Imaging the scattered light of a nanoparticle through a cylindrical capillary.

In many experiments, nanoparticles are located inside a microfluidic channel, and the light scattered by the particles becomes diffracted through the walls of the capillary. We here derive a simple but accurate approach for simulating the imaging of light through a cylindrical capillary under the assumption that the dimensions of the capillary are much larger than the wavelength of light. A comparison of the simulated images with experimental results shows very good agreement.

Unified Simulation Platform for Interference Microscopy.

Interferometric scattering microscopy is a powerful technique that enables various applications, such as mass photometry and particle tracking. Here, we present a numerical toolbox to simulate images obtained in interferometric scattering, coherent bright-field, and dark-field microscopies. The scattered fields are calculated using a boundary element method, facilitating the simulation of arbitrary sample geometries and substrate layer structures.

Optofluidic Force Induction Meets Raman Spectroscopy and Inductively Coupled Plasma-Mass Spectrometry: A New Hyphenated Technique for Comprehensive and Complementary Characterizations of Single Particles.

Nanoparticles are produced at accelerating rates, are increasingly integrated into scientific and industrial applications, and are widely discharged into the environment. Analytical techniques are required to characterize parameters such as particle number concentrations, mass and size distributions, molecular and elemental compositions, and particle stability. This is not only relevant to investigate their utility for various industrial or medical applications and for controlling the manufacturing processes but also to assess toxicity and environmental fate.

Optofluidic force induction as a process analytical technology.

Manufacturers of nanoparticle-based products rely on detailed information about critical process parameters, such as particle size and size distributions, concentration, and material composition, which directly reflect the quality of the final product. These process parameters are often obtained using offline characterization techniques that cannot provide the temporal resolution to detect dynamic changes in particle ensembles during a production process. To overcome this deficiency, we have recently introduced Optofluidic Force Induction (OF2i) for optical real-time counting with single particle sensitivity and high throughput.

Tomographic Reconstruction of Quasistatic Surface Polariton Fields.

We theoretically investigate the tomographic reconstruction of the three-dimensional photonic environment of nanoparticles. As input for our reconstruction we use electron energy loss spectroscopy (EELS) maps for different rotation angles. We perform the tomographic reconstruction of surface polariton fields for smooth and rough nanorods and compare the reconstructed and simulated photonic local density of states, which are shown to be in very good agreement.

PeakForest: a multi-platform digital infrastructure for interoperable metabolite spectral data and metadata management.

Introduction: Accuracy of feature annotation and metabolite identification in biological samples is a key element in metabolomics research. However, the annotation process is often hampered by the lack of spectral reference data in experimental conditions, as well as logistical difficulties in the spectral data management and exchange of annotations between laboratories.

Objectives: To design an open-source infrastructure allowing hosting both nuclear magnetic resonance (NMR) and mass spectra (MS), with an ergonomic Web interface and Web services to support metabolite annotation and laboratory data management.

Milk metabolome reveals variations on enteric methane emissions from dairy cows fed a specific inhibitor of the methanogenesis pathway.

Metabolome profiling in biological fluids is an interesting approach for exploring markers of methane emissions in ruminants. In this study, a multiplatform metabolomics approach was used for investigating changes in milk metabolic profiles related to methanogenesis in dairy cows. For this purpose, 25 primiparous Holstein cows at similar lactation stage were fed the same diet supplemented with (treated, n = 12) or without (control, n = 13) a specific antimethanogenic additive that reduced enteric methane production by 23% with no changes in intake, milk production, and health status.

Three-dimensional vectorial imaging of surface phonon polaritons.

Surface phonon polaritons (SPhPs) are coupled photon-phonon excitations that emerge at the surfaces of nanostructured materials. Although they strongly influence the optical and thermal behavior of nanomaterials, no technique has been able to reveal the complete three-dimensional (3D) vectorial picture of their electromagnetic density of states. Using a highly monochromated electron beam in a scanning transmission electron microscope, we could visualize varying SPhP signatures from nanoscale MgO cubes as a function of the beam position, energy loss, and tilt angle.

Fundamental Limit of Plasmonic Cathodoluminescence.

We use cathodoluminescence (CL) spectroscopy in a transmission electron microscope to probe the radial breathing mode of plasmonic silver nanodisks. A two-mirror detection system sandwiching the sample collects the CL emission in both directions, that is, backward and forward with respect to the electron beam trajectory. We unambiguously identify a spectral shift of about 8 nm in the CL spectra acquired from both sides and show that this asymmetry is induced by the electron beam itself.

Investigation of space charge effects and ion trapping capacity on direct introduction ultra-high-resolution mass spectrometry workflows for metabolomics.

Ultra-high-resolution mass spectrometry, in the absence of chromatography, is finding its place for direct analyses of highly complex mixtures, such as those encountered during untargeted metabolomics screening. Advances, however, have been tempered by difficulties such as uneven signal suppression experienced during electrospray ionization. Moreover, ultra-high-resolution mass spectrometers that use Orbitrap and ICR analyzers both suffer from limited ion trapping capacities, owing principally to space-charge effects.

Novel Modal Approximation Scheme for Plasmonic Transmission Problems.

The concept of resonances and modes for the description of particle plasmons has recently received great interest, both in the context of efficient simulations as well as for an intuitive interpretation in physical terms. While resonance modes have been successfully employed for geometries whose optical response is governed by a few modes only, the resonance mode description exhibits considerable difficulties for larger nanoparticles with their richer mode spectra. We analyze the problem using a boundary element method approach together with a Mie solution for spherical particles, and identify the fixed link between the electric and magnetic components of the resonance modes as the main source for this shortcoming.

