A drug delivery system comprising pH triggerable particles is described. The pH triggerable particles comprise and agent(s) to be delivered, which is encapsulated in a matrix comprising a pH trigger agent and a polymer. Agents including nucleic acids may be delivered intracellularly using the inventive pH triggerable particles. Upon exposure to an acidic environment such as the endosome or phagosome of a cell, the particles dissolve or disrupt due to protonation or an increase in solubility of the pH triggering agent. Pharmaceutical compositions and methods of preparing and administering these particles are also described. These particles may be particularly useful in genetic vaccination.