No abstract

Raman spectroscopy is a label-free, real-time diagnostic tool that shows great promise in identifying cell differences. We have evaluated the discriminatory power of Raman spectroscopy using a unique model system consisting of two isogenic cancer cell lines derived from the MDA-MB-435 cell line. The two cell lines are equally tumorigenic in mice, but while M-4A4 gives rise to metastasis, NM-2C5 only disseminates single cells that remain dormant in distant organs. Previous comparative proteomic and transcriptomic analyses of the two cell lines have shown that they differ only in the expression level of a few proteins and genes. Raman maps were recorded of single cells after fixation and drying using 785 nm laser excitation. K-means clustering reduced the amount of data from each cell and improved the signal-to-noise ratio of cluster-averaged spectra. Spectra representing the nucleus were discarded as they showed much smaller differences between the two cell lines compared to cytoplasm spectra. Partial least squares-discriminant analysis (PLS-DA) was applied to distinguish the two cell lines. A cross-validated PLS-DA resulted in 92% correctly classified samples. Spectral differences were assigned to a higher unsaturated fatty acid content in the metastatic vs nonmetastatic cell line. Our study demonstrates the unique ability of Raman spectroscopy to distinguish minute differences at the subcellular level and yield new biological information. Our study is the first to demonstrate the association between polyunsaturated fatty acid content and metastatic ability in this unique cell model system and is in agreement with previous studies on this topic.

A new technique for fabrication of large-area self-organizing variably ordered gold nanostructures with sub-10 nm gaps on templates of hexagonally ordered porous anodic aluminum oxide is demonstrated. The size as well as the interparticle distance of the fabricated gold nanostructures are adjusted by application of various electrolytes used in anodization of the aluminum template and the thickness of gold sputter-coated on the pore layer. The fabricated substrates are characterized by SEM and optical extinction measurements in reflection. The applicability as SERS substrates is investigated by adsorption of rhodamine 6G on the nanostructures. These substrates are found to exhibit high and uniform enhancement of the Raman signal across the entire surface. The nanostructures can be utilized as low-cost SERS-active substrates that within a short time can be fabricated reproducibly in large amounts.

In this article, we demonstrate how the formation of large-area self-organizing gold nanostructures formed on porous alumina templates can be grown with interparticle gaps that can be tuned both by appropriate choice of anodization technique and by the amount of deposited gold. The gold nanostructures reported in this work are formed by sputter-coating the porous alumina templates made with a hard anodization technique in oxalic acid, and the interparticle gap size is reproducibly controlled simply by adjusting the amount of sputter-coated gold. To make a change from mild and into hard anodization regimes in oxalic acid, several stages are used in the anodization procedure, including the use of a protective porous oxide layer initially created under mild anodization conditions. This simple stepwise anodization technique, which only uses electrolyte cooling, can facilitate burn-free anodization at even higher voltages during hard anodization processing in oxalic acid. The formation of the gold nanostructures is studied with scanning electron microscopy, and the influence of the morphology on the optical properties of the nanostructures is investigated by optical reflectance spectroscopy. Tunability of the localized surface plasmon resonances is demonstrated, and it can be optimized and exploited with a special view to surface enhanced molecular sensing techniques.

In this letter, we report on the effect of oxygen partial pressure and sputtering power on amorphous DC-sputtered MoOx films. We observe abrupt changes in the optoelectronic properties of the reported films by increasing the oxygen partial pressure from 1.00 × 10−3 mbar to 1.37 × 10−3 mbar during the sputtering process. A strong impact on the electrical conductivity, varying from 1.6 × 10−5 S/cm to 3.22 S/cm, and on the absorption coefficient in the range of 0.6–3.0 eV is observed for the nearly stoichiometric MoO3.00 and for the sub-stoichiometric MoO2.57 films, respectively, without modifying significantly the microstructure of the studied films. The presence of states within the band gap due to the lack of oxygen is the most probable mechanism for generating a change in electrical conductivity as well as optical absorption in DC-sputtered MoOx. The large tuning range of the optoelectronic properties in these films holds strong promise for their implementation in optoelectronic devices.

In this paper a new biological application of quantitative Raman spectroscopy is proposed. Native human plasma C-Reactive Protein (CRP) is used as a clinical biomarker of bacterial infection and tissue damage. The protein circulates in the blood and the concentration rises as inflammation occurs. For the first time the Raman spectrum of CRP in a buffered aqueous solution has been acquired using 785 nm excitation. The concentration of CRP has been measured in blood plasma, using near-infrared (NIR) Raman spectroscopy. Spectra were acquired with an in situ Inspector Raman spectrometer using 785 nm excitation. Raman spectra were collected from blood plasma drawn from 40 individuals. Quantitative predictions of CRP were made by means of Partial Least Squares (PLS) analysis and a variable selection method Interval PLS (IPLS). The similarity of the features in the PLS regression vector to that of CRP's Raman spectrum illustrates that the prediction is sensitive to the molecular information carried by the Raman scattered light. The IPLS algorithm is applied to optimize the calibration model to near clinical accuracy. This demonstrates the feasibility of using Raman spectroscopy for quantitative measurements of CRP in blood plasma.

Polarized Raman excitation spectra of various Raman lines in naphthalene and anthracene were measured with high resolution in the pre-resonance region of the lowest allowed electronic transitions. The investigated non-totally symmetric modes exhibit a prominent anti-resonance, but show no polarization dispersion, while the investigated symmetric modes show a hidden anti-resonance, i.e. an anti-resonance with no minimum in the excitation profile, but with a deviating wavenumber behaviour, followed by a strong polarization dispersion. The experimental data are interpreted in terms of a vibronic model using up to three electronic states. It is shown that only when both linearly polarized excitation spectra are measured is it possible to distinguish uniquely between the different scattering models.

The anti-resonance phenomenon in Raman scattering was studied in the preresonance region of an allowed electronic transition. It is shown that the anti-resonance in the scattering of both totally and non-totally symmetric modes can be explained in terms of an analytical model. The necessary and general conditions for obtaining an anti-resonance are derived. The importance of comparing resonance and preresonance data (showing the antiresonance e †ect), in order to obtain reliable molecular parameters from the experiments, is demonstrated. For both totally and non-totally symmetric modes it is shown that, depending on the nature and number of the electronic states that contribute to the scattering, the anti-resonance in the excitation proÐle may be followed by a dramatic dispersion in the depolarization ratio. By comparing model calculations of the depolarization ratio and the excitation proÐle with experimental data, it is shown that both of these quantities are needed in order to discriminate between di †erent theoretical models.