The bactericidal effectiveness of metal nanoparticles has been suggested to be due to both their size and high surface-to-volume ratio. Such characteristics allow them to interact closely with bacterial membranes.

For instance, CuO nanoparticles also effective in killing a renge of bacterial pathogens. However, in comparison with nano Ag and Cu, higher concentrations of nano CuO are required to achieve a bactericidal effect.

Nanoparticles such as Ag and Cu release Ag+ and Cu2+ ions that cause local pH and conductivity changes near or into bacteria membrane or viruses. Relese of these ions for complex material is smaller and have insignificant changes in the environment near the cell.

The bactericidal effectiveness of metal nanoparticles is due to both their size and high surface-to-volume ratio. Such characteristics allow them to interact closely with bacterial membrane For example , CuO nanoparticles also effective in killing bacterial pathogens,but compared with nano silver and copper, higher concentrations of nano copper oxide are required to achieve a bactericidal effect.Nanoparticles such as Cu releases Cu2+ ions that make pH and conductivity changes near or into bacteria membrane or viruses. Relese of these ions for complex material is smaller and have insignificant changes in the environment near the cell.

To me it sounds like as if these nanoparticles would eventually induce Fenton reaction after release of atomic copper into the medium, similar what is known from Fe(III) taken up into bacteria. The questions is if these particles are really taken up (which I doubt) but they may locally interact with bacterial membranes and inject some poisoning concentration via uptake of siderophores. Although E. coli has no uptake system for copper in the outer membrane, there are systems in the inner membrane which would lead to enhanced Cu concentrations, most likely Cu(I) in the reducing milieu of the cytoplasm. Copper can be stored in Dps enzymes and therefore an overexpression strain may be less susceptible.

Seems like the basic consideration is whether, under a given set of conditions, the compounds you mention (CuS, CuO, Cu2O) undergo surface break down and release Cu ions, and if so at what rate. It sounds as if CuS does not undergo breakdown under the conditions of your experiment. If the compounds break down, then the amount of release per gram of particles will be proportional to surface area per gram of particles (unless the reaction is curtailed by e.g. local build up of Cu ions in solution). The antimicrobial efficacy will then depend on the concentration of released ions proximal to the bacteria.

@Bibekananda De

With thanks to all "woodoo scientists" :-), right info see at attached link.

NP is not best solution, you can try relative simple solution as application of "copper soap" - much more effective and compartable with plasics material.

Article Metallic nanoparticles: Mechanism of antibacterial action an...

Size and surface-to-volume ratio of nanoparticles are not very important for the compounds with very low solubility in analyzed media. For example, CuS has very low solubility (2.41E-17 g/100 of water - http://en.wikipedia.org/wiki/Solubility_table), it is not dependent on the size of particles. Even if you use the nanosized suspension of CuS, amount of dissolved Cu(2+) ions, which defines the antimicrobial activity, is limited by solubility of CuS. Of course, you could reach the equilibrium faster with nanosized CuS due to high surface-to-volume ratio compared to bulk CuS but in the end the low solubility of CuS is the main reason for its low antimicrobial activity in water-based solutuon.

Thanks to all of you for your valuable responces

@Alex Kronfeld

Copper NP was also considered in this actual review.

After comparing the bioactivity of nanoparticles, we can see often that they are in comparable concentrations more dangerous to humans than for bacteria.

http://www.collegiumramazzini.org/download/HOWARD08.pdf

@Alex Kronfeld

You are really waste our time. Trash publication, "woodoo science" in terms of methodology and experiment quality . Infact it is repeating of previous preps of nano CuO and CuS on cotton, and bioactivity of Cu-ions solutions (also known a long time before)

It contains a lot of funny mistakes, for example header of table:

Table 1 Antibacterial activity of ZnO- and ZnS-coated cotton against E. coli and S. aureus

But in contents of the table we see copper instead of zinc :-)

Please read carefully publication in my answers. To avoid offtopic, it seems to be better to create your own question - and I'm happy to answer your new questions.

Let me give an other aspect - agreying with most of the answers - the antimicrobial acitivty is mainly depends on the concentration and releasing of Cu-ions (I or II) from the nanoprticle surfaces. The released amount- which can or cannot reach the minimal inhibitory concentration -also depends on the type and composition of the medium. If CuS did not show activity in water - because of low solubility product and low Cu-concn. in the solution, even might show effect in a medium which contains e.g. complex forming materials. It is true, this is a question whetehr this complex can go across the cell membrane or not, toxic for a microorgansim or not, etc.