Synthesis of nanometric silica particles via a modified Stöber synthesis route

Systematic Study of Reaction Conditions for Size-Controlled Synthesis of Silica Nanoparticles

This study presents a reproducible and scalable method for synthesizing silica nanoparticles (SNPs) with controlled sizes below 200 nm, achieved by systematically varying three key reaction parameters: ammonium hydroxide concentration, water concentration, and temperature. SNPs with high monodispersity and controlled dimensions were produced by optimizing these factors. The results indicated a direct correlation between ammonium hydroxide concentration and particle size, while higher temperatures resulted in smaller particles with increased polydispersity. Water concentration also influenced particle size, with a quadratic relationship observed. This method provides a robust approach for tailoring SNP sizes, with significant implications for biomedical applications, particularly in drug delivery and diagnostics. Using eco-friendly solvents such as ethanol further enhances the sustainability and cost-effectiveness of the process.

Enhancing Slurry Stability and Surface Flatness of Silicon Wafers through Organic Amine-Catalyzed Synthesis Silica Sol

The stability of slurries used for chemical mechanical polishing (CMP) is a crucial concern in industrial chip production, influencing both the quality and cost-effectiveness of polishing fluids. In silicon wafer polishing, the conventional use of commercial neutral silica sol combined with organic bases often leads to slurry instability. To address this issue, this study proposes organic amines-specifically ethanolamine (MEA), ethylenediamine (EDA), and tetramethylammonium hydroxide (TMAOH)-as catalysts for synthesizing alkaline silica sol tailored for silicon wafer polishing fluids. Sol-gel experiments and zeta potential measurements demonstrate the efficacy of this approach in enhancing the stability of silica sol. The quantitative analysis of surface hydroxyl groups reveals a direct correlation between enhanced stability and increased hydroxyl content. The application of the alkaline silica sol in silicon wafer polishing fluids improves polishing rates and enhances surface flatness according to atomic force microscopy (AFM). In addition, electrochemical experiments validate the capability of this polishing solution to mitigate corrosion on silicon wafer surfaces. These findings hold significant implications for the advancement of chemical mechanical polishing techniques in the field of integrated circuit fabrication.

Synthesis of Silica Particles with Controlled Microstructure via the Choline Hydroxide Cocatalyzed Stöber Method

This study investigates the utilization of choline hydroxide as a cocatalyst in the Stöber method to synthesize silica particles with controlled microstructure. Under low ammonia concentration, we add a robust organic base choline hydroxide and systematically explore the influence of choline hydroxide concentration on the hydrolysis and condensation equilibrium of tetraethyl orthosilicate (TEOS). Through the rational control of the water content, we significantly enhance both the size range and polydispersity of the resulting silica particles. Taking advantage of the regulated microstructure induced by controlled hydrolysis and condensation catalyzed by choline hydroxide, we achieved silica particles with hollow structures through hot water etching, exhibiting significantly enhanced surface area. These findings demonstrate the versatility of choline hydroxide as a cocatalyst in tailoring the microstructure of silica particles. In addition, due to its reducing ability and biocompatibility, which are not shared by other reported catalysts, the use of choline hydroxide opens up opportunities for applications in catalysis, sensing, and drug delivery.

Greening the pathways: a comprehensive review of sustainable synthesis strategies for silica nanoparticles and their diverse applications

Silica nanoparticles (SiNPs) have emerged as a multipurpose solution with wide-ranging applications in various industries such as medicine, agriculture, construction, cosmetics, and food production. In 1961, Stöber introduced a ground-breaking sol-gel method for synthesizing SiNPs, which carried a new era of exploration both in academia and industry, uncovering numerous possibilities for these simple yet multifaceted particles. Inspite of numerous reported literature with wide applicability, the synthesis of these nanoparticles with the desired size and functionalities poses considerable challenges. Over time, researchers have strived to optimize the synthetic route, particularly by developing greener approaches that minimize environmental impact. By reducing hazardous chemicals, energy consumption, and waste generation, these greener synthesis methods have become an important focus in the field. This review aims to provide a comprehensive analysis of the various synthetic approaches available for different types of SiNPs. Starting from the Stöber' method, we analyze other methods as well to synthesis different types of SiNPs including mesoporous, core-shell and functionalized nanoparticles. With increasing concerns with the chemical methods associated for environmental issues, we aim to assist readers in identifying suitable greener synthesis methods tailored to their specific requirements. By highlighting the advancements in reaction time optimization, waste reduction, and environmentally friendly precursors, we offer insights into the latest techniques that contribute to greener and more sustainable SiNPs synthesis. Additionally, we briefly discuss the diverse applications of SiNPs, demonstrating their relevance and potential impact in fields such as medicine, agriculture, and cosmetics. By emphasizing the greener synthesis methods and economical aspects, this review aims to inspire researchers and industry professionals to adopt environmentally conscious practices while harnessing the immense capabilities of SiNPs.

