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Protein misfolding products - amyloids - tend to form distinct fibrillar structures of the characteristic fold for a given neurodegenerative disease or pathology. Moreover, amyloids (also in the intermediate or distorted state) can act as secondary nuclei for

Noble metal nanoclusters allow for the atomically- precise control of their composition. However, to create nanoclusters with pre-defined optical properties, comprehensive description of their structure-property relation is required. Here, we report the gold atom doping impact on one-photon and two-photon absorption (TPA) and luminescence properties of ligated silver nanoclusters via combined experimental studies and time-dependent density functional theory simulations (TD-DFT). We synthesized a series of Ag25−xAux(DMBT)18 nanoclusters where x=0, 1 and 5–10. For Ag24Au1(DMBT)18 we demonstrate that the presence of the central Au dopant strongly influences linear and non-linear optical properties, increasing photoluminescence quantum yield and two-photon brightness, with respect to undoped silver nanoclusters. With improved TPA and luminescence, atomically-precise AuAg alloys presented in our work can serve as robust luminescent probes e.g. for bioimaging in the second biological window.

Chiral nanomaterials attract broad attention, as they offer new possibilities of modulation of optical properties and dissymmetry factors outperforming organic materials. Among various nanoparticles, plasmonic bipyramids present numerous advantages as building blocks of chiral nanomaterials (well-defined modulation of optical properties with the morphology of nanoparticles, narrow optical resonances, and high size and shape uniformity of synthesized particles). We study different possible orientations of gold bipyramids with respect to each other in dimers obtained by wet chemistry methods. For circularly polarized incident light we evaluate linear optical cross sections and plasmonic local field enhancement using COMSOL Multiphysics. We observe coupling of the nanoparticles' local fields and thus changes in extinction spectra, which modulate chiroptical properties of dimers. To assess the chirality of various arrangements, we note differences in cross sections for left- and right-handed polarized light which we further evaluate as the dissymmetry g-factor. Our results provide BPs configurations with dissymmetry factor as high as -0.3.

Amyloids are broadly investigated protein misfolding products with characteristic β-sheet assemblies that have an important role in neurodegenerative diseases (e.g., Alzheimer's disease). While they are usually visualized by staining with Thioflavin-T, Congo Red, or other fluorescent markers, it still arouses a controversy over possible staining molecule influence on the amyloid structure or aggregation process. In this work we present, for the first time, the polarization analysis of two-photon excited autofluorescence of amyloids and confirm that polarization dependence of the observed emission can be correlated with the orientation of fibrils. We show the potential of two-photon excited autofluorescence for resolution of molecular organization of fibrils within amyloid superstructures. This label-free method is compatible with two-photon imaging already applied in investigation of neurodegeneration model in mice.

The inner ear of the rainbow trout contains biominerals called otoliths that are composed of calcium carbonate crystals and a protein organic matrix. The organic matrix macromolecule – 64 (OMM-64) ...

The biological mediation of mineral formation (biomineralization) is realized through diverse organic macromolecules that guide this process in a spatial and temporal manner. Although the role of these molecules in biomineralization is being gradually revealed, the molecular basis of their regulatory function is still poorly understood. In this study, the incorporation and distribution of the model intrinsically disordered starmaker‐like (Stm‐l) protein, which is active in fish otoliths biomineralization, within calcium carbonate crystals, is revealed. Stm‐l promotes crystal nucleation and anisotropic tailoring of crystal morphology. Intracrystalline incorporation of Stm‐l protein unexpectedly results in shrinkage (and not expansion, as commonly described in biomineral and bioinspired crystals) of the crystal lattice volume, which is described herein, for the first time, for bioinspired mineralization. A ring pattern was observed in crystals grown for 48 h; this was composed of a protein‐enriched region flanked by protein‐depleted regions. It can be explained as a result of the Ostwald‐like ripening process and intrinsic properties of Stm‐l, and bears some analogy to the daily growth layers of the otolith., Controlled growth: The starmaker‐like (Stm‐l) protein promotes calcium carbonate nucleation and anisotropic tailoring of crystal morphology. Intracrystalline incorporation of protein results in shrinkage of the crystal lattice volume (see figure). The ring pattern, which is composed of a protein‐enriched region flanked by protein‐depleted regions, is a result of both the Ostwald‐like ripening process and intrinsic properties of Stm‐l.

