Best method of sterilizing disposable syringes is -
Ionizing radiation: commercial plants use gamma radiation for sterilizing items like plastics, syringes, swabs, catheters, animal feeds, cardboard, oils, greases, fabrics, and metal foils REF:Ananthanarayan and Panicker's Textbook of Microbiology 8thEdition pg no:35
Hot air oven
UV rays
Boiling
Gamma rays
general microbiology