Analysis of cosmetic residues on a single human hair by ATR FT-IR microspectroscopy.

In this work, ATR FT-IR spectra of single human hair and cosmetic residues on hair surface are successfully collected using a homemade dome-shaped Ge µIRE accessary installed on an infrared microscope. By collecting ATR spectra of hairs from the same person, the spectral patterns are identical and superimposed while different spectral features are observed from ATR spectra of hairs collected from different persons. The spectral differences depend on individual hair characteristics, chemical treatments, and cosmetics on hair surface. The "Contact-and-Collect" technique that transfers remarkable materials on the hair surface to the tip of the Ge µIRE enables an identification of cosmetics on a single hair. Moreover, the differences between un-split and split hairs are also studied in this report. These highly specific spectral features can be employed for unique identification or for differentiation of hairs based on the molecular structures of hairs and cosmetics on hairs.

Facile and Sensitive Detection of Carbofuran Carbamate Pesticide in Rice and Soybean Using Coupling Reaction-based Surface-Enhanced Raman Scattering.

In this research, a sensitive and selective method for detecting one of the most toxic insecticides, "carbofuran", in rice and soybean is presented. This method is based on the coupling reaction of diazonium ion combined with a surface-enhanced Raman scattering technique. Diazonium ion produced from p-aminothiophenol reacts specifically with carbofuran phenol from the hydrolysis of carbofuran. The generated azo compounds attach to the surface of silver nanoparticles via the Ag-S bond. Therefore, a strong Raman intensity can be obtained. The concentration of carbofuran can be determined by following the intensity of the peak at 1201 cm-1, attributed to the C-N stretching vibration of the azo compound. The result shows a good linear correlation (R2 = 0.9786) against carbofuran concentrations (0.1 - 5 ppm) with a detection limit of 0.452 ppm. Our proposed protocol is insignificantly influenced by various common interferences. Moreover, this method has been successfully validated to determine carbofuran concentrations in rice and soybean with detection limits of 0.446 and 0.520 ppm, respectively.

Effect of urchin-like gold nanoparticles in organic thin-film solar cells.

In this study, urchin-like gold nanoparticles (UL-AuNPs) are used in the fabrication of organic thin-film solar cells (OSCs). UL-AuNPs, which have gold nanothorns on their surface, enhance light accumulation by acting as light-trapping materials. This is due to the enhanced electric field and light scattering attributed to the nanothorns on the surface of the nanoparticles. UL-AuNPs were incorporated into a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) ( PEDOT: PSS) thin-film layer of organic thin-film solar cells (OSCs). UV-vis spectra, atomic force microscopy (AFM) images, current density versus voltage properties, and the impedance spectra of the fabricated devices were recorded at various concentrations of UL-AuNPs. We found that the efficiency of the OSCs with UL-AuNPs was not only higher than that of a reference cell without nanoparticles but also higher than that of OSCs with spherical AuNPs. Finite-difference time-domain (FDTD) simulation indicated that the electric field around the UL-AuNPs increased due to the presence of nanothorns.

Selective colors reflection from stratified aragonite calcium carbonate plates of mollusk shells.

An interaction between the incident light and the structural architecture within the shell of Asian green mussel (Perna viridis) induces observable pearlescent colors. In this paper, we investigate the influence of the structural architecture on the expressed colors. After a removal of the organic binder, small flakes from crushed shells show vivid rainbow reflection under an optical microscope. An individual flake expresses vivid color under a bright-field illumination while become transparent under a dark-field illumination. The expressed colors of the aragonite flakes are directly associated with its structural architecture. The flakes with aragonite thickness of 256, 310, and 353 nm, respectively, appear blue, green, and red under an optical microscope. The spectral simulation corroborates the experimentally observed optical effects as the flakes with thicker aragonite layers selectively reflected color with longer wavelengths. Flakes with multiple aragonite thicknesses expressed multi-color as the upper aragonite layers allow reflected colors from the lower layers to be observed.

Investigation of localized surface plasmon/grating-coupled surface plasmon enhanced photocurrent in TiO2 thin films.

We fabricated plasmonic gold nanoparticle (AuNP)-TiO2 nanocomposite films and measured the photocurrent that originates from the water-splitting reaction catalyzed by the AuNP-TiO2 nanocomposite photoelectrocatalytic (PEC) electrode. The localized surface plasmon resonance (LSPR) of the gold nanoparticles affected the generation of photocurrent by TiO2 upon illumination with visible light. Electrochemical impedance spectroscopy (EIS) revealed that the improvement in the photocurrent generation originates from an enhancement in electron-hole pair generation induced by the SPR of the plasmonic gold nanoparticles rather than the extension of the electron lifetime. Moreover, we introduced a novel method to enhance the photocurrent of TiO2 by a multiple plasmonic effect, i.e., LSPR of plasmonic gold nanoparticles and the grating-coupled propagating SP on a gold grating. We fabricated the AuNP-TiO2 nanocomposites on a gold-coated Blu-ray disc recordable (BD-R). The enhancement of the photocurrent due to the combination of LSPR and the grating-coupled SP was investigated.

