Quantum Yield of Polariton Emission from Hybrid Light-Matter States

The efficiency of light-matter strong coupling is tuned by precisely varying the spatial position of a thin layer of cyanine dye J-aggregates in Fabry–Perot microcavities, and their photophysical properties are determined. Placing the layer at the cavity field maximum affords an interaction energy (Rabi splitting) of 503 meV, a 62% increase over that observed if the aggregates are simply spread evenly through the cavity, placing the system in the ultrastrong coupling regime. The fluorescence quantum yield of the lowest polaritonic state P– integrated over k-space is found to be ∼10^–2. The same value can be deduced from the 1.4 ps lifetime of P– measured by femtosecond transient absorption spectroscopy and the calculated radiative decay rate constant. Thus, the polariton decay is dominated by nonradiative processes, in contrast with what might be expected from the small effective mass of the polaritons. These findings provide a deeper understanding of hybrid light-molecule states and have implications for the modification of molecular and material properties by strong coupling

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Important cellular events such as division require drastic changes in the shape of the membrane. These remodeling processes can be triggered by the binding of specific proteins or by changes in membrane composition and are linked to phospholipid metabolism for which dedicated enzymes, named phospholipases, are responsible. Here wide-field fluorescence microscopy is used to visualize shape changes induced by the action of phospholipase A1 on dye-labeled supported membranes of POPC (1-palmitoyl-2-oleoly-<i>sn</i>-glycero-3-phosphocholine). Time-lapse imaging demonstrates that layers either shrink and disappear or fold and collapse into vesicles. These vesicles can undergo further transformations such as budding, tubulation, and pearling within 5 min of formation. Using dye-labeled phospholipases, we can monitor the presence of the enzyme at specific positions on the membrane as the shape transformations occur. Furthermore, incorporating the products of hydrolysis into POPC membranes is shown to induce transformations similar to those observed for enzyme action. The results suggest that phospholipase-mediated hydrolysis plays an important role in membrane transformations by altering the membrane composition, and a model is proposed for membrane curvature based on the presence and shape of hydrolysis products

Quantum Strong Coupling with Protein Vibrational Modes

In quantum electrodynamics, matter can be hybridized to confined optical fields by a process known as light–matter strong coupling. This gives rise to new hybrid light–matter states and energy levels in the coupled material, leading to modified physical and chemical properties. Here, we report for the first time the strong coupling of vibrational modes of proteins with the vacuum field of a Fabry–Perot mid-infrared cavity. For two model systems, poly­(l-glutamic acid) and bovine serum albumin, strong coupling is confirmed by the anticrossing in the dispersion curve, the square root dependence on the concentration, and a vacuum Rabi splitting that is larger than the cavity and vibration line widths. These results demonstrate that strong coupling can be applied to the study of proteins with many possible applications including the elucidation of the role of vibrational dynamics in enzyme catalysis and in H/D exchange experiments

Field-Controlled Charge Separation in a Conductive Matrix at the Single-Molecule Level: Toward Controlling Single-Molecule Fluorescence Intermittency

The fluorescence intermittency or “blinking” of single molecules of ATTO647N (ATTO) in the conductive matrix polyvinylcarbazole (PVK) is described in the presence of an external applied electric field. It is shown that due to the energy distribution of the highest occupied molecular orbital (HOMO) level of PVK, which is energetically close to the HOMO of ATTO, sporadic electron transfer occurs. As a result, the on/off dynamics of blinking can be influenced by the electric field. This field will, depending on the respective position and orientation of the dye/polymer system with respect to those of the electrodes, either enhance or suppress electron transfer from PVK to ATTO as well as the back electron transfer from reduced ATTO to PVK. After the charge-transfer step, the applied field will pull the hole in PVK away from the dye, increasing the overall time the dye resides in a dark state

