Silver Colloidal Solution Research Articles

Bacteriostasis and Skin Innoxiousness of Nanosize Silver Colloids on Textile Fabrics

This research deals with the bacteriostasis and the skin-innoxiousness of a nanosize silver colloidal solution used as an agent for the antibacterial treatment of textile fabrics. We placed nanosize silver colloidal solutions and the textile fabrics treated with the same solutions on germ-containing agar plates, respectively, and calculated the bacterial reduction after certain contact times to evaluate the antibacterial efficacy of nanosilver in colloidal solutions and textile fabrics. The antibacterial treatment of textile fabrics was easily achieved by using nanosize silver colloidal solution. The result of skin-irritation testing of a nanosilver colloidal solution showed the skin-innoxiousness of nanosilver to animals. The TEM observation of silver nanoparticles showed their shape and size distribution. The SEM image of the treated fabric indicated silver nanoparticles were well dispersed on the fabric surface.

Electrostatic-assembly metallized nanoparticles network by DNA template

Eighteen-nanometer gold and 3.5-nm silver colloidal particles closely packed by cetyltrimethylammonium bromide (CTAB) to form its positively charged shell. The DNA network was formed on a mica substrate firstly. Later, CTAB–capped gold or silver colloidal solutions were cast onto DNA network surface. It was found that the gold or silver nanoparticles metallized networks were formed owing to the electrostatic-driven template assembling of positive charge of CTAB–capped gold and silver particles on the negatively charged phosphate groups of DNA molecules by the characterizations of AFM, XPS and UV–vis. This method may provide a novel and simple way to studying nanoparticles assembly conjugating DNA molecules and offer some potential promising applications in nanocatalysis, nanoelectronics, and nanosensor on the basis of the fabricated metal nanoparticles network.

Surface‐enhanced hyper Raman scattering in silver colloidal solutions

AbstractWe report surface‐enhanced hyper Raman scattering (SEHRS) from molecules in silver colloidal solutions using high repetition rate mode‐locked picosecond excitation at 1064 nm. SEHRS was is studied under non‐resonant and resonant conditions by choosing adenine and crystal violet as test molecules. Compared with its SERS spectrum, the SEHRS spectrum of adenine displays strong ‘new’ lines, which, in agreement with theory, in most cases also show up in the infrared absorption spectrum. We also explore the capability of SEHRS for trace detection and demonstrate detection and identification of crystal violet based on its SEHRS signals down to nanomolar concentrations. Copyright © 2005 John Wiley & Sons, Ltd.

Etheric biology

Several observations made during the course of studies on stealth-adapted viruses are explainable by a pervasive, energy-rich, ether environment. Activation of an alternative cellular energy (ACE) pathway provides stealth virus damaged cells with a repair mechanism that is independent of the cellular immune response. ACE activation can also assist in the systemic healing of infections caused by conventional viruses such as Herpes simplex virus, Herpes zoster virus and human papillomavirus. ACE pigments convert conventional forms of physical energies into a biological cell healing energy, the nature of which is still uncertain. More recent studies suggest that ACE pigments may also capture etheric energy. In addition to cellular repair, ACE pigment activation can lead to the biogenesis of lipid-like chemical structures. ACE pigment and virus culture healing activities were also seen with several natural products, including a homeopathic formulation. A colloidal silver solution appeared to facilitate the transmission of ACE and to enhance its biosynthetic activity. These results open a window into a greater understanding of a fundamental force of nature of potential therapeutic importance.

Influence of the Solvent on the Surface-Enhanced Raman Spectra of Ruthenium(II) Bipyridyl Complexes

In the present work a new dye, [Ru(dcbpyH2)2(bpy-TPA2)](PF6)2, and the well-known (Bu4N)2[Ru(dcbpyH)2(NCS)2] complex were investigated. The electronic transitions of both dyes showed solvatochromic shifts due to specific interactions of the ligands with the solvent molecules. The surface-enhanced Raman (SER) spectra of the dyes dissolved in water, ethanol, and acetonitrile were measured in silver and gold colloidal solutions. The results demonstrate that the dyes were adsorbed on the metallic nanoparticles in different ways for different solvents. It was also found that in the gold colloid, the aqueous solutions of both dyes did not produce any SERS signal, whereas in ethanolic solution the SERS effect was very weak. Deprotonation, H-bonding, and donor-acceptor interactions seem to determine these different behaviors. Our results indicate the important role of the charge-transfer mechanism in SERS.

