Inelastic Light Scattering by Long Narrow Gold Nanocrystals: When Size, Shape, Crystallinity, and Assembly Matter

Sensitivity of Localized Surface Plasmon Resonance and Acoustic Vibrations to Edge Rounding in Silver Nanocubes

Precise knowledge of the dependence of nano-object properties on their structural characteristics such as their size, shape, composition, or crystallinity, in turn, enables them to be finely characterized using appropriate techniques. Spectrophotometry and inelastic light scattering spectroscopy are noninvasive techniques that are proving highly robust and efficient for characterizing the optical response and vibrational properties of metal nano-objects. Here, we investigate the optical and vibrational properties of monodomain silver nanocubes synthesized by the chemical route, with edge length ranging from around 20 to 58 nm. The synthesized nanocrystals are not perfectly cubic and exhibit rounded edges and corners. This rounding was quantitatively taken into account by assimilating the shape of the nanocubes to superellipsoids. The effect of rounding on their optical response was clearly evidenced by localized surface plasmon resonance spectroscopy and supported by calculations based on the discrete dipole approximation method. The study of their acoustic vibrations by high-resolution low-frequency Raman scattering revealed a substructure of the T2g band, which was analyzed as a function of rounding. The measured frequencies are consistent with the existence of an anticrossing pattern of the two T2g branches. Such an avoided crossing in the T2g modes is clearly evidenced by calculating the vibrational frequencies of silver nanocubes using the Rayleigh-Ritz variational method that accounts for both their real size, shape, and cubic elasticity. These results show that it is possible to assess the rounding of nanocubes, including by means of ensemble spectroscopic measurements on well-calibrated particles.

Optomechanical Hot-Spots in Metallic Nanorod-Polymer Nanocomposites

Plasmonic coupling between adjacent metallic nanoparticles can be exploited for acousto-plasmonics, single-molecule sensing, and photochemistry. Light absorption or electron probes can be used to study plasmons and their interactions, but their use is challenging for disordered systems and colloids dispersed in insulating matrices. Here, we investigate the effect of plasmonic coupling on optomechanics with Brillouin light spectroscopy (BLS) in a prototypical metal-polymer nanocomposite, gold nanorods (Au NRs) in polyvinyl alcohol. The intensity of the light inelastically scattered on thermal phonons captured by BLS is strongly affected by the wavelength of the probing light. When light is resonant with the transverse plasmons, BLS reveals mostly the normal vibrational modes of single NRs. For lower energy off-resonant light, BLS is dominated by coupled bending modes of NR dimers. The experimental results, supported by optomechanical calculations, document plasmonically enhanced BLS and reveal energy-dependent confinement of coupled plasmons close to the tips of NR dimers, generating BLS hot-spots. Our work establishes BLS as an optomechanical probe of plasmons and promotes nanorod-soft matter nanocomposites for acousto-plasmonic applications.

Development of a multi-arm polyrotaxanes modified mesoporous silica-coated gold nanoplatform for protecting endothelial progenitor cells against high glucose environment

Recent study reported that endothelial progenitor cells (EPCs) have potential to treat diabetic macroangiopathy. High glucose environment of diabetes can affect the adhesion of EPCs by decreasing the expression of CXC chemokine receptor 4 (CXCR4) and affect the proliferation of EPCs by decreasing the expression of miR-126. The results showed that the cytotoxicity of GNR@MSNs@PEI to EPCs was significantly lower than PEI; the temperature of GNR@MSNs@PEI solution can be controlled between 38-40°C under 808 nm laser irradiation. 25.67 µg of pcDNA3.1-GFP-CXCR4 and 5.36 µg of FITC-miR-126 could be loaded in 1 mg of GNR@MSNs@PEI; GNR@MSNs@PEI has gene transfection almost the same as Lipofectamine 3000. Subsequent in vitro studies showed that pcDNA3.1-GFP-CXCR4 and miR-126 loaded GNR@MSNs@PEI can significantly increase the adhesion and proliferation and decrease the apoptosis of EPCs treated with high glucose under 808 nm laser irradiation. In conclusion, nano-carriers (GNR@MSNs@PEI) with high pcDNA3.1-CXCR4 and miR-126 loading capacity, high biocompatibility, well cell internalization, and controllable release ability were constructed to transfer CXCR4 expression plasmid (pcDNA3.1-CXCR4) and miR-126 into EPCs efficiently. Further in vitro studies indicated that pcDNA3.1-CXCR4 and miR-126-loaded GNR@MSNs@PEI could protect EPCs against high glucose-induced injury.