Recent Studies on Metal-Embedded Silica Nanoparticles for Biological Applications

Recently, silica nanoparticles (NPs) have attracted considerable attention as biocompatible and stable templates for embedding noble metals. Noble-metal-embedded silica NPs utilize the exceptional optical properties of novel metals while overcoming the limitations of individual novel metal NPs. In addition, the structure of metal-embedded silica NPs decorated with small metal NPs around the silica core results in strong signal enhancement in localized surface plasmon resonance and surface-enhanced Raman scattering. This review summarizes recent studies on metal-embedded silica NPs, focusing on their unique designs and applications. The characteristics of the metal-embedded silica NPs depend on the type and structure of the embedded metals. Based on this progress, metal-embedded silica NPs are currently utilized in various spectroscopic applications, serving as nanozymes, detection and imaging probes, drug carriers, photothermal inducers, and bioactivation molecule screening identifiers. Owing to their versatile roles, metal-embedded silica NPs are expected to be applied in various fields, such as biology and medicine, in the future.

Glycopolymer-grafted nanoparticles as glycosaminoglycan mimics with cell proliferation and anti-tumor metastasis activities

Glycosaminoglycans (GAGs) are naturally existing extracellular components with a variety important biological functions. However, their heterogeneous chemical compositions and the challenges in purification have become the main disadvantages for clinical applications. Thus, various synthetic glycopolymers have been designed to mimic the structures and functions of natural GAGs. In the current study, glycopolymers from structurally simple glucose or N-acetylglucosamine monomers were synthesized, which were further subjected to sulfation of different degrees and grafting onto silica nanoparticles, leading to spherical-shaped nano-structures of uniform diameters. With the successively strengthened multivalent effect, the obtained glycopolymer nanoparticles not only showed excellent effects on promotion of cell proliferation by stabilizing growth factors, but also significantly inhibited tumor metastasis by weakening the adhesion between tumor cells and activated platelets. Among the prepared nanoparticles, S3-PGNAc@Si with N-acetylglucosamine segment and the highest sulfation degree exhibited the strongest bioactivities, which were even close to those of heparin. This work presents a novel approach for structural and functional mimicking of natural GAGs from simple and low-cost monosaccharides, holding great potential for a range of biomedical applications.

FeCO3 Synthesis Pathways: The Influence of Temperature, Duration, and Pressure

FeCO₃ is present as scales in process equipment, corrosion products, geological systems, and carbon storage. It is therefore crucial to investigate the properties of FeCO₃ to understand scaling in all these systems. However, FeCO₃ is not commercially available, and when used in the lab it is either obtained through extraction of geological formations or synthesized in-house. Geologically formed FeCO₃ contains multiple impurities, which will affect its overall properties, and the synthesized product is highly sensitive to either oxidation or the synthesis pathways. This work explores the parameter space of a synthesis route routinely and pathways for FeCO₃. We characterized the structure of FeCO₃ using X-ray powder diffraction and its thermal properties with thermogravimetric analysis and scanning electron microscopy. We show how synthesis parameters influence either the macroscopic or microscopic properties of the synthesized product. Our study serves as a guideline for future research regarding what parameters to choose when synthesizing FeCO₃ and what product can be obtained. We herein present a novel fundamental understanding of FeCO₃.

Hollow Silica Nano and Micro Spheres with Polystyrene Templating: A Mini-Review

Synthesis of monodisperse hollow silica nanospheres, especially using a hard template route, has been shown to be successful, but a high yield is needed for this strategy to be used on an industrial scale. On the other hand, there is a research gap in the synthesis of hollow silica microspheres due to the popularity and easiness of the synthesis of silica nanospheres despite the larger spheres being beneficial in some fields. In this review, current trends in producing hollow silica nanospheres using hard templates, especially polystyrene, are briefly presented. Soft templates have also been used to make highly polydisperse hollow silica spheres, and complex designs have improved polydispersity. The effect of the main parameters on the coating is presented here to provide a basic understanding of the interactions between the silica and template surface in the absence or presence of surfactants. Surface charge, surface modification, parameters in the sol-gel method and interaction between the silica and templates need to be further improved to have a uniform coating and better control over the size, dispersity, wall thickness and porosity. As larger organic templates will have lower surface energy, the efficiency of the micro sphere synthesis needs to be improved. Control over the physical structure of hollow silica spheres will open up many opportunities for them to be extensively used in fields ranging from waste removal to energy storage.

