Hollow gold nanoparticles, also known as gold nanocages, are effective vehicles for the transport and administration of therapeutic agents, bioactive compounds, biomolecular reagents, biocatalysts, and other molecular compounds of interest. However, better control of the bioavailability of gold nanocages content is needed. The patent describes a gold nanocage with pores, charged ligand molecules covalently bound to internal surfaces of the gold nanocage, and payload molecules electrostatically adsorbed onto the charged ligand molecules. The method of making the nanocages includes a galvanic replacement reaction to convert a silver nanocube into a gold nanocage with pores, replacing capping agent molecules with charged ligand molecules covalently bound to the gold nanocage, and electrostatically adsorbing payload molecules onto the charged ligand molecules. The nanoparticles are advantageously used for the transport and administration of those payload molecules, such as therapeutic agents, bioactive compounds, biomolecular reagents, biocatalysts, and other molecular compounds of interest. Slow, long term release of payload molecules from nanocages may beneficially cause a sustained, steady-state level of exposure of tissue to payload molecules compared to what can be obtained with traditional methods for administering therapeutics or other molecules.