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  • 1
    Language: English
    In: Analytical chemistry, 01 April 2010, Vol.82(7), pp.2766-72
    Description: We report the development of a new technique for label-free microarray readout based on surface-enhanced Raman scattering (SERS). In doing so, an investigation on optimized SERS substrates for the application to in situ microorganism analysis by Raman microscopy was carried out. Chemically synthesized nanoparticles were successfully applied to an immunoassay for label-free detection of single microorganisms. In this way, species specific, reproducible, and strong SERS spectra were collected from different bacteria immobilized on a chip. Furthermore, quantitative analysis of the microorganisms was performed using Raman mapping. Unlike conventional SERS detection of bacteria, which requires dehydration prior to analysis, our system enables us to detect and quantify microorganisms in an aqueous environment in situ. Hence, the nondestructive analysis of living bacteria cells is possible. Moreover, the "whole-organism fingerprint" SERS spectra can be adopted for further chemical characterization of microorganisms.
    Keywords: Bacteria -- Isolation & Purification ; Spectrum Analysis, Raman -- Methods
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 2
    Language: English
    In: The Science of the Total Environment, Dec 1, 2015, Vol.535, p.122(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2014.12.026 Byline: Melanie Kuhn, Natalia P. Ivleva, Sondra Klitzke, Reinhard Niessner, Thomas Baumann Abstract: The widespread use of engineered inorganic nanoparticles (EINP) leads to a growing risk for an unintended release into the environment. Despite the good characterization of EINP in regard to their function scale and the application areas, there is still a gap of knowledge concerning their behaviour in the different environmental compartments. Due to their high surface to volume ratio, surface properties and existence or development of a coating are of high importance for their stability and transport behaviour. However, analytical methods to investigate organic coatings on nanoparticles in aqueous media are scarce. We used Raman microspectroscopy in combination with surface-enhanced Raman scattering (SERS) to investigate humic acid coatings on silver nanoparticles under environmentally relevant conditions and in real world samples. This setup is more challenging than previous mechanistic studies using SERS to characterize the humic acids in tailored settings where only one type of organic matter is present and the concentrations of the nanoparticles can be easily adjusted to the experimental needs. SERS offers the unique opportunity to work with little sample preparation directly with liquid samples, thus significantly reducing artefacts. SERS spectra of different natural organic matter brought into contact with silver nanoparticles indicate humic acid in close proximity to the nanoparticles. This coating was also present after several washing steps by centrifugation and resuspension in deionized water and after an increase in ionic strength. Article History: Received 15 October 2014; Revised 5 December 2014; Accepted 5 December 2014
    Keywords: Nanoparticles – Investigations ; Coatings – Investigations ; Humic Acids – Investigations
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Analytical chemistry, 07 July 2015, Vol.87(13), pp.6622-30
    Description: Raman microspectroscopy is a prime tool to characterize the molecular and isotopic composition of microbial cells. However, low sensitivity and long acquisition times limit a broad applicability of the method in environmental analysis. In this study, we explore the potential, the applicability, and the limitations of stable isotope Raman microspectroscopy (SIRM), resonance SIRM, and SIRM in combination with surface-enhanced Raman scattering (SERS) for the characterization of single bacterial cells. The latter two techniques have the potential to significantly increase sensitivity and decrease measurement times in SIRM, but to date, there are no (SERS-SIRM) or only a limited number (resonance SIRM) of studies in environmental microbiology. The analyzed microorganisms were grown with substrates fully labeled with the stable isotopes (13)C or (2)H and compounds with natural abundance of atomic isotopes ((12)C 98.89% or (1)H 99.9844%, designated as (12)C or (1)H, respectively). Raman bands of bacterial cell compounds in stable isotope-labeled microorganisms exhibited a characteristic red-shift in the spectra. In particular, the sharp phenylalanine band was found to be an applicable marker band for SIRM analysis of the Deltaproteobacterium strain N47 growing anaerobically on (13)C-naphthalene. The study of G. metallireducens grown with (13)C- and (2)H-acetate showed that the information on the chromophore cytochrome c obtained by resonance SIRM at 532 nm excitation wavelength can be successfully complemented by whole-organism fingerprints of bacteria cells achieved by regular SIRM after photobleaching. Furthermore, we present here for the first time the reproducible SERS analysis of microbial cells labeled with stable isotopes. Escherichia coli strain DSM 1116 cultivated with (12)C- or (13)C-glucose was used as a model organism. Silver nanoparticles synthesized in situ were applied as SERS media. We observed a reproducible red-shift of an adenine-related marker band from 733 to 720 cm(-1) in SERS spectra for (13)C-labeled cells. Additionally, Raman measurements of (12)C/(13)C-glucose and -phenylalanine mixtures were performed to elucidate the feasibility of SIRM for nondestructive quantitative and spatially resolved analysis. The performed analysis of isotopically labeled microbial cells with SERS-SIRM and resonance SIRM paves the way toward novel approaches to apply Raman microspectroscopy in environmental process studies.