Synthesis of silver nanoparticles with flake-like shapes

Flake-like silver nanoparticles have been synthesized in large quantity by simply aging the aqueous solution of silver and urotropine in the presence of poly-(vinylpyrrolidone) (PVP). Silver nanoflakes of different shapes from circular to polygonal could be obtained in different reaction stages. PVP molecules play an important role in the anisotropic growth of silver nanoflakes. The as-synthesized silver colloidal solution remained stable for at least 1 month. Electron diffraction analysis showed that the nanoflakes are well crystallized. The UV-VIS absorption properties have also been studied.

The SERS spectrum of 1,2-diaminoanthraquinone studied on silver colloid

1,2-Diaminoanthraquinone (1,2-DAAQ) was recently shown to recognize several anions selectively. In the presence of fluoride, it gives origin to a strongly coloured solution, as a consequence of a strong absorption band at ca. 550 nm. The detailed nature of such interaction is not known, although there are evidences for the formation of a hydrogen bonding involving the anion and the amino moieties. In particular, the use of resonance Raman spectroscopy, that would be one of techniques of choice for unveiling the nature of the chromophoric moiety responsible for the coloured solutions of 1,2-DAAQ with anions, is precluded by the intense fluorescence over the visible region. In the present work the SERS technique using silver colloid was employed to overcome such difficulties, besides aiming to reveal the interaction site of 1,2-DAAQ with the surface of the silver colloidal particles. In this work it was possible to determine that the site of the 1,2-DAAQ/F − interaction is one of the amino moieties of the molecule. Such interaction involves a hydrogen bonding of moderate strength. As a consequence of such interaction, the CT transition involving the amino moiety and the π system of 1,2-DAAQ is shifted to lower energies. In the presence of 1,2-DAAQ it appears two new bands at ca. 530 and 405 nm in the silver colloidal solution, assigned to silver aggregates of different sizes. Excitation of the SERS spectra at several wavelengths show that depending on the closeness of the excitation to the CT transition of 1,2-DAAQ, the RR contribution to the SERS enhancement can be significant. The outstanding solvatochromic behavior of 1,2-DAAQ, as shown by its UV–Vis spectra in several solvents, is not reflected in the SERS spectra at two different solvents (dichloromethane and acetonitrile) that show slight differences both in frequency values and relative intensities.

Enhancement of second order hyperpolarizabilities via SERS techniques in organic materials

The usual strategy to improve molecular hyperpolarizabilities (β and γ) is the chemical functionalization of polyconjugated molecular chromophores (e.g. by increasing the number of delocalized π electrons or adding suitable electron-donating or electron-withdrawing functional groups) with the result of an increased molecular polarizability. In this work, we show that it is possible to increase the molecular polarizability in the presence of metal nanoparticles. The vibrational contribution to molecular polarizabilities has been evaluated by using experimental Raman intensities. SERS (surface enhanced Raman spectroscopy) techniques can enhance such signals and therefore improve the second-order hyperpolarizability by orders of magnitude. In particular we have measured the mean value over the entire scattering volume of the second-order hyperpolarizability for some organic molecules in a silver colloidal solution. We have observed an increase of second-order hyperpolarizability of about six orders of magnitude reaching values of about 10−28 esu. This large value of γv has been reached in spite of the fact that molecules used in the experiments were not optimized for third order nonlinear optics as shown by the low value of the second order hyperpolarizability of the isolated molecule (≤10−34 esu). Copyright © 2005 John Wiley & Sons, Ltd.

Antimicrobial effects of colloidal silver washes against Salmonella and Escherichia coli O157:H7 on fresh beef (2005)

