Comparability of Raman Spectroscopic Configurations: A Large Scale Cross-Laboratory Study

This is the final version. Available on open access from the American Chemical Society via the DOI in this recordThe variable configuration of Raman spectroscopic platforms is one of the major obstacles in establishing Raman spectroscopy as a valuable physicochemical method within real-world scenarios such as clinical diagnostics. For such real world applications like diagnostic classification, the models should ideally be usable to predict data from different setups. Whether it is done by training a rugged model with data from many setups or by a primary-replica strategy where models are developed on a 'primary' setup and the test data are generated on 'replicate' setups, this is only possible if the Raman spectra from different setups are consistent, reproducible, and comparable. However, Raman spectra can be highly sensitive to the measurement conditions, and they change from setup to setup even if the same samples are measured. Although increasingly recognized as an issue, the dependence of the Raman spectra on the instrumental configuration is far from being fully understood and great effort is needed to address the resulting spectral variations and to correct for them. To make the severity of the situation clear, we present a round robin experiment investigating the comparability of 35 Raman spectroscopic devices with different configurations in 15 institutes within seven European countries from the COST (European Cooperation in Science and Technology) action Raman4clinics. The experiment was developed in a fashion that allows various instrumental configurations ranging from highly confocal setups to fibre-optic based systems with different excitation wavelengths. We illustrate the spectral variations caused by the instrumental configurations from the perspectives of peak shifts, intensity variations, peak widths, and noise levels. We conclude this contribution with recommendations that may help to improve the inter-laboratory studies.COST (European Cooperation in Science and Technology)Portuguese Foundation for Science and TechnologyNational Research Fund of Luxembourg (FNR)China Scholarship Council (CSC)BOKU Core Facilities Multiscale ImagingDeutsche Forschungsgemeinschaft (DFG, German Research Foundation

Characterization of La-Doped TiO 2

Titanium dioxide $(TiO_2)$ nanopowders doped with 0.65, 1, 2, 3 and 4 wt.% of lanthanum ions $(La^{3+})$ were synthesized by sol-gel technology. Dependence of structural and morphological characteristics of nanopowders on $La^{3+}$ content and synthesis conditions is investigated by the Raman spectroscopy. Very intensive modes observed in the Raman spectra of all nanopowder samples are assigned to anatase phase of $TiO_2$. Additional Raman modes of extremely low intensity can be related to the presence of certain amount of highly disordered brookite phase in nanopowders. Dependence of the intensity ratio of the Raman modes which originate from anatase and brookite on doping conditions is specially analyzed. In order to estimate the variation of nanocrystallite size with dopant content, shift and asymmetrical broadening of the most intensive $E_g$ Raman mode of anatase are analyzed by phonon confinement model. The obtained results are compared with the results of X-ray diffraction spectroscopy. Special attention is dedicated to the changes in the Raman spectra of pure and La-doped $TiO_2$ nanopowders observed after high temperature treatment

Raman Scattering from ZnSe Nanolayers

A series of ZnSe single layers having thickness between 30 nm and 1 μm was deposited on c-Si and glass substrates at room substrate temperature. Thermal evaporation of ZnSe powder in high vacuum has been applied. Moreover, $SiO_x$/ZnSe periodic multilayers prepared by the same deposition technique and having ZnSe layer thickness of 2 and 4 nm have been studied. Raman spectra were measured at 295 K, using the 442 nm line of a He-Cd laser as well as different lines of the $Ar^+$ or $Ar^+//Kr^+$ lasers. The observed Raman features have been related to multiple optical phonon (1LO to 4LO) light scattering and connected with the existence of randomly oriented crystalline ZnSe grains in both ZnSe single layers and ZnSe layers of the multilayers. Relatively large line width ( ≈ 15 $cm^{-1}$) of the 1LO band has been observed and related to lattice distortion in the crystalline grains and existence of amorphous phase in the layers thinner than 100 nm. The Raman spectra measured on both ZnSe single layers and $SiO_x$/ZnSe multilayers using the 488 nm line with a gradually increased laser beam power indicate an increased crystallinity at high irradiation levels

