SERS sample preparation

Introduction to microwave sample preparation, Kinston, H. M., Jassie, L. B. (eds.), ACS Professional Reference Ser., Washington, American Chemical Society, 1989... 

Solid-state 13C NMR has been shown to be a more effective analytical tool for demonstrating the formation of P-sheets in polypeptides and proteins, because the isotropic 13C NMR chemical shifts of carbon atoms in proteins are sensitive to the P-sheet s secondary structure. It is well established that SF conformations are dependent upon the species of silkworms and conditions of the sample preparation. In particular, has been reported that fibroin from Bomhyx mori adopts two dimorphic structures, silk I and silk II. The silk II form is identified by the C chemical shifts of glycine (Gly), serine (Ser), and alanine (Ala) that are indicative of P-sheets, while the silk I form produces chemical shifts that are associated with a loose helix or distorted P-tum. However, when compared with silk II, the less stable silk I shows a relatively unresolved structure, and the conformation of the soluble form of SF rapidly undergoes a transition to the insoluble silk II conformation. 

In the present work, intensity of ultramarine Raman spectra have been enhanced by the order of magnitude with solid nanosized Ag particles. Model samples have been prepared as powder mixtures of the pigment and silver particles without any compressing pretreatment. This makes the sample preparation process more easy in contrast to a more traditional way based on SERS-active film from colloidal solution of nanosized Ag particles. The technique does not require much sample material from art objects and preparation of aqueous suspension from a sample. Taking into consideration the low solubility of art pigments in water we propose the sensitive method of pigment identification in real art objeets. 

The use of solid silver nanoparticles indicates the 10-fold enhancement of Raman signals due to presence of art pigments. The enhancement of the order of magnitude is not SERS effect. However it is high enough to identify very small quantities of such specific samples as art pigment from canvas paintings. The proposed technique does not require any complex procedures for sample preparation. 

Parliment T.H. (1986) Sample preparation techniques for gas-liquid chromatographic analysis of biologically derived aromas. Am. Chem Soc. Symp. Ser. 317, 34-52. 

Iyengar GV and Sansoni B (1980) Sample preparation of biological materials for trace element analysis. In Elemental Analysis of Biological Materials, IAEA Tech Rep Ser 197, pp. 73-101, International Atomic Energy Agency, Vienna. 

The examples of SERS and SERRS measurements in the biochemical field reviewed in this article were selected to illustrate the sensitivity, molecular specificity of adsorption process, accuracy, ease of sample preparation, and significant manifold apphcations of Raman analysis by SERS and SERRS for biomolecules in the adsorbed state. 

Because of the huge signal enhancement, SERS is particularly useful for trace analysis and for in-situ investigations of various interfacial processes or of mono-layers adsorbed on metals. However, sample preparation is a rather tedious procedure. For this reason, SERS is still more an academic tool rather than a routine analytical instrument. Some applications of SERS are given in [31]. 

The resulting spectra provide molecular information and are unique to individual molecules. Sample preparation is simple and it is possible to undertake analysis in situ under water or in air or in vacuum. Since there are new selection rules and the effect is dependent on the metal used and the degree of surface roughness, there is a wealth of surface information to be obtained from SERS provided the limitations in terms of contamination and photodecomposition are remembered. The main problems are the limited number of surfaces to which the method can be applied and difficulties in interpreting the spectra. 

Bacteraemia, the presence of bacteria in the patient s blood, resulting from severe infections in the body, surgical wounds, or contaminated implanted devices may lead to a sepsis. Its onset is very fast. The current standard testing methods in hospitals are based on cultivation bacteria. However, this procedure normally takes up to 3 days. Therefore, the big advantage of SERS is the speed of identification. Effort is made to improve SERS detection of pathogens in human body fluids using portable Raman microscopes, robust metallic substrates and by a simplification of sample preparations (Premasiri et al. 2012b, 2014). 

The main features of PC are low cost, need for small sample amount, high level of resolution, ease of detection and quantitation, simplicity of apparatus and use, difficult reproducibility (because of variation in fibres) and susceptibility to chemical attack. Identification of the separated components is facilitated by the reproducible Rj values. Detection methods in PC have been reviewed [368]. Fluorescence has been used for many years as a means of locating the components of a mixture separated by PC or TLC. However, also ATR-IR and SERS are useful. Preparative PC is unsuitable for trace analysis because filter paper inevitably contains contaminants (e.g. phthalate esters, plasticisers) [369]. For that purpose an acceptable substitute is glass-fibre paper [28]. 

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