It's thought that ionized silver is better than silver nanoparticles !!!
Sellam Mohamed In theory, silver nanoparticles have no bactericide properties at all - metals do not dissolve in water.. It's the sparingly soluble silver oxide on the surface forming the Ag+ ion in solution that is key. The latter is the bactericide. Take a look at (where there are more references):
Silver colloids and invisible ink
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W150902SilverColloidInvisibleInk.html
and:
Metal colloids - their preparation, application and characterization
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W160218MetalColloids.html
I agree with Alan F Rawle . If the colloidal silver is pure silver, i.e. the nanoparticles are not oxidized, they do not show any toxicity. However, if silver oxide is formed on the surface of the nanoparticles, they release the metallic ion Ag+ and enhance the local release of reactive oxygen species (ROS) such as hydrogen peroxide, hydroxyl radical and superoxide anion, which induce oxidative stress in bacteria and cancer cells and eventually kill them.
Such a property exists for many metallic oxides. For instance, in these works we have studied the antibacterial and anticancer properties of Te nanorods:
Article Citric Juice-mediated Synthesis of Tellurium Nanoparticles w...
Article Synergic antibacterial coatings combining titanium nanocolum...
In clear contrast, in the Supplementary Information of the latter publication you can see that silver nanoparticles fabricated by a physical method (a sputtering-based cluster source) are pure and do not show any antibacterial behavior.
Although ionic silver solutions are useful in certain external applications, they are limited by their reactive capacity. In many cases the silver compounds formed are non-effective and/or undesirable in high dosage.
True colloids of silver nanoparticles do not suffer from this disadvantage as they do not readily form compounds in the human organism.
Goutam Kumar Jena In air the surface of 'silver' nanoparticles is always fully oxidized (i.e. Ag+). There is no silver in the 0 oxidation (i.e. metallic) state. ESCA/XPS shows this.
Dear Alan F Rawle sir i think we can synthesize biogenic silver nanoparticles
using Althaea officinalis as reducing agent.
Toxic means harmful to human body. Toxicity of a material depends on its reactivity and reaction time. As you know that ionic materials/solutions are highly reactive in human. It takes about 7 seconds for Silver ions to react with free chloride ions found in human body. Unlike this, colloidal silver has low reactivity in human body. Thus based on reactivity with human body, one can easily find which form of a material is more toxic.
For more detail, you can take help from the following:
https://www.news-medical.net/news/20191106/Differences-between-colloidal-silver-and-ionic-silver-solutions.aspx
Dr.Alan F Rawle, earlier you mentioned the answer session in the following line, In air, the surface of 'silver' nanoparticles is always fully oxidized (i.e. Ag+). There is no silver in the 0 oxidation (i.e. metallic) state. ESCA/XPS shows this. it is very interesting to know more about this topic, do you have any references based on ESCA/XPS. could you pls. forward it. Thanks
Sivakumar Muthusamy
I studied this (silver/oxide) phenomena in the late-1970's during my Ph.D. There are many more references available now. However, for the background to my comment (including early ESCA/XPS results) , then see the first mentioned webinar above (registration required):
Silver colloids and invisible ink
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W150902SilverColloidInvisibleInk.html
The second sentence of the Wiki article hints at this:
https://en.wikipedia.org/wiki/Silver_nanoparticle
Look at the text above Figure 5 in the attached.
Also: Article The investigation of oxidized silver nanoparticles prepared ...
Temperature programmed reduction (TPR) by H2 also shows the presence of oxide in the 'Ag' catalysts - pure silver would not show a reduction peak at room temperature or just above.
True to Alan F Rawle 's statement, Ag element will show insignificant direct elemental cytotoxic behaviour. It's Ag ions, which has the cytotoxic nature. But thing is, if you are looking at Ag colloid or ions for biological application, you can not have Ag as element in biological milieu where there are so many entities ready to interact, having binding energy more than the band gap energy of Ag element. It is destined to desorb and produce Ag ions. Hence, depending upon your applications, as Pervaiz has mentioned, about exposure time and surface functionalities (its somehow slows down the silver dissolution in biological milieu), you can choose either of it.
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