Beef carcasses and fresh fabricated beef products potentially can be contaminated with disease causing microorganisms (pathogens) via animal dressing procedures and contamination from the plant environment or workers. Concentrated efforts have been made by the meat industry to develop and implement a wide array of strategies to control such contamination. Spraying beef flank (Rectus abdominus) samples with 32 ppm colloidal silver (ASAP®, American Biotech Labs) solution for 20 seconds reduced Salmonella and Escherichia coli O157:H7 numbers by greater than 90% after 4 hours. Inoculated samples treated with 22 ppm colloidal silver, 22 ppm colloidal silver plus 1.5% hydrogen peroxide, 10 ppm colloidal silver, or 10 ppm colloidal silver plus potassium persulfate had moderate to slight pathogen reductions compared with those treated with 32 ppm colloidal silver. Although not yet approved for use on foods (but approved for other human health applications), a colloidal silver rinse implemented in conjunction with other antimicrobial intervention technologies during the beef carcass conversion and/or fabrication processes could be an effective strategy against Salmonella and E. coli O157:H7. Further studies should be conducted on colloidal silver's antimicrobial effectiveness on lean tissues versus adipose tissue, and on sensory and functional effects on fresh meat products during storage.

New light on Ag-colloid preparation for surface-enhanced FT-Raman spectroscopy: the role of aggregation

Silver-colloid solutions have been used as the medium for surface-enhanced Raman spectroscopy (SERS) for over two decades. UV-Vis absorption is often used to determine the state of aggregation of the colloid, considered a critical parameter for a successful SERS experiment, especially when using an IR excitation source such as an Nd:YAG laser. We present results from parallel studies of silver colloid aggregation and UV-Vis absorption showing that a significant change in the aggregation state of the colloid does not necessarily translate into a better SERS substrate when using an IR excitation source. Conversely, we show that a small addition of chloride ions sufficient for inducing FT-IR SERS does not produce any detectable colloid particle aggregation. These results may give new insight into how to optimize experimental conditions for SERS when using a near-IR excitation source. Copyright © 2005 John Wiley & Sons, Ltd.

Surface-enhanced Raman scattering studies on the recognition mechanism of glutathione peroxidase mimics, bis-cyclodextrin diselenide

Surface-enhanced Raman scattering (SERS) spectroscopy has been used to explore the recognition mechanism between a selenium-containing glutathione peroxidase (GPX) mimic, 2,2′-diseleno-bis-β-cyclodextrin (2-SeCD) and two glutathione (GSH) alternatives, S-dinitrophenyl-glutathione (GSH- S-DNP) and 4,4′-bis(carboxymethyleneoxy)azobenzene (BCMAB). SERS spectra have been employed to investigate how these alternatives bind with β-CD and 2-SeCD. SERS signals of the spectra of GSH- S-DNP and BCMAB are much intense in comparison with those of theirs complexes, GSH- S-DNP/CDs and BCMAB/CDs in silver colloid solutions, which suggest that GSH- S-DNP and BCMAB are included into the CD cavity when they bind with β-CD or 2-SeCD. Weak Raman signals in the SERS spectra of the GSH- S-DNP/CDs in silver colloid solution make it difficult to investigate the recognition mechanism between CDs and GSH- S-DNP by using SERS efficiently. The bands at 1388 and 1379 cm −1 in the SERS spectra of BCMAB/CDs strongly suggest that BCMAB does not bind with β-CD or 2-SeCD via its COOH group.

Nonlinear optical properties of colloidal silver nanoparticles produced by laser ablation in liquids

The optical and nonlinear optical properties of colloidal solutions of silver obtained by laser ablation in water and ethanol are studied. It is shown that freshly prepared colloids experience a full or partial sedimentation by changing their nonlinear optical properties. Aqueous colloids undergo a partial sedimentation and their nonlinear optical absorption changes to nonlinear optical transmission. The obtained results are interpreted using the Drude model for metal particles taking the particle size into account and can be explained by the sedimentation of larger silver particles accompanied by the formation of a stable colloid containing silver nanoparticles with a tentatively silver oxide shell. The characteristic size of particles forming such a stable colloid is determined and its optical nonlinearity is estimated.

Surface-enhanced Raman scattering of a series of n-hydroxybenzoic acids ( n = P, M and O) on the silver nano-particles

Surface-enhanced Raman scattering (SERS) spectra of a series of n-hydroxybenzoic acids ( n-HBA, n = P, M and O) adsorbed on the silver nano-particles were studied, respectively, in the silver colloidal solution and on the dried silver-coated filter paper. On the same substrate, the different molecules’ SERS spectra were different, while on the different substrates the same molecules’ SERS spectra were also different. Significant changes were found in the SERS spectra of PHBA molecules adsorbed on the two substrates, and the changes found in MHBA’s spectra on two substrates were next to PHBA’s, while almost no changes were found in the spectra of OHBA molecules. Moreover, it was found, on the filter paper, that the SERS spectra of the same molecules would change with the coverage density of the silver nano-particles. The analyses showed that the origins of these changes were the different adsorption behavior of molecules adsorbed on the silver nano-particles. Because in these three molecules the relative positions of the carboxyls and hydroxyls on the benzenes are different, the adsorption behaviors of these three molecules adsorbed on the silver surfaces are also different. The experimental results suggest that the surface characteristic of the substrate and the surface configuration of the adsorbate could exert a great influence on the adsorption behavior of the adsorbates on the substrates.