Structural, Optical, and Morphological Characterization of Silica Nanoparticles Prepared by Sol-Gel Process

In the current years, silica nanoparticles have become more favorable in various disciplines like medicine, nano-biotechnology, the food industry, and drug delivery due to their tunable physicochemical characteristics. In this paper, the silica nanoparticles were synthesized by hydrolysis and condensation of tetra-ethyl-ortho-silicate (TEOS) in an ethanolic medium using ammonia as a stimulator in the reaction. The chemical bond structures of silica nanoparticles were analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) which confirmed the existence of the Si-O bonds according to the different absorption peaks of the samples. The amorphous structure of these nanoparticles was certified by finding the board peaks in the X-Ray Diffraction (XRD) patterns. The elemental chemical composition of silica nanoparticles was investigated by Energy Dispersive X-Ray Spectroscopy (EDX) where 61.48wt % of silicon and 23.48wt% of oxygen were found. Almost round-shaped spherical and uniform silica nanoparticles with smooth surfaces were investigated by Scanning Electron Microscopy (SEM) measurement. The different particle sizes of silica nanoparticles within the range of 95±5.59 to 280±7.8 nm were found by controlling the concentration of TEOS. The optical absorption spectra and band gap calculations were also analyzed by Ultraviolet-Visible (UV-Vis) spectrophotometry for the different concentrations of TEOS. The results revealed that with increasing the concentration of TEOS, the absorption spectra of silica nanoparticles increased and their optical bandgap decreased from 3.92 eV to 3.79 eV.

Effect of the Coupling Agent (3-Aminopropyl) Triethoxysilane on the Structure and Fire Behavior of Solvent-Free One-Pot Synthesized Silica-Epoxy Nanocomposites

Uniformly distributed silica/epoxy nanocomposites (2 and 6 wt.% silica content) were obtained through a “solvent-free one-pot” process. The inorganic phases were obtained through “in situ” sol-gel chemistry from two precursors, tetraethyl orthosilicate (TEOS) and (3-aminopropyl)-triethoxysilane (APTES). APTES acts as a coupling agent. Surprisingly when changing TEOS/APTES molar ratio (from 2.32 to 1.25), two opposite trends of glass transformation temperature (Tg) were observed for silica loading, i.e., at lower content, a decreased Tg (for 2 wt.% silica) and at higher content an increased Tg (for 6 wt.% silica) was observed. High-Resolution Transmission Electron Microscopy (HRTEM) showed the formation of multi-sheet silica-based nanoparticles with decreasing size at a lower TEOS/APTES molar ratio. Based on a recently proposed mechanism, the experimental results can be explained by the formation of a co-continuous hybrid network due to reorganization of the epoxy matrix around two different “in situ” sol-gel derived silicatic phases, i.e., micelles formed mainly by APTES and multi-sheet silica nanoparticles. Moreover, the concentration of APTES affected the size distribution of the multi-sheet silica-based nanoparticles, leading to the formation of structures that became smaller at a higher content. Flammability and forced-combustion tests proved that the nanocomposites exhibited excellent fire retardancy.

Structure and Bottom-up Formation Mechanism of Multisheet Silica-Based Nanoparticles Formed in an Epoxy Matrix through an In Situ Process

Organic/inorganic hybrid composite materials with the dispersed phases in sizes down to a few tens of nanometers raised very great interest. In this paper, it is shown that silica/epoxy nanocomposites with a silica content of 6 wt % may be obtained with an "in situ" sol-gel procedure starting from two precursors: tetraethyl orthosilicate (TEOS) and 3-aminopropyl-triethoxysilane (APTES). APTES also played the role of a coupling agent. The use of advanced techniques (bright-field high-resolution transmission electron microscopy, HRTEM, and combined small- and wide-angle X-ray scattering (SAXS/WAXS) performed by means of a multirange device Ganesha 300 XL+) allowed us to evidence a multisheet structure of the nanoparticles instead of the gel one typically obtained through a sol-gel route. A mechanism combining in a new manner well-assessed knowledge regarding sol-gel chemistry, emulsion formation, and Ostwald ripening allowed us to give an explanation for the formation of the observed lamellar nanoparticles.

