Bulky Counterions: Enhancing the Two-Photon Excited Fluorescence of Gold Nanoclusters

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pH-Induced transformation of ligated Au 25 to brighter Au 23 nanoclusters

Thiolate-protected gold nanoclusters have recently attracted considerable attention due to their size-dependent luminescence characterized by a long lifetime and large Stokes shift. However, the optimization of nanocluster properties such as the luminescence quantum yield is still a challenge. We report here the transformation of Au25Capt18 (Capt labels captopril) nanoclusters occurring at low pH and yielding a product with a much increased luminescence quantum yield which we have identified as Au23Capt17. We applied a simple method of treatment with HCl to accomplish this transformation and we characterized the absorption and emission of the newly created ligated nanoclusters as well as their morphology. Based on DFT calculations we show which Au nanocluster size transformations can lead to highly luminescent species such as Au23Capt17

Zwitterion functionalized gold nanoclusters for multimodal near infrared fluorescence and photoacoustic imaging

International audienceGold nanoclusters (Au NCs) are an emerging type of theranostic agents combining therapeutic and imaging features with reduced toxicity. Au NCs stabilized by a zwitterion ligand with a fine control of the metal core size and the ligand coverage were synthesized by wet chemistry. Intense fluorescence signal is reported for the highest ligand coverage whereas photoacoustic signal is stronger for the largest metal core. The best Au NCs candidate with an average molecular weight of 17 kDa could be detected with high sensitivity on a 2D-NIR imaging instrument (LOD = 2.3 µM) and by photoacoustic imaging. In vitro and in vivo experiments demonstrate an efficient cell uptake in U87 cell lines, a fast renal clearance (t 1/2 α = 6.5±1.3 min) and a good correlation between near 2 infrared fluorescence and photoacoustic measurements to follow the early uptake of Au NCs in liver

Photoluminescence of Fully Inorganic Colloidal Gold Nanocluster and Their Manipulation Using Surface Charge Effects

International audienceFully inorganic, colloidal gold nanoclusters (NCs) constitute a new class of nanomaterials that are clearly distinguishable from their commonly studied metal–organic ligand-capped counterparts. As their synthesis by chemical methods is challenging, details about their optical properties remain widely unknown. In this work, laser fragmentation in liquids is performed to produce fully inorganic and size-controlled colloidal gold NCs with monomodal particle size distributions and an fcc-like structure. Results reveal that these NCs exhibit highly pronounced photoluminescence with quantum yields of 2%. The emission behavior of small (2–2.5 nm) and ultrasmall (<1 nm) NCs is significantly different and dominated by either core- or surface-based emission states. It is further verified that emission intensities are a function of the surface charge density, which is easily controllable by the pH of the surrounding medium. This experimentally observed correlation between surface charge and photoluminescence emission intensity is confirmed by density functional theoretical simulations, demonstrating that fully inorganic NCs provide an appropriate material to bridge the gap between experimental and computational studies of NCs. The presented study deepens the understanding of electronic structures in fully inorganic colloidal gold NCs and how to systematically tune their optical properties via surface charge density and particle size

Temperature-controlled IMS-IMS measurements for conformational thermodynamics

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Structural insights into glutathione-protected gold Au

Gold nanoclusters protected by ligands present well-defined compositions and tunable structures, which builds a solid basis for correlation between structures and properties. We report a combined ion mobility-mass spectrometry approach for the analysis of ultra-small gold nanoclusters protected by glutathione (SG) as ligand molecules, Au10−12(SG)10−12. Collision cross section (CCS) measurements are reported for different charge states for Au10(SG)10, Au11(SG)11 and Au12(SG)12 nanoclusters. Computational calculations, at the PM7 semi-empirical level of theory, are performed to optimize geometrical structures and use them to compute CCS. The comparison of the experimentally and theoretically determined CCS allows drawing conclusions on the structural changes, in particular partial unfolding of SG ligands, upon charging

Structure and Charge Heterogeneity in Isomeric Au25(MBA)18 Nanoclusters—Insights from Ion Mobility and Mass Spectrometry

International audienceAtomically precise Au25(MBA)18 nanoclusters were investigated by mass spectrometry and ion mobility spectrometry. We show that clusters sharing the same chemical composition and bearing the same net charge may display different structures and different charge repartition patterns, namely, the number of charges corresponding to deprotonation of the ligand moieties through carboxyl groups is not the same for all detected species. Part of the observed heterogeneity is a consequence of spontaneous electron loss occurring in the gas phase, which modifies the net charge of the clusters while maintaining the initial (de)protonation state

Negatively charged liganded gold clusters: where is the charge? Insight from IMS-MS

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