Formation of nanostructured silica materials templated with nonionic fluorinated surfactant followed by in situ SAXS

Nanoparticle-Protein Interaction: Demystifying the Correlation between Protein Corona and Aggregation Phenomena

Protein corona formation and nanoparticles' aggregation have been heavily discussed over the past years since the lack of fine-mapping of these two combined effects has hindered the targeted delivery evolution and the personalized nanomedicine development. We present a multitechnique approach that combines dynamic light and small-angle X-ray scattering techniques with cryotransmission electron microscopy in a given fashion that efficiently distinguishes protein corona from aggregates formation. This methodology was tested using ∼25 nm model silica nanoparticles incubated with either model proteins or biologically relevant proteomes (such as fetal bovine serum and human plasma) in low and high ionic strength buffers to precisely tune particle-to-protein interactions. In this work, we were able to differentiate protein corona, small aggregates formation, and massive aggregation, as well as obtain fractal information on the aggregates reliably and straightforwardly. The strategy presented here can be expanded to other particle-to-protein mixtures and might be employed as a quality control platform for samples that undergo biological tests.

Nonionic Fluorinated Surfactant Removal from Mesoporous Film Using sc-CO2

Surfactant templated silica thin films were self-assembled on solid substrates by dip-coating using a partially fluorinated surfactant R₈^F(EO)₉ as the liquid crystal template. The aim was 2-fold: first we checked which composition in the phase diagram was corresponding to a 2D rectangular highly ordered crystalline phase and second we exposed the films to sc-CO₂ to foster the removal of the surfactant. The films were characterized by in situ X-ray reflectivity (XRR) and grazing incidence small angle X-ray scattering (GISAXS) under CO₂ pressure from 0 to 100 bar at 34 °C. GISAXS patterns reveal the formation of a 2-D rectangular structure at a molar ratio R₈^F(EO)₉/Si equal to 0.1. R₈^F(EO)₉ micelles have a cylindrical shape, which have a core/shell structure ordered in a hexagonal system. The core contains the R₈^F part and the shell is a mixture of (EO)₉ embedded in the silica matrix. We further evidence that the extraction of the template using supercritical carbon dioxide can be successfully achieved. This can be attributed to both the low solubility parameter of the surfactants and the fluorine and ethylene oxide CO₂-philic groups. The initial 2D rectangular structure was well preserved after depressurization of the cell and removal of the surfactant. We attribute the very high stability of the rinsed film to the large value of the wall thickness relatively to the small pore size.

Identification of a major intermediate along the self-assembly pathway of an icosahedral viral capsid by using an analytical model of a spherical patch

Viruses are astonishing edifices in which hundreds of molecular building blocks fit into the final structure with pinpoint accuracy. We established a robust kinetic model accounting for the in vitro self-assembly of a capsid shell derived from an icosahedral plant virus by using time-resolved small-angle X-ray scattering (TR-SAXS) data at high spatiotemporal resolution. By implementing an analytical model of a spherical patch into a global fitting algorithm, we managed to identify a major intermediate species along the self-assembly pathway. With a series of data collected at different protein concentrations, we showed that free dimers self-assembled into a capsid through an intermediate resembling a half-capsid. The typical lifetime of the intermediate was a few seconds and yet the presence of so large an oligomer was not reported before. The progress in instrumental detection along with the development of powerful algorithms for data processing contribute to shedding light on nonequilibrium processes in highly complex systems such as viruses.