The objective of this study is to investigate the bactericidal efficiency of atmospheric pressure non-thermal (cold) dielectric barrier discharge plasma on biofilms of Staphylococcus aureus and Escherichia coli. In general, cold plasma is a mixture of electrons, ions, neutral atoms and molecules. The different particles in cold plasmas exhibit different energies, i.e. electrons are much more energetic than other particles. This feature of cold plasmas allows to produce chemically reactive species at near room temperature that can be used in biological applications. Bacteria inactivation was performed using the air direct plasma (with reactive species, UV light, excited species and electric fields). Discharge power density during the experiment was equal to 70 mW/cm2 and plasma dose was regulated by the treatment time. Bacterial biofilms were treated with the non-thermal plasma for 10–300 s. The most effective reduction in the number of S. aureus cells was found after 300 s of treatment and was 2.77 log10 that is 99.83%. When the biofilm of E. coli was used in the experiment, killing of bacteria was independent of the exposure time and the mortality of cells did not exceed 0.48 that is 66.7% kill. The lethal effect on E. coli and S. aureus cells were observed after 300 and 120 s of plasma treatment, respectively but it was necessary to remove the layers of dead cells. The proposed process of removing dead cell layers was carried out due to the probable shielding effect, i.e. dead cells prevent further penetration of active plasma species into the deeper layers of the biofilm. It was shown that the effectiveness of cell destruction by the non-thermal plasma depends on the thickness of biofilm.

Many essential similarities between the behavior and arrangement of biological structures and liquid crystals can be found. Moreover, some of biomacromolecules, such as DNA, are shown to exhibit lyotropic liquid crystalline phases both in vitro and in vivo. In this study, we used natural DNA concentration condition to form DNA liquid crystal (LC) phases as a simplified in vitro model of DNA self-ordering in cells. Due to the increasing interest in the use of nanoparticles as optical markers, we investigated possible applications of silver-doped gold nanoclusters (AuAgNCs) for one- and two-photon imaging in condensed DNA samples. We studied the influence of NCs doping on the DNA LC properties and the distribution of NCs within the liquid crystalline matrix. Depending on the type of DNA liquid crystalline phase we observed different emission patterns of AuAgNCs correlated with the degree of DNA ordering.

Fluorescence imaging probes for specific G-quadruplex (G4) conformations are of considerable interest in biomedical research. Herein, we present the synthesis and the binding properties of a new water-soluble near-infrared (NIR) amphiphilic squaraine dye (CAS-C1) which is capable of selective detection of parallel over non-parallel and non G4 topologies. The striking changes in its linear optical response upon binding to parallel G4s give rise to high fluorescence quantum yields (Φf ≈ 0.7) and one-photon molecular brightness in the far-red-NIR region. The outstanding recognition process of CAS-C1 for parallel G4s via end-stacking provides binding constants in the nanomolar regime (Kb = 107 to 108 M−1) awarding it as one of the most potent parallel G4 binders currently available. Moreover, the CAS-C1-parallel G4 system exhibits large two-photon absorption (TPA) cross-sections and molecular brightness in the second NIR biological transparency window (λ ≈ 1275 nm), making it an ideal candidate for NIR-to-NIR ultrasensitive two-photon procedures.

We report on two-photon excitation properties of small silver-doped gold nanoclusters (AuAgNCs) and on their three-dimensional arrangement in a hybrid system composed of DNA liquid crystals (LCs) and AuAgNCs. UV-vis and fluorescence spectroscopy, transmission electron microscopy (TEM), and multiphoton excitation spectroscopy were used to characterize the nanoparticles. We show that AuAgNCs exhibit two-photon excited luminescence (2PL) emission and second-harmonic generation (SHG) and that these properties remain the same in liquid crystalline matrix. The results are described in detail and discussed in the context of possible imaging application of AuAgNC and specific AuAgNCs organization induced by liquid crystalline ordering of DNA molecules.

