| 1. |
- Lorén, Anders, 1974, et al.
(författare)
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Internal standard in surface-enhanced Raman spectroscopy
- 2004
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 76:24, s. 7391-7395
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented for the use of SAM layers as internal standards for calibration in surface-enhanced Raman spectroscopy. Three cyano-containing compounds were attached to gold colloids via a metal-sulfur bond and evaluated for spectral stability and normalization capacity. The results show that the analyte, rhodamine 6G, and the internal standard signal enhancement covaried, and it was possible to quantify the analyte with PLS. The fact that the enhancing substrate was chaotic assemblies with large variation in signal enhancement shows the versatility of this method.
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| 2. |
- Abrahamsson, Katarina, 1957, et al.
(författare)
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Air-sea exchange of halocarbons: the influence of diurnal and regional variations and distribution of pigments
- 2004
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Ingår i: Deep-Sea Research Part Ii-Topical Studies in Oceanography. - : Elsevier BV. - 0967-0645. ; 51:22-24, s. 2789-2805
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Tidskriftsartikel (refereegranskat)abstract
- Diurnal cycles of halocarbons, except methyl bromide and methyl chloride, were observed at six 24-h stations occupied in three different regions, the Summer Ice Edge, the Winter Ice Edge, and the Antarctic Polar Front, in the Atlantic sector of the Southern Ocean during a Swedish-South African expedition in 1997/1998. The diurnal cycles contained three phases; a productive phase, a phase of losses and a phase with steady state. The duration of the different phases varied for the different stations as well as for individual compounds. The measured production and losses of organo-halogens in the Antarctic Ocean based on values from each station, were in the order of a few to hundreds of Tg yr(-1). Bromochloromethane, tribromomethane, trichloroethene and diiodomethane were the four compounds found in highest concentrations throughout the investigation, and they were found to be the major contributors of organohalogens. Only the presence of the photosynthetic pigment 19'-hexanoyloxyfucoxanthin, biomarker pigment of haptophytes, could explain some of the variations in the distribution and production of halocarbons, and then only for iodinated compounds. The flux of organo-halogens from the oceans to the atmosphere was estimated in two ways, either based on calculations according to models or based on the measured concentrations. Large discrepancies were found, which could not be explained by chemical or biological degradation or adsorption to particles. This investigation, therefore, shows the need for assessing the rates of degradation and the air-sea exchange more accurately. (C) 2004 Elsevier Ltd. All rights reserved.
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| 3. |
- Abrahamsson, Katarina, 1957, et al.
(författare)
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Variations of biochemical parameters along a transect in the Southern Ocean, with special emphasis on volatile halogenated organic compounds
- 2004
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Ingår i: Deep-sea research. Part II, Topical studies in oceanography. - : Elsevier BV. - 0967-0645. ; 51:22-24, s. 2745-2756
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Tidskriftsartikel (refereegranskat)abstract
- A number of parameters of biogeochemical interest were monitored along a north-southerly transect (S 43-S 63degrees) in the Atlantic Sector of the Southern Ocean from the 8th to the 20th of December 1997. Changes in total dissolved inorganic carbon (C-T) and total alkalinity (A(T)) were mostly dependent on temperature and salinity until the ice edge was reached. After this point only a weak correlation was seen between these. Highest mean values of C-T and A(T) were observed in the Winter Ice Edge (WIE) (2195 and 2319 mumol kg(-1), respectively). Lowest mean AT (2277 mumol kg(-1)) was observed in the Sub-Antarctic Front (SAF), whereas lowest mean CT concentration (2068 mumol kg(-1)) was associated with the Sub-Tropical Front (STF). The pH in situ varied between 8.060 and 8.156 where the highest values were observed in the southern part of the Antarctic Polar Front (APF) and in the Summer Ice Edge (SIE) Region. These peaks were associated with areas of high chlorophyll a (chl a) and tribromomethane values. In the other areas the pH in situ was mainly dependent on hydrography. Bacterial abundance decreased more than one order of magnitude when going from north to south. The decrease appeared to be strongly related to water temperature and there were no elevated abundances at frontal zones. Microphytoplankton dominated in the SAF and APF, whereas the nano- and picoplankton dominated outside these regions. Volatile halogenated compounds were found to vary both with regions, and with daylight. For the iodinated compounds, the highest concentrations were found north of the STF. Brominated hydrocarbons had high concentrations in the STF, but elevated concentrations were also found in the APF and SIE regions. No obvious correlation could be found between the occurrence of individual halocarbons and chl a. On some occasions trichloroethene and tribromomethane related to the presence of nano- and microplankton, respectively.
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| 4. |
- Eliasson, Charlotte, 1973, et al.
(författare)
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Multivariate evaluation of doxorubicin surface-enhanced Raman spectra.
- 2001
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Ingår i: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy. - 1386-1425. ; 57:9, s. 1907-15
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Tidskriftsartikel (refereegranskat)abstract
- Multivariate evaluation of surface-enhanced Raman spectra of doxorubicin in plasma was performed. In a principal component analysis (PCA) all spectral features were modelled into three principal components. The major variation of the data was shown to be the variation of doxorubicin Raman signal together with the doxorubicin fluorescence, whereas the variation due to plasma was of minor importance. It was also shown that the surface-enhanced Raman scattering (SERS) measurements were independent on such factors as measurement occasion and silver colloids. The presented results show that with some improvements, quantification of doxorubicin directly in plasma could be possible.
