Photothermal stability of biologically and chemically synthesized gold nanoprisms.

We report here the influence of the irradiation with femtosecond laser pulses on the gold nanoprisms synthesized using biological and chemical methods. For the bio-mediated growth, we used plant extract as a source of reducing, structure-directing, and stabilizing agents, while for the chemical method, we applied three-step protocol, involving chemicals commonly used in the synthesis of nanostructures. Exposition of the nanostructures to the laser beam causes morphological changes, which affect their extinction spectra. These modifications were followed using absorption spectroscopy and transmission electron microscopy. The observed effects depend on the applied laser power and excitation wavelength. Under resonance conditions, rounding of the tips of triangular nanoparticles and transformation towards more stable, spherical form were noticed. These changes were faster under higher laser power. Such shape modifications were weaker under off-resonance conditions. Moreover, chemically synthesized gold nanoprisms were less susceptible to the morphological changes than those obtained using plant extract; however, their colloidal stability was disrupted by long-time irradiation. Graphical abstractᅟ.

Bio-mediated synthesis, characterization and cytotoxicity of gold nanoparticles.

We report here a "green" approach for the synthesis of gold nanoparticles (GNPs) in which the Mentha piperita extract was applied for the bioreduction of chloroauric acid and the stabilization of the formed nanostructures. The obtained GNPs were characterized by UV-Vis absorption spectroscopy and transmission electron microscopy (TEM). The reduction of gold ions with the plant extract leads to the production of nanoparticles with various shapes (spherical, triangular and hexagonal) and sizes (from 10 to 300 nm). The kinetics of the reaction was monitored and various conditions of the synthesis were investigated. As a result, we established protocols optimized towards the synthesis of nanospheres and nanoprisms of gold. The cytotoxic effect of the obtained gold nanoparticles was studied by performing MTT assay, which showed lower cytotoxicity of the biosynthesized GNPs compared to gold nanorods synthesized using the usual seed-mediated growth. The results suggest that the synthesis using plant extracts may be a useful method to produce gold nanostructures for various biological and medical applications.

Weighing polyelectrolytes packaged in viruslike particles.

This Letter reports on the remarkable selectivity of capsid proteins for packaging synthetic polyelectrolytes in viruslike particles. By applying the contrast variation method in small-angle neutron scattering, we accurately estimated the mean mass of packaged polyelectrolytes ⟨Mp⟩ and that of the surrounding capsid ⟨Mcap⟩. Remarkably, the mass ratio ⟨Mp⟩/⟨Mcap⟩ was invariant for polyelectrolyte molecular weights spanning more than 2 orders of magnitude. To do so, capsids either packaged several chains simultaneously or selectively retained the shortest chains that could fit the capsid interior. Our data are in qualitative agreement with theoretical predictions based on free energy minimization and emphasize the importance of protein self-energy. These findings may give new insights into the nonspecific origin of genome selectivity for a number of viral systems.