Synthesis of gold nanoparticle-immobilized biodegradable polymer nanoparticles and their degradation properties

As nanoparticles are increasingly used as contrast agents in X-ray imaging, excreting these particles after the completion of imaging is essential. This study proposes a method for fabricating poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles, whose surface is modified with chitosan (CS) and immobilized using Au nanoparticles (PLGA/CS/Au), for diagnostic imaging. The proposed method involves three steps. In the first step, PLGA nanoparticles with a diameter of 50.7 ± 8.8 nm were synthesized using an antisolvent crystallization method with dimethyl sulfoxide as the good solvent, water as the poor solvent, and polyvinyl alcohol as the stabilizer. In the second step, the surface of PLGA nanoparticles was cationized with CS (PLGA/CS) to increase the affinity between PLGA and Au. CS modification was performed by adding an aqueous solution of CS to a PLGA nanoparticle colloidal solution. The third step was the immobilization of Au nanoparticles on the PLGA/CS nanoparticle surfaces. Initially, the Au nanoparticles with a diameter of 2.4 ± 0.4 nm were synthesized based on the reduction of hydrogen tetrachloroaurate (III) trihydrate with tetrakis (hydroxymethyl) phosphonium chloride (THPC) in a sodium hydroxide aqueous solution. Subsequently, they were added to the as-prepared PLGA/CS nanoparticle colloidal solution. The maximum Au-immobilization ratio was 39.5% for an initial Au concentration. The PLGA/CS/Au nanoparticles exhibited X-ray imaging ability and were hydrolytically degraded in a phosphate-buffered saline solution, indicating that the PLGA/CS/Au nanoparticles could function as excretable X-ray contrast agents.