Pulse length variation causing spectral distortions in OPO-based hyperspectral coherent Raman scattering microscopy

Pilger C, Hachmeister H, Greife P, Weiss A, Wiebusch G, Huser T. Pulse length variation causing spectral distortions in OPO-based hyperspectral coherent Raman scattering microscopy. Optics Express. 2018;26(22):28312-28322.Picosecond optical parametric oscillators (OPOs) with broad wavelength tunability are frequently used as light sources in hyperspectral coherent Raman scattering (CRS) microscopy. We investigate how changes in the pulse length during OPO wavelength tuning of the pump beam affect hyperspectral CRS imaging. We find that significant distortions of the resulting CRS spectra occur if the OPO is operated without monitoring pulse length variations. By utilizing a custom-written MATLAB based control program to counteract changes in pulse length, normalized and reproducible data sets can be acquired. We demonstrate this by comparing hyperspectral data obtained from pure substances, as well as relevant biological specimens

Vibrational spectroscopic imaging and live cell video microscopy for studying differentiation of primary human alveolar epithelial cells.

Vukosavljevic B, Hittinger M, Hachmeister H, et al. Vibrational spectroscopic imaging and live cell video microscopy for studying differentiation of primary human alveolar epithelial cells. Journal of Biophotonics. 2019;12(6): e201800052

High-contrast, fast chemical imaging by coherent Raman scattering using a self-synchronized two-colour fibre laser

Kong C, Pilger C, Hachmeister H, et al. High-contrast, fast chemical imaging by coherent Raman scattering using a self-synchronized two-colour fibre laser. Light: Science &amp; Applications. 2020;9(1): 25.Coherent Raman scattering (CRS) microscopy is widely recognized as a powerful tool for tackling biomedical problems based on its chemically specific label-free contrast, high spatial and spectral resolution, and high sensitivity. However, the clinical translation of CRS imaging technologies has long been hindered by traditional solid-state lasers with environmentally sensitive operations and large footprints. Ultrafast fibre lasers can potentially overcome these shortcomings but have not yet been fully exploited for CRS imaging, as previous implementations have suffered from high intensity noise, a narrow tuning range and low power, resulting in low image qualities and slow imaging speeds. Here, we present a novel high-power self-synchronized two-colour pulsed fibre laser that achieves excellent performance in terms of intensity stability (improved by 50 dB), timing jitter (24.3 fs), average power fluctuation (20 dB) and pulse width variation (<1.8%) over an extended wavenumber range (2700–3550 cm−1). The versatility of the laser source enables, for the first time, high-contrast, fast CRS imaging without complicated noise reduction via balanced detection schemes. These capabilities are demonstrated in this work by imaging a wide range of species such as living human cells and mouse arterial tissues and performing multimodal nonlinear imaging of mouse tail, kidney and brain tissue sections by utilizing second-harmonic generation and two-photon excited fluorescence, which provides multiple optical contrast mechanisms simultaneously and maximizes the gathered information content for biological visualization and medical diagnosis. This work also establishes a general scenario for remodelling existing lasers into synchronized two-colour lasers and thus promotes a wider popularization and application of CRS imaging technologies

Label-free nonlinear optical microscopy detects early markers for osteogenic differentiation of human stem cells

Hofemeier AD, Hachmeister H, Pilger C, et al. Label-free nonlinear optical microscopy detects early markers for osteogenic differentiation of human stem cells. Scientific Reports. 2016;6(1): 26716.Tissue engineering by stem cell differentiation is a novel treatment option for bone regeneration. Most approaches for the detection of osteogenic differentiation are invasive or destructive and not compatible with live cell analysis. Here, non-destructive and label-free approaches of Raman spectroscopy, coherent anti-Stokes Raman scattering (CARS) and second harmonic generation (SHG) microscopy were used to detect and image osteogenic differentiation of human neural crest-derived inferior turbinate stem cells (ITSCs). Combined CARS and SHG microscopy was able to detect markers of osteogenesis within 14 days after osteogenic induction. This process increased during continued differentiation. Furthermore, Raman spectroscopy showed significant increases of the PO43− symmetric stretch vibrations at 959 cm−1 assigned to calcium hydroxyapatite between days 14 and 21. Additionally, CARS microscopy was able to image calcium hydroxyapatite deposits within 14 days following osteogenic induction, which was confirmed by Alizarin Red-Staining and RT- PCR. Taken together, the multimodal label-free analysis methods Raman spectroscopy, CARS and SHG microscopy can monitor osteogenic differentiation of adult human stem cells into osteoblasts with high sensitivity and spatial resolution in three dimensions. Our findings suggest a great potential of these optical detection methods for clinical applications including in vivo observation of bone tissue–implant-interfaces or disease diagnosis

SBML Level 3: an extensible format for the exchange and reuse of biological models

