The thermal behavior and molecular interaction of a new type of bacterial copolyester, poly-(3-hydroxybutyrate-co-3-hydroxyhexanoate), P(HB-co-HHx) (HHx ) 12 mol %), was investigated by using wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The WAXD measurements were carried out over a temperature range from 25 to 110 °C in the scattering angle range of 2θ ) 5-13°. The WAXD pattern at room temperature shows that the P(HB-co-HHx) copolymer has an orthorhombic system (R ) β ) γ ) 90°) with a ) 5.76 Å, b ) 13.20 Å, and c ) 5.96 Å (fiber repeat), which is identical to the crystal system of poly(3-hydroxybutyrate) (PHB) homopolymer. However, temperaturedependent variations in the lattice parameters, a and b, of P(HB-co-HHx) are quite different from those of PHB. Only the a lattice parameter increases with temperature, while the b lattice parameter changes very little in the case of crystalline P(HB-co-HHx). It seems that the intermolecular and intramolecular interactions between the CdO group and the CH 3 group decrease along the a axis of crystalline P(HBco-HHx) with temperature. The (110) peak area of P(HB-co-HHx) starts decreasing from around 50 °C while that of PHB changes little at least until 140 °C, indicating that the crystallinity of PHB remains almost unchanged until 140 °C, but that of P(HB-co-HHx) decreases gradually from fairly low temperature (∼50 °C). The DSC measurement of the chloroform solution cast P(HB-co-HHx) shows a recrystallization peak around 51 °C. The (110) peak area of WAXD pattern of the chloroform solution cast P(HB-co-HHx) shows a maximum value at around 54 °C. The maximum of the (110) peak area demonstrates the recrystallization process of P(HB-co-HHx). The result is in a good agreement with the result of the DSC measurement.

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.

Time-resolved surface enhanced infrared absorption (SEIRA) spectroscopy is employed to analyse the dynamics of the protein structural changes coupled to the electron transfer process of immobilised cytochrome c (Cyt-c). Upon electrostatic binding of Cyt-c to Au electrodes coated with self-assembled monolayers (SAMs) of carboxyl-terminated thiols, cyclic voltammetric measurements demonstrate a reversible redox process with a redox potential that is similar to that of Cyt-c in solution, and a non-exponential distance-dependence of the electron transfer rate as observed previously (D. H. Murgida and P. Hildebrandt, Chem. Soc. Rev. 2008, 37, 937). On the basis of characteristic redox-state-sensitive amide I bands, the protein structural changes triggered by the electron transfer are monitored by rapid scan and step scan SEIRA spectroscopy in combination with the potential jump technique. Whereas the temporal evolution of the conjugate bands at 1693 and 1673 cm(-1) displays the same rate constants as electron transfer, the time-dependent changes of the 1660-cm(-1) band are slower by about a factor of 2. The study demonstrates that time-resolved SEIRA spectroscopy provides further information about the dynamics and mechanism of interfacial processes of redox proteins, thereby complementing the results obtained from other surface-sensitive techniques. In comparison with previous surface enhanced resonance Raman spectroscopic findings, the present results are discussed in terms of the local electric field strengths at the Au/SAM/Cyt-c interface.

ABSTRACT. 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.KEY WORDS: acute toxicity, colloidal silver nanoparticles, dermal, eye, oral.J. Vet. Med. Sci. 73(11): 1417-1423, 2011 Engineered nanoparticles (NP) are defined as materials produced within the nanoscale range of 1-100 nm in length or diameter that exhibit unique novel properties of the structural integrity as well as physical and chemical properties [26]. Over the past few decades, nanomaterials have had a great impact and gained enormous attention in science, technology and business because of their potential for achieving specific processes and selectivity. Although the applications and benefits of these engineered nanomaterials are extensively and currently being widely used in modern technology and many commercial and medical sectors, there is still limited information concerning human health and environmental impacts. Several studies expected that nanoparticles could lead to unexpected health or environmental hazards because of their unique properties such as extremely high surface area and increased reactivity [7].Silver nanoparticles (AgNPs), one of the most commonly used metal-nanoparticles, have been known to have a wide range of applications including solar energy absorption coatings, chemical catalysts and especially antimicrobial agents. AgNPs have potentials for inhibitory and bactericidal effects as well as retarding the growth of mold, harmful spores and germs [5]. Compared to bulk silver metal, AgNPs are expected to have higher antimicrobial activity...

