Ag nanoparticle is full of Ag, when released as Ag+ it shows antimicrobial activities. Then we can use Ag+ directly instead preparing Ag nanomaterial.
The surface of an 'Ag nanoparticle' is actually fully oxidized on the surface - Ag2O - and this has solubility (forming the hydroxide) and is the bactericide. As you'll be aware Ag metal is not soluble. You could use AgNO3 which is effective but then there are risks of turning blue. See:
Silver colloids and invisible ink
https://www.brainshark.com/malvern/vu?pi=560497681&b=1&tx=120486&c1=22
In addition to Prof. Rawle's answer:
Ag nanoparticles provide gradual/continuous release of Ag+ ions
Yes, Leonid. Good point. I thought of that after I wrote my reply. Contolled release rate is important here to avoid argyria.
AgNO3 is a well-known primary antibacterial agent.
Article Antibacterial activity of silver-killed bacteria: The "zombies" effect
The question is analogous to 'Why make a pill to dissolve in the stomach when you can have the API in solution already?' Here there are 2 considerations - control of the drug release (as stated for Ag+ above) and the fact that the stomach has a pH of 1 any any drug in solution may have issues if swallowed as a solution. However, oranges and lemons have a similar pH. An API (for example, in the hydrochloride form) in the form of a pill/tablet can be passed into the stomach where it begins the dissolution process.
Similarly ingestion of AgNO3 solution (one of the few soluble silver salts) could have major issues. Silver citrate conceivably could be used - sparingly soluble in water but better in citric acid.
Dear Alan:
"Controlled Release" are the key words of this discussion.
Best Regards
Leonid
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