Fig. 5. (Top) A model showing the displacement of adsorbed weak buffers such as phosphate and then aggregation caused by Na⁺, or the buffer is not displaced (e.g. by F⁻) followed by aggregation at a higher concentration of Na⁺. (Bottom) Strongly adsorbed HEPES is not displaced by F⁻ or Br⁻, and the co-adsorbed Br⁻ further stabilized the AuNPs.