Plasmons in strongly coupled metallic nanostructures.

Nano-silver is used in an increasing number of products. Some of the applications have resulted in the concern of governments and the public, since little is known about the potential risks of nano-silver. In this review, an inventory is made to identify knowledge gaps that have to be filled before risks for both man and the environment can be assessed as reliable as for ‘non-nanosized’ chemicals. It is hypothesized that the toxic effects of nano-silver are due to a combination of the specific properties of silver nanoparticles and the generation of ions from them. The main topic for future research is validation of our ‘0-hypothesis’ that toxic effects of nano-silver are proportional to the activity of free silver ions released by the nanoparticles. Furthermore, it must be determined whether – or to what extent – nano-silver particles will enter the body. The outcomes of these tests will determine the requirements for further toxicity testing.

Nano-silver – a review of available data and knowledge gaps in human and environmental risk assessment

A review on the application of inorganic nano-structured materials in the modification of textiles: focus on anti-microbial properties

Raman spectra of biological materials are very complex, because they consist of signals from all molecules present in cells. In order to obtain chemical information from these spectra, it is necessary to know the Raman patterns of the possible components of a cell. In this paper, we present a collection of Raman spectra of biomolecules that can serve as references for the interpretation of Raman spectra of biological materials. We included the most important components present in a cell: (1) DNA and RNA bases (adenine, cytosine, guanine, thymine and uracil), (2) amino acids (glycine, L-alanine, L-valine, L-serine, L-glutamic acid, L-arginine, L-phenylalanine, L-tyrosine, L-tryptophan, L-histidine, L-proline), (3) fatty acids and fats (lauric acid, myristic acid, palmitic acid, stearic acid, 12-methyltetradecanoic acid, 13-methylmyristic acid, 14-methylpentadecanoic acid, 14-methylhexadecanoic acid, 15-methylpalmitic acid, oleic acid, vaccenic acid, glycerol, triolein, trilinolein, trilinolenin), (4) saccharides (β-D-glucose, lactose, cellulose, D-(+)-dextrose, D-(+)-trehalose, amylose, amylopectine, D-(+)-mannose, D-(+)-fucose, D-(−)-arabinose, D-(+)-xylose, D-(−)-fructose, D-(+)-galactosamine, N-acetyl-D-glucosamine, chitin), (5) primary metabolites (citric acid, succinic acid, fumarate, malic acid, pyruvate, phosphoenolpyruvate, coenzyme A, acetyl coenzyme A, acetoacetate, D-fructose-6-phosphate) and (6) others (β-carotene, ascorbic acid, riboflavin, glutathione). Examples of Raman spectra of bacteria and fungal spores are shown, together with band assignments to the reference products. Copyright © 2007 John Wiley & Sons, Ltd.

Reference database of Raman spectra of biological molecules

Surface enhanced Raman scattering (SERS) at extremely high enhancement level turns the weak inelastic scattering effect of photons on vibrational quantum states into a structurally sensitive single-molecule and nanoscale probe. The effect opens up exciting opportunities for applications of vibrational spectroscopy in biology. The concept of SERS can be extended to two-photon excitation by exploiting surface enhanced hyper-Raman scattering (SEHRS). This critical review introduces the physics behind single-molecule SERS and discusses the capabilities of the effect in bioanalytics (100 references).

SERS--a single-molecule and nanoscale tool for bioanalytics.

Treatment of bacteria with silver yields intense and highly specific surface-enhanced Raman spectroscopy (SERS) spectra from various cellular chemical components located in the vicinity of the silver colloids. In particular, we demonstrate an extreme sensitivity to flavin components associated with the cell envelope and to their state of oxidation. Different spectra, possibly associated with DNA, carboxylates, and perhaps phosphates, are obtained from the soluble interior fraction of the cell.

http://lifeserv.bgu.ac.il/wb/jeichler/media/papers/Raman.pdf

Surface-enhanced Raman spectroscopy as a tool for probing specific biochemical components in bacteria.

Silver metal induced surface enhanced Raman of bacteria

Aqueous solutions of the calcium and sodium salts of dipicolinic acid (DPA) were shown to have weak fluorescence when excited at wavelengths near 300nm, but no fluorescence was observed from DPA alone. Upon UV irradiation at 254nm the fluorescence of all three forms increases dramatically. The emission spectrum of calcium-DPA (CaDPA) has a maximum at 406nm with full width at half-maximum of 70nm. Changes in the absorption spectrum of the irradiated solution and the fact that the changes neither in absorption nor in fluorescence reverse after several days in the dark indicate that a photochemical reaction has taken place. The shapes of the emission spectra for all three DPA forms were very close to identical for excitation wavelengths in the range of 270 to 310 nm and for UV irradiation up to three hours, suggesting that one particular photoproduct dominates in producing the enhanced fluorescence. Index Headings: Dipicolinic acid; Calcium dipicolinate; Fluorescence spectroscopy; Photochemical reaction.

Fluorescence Emission Derived from Dipicolinic Acid, its Sodium, and its Calcium Salts:

We present a novel method to measure Raman spectra from whole bacteria cells by using Surface Enhanced Raman Scattering (SERS). We deposit a silver coat on Escherichia coli and Bacillus megaterium bacteria and measure strongly enhanced (greater than 400,000 fold) and highly reproducible Raman spectra. The spectra are rich but not overly congested, as the surface enhancement is selective to the precise chemical nature of the biochemical molecules, and their proximity to the silver particulate matter. The main bands we observe can be associated with peptides and polysaccharides in the cell- wall and its membrane. The spectra from E. coli (a Gram- negative bacterium) and B. megaterium (a Gram-positive bacterium) are similar in their general form, but differ in detail. The spectrum from a commercial yeast extract is vastly different. This approach can be extended to probe the internal chemical environment within bacteria and applied to the identification of micro-organisms also applied to studying other biochemical problems and phenomena, such as biomineralization, heavy metal toxicity, cell-wall structure and others.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Surface enhanced Raman spectroscopy of bacteria coated by silver

Dipicolinic acid (DPA) and the Ca2+ complex of DPA (CaDPA) are well-known and are major chemical components of bacterial spores. DPA's native fluorescence is very weak and is thought to be completely masked by the fluorescence of tryptophan when this compound is presented. Thus fluorescence related to DPA in spores is assumed by many authors to be completely absent. AWe show that the fluorescence of CaDPA is substantial for excitation between about 290 nm and 310 nm with emission peaking near 400 nm. This emission is at the long wavelength tail for emission form tryptophan. We examine whether the emission of CaDPA could contribute to the total emission spectrum when bacterial spores are present in an aerosol, for excitation wavelength in the neighborhood of 310 nm. In this report we present measurements of fluorescence excitation and emission for CaDPA and compare them with that of DPA and tryptophan.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

S. Efrima

Papers

Surface-enhanced Raman spectroscopy as a tool for probing specific biochemical components in bacteria.

Silver metal induced surface enhanced Raman of bacteria

Fluorescence Emission Derived from Dipicolinic Acid, its Sodium, and its Calcium Salts:

Surface enhanced Raman spectroscopy of bacteria coated by silver

Fluorescence of dipicolinic acid as a possible component of the observed UV emission spectra of bacterial spores