Palladium nanoparticles synthesized by reducing species generated during a successive acidic/alkaline treatment of sucrose.

Uniform spherical palladium nanoparticles with an average particle size of 4.3±0.5 nm were successfully synthesized by reducing H2PdCl4 with intermediates in situ generated during a successive acidic/alkaline treatment of sucrose. A successive acidic/alkaline treatment plays an important role on converting the non-reducing sucrose into efficient reducing species containing aldehyde functionality. The Benedict's test corroborates the development and vanishing of the in situ generated reducing species upon prolonged degradation. An increase in alkalinity drastically improves the reduction efficiency. ATR FT-IR spectroscopy indicated spontaneous development of carboxylate after the alkaline treatment. Under the employed condition, small organic species with carbonyl groups (aldehyde, acid, and acid salt) were generated through the sucrose degradation before being oxidized to carbonate after an hour of the treatment. Sucrose was completely decomposed into carbonate after a 24-h successive acidic/alkaline treatment. The synthesized palladium nanoparticles express a good catalytic activity in the decolorization process of Congo red by sodium borohydride.

Chemometric analysis of spectroscopic data on shape evolution of silver nanoparticles induced by hydrogen peroxide.

The study on the shape evolution of metal nanoparticles (MNPs) is crucial to gain an understanding on controlling the shape and size of metal nanostructures. In this work, a detailed study on shape evolution of silver (Ag) nanospheres to nanoplates induced by hydrogen peroxide (H2O2) was performed. According to the growth mechanism of Ag nanoplates, the spectrophotometric method combined with chemometric analysis has potential to reveal the structural evolution process as observed by surface plasmon resonance phenomena. The extinction spectra of the evolving nanostructures were analyzed by factor analysis and error indicator functions. Five major components attributed to the different particle shapes and sizes were theoretically predicted. Furthermore, the concentration profiles and pure spectra of these components were resolved using multivariate curve resolution-alternative least squares (MCR-ALS) analysis. The evolution profiles show that the spherical Ag particles systematically evolved into plate structures of different sizes. Larger nanoplates were obtained when higher concentrations of H2O2 were employed. An evidence of nanoplate disintegration was observed when a large amount of H2O2 was employed. The predicted structural morphologies of each component given by chemometric calculation were in excellent agreement with those observed by transmission electron microscope (TEM) images.

Enhancement of the reduction efficiency of soluble starch for platinum nanoparticles synthesis.

In this work, the efficiency of soluble starch as a reducing and a stabilizing agent in the synthesis of platinum nanoparticles under acidic-alkaline treatment is systematically studied. The degraded intermediates with reducing potential (i.e., small molecules containing aldehyde and α-hydroxy ketone moieties) are concomitantly generated when the alkaline concentration is greater than 0.025 M. The in situ generated species could completely reduce platinum ions (20 mM) and sufficiently stabilize the obtained platinum nanoparticles (5 mM) of uniform particle size (2-4 nm). The reduction is efficient and rapid as a complete conversion is achieved within 5 min. In a stronger alkaline condition, the platinum nanoparticles tend to aggregate and form a bigger domain because extensive degradation generates small starch fragments with less stabilization efficiency. This observation suggests that starch is a promising green material which could be chemically treated and transformed to a powerful reducing agent and stabilizer for the synthesis of metal nanoparticles.

Micrometer-sized gold nanoplates: starch-mediated photochemical reduction synthesis and possibility of application to tip-enhanced Raman scattering (TERS).

In this report, we propose a novel starch-mediated photochemical reduction method for synthesizing micrometer-sized gold nanoplates and the possibility of using them as a tip-enhanced Raman scattering (TERS) substrate. To reduce gold ions, a starch chain firstly forms a complex with AuCl(4)(-), and the gold ion is subsequently reduced by receiving an electron from a chloride ion and generating a chloride radical when the [AuCl(4)(-)-starch] complex is irradiated by sunlight. Due to the slow reaction rate and the capability of starch as a template, gold structure can thermodynamically grow along the (111) facet which is the lowest energy facet of the gold face-centered cubic (fcc) crystal. This method can provide various shapes of gold plates such as triangle, truncated triangle, hexagon, polygon, etc. The plate size can be controlled in the range from a few micrometers to more than one hundred micrometers by increasing the acidity of solution while the plate thickness is less than 100 nm. Potential application of the gold plates as TERS substrates is demonstrated by collecting Raman signals while approaching a silver-coated tungsten tip to the surface of the micrometer-sized gold nanoplate covered by crystal violet (CV) molecules. The results show that less than one hundred CV molecules can be detected in our study.

An evaluation of acute toxicity of colloidal silver nanoparticles.

