Provided is a gold nanocage with pores, charged ligand molecules covalently bound to internal surfaces of the gold nanocage, and payload molecules electrostatically adsorbed onto said charged ligand molecules, wherein a pore diameter is between 1.2 and 20 times a gyration radius of the payload molecule. Also provided is a method for making a nanoparticle, including using polyvinylpyrrolidone as a capping agent in a galvanic replacement reaction to convert a silver nanocube into a gold nanocage having pores, replacing the polyvinylpyrrolidone on internal surfaces with charged ligand molecules, and electrostatically adsorbing payload molecules onto the charged ligand molecules, with a pore diameter less than twenty times a gyration radius of the payload molecule. Also provided is a method of delivering a pharmacological agent to a mammalian cell, including contacting the cell with a gold nanocage having pores, ligand molecules bound to internal surfaces, and pharmacological agent adsorbed onto ligand molecules.