Green Synthesis of Robust Selenium Nanoparticles via Polysaccharide–Polyphenol Interaction: Design Principles and Structure–Bioactivity Relationship

Selenium is an essential micronutrient and is well known for its role in regulating metabolism. However, it is also highly toxic in some of its forms and above certain concentration levels. Amorphous selenium nanoparticles (SeNPs) are extremely unstable and convert into non-bioactive or gray elemental selenium with crystal-type structures due to aggregation, which limits its antioxidant and anti-tumor activities. To overcome these limitations, monodisperse SeNPs were obtained by stabilizing SeNPs with glucan and rosmarinic acid (RA) via Se–O bonds and polysaccharide–polyphenol interactions. The prepared glucan-RA-SeNPs were found much more stable than both SeNPs and glucan-stabilized SeNPs. Meanwhile, glucan-RA-SeNPs displayed enhanced bioactivities including an improved free radical scavenging ability and an increased cytotoxicity toward cancer cells. The underlying mechanism might be related to caspase activation by glucan-RA-SeNPs, thus overproducing intracellular reactive oxygen species and eventually resulting in cancer cell apoptosis. Our work proposes a feasible strategy for improving the structure–bioactivity of SeNPs through polysaccharide–polyphenol interaction.