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Heterogeneous metal nanocatalysts have recently emerged as attractive catalysts for a variety of couplings (e.g., C−C, C−N, C−S, C−O, etc.). However, the characterization of the catalytic pathway remains challenging. By exploiting localized surface plasmon resonance (LSPR) of the catalytically relevant gold (Au) nanostructure, we show that UV−vis spectroscopy can be used to confirm the homogeneous catalytic pathway. Specifically, we have demonstrated that Au nanoparticles under C−C coupling conditions undergo substrate-induced leaching to form homogeneous Au catalytic species. The LSPR spectroscopic approach opens a new door to track stability of nanocatalysts and characterize the catalytic pathway in a range of coupling reactions.

The aim of the present study was to evaluate a library of poly-L-lysine (PLL)-graft (g)-polyethylene glycol (PEG) copolymers for the ability to encapsulate effectively a model protein, bovine serum albumin (BSA), and to characterize the stability and protein function of the resulting nanoparticle. A library of nine grafted copolymers was produced by varying PLL molecular weight and PEG grafting ratio. Electrostatic self-assembly of the protein and the grafted copolymer drove encapsulation. The formation of protein/polymer nanoparticles with a core/shell structure was confirmed using PAGE, dynamic light scattering, and electron microscopy. Encapsulation of the BSA into nanoparticles was strongly dependent on the copolymer-to-protein mass ratio, PEG grafting ratio, and PLL molecular weight. A copolymer-to-protein mass ratio of 7:1 and higher was generally required for high levels of encapsulation, and under these conditions, no loss of protein activity was observed. Copolymer characteristics also influenced nanoparticle resistance to polyanions and protease degradation. The results indicate that a copolymer of 15-30 kDa PLL, with a PEG grafting ratio of 10:1, is most promising for protein delivery.

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Plasmonic devices, consisting of nanoparticle monolayers, are conveniently fabricated by deposition techniques, wherein thermodynamics often favor the particle shape to be close to hemispherical. The present work investigates plasmon modes in Ag nanohemispheres (NHSs) using s-and p-polarized incident radiation at varying angles. The Ag NHSs, immobilized on nanoposts, resembling mushroom structures, allow for reduced substrate coupling and convenient resolution of the modes. Additionally, the modes are studied by in situ extinction acquisitions during nanoparticle synthesis and elucidated by numerical simulations. It is revealed that the broken symmetry by asymmetric particle shape leads to dipolar modes parallel and normal to the base, which are significantly different in terms of energy, excitation dependence on polarization, and particle−particle as well as particle−substrate couplings. In particular, the major parallel mode offers distinct advantages in plasmonics applications over nanospheres. For example, its strong substrate coupling may benefit thin film photovoltaics by efficient light coupling. Higher field concentrations are induced at the sharp edges of a NHS that may enhance hot electron injection in a photocatalyst. Unlike in a spherical dimer, where the field intensity peaks in the middle of the gap, the maximum field in a NHS dimer gap occurs on the metal surface (i.e., at the edges), overlaying with the chemical enhancement. Hence, a higher surface enhancement factor can be achieved in Raman scattering.

The present work discloses the unusual photooxidation observed for V3O7·H2O nanowires under 514 nm excitation above a threshold intensity of 0.30 kW/cm2. We explicate this phenomenon by in-situ Raman and photoluminescence spectroscopy at varying laser intensities as well as models for the transformation kinetics and energy band structure associated with H2OVO5 octahedron. The photooxidation is found to be triggered by two-photon cleavage of the H2O–V bond through excitation via nonbonding d-states. Subsequently, V3O7 spontaneously oxidizes to V2O5. However, the competing process of H2O’s rebonding is also realized. Hence, transformation to V2O5 occurs only if the H2O–V bond-cleavage rate exceeds a threshold, pushing the number of concomitantly broken bonds in the smallest structural unit to a critical number.

Trans↔cis isomerization in single azobenzene molecules were captured by Surface-enhanced Raman Scattering (SERS) using nanoAg-on-Ge substrates. Isomerization was observed to occur more frequently in the presence of 365 nm LED excitation in addition to the 532 nm Raman probe laser. Under these excitation conditions, the trans→cis isomerization frequency (i.e., ~0.1 s -1 ) is observed to be much lower than the theoretical estimate (i.e., ~100 s -1 without the surface enhancement effect). This "slowing down" effect allows us to resolve azobenzene's conformational changes at a time scale of 40 ms. We attribute this dramatic reduction in isomerization frequency to adsorption of azobenzene to silver that restrains its rotational freedom. As deduced from statistical analysis of the single molecule spectra, this restraint is higher for the trans form that we explain its stronger chemisorption due to its planar geometry.

The present work demonstrates hydrogen generation by nanowire-nanoparticle conjugate structures under visible radiation. The mechanism of hydrogen generation is attributed to photolytic cleavage of water. The nanostructures are synthesized by sol-gel and reduction chemistries and characterized by XRD, SEM, TEM, and optical spectroscopy. Photolysis is analyzed by gas chromatography. We discuss the possible mechanisms involved in the observed photolysis in terms of unique attributes of the multifunctional nanostructures, such as efficient channeling of photocarriers to redox reactions at the interfaces and self-alignment of energy levels leading to efficient charge transfer. We demonstrate conversion and quantum efficiencies of 10.6% and 22.5%, respectively, for the first hour of photolysis, under 470 nm excitation.