Sculpting Silica Colloids by Etching Particles with Nonuniform Compositions

Determination of Adsorption of Methylene Blue Dye by Incense Stick Ash Waste and Its Toxicity on RTG-2 Cells

Incense stick ash (ISA) has traces of toxic heavy metals which have an adverse effect on the environment. Every year, tonnes of ISA are disposed of in rivers and other water bodies which leads to water pollution and affects the natural water resources. ISA has several value-added minerals which could be modified or functionalized for environmental cleanup. Here, in the current research work, ISA was transformed into a flower-like noble porous material by mixing ISA and NaOH in a 1 : 1 ratio followed by calcination at 600°C for six hours in a muffle furnace. The developed material was analyzed by sophisticated instruments for the identification of the properties. The microscopic techniques revealed the micron-sized flower-like structure, while the XRD showed peaks at 30–33° which indicates the transformation of the calcite and silicate phases into new-phase mineral. FTIR also revealed bands in regions of 500–1200 cm−1 and new bands near 450 cm−1. EDS confirmed the presence of Na in the sintered product and the transformation of the ISA. Finally, the sintered product potential was assayed for the removal of methylene blue dye from wastewater using an adsorption mechanism. The removal efficiency of dye reached up to 70% within one hour only. It was found that the ISA sintered product has the potential to remove MB dye efficiently from wastewater and also reduce solid waste pollution. Microculture tetrazolium assay (MTT) and lactate dehydrogenase (LDH) assays were performed to evaluate the cytotoxicity of the sintered incense stick ash product on RTG-2 cells. The sintered incense stick ash product induced cytotoxicity on RTG-2 cells in a dose-dependent manner. Sintered ISA products have the potential to remove methylene blue dye efficiently from wastewater and reduce solid waste pollution.

Asymmetrical ring-shaped colloidal particles for self-assembly and superhydrophobic coatings

A frame-guided wetting strategy is reported to synthesize highly uniform but asymmetrical colloidal particles from rings to oblate ellipsoids through symmetrical discs, which can self-assemble into diversified highly open 2D superstructures. In particular, ring-shaped particle monolayers have a higher contact angle of water than similar spherical ones, suggesting an attractive particle material for self-cleaning superhydrophobic coatings.

Role of Aqueous-Phase Calcination in Synthesis of Ultra-Stable Dye-Embedded Fluorescent Nanoparticles for Cellular Probing

Fluorescence imaging is a major driver of discovery in biology, and an invaluable asset in clinical diagnostics. To overcome quenching limitations of conventional fluorescent dyes and further improve intensity, nanoparticle-based constructs have been the subject of intense investigation, and within this realm, dye-doped silica-coated nanoparticles have garnered significant attention. Despite their growing popularity in research, fluorescent silica nanoparticles suffer from a significant flaw. The degradation of these nanoparticles in biological media by hydrolytic dissolution is underreported, leading to serious misinterpretations, and limiting their applicability for live cell and in vivo imaging. Here, the development of an ultra-stable, dye-embedded, silica-coated metal nanoparticle is reported, and its superior performance in long-term live cell imaging is demonstrated. While conventional dye-doped silica nanoparticles begin to degrade within an hour in aqueous media, by leveraging a modified liquid calcination process, this new construct is shown to be stable for at least 24 h. The stability of this metal-enhanced fluorescent probe in biologically relevant temperatures and media, and its demonstrated utility for cell imaging, paves the way for its future adoption in biomedical research.

Dual Roles of Polymeric Capping Ligands in the Surface-Protected Etching of Colloidal Silica

In this work, we reveal the dual roles of polymeric capping ligands in the hollowing of silica nanospheres during their surface-protected etching. We first show that polymeric capping ligands, if they have a stronger interaction with the surface Si-OH groups than water, can reduce the condensation of the silica network, allowing the diffusion of OH^- ions through the shell to dissolve the inner silica. Also, the polymeric ligands can passivate the surface silica, making it less likely to be dissolved by OH^- ions. The combination of these two roles ensures highly selective etching of the interior of the colloidal silica spheres, making the surface-protected etching a robust process for the synthesis of hollow silica nanoshells. Our insight into the specific roles of the ligands is expected to elucidate the impact of polymeric ligands on the colloidal chemistry of silica, particularly in its condensation and etching behaviors, and offer new opportunities in the design of silica and other oxide-based nanostructures.

