Strong and Coherent Coupling of a Plasmonic Nanoparticle to a Subwavelength Fabry–Pérot Resonator

A major aim in experimental nano- and quantum optics is observing and controlling the interaction between light and matter on a microscopic scale. Coupling molecules or atoms to optical microresonators is a prominent method to alter their optical properties such as luminescence spectra or lifetimes. Until today strong coupling of optical resonators to such objects has only been observed with atom-like systems in high quality resonators. We demonstrate first experiments revealing strong coupling between individual plasmonic gold nanorods (GNR) and a tunable low quality resonator by observing cavity-length-dependent nonlinear dephasing and spectral shifts indicating spectral anticrossing of the luminescent coupled system. These phenomena and experimental results can be described by a model of two coupled oscillators representing the plasmon resonance of the GNR and the optical fields of the resonator. The presented reproducible and accurately tunable resonator allows us to precisely control the optical properties of individual particles

Synthesis and SHG Properties of Two New Cyanurates: Sr₃(O₃C₃N₃)₂ (SCY) and Eu₃(O₃C₃N₃)₂ (ECY)

The new cyanurates Sr₃(O₃C₃N₃)₂ (SCY) and Eu₃(O₃C₃N₃)₂ (ECY) were prepared via exothermic solid state metathesis reactions from MCl₂ (M = Sr, Eu) and K­(OCN) in silica tubes at 525 °C. Both structures were characterized by means of powder and single crystal X-ray diffraction, and their structures are shown to crystallize with the noncentrosymmetric space group <i>R</i>3<i>c</i> (No. 161). Infrared spectra and nonlinear optical properties (NLO) of SCY and ECY are reported in comparison to those of CCY and β-BaB₂O₄ (β-BBO)

Synthesis and SHG Properties of Two New Cyanurates: Sr₃(O₃C₃N₃)₂ (SCY) and Eu₃(O₃C₃N₃)₂ (ECY)

The new cyanurates Sr₃(O₃C₃N₃)₂ (SCY) and Eu₃(O₃C₃N₃)₂ (ECY) were prepared via exothermic solid state metathesis reactions from MCl₂ (M = Sr, Eu) and K­(OCN) in silica tubes at 525 °C. Both structures were characterized by means of powder and single crystal X-ray diffraction, and their structures are shown to crystallize with the noncentrosymmetric space group <i>R</i>3<i>c</i> (No. 161). Infrared spectra and nonlinear optical properties (NLO) of SCY and ECY are reported in comparison to those of CCY and β-BaB₂O₄ (β-BBO)

Nanometer-Scale Structure Property of WS₂ Flakes by Nonlinear Optical Microscopy: Implications for Optical Frequency Converted Signals

Structural irregularities have attracted increasing attention in two-dimensional transition metal dichalcogenides (TMDCs), whose impacts on the electronic structure cannot be neglected. Here, nonlinear optical spectroscopy and microscopy are used to investigate these effects in tungsten disulfide (WS2) flakes based on the spatially resolved second harmonic generation (SHG) and room-temperature two-photon photoluminescence (2PPL). Notably, SHG intensity appears the strongest at these flake edges, which is anticorrelated with the room-temperature 2PPL response in monolayer WS2. This work provides a convenient method to probe the second-order susceptibility of TMDCs for the purpose of achieving a high optical frequency converted signal for nonlinear optical applications

Enhancement of Radiative Plasmon Decay by Hot Electron Tunneling

Here we demonstrate that photon emission induced by inelastic tunneling through a nanometer single gap between a sharp Au tip and an Au substrate can be significantly enhanced by the illumination of the junction with 634 nm laser light with an electric field component oriented parallel to the tip-axis, <i>i.e.</i>, perpendicular to the sample. Analyzing photoluminescence (PL) spectra recorded as a function of bias voltage allows us to distinguish between PL from (1) the decay of electron–hole pairs created by the laser excited sp/d interband transition with a characteristic band at 690 nm and (2) the red-shifted radiative decay of characteristic plasmon modes formed by the gap. Since the electroluminescence spectra (without laser) already show the plasmonic gap modes, we conclude that the enhanced intensity induced by laser illumination originates from the radiative decay of hot electrons closely above the Fermi level <i>via</i> inelastic tunneling and photon emission into the plasmon modes. Since these processes can be independently controlled by laser illumination and the amplitude of the bias voltage, it is of great interest for designing new switchable photon emission plasmonic devices

Au Nanotip as Luminescent Near-Field Probe

We introduce a new optical near-field mapping method, namely utilizing the plasmon-mediated luminescence from the apex of a sharp gold nanotip. The tip acts as a quasi-point light source which does not suffer from bleaching and gives a spatial resolution of ≤25 nm. We demonstrate our method by imaging the near field of azimuthally and radially polarized plasmonic modes of nonluminescent aluminum oligomers

Chimeric Autofluorescent Proteins as Photophysical Model System for Multicolor Bimolecular Fluorescence Complementation