Study of thiacyanine dye J-aggregates on single silver nanoparticle assemblies by surface enhanced Raman scattering and atomic force microscopy

Silver nanoparticles (AgNPs) capped with dye molecules and their J-aggregates often have remarkable optical properties that can lead to applications ranging from nanoscale sensing, light harvestering and bio-labelling to advanced composite materials for novel active and nonlinear optical devices. Here we investigate the J-aggregation of a thiacyanine dye (TC) on the surface of citrate capped AgNP nanoasseblies in which the average diameter of individual AgNPs is around 10 nm. Combining Raman mapping, surface-enhanced Raman spectroscopy (SERS) and atomic force microscopy (AFM), we study the influence of TC concentration on its J-aggregation on AgNPs surface. The TC – AgNPs assemblies were deposited onto freshly cleaved highly oriented pyrolytic graphite and mica surfaces. The spectral signature of citrate ions is identified by (i) the O-H band around 220 cm-1, (ii) the C-H band around 2960 cm-1 and (iii) pronounced blinking in the 1000-1800 cm-1 range. In contrast, dye molecules adsorbed on the nanoparticles are recognized by several stable Raman bands between 200 and 1600 cm-1. In situ AFM measurements indicate that the 'hot spots' are formed either on large single nanoparticles (diameter > 100 nm) or within aggregates of small nanoparticles (with diameters in the 10 - 50 nm range). However, only the latter are found to yield a citrate or TC dye SERS signal. Our study indicates that even in highly concentrated dye solutions, some citrate ions remain attached to the nanoparticles.2nd Optical Nanospectroscopy Conference : March 18-20, Dublin, Ireland, 2015.The second annual conference of COST Action MP130

Low-Frequency Raman Spectroscopy of Pure and La-Doped TiO 2

Pure and La-doped titania $(TiO_2)$ nanopowders are synthesized by sol-gel technology. The crystallite sizes determined by X-ray diffraction measurements range from 10 to 15 nm. Dependence of structural and morphological characteristics of nanopowders on synthesis conditions and $La^{3+}$ content is investigated by the Raman spectroscopy. Very intensive modes observed in the Raman spectra of all nanopowder samples are assigned to anatase phase of $TiO_2$. Additional Raman modes of extremely low intensity can be related to the presence of a small amount of brookite amorphous phase in nanopowders, which is in accordance with the results of X-ray diffraction analysis. The particle size distribution in TiO_2 nanopowders was estimated from the low frequency Raman spectra, using the fact that the phonon modes in nanosized $TiO_2$ observed in the low frequency region (ω <40 $cm^{-1}$) can be well described by the elastic continuum model, assuming that nanoparticles are of perfect spherical shape and isotropic. The nanosized particle distribution obtained by this method is used for the calculation of the frequency and shape of the most intensive $E_g$ Raman mode in anatase $TiO_2$ by the phonon confinement model. The calculated broadening of this mode, associated with the particle size distribution, coincides well with the characteristics of $E_g$ mode observed in measured Raman spectra of $TiO_2$ nanopowders. This confirms the Raman spectroscopy method as a powerful tool for determination of particle size distribution in nanosized materials

Low-Frequency Raman Spectroscopy of Pure and La-Doped TiO2TiO_2 Nanopowders Synthesized by Sol-Gel Method

Pure and La-doped titania $(TiO_2)$ nanopowders are synthesized by sol-gel technology. The crystallite sizes determined by X-ray diffraction measurements range from 10 to 15 nm. Dependence of structural and morphological characteristics of nanopowders on synthesis conditions and $La^{3+}$ content is investigated by the Raman spectroscopy. Very intensive modes observed in the Raman spectra of all nanopowder samples are assigned to anatase phase of $TiO_2$. Additional Raman modes of extremely low intensity can be related to the presence of a small amount of brookite amorphous phase in nanopowders, which is in accordance with the results of X-ray diffraction analysis. The particle size distribution in TiO_2 nanopowders was estimated from the low frequency Raman spectra, using the fact that the phonon modes in nanosized $TiO_2$ observed in the low frequency region (ω <40 $cm^{-1}$) can be well described by the elastic continuum model, assuming that nanoparticles are of perfect spherical shape and isotropic. The nanosized particle distribution obtained by this method is used for the calculation of the frequency and shape of the most intensive $E_g$ Raman mode in anatase $TiO_2$ by the phonon confinement model. The calculated broadening of this mode, associated with the particle size distribution, coincides well with the characteristics of $E_g$ mode observed in measured Raman spectra of $TiO_2$ nanopowders. This confirms the Raman spectroscopy method as a powerful tool for determination of particle size distribution in nanosized materials