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.

A novel approach for the synthesis of colloidal silver nanoprisms (AgNPrs) with controllable localized surface plasmon resonance (LSPR) via a chemical shape transformation of silver nanospheres (AgNSs) is presented. The shape conversion is carried out by feeding hydrogen peroxide (H 2 O 2 ) solution into a starchstabilized AgNS colloid under ambient conditions. Oxidative dissolution and the mild reducing action of H 2 O 2 under alkaline conditions serve as the principal reactions for the shape transformation process. After addition of H 2 O 2 , the instantaneous shape transformation events can be visualized by the naked eye through the color change of the colloid. Initial concentration of AgNSs, molar ratio of H 2 O 2 : AgNSs, H 2 O 2 injection rate, and mixing efficiency are the key parameters for controlling the LSPR wavelengths of AgNPrs as the in-plane dipole plasmon resonance can be selectively tuned across visible and near infrared regions (i.e., 460-850 nm). The obtained AgNPrs exhibited mixed geometries e.g. hexagonal, truncated triangular, rounded-tip triangular prisms, and circular disks with average bisector lengths of 30 to 120 nm and the thickness of 10 to 20 nm. A colloid of highly concentrated AgNPrs having a final concentration up to 11 mM can be produced within 10 min.

A nanoscale pH-profile on a 4×4 µm 2 area of NH 2 -anchored glass slide in an aqueous solution is constructed using chemically modified tip-enhanced Raman scattering (TERS). Para-mercaptobenzoic acid (pMBA) and para-aminothiophenol (pATP) are bonded to the tip surface. A pH change can be detected from a peak at 1422 cm -1 due to the -COOstretching vibration from pMBA and that at 1442 cm -1 due to the N=N stretching vibration arising from the formation of 4,4′-dimercaptoazobenzene (DMAB) on the pATP-modified tip.The pMBA-and pATP-modified tip can be used to determine pH in the range of 7-9 and 1-2, respectively. The spatial resolution to differentiate pH of two areas can be considered as ~400 nm. The measured pH becomes the pH of the bulk solution when the tip is far by ~200 nm from the surface. This technique suggests a possibility for the pH sensing in wet biological samples.TERS tips could also be chemically modified with other molecules to determine other properties in a solution.

In this study, a ‘green chemistry’ approach was introduced to synthesize silk sericin (SS)-capped silver nanoparticles (AgNPs) under an alkaline condition (pH 11) using SS as a reducing and stabilizing agent instead of toxic chemicals. The SS-capped AgNPs were successfully synthesized at various concentrations of SS and AgNO3, but the yields were different. A higher yield of SS-capped AgNPs was obtained when the concentrations of SS and AgNO3 were increased. The SS-capped AgNPs showed a round shape and uniform size with diameter at around 48 to 117 nm. The Fourier transform infrared (FT-IR) spectroscopy result proved that the carboxylate groups obtained from alkaline degradation of SS would be a reducing agent for the generation of AgNPs while COO− and NH2 + groups stabilized the AgNPs and prevented their precipitation or aggregation. Furthermore, the SS-capped AgNPs showed potent anti-bacterial activity against various gram-positive bacteria (minimal inhibitory concentration (MIC) 0.008 mM) and gram-negative bacteria (MIC ranging from 0.001 to 0.004 mM). Therefore, the SS-capped AgNPs would be a safe candidate for anti-bacterial applications.