Bacteriostasis of Nanosized Colloidal Silver on Polyester Nonwovens

This research deals with the antibacterial efficacy of a nanosized silver colloidal solution and its application to nonwoven fabrics. The nutrient solution including the nanosized silver colloidal solution or the nanosilver treated nonwovens are placed on germ containing agar plates and inoculated with gram-positive and gram-negative bacteria and evaluated for bacteriostasis and calculated bacterial reduction, respectively. Nanosized silver colloids and nanosilver treated nonwovens have good bacteriostasis. TEM observa tions of silver nanoparticles show their shape and size distribution. SEM images of treated fabrics indicate silver nanoparticles are well dispersed on the surfaces of specimens. Antibacterial treatment of nonwoven fabrics is easily achieved by the nanaosized silver colloidal solution.

Two-dimensional correlation spectroscopic studies on the recognition mechanism of a glutathione peroxidase mimic, bis-cyclodextrin diselenide

Ultraviolet-visible (UV-Vis) absorption, surface-enhanced Raman scattering (SERS) spectroscopy have been used to explore the recognition mechanism between a selenium-containing glutathione peroxidase (GPX) mimic, 2,2′-diseleno-bis-β-cyclodextrin (2-diSeCD) and two glutathione (GSH) alternatives, S-dinitrophenyl-glutathione (GSH- S-DNP) and 4,4′-bis(carboxymethyleneoxy)azobenzene (BCMAB). UV-Vis spectra have been applied to reveal whether these alternatives bind with 2-diSeCD or not while SERS spectra have been employed to investigate how these alternatives bind with 2-diSeCD. Two-dimensional (2D) correlation spectra analysis has been applied to the host concentration-dependent UV-Vis spectra of probe in order to clarify the different species of it before and after binding with 2-diSeCD. Results obtained from UV-Vis spectra indicate that these two molecules can be included into the cavities of 2-diSeCD upon the complexation. SERS signals of the Raman spectra of GSH- S-DNP and BCMAB are much intense in comparison with Raman spectra of theirs complexes, GSH- S-DNP/2-diSeCD and BCMAB/2-diSeCD in silver colloid solutions, suggesting again that GSH- S-DNP and BCMAB are included into the CD cavities when they bind with 2-diSeCD. Weak signal in the SERS spectrum of GSH- S-DNP/2-diSeCD complex in silver colloid solution makes it difficult to investigate the recognition mechanism between 2-diSeCD and GSH- S-DNP by using SERS spectroscopy efficiently. High signal in SERS spectrum of BCMAB/2-diSeCD complex strongly suggests that BCMAB does not bind with 2-diSeCD via its –COOH group.

Surface-enhanced Raman scattering of pyridine and p-nitrophenol studied by density functional theory calculations

A new methodology based on density functional theory (DFT) calculation to simulate surface-enhanced Raman scattering (SERS) spectra has been proposed, improving the theoretical approach by Aroca et al. This methodology aims at predicting differences in the enhancement factors among Raman bands in a SERS spectrum, thereby, helping one to interpret the SERS spectrum. A SERS spectrum of pyridine was simulated using Hartree–Fock, Møller–Plesset, and DFT methods. It has been found that the adsorption of pyridine is ascribed to a dipole–dipole interaction and that the DFT calculation is more efficient than the others from the viewpoints of the accuracy and computation time. A SERS spectrum of p-nitrophenol (PNP), which is a charge-separated molecule, was measured in a silver colloidal solution and simulated with the DFT calculation. The DFT calculation suggests that the adsorption of p-nitrophenol is attributed to a Coulombic interaction. In addition, the normal coordinate analysis of p-nitrophenol was performed on the basis of GF matrix method using the DFT force field, and the Raman bands that showed the strong SERS effect were assigned. It has been found from the assignments that an adsorption site cannot be specified when there are more than two adsorption sites even if the adsorption orientation of a molecule on a colloid is determined by surface selection rules, as defined by Moskovits et al. Consequently, the new methodology based on the DFT calculation is useful to predict the SERS effect for each band and will cut new path to apply SERS spectroscopy to quantitative microanalyses.

