Highly Flexible Platform for Tuning Surface Properties of Silica Nanoparticles and Monitoring Their Biological Interaction

Abstract

The following work presents a simple, reliable and scalable seeding-growth methodology to prepare silica nanoparticles (SiO2 NPs) (20, 30, 50 and 80 nm) directly in aqueous phase, both as plain- as well as fluorescent-labeled silica. The amount of fluorescent label per particle remained constant regardless of size, which facilitates measurements in terms of number-based concentrations. SiO2 NPs in dispersion were functionalized with an epoxysilane, thus providing a flexible platform for the covalent linkage of wide variety of molecules under mild experimental conditions. This approach was validated with ethylenediamine, two different amino acids and three akylamines to generate a variety of surface modifications. Accurate characterization of particle size, size distributions, morphology and surface chemistry is provided, both for as-synthesized particles and after incubation in cell culture medium. The impact of physicochemical properties of SiO2 NPs was investigated with human alveolar basal epithelial cells (A549) such as the effect in cytotoxicity, cell internalization and membrane interaction.

XRF mapping and TEM analysis of coated and uncoated silica nanoparticles in A549 cells and human monocytes

“…The dimension of the nanoparticles has been measured by disc‐centrifugal liquid sedimentation (CLS) performed on a CLS Disc Centrifuge model DC24000UHR (CPS Instruments Europe, Netherlands) in a sucrose density gradient 8%–24% ( w /w) running at 22,000 rpm; prior to each measurement, the instrument was calibrated using as a reference spheres of poly (vinylchloride) of 377 nm diameter in an aqueous solution . To confirm the formation of the epoxy coating on the nanoparticle surface, they were reacted with 5‐(aminomethyl) fluorescein hydrochloride (Invitrogen, Italy) as described elsewhere . UV‐vis absorption spectra were recorded with an Evolution 300 UV–Vis spectrophotometer (Thermo Scientific, USA) functioning between 300 and 800 nm at room temperature.…”

“…[16] To confirm the formation of the epoxy coating on the nanoparticle surface, they were reacted with 5-(aminomethyl) fluorescein hydrochloride (Invitrogen, Italy) as described elsewhere. [16][17][18] UV-vis absorption spectra were recorded with an Evolution 300 UV-Vis spectrophotometer (Thermo Scientific, USA) functioning between 300 and 800 nm at room temperature. Uncoated silica nanoparticles do not absorb at 492 nm, and therefore, the intensity of the registered absorbance is due to the reaction of the amine group of the fluorescein dye and the epoxy group coating the silica nanoparticles.…”

Biocompatibility of Amine‐Functionalized Silica Nanoparticles: The Role of Surface Coverage

“…To corroborate the surface coverage with amino groups, a more sophisticated method was established. Magic angle spinning (MAS) 29 Si-NMR can identify different silicon coordinations and distinguish, e.g., silanols or silicon bonded to carbon ( Figure S3, Supporting Information). Quantitative NMR analysis thus allows for the direct estimation of the surface coverage by deconvoluting the different contributions to the 29 Si-NMRspectra.…”

“…Small 2019, 15, 1805400 Figure 1. Magic angle spinning 29 Si-NMR characterization of NPs. Direct polarization (DP) and cross polarization (CP) was used to distinguish bulk material from the surface-exposed silanol groups, respectively.…”

“…TEM analysis indicated an increased porosity and dissolution of SiO 2 NPs in accordance with previous findings on Stöber-type silica ( Figure S4, Supporting Information). [28,29] As a consequence of partial dissolution, loss of amino groups from the silica surface might also decrease the inter-particle attractive forces and, hence, particles suspensions should become more stable again, as suggested by decreased hydrodynamic radii (Table 1).…”