Fluorescent silica nanoparticles with chemically reactive surface: Controlling spatial distribution in one-step synthesis

Controllable Synthesis of Amino-Functionalized Silica Particles via Co-condensation of Tetraethoxysilane and (3-Aminopropyl)triethoxysilane

Amino-functionalized silica has attracted a great deal of interest due to its high surface reactivity and potential for diverse applications across various fields. While the classical co-condensation method is commonly used to synthesize amino-functionalized silica particles, the mechanism of the reaction between (3-aminopropyl)triethoxysilane (APTES) and tetraethoxysilane under different conditions remains unclear, leading to unexpected self-nucleation or cross-linking between silica particles and consequently hindering rational control over the extent of functionalization. To address this issue, we systematically explored the co-condensation growth mechanism of amino-functionalized silica particles in the Stöber method by investigating the effects of APTES concentration and water content on the hydrolysis and condensation of silanes. The experimental results revealed that APTES could decrease the rate of hydrolysis/condensation, while the moderate water content promoted both the rate of hydrolysis/condensation and the overall quality of the silica particles. Consequently, we successfully demonstrated the rational synthesis of amino-functionalized silica particles with diameters ranging from 213 to 670 nm and a nitrogen content of ≤2.8 wt %. The relationship between the APTES concentration and particle properties exhibited a biphasic trend. At low APTES concentrations (≤2.0 mM), the particle size remained stable while the isoelectric point increased rapidly. Further increasing the APTES concentration from 2.0 to 100.0 mM induced a decrease in particle size due to APTES's inhibitory effect on silica growth, with nitrogen content continuing to increase even after the isoelectric point remained unchanged. These silica particles, featuring varying surface amino group densities, were utilized as matrices for loading Au nanoparticles. The resulting functionalized particles exhibited distinctive catalytic ability in the reduction of 4-nitroaniline, demonstrating significant potential for applications across various fields.

Combining Bioorthogonal Chemistry with Fluorescent Silica Nanoparticles for the Ultrasensitive Detection of the HIV-1 p24 Antigen

Early detection and viral concentration monitoring of human immunodeficiency virus in resource-poor settings are important to control disease spread and reduce mortality. Nucleic acid amplification tests are expensive for low-resource settings. Lateral flow antibody tests are not sensitive if testing is performed within 7-10 days, and these tests are not quantitative. We describe a signal enhancement technique based on fluorescent silica nanoparticles and bioorthogonal chemistries for the femtomolar detection of the HIV-1 p24 antigen. We developed a magnetic bead-based assay, wherein we used fluorescent-dye-encapsulated silica nanoparticles as reporters. The number of reporters was increased by using bioorthogonal chemistry to provide signal enhancement. The limit and range of detection of the sandwich immunoassay using alternating multiple layers for p24 in human serum were found to be 46 fg/mL (1.84 fM) and 46 fg/mL to 10 ng/mL, respectively. This simple assay was 217-fold higher in sensitivity compared to that of commercial enzyme-linked immunoassays (limit of detection of 10 pg/mL).

A Brief Review of Carbon Dots-Silica Nanoparticles Synthesis and their Potential Use as Biosensing and Theragnostic Applications

Carbon dots (CDs) are carbon nanoparticles with sizes below 10 nm and have attracted attention due to their relatively low toxicity, great biocompatibility, water solubility, facile synthesis, and exceptional photoluminescence properties. Accordingly, CDs have been widely exploited in different sensing and biomedical applications, for example, metal sensing, catalysis, biosensing, bioimaging, drug and gene delivery, and theragnostic applications. Similarly, the well-known properties of silica, such as facile surface functionalization, good biocompatibility, high surface area, and tunable pore volume, have allowed the loading of diverse inorganic and organic moieties and nanoparticles, creating complex hybrid nanostructures that exploit distinct properties (optical, magnetic, metallic, mesoporous, etc.) for sensing, biosensing, bioimaging, diagnosis, and gene and drug delivery. In this context, CDs have been successfully grafted into diverse silica nanostructures through various synthesis methods (e.g., solgel chemistry, inverse microemulsion, surfactant templating, and molecular imprinting technology (MIT)), imparting hybrid nanostructures with multimodal properties for distinct objectives. This review discusses the recently employed synthesis methods for CDs and silica nanoparticles and their typical applications. Then, we focus on combined synthesis techniques of CD-silica nanostructures and their promising biosensing operations. Finally, we overview the most recent potential applications of these materials as innovative smart hybrid nanocarriers and theragnostic agents for the nanomedical field.

