Formation of organosilica nanoparticles with dual functional groups and simultaneous payload entrapment

Synthetic strategies for nonporous organosilica nanoparticles from organosilanes

Organosilica nanoparticles refer to silica nanoparticles containing carbon along with organic or functional groups and can be divided into mesoporous organosilica nanoparticles and nonporous organosilica nanoparticles. During the past few decades, considerable efforts have been devoted to the development of organosilica nanoparticles directly from organosilanes. However, most of the reports have focused on mesoporous organosilica nanoparticles, while relatively few are concerned with nonporous organosilica nanoparticles. The synthesis of nonporous organosilica nanoparticles typically involves (i) self-condensation of an organosilane as the single source, (ii) co-condensation of two or more types of organosilanes, (iii) co-condensation of tetraalkoxysilane and an organosilane, and (iv) spontaneous emulsification and the subsequent radical polymerization of 3-(trimethoxysilyl)propyl methacrylate (TPM). This article aims to provide a review on the synthetic strategies of this important type of colloidal particle, followed by a brief discussion on their applications and future perspectives.

Stable Encapsulation of Methylene Blue in Polysulfide Organosilica Colloids for Fluorescent Tracking of Nanoparticle Uptake in Cells

Methylene blue (MB), a century-old drug and a fluorescent dye, has a long history of diverse applications, both in drug therapy and as a tissue-staining agent. However, MB is inherently unstable when exposed to light and reducing agents. In this study, we aim to prepare and characterize polysulfide-based organosilica colloidal particles for efficient, stable, and protective encapsulation of MB. Disulfide- and tetrasulfide-containing organosilane congeners were used as organosilica precursors for direct synthesis of organosilica colloids based on the silica ouzo effect. MB was spontaneously entrapped into the colloidal particles during the particle formation process. The following properties of the colloidal MB were evaluated: particle size, surface charge, atomic distribution, encapsulation efficiency, MB release, photodynamic activity, thiol and ascorbate reactivity, and cytotoxicity. The DLS measurements show that the size of colloidal MB is tunable in a range of 100 nm to 1 μm. SEM images reveal spherical particles with composition-dependent particle sizes of 70-120 nm (coefficient of variation: 15-18%). MB was encapsulated in the colloidal particles with a maximal efficiency of 95%. The release of MB from the colloids was <1% at 4 h and <3.5% at 48 h. The colloidal particles show much reduced photodynamic activity, low reactivity toward reducing agents, and low cytotoxicity. Accordingly, the colloidal MB was proposed and further investigated as a fluorescent particle tracer for the study of cell-nanoparticle interactions. In conclusion, MB can be efficiently and stably loaded into polysulfide organosilica colloidal particles using a simple and convenient physical route.

Kinetics of fluoride-catalysed synthesis of organosilica colloids in aqueous solutions of amphiphiles

Reactions involving hydrophobic reactants in water can be much accelerated in organic solvent-free solutions containing amphiphiles at neutral pH and room temperature. Previously, we demonstrated that organosilica colloidal particles could be conveniently synthesized by a versatile salt-catalysis method in solutions modified with various amphiphilic molecules. The method precludes the use of any solvent, any added form of energy (thermal or mechanical), and any strong (or hazardous) acids/bases. Herein, the kinetic properties of the reaction were systematically investigated for fluoride-catalysed synthesis of colloidal organosilica from a thiol-functionalized organosilane precursor, (3-mercaptopropyl)trimethoxysilane. Continuous, real-time ATR-FTIR measurements allowed probing the time evolution of organosilica condensation in different reaction systems, containing one of the following: non-ionic surfactants (Tween 20, Tween 40, Tween 60, Tween 80, Triton X-100), anionic surfactant (sodium dodecyl sulphate; SDS), cationic surfactant (cetyltrimethylammonium bromide; CTAB), and amphiphilic polymers (polyvinyl alcohol and polyvinylpyrrolidone). Overall, while some amphiphile-specific properties were revealed, fluoride-catalysed synthesis was ultrafast with a universal two-phase kinetic scheme (e.g. transition within 5–10 min) for all amphiphiles studied.

Systematic real-time ATR-FTIR studies reveal ultrafast two-phase kinetics of sodium fluoride-catalysed synthesis of organosilica colloids in purely aqueous, amphiphile-assisted systems.