A drug carrier includes a structure represented by formula (1) defined as in the specification is provided. The drug carrier can be used as a drug delivery system. The drug delivery system can include the drug carrier and an effective amount of a nucleic acid, in which the nucleic acid is encapsulated in the drug carrier. The drug delivery system also can include the drug carrier and an effective amount of an active substance, in which the active substance is encapsulated in the drug carrier.
