Relating Mobility of dsRNA in Nanoporous Silica Particles to Loading and Release Behavior

Abstract

Nanoparticle delivery of polynucleic acids traditionally relies on the modulation of surface interactions to achieve loading and release. This work investigates the additional role of confinement in mobility of dsRNA (84 and 282 base pair (bp) sequences of Spodoptera frugiperda) as a function of silica nanopore size (nonporous, 3.9, 8.0, and 11.3 nm). Amine-functionalized nanoporous silica microspheres (NPSMs, ∼10 μm) are used to directly visualize the loading and exchange of fluorescently labeled dsRNA. Porous particles are fully accessible to both lengths of dsRNA by passive diffusion, except for 282 bp dsRNA in 3.9 nm pores. The stiffness of dsRNA suggests that encapsulation occurs by threading into nanopores, which is inhibited when the ratio of dsRNA length to pore size is large. The mobility of dsRNA at the surface and in the core of NPSMs, as measured by fluorescence recovery after photobleaching, is similar. The mobility increases with pore size (from 0.0002 to 0.001 μm2/s for 84 bp dsRNA in 3.9–11.3 nm pores) and decreases with the length of dsRNA. However, when the dsRNA is unable to load into the pores (on nonporous particles and for 282 bp dsRNA in 3.9 nm pores), surface mobility is not detectable. The pore structure appears to serve as a “source” to provide a mobile network of dsRNA at the particle surface. The importance of mobility is demonstrated by exchange experiments, where NPSMs saturated with mobile dsRNA can exchange dsRNA with the surrounding solution, while immobile dsRNA is not exchanged. These results indicate that nanoparticle synthesis techniques that provide pores large enough to take up polynucleic acids internally (and not simply on the external surface of the particle) can be harnessed to design polynucleic acid/nanoporous silica combinations for controlled mobility as a path forward toward effective nanocarriers.

Covalent Organic Frameworks as Nano‐Reservoir for Room Temperature RNA Storage

“…As a new class of fully organic material, the RNA loading capacities in COFs are appreciable compared to various established inorganic or hybrid materials like silica, silicon, MOFs etc. and can be improved further by structure and morphology tuning of COFs in the future [19–25] . For comparison, Grass et al .…”

“…and can be improved further by structure and morphology tuning of COFs in the future. [19][20][21][22][23][24][25] For comparison, Grass et al calculated RNA loading of 0.5 μg mg À 1 of silica microcapsules for long-term room-temperature storage. [17] Voelcker et al achieved an impressive siRNA loading capacity of 413 μg mg À 1 of porous silicon nanoparticles.…”

“…On the other hand, RNA recovery from silica microcapsules required the chemical dissolution of the outer silica layer, which made the process inconvenient. RNA has also been loaded inside mesoporous silica for various directed therapeutic applications including intracellular RNA delivery [18–23] . Similarly, mesoporous silicon particles have also been used for RNA loading [24–25] .…”

“…RNA has also been loaded inside mesoporous silica for various directed therapeutic applications including intracellular RNA delivery. [18][19][20][21][22][23] Similarly, mesoporous silicon particles have also been used for RNA loading. [24][25] Furthermore, metal organic frameworks (MOFs) have been used to load and deliver small interfering RNA (siRNA) for gene-knockdown studies.…”