The optical quality of these particles can be adjusted by changing their shape and size and is widely used in many applications. Uncoated gold nanoparticles are prone to aggregation and melting in solution when exposed to laser irradiation, resulting in significant changes in their optical attributes. Once their surfaces are properly passivated through chemical functionalization, these gold nanoparticles can resist clumping and shape distortion under different biological, physical, and environmental conditions, thereby maintaining their optical properties. Silicon dioxide coating is a powerful functionalization that can enhance the thermodynamic and chemical stability of gold nanoparticles.
Surface chemistry and synthesis of silica-coated gold
The silica coating of gold nanoparticles was achieved through the St. Ber method. This traditional technique utilizes tetraethyl orthosilicate (TEOS) to generate mesoporous, highly branched siloxane polymers on the gold surface.
By operating the reaction time and reagent concentration, the gauge of the silica layer on the gold surface can be controlled. The obtained siloxane polymer (referred to as silica) carries hydroxyl (- OH) groups and can serve as a connecting point for further functionalization.
In addition, the heterobifunctional silane linker easily interacts with silica, providing a method for fixing various ligands (such as polyethylene glycol (PEG)) onto the surface of silica.
Characteristics and advantages of gold nanoparticles coated with silica
The silica coating of gold is beneficial for various applications of gold nanoparticles. When used with pulsed lasers, the silica coating can significantly improve the stability of gold nanorods.
Gold nanorods with traditional coatings such as PEG, cetyltrimethylammonium bromide (CTAB), or other small polymers can absorb sufficient energy from pulsed lasers for melting. This shape change causes their light absorption and scattering to shift from near-infrared (NIR) wavelengths to visible spectra.
For applications that rely on consistent near-infrared light absorption, these regularly coated gold nanorods may produce unreliable results. On the contrary, gold nanorods coated with silica can resist shape changes and maintain their optical properties even at higher levels of light intensity (fluence).
In addition to thermodynamic and colloidal stability, the silica coating of gold nanorods also has other important characteristics and advantages. For example, the silica coating increases the surface area of antibody or other targeting element conjugation.
The porous properties of silica enable it to load drugs, dye molecules, or other imaging agents through physical adsorption or covalent attachment. This coating also limits the compactness of nanorods at high concentrations, minimizing the influence of plasma coupling and ensuring that their optical properties are maintained regardless of the concentration. The characteristics and advantages of nano silica powder determine its wide range of applications.
The application of nano silica powder
One of the significant biomedical applications of nano silica is as a vehicle for drug delivery via eye drops, intravenous injection, oral tablets, or pulmonary inhalation routes.
In textiles, nano silicon can reflect ultraviolet light, resist aging, increase weather resistance, increase strength, and other effects. After testing, it was found that the fiber contains nano silicon that can reflect 75% of 400nm wavelength ultraviolet radiation, and nano silicon below 100nm has antibacterial and deodorizing effects.
In epoxy resin, nanosilicon enhances the properties of acid and alkali resistance, chemical stability, high-temperature resistance, surface hardness, scratch resistance, waterproofing, insulation, etc. Adding less than 20% of nano silicon can double the product’s strength, reducing resin usage and production costs.
In rubber silicone modification: Nano silicon is a product reinforcing agent designed explicitly for rubber silicone modification. Because of pure rubber’s low performance, it is unsuitable for many scenarios and needs to be filled with modified nanosilicon to enhance its reinforcement performance. Controlling the amount of nano silicon used can increase properties such as hardness, temperature resistance, wear resistance, insulation, and dielectric properties.
In coatings: Nano silicon micro powder increases substrate adhesion and film hardness in coatings, paints, primers, and topcoats, preventing surface warping, enhancing corrosion resistance, penetration resistance, self-cleaning, high-temperature resistance, waterproofing, UV resistance, scratch resistance, and other effects. After filling, it can be suspended in the paint film for a long time without affecting transparency, preventing the paint from turning yellow.
Ceramic field: In concrete and refractory materials, silicon micro powder is added to unique refractory materials to form a multi-layer protective layer during oxidation, which has good mechanical properties and high-temperature oxidation resistance. After adding ultrafine silicon powder to special refractory materials, their flowability, sintering ability, bonding ability, and filling porosity performance are all improved to varying degrees, improving structural density and strength, reducing material wear rate, and enhancing corrosion resistance.
Luoyang Tongrun Nanotechnology Co, Ltd., as a global chemical material purveyor and manufacturer with over 12 years of experience, is highly trusted for providing high-quality chemicals and nanomaterials such as graphite powder, zinc sulfide, nitride powder, calcium nitride, Ca3N2, 3D printing powder, concrete foaming agent, etc.
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