A new method is introduced for self-assembling citrate-capped gold nanoparticles into supraparticles with crystallographically aligned building blocks. It consists in confining gld nanoparticles inside a cellulose acetate membrane. The constituent nanoparticles are in close contact in the superstructure, and therefore generate hot spots leading to intense Surface-Enhanced Raman Scattering (SERS) signals. They also generate more plasmonic heat than the nanoparticle building blocks. The supraparticles are internalized by cells and show low cytotoxicity, but can kill cancer cells when irradiated with a laser. This, along with the improved plasmonic properties arising from their assembly, makes the gold supraparticles promising materials for applications in bioimaging and nanomedicine.