Dye-doped silica nanoparticles: synthesis, surface chemistry and bioapplications

Background

Fluorescent silica nanoparticles have been extensively utilised in a broad range of biological applications and are facilitated by their predictable, well-understood, flexible chemistry and apparent biocompatibility. The ability to couple various siloxane precursors with fluorescent dyes and to be subsequently incorporated into silica nanoparticles has made it possible to engineer these fluorophores-doped nanomaterials to specific optical requirements in biological experimentation. Consequently, this class of nanomaterial has been used in applications across immunodiagnostics, drug delivery and human-trial bioimaging in cancer research.

Main body

This review summarises the state-of-the-art of the use of dye-doped silica nanoparticles in bioapplications and firstly accounts for the common nanoparticle synthesis methods, surface modification approaches and different bioconjugation strategies employed to generate biomolecule-coated nanoparticles. The use of dye-doped silica nanoparticles in immunoassays/biosensing, bioimaging and drug delivery is then provided and possible future directions in the field are highlighted. Other non-cancer-related applications involving silica nanoparticles are also briefly discussed. Importantly, the impact of how the protein corona has changed our understanding of NP interactions with biological systems is described, as well as demonstrations of its capacity to be favourably manipulated.

Conclusions

Dye-doped silica nanoparticles have found success in the immunodiagnostics domain and have also shown promise as bioimaging agents in human clinical trials. Their use in cancer delivery has been restricted to murine models, as has been the case for the vast majority of nanomaterials intended for cancer therapy. This is hampered by the need for more human-like disease models and the lack of standardisation towards assessing nanoparticle toxicity. However, developments in the manipulation of the protein corona have improved the understanding of fundamental bio–nano interactions, and will undoubtedly assist in the translation of silica nanoparticles for disease treatment to the clinic.

Shaping Silica Rods by Tuning Hydrolysis and Condensation of Silica Precursors

We present the synthesis of colloidal silica particles with new shapes by manipulating the growth conditions of rods that are growing from polyvinylpyrrolidone-loaded water-rich droplets containing ammonia and ethanol. The silica rods grow by ammonia-catalyzed hydrolysis and condensation of tetraethoxysilane (TEOS). The lengthwise growth of these silica rods gives us the opportunity to change the conditions at any time during the reaction. In this work, we vary the availability of hydrolyzed monomers as a function of time and study how the change in balance between the hydrolysis and condensation reactions affects a typical synthesis (as described in more detail by our group earlier1). First, we show that in a "standard" synthesis, there are two silica growth processes occurring; one in the oil phase and one in the droplet. The growth process in the water droplet causes the lengthwise growth of the rods. The growth process in the oil phase produces a thin silica layer around the rods, but also causes the nucleation of 70 nm silica spheres. During a typical rod growth, silica formation mainly takes place in the droplet. The addition of partially hydrolyzed TEOS or tetramethoxysilane (TMOS) to the growth mixture results in a change in balance between the hydrolysis and condensation reaction. As a result, the growth also starts to take place on the surface of the water droplet and thus from the oil phase, not only from inside the droplet onto a silica rod sticking out of the droplet. Carefully tuning the growth from the droplet and the growth from the oil phase allowed us to create nanospheres, hollow silica rods, hollow sphere rod systems (colloidal matchsticks), and bent silica rods.

Regiospecific Nucleation and Growth of Silane Coupling Agent Droplets onto Colloidal Particles

Nucleation-and-growth processes are used extensively in the synthesis of spherical colloids, and more recently regiospecific nucleation-and-growth processes have been exploited to prepare more complex colloids such as patchy particles. We demonstrate that surface geometry alone can be made to play the dominant role in determining the final particle geometry in such syntheses, meaning that intricate chemical surface patternings are not required. We present a synthesis method for "lollipop"-shaped colloidal heterodimers (patchy particles), combining a recently published nucleation-and-growth technique with our recent findings that particle geometry influences the locus of droplet adsorption onto anisotropic template particles. Specifically, 3-methacryloxypropyl trimethoxysilane (MPTMS) is nucleated and grown onto bullet-shaped and nail-shaped colloids. The shape of the template particle can be chosen such that the MPTMS adsorbs regiospecifically onto the flat ends. In particular, we find that particles with a wider base increase the range of droplet volumes for which the minimum in the free energy of adsorption is located at the flat end of the particle compared with bullet-shaped particles of the same aspect ratio. We put forward an extensive analysis of the synthesis mechanism and experimentally determine the physical properties of the heterodimers, supported by theoretical simulations. Here we numerically optimize, for the first time, the shape of finite-sized droplets as a function of their position on the rod-like silica particle surface. We expect that our findings will give an impulse to complex particle creation by regiospecific nucleation and growth.