Optical Heterodyne-Detected Raman-Induced Kerr Effect (OHD-RIKE) Microscopy

Label-free microscopy based on Raman scattering has been increasingly used in biomedical research to image samples that cannot be labeled or stained. Stimulated Raman scattering (SRS) microscopy allows signal amplification of the weak Raman signal for fast imaging speeds without introducing the nonresonant background and coherent image artifacts that are present in coherent anti-Stokes Raman scattering (CARS) microscopy. Here we present the Raman-induced Kerr effect (RIKE) as a contrast for label-free microscopy. RIKE allows us to measure different elements of the nonlinear susceptibility tensor, both the real and imaginary parts, by optical heterodyne detection (OHD-RIKE). OHD-RIKE microscopy provides information similar to polarization CARS (P-CARS) and interferometric CARS (I-CARS) microscopy, with a simple modification of the two-beam SRS microscopy setup. We show that, while OHD-RIKE microspectroscopy can be in principle more sensitive than SRS, it does not supersede SRS microscopy of heterogeneous biological samples, such as mouse skin tissue, because it is complicated by variations of linear birefringence across the sample.Chemistry and Chemical Biolog

Maternal exposure to ambient black carbon particles and their presence in maternal and fetal circulation and organs : an analysis of two independent population-based observational studies

Funding European Research Council, Flemish Scientific Research Foundation, Kom op Tegen Kanker, UK Medical Research Council, and EU Horizon 2020. Acknowledgments The ENVIRONAGE birth cohort was initiated by the European Research Council (ERC-2012-StG 310898) and received additional funding from the Flemish Scientific Research Foundation and Kom op Tegen Kanker (KoTK). The detection equipment was funded by the METHUSALEM Program and the INCALO project (ERC-PoC). We acknowledge the Flemish Scientific Research Foundation (FWO; 1150920N to EB and G082317N). The SAFeR study was funded by the UK Medical Research Council (MR/L010011/1 and MR/P011535/1) and the EU's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie project PROTECTED (grant agreement number 722634) and FREIA project (grant agreement number 825100) as well as by NHS Grampian Endowments grants (16/11/056, 17/034, 18/14, 19/029, and 20/031) to PAF. We thank the midwives from the maternity ward of the East-Limburg Hospital in Genk, Belgium, for coordinating and supporting the study at the ward. We thank the Advanced Optical Microscopy Centre for the maintenance of the microscopic instruments. Moreover, we thank our colleagues from the Centre for Environmental Sciences for their hard work in collecting and processing the samples for the ENVIRONAGE birth cohort. Additionally, we thank the NHS Grampian Research Nurses and NHS Grampian R&D for their tireless recruitment work for the SAFeR study. We thank the past and present SAFeR team for their hard work with the fetuses and placentae. Finally, we thank the NHS Grampian Biorepository for their oversight role in SAFeR and assistance in processing and preparation of tissue sections.Peer reviewedPublisher PD

Label-Free Live-Cell Imaging of Nucleic Acids Using Stimulated Raman Scattering Microscopy

Imaging of nucleic acids is important for studying cellular processes such as cell division and apoptosis. A noninvasive label-free technique is attractive. Raman spectroscopy provides rich chemical information based on specific vibrational peaks. However, the signal from spontaneous Raman scattering is weak and long integration times are required, which drastically limits the imaging speed when used for microscopy. Coherent Raman scattering techniques, comprising coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) microscopy, overcome this problem by enhancing the signal level by up to five orders of magnitude. CARS microscopy suffers from a nonresonant background signal, which distorts Raman spectra and limits sensitivity. This makes CARS imaging of weak transitions in spectrally congested regions challenging. This is especially the case in the fingerprint region, where nucleic acids show characteristic peaks. The recently developed SRS microscopy is free from these limitations; excitation spectra are identical to those of spontaneous Raman and sensitivity is close to shot-noise limited. Herein we demonstrate the use of SRS imaging in the fingerprint region to map the distribution of nucleic acids in addition to proteins and lipids in single salivary gland cells of Drosophila larvae, and in single mammalian cells. This allows the imaging of DNA condensation associated with cell division and opens up possibilities of imaging such processes in vivo.Chemistry and Chemical Biolog