Plasmonic Dispersion Relations and Intensity Enhancement of Metal-Insulator-Metal Nanodisks.

We show that the plasmon modes of vertically stacked Ag-SiO-Ag nanodisks can be understood and classified as hybridized surface and edge modes. We describe their universal dispersion relations and demonstrate that coupling-induced spectral shifts are significantly stronger for surface modes than for edge modes. The experimental data correspond well to numerical simulations.

Effectiveness of Interventions to Modulate the Rumen Microbiota Composition and Function in Pre-ruminant and Ruminant Lambs.

Modulating the assembly of the ruminal microbiota might have practical implications in production. We tested how an early-life dietary intervention in lambs influences the diversity and function of the ruminal microbiota during and after the intervention. Microbiota resilience during a repeated dietary intervention was also tested.

Evaluation of the High-Field Orbitrap Fusion for Compound Annotation in Metabolomics.

Annotation of signals of interest represents a key point in mass spectrometry-based metabolomics studies. The first level of investigation is the elemental composition, which can be deduced from accurately measured masses and isotope patterns. However, accuracy of these two parameters remains to be evaluated on last generation mass spectrometers to determine the level of confidence that can be used during the annotation process.

Excitation of long-wavelength surface optical vibrational modes in films, cubes and film/cube composite system using an atom-sized electron beam.

Using spatially resolved Electron Energy-Loss Spectroscopy, we investigate the excitation of long-wavelength surface optical vibrational modes in elementary types of nanostructures: an amorphous SiO2 slab, an MgO cube, and in the composite cube/slab system. We find rich sets of optical vibrational modes strongly constrained by the nanoscale size and geometry. For slabs, we find two surface resonances resulting from the excitation of surface phonon polariton modes.

proFIA: a data preprocessing workflow for flow injection analysis coupled to high-resolution mass spectrometry.

Motivation: Flow Injection Analysis coupled to High-Resolution Mass Spectrometry (FIA-HRMS) is a promising approach for high-throughput metabolomics. FIA-HRMS data, however, cannot be preprocessed with current software tools which rely on liquid chromatography separation, or handle low resolution data only.

Results: We thus developed the proFIA package, which implements a suite of innovative algorithms to preprocess FIA-HRMS raw files, and generates the table of peak intensities.

3D Imaging of Gap Plasmons in Vertically Coupled Nanoparticles by EELS Tomography.

Plasmonic gap modes provide the ultimate confinement of optical fields. Demanding high spatial resolution, the direct imaging of these modes was only recently achieved by electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). However, conventional 2D STEM-EELS is only sensitive to components of the photonic local density of states (LDOS) parallel to the electron trajectory.

Mapping vibrational surface and bulk modes in a single nanocube.

Imaging of vibrational excitations in and near nanostructures is essential for developing low-loss infrared nanophotonics, controlling heat transport in thermal nanodevices, inventing new thermoelectric materials and understanding nanoscale energy transport. Spatially resolved electron energy loss spectroscopy has previously been used to image plasmonic behaviour in nanostructures in an electron microscope, but hitherto it has not been possible to map vibrational modes directly in a single nanostructure, limiting our understanding of phonon coupling with photons and plasmons. Here we present spatial mapping of optical and acoustic, bulk and surface vibrational modes in magnesium oxide nanocubes using an atom-wide electron beam.

Mapping the local particle plasmon sensitivity with a scanning probe.

We probe the local sensitivity of an optically excited plasmonic nanoparticle by changing the local dielectric environment through a scanning glass fiber tip. Recording the particle plasmon scattering spectrum for each tip position allows us to observe spectral resonance shifts concurrent with changes in scattering intensity and plasmon damping. For the tip-induced spectral shifts we find the strongest sensitivity at the particle edges, in accordance with the spatial plasmonic field profile.

Mechanistic study of competitive releases of HO, NH and CO from deprotonated aspartic and glutamic acids: Role of conformation.

The aims of this study were to highlight the impact of minor structural differences (e.g. an aminoacid side chain enlargement by one methylene group), on ion dissociation under collision-induced dissociation conditions, and to determine the underlying chemical mechanisms.

Edge Mode Coupling within a Plasmonic Nanoparticle.

The coupling of plasmonic nanoparticles can strongly modify their optical properties. Here, we show that the coupling of the edges within a single rectangular particle leads to mode splitting and the formation of bonding and antibonding edge modes. We are able to unambiguously designate the modes due to the high spatial resolution of electron microscopy-based electron energy loss spectroscopy and the comparison with numerical simulations.

Exciton-exciton annihilation and biexciton stimulated emission in graphene nanoribbons.

Graphene nanoribbons display extraordinary optical properties due to one-dimensional quantum-confinement, such as width-dependent bandgap and strong electron-hole interactions, responsible for the formation of excitons with extremely high binding energies. Here we use femtosecond transient absorption spectroscopy to explore the ultrafast optical properties of ultranarrow, structurally well-defined graphene nanoribbons as a function of the excitation fluence, and the impact of enhanced Coulomb interaction on their excited states dynamics. We show that in the high-excitation regime biexcitons are formed by nonlinear exciton-exciton annihilation, and that they radiatively recombine via stimulated emission.

Three dimensional sensitivity characterization of plasmonic nanorods for refractometric biosensors.

An experimental three dimensional characterization of the local refractive index sensitivity of plasmonic gold nanorods is performed by controlled apposition of lithographic nanostructures. We show up to seven times higher sensitivity values to local changes in the refractive index at the particle tip than center. In addition, successive deposition of defined nm-thin dielectric layers on nanorods covered with stripe masks allows us to study the sensitivity decrease normal to the particle surface separately for different particle sites.