Poly(N-isopropylacrylamide)-gated Fe3O4/SiO2 core shell nanoparticles with expanded mesoporous structures for the temperature triggered release of lysozyme

• Synthesis of expanded pore, core-shell Fe3O4/SiO2 MCM-41 type mesoporous silica nanoparticles.
• Thermo-responsive PNIPAM-gating mechanism that allows for temperature controlled release.
• Ability to load and release lysozyme protein due to the enlarged pore size.
• Demonstration of the anti-bacterial properties of the lysozyme-loaded nanoparticles.

Core-shell nanoparticles comprised of Fe3O4 cores and a mesoporous silica shell with an average expanded pore size of 6.07 nm and coated with a poly(N-isopropylacrylamide) (PNIPAM) layer (CS–MSNs–EP–PNIPAM) were prepared and characterized. The nanoparticles was loaded with (Ru(bipy)32+) dye or an antibacterial enzyme, lysozyme, to obtain CS–MSNs–EP–PNIPAM–Ru(bipy)32+ and CS–MSNs–EP–PNIPAM–Lys, respectively. The lysozyme loading was determined to be 160 mg/g of nanoparticle. It was seen that Ru(bipy)32+ and lysozyme release was minimal at a room temperature of 25 °C while at physiological temperature (37 °C), abrupt release was observed. The applicability of the CS–MSNs–EP–PNIPAM–Lys was further tested with two Gram-positive bacteria samples, Bacillus cereus and Micrococcus luteus. At physiological temperature, the nanoparticles were shown to reduce bacterial growth, indicating a successful release of lysozyme from the nanoparticles. This nanoparticle system shows potential as a nanocarrier for the loading of similarly sized proteins or other species as a drug delivery platform.

The schematic illustrates the mechanism by which the PNIPAM gating operates in the nanoparticle system. At room temperature (25 °C), the PNIPAM brushes are hydrated and expand around the exterior of the nanoparticle, while at elevated temperatures beyond its transition temperature, the brushes collapse and shrink as the water molecules are expelled. As a result, the expanded pores can be exposed and release the cargo stored in the mesoporous silica nanoparticle.Figure optionsDownload as PowerPoint slide