Efficient functionalization of gold nanoparticles using cysteine conjugated protoporphyrin IX for singlet oxygen production in vitro

Gold nanoparticles with suitable properties are supreme therapeutic agents and provide effective signal enhancement in photodynamic therapy (PDT). In this study, protoporphyrin IX (PpIX) conjugated gold nanoparticles (GNPs) were prepared using covalent conjugation with cysteine as the adaptable linkage. The thiol group of cysteine was bound to the gold nanoparticles and also the formation of the amide linkage between PpIX and cysteine was confirmed using FT-IR. The spectroscopic characterizations (FT-IR and UV-vis) proved the formation of the PpIX conjugated gold nanoparticles. The reaction process was also followed using thin layer chromatography. Two different laser sources were used to activate the PpIX molecule in the ground state which was highly associated with the amount of singlet oxygen produced. Gold nanoparticles revealed a significant improvement in the singlet oxygen production of the PpIX molecule. The photocytotoxicity of the PpIX conjugated gold nanoparticles was also investigated using spermatogonial cells in vitro. The results confirm that the designed PpIX conjugated gold nanoparticles have provided a highly efficient agent for cellular photodynamic therapy.