Outset of the Morphology of Nanostructured Silica Particles during Nucleation Followed by Ultrasmall-Angle X-ray Scattering

Nucleation and growth of SBA-15 silica nanostructured particles with well-defined morphologies has been followed with time by small-angle X-ray scattering (SAXS) and ultrasmall-angle X-ray scattering (USAXS), using synchrotron radiation. Three different morphologies have been compared: platelets, toroids, and rods. SEM observations of the particles confirm that two key physical parameters control the morphology: the temperature and the stirring of the solution. USAXS curves demonstrate that primary particles with a defined shape are present very early in the reaction mixture, immediately after a very fast nucleation step. This nucleation step is detected at 10 min (56 °C) or 15 min (50 °C) after the addition of the silica precursor. The main finding is that the USAXS signal is different for each type of morphology, and we demonstrate that the difference is related to the shape of the particles, showing characteristic form factors for the different morphologies (platelet, toroid, and rod). Moreover, the size of the mesocrystal domains is correlated directly with the particle dimensions and shape. When stirred, aggregation between primary particles is detected even after 12 min (56 °C). The platelet morphology is promoted by constant stirring of the solution, through an oriented aggregation step between primary particles. In contrast, toroids and rods are only stabilized under static conditions. However, for toroids, aggregation is detected almost immediately after nucleation.

A New Insight into Growth Mechanism and Kinetics of Mesoporous Silica Nanoparticles by in Situ Small Angle X-ray Scattering

The growth mechanism and kinetics of mesoporous silica nanoparticles (MSNs) were investigated for the first time by using a synchrotron time-resolved small-angle X-ray scattering (SAXS) analysis. The synchrotron SAXS offers unsurpassed time resolution and the ability to detect structural changes of nanometer sized objects, which are beneficial for the understanding of the growth mechanism of small MSNs (∼20 nm). The Porod invariant was used to quantify the conversion of tetraethyl orthosilicate (TEOS) in silica during MSN formation, and the growth kinetics were investigated at different solution pH and temperature through calculating the scattering invariant as a function of reaction time. The growth of MSNs was found to be accelerated at high temperature and high pH, resulting in a higher rate of silica formation. Modeling SAXS data of micelles, where a well-defined electrostatic interaction is assumed, determines the size and shape of hexadecyltrimethylammonium bromide (CTAB) micelles before and after the addition of TEOS. The results suggested that the micelle size increases and the micelle shape changes from ellipsoid to spherical, which might be attributed to the solubilization of TEOS in the hydrophobic core of CTAB micelles. A new "swelling-shrinking" mechanism is proposed. The mechanism provides new insights into understanding MSN growth for the formation of functional mesoporous materials exhibiting controlled morphologies. The SAXS analyses were correlated to the structure of CTAB micelles and chemical reaction of TEOS. This study has provided critical information to an understanding of the growth kinetics and mechanism of MSNs.

Partial aggregation of silver nanoparticles induced by capping and reducing agents competition

It is well known that nanomaterials properties and applications are dependent on the size, shape, and morphology of these structures. Among nanomaterials, silver nanoparticles (AgNPs) have attracted attention since they have considerably versatile properties, such as a variable surface area to volume ratio, which is very useful for many biomedical and technological applications. Within this scenario, small nanoparticle aggregates can have their properties reduced due to the increased size and alterations in their shape/morphology. In this work, silver nanoparticles aggregation was studied through chemical reduction of silver nitrate in the presence of sodium borohydride (reducing agent) and sodium citrate (capping agent). By changing the amount of reducing agent along the reaction, unaggregated and partially aggregated samples were obtained and characterized by UV-vis, zeta potential, and SAXS techniques. pH was measured in every step of the reaction in order to correlate these results with those obtained from structural techniques. Addition of the reducing agent first causes the reduction of Ag(+) to silver nanoparticles. For higher concentrations of sodium borohydrate, the average AgNPs size is increased and NPs aggregation is observed. It was found that zeta potential and pH values have a strong influence on AgNPs formation, since reducing agent addition can induce partial removal of citrate weakly associated on the AgNPs surface and increase the ionic strength of the solution, promoting partial aggregation of the particles. This aggregation state was duly identified by coupling SAXS, zeta potential and pH measurements. In addition, the SAXS technique showed that aggregates formed along the process are elongated-like particles due to the exponential decay evidenced through SAXS curves.