Edwin Ostertag

Quantitative Raman spectroscopy in turbid matter: reflection or transmission mode?

AbstractRaman intensities from reflection (XR) and transmission (XT) setups are compared by calculations based on random walk and analytical approaches with respect to sample thickness, absorption, and scattering. Experiments incorporating strongly scattering organic polymer layers and powder tablets of pharmaceutical ingredients validate the theoretical findings. For nonabsorbing layers, the Raman reflection and transmission intensities rise steadily with the layer thickness, starting for very thin layers with the ratio XT/XR = 1 and approaching for thick layers, a lower limit of XT/XR = 0.5. This result is completely different from the primary irradiation where the ratio of transmittance/reflectance decays hyperbolically with the layer thickness to zero. In absorbing materials, XR saturates at levels that depend strongly on the absorption and scattering coefficients. XT passes through a maximum and decreases then exponentially with increasing layer thickness to zero. From the calculated radial intensity spreads, it follows that quantitative transmission Raman spectroscopy requires diameters of the detected sample areas be about six times larger than the sample thickness. In stratified systems, Raman transmission allows deep probing even of small quantities in buried layers. In double layers, the information is independent from the side of the measurements. In triple layers simulating coated tablets, the information of XT originates mainly from the center of the bulk material whereas XR highlights the irradiated boundary region. However, if the stratified sample is measured in a Raman reflection setup in front of a white diffusely reflecting surface, it is possible to monitor the whole depth of a multiple scattering sample with equal statistical weight. This may be a favorable approach for inline Raman spectroscopy in process analytical technology. FigureRaman spectroscopy in turbid matter

Process analytical techniques for hot-melt extrusion and their application to amorphous solid dispersions

Newly developed active pharmaceutical ingredients (APIs) are often poorly soluble in water. As a result the bioavailability of the API in the human body is reduced. One approach to overcome this restriction is the formulation of amorphous solid dispersions (ASDs), e.g., by hot-melt extrusion (HME). Thus, the poorly soluble crystalline form of the API is transferred into a more soluble amorphous form. To reach this aim in HME, the APIs are embedded in a polymer matrix. The resulting amorphous solid dispersions may contain small amounts of residual crystallinity and have the tendency to recrystallize. For the controlled release of the API in the final drug product the amount of crystallinity has to be known. This review assesses the available analytical methods that have been recently used for the characterization of ASDs and the quantification of crystalline API content. Well-established techniques like near- and mid-infrared spectroscopy (NIR and MIR, respectively), Raman spectroscopy, and emerging ones like UV/VIS, terahertz, and ultrasonic spectroscopy are considered in detail. Furthermore, their advantages and limitations are discussed with regard to general practical applicability as process analytical technology (PAT) tools in industrial manufacturing. The review focuses on spectroscopic methods which have been proven as most suitable for in-line and on-line process analytics. Further aspects are spectroscopic techniques that have been or could be integrated into an extruder.

Multimodal spatially resolved near-field scattering and absorption spectroscopy

Far-field microscopy techniques are routinely used for the visualization of biological systems, but are limited according to Abbe`s criteria to about λ/2. The objective of this work is to integrate a solid immersion lens (SIL) as a near-field probe into a standard microscope spectrophotometer in order to perform polychromatic illumination near-field microscopy as well as near-field spectroscopy. The SIL concept can achieve a higher resolution than expected by the increase of the numerical aperture. Even with a tip diameter of 700nm and a tip point angle of 130° the lateral resolution is in the range of about 30 nm, therefore overcoming the tradeoff between the resolution and intensity restrictions in aperture limited SNOM probes. In this paper the optical setup of the system is described and some images of biological samples on a nanoscale with high contrast are presented.

Label-free multimodal microspectroscopic differentiation of glioblastoma tumor model cell lines combined with multivariate data analysis

Glioblastoma multiforme represents a highly lethal brain tumor. A tumor model has been developed based on the U-251 MG cell line from a human explant. The tumor model simulates different malignancies by controlled expression of the tumor suppressor proteins PTEN and TP53 within the cell lines derived from the wild type. The cells from each different malignant cell line are grown on slides, followed by a paraformaldehyde fixation. UV / VIS and IR spectra are recorded in the cell nuclei. For the differentiation of the cell lines a principal component analysis (PCA) is performed. The PCA demonstrates a good separation of the tumor model cell lines both with UV / VIS spectroscopy and with IR spectroscopy.

Extension of solid immersion lens technology to super-resolution Raman microscopy

Abstract Scanning Near-Field Optical Microscopy (SNOM) has developed during recent decades into a valuable tool to optically image the surface topology of materials with super-resolution. With aperture-based SNOM systems, the resolution scales with the size of the aperture, but also limits the sensitivity of the detection and thus the application for spectroscopic techniques like Raman SNOM. In this paper we report the extension of solid immersion lens (SIL) technology to Raman SNOM. The hemispherical SIL with a tip on the bottom acts as an apertureless dielectric nanoprobe for simultaneously acquiring topographic and spectroscopic information. The SIL is placed between the sample and the microscope objective of a confocal Raman microscope. The lateral resolution in the Raman mode is validated with a cross section of a semiconductor layer system and, at approximately 180 nm, is beyond the classical diffraction limit of Abbe.

Markerfreie Karyotypisierung von Chromosomen durch spektrales Imaging

Karyotyping is currently based on staining techniques. These methods lack reproducibility, are time-consuming and require complex expert knowledge. This paper introduces a new marker-free, fully automated and reliable screening procedure for chromosomes. The method is based on multimodal, spatially resolved spectroscopy combined with multivariate data analysis and can easily be integrated into a standard light microscope.

Elastic and inelastic light scattering spectroscopy and its possible use for label-free brain tumor typing

AbstractThis paper presents an approach for label-free brain tumor tissue typing. For this application, our dual modality microspectroscopy system combines inelastic Raman scattering spectroscopy and Mie elastic light scattering spectroscopy. The system enables marker-free biomedical diagnostics and records both the chemical and morphologic changes of tissues on a cellular and subcellular level. The system setup is described and the suitability for measuring morphologic features is investigated. Graphical AbstractBimodal approach for label-free brain tumor typing. Elastic and inelastic light scattering spectra are collected laterally resolved in one measurement setup. The spectra are investigated by multivariate data analysis for assigning the tissues to specific WHO grades according to their malignancy