Pump-Selective Spectral Shaping of the Ultrafast Response in Plasmonic Nanostars

Plasmonic nanostructures are, to date, well-known to offer unique possibilities for the tailoring of light–matter interactions at the nanoscale. Most recently, a new route to ultrafast all-optical modulation has been disclosed by combining the resonant features of plasmonic nanostructures with the giant third-order optical nonlinearity of noble metals regulated by highly energetic (hot) carriers. In this framework, a variety of nanostructures have been designed, with special attention to shapes featuring tips, where extreme and highly sensitive field enhancements (hot spots) can be attained. Here, we report on a broadband pump–probe spectroscopy analysis of an ensemble of spiky star-shaped nanoparticles, exploring both the perturbative and nonperturbative regimes of photoexcitation. The experiments are corroborated by semiclassical numerical simulations of the ultrafast optical response of the sample. We found that the peculiar hot spots supported by the star tips allow one to easily control the spectral shape of the transient optical signal, upon tuning of the pump wavelength. Our results elucidate the ultrafast response of hot electrons in star-shaped nanostructures and contribute to the understanding of the tip-mediated enhanced nonlinearities. This work paves the way to the development of ultrafast all-optical plasmonic modulators for pump-selective spectral shaping

Synthesis of Water Dispersible and Catalytically Active Gold-Decorated Cobalt Ferrite Nanoparticles

Hetero-nanoparticles represent an important family of composite nanomaterials that in the past years are attracting ever-growing interest. Here, we report a new strategy for the synthesis of water dispersible cobalt ferrite nanoparticles (Co_<i>x</i>Fe_3–<i>x</i>O₄ NPs) decorated with ultrasmall (2–3 nm) gold nanoparticles (Au NPs). The synthetic procedure is based on the use of 2,3-<i>meso</i>-dimercapto­succinic acid (DMSA), which plays a double role. First, it transfers cobalt ferrite NPs from the organic phase to aqueous media. Second, the DMSA reductive power promotes the <i>in situ</i> nucleation of gold NPs in proximity of the magnetic NP surface. Following this procedure, we achieved a water dispersible nanosystem (Co_<i>x</i>Fe_3–<i>x</i>O₄–DMSA–Au NPs) which combines the cobalt ferrite magnetic properties with the catalytic features of ultrasmall Au NPs. We showed that Co_<i>x</i>Fe_3–<i>x</i>O₄–DMSA–Au NPs act as an efficient nanocatalyst to reduce 4-nitrophenol to 4-aminophenol and that they can be magnetically recovered and recycled. It is noteworthy that such nanosystem is more catalytically active than Au NPs with equal size. Finally, a complete structural and chemical characterization of the hetero-NPs is provided

Synthesis of a Structural Analogue of the Repeating Unit from <i>Streptococcus pneumoniae</i> 19F Capsular Polysaccharide Based on the Cross-Metathesis–Selenocyclization Reaction Sequence

Pseudo-oligosaccharides have attracted much interest as scaffolds for the synthesis of sugar mimics endowed with very similar biological properties but structurally and synthetically simpler than their natural counterparts. Herein, the synthesis of pseudo-oligosaccharides using the cross-metathesis reaction between distinct sugar-olefins followed by intramolecular selenocyclization of the obtained heterodimer as key steps is first investigated. This methodology has been then applied to the preparation of structural analogues of the trisaccharide repeating unit from <i>Streptococcus pneumoniae</i> 19F. The inhibition abilities of the synthetic molecules were evaluated by a competitive ELISA assay using a rabbit polyclonal anti-19F serum

Synthesis of a Structural Analogue of the Repeating Unit from <i>Streptococcus pneumoniae</i> 19F Capsular Polysaccharide Based on the Cross-Metathesis–Selenocyclization Reaction Sequence

Pseudo-oligosaccharides have attracted much interest as scaffolds for the synthesis of sugar mimics endowed with very similar biological properties but structurally and synthetically simpler than their natural counterparts. Herein, the synthesis of pseudo-oligosaccharides using the cross-metathesis reaction between distinct sugar-olefins followed by intramolecular selenocyclization of the obtained heterodimer as key steps is first investigated. This methodology has been then applied to the preparation of structural analogues of the trisaccharide repeating unit from <i>Streptococcus pneumoniae</i> 19F. The inhibition abilities of the synthetic molecules were evaluated by a competitive ELISA assay using a rabbit polyclonal anti-19F serum

A Synthetic Disaccharide Analogue from Neisseria meningitidis A Capsular Polysaccharide Stimulates Immune Cell Responses and Induces Immunoglobulin G (IgG) Production in Mice When Protein-Conjugated

Some new phosphonoester-linked oligomers, stabilized analogues of the corresponding phosphate-bridged oligomers of Neisseria meningitidis A (MenA) capsular polysaccharide (CPS), were conjugated to human serum albumin (HSA), as a protein carrier model, and studied for immunological activities. We determined (i) in vitro, their biocompatibility (CAM test) and activity in inducing both T cell proliferation (CFSE method) and IL-2 release (ELISA), and (ii) in vivo, their ability to stimulate specific IgG antibody production (ELISA). All HSA-conjugated compounds induce T cell proliferation (40% of proliferation at 10² μM), whereas only the phosphonodisaccharide was effective (28% of proliferation at 10² μM) among the unconjugated forms. IL-2 release confirmed these results. In addition, the HSA-conjugated showed in vivo the capacity of eliciting the production of specific IgG antibodies. In conclusion, we obtained novel biocompatible, water-stable, and immunoactive MenA CPS analogues. A short disaccharide fragment showed the unusual behavior of triggering T cell proliferation in vitro

Immunoactivity of Protein Conjugates of Carba Analogues from <i>Neisseria meningitidis</i> A Capsular Polysaccharide

<i>Neisseria meningitidis</i> type A (MenA) is a Gram-negative encapsulated bacterium that is a major cause of epidemic meningitis, especially in the sub-Saharan region of Africa. The development and manufacture of a liquid glycoconjugate vaccine against MenA are hampered by the poor hydrolytic stability of its capsular polysaccharide (CPS), consisting of (1→6)-linked 2-acetamido-2-deoxy-α-d-mannopyranosyl phosphate repeating units. The replacement of the ring oxygen with a methylene group to generate a carbocyclic analogue leads to enhancement of its chemical stability. Herein, we report conjugation of carbocyclic analogue monomer, dimer, and trimer to the protein carrier CRM₁₉₇. After immunization in mice, only the conjugated trimer was able to induce specific anti-MenA polysaccharide IgG antibodies with <i>in vitro</i> bactericidal activity, although to a lesser extent than pentadecamer and hexamer oligomers obtained from mild acid hydrolysis of the native polysaccharide conjugated to the same protein carrier. This study represents the first proof-of-concept that hydrolytically stable structural analogues of saccharide antigens can be used for the development of efficacious antimicrobial preventative therapies. Conjugates with longer carbocyclic oligomers and/or precise acetylation patterns could further increase the induced immune response to a level comparable with those of commercially available anti-meningococcal glycoconjugate vaccines