Characterization of La-Doped TiO2TiO_2 Nanopowders by Raman Spectroscopy

Titanium dioxide $(TiO_2)$ nanopowders doped with 0.65, 1, 2, 3 and 4 wt.% of lanthanum ions $(La^{3+})$ were synthesized by sol-gel technology. Dependence of structural and morphological characteristics of nanopowders on $La^{3+}$ content and synthesis conditions is investigated by the Raman spectroscopy. Very intensive modes observed in the Raman spectra of all nanopowder samples are assigned to anatase phase of $TiO_2$. Additional Raman modes of extremely low intensity can be related to the presence of certain amount of highly disordered brookite phase in nanopowders. Dependence of the intensity ratio of the Raman modes which originate from anatase and brookite on doping conditions is specially analyzed. In order to estimate the variation of nanocrystallite size with dopant content, shift and asymmetrical broadening of the most intensive $E_g$ Raman mode of anatase are analyzed by phonon confinement model. The obtained results are compared with the results of X-ray diffraction spectroscopy. Special attention is dedicated to the changes in the Raman spectra of pure and La-doped $TiO_2$ nanopowders observed after high temperature treatment

Effects of cerium-dioxide nanoparticles in cervical cancer cells studied by Raman spectroscopy

Study of the interaction between nanoparticles and human cells is usually performed using customized biochemical assays that mostly offer measurements of a single quantity/property and use labels. Raman spectroscopy on the other hand offers integral insight into complex information on biomolecular composition and molecule conformation inside cells by measuring vibrational spectra from the entire cell [1]. Furthermore, it does not require dyes nor other labels and sample preparation is very simple, which reduces time consumation and possibility of cell damage during preparation. Cerium-dioxide (CeO2) nanoparticles are known for their controversial dual activity in numerous studied cancer cell lines: while protecting some cell types from oxidative damage, their cytotoxic effect in other cell lines is also reported [2, 3]. Here, effects of two types of CeO2 nanoparticles: uncoated and dextran-coated, were studied in HeLa cells, a cervical carcinoma derived cell line. Nanoparticle-treated cells were probed by routinely used biological assays for cell growth and viability, based on dying with Sulforhodamine B and Trypan Blue, respectively [3]. The tests have shown that the nanoparticles have more prominent effect on cell growth than on viability. In the light of this information Raman spectroscopy was employed in order to investigate the changes in biomolecular content of the cervical cancer cells after treatment with nanoparticles and find connection between these changes and the resulting cell status. Raman spectra of nanoparticletreated and control (untreated) cells were obtained using 532 nm laser line as an excitation probe. From each experimental group, at least 250 cell spectra were measured. Principal component analysis (PCA) covering the spectral regions (700-1800) cm-1 and (2800-3200) cm-1 has extracted the differences between vibrational spectra features of nanoparticle-treated and control cells, but also between spectra of cells treated with uncoated and coated CeO2 nanoparticles. These changes have been associated with induced alterations of prominent groups of biomolecules, DNA, lipids and proteins. Reduced total DNA content and/or breaking of O-P-O bonds leads to the decreased vibrational intensity of 785 cm-1 peak which differentiates to a large degree treated and control cells. Amide I vibrational band (1600-1670) cm-1 , characteristic for peptide bonds and modulated by proteins secondary structure, differentiates between cells treated with coated and uncoated nanoparticles. Correlation of the spectral information with the results of biological assays was performed.VII International School and Conference on Photonics : PHOTONICA2019 : Abstracts of Tutorial, Keynote, Invited Lectures, Progress Reports and Contributed Papers; August 26-30; Belgrad