    Keywords: Spectrum Analysis, Raman -- Methods
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 4
    Language: English
    In: Inorganic Chemistry, 2012-04-02, Vol.51(7), pp.4058-4065
    Description: Semitransparent dark-red or ruby-red moisture- and air-sensitive single crystals of A 10+x[Ge 9] 2[W 1-xNb xO 4] (A = K, Rb; x = 0, 0.35) were obtained by high-temperature solid-state reactions. The crystal structure of the compounds was determined by...
    Keywords: Naturvetenskap ; Kemi ; Oorganisk Kemi ; Natural Sciences ; Chemical Sciences ; Inorganic Chemistry
    ISSN: 0020-1669
    E-ISSN: 1520510X
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  • 5
    Language: English
    In: Analytical chemistry, 17 April 2012, Vol.84(8), pp.3586-92
    Description: In this study we summarize the possibilities and limitations of a conductometric measurement principle for soot sensing. The electrical conductivity of different carbon blacks (FW 200, lamp black 101, Printex 30, Printex U, Printex XE2, special black 4, and special black 6), spark discharge soot (GfG), and graphite powder was measured by a van der Pauw arrangement. Additionally the influence of inorganic admixtures on the conductivity of carbonaceous materials was proven to follow the percolation theory. Structural and oxidation characteristics obtained with Raman microspectroscopy and temperature programmed oxidation, respectively, were correlated with the electrical conductivity data. Moreover, a thermophoretic precipitator has been applied to deposit soot particles from the exhaust stream between interdigital electrodes. This combines a controlled and size independent particle collection method with the conductivity measurement principle. A test vehicle was equipped with the AVL Micro Soot Sensor (photoacoustic soot sensor) to prove the conductometric sensor principle with an independent and reliable technique. Our results demonstrate promising potential of the conductometric sensor for on-board particle diagnostic. Furthermore this sensor can be applied as a simple, rapid, and cheap analytical tool for characterization of soot structure.
    Keywords: Forensic Ballistics ; Soot -- Analysis
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 6
    Language: English
    In: Analytical chemistry, 15 February 2011, Vol.83(4), pp.1173-9
    Description: Multiwavelength Raman microspectroscopy (MWRM) analysis for characterization of soot structure and reactivity was developed. This new method is based on the dispersive character of carbon D mode in Raman spectra (i.e., red shift and increase in intensity at higher excitation wavelength, λ(0)). The approach was proven by investigating various diesel soot samples and related carbonaceous materials at different λ(0) (785, 633, 532, and 514 nm). In order to compare the behavior of the D mode for various samples and to derive a single parameter characterizing the soot structure, the difference of integrals for pairs of spectra collected at different λ(0) was calculated. MWRM analysis revealed substantial differences in the structural ordering which decreases from graphite, over Printex XE2 and various diesel soot samples, to spark discharge soot. To obtain the relation between structure and reactivity of soot, MWRM analysis was combined with temperature-programmed oxidation (TPO). TPO allowed us to characterize the oxidation behavior of soot in terms of the maximum emission (CO + CO(2)) temperature and reactivity index. The latter was calculated by introducing the reactivity limits: spark discharge soot containing a large amount of disorder represents the upper limit, whereas the lower limit is given by graphite powder with high structural order. The comparison of MWRM (viz., the observed Raman difference integrals) and TPO data revealed a linear correlation between soot structure and oxidation reactivity. Thus, we demonstrated for the first time the potential of MWRM for a robust and rapid prediction of diesel soot reactivity based on the structure-reactivity correlation.