Surface-enhanced Raman scattering spectroscopy and density functional theory calculation studies on adsorption of o-, m-, and p-nitroaniline on silver and gold colloid

Raman and surface-enhanced Raman scattering (SERS) spectra of o-, m-, and p-nitroaniline in silver and gold colloidal solutions were measured under off-resonance conditions. The SERS effect was observed for o- and p-nitroaniline but not for m-nitroaniline. The energies, structures, electrostatic properties, vibrational frequencies, and Raman scattering intensities of the three nitroanilines were calculated by use of the density functional theory (DFT) method. The DFT calculation suggested that not only an inherent dipole moment of a molecule but also its induced dipole moment associated with the polarizability on the electric field produced by the surface plasmon contribute to the adsorption of the molecule to metal colloid. In addition, transition dipole moments and transition polarizabilities associated with the bands, which give rise to the great SERS effect for o- and p-nitroaniline, were calculated by DFT method. It was suggested from the DFT calculation as well as the SERS spectra that o-nitroaniline has different orientation from p-nitroaniline on the metal colloids, though the two nitroanilines have the same structural formula. Consequently, the substitution effect in the nitroanilines gives the different adsorption orientations on the metal colloids. The combination of SERS spectroscopy and DFT calculation is quite useful for studies of the adsorption orientation of a molecule on a metal colloid.

Antibacterial effect of nanosized silver colloidal solution on textile fabrics

This paper deals with the antibacterial efficacy of nanosized silver colloidal solution on the cellulosic and synthetic fabrics. Two kinds of Bacteria; Gram-positive and Gram-negative, were used. TEM observation of silver nanoparticles showed their shape, and size distribution. The particles were very small (2–5 nm) and had narrow distribution. SEM images of treated fabrics indicated silver nanoparticles were well dispersed on the surfaces of specimens. WAXS patterns did not show any peak of silver as the fabric had very small quantity of silver particles. However, ICP-MS informed the residual concentration of silver particles on fabrics before/after laundering. The antibacterial treatment of the textile fabrics was easily achieved by padding them with nanosized silver colloidal solution. The antibacterial efficacy of the fabrics was maintained after many times laundering.

Polarization effects in nanoaggregates of silver caused by local and nonlocal nonlinear-optical responses

A theoretical and experimental study is made into the combined manifestation of local and nonlocal optical responses in a cubic nonlinear isotropic medium such as an aggregated colloidal silver solution. The phenomenological treatment of polarization effects is performed for the general case with due regard for the frequency dispersion of both local and nonlocal nonlinearities and for the noncollinear propagation of pump and probe light waves. The inverse Faraday effect, the optical Kerr effect, and the self-rotation of the polarization ellipse in a fractal-disordered nonlinear medium are observed for the first time. The tensor components of the local and nonlocal cubic nonlinearities of colloidal silver solutions are measured for different degrees of aggregation. It is demonstrated that, as the size of silver aggregate increases, the nonlocal nonlinear response increases much more strongly than the local one. An inference is made that the mechanical motion of metal nanoparticles because of their dynamic interaction with the light wave field can contribute to the nonlinear polarization effects.

A surface-enhanced FT-Raman spectroscopic method for studying viologen dye in an electrochromic device

Surface-enhanced Raman spectroscopy (SERS) has been used to study, in situ, the molecular structure of an electrochromic device composed of a thin nanoporous, nanocrystalline film of anatase titania (TiO 2) derivatised with the viologen 1-ethyl-1′-ethylphosphonato-4,4′-bipyridyl dichloride (EPV). Silver colloid solution was added to the surface of the TiO 2 film to provide the SERS activity. Raman spectra of the EPV were obtained as the potential was varied, giving a unique insight into the molecular structural changes giving rise to the electrochromic effect. The presence of the small amount of Ag colloid did not affect the performance of the device. Incorporation of silver particles directly into the TiO 2 layer, instead of adding colloid solution to the surface, was not successful.