1. Introduction

Nanoparticles have attracted a great deal of interest in the scientific community due to their unique physicochemical properties, such as high surface area, size-dependent optical and electronic properties, and biocompatibility. Among the various types of nanoparticles, gold nanoparticles (AuNPs) have received significant attention due to their biocompatibility, stability, and ease of synthesis. In recent years, researchers have explored the use of gold nanoparticles for drug delivery, as they have the potential to enhance the therapeutic efficacy of drugs and reduce their side effects. This encyclopedia entry discusses the synthesis and characterization of gold nanoparticles coated with silica and polyethylene glycol (PEG), and the loading and release of ibuprofen, an anti-inflammatory drug, onto the coated nanoparticles. PEG (polyethylene glycol) and silica are two materials commonly used in the coating of nanoparticles for biomedical applications. The properties of PEG and silica coatings can be tailored to meet specific requirements for biomedical applications, such as drug delivery or imaging. The choice of coating material and its properties can impact the stability, biocompatibility, and functionality of the nanoparticles.

PEG

PEG is a water-soluble polymer that can form a hydrophilic coating on the surface of nanoparticles, which can improve their stability in aqueous solutions and reduce their clearance by the immune system. PEG coatings can also prevent the aggregation of nanoparticles and reduce their interactions with proteins and other biomolecules in the bloodstream. The thickness of the PEG coating can be controlled by adjusting the concentration and molecular weight of the polymer used in the coating process.

Silica

Silica, on the other hand, is a hard and inert material that can provide a protective barrier around nanoparticles. The coating of nanoparticles with silica can improve their stability in harsh environments and reduce their toxicity. Silica coatings can also be functionalized with a variety of biomolecules, such as antibodies or peptides, to target specific cells or tissues in the body. The thickness of the silica coating can be controlled by adjusting the concentration and reaction time of the precursor solution used in the coating process.

2. Synthesis and Characterization of Gold Nanoparticles

The synthesis of gold nanoparticles was carried out using chloric auric acid (HAuCl₄) as the precursor salt and citrate as the reducing agent. The reduction reaction of AuHCl₄ to obtain gold nanoparticles is a well-known method for synthesizing gold nanoparticles. This method is widely used due to its simplicity, reproducibility, and scalability. The reaction involves the reduction of AuHCl4 with citric acid. The reduction reaction starts by heating the mixture of AuHCl₄, citric acid, and sodium citrate to a temperature of around 80°C. The citric acid acts as a reducing agent, which reduces the Au(III) ions in the AuHCl₄ to Au(0) atoms. Citrate, on the other hand, acts as a stabilizer, which prevents the nanoparticles from aggregating by forming a protective layer around the particles. Once the reduction reaction is complete, the gold nanoparticles are formed, which can be characterized using various techniques such as electron microscopy and UV-visible spectroscopy. The size and shape of the nanoparticles can be controlled by adjusting the concentration of the reagents, the reaction temperature, and the reaction time. The gold nanoparticles obtained through this method have unique properties, making them suitable for various applications such as biomedical imaging, drug delivery, catalysis, and sensing. Moreover, the simplicity and scalability of the synthesis method make it an attractive choice for large-scale production of gold nanoparticles. The size and size distribution of the synthesized nanoparticles were characterized using scanning electron microscopy (SEM) and dynamic light scattering (DLS). SEM images revealed that the gold nanoparticles were spherical in shape and had a narrow size distribution with an average size of 50 nm. DLS analysis confirmed the size and size distribution of the nanoparticles.

3. Coating of Gold Nanoparticles

Silica-coated gold nanoparticles were produced by mixing an ethanolic solution of 4 mM cetyltrimethylammonium bromide (CTAB) and 1 mM tetraethyl orthosilicate (TEOS) with the synthesized AuNPs and exposing the mixture to ultrasonic treatment. The presence of silica coating was confirmed using Fourier transform infrared spectroscopy (FTIR). FTIR spectra showed the presence of Si-O-Si and Si-O-Au peaks, indicating the successful coating of AuNPs with silica.

PEG-coated gold nanoparticles were prepared by mixing a 30 mg/mL solution of PEG 3350 polymer with the AuNPs and adjusting the pH to 9-10 using NaOH solution. The presence of PEG coating was confirmed using FTIR. FTIR spectra showed the presence of C-O and C-C peaks, indicating the successful coating of AuNPs with PEG.

4. Drug Loading

The drug loading properties of the nanoparticles were evaluated using UV-Vis spectroscopy. The concentration of ibuprofen in the solution was determined using a NANODROP 2000 spectrophotometer. Drug loading onto gold nanoparticles was performed using a 3:1 ratio solution of acetone and water to dissolve the drug, followed by centrifugation to precipitate the AuNPs and recover the liquid solution. The liquid solution was then analyzed using UV-Vis spectroscopy to determine the drug concentration. The loading efficiency of ibuprofen onto the nanoparticles was found to be higher in coated nanoparticles. This difference in the drug loading behavior between the two types of coated nanoparticles can be attributed to the differences in the surface chemistry and physicochemical properties of the coatings.

5. Applications

The development of drug delivery systems based on gold nanoparticles coated with silica and PEG has potential applications in the biomedical field. The sustained release of ibuprofen from silica-coated gold nanoparticles can be used for the treatment of chronic inflammatory diseases, such as rheumatoid arthritis, while the faster initial release of the drug from PEG-coated gold nanoparticles can be used for the treatment of acute pain. In addition, gold nanoparticles coated with silica and PEG have potential applications in cancer therapy. The unique optical properties of gold nanoparticles, such as surface plasmon resonance, enable them to selectively absorb and scatter light, which can be used for photothermal therapy and photodynamic therapy. In addition, gold nanoparticles can be functionalized with targeting ligands, such as antibodies or peptides, for targeted drug delivery to cancer cells.

6. Conclusion

In conclusion, gold nanoparticles coated with silica and PEG have been synthesized and characterized for drug delivery applications. The size and size distribution of the synthesized nanoparticles were characterized using SEM and DLS, while FTIR was used to determine the functional groups of the coatings. Silica-coated gold nanoparticles and PEG-coated gold nanoparticles were produced, and their drug loading and release properties were evaluated using UV-Vis spectroscopy. The development of drug delivery systems based on gold nanoparticles coated with silica and PEG has potential applications in the biomedical field, including the treatment of chronic inflammatory diseases and cancer therapy. In conclusion, the synthesis and characterization of gold nanoparticles coated with silica and PEG, and the loading and release of ibuprofen onto the coated nanoparticles, have been successfully demonstrated ^[1].