Effect of Silica Nanoparticles with Different Surface Charges on the Secondary Structure of Bovine Serum Albumin...

Although nanoparticles (NPs) show promise for use in bioimaging and drug delivery systems, their interactions with biomolecules remain largely unknown. Physicochemical differences among nanoparticles, such as differences in their size and charge, potentially influence the secondary structure of proteins. This study used silica NPs (SiNPs), the most commonly used NPs for biological applications, and bovine serum albumin (BSA), the most abundant protein in serum, to investigate the effects of NP surface charge on the secondary structure and adsorption behavior of BSA. We used SiNPs (diameter: 30 nm) modified with amino or carboxyl groups. Thioflavin T fluorescence measurements revealed that SiNPs increased the number of β-sheets in BSA, with the greatest increase observed for positively charged SiNPs. Liquid-film Fourier-transform infrared (FT-IR) and circular dichroism (CD) measurements provided comprehensive information on the secondary structure of BSA, confirming that positively charged SiNPs increased the number of β-sheets in BSA. Molecular dynamics simulations showed that BSA, with a total charge of -16, was not adsorbed onto negatively charged SiNPs because of electrostatic interactions but was adsorbed onto positively charged SiNPs. The IA subdomain, with a negative charge of -9, exhibited the highest adsorption tendency on the Si-NH₂ surface. These results suggest that positively charged SiNPs may contribute to the abnormal structure of BSA, potentially aiding in the design of highly biocompatible NPs.