XPCS Microrheology and Rheology of Sterically Stabilized Nanoparticle Dispersions in Aprotic Solvents

X-ray photon correlation spectroscopy (XPCS) microrheology and conventional bulk rheology were performed on silica nanoparticle dispersions associated with battery electrolyte applications to probe the properties of these specific complex materials and to explore the utility of XPCS microrheology in characterizing nanoparticle dispersions. Sterically stabilized shear-thickening electrolytes were synthesized by grafting poly(methyl methacrylate) chains onto silica nanoparticles. Coated silica dispersions containing 5-30 wt % nanoparticles dispersed in propylene carbonate were studied. In general, both XPCS microrheology and conventional rheology showed that coated silica dispersions were more viscous at higher concentrations, as expected. The complex viscosity of coated silica dispersions showed shear-thinning behavior over the frequency range probed by XPCS measurements. However, measurements using conventional mechanical rheometry yielded a shear viscosity with weak shear-thickening behavior for dispersions with the highest concentration of 30% particles. Our results indicate that there is a critical concentration needed for shear-thickening behavior, as well as appropriate particle size and surface polymer chain length, for this class of nanoparticle-based electrolytes. The results of this study can provide insights for comparing XPCS microrheology and bulk rheology for related complex fluids and whether XPCS microrheology can capture expected macroscopic rheological properties by probing small-scale particle dynamics.

Hybrid Sol-Gel Superhydrophobic Coatings Based on Alkyl Silane-Modified Nanosilica

Hybrid sol-gel superhydrophobic coatings based on alkyl silane-modified nanosilica were synthesized and studied. The hybrid coatings were synthesized using the classic Stöber process for producing hydrophilic silica nanoparticles (NPs) modified by the in-situ addition of long-chain alkyl silanes co-precursors in addition to the common tetraethyl orthosilicate (TEOS). It was demonstrated that the long-chain alkyl substituent silane induced a steric hindrance effect, slowing the alkylsilane self-condensation and allowing for the condensation of the TEOS to produce the silica NPs. Hence, following the formation of the silica NPs the alkylsilane reacted with the silica's hydroxyls to yield hybrid alkyl-modified silica NPs having superhydrophobic (SH) attributes. The resulting SH coatings were characterized by contact angle goniometry, demonstrating a more than 150° water contact angle, a water sliding angle of less than 5°, and a transmittance of more than 90%. Confocal microscopy was used to analyze the micro random surface morphology of the SH surface and to indicate the parameters related to superhydrophobicity. It was found that a SH coating could be obtained when the alkyl length exceeded ten carbons, exhibiting a raspberry-like hierarchical morphology.

Renaissance of Stöber method for synthesis of colloidal particles: New developments and opportunities

Colloidal silica particles have received a widespread interest because of their potential applications in adsorption, ceramics, catalysis, drug delivery and more. Among many approaches towards fabrication of these colloidal particles, Stöber, Fink and Bohn (SFB) method, known as Stöber synthesis is an effective sol-gel strategy for production of uniform, monodispersed silica particles with highly tailorable size and surface properties. This review, after a brief introduction showing the importance of colloidal chemistry, is focused on the Stöber synthesis of silica spheres including discussion of the key factors affecting their particle size, porosity and surface properties. Next, further developments of this method are presented toward fabrication of polymer, carbon, and composite spheres.

Stealth Polymer-Coated Graphene Oxide Decorated Mesoporous Titania Nanoplatforms for In Vivo Chemo-Photodynamic Cancer Therapy

PURPOSE

The goal of this study was to develop chemotherapeutic drug-loaded photoactivable stealth polymer-coated silica based- mesoporous titania nanoplatforms for enhanced antitumor activity.

METHODS

Both in vitro and in vivo models of solvothermal treated photoactivable nanoplatforms were evaluated for efficient chemo-photothermal activity. A versatile nanocomposite that combined silica based- mesoporous titania nanocarriers (S-MTN) with the promising photoactivable agent, graphene oxide (G) modified with a stealth polymer (P) was fabricated to deliver chemotherapeutic agent, imatinib (I), (referred as S-MTN@IG-P) for near-infrared (NIR)-triggered drug delivery and enhanced chemo-photothermal therapy.