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| 5. |
- Eliasson, Charlotte, 1973, et al.
(författare)
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Multivariate methodology for surface enhanced Raman chemical imaging of lymphocytes
- 2006
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Ingår i: Chemometrics and Intelligent Laboratory Systems. - : Elsevier BV. - 0169-7439 .- 1873-3239. ; 81:1, s. 13-20
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Tidskriftsartikel (refereegranskat)abstract
- Surface enhanced Raman spectroscopy (SERS) was used to study the uptake of rhodamine 6G in human lymphocytes. In total four Raman images of lymphocytes were used. The aim was to find a multivariate methodology capable of separating spectra with chemical information from those that mainly contained the surface enhanced background, in order to create chemical images. The standard PCA procedure was compared with PCA of standard normal variate (SNV) corrected spectra, spectra baseline corrected in the wavelet domain, and variable trimming before PCA, to isolate unique spectra. It was not straightforward to perform a standard PCA for overview, since the small background variation in many variables dominated over the Raman band variation that only occur in few variables. It was shown that wavelet filtering could remove background variations and that variable trimming followed by PCA modelling left the unique Raman spectra as outliers, which facilitated interpretation of the Raman score images.
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| 6. |
- Eliasson, Charlotte, 1973, et al.
(författare)
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Surface-enhanced Raman scattering imaging of single living lymphocytes with multivariate evaluation
- 2005
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Ingår i: Spectrochimica Acta Part A-Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425. ; 61:4, s. 755-760
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Tidskriftsartikel (refereegranskat)abstract
- This paper is aimed to show the possibility to determine individual organic compounds introduced into single living cells with surface-enhanced Raman spectroscopy (SERS). Surface enhancement was achieved with gold colloids that were allowed to diffuse into lymphocytes. An introduced analyte, rhodamine 6G, could be imaged together with for example nucleotides and amino acids of the cell. Multivariate evaluation of surface-enhanced Raman images proved to be a powerful tool for the separation of spectral information of various intracellular components. The principal component analysis (PCA) enabled identification of spectra containing different chemical information and separation of the spectral contribution of rhodamine 6G from the complex cellular matrix.
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| 7. |
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| 8. |
- Lorén, Anders, 1974, et al.
(författare)
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Feasibility of quantitative determination of doxorubicin with surface-enhanced Raman spectroscopy
- 2001
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 32:11, s. 971-974
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Tidskriftsartikel (refereegranskat)abstract
- Surface-enhanced Raman spectroscopy (SERS) was performed using excitation at 488 nm in a blood plasma-doxorubicin-silver colloid system. With a blood plasma content of 1%, a partial least-squares calibration of the doxorubicin was made in the 10-750 nM range. Predictions for a test set generated a root mean square error of prediction of 70 nM. The use of SERS and chemometrics in complex systems made it possible to use the highly informative Raman signals even at low concentrations without the need for sample pretreatment such as extraction. Copyright © 2001 John Wiley & Sons, Ltd.
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| 9. |
- Lorén, Anders, 1974
(författare)
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Quantitative Surface Enhanced Raman Spectroscopy
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surface enhanced Raman spectroscopy (SERS) is a very attractive technique for detection of various organic and inorganic molecules due to its sensitivity and selectivity. The surface enhancement is achieved when the molecules of interest are on or in the vicinity of a metal surface, usually gold and silver. This proximity can increase the Raman signal with up to 14 orders of magnitude. The aim of this thesis was to investigate SERS as a quantitative technique for determination of organic compounds in complex matrices such as different biological fluids and single living cells. Metal colloids were used for surface enhancement due to their high enhancing capacity, ease of production and high flexibility. Determination of the anti-cancer drug doxorubicin, in blood plasma, was performed using silver particles as enhancers of Raman scattering and quenchers of the fluorescent background. The spectra obtained were evaluated with multivariate statistics, principal components analysis (PCA) and partial least squares (PLS). Even if the surface enhancement was large enough to enable determinations at low concentrations, the reproducibility, due to uncontrollable variation in the enhancement was poor. To increase the reproducibility, a novel technique to normalise the intensities of the spectral bands is presented. The internal standard was organised in a self-assembled monolayer (SAM) onto the gold or silver surfaces. The collective behaviour among the enhancing colloids, such as aggregation, could thereby be corrected for, and an increase of the precision with one order of magnitude was reached. Different SAM layers were evaluated for spectral stability and signal strength. Selection criteria for such an internal standard should be spectral and chemical stability, few and selective bands and weak to moderate signal intensities.
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| 10. |
- Lorén, Anders, 1974, et al.
(författare)
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Self-assembled monolayer coating for normalization of surface enhanced Raman spectra
- 2004
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 4:2, s. 309-312
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that the use of a self-assembled monolayer, consisting of a thiol derivative of Dabcyl, can be used to normalize surface enhanced Raman signals (SERS) with respect to varying enhancement. Chaotic assemblies of gold nanoparticles exhibit large spatial variation in enhancement. Our work shows that in such a system the signals from the reporting molecules in the SAM co-vary with the signal from the analyte solution. With this knowledge, a normalization procedure was used to increase the precision of the analyte signal by 1 order of magnitude, to 8-13%, fully acceptable for quantitative work.
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