Search

International audience; The fluorescence-free measurement of molecular second-order nonlinear optical properties (i.e. the first hyperpolarizability β) in solution for a set of fluorescent proteins and channel rhodopsins is reported. Because removing the fluorescence contribution is critical in providing accurate values for this nonlinear optical property, especially for the fluorescent proteins, we use and critically compare two different approaches to correct hyper Rayleigh scattering from the multiphoton fluorescence contribution. On the one hand, we use the frequency domain where the delayed fluorescence contribution is separated from the instantaneous hyper-Rayleigh scattering contribution through amplitude modulation and on the other hand we use the spectral domain where the broadband fluorescence spectrum is subtracted from the narrower hyper Rayleigh scattering line. The two methods, discussed in terms of their efficiency for routine measurements, yield similar first hyperpolarizability values, therefore establishing the robustness of the two approaches to correct for the fluorescence. From the data reported, the previously observed trend where more red-shifted fluorescent proteins have larger hyperpolarizability values because of their longer conjugated chromophore is unambiguously confirmed. For the channel rhodopsins, it is shown that despite their obligate dimeric and fairly symmetric nature, large first hyperpolarizabilities are measured, pointing to their potential use for second-harmonic imaging and membrane potential measurements in nonlinear optogenetics.

We developed a new heterobifunctional polyethylene glycol ligand for iron oxide nanoparticles with a group for covalent surface attachment and for chelating metal ions. After introduction of nickel ions, His-tagged fluorescent proteins were magnetically purified from a cell lysate. A high purity product and efficient magnetic separation were observed.

Evolution can increase the complexity of matter by self-organization into helical architectures, the best example being the DNA double helix. One common aspect, apparently shared by most of these architectures, is the presence of covalent bonds within the helix backbone. Here, we report the unprecedented crystal structures of a metal complex that self-organizes into a continuous double helical structure, assembled by non-covalent building blocks. Built up solely by weak stacking interactions, this alternating tread stairs-like double helical assembly mimics the DNA double helix structure. Starting from a racemic mixture in aqueous solution, the ruthenium(II) polypyridyl complex forms two polymorphic structures of a left-handed double helical assembly of only the Λ-enantiomer. The stacking of the helices is different in both polymorphs: a crossed woodpile structure versus a parallel columnar stacking. ispartof: Angewandte Chemie - International Edition vol:53 issue:34 pages:8959-8962 ispartof: location:Germany status: published

Thiolate-protected gold clusters are promising candidates for imaging applications due to their interesting, size-dependent properties. Their high stability and the ability to functionalize the clusters with biocompatible ligands render the clusters interesting for various imaging techniques such as fluorescence microscopy or second-harmonic generation microscopy. The latter nonlinear optical effect has not yet been observed on this type of ultrasmall nanoparticle. We hereby present second- and third-harmonic generation and multiphoton fluorescence of two thiolate-protected gold clusters: Au25(SCH 2CH2Ph)18 and Au38(SCH2CH2Ph)24. At a fundamental wavelength of 800 nm, the Au38(SCH2CH2Ph)24 cluster is active. In contrast, Au25(SCH2CH2Ph)18 does not yield significant SHG signal. We ascribe this to the center of inversion in the Au25 cluster. Measurements on chiral Au25(capt)18 (capt: captopril) gave an SHG response, supporting this interpretation. We also observed third-harmonic generation at a fundamental wavelength of 1200 nm. At 800 and 1100 nm, the clusters decompose after short illumination time but are stable at illumination at 1200 nm. This may be exploited in combined deep tissue imaging and photothermal heating for theranostics applications