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.

In vitro and in vivo uterine metabolic disorders induced by silica nanoparticle through the AMPK signaling pathway

Exposure to silica nanoparticles (SiNPs) has been suggested to cause physical disorders, yet the effects of SiNPs on female reproduction have not been illustrated. This study was implemented to explore the reproductive toxicity of SiNPs on female and reveal its underlying mechanisms. Methodologically, the fluorescein isothiocyanate (FITC)-SiNPs were synthesized by coupling with FITC and then used to track the biodistribution of SiNPs in vitro and in vivo. In total, 30 mice were intratracheally injected 0.25 g of FITC-SiNPs, and 6 mice injected with the same volume of saline were used as controls. The results showed that SiNPs penetrated the cellular membrane, triggering apoptosis and inhibiting proliferation, tube formation, and invasion of trophoblast. Mechanistically, SiNPs was demonstrated to dysregulate Fbp2, Cpt1a, Scd1, and Pfkl, and further induced accumulation of pyruvate and fatty acid in mitochondria through the AMPK signaling pathway, which finally activated the Caspase-3-dependent apoptosis. Consistently, the similar alterations of these genes were detected in vivo, and the uterine inflammatory infiltration aggravated with the extension of the observation duration. These results suggested that SiNPs induced trophoblast apoptosis and uterine inflammation, and ultimately caused acute reproductive toxicity on female. The underlying mechanism might be explained by the dysregulation of Fbp2/Cpt1a/Pfkl/Scd1 axis, which promoted the overload of glucose and lipid through the AMPK signaling pathway. These findings were of great significance to guide a comprehensive understanding of the reproductive toxicity of SiNPs as well as the development of environmental standards.

Design of PEGylated Three Ligands Silica Nanoparticles for Multi-Receptor Targeting

The synthesis of silica nanoparticles (SiNPs) decorated on their surface with a range of various elements (e.g., ligands, drugs, fluorophores, vectors, etc.) in a controlled ratio remains a big challenge. We have previously developed an efficient strategy to obtain in one-step, well-defined multifunctional fluorescent SiNPs displaying fluorophores and two peptides ligands as targeting elements, allowing selective detection of cancer cells. In this paper, we demonstrate that additional level of controlled multifunctionality can be achieved, getting even closer to the original concept of “magic bullet”, using solely sol–gel chemistry to achieve conjugation of PEG chains for stealth, along with three different ligands. In addition, we have answered the recurrent question of the surface ungrafting by investigating the stability of different siloxane linkages with the ERETIC Method (Electronic Reference to Access In Vivo Concentrations) by ¹⁹F NMR quantification. We also compared the efficiency of the hybrid silylated fluorophore covalent linkage in the core of the SiNP to conventional methods. Finally, the tumor-cell-targeting efficiency of these multi-ligand NPs on human endothelial cells (HUVEC or HDMEC) and mixed spheroids of human melanoma cells and HUVEC displaying different types of receptors were evaluated in vitro.

Fluorescent Mesoporous Nanoparticles for β-Lactamase Screening Assays

We present a sensitive and rapid screening method for the determination of β-lactamase activity of antibiotic-resistant bacteria, by designing a pH-sensitive fluorescent dye-doped mesoporous silica nanoparticle encapsulated with penicillin G as a substrate. When penicillin G was hydrolysed by β-lactamase and converted into penicilloic acid, the acidic environment resulted in fluorescence quenching of the dye. The dye-doped mesoporous nanoparticles not only enhanced the β-lactamase-catalyzed reaction rate but also stablized the substrate, penicillin G, which degrades into penicilloic acid in a water solution without β-lactamase. Twentyfive clinical bacterial samples were tested and the antibiotic resistant and susceptible strains were identified. The proposed method may detect the presence of β -lactamases of clinically relevant samples in less than 1 hour. Moreover, the detection limit of β-lactamase activity was as low as 7.8×10-4 U/mL, which was determined within two hours.