Tests for acute oral toxicity, eye irritation, corrosion and dermal toxicity of colloidal silver nanoparticles (AgNPs) were conducted in laboratory animals following OECD guidelines. Oral administration of AgNPs at a limited dose of 5,000 mg/kg produced neither mortality nor acute toxic signs throughout the observation period. Percentage of body weight gain of the mice showed no significant difference between control and treatment groups. In the hematological analysis, there was no significant difference between mice treated with AgNPs and controls. Blood chemistry analysis also showed no differences in any of the parameter examined. There was neither any gross lesion nor histopathological change observed in various organs. The results indicated that the LD(50) of colloidal AgNPs is greater than 5,000 mg/kg body weight. In acute eye irritation and corrosion study, no mortality and toxic signs were observed when various doses of colloidal AgNPs were instilled in guinea pig eyes during 72 hr observation period. However, the instillation of AgNPs at 5,000 ppm produced transient eye irritation during early 24 hr observation time. No any gross abnormality was noted in the skins of the guinea pigs exposed to various doses of colloidal AgNPs. In addition, no significant AgNPs exposure relating to dermal tissue changes was observed microscopically. In summary, these findings of all toxicity tests in this study suggest that colloidal AgNPs could be relatively safe when administered to oral, eye and skin of the animal models for short periods of time.

A novel ATR FT-IR microspectroscopy technique for surface contamination analysis without interference of the substrate.

Surface contaminants, such as powder and thin film on various solid surfaces, were analyzed by ATR FT-IR microspectroscopy. An ATR accessory consisting of a miniature-Ge IRE with contact area smaller than 50 microm, in diameter was fabricated and employed for a non-destructive characterization. The IRE was pre-aligned and fixed onto a 15x Schwarzschild-Cassegrain infrared objective. Easy maneuvering of the microscope stage enabled an accumulative collection of the contaminant at the tip of a miniature-Ge IRE, where the contaminants were analyzed under the ATR condition. By making a gentle contact between the Ge tip and selected area on the surface, any removable contaminants were transferred onto the Ge tip where its molecular information was acquired without any interference from the solid substrate. A thin organic film (i.e., mineral oil or fluorolube) was coated at the tip of the IRE in order to enhance the collecting efficiency of the removable contaminants.

Influence of the metal film thickness on the sensitivity of surface plasmon resonance biosensors.

The influence of the metal film thickness (i.e., the chromium adhesion promoting film and the gold film) on the sensitivity of surface plasmon resonance (SPR) signals (i.e., resonance angle shift and reflectance change) towards the thickness variation of the nonabsorbing dielectric film is investigated. The sensitivity of reflectance change decreases when a thick chromium film or a thin gold film is employed. Its linear range becomes narrower as the thickness of the metal films increases. The sensitivity and linear range of the resonance angle shift are not affected by the thickness variation of the metal films. The phenomena were theoretically explained based on the attenuated total reflection (ATR) generated evanescent field at the prism/metal interface and the SPR-generated evanescent field at the metal/dielectric interface.

Evanescent field in surface plasmon resonance and surface plasmon field-enhanced fluorescence spectroscopies.

The highly sensitive nature of surface plasmon resonance (SPR) spectroscopy and surface plasmon field-enhanced fluorescence spectroscopy (SPFS) are governed by the strong surface plasmon resonance-generated evanescent field at the metal/dielectric interface. The greatest evanescent field amplitude at the interface and the maximum attenuation of the reflectance are observed when a nonabsorbing dielectric is employed. An absorbing dielectric decreases the evanescent field enhancement at the interface. The SPR curve of an absorbing dielectric is characterized by a greater reflectance minimum and a broader curve, as compared to those of the nonabsorbing dielectric with the same refractive index. For a weakly absorbing dielectric, such as nanometer-thick surface-confined fluorophores, the absorption is too small to induce a significant change in the SPR curve. However, the presence of a minute amount of the fluorophore can be detected by the highly sensitive SPFS. The angle with the maximum fluorescence intensity of an SPFS curve is always smaller than the resonance angle of the corresponding SPR curve. This discrepancy is due to the differences of evanescent field distributions and their decay characteristics within the metal film and the dielectric medium. The fluorescence intensity in an SPFS curve can be expressed in terms of the evanescent field amplitude. Excellent correlations between the experimentally measured fluorescence intensities and the evanescent field amplitudes are observed.

Surface plasmon resonance spectroscopy based on evanescent field treatment.

The reflectance in a surface plasmon resonance (SPR) curve can be expressed in terms of the integration of the product between the evanescent electric field and the imaginary part of the dielectric constant of all absorbing media. The evanescent field in the metal film consists of two fields, one originating at the prism/metal interface and the other at the metal/dielectric interface. Near the resonance angle, the evanescent field strength at the metal/dielectric interface is much greater than that at the prism/metal interface. The evanescent field in dielectric medium has a single origin at the metal/dielectric interface. Due to the optical enhancement at the interface, the amplitude of the evanescent electric field in the dielectric medium is much greater than that in the metal film. This field, however, is not being utilized in conventional SPR where changes in the refractive index of the nonabsorbing dielectric media are of interest. In a system with an absorbing dielectric medium, the absorption of the medium is enhanced by the strong evanescent electric field. The evanescent field distributions in the metal film and in the dielectric medium are significantly altered by the absorbing dielectric, which results in shifting of the resonance angle, increasing of the reflectance, and broadening of the SPR curve. Since the absorption contribution from the absorbing dielectric can be separated from that of the metal film via knowledge of evanescent field distribution, an in-depth analysis of the SPR curve of an absorbing medium and its relationship with the material characteristics are possible.