    Keywords: Oxidation-reduction Reactions -- Research ; Raman Spectroscopy -- Methods ; Soot -- Chemical Properties ; Soot -- Identification And Classification;
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 7
    Language: English
    In: Analytical and Bioanalytical Chemistry, 2017, Vol.409(18), pp.4353-4375
    Description: Biofilms represent the predominant form of microbial life on our planet. These aggregates of microorganisms, which are embedded in a matrix formed by extracellular polymeric substances, may colonize nearly all interfaces. Detailed knowledge of microorganisms enclosed in biofilms as well as of the chemical composition, structure, and functions of the complex biofilm matrix and their changes at different stages of the biofilm formation and under various physical and chemical conditions is relevant in different fields. Important research topics include the development and improvement of antibiotics and medical devices and the optimization of biocides, antifouling strategies, and biological wastewater treatment. Raman microspectroscopy is a capable and nondestructive tool that can provide detailed two-dimensional and three-dimensional chemical information about biofilm constituents with the spatial resolution of an optical microscope and without interference from water. However, the sensitivity of Raman microspectroscopy is rather limited, which hampers the applicability of Raman microspectroscopy especially at low biomass concentrations. Fortunately, the resonance Raman effect as well as surface-enhanced Raman scattering can help to overcome this drawback. Furthermore, the combination of Raman microspectroscopy with other microscopic techniques, mass spectrometry techniques, or particularly with stable-isotope techniques can provide comprehensive information on monospecies and multispecies biofilms. Here, an overview of different Raman microspectroscopic techniques, including resonance Raman microspectroscopy and surface-enhanced Raman scattering microspectroscopy, for in situ detection, visualization, identification, and chemical characterization of biofilms is given, and the main feasibilities and limitations of these techniques in biofilm research are presented. Future possibilities of and challenges for Raman microspectroscopy alone and in combination with other analytical techniques for characterization of complex biofilm matrices are discussed in a critical review. Graphical Abstract Applicability of Raman microspectroscopy for biofilm analysis
    Keywords: Biofilm ; Microorganisms ; Extracellular polymeric substances ; Biofilm characterization ; Raman microspectroscopy ; Resonance Raman microspectroscopy ; Surface-enhanced Raman scattering ; Stable-isotope Raman microspectroscopy
    ISSN: 1618-2642
    E-ISSN: 1618-2650
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  • 8
    Language: English
    In: Analytical and Bioanalytical Chemistry, 2012, Vol.402(8), pp.2663-2667
    Description: We present an immunoassay microarray flow-through system for the surface-enhanced Raman scattering (SERS) analysis of bacteria. The system has been constructed to support and automatize the nondestructive in situ analysis of different microorganisms in aqueous environment. After the immobilization of the desired antibodies to an activated PEG-coated surface, the chip is placed into the flow cell which is then flushed with the contaminated sample. Finally, colloidal metal nanoparticles are added and the cells are detected label-free by SERS. Here, we introduce the successful imaging of single microorganisms in the flow cell as well as the quantification of microorganisms in water by SERS mapping with a linear range between 4.3 × 10 3 to 4.3 × 10 5  cells/mL. The method has potential for routine application, e.g. for drinking water control.
    Keywords: Flow cell ; SERS ; Microorganisms ; Microarray
    ISSN: 1618-2642
    E-ISSN: 1618-2650
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  • 9
    Language: English
    In: Analytical and Bioanalytical Chemistry, 2013, Vol.405(16), pp.5387-5392
    Description: Bacterial contamination of indoor air is a serious threat to human health. Pathogenic germs can be transferred from the liquid to the aerosol phase, for instance, when water is sprayed in the air, such as in shower rooms, air conditioners, or fountains. Existing analytical methods for biological indoor air-quality assessment and contamination monitoring are mostly time consuming as they generally require a cultivation step. The need for a rapid, sensitive, and selective detection method for bioaerosols is evident. Our approach is based on the combination of a commercial wet particle sampler (Coriolis μ, Bertin Technologies, France) and a label-free microarray readout based on surface-enhanced Raman scattering (SERS) for detection, which was established in our laboratories. Heat-inactivated Escherichia coli bacteria were used as test microorganisms. An E. coli suspension was sprayed into the chamber by a jet air nebulizer. The resulting bioaerosol was dried, neutralized, and then collected by a Coriolis μ sampler. The bacteria collected were detected by a recently developed microarray readout system, based on label-free SERS detection. A special data evaluation procedure was applied in order to fully exploit the selectivity of the detection scheme, resulting in a detection limit of 144 particles per cubic centimeter.
    Keywords: Bioaerosol ; Escherichia coli ; Surface-enhanced Raman scattering ; Cyclone sampler ; Aerosol
    ISSN: 1618-2642
    E-ISSN: 1618-2650
    Source: Springer Science & Business Media B.V.
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  • 10
    Language: English
    In: Journal of Physical Chemistry B, August 12, 2010, Vol.114(31), p.10184-10194
    Keywords: Microbial Mats -- Structure ; Microbial Mats -- Chemical Properties ; Microbial Mats -- Optical Properties ; Polymers -- Structure ; Polymers -- Chemical Properties ; Polymers -- Optical Properties ; Raman Spectroscopy -- Usage
    ISSN: 1520-6106
    Source: Cengage Learning, Inc.
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