LbL Polyelectrolyte Adsorption: Poly(sodium-4-styrenesulfonate) (PSS), M w 15 200, (Polysciences) and poly(diallyldimethylammonium chloride) (PDAD-MAC), M w 20 000, (10 mg mL Β±1 , 1 mM NaCl solution) were used as stock solutions. 100 lL PDADMAC solution was added to 1 mL of the monolayerprotected gold suspended in 1 mM NaCl. After a minimum of 20 min the excess polymer was removed in the supernatant fraction after centrifugation. The nanoparticles were then re-dispersed in water, re-centrifuged and the supernatant removed. This washing process was repeated two more times. NaCl was then added to the nanoparticle suspension to give a bulk concentration of 1 mM salt. This process was then repeated with the addition of 100 lL PSS solution, then PDADMAC, then PSS, etc. The nanoparticle-containing solutions always had a salt concentration of 1 mM before addition of an aliquot of polyelectrolyte. If the repetitive coating process had to be stopped for any length of time, it was halted after addition of polymer and before the first washing step. Higher salt concentrations increase the flexibility of the polymer chains needed, but also induce flocculation of the nanoparticles, whereas lower salt concentrations stabilize the particles but cause self-repulsion of the pendant ions on the polymer chain. Higher molecular weight polymers produce thicker coatings required to shield the particle's interior charge from the surface charge of other particles, but the system does not have the energy required to coil the chain around a highly curved surface. In contrast, lower molecular weight polymers coat well, but once adsorbed, contain fewer loops and tails necessary to increase the particleΒ±particle repulsive charge. This will be discussed in detail in a subsequent publication.
Core Dissolution: A stock cyanide solution was made by dissolving 70 mg KCN in 15 mL H 2 O. 100 lL of the stock cyanide solution was added to 1 mL of the coated particles and left overnight. The dissolution process occurs via Equation 1.
The dissolution process was monitored by spectrophotometric study of the disappearance of the plasmon absorption band. After 3 h the solution was transferred to a dialysis unit (SPECTRAPOR, regenerated cellulose) and dialyzed three times against water over 24 h. Capsule solutions were then concentrated by evaporation and analyzed by TEM.