Ionic Strength and the Supporting Material Strongly Influence the Adhesion of Silica to Supported Lipid Bilayers

Abstract

In the context of cell–nanoparticle interaction, the question arises how ions influence the adhesion between nanoparticles and cell membranes. Here, the question is addressed how the adhesion energy between supported lipid bilayers and silica particles helps to understand nanoparticle uptake. Supported lipid bilayers on mica and glass substrates serve as simple, well‐defined, and reproducible membrane models. Using atomic force microscopy with modified cantilevers, the interaction energy of both is found to result in a distinctive dependence on the supporting material. The adhesion energy for 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine on mica substrates shows a clear dependence on the NaCl concentration. On glass supports, in contrast, stronger adhesive forces lacking a systematic dependence are found. This is related to experiments where the uptake of silica nanoparticles in free‐standing vesicles is observed. While the qualitative dependence of the interaction strength on the ion concentration is definitely confirmed, the quantitative values of the adhesion energy can hardly be transferred to vesicles. These prospects and challenges also hold for investigations of more complex biological cell membranes in which increasing complexity inevitably also will increase the challenges. Due to the limited transferability of results obtained in situations of different symmetry and geometry, the combination of different methods is suggested.

Phase-State-Dependent Silica Nanoparticle Uptake of Giant Unilamellar Vesicles

“…However, adhesion energies ranging from 10 −5 to 1 mJ/m 2 are well-known under different conditions, 57,58 where adhesion can be measured without contact in the weak and ultraweak regimes. 59,60 A study of our group regarding the ion concentration switching on and off the adhesion energy was reported by Wittman et al 61 For a supported lipid bilayer in the fluid phase (DOPC) and a micrometer-sized silica bead, we found a saltdependent attraction threshold value, at about c crit = 15 mM NaCl. At higher salt concentrations, the adhesion energy saturates at about E adh = 60 μJ/m 2 , being significantly smaller than the one cited above.…”

Phase-State Dependent Silica Nanoparticle Uptake of Giant Unilamellar Vesicles

“…A study of our group regarding the ion concentration switching on and off the adhesion energy, was reported by Wittman et al [54]. For a supported lipid bilayer in the fluid phase (DOPC) and a micrometer sized silica bead, we found a salt dependent attraction threshold value, at about ccrit = 15 mM NaCl.…”

Ion controlled passive nanoparticle uptake in lipid vesicles in theory and experiment

“…Particle-size-dependent correlation between uptake rate and ionic concentration For the system studied in this work, a specific ionic environment is prerequisite in order to observe passive NP uptake. It has been shown that adhesion strength between silica particles and lipid membranes is strongly correlated to the ion concentration of the surrounding medium [14,34]. In the following section, we quantitatively determine the influence of salt concentration on the NP uptake.…”

“…For a deeper understanding of these effects, we here present additional data on uptake dynamics and dependencies on particle concentration and adhesion strength. In particular, we varied the adhesion strength and thus the driving force for NP uptake by adjusting the salt concentration for different particle sizes and concentrations [14]. In-depth experiments on these aspects will be followed by a discussion of a plausible theoretical picture of adhesion-driven particle uptake.…”