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Permalink Reply by Carlos Espinoza-González on January 30, 2010 at 7:44pm

Hi Vishnu Kiran

Well, I have been labored during 3 years in the synthesis and characterization of silver-polymer nanocomposites using both chemical and physics dispersion methods.

The answers to these questions is still not well understood. However, several reports including my experimentals results obtained, show that the biocide effect of the silver nanoparticles strongly depend of the chemical composition of the cell wall of bacterias, virus and fungus. The silver nanoparticles have a strong interaction mainly with amino (-NH-, -NH2, -NH3), thiols (-SH), hidroxil (-OH) groups. For example, the Gram-positive bacterias like Staphylococcus aureus are principally composed of a thick layer (about 20–80 nm) of peptidoglycan, consisting of linear polysaccharide chains cross-linked by short peptides to form a rigid structure. The rigidity and extended cross-linking not only endow the cell walls with fewer anchoring sites for the silver nanoparticles but also make them difficult to penetrate. This is the reason why the Minimum Bactericide Concentration (MBC) is higher concerning to the Gram-negative becteria like Escherichia coli. This latter, have a layer of lipopolysaccharide at the exterior, followed underneath by a thin (about 7–8 nm) layer of peptidoglycan. Although the lipopolysaccharides are composed of covalently linked lipids and polysaccharides, they lack strength and rigidity.

In relation with the antifungus activity, there are few reports about this. Our experimentals results shown that silver nanoparticles with average size between 2-15nm has a acceptable antifungus activity (~60%) to spore level. Maybe, the reason of this low activity is not far from the above reason. The Aspergillus niger has a layer of carbohydrates with neutral electronic density, also it has a very low content of amino groups (>10%).

Well, you can find more explanations to your question in this two good reports.

1.-Siddhartha Shrivastava, T.B., Arnab Roy, Gajendra Singh, Ramachandrarao,
Debabrata Dash, Characterization of enhanced antibacterial effects of novel silver
nanoparticles. Nanotechnology, 2007. 18: p. 1-9.

2.-Johnston, I.R., The composition of the cell wall of Aspergillius niger.
Biochemistry Journal, 1965. 96: p. 651-658.

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Permalink Reply by Vishnu Kiran M on February 1, 2010 at 1:35pm

Dear Mr Carlos,

Thank you so much for your clarification to my questions, its been a great help from your side and hope the same in the future for further discussions.

Thanks & Regards
Vishnu

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