Waveguide and Plasmonic Absorption-Induced Transparency

Absorption-induced transparency (AIT) is one of the family of induced transparencies that has emerged in recent decades in the fields of plasmonics and metamaterials. It is a seemingly paradoxical phenomenon in which transmission through nanoholes in gold and silver is dramatically enhanced at wavelengths where a physisorbed dye layer absorbs strongly. The origin of AIT remains controversial, with both experimental and theoretical work pointing to either surface (plasmonic) or in-hole (waveguide) mechanisms. Here, we resolve this controversy by carefully filling nanoholes in a silver film with dielectric material before depositing dye on the surface. Our experiments and modeling show that not only do plasmonic and waveguide contributions to AIT both exist, but they are spectrally identical, operating in concert when the dye is both in the holes and on the surface

Ultrasensitive, Multiplex Raman Frequency Shift Immunoassay of Liver Cancer Biomarkers in Physiological Media

Highly sensitive multiplex biomarker detection is critical for the early diagnosis of liver cancer. Here, a surface-enhanced Raman scattering (SERS) frequency-shift immunoassay is developed for detection of liver cancer biomarkers α-fetoprotein and Glypican-3 down to subpicomolar concentrations in saline solution. A high temperature modification of the Tollen’s method affords silver nanoparticle films with excellent SERS response upon which ordered domains of Raman reporters are chemisorbed by microcontact printing. Shifts in the reporters SERS spectrum in response to a bound antibody’s biomarker recognition constitutes the frequency shift assay, exhibiting here exceptional sensitivity and specificity and shown to function in fetal calf serum and in the serum of a patient with hepatocellular carcinoma

Surface Density-of-States Engineering of Anatase TiO₂ by Small Polyols for Enhanced Visible-Light Photocurrent Generation

Enhancement of visible-light photocurrent generation by sol–gel anatase TiO₂ films was achieved by binding small polyol molecules to the TiO₂ surface. Binding ethylene glycol onto the surface, enhancement factors up to 2.8 were found in visible-light photocurrent generation experiments. Density functional theory calculations identified midgap energy states that emerge as a result of the binding of a range of polyols to the TiO₂ surface. The presence and energy of the midgap state is predicted to depend sensitively on the structure of the polyol, correlating well with the photocurrent generation results. Together, these results suggest a new, facile, and cost-effective route to precise surface band gap engineering of TiO₂ toward visible-light-induced photocatalysis and energy storage

Electronic Light–Matter Strong Coupling in Nanofluidic Fabry–Pérot Cavities

Electronic light–matter strong coupling has been limited to solid molecular films due to the challenge of preparing optical cavities with nanoscale dimensions. Here we report a technique to fabricate such Fabry–Pérot nanocavities in which solutions can be introduced such that light–molecule interactions can be studied at will in the liquid phase. We illustrate the versatility of these cavities by studying the emission properties of Chlorin e6 solutions in both the weak and strong coupling regimes as a function of cavity detuning. Liquid nanocavities will broaden the investigation of strong coupling to many solution-based molecular processes

Vibro-Polaritonic IR Emission in the Strong Coupling Regime

The strong coupling regime of light–matter interaction has recently been extended to IR active molecular vibrations coupled to microcavities, resulting in the formation of so-called vibro-polaritonic states. Here we demonstrate the emissivity of such hybrid states. Using thermal excitation, we achieve polaritonic IR emission from a strongly coupled polymer. Thermal excitation of vibro-polaritons, thus, constitutes an original way of establishing sizable excited-states populations in strongly coupled systems and opens new routes to the study of interacting vibro-polaritons

Coherent Coupling of WS₂ Monolayers with Metallic Photonic Nanostructures at Room Temperature

Room temperature strong coupling of WS₂ monolayer exciton transitions to metallic Fabry–Pérot and plasmonic optical cavities is demonstrated. A Rabi splitting of 101 meV is observed for the Fabry–Pérot cavity. The enhanced magnitude and visibility of WS₂ monolayer strong coupling is attributed to the larger absorption coefficient, the narrower line width of the <i>A</i> exciton transition, and greater spin–orbit coupling. For WS₂ coupled to plasmonic arrays, the Rabi splitting still reaches 60 meV despite the less favorable coupling conditions, and displays interesting photoluminescence features. The unambiguous signature of WS₂ monolayer strong coupling in easily fabricated metallic resonators at room temperature suggests many possibilities for combining light–matter hybridization with spin and valleytronics