microorganisms that inhibit the AF production by fungi, and for the characterization of the fungi infecting corn kernels. Thus, the DV-AM method can provide a highly sensitive and visible indicator for the detection of aflatoxigenic fungi.

American Journal of Agricultural Science and Technology, 2013

The feasibility of using a compact, economical NIR instrument to predict moisture content (MC) an... more The feasibility of using a compact, economical NIR instrument to predict moisture content (MC) and total fat content (TFC) in minced pork was demonstrated. The instrument was evaluated using two different interactance geometries of the measuring head. Results were compared with those from the NIRS6500, which is commonly used as a standard NIR research instrument. Minced pork samples were prepared from loin, ham, bacon and shank muscles. PLS calibration indicated that using spectra from the short wavelength region from 700 nm to 1050 nm provided similar results between instruments. The standard error of cross validation (SECV) for MC and TFC were 2.4 % W/W and 2.5% W/W dry weight. The ratio of the standard deviation of the reference data to the standard error of cross validation (RPD) was 3.8 for MC and 4.3 for TFC, indicating that the compact NIR instrument is suitable for screening applications. NIR instruments are routinely used in the food industry to determine quality characteristics such as MC and TFC. However, the equipment is typically expensive. This research demonstrates that compact, economical NIR instruments have the potential for alleviating the issue.

ScienceAsia

Surface-enhanced infrared absorption (SEIRA) spectra of manganese (III) tetraphenylporphine chlor... more Surface-enhanced infrared absorption (SEIRA) spectra of manganese (III) tetraphenylporphine chloride (Mn(TPP)Cl) on metal island films were measured in transmission mode. Dependences of the enhancement factor of SEIRA on both the sample quantity and the type of evaporated metal were investigated by subsequently increasing the amount of Mn(TPP)Cl on gold and silver substrates. The enhancement increases nonlinearly with the amount of sample and varies slightly with the thickness of metal islands. In particular, the SEIRA transmission method presents an anomalous spectral enhancement by a factor of 579, with substantial spectral shifts, observed only for the physisorbed Mn(TPP)Cl that remained on a 3-nm-thick gold film after immersion of the substrates into acetone. A charge-transfer (CT) interaction between the porphyrinic Mn and gold islands is therefore proposed as an additional factor in the SEIRA mechanism of the porphyrin system. The number of remaining porphyrin molecules was es...

Subsurface and Surface Sensing Technologies and Applications III, 2001

ABSTRACT

Journal of the Spectroscopical Society of Japan, 2008

Encyclopedia of Biophysics, 2013

The Journal of Physical Chemistry B, 2006

We observed a background luminescence emission that was associated with surface-enhanced resonanc... more We observed a background luminescence emission that was associated with surface-enhanced resonance Raman scattering (SERRS) of rhodamine 6G (R6G) molecules adsorbed on single Ag nanoaggregates and investigated the origin of the background luminescence. Thanks to the observation of single nanoaggregates, we clearly identified nanoaggregate-by-nanoaggregate variations in the steady-state and time-resolved background luminescence spectra of each nanoaggregate. From the variations in the steady-state spectra, two kinds of key properties were revealed. First, the background luminescence spectra were divided into four components: one fluorescence band corresponding to the monomers of R6G and three Lorentzian bands whose maxima were red-shifted from the fluorescence maximum of the monomer by several tens of nanometers. On the basis of the red-shifted luminescence maxima, and experimental and theoretical studies of background luminescence, we attributed the three background luminescences to fluorescence from aggregates (dimer and two kinds of higher-order aggregates) of R6G molecules on an Ag surface. Second, a positive correlation was observed between wavelengths of background luminescence maxima and wavelengths of plasmon resonance maxima. This positive correlation invoked the idea that the dipoles of both the background luminescence and the plasmon radiation are coupled with each other. From the key observations in the steadystate background luminescence spectra, we propose that two factors contribute to the variations in the steadystate background luminescence spectra; one is the aggregation (monomer, dimer, and two kinds of higherorder aggregates) of R6G molecules on an Ag surface, and the other is plasmon resonance maxima of single Ag nanoaggregates. Considering these two factors, we propose that the variations in the time-resolved background luminescence spectra are associated with deaggregation of R6G molecules (higher-to lowerorder aggregates) and temporal shifts in the plasmon resonance maxima of single Ag nanoaggregates.

