Surface modification of nanoparticles plays a crucial role in determining their stability in aqueous solutions. The stability of nanoparticles in aqueous solutions is mainly influenced by factors such as surface charge, hydrophilicity, and the presence of stabilizing agents. Surface modification can alter these factors, thereby affecting the stability of nanoparticles in the following ways:1. Surface charge: Modifying the surface of nanoparticles can change their surface charge either positive or negative . A higher surface charge leads to increased electrostatic repulsion between the nanoparticles, preventing them from aggregating and improving their stability in aqueous solutions.2. Hydrophilicity: Surface modification can increase the hydrophilicity of nanoparticles, making them more compatible with water. Hydrophilic nanoparticles are more likely to disperse evenly in aqueous solutions, leading to better stability.3. Steric stabilization: Surface modification can introduce steric stabilizers, such as polymers or surfactants, onto the surface of nanoparticles. These stabilizers form a protective layer around the nanoparticles, preventing them from coming into close contact with each other and aggregating. This enhances the stability of nanoparticles in aqueous solutions.4. Biocompatibility: Surface modification can also improve the biocompatibility of nanoparticles, making them more suitable for biomedical applications. For example, modifying the surface with polyethylene glycol PEG can reduce protein adsorption and increase the circulation time of nanoparticles in the body, leading to better stability in biological fluids.5. Specific interactions: Surface modification can introduce functional groups that can interact specifically with target molecules or ions in the solution. These specific interactions can help to anchor the nanoparticles in the solution, preventing them from aggregating and improving their stability.In summary, surface modification of nanoparticles can significantly affect their stability in aqueous solutions by altering their surface charge, hydrophilicity, steric stabilization, biocompatibility, and specific interactions. These modifications can help to prevent aggregation and improve the overall performance of nanoparticles in various applications, such as drug delivery, imaging, and sensing.