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Dive into the research topics where Angela Walter is active.

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Featured researches published by Angela Walter.


Analytica Chimica Acta | 2011

How to pre-process Raman spectra for reliable and stable models?

Thomas Bocklitz; Angela Walter; Katharina Hartmann; Petra Rösch; Jürgen Popp

Raman spectroscopy in combination with chemometrics is gaining more and more importance for answering biological questions. This results from the fact that Raman spectroscopy is non-invasive, marker-free and water is not corrupting Raman spectra significantly. However, Raman spectra contain despite Raman fingerprint information other contributions like fluorescence background, Gaussian noise, cosmic spikes and other effects dependent on experimental parameters, which have to be removed prior to the analysis, in order to ensure that the analysis is based on the Raman measurements and not on other effects. Here we present a comprehensive study of the influence of pre-processing procedures on statistical models. We will show that a large amount of possible and physically meaningful pre-processing procedures leads to bad results. Furthermore a method based on genetic algorithms (GAs) is introduced, which chooses the spectral pre-processing according to the carried out analysis task without trying all possible pre-processing approaches (grid-search). This was demonstrated for the two most common tasks, namely for a multivariate calibration model and for two classification models. However, the presented approach can be applied in general, if there is a computational measure, which can be optimized. The suggested GA procedure results in models, which have a higher precision and are more stable against corrupting effects.


Applied Spectroscopy | 2011

From bulk to single-cell classification of the filamentous growing Streptomyces bacteria by means of Raman spectroscopy.

Angela Walter; Wilm Schumacher; Thomas Bocklitz; Martin Reinicke; Petra Rösch; Erika Kothe; Jürgen Popp

Classification of Raman spectra recorded from single cells is commonly applied to bacteria that exhibit small sizes of approximately 1 to 2 μm. Here, we study the possibility to adopt this classification approach to filamentous bacteria of the genus Streptomyces. The hyphae can reach extensive lengths of up to 35 μm, which can correspond to a single cell identified in light microscopy. The classification of Raman bulk spectra will be demonstrated. Here, ultraviolet resonance Raman (UV RR) spectroscopy is chosen to classify six Streptomyces species by the application of a tree-like classifier. For each knot of the hierarchical classifier, estimated classification accuracies of over 94% are accomplished. In contrast to the classification of bulk spectra, the classification of single-cell spectra requires a homogenous substance distribution within the cell. Consequently, the bacterial cell chemistry can be represented by one individual spectrum. This requirement is not fulfilled when different spectra are processed from different locations within the cell. Bacteria of the investigated genus Streptomyces exhibit, besides the normal bacterial spectra, lipid-rich spectra. The occurrence of lipid enrichment depends on culture age and nutrition availability. With this study, we investigate the cell substance distribution, especially of lipid-rich fractions. The classification utilizing a tree-like classifier is also applied to the Streptomyces single-cell spectra, resulting in classification accuracies between 80 and 93% for the investigated Streptomyces species.


Biomedical spectroscopy and imaging | 2011

The multifunctional application of microfluidic lab-on-a-chip surface enhanced Raman spectroscopy (LOC-SERS) within the field of bioanalytics

Anne März; Bettina Mönch; Angela Walter; Thomas Bocklitz; Wilm Schumacher; Petra Rösch; Michael Kiehntopf; Jürgen Popp

This contribution will present a variety of applications of lab-on-a-chip surface enhanced Raman spectroscopy in the field of bioanalytic. Beside the quantification and online monitoring of drugs and pharmaceuticals, determination of enzyme activity and discrimination of bacteria are successfully carried out utilizing LOC-SERS. The online-monitoring of drugs using SERS in a microfluidic device is demonstrated for nicotine. The enzyme activity of thiopurine methyltransferase (TPMT) in lysed red blood cells is determined by SERS in a lab-on-a-chip device. To analyse the activity of TPMT the metabolism of 6-mercaptopurine to 6-methylmercaptopurine is investigated. The discrimination of bacteria on strain level is carried out with different E. coli strains. For the investigations, the bacteria are busted by ultra sonic to achieve a high information output. This sample preparation provides the possibility to detect SERS spectra containing information of the bacterial cell walls as well as of the cytoplasm. This contribution demonstrates the great potential of LOC-SERS in the field of bioanalytics.


Lab on a Chip | 2011

Towards a fast, high specific and reliable discrimination of bacteria on strain level by means of SERS in a microfluidic device

Angela Walter; Anne März; Wilm Schumacher; Petra Rösch; Jürgen Popp


Analytical and Bioanalytical Chemistry | 2011

Raman spectroscopic detection of physiology changes in plasmid-bearing Escherichia coli with and without antibiotic treatment

Angela Walter; Martin Reinicke; Thomas Bocklitz; Wilm Schumacher; Petra Rösch; Erika Kothe; Jürgen Popp


Analyst | 2010

Analysis of the cytochrome distribution via linear and nonlinear Raman spectroscopy

Angela Walter; Susann Erdmann; Thomas Bocklitz; Elke-Martina Jung; Nadine Vogler; Denis Akimov; Benjamin Dietzek; Petra Rösch; Erika Kothe; Jürgen Popp


Vibrational Spectroscopy | 2006

Investigation of eucalyptus essential oil by using vibrational spectroscopy methods

Malgorzata Baranska; Hartwig Schulz; Angela Walter; Petra Rösch; Rolf Quilitzsch; Gerd Lösing; Jürgen Popp


Journal of Raman Spectroscopy | 2012

Raman spectroscopic detection of Nickel impact on single Streptomyces cells – possible bioindicators for heavy metal contamination

Angela Walter; Susanne Kuhri; Martin Reinicke; Thomas Bocklitz; Wilm Schumacher; Petra Rösch; Dirk Merten; Georg Büchel; Erika Kothe; Jürgen Popp


European Journal of Inorganic Chemistry | 2006

Zinc Thiolate Complexes [ZnLn(SR)]+ with Azamacrocyclic Ligands, Part II: Mechanism of the Reaction with CS2†

Johannes Notni; Stephan Schenk; Arne Roth; Winfried Plass; Helmar Görls; Ute Uhlemann; Angela Walter; Michael Schmitt; Jürgen Popp; Susana Chatzipapadopoulos; Thomas Emmler; Hergen Breitzke; Jörg Leppert; Gerd Buntkowsky; Kristian Kempe; Ernst Anders


Handbook of Biophotonics | 2013

Identification and Characterization of Microorganisms by Vibrational Spectroscopy

Stephan Stöckel; Angela Walter; Anja Boßecker; Susann Meisel; Valerian Ciobotaˇ; Wilm Schumacher; Petra Rösch; Jürgen Popp

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Jürgen Popp

Leibniz Institute of Photonic Technology

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Thomas Bocklitz

Leibniz Institute of Photonic Technology

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