Carbohydrate coated fluorescent mesoporous silica particles for bacterial imaging

This work investigated the synthesis of carbohydrate functionalized methylene blue doped amine grafted mesoporous silica nanoparticles (MB AMSN) and their application in bioimaging. A single-pot synthesis methodology was developed via a modified co-condensation sol-gel technique for simultaneous incorporation of the dye molecule in the nanoparticles, with amine grafting for subsequent functionalization. The obtained nanoparticles (∼ 450 nm) are mesoporous and have a high surface area (538 m²/g), pore-volume (0.3 cm³/g), showed excellent UV-vis absorbance, and dye encapsulation efficiency (> 75 %). These fluorescent nanoparticles were further functionalized with carbohydrate molecules before application as contrast agents in bacterial cells. In the present study, gram-positive (E. coli) and gram-negative (B. subtilis) bacteria were used as model organisms. Confocal laser microscopy results showed that the nanoparticles are highly fluorescent, and SEM of glucose conjugated MB doped nanoparticles indicated close interaction with E. coli with no toxicity observed towards either bacterial cells. The results demonstrate that by suitable surface functionalization, the methylene blue doped silica nanoparticles can be used as bioimaging agents.

One-pot ultrafast preparation of silica quantum dots and their utilization for fabrication of luminescent mesoporous silica nanoparticles

Silica quantum dots (SiQDs) and their luminescent composites have displayed great potential for biomedical applications owing to their chemical inert and low cost. In this work, we report a facile, cost-effective and ultrafast strategy to prepare a stable luminescent SiQDs using N-[3-(trimethoxysilyl)propyl]ethylenediamine (EDAS) and salicylaldehyde as precursors for the first time. These luminescent SiQDs were further utilized for fabrication of luminescent mesoporous silica nanoparticles (MSNs) through direct encapsulation of SiQDs by MSNs. The novel synthetic and modified SiQDs uses commercial raw materials and the entire reaction can be completed within 30 s. The successful preparation of SiQDs and SiQDs@MSNs were characterized by various characterization equipments. The cell viability as well as cell uptake behavior of SiQDs@MSNs were also examined to evaluate their potential for biomedical applications. We demonstrated that these SiQDs@MSNs are low toxicity and of great potential for biological imaging. Based on the above results, we believe that these SiQDs@MSNs should be novel and promising candidates for biomedical applications owing to their intense fluorescence, biocompatibility and high specific surface areas.

A one-step ultrasonic irradiation assisted strategy for the preparation of polymer-functionalized carbon quantum dots and their biological imaging

Fluorescent carbon nanoparticles (FCNs) have gradually become the most promising alternative candidates to other traditional fluorescent nanomaterials for biological applications on account of their excellent fluorescence property and remarkable biocompatibility. Although many methods have reported on the preparation of FCNs, to date, no studies have reported the preparation of polymers of functionalized FCNs. A high-efficiency method was developed in this work to synthesize high-quality poly(ethylene oxide) (PEG)-functionalized FCNs from cigarette ash and thiol group-containing PEG via a facile one-pot ultrasonic irradiation treatment. A series of characterization techniques demonstrated the uniform nanoscale size, good fluorescence stability, high water dispersibility and remarkable biocompatibility of the generated FCNs. Furthermore, cell imaging was easily achieved at high resolution using the synthetic FCNs as probes, which validates their potential for bioimaging applications. In summary, an efficient one-pot strategy is reported for the first time on the preparation of PEG-functionalized FCNs with the assistance of ultrasonic irradiation. This method should be of great research interest for the fabrication of other polymer-functionalized FCNs with designable properties and functions.