Rheological Behavior of Protein-Silica Nanoparticle Suspensions

Silica nanoparticles are widely utilized in biomedical applications, ranging from biosensing to drug delivery. Due to silica's low isoelectric point (IEP) and high reactivity, understanding its behavior in biological environments is critical for optimizing these applications. This study investigates the rheological properties—specifically viscosity and shear modulus—of protein–silica nanoparticle suspensions at varying protein concentrations and pH levels. Lysozyme, a common antimicrobial enzyme naturally present in the body, was selected as the model protein. Given that lysozyme and silica have IEPs of approximately pH 11 and pH 2, respectively, pH conditions were strategically chosen to explore the range of electrostatic interactions between the components. The results showed that suspensions exhibited increased viscosity and shear modulus within the pH range of 3–9, particularly at higher protein concentrations. These experimental findings were further supported by computational simulations of the suspensions, offering insight into the underlying molecular interactions.