The yellow fluorescent protein (YFP) is frequently used in a protein complementation assay called bimolecular fluorescence complementation (BiFC), and is employed to visualize protein–protein interactions. In this analysis, two different, nonfluorescent fragments of YFP are genetically attached to proteins of interest. Upon interaction of these proteins, the YFP fragments are brought into proximity close enough to reconstitute their original structure, enabling fluorescence. BiFC allows for a straightforward readout of protein–protein interactions and furthermore facilitates their functional investigation by in vivo imaging. Furthermore, it has been observed that the available color range in BiFC can be extended upon complementing fragments of different proteins that are, like YFP, derived from the Aequorea victoria green fluorescent protein, thereby allowing for a multiplexed investigation of protein–protein interactions. Some spectral characteristics of “multicolor” BiFC (mcBiFC) complexes have been reported before; however, no in-depth analysis has been performed yet. Therefore, little is known about the photophysical characteristics of these mcBiFC complexes because a proper characterization essentially relies on in vitro data. This is particularly difficult for fragments of autofluorescent proteins (AFPs) because they show a very strong tendency to form supramolecular aggregates which precipitate ex vivo. In this study, this intrinsic difficulty is overcome by directly fusing the coding DNA of different AFP fragments. Translation of the genetic sequence in Escherichia coli leads to fully functional, highly soluble fluorescent proteins with distinct properties. On the basis of their construction, they are designated chimeric AFPs, or BiFC chimeras, here. Comparison of their spectral characteristics with experimental in vivo BiFC data confirmed the utility of the chimeric proteins as a BiFC model system. In this study, nine different chimeras were thoroughly analyzed at both the ensemble and the single-molecular level. The data indicates that mutations believed to be photophysically silent significantly alter the properties of AFPs

Three-Dimensional (3D) Surface-Enhanced Raman Spectroscopy (SERS) Substrates: Fabrication and SERS Applications

This study introduces a straightforward approach to construct three-dimensional (3D) surface-enhanced Raman spectroscopy (SERS) substrates using chemically modified silica particles as microcarriers and by attaching metal nanoparticles (NPs) onto their surfaces. Tollens’ reagent and sputtering techniques are utilized to prepare the SERS substrates from mercapto-functionalized silica particles. Treatment with Tollens’ reagent generates a variety of silver NPs, ranging from approximately 10 to 400 nm, while sputtering with gold (Au) yields uniformly distributed NPs with an island-like morphology. Both substrates display wide plasmon resonances in the scattering spectra, making them effective for SERS in the visible spectral range, with enhancement factors (ratio of the analyte’s intensity at the hotspot compared to that on the substrate in the absence of metal nanoparticles) of up to 25. These 3D substrates have a significant advantage over traditional SERS substrates because their active surface area is not limited to a 2D surface but offers a much greater active surface due to the 3D arrangement of the NPs. This feature may enable achieving much higher SERS intensity from within streaming liquids or inside cells/tissues

Table_4_OneFlowTraX: a user-friendly software for super-resolution analysis of single-molecule dynamics and nanoscale organization.docx

Super-resolution microscopy (SRM) approaches revolutionize cell biology by providing insights into the nanoscale organization and dynamics of macromolecular assemblies and single molecules in living cells. A major hurdle limiting SRM democratization is post-acquisition data analysis which is often complex and time-consuming. Here, we present OneFlowTraX, a user-friendly and open-source software dedicated to the analysis of single-molecule localization microscopy (SMLM) approaches such as single-particle tracking photoactivated localization microscopy (sptPALM). Through an intuitive graphical user interface, OneFlowTraX provides an automated all-in-one solution for single-molecule localization, tracking, as well as mobility and clustering analyses. OneFlowTraX allows the extraction of diffusion and clustering parameters of millions of molecules in a few minutes. Finally, OneFlowTraX greatly simplifies data management following the FAIR (Findable, Accessible, Interoperable, Reusable) principles. We provide a detailed step-by-step manual and guidelines to assess the quality of single-molecule analyses. Applying different fluorophores including mEos3.2, PA-GFP, and PATagRFP, we exemplarily used OneFlowTraX to analyze the dynamics of plant plasma membrane-localized proteins including an aquaporin, the brassinosteroid receptor Brassinosteroid Insensitive 1 (BRI1) and the Receptor-Like Protein 44 (RLP44).</p

Table_2_OneFlowTraX: a user-friendly software for super-resolution analysis of single-molecule dynamics and nanoscale organization.docx

Super-resolution microscopy (SRM) approaches revolutionize cell biology by providing insights into the nanoscale organization and dynamics of macromolecular assemblies and single molecules in living cells. A major hurdle limiting SRM democratization is post-acquisition data analysis which is often complex and time-consuming. Here, we present OneFlowTraX, a user-friendly and open-source software dedicated to the analysis of single-molecule localization microscopy (SMLM) approaches such as single-particle tracking photoactivated localization microscopy (sptPALM). Through an intuitive graphical user interface, OneFlowTraX provides an automated all-in-one solution for single-molecule localization, tracking, as well as mobility and clustering analyses. OneFlowTraX allows the extraction of diffusion and clustering parameters of millions of molecules in a few minutes. Finally, OneFlowTraX greatly simplifies data management following the FAIR (Findable, Accessible, Interoperable, Reusable) principles. We provide a detailed step-by-step manual and guidelines to assess the quality of single-molecule analyses. Applying different fluorophores including mEos3.2, PA-GFP, and PATagRFP, we exemplarily used OneFlowTraX to analyze the dynamics of plant plasma membrane-localized proteins including an aquaporin, the brassinosteroid receptor Brassinosteroid Insensitive 1 (BRI1) and the Receptor-Like Protein 44 (RLP44).</p