Nanoparticle Size

Membrane budding and wrapping of particles, such as viruses and nano-particles, play a key role in intracellular transport and have been studied for a variety of biological and soft matter systems. We study nano-particle wrapping by numerical minimization of bending, surface tension, and adhesion energies. We calculate deformation and adhesion energies as a function of membrane elastic parameters and adhesion strength to obtain wrapping diagrams. We predict unwrapped, partially wrapped, and completely wrapped states for prolate and oblate ellipsoids with various aspect ratios and particle sizes. In contrast to spherical particles, where partially wrapped states exist only for finite surface tensions, partially wrapped states for ellipsoids occur already for tensionless membranes. In addition, the partially wrapped states are long-lived, because of an increased energy cost for wrapping of the highly curved tips. Our results suggest a lower uptake rate of ellipsoidal particles by cells and thereby a higher virulence of tubular viruses compared with icosahedral viruses, as well as co-operative budding of ellipsoidal particles on membranes.

G5-NH2-TAMRAn (n = 1−4, 5+, and 1.5avg)
were prepared with n = 1−4 as a precise dye:dendrimer ratio,
5+ as a mixture of dendrimers with 5 or more dye per
dendrimer, and 1.5avg as a Poisson distribution of dye:dendrimer
ratios with a mean of 1.5 dye per dendrimer. The
absorption intensity increased sublinearly with n whereas the
fluorescence emission and lifetime decreased with an
increasing number of dyes per dendrimer. Flow cytometry
was employed to quantify uptake into HEK293A cells. Dendrimers with 2−4 dyes were found to have greater uptake than
dendrimer with a single dye. Fluorescence lifetime imaging microscopy (FLIM) showed that the different dye:dendrimer ratio
alone was sufficient to change the fluorescence lifetime of the material observed inside cells. We also observed that the lifetime of
G5-NH2-TAMRA5+ increased when present in the cell as compared to solution. However, cells treated with G5-NH2-
TAMRA1.5avg did not exhibit the high lifetime components present in G5-NH2-TAMRA1 and G5-NH2-TAMRA5+. In general, the effects of the dye:dendrimer ratio on fluorescence lifetime were of similar magnitude to environmentally induced lifetime shifts.