RESULTS

The fabricated S-MTN@IG-P nanoplatform showed higher drug loading (~20%) and increased drug release (~60%) in response to light in acidic condition (pH 5.0). As prepared nanoplatform significantly converted NIR light into thermal energy (43.2°C) to produce reactive oxygen species (ROS). The pronounced cytotoxic effect was seen in both colon cancer cells (HCT-116 and HT-29) that was mediated through the chemotherapeutic effect of imatinib and the photothermal and ROS generation effects of graphene oxide. In vivo study also showed that S-MTN@IG-P could significantly accumulate into the tumor area and suppress the tumor growth under NIR irradiation without any biocompatibility issues.

CONCLUSION

Cumulatively, the above results showed promising effects of S-MTN@IG-P for effective chemo-phototherapy of colon cancer.

"DIY" Silica Nanoparticles: Exploring the Scope of a Simplified Synthetic Procedure and Absorbance-Based Diameter Measurements

In this study, the classical Stöber silica synthesis protocol was used to test the limits of simplification in the preparation and size determination of nanoparticles. The scope of three-ingredient, one-pot synthesis was established in conditions of regular 96% and 99.8% ethanol as solvent, with aqueous ammonia as the only source of base and water. Particles with diameters in the 15-400 nm range can be reliably obtained with this straightforward approach, and the direct relationship between the size and the product of concentrations of water and ammonia is evidenced. Furthermore, the idea of a linear approximation for Mie scattering in particular conditions is discussed, using experimental data and theoretical calculations. A simple, fast method for particle size determination utilizing a UV-Vis spectrophotometer-an easily accessible instrument-is explained, and shows a level of error (<0.5 SD) that can be acceptable for less rigorous laboratory use of nanoparticles or serve as a quick means for testing the influence of minor alterations to known synthetic protocols. This work aims to show that nanoparticle synthesis can (and should) become a regular occurrence, even in non-specialized labs, facilitating research into their new applications and inspiring outside-the-box solutions, while discussing the drawbacks of a more relaxed synthetic regimen.

EGFR detection in extracellular vesicles of breast cancer patients through immunosensor based on silica-chitosan nanoplatform

In the present work, we designed a microfluidic electrochemical immunosensor with enough sensibility and precision to quantify epithermal growth factor receptor (EGFR) in plasma extracellular vesicles (EVs) of plasma from breast cancer patients. The sensor employs SiNPs coated with chitosan (SiNPs-CH) as reaction's platform, based on the covalently immobilization of monoclonal anti-EGFR on SiNPs-CH retained in the central channel (CC) of the microfluidic device. The synthetized SiNPs-CH were characterized by UV-visible spectroscopy (UV-visible), energy dispersive spectrometry (EDS), Nanoparticle Tracking Analysis (NTA) and transmission electron microscopy (TEM). EGFR was quantified by a direct sandwich immunoassay measuring through a horseradish peroxidase (HRP)-conjugated anti-EGFR. The enzymatic product (benzoquinone) was detected by reduction at - 100 mV on a sputtering gold electrode. The measured current was directly proportional to the level of EGFR in human serum samples. The linear range was from 0 ng mL^-1 to 50 ng mL^-1. The detection limit was 1.37 pg mL^-1, and the within- and between-assay coefficients of variation were below 6.25%. Finally, plasma samples from 30 early breast cancer patients and 20 healthy donor were analyzed by the novel method. EGFR levels in EVs (EVs-EGFR) were significantly higher than in the healthy control group (p = 0.002) and also, more sensitivity and specificity than normal serum markers like CEA and CA15.3 has been observed. EVs-EGFR concentration correlates with EGFR tumor status (p = 0.0003) as well as it correlate with the tumor size and pathological grade. To conclude, plasma EVs are suitable for proteomic characterization of cancer disease, as long as the employed method has sufficient sensitivity, like the case of immune-electrochemical nanosensors with incremented reaction surface.

A Tube-Integrated Painted Biosensor for Glucose and Lactate

Developing a simple and direct approach for sensitive, specific, and rapid detection of metabolic compounds is of great importance for a variety of biological, medical, and food applications. Tubes are a highly portable and accessible container shape which are widely used for scientific research in cell biology and chemical synthesis, and which are also of great use in domestic health care applications. Here, we show for the first time the development of a tube-based painted amperometric biosensor for the detection of glucose and lactate. The sensor was prepared by printing carbon graphite and silver/silver chloride inks on the interior wall of the tube and then immobilizing glucose oxidase or lactate oxidase on the sensor. The sensor showed a sensitive, rapid, and reliable detection of glucose and lactate. We anticipate that these results could open new avenues for the development of painted biosensors, and toward advanced biosensor applications.