Systems biology has experienced dramatic growth in the number, size, and complexity of computational models. To reproduce simulation results and reuse models, researchers must exchange unambiguous model descriptions. We review the latest edition of the Systems Biology Markup Language (SBML), a format designed for this purpose. A community of modelers and software authors developed SBML Level 3 over the past decade. Its modular form consists of a core suited to representing reaction-based models and packages that extend the core with features suited to other model types including constraint-based models, reaction-diffusion models, logical network models, and rule-based models. The format leverages two decades of SBML and a rich software ecosystem that transformed how systems biologists build and interact with models. More recently, the rise of multiscale models of whole cells and organs, and new data sources such as single-cell measurements and live imaging, has precipitated new ways of integrating data with models. We provide our perspectives on the challenges presented by these developments and how SBML Level 3 provides the foundation needed to support this evolution

A Multimodal Imaging Platform to enable Hyperspectral Coherent Raman Spectroscopy

Hachmeister H. A Multimodal Imaging Platform to enable Hyperspectral Coherent Raman Spectroscopy. Bielefeld: Universität Bielefeld; 2021

Surface-Enhanced Raman Spectroscopy of Carbon Nanomembranes from Aromatic Self-Assembled Monolayers

Zhang X, Mainka M, Paneff F, et al. Surface-Enhanced Raman Spectroscopy of Carbon Nanomembranes from Aromatic Self-Assembled Monolayers. LANGMUIR. 2018;34(8):2692-2698.Surface-enhanced Raman scattering spectroscopy (SERS) was employed to investigate the formation of self assembled monolayers (SAMs) of biphenylthiol, 4'-nitro-1,1'-biphenyl-4-thiol, and p-terphenylthiol on Au surfaces and their structural transformations into carbon nanomembranes (CNMs) induced by electron irradiation. The high sensitivity of SERS allows us to identify two types of Raman scattering in electron-irradiated SAMs: (1) Raman-active sites exhibit similar bands as those of pristine SAMs in the fingerprint spectral region, but with indications of an amorphization process and (2) Raman inactive sites show almost no Raman-scattering signals, except a very weak and broad D band, indicating a lack of structural order but for the presence of graphitic domains. Statistical analysis showed that the ratio of the number of Raman-active sites to the total number of measurement sites decreases exponentially with increasing the electron irradiation dose. The maximum degree of cross-linking ranged from 97 to 99% for the three SAMs. Proof-of-concept experiments were conducted to demonstrate potential applications of Raman-inactive CNMs as a supporting membrane for Raman analysis

Analyzing life-history traits and lipid storage using CARS microscopy for assessing effects of copper on the fitness of Caenorhabditis elegans

Füser H, Majdi N, Hägerbäumer A, et al. Analyzing life-history traits and lipid storage using CARS microscopy for assessing effects of copper on the fitness of Caenorhabditis elegans. Ecotoxicology and Environmental Safety. 2018;156:255-262

Label-free in vivo analysis of intracellular lipid droplets in the oleaginous microalga Monoraphidium neglectum by coherent Raman scattering microscopy

Jaeger D, Pilger C, Hachmeister H, et al. Label-free in vivo analysis of intracellular lipid droplets in the oleaginous microalga Monoraphidium neglectum by coherent Raman scattering microscopy. Scientific Reports. 2016;6(1): 35340

Generation of a mu-1,2-hydroperoxo FeIIIFeIII and a mu-1,2-peroxo FeIVFeIII Complex

Walleck S, Zimmermann TP, Hachmeister H, et al. Generation of a mu-1,2-hydroperoxo FeIIIFeIII and a mu-1,2-peroxo FeIVFeIII Complex. Nature Communications . 2022;13(1): 1376.mu-1,2-Peroxo-diferric intermediates (P) of non-heme diiron enzymes are proposed to convert upon protonation either to high-valent active species or to activated P' intermediates via hydroperoxo-diferric intermediates. Protonation of synthetic mu-1,2-peroxo model complexes occurred at the mu-oxo and not at the mu-1,2-peroxo bridge. Here we report a stable mu-1,2-peroxo complex {FeIII(mu-O)(mu-1,2-O2)FeIII} using a dinucleating ligand and study its reactivity. The reversible oxidation and protonation of the mu-1,2-peroxo-diferric complex provide mu-1,2-peroxo FeIVFeIII and mu-1,2-hydroperoxo-diferric species, respectively. Neither the oxidation nor the protonation induces a strong electrophilic reactivity. Hence, the observed intramolecular C-H hydroxylation of preorganized methyl groups of the parent mu-1,2-peroxo-diferric complex should occur via conversion to a more electrophilic high-valent species. The thorough characterization of these species provides structure-spectroscopy correlations allowing insights into the formation and reactivities of hydroperoxo intermediates in diiron enzymes and their conversion to activated P' or high-valent intermediates. © 2022. The Author(s)