International audience; By attaching pyridine groups to a diaza[6]helicene, a helical, bis-ditopic, bis-N N-coordinating ligand can be accessed. Dinuclear rhenium complexes featuring this bridging ligand, of the form [{Re(CO) Cl} (N N-N N)], have been prepared and resolved to give enantiopure complexes. These complexes are phosphorescent in solution at room temperature under one- and two-photon excitation. Their experimental chiroptical properties (optical rotation, electronic circular dichroism and circularly polarized emission) have been measured. They show, for instance, emission dissymmetry factors of c.a. ±3x10 . Quantum-chemical calculations indicate the importance of stereochemistry on the optical activity, pointing towards further design improvements in such types of complexes.

Nonlinear optical microscopy was employed to investigate the properties of microstructures of quinacridone, a hydrogen-bonded pigment, derivative of quinacridine. Recently, quinacridone hierarchical microstructures (μ-QNC) having different nature-inspired morphologies were reported, e.g. in the shape of hedgehogs formed by self-assembled nano-needles. We find that such microcrystals have structure-dependent linear optical properties and exhibit strong two-photon excited fluorescence when irradiated with a near-infrared femtosecond laser. μ-QNCs exhibit different nonlinear optical properties for different crystal structures, including the emergence of symmetry-forbidden second-harmonic generation.

Atomically-precise chiral gold nanoclusters hold promise for an accurate manipulation of chiro-optical properties, both in linear and nonlinear optics regimes. Here, we present the determination of two-photon linear-circular dichroism and two-photon circular dichroism (TPCD) of Au25[(Capt)18]- (where Capt is captopril). TPCD is found to be two orders of magnitude higher than one-photon circular dichroism.

The optical properties of atomically-precise gold nanoclusters differ significantly from those of plasmonic gold nanoparticles, in both linear and nonlinear regimes. Here, we present a systematic study on the third-order nonlinear optical (NLO) properties of thiol-protected gold clusters in a wide range of wavelengths. We applied the Z-scan technique to evaluate the wavelength dispersion of two-photon absorption (2PA) and nonlinear refraction of the nanoclusters in water. The results are discussed with reference to 2PA of plasmonic gold nanoparticles and literature data on NLO properties of gold nanoclusters.

We have studied the interaction of a polymeric water soluble anthracenyl derivative () with salmon testes DNA. The results from UV-Vis, fluorescence, Fourier transform infrared (FT-IR) and circular dichroism spectroscopies indicate that the groove binding process regulates the interaction between and DNA. The binding constants, calculated by absorption spectroscopy at 298, 304 and 310 K, were equal to 3.2 × 10(5) M(-1), 4.7 × 10(5) M(-1), and 6.6 × 10(5) M(-1) respectively, proving a relatively high affinity of for salmon testes DNA. Results of Hoechst 33258 displacement assays strongly support the groove binding mode of to DNA. The association stoichiometry of the :DNA adduct was found to be 1 for every 5 base pairs. FT-IR spectra, recorded at different /DNA molar ratios, indicate the involvement of the phosphate groups and adenine and thymine DNA bases in the association process. Thermodynamic results suggest that hydrophobic forces regulate the binding of with DNA without excluding some extent of involvement of van der Waals forces and hydrogen bonding arising due to surface binding between the hydrophilic polymeric arms of the ligand and the functional groups positioned on the edge of the groove. The resulting composite biomaterial could constitute a valuable candidate for future biological and/or photonic applications.

We report on synthesis and optical properties of new organic compounds based on substituted pyrazole ring. The investigated pyrazoline derivatives (PRDs) exhibit efficient broadband photoluminescence which covers nearly whole visible spectrum. The experimental results are compared to quantum chemical calculations. Amplified spontaneous emission and photodegradation measurements were performed for hybrid systems based on selected PRDs doped into poly(methyl methacrylate) matrix proving the potential utility of such systems in lasing applications. Two-photon absorption (TPA) properties were characterized by the femtosecond Z-scan technique.