The Journal of Physical Chemistry A, 2010

The effect of cations (Li + , Na + , K + , Rb + , and Cs +) on the first electronic transition (Ã... more The effect of cations (Li + , Na + , K + , Rb + , and Cs +) on the first electronic transition (Ã r X) of liquid water was investigated by attenuated total reflection far ultraviolet spectroscopy. To negate the effect of anions, aqueous solutions of 1 M alkali metal nitrates and bromides were compared at a temperature of 25°C. It is found that the peak energy of the Ã r X band of water, which shows a marked red shift with decreasing hydrogen-bond strength, decreases with increasing cation size. The peak energies of the Ã r X band can be approximated by a linear function of the inverse of the ionic radii of the alkali metal cations, which indicates (according to the Born equation) that the first electronic transition of water is characterized by the solvation energy of the cations.

Review of Scientific Instruments, 2012

A far-ultraviolet transient absorption spectrometer based on time-resolved attenuated total refle... more A far-ultraviolet transient absorption spectrometer based on time-resolved attenuated total reflectance (ATR) has been developed and tested for aqueous solutions of phenol and tryptophan in the region 170–185 nm. In this region, a stable tunable laser was not available, and therefore, white light from a laser-driven Xe lamp source was used. The time resolution, which was determined by the time response of a continuous light detector, was 40 ns. A new ATR cell where a sample liquid is exchanged continuously by a flow system was designed to reduce efficiently the stray light from the excitation light. We have tested the performance of the instrument by using aqueous solutions of phenol and tryptophan, whose photochemistry is already well known. Phenol and tryptophan have very strong absorptions due to a π–π* transition near 180 nm. Even for dilute solutions (10−3 mol dm−3), we could observe decreases in their concentrations due to photochemistry that occurred upon their irradiation wi...

Polymer Journal, 2001

The equilibrium volume change and the elastic modulus of poly(N-isopropylacrylamide) (PNIPA) gels... more The equilibrium volume change and the elastic modulus of poly(N-isopropylacrylamide) (PNIPA) gels containing styrene-butadiene latex were investigated. It is considered that the presence of latex particles restricts the space for polymerization and which also affects on the elastic contribution of PNIPA gels. It was found that the swelling behavior of these gels was very similar to those found in the case of dependence of cross-link density. On the other hand, tensile modulus of the gels increased drastically, although these gels seem to be swelling enough. This anomalous increment of the elasticity is assumed to depend on the way to bind two elastic components, which are the highly dense PNIPA gel phase around the latex particles and the usual PNIPA gel network. It appears that the increment of elasticity against latex concentration could be classified into two mechanisms. The first, in the low latex concentration range, the dense gel phases are dispersed apart each other, the second, in the range of high latex concentration, C ≥ 12.0 wt%, the elasticity of the gel obeyed parallel model because of the formation of macro network with dense gel phases overlapped whole volume of gels.

Nippon Shokuhin Kagaku Kogaku Kaishi, 2011

Journal of Colloid and Interface Science, 2005

Langmuir monolayers and Langmuir-Blodgett (LB) films of 5,10,15,20-tetra-(p-chlorophenyl) terbium... more Langmuir monolayers and Langmuir-Blodgett (LB) films of 5,10,15,20-tetra-(p-chlorophenyl) terbium/gadolinium porphyrin hydroxyl compound (TbOH and GdOH) and their mixtures with stearic acid (SA) in a molar ratio of 1:1 were investigated by Brewster angle microscopy (BAM), ultraviolet-visible (UV-vis), and infrared (IR) spectroscopy and atomic force microscopy (AFM). π-A isotherms showed that well-defined Langmuir monolayers were formed at an air/water interface for the porphyrins and their mixture with SA. The BAM observations suggest that the π-π interaction between the GdOH molecules is stronger than that between the TbOH molecules. This result can be further confirmed by the AFM measurements. After the introduction of SA, the π-π interaction between the TbOH molecules is broken and thus two phases formed in the mixed LB film. However, it cannot break the stronger π-π interaction between the GdOH molecules. Therefore, no phase separation is observed in the GdOH/SA LB film. IR reflection-absorption (RA) spectra showed that the COOH groups of SA are partly converted to COO − groups, suggesting that there is an interaction between MOH and SA in the films. This interaction leads the benzene rings of TbOH to rotate toward parallel to the substrate and those of GdOH to rotate toward perpendicular to the substrate. All these results have demonstrated that the central metal ions have great effects on the organization and formation of the films.