Carbonaceous Nanoparticle Air Pollution: Toxicity and Detection in Biological Samples

Among the different air pollutants, particulate matter (PM) is of great concern due to its abundant presence in the atmosphere, which results in adverse effects on the environment and human health. The different components of PM can be classified based on their physicochemical properties. Carbonaceous particles (CPs) constitute a major fraction of ultrafine PM and have the most harmful effects. Herein, we present a detailed overview of the main components of CPs, e.g., carbon black (CB), black carbon (BC), and brown carbon (BrC), from natural and anthropogenic sources. The emission sources and the adverse effects of CPs on the environment and human health are discussed. Particularly, we provide a detailed overview of the reported toxic effects of CPs in the human body, such as respiratory effects, cardiovascular effects, neurodegenerative effects, carcinogenic effects, etc. In addition, we also discuss the challenges faced by and limitations of the available analytical techniques for the qualitative and quantitative detection of CPs in atmospheric and biological samples. Considering the heterogeneous nature of CPs and biological samples, a detailed overview of different analytical techniques for the detection of CPs in (real-exposure) biological samples is also provided. This review provides useful insights into the classification, toxicity, and detection of CPs in biological samples

Resolving the Acid Site Distribution in Zn-Exchanged ZSM-5 with Stimulated Raman Scattering Microscopy

Zeolites are widely used acid catalysts in research and in industrial processes. The catalytic performance of these materials is affected by the nature and concentration of Brønsted and Lewis acid sites. The balance between these types of active sites—and thus the activity and selectivity of the zeolite—can be altered by the introduction of metal species, e.g., by ion exchange. Although the acidic properties of zeolites are routinely characterized by bulk-scale techniques, this ensemble-averaged approach neglects the local variations in the material. Insights into the distribution of active sites at the single-particle level are thus critical to better understand the impact of post-synthetic modifications on the zeolite acidity. In this contribution, we spatially resolve Brønsted and Lewis acid sites in protonated and Zn-exchanged ZSM-5 crystals. To this end, the vibrational modes of pyridine chemisorbed on active sites are mapped with stimulated Raman scattering (SRS) microscopy. The SRS images reveal sharp inter- and intra-particle heterogeneities in the distribution of Lewis acid sites introduced upon ion exchange, ascribed to local variations in the Al content. Besides assessing the impact of Zn exchange on the active site distribution in ZSM-5 crystals, this approach enables uniquely to map the distribution of Lewis acid sites in catalysts at the single-particle level

Efficient Photocatalytic CO2 Reduction with MIL-100(Fe)-CsPbBr3 Composites

Bromide-based metal halide perovskites (MHPs) are promising photocatalysts with strong blue-green light absorption. Composite photocatalysts of MHPs with MIL-100(Fe), as a powerful photocatalyst itself, have been investigated to extend the responsiveness towards red light. The composites, with a high specific surface area, display an enhanced solar light response, and the improved charge carrier separation in the heterojunctions is employed to maximize the photocatalytic performance. Optimization of the relative composition, with the formation of a dual-phase CsPbBr3 to CsPb2Br5 perovskite composite, shows an excellent photocatalytic performance with 20.4 μmol CO produced per gram of photocatalyst during one hour of visible light irradiation

Single Molecule Nanospectroscopy Visualizes Proton-Transfer Processes within a Zeolite Crystal

Visualizing proton-transfer processes at the nanoscale is essential for understanding the reactivity of zeolite-based catalyst materials. In this work, the Brønsted-acid-catalyzed oligomerization of styrene derivatives was used for the first time as a single molecule probe reaction to study the reactivity of individual zeolite H-ZSM-5 crystals in different zeolite framework, reactant and solvent environments. This was accomplished via the formation of distinct dimeric and trimeric fluorescent carbocations, characterized by their different photostability, as detected by single molecule fluorescence microscopy. The oligomerization kinetics turned out to be very sensitive to the reaction conditions and the presence of the local structural defects in zeolite H-ZSM-5 crystals. The remarkably photostable trimeric carbocations were found to be formed predominantly near defect-rich crystalline regions. This spectroscopic marker offers clear prospects for nanoscale quality control of zeolite-based materials. Inter..