We report the synthesis and characterization of new organometallic assemblies consisting of a central Zn(II) tetraphenylporphyrin (ZnTPP) core surrounded by four Ru(II) alkynyl complexes ( trans -Ru(dppe) 2 R) appended at the para phenyl positions and acting as peripheral donor groups. The synthesis of the tetra-chlorido derivative 2 (R=Cl) is reported first, followed by that of three extended homologues ( 3 –X) obtained from this building block by substitution of the chlorido ligands by functionalized arylacetylenes (R=C C(4-C 6 H 4 X); X=NO 2 , H, OMe). Measurement of the nonlinear absorption properties of the pentametallic derivatives 3 –X reveals that these extended π-networks incorporating polarizable organometallic units behave as good two-photon absorbers in the visible and near-IR range.

International audience; We report on the investigation of the structure of DNA liquid crystal (LC) phases by means of polarization sensitive two-photon microscopy (PSTPM). DNA was stained with fluorescent dyes, an intercalator propidium iodide or a groove binder Hoechst 3342 and the angular dependence of the intensity of two-photon excited fluorescence (TPEF) emitted by the dye was collected. The local orientation of DNA molecules in cholesteric and columnar liquid crystal phases was established on the basis of the relative angle between the transition dipole of the dye and the long axis of DNA helix. Three dimensional images of the cholesteric phase were obtained making use of the intrinsic 3D resolving ability of two-photon microscopy. We also discuss the influence of dyes on the parameters of DNA LC phases and comment on advantages and limitations of the PSTPM technique in comparison with other LC characterization techniques. © 2011 Wiley Periodicals, Inc. Biopolymers, 2011.

We report on the impact of doping with gold nanorods (NRs) on the formation and stability of DNA liquid crystals (LCs). Cetyl trimethylammonium (CTAB)-stabilized gold NRs were synthesized using the wet chemistry method. Different textures of cholesteric and columnar mesophases, as well as phase transitions, were observed using a polarized light microscope. It was found that liquid crystalline phases formed in the samples were qualitatively the same and the phase appearance sequence was preserved in the samples regardless of the doping. We show that depending on the concentration of gold NRs present in the phase, nanoparticle-doped cholesteric and columnar hexagonal phases existed in wider temperature ranges compared to pure DNA LCs. The potential applications of these liquid crystal–nanoparticle hybrid systems may include the fabrication of new optoelectronic devices and sensors.

A new type of dinuclear iridium complex, based on a quadrupolar Schiff base ligand, is synthesized and its structure fully characterized. Its linear and nonlinear spectroscopic properties are investigated, evidencing a strong contribution of the metal-to-ligand transitions not only to the linear absorption but also to the two- and three-photon absorption properties.

The Z-scan technique was used to determine the spectral dependence of the nonlinear absorption in well-known DNA intercalators: ethidium bromide and its homodimer. It is found that the compounds show essentially the same features of their nonlinear absorption spectra with the magnitudes of the relevant cross sections scaling with molecular weight of chromophore compound.

We show how a single gold nanorod can serve as a multifunctional probe in an organized DNA matrix. Polarization analysis of two-photon luminescence excited with a femtosecond laser enables imaging of the orientation of a single nanorod, which reports the orientation of DNA strands. Carefully controlled photoinduced heating by the same laser is able to degrade the DNA matrix in a highly localized volume.

Deoxyribonucleic acid (DNA) chains can be engineered for diverse nanophotonics applications by the insertion of molecular groups in different spatial configurations. DNA chains can be assembled into wire-like structures, origami structures, photonic crystal-like assemblies, liquid-crystal phases, and thin films. These structures can be made to serve as scaffolds for the organization of various organic molecules and nanoparticles. The properties of nanostructures can be modified by the use of DNA and DNA modified by the surfactants.