Dear Niranjan,

Previous studies suggest that the methods used to prepare nanoparticles and, importantly, their surface coatings are critical to determining the long-term stability of these materials. It is this surface coating that interacts with the environment surrounding the nanoparticle. Every nanoparticle has a surface coating. Examples of a surface coating include an oxide, an organic polymer, or self-assembled

monolayers of organic molecules. The composition and uniformity of the coating, and its interaction with the core of the nanoparticle determines the robustness of this layer to oxidative or other methods of degradation. Degradation of the capping layer will expose the underlying particle to chemical and physical attack from the environment. These instabilities can result in particle aggregation or the release

of material from the nanoparticle. To avoid degradation of the nanoparticles it is important that the stabilizing layer remain intact throughout their use. Creating a stable capping layer, and thus a stable nanoparticle, requires a high quality capping layer. The capping layer should be covalently linked to the nanoparticles and contain minimal irregularities that could expose the underlying material to the surrounding environment.

Stability of Nanoparticles-Examples:

1-A study entitled " Determining the Stability of Nanoparticles in Solution

and Implications for Using these Materials " by Gates and coworkers assessed the long-term stability of colloidal nanoparticles, demonstrating a correlation of this

stability to the quality of the surface chemistry of these particles to resist oxidative damage and other changes. Month-long experiments were carried out on gold nanoparticles as a model for other particles. This particle type was chosen for its widespread use in the literature, and the relative inertness of gold to many other materials. Our results show that these particles can have short-term stability over a few days, but become destabilized after a week or more. Results were compiled from four independent experiments to determine the reproducibility of the results associated with these studies. The Authors  suggested, through the use of preliminary results, a method for optimizing the surface chemistry of nanoparticles in order to make particles that have longer-term stability.

http://www.wcb.ns.ca/Portals/wcb/Gates_StabilityNanoparticles.pdf

2-A study entitled " Colloidal stability of polymeric nanoparticles in biological fluids" by Moscatelli and coworkers revealed:

To design effective polymeric NPs for drug delivery, their stability has to be assessed thoroughly not only in stock solutions but also in fluids mimicking biological ones and in organ homogenates. Colloidal stability and polymer degradation of NPs in synthetic gastrointestinal fluids, serum and tissue homogenates was evaluated for 48–60 h, to reproduce their typical time of persistence in the body, and up to 200 h in stock solutions. While PMMA NPs remained stable in all the fluids, PLA NPs aggregated in gastric juice and in spleen homogenate.

These data also indicate that DLS is a powerful tool to evaluate NP colloidal stability in vitro/ex vivo experiments and that SPF analysis can be used to assess the stability as well. Qualitative accordance was found between DLS and spectrophotofluorimetry proving that this latter technique can indeed be used when switching from in vitro to ex vivo analysis to overcome opacity of the biological samples. These stability evaluation procedures should be therefore adopted for any new NP formulation before attempting in vivo studies.

http://link.springer.com/article/10.1007/s11051-012-0920-7

3-A study conducted by our group on the stability of ODTMA clay-micelles complex and SLS-Charcoal micelles complex revealed that these nanoparticles will be stable in their solid state for about one year if kept in closed containers. No study was done on their stability in solutions.

4-When nanoparticles are exposed to high salt solutions such as those present in most biologically compatible media, agglomeration can occur. Depending on the nanoparticle material, size, and surface, the agglomeration can happen instantaneously or over a period of days. Once the particles agglomerate, they behave like much larger particles and can have rapid settling rates, and the optical properties of the aggregated particles are typically dramatically different that those of individually dispersed particles.

http://nanocomposix.com/pages/salt-stability-of-nanoparticles

Hoping this will be helpful,

Rafik

Dear Niranjan,

Previous studies suggest that the methods used to prepare nanoparticles and, importantly, their surface coatings are critical to determining the long-term stability of these materials. It is this surface coating that interacts with the environment surrounding the nanoparticle. Every nanoparticle has a surface coating. Examples of a surface coating include an oxide, an organic polymer, or self-assembled

monolayers of organic molecules. The composition and uniformity of the coating, and its interaction with the core of the nanoparticle determines the robustness of this layer to oxidative or other methods of degradation. Degradation of the capping layer will expose the underlying particle to chemical and physical attack from the environment. These instabilities can result in particle aggregation or the release

of material from the nanoparticle. To avoid degradation of the nanoparticles it is important that the stabilizing layer remain intact throughout their use. Creating a stable capping layer, and thus a stable nanoparticle, requires a high quality capping layer. The capping layer should be covalently linked to the nanoparticles and contain minimal irregularities that could expose the underlying material to the surrounding environment.

Stability of Nanoparticles-Examples:

1-A study entitled " Determining the Stability of Nanoparticles in Solution

and Implications for Using these Materials " by Gates and coworkers assessed the long-term stability of colloidal nanoparticles, demonstrating a correlation of this

stability to the quality of the surface chemistry of these particles to resist oxidative damage and other changes. Month-long experiments were carried out on gold nanoparticles as a model for other particles. This particle type was chosen for its widespread use in the literature, and the relative inertness of gold to many other materials. Our results show that these particles can have short-term stability over a few days, but become destabilized after a week or more. Results were compiled from four independent experiments to determine the reproducibility of the results associated with these studies. The Authors  suggested, through the use of preliminary results, a method for optimizing the surface chemistry of nanoparticles in order to make particles that have longer-term stability.

http://www.wcb.ns.ca/Portals/wcb/Gates_StabilityNanoparticles.pdf

2-A study entitled " Colloidal stability of polymeric nanoparticles in biological fluids" by Moscatelli and coworkers revealed:

To design effective polymeric NPs for drug delivery, their stability has to be assessed thoroughly not only in stock solutions but also in fluids mimicking biological ones and in organ homogenates. Colloidal stability and polymer degradation of NPs in synthetic gastrointestinal fluids, serum and tissue homogenates was evaluated for 48–60 h, to reproduce their typical time of persistence in the body, and up to 200 h in stock solutions. While PMMA NPs remained stable in all the fluids, PLA NPs aggregated in gastric juice and in spleen homogenate.

These data also indicate that DLS is a powerful tool to evaluate NP colloidal stability in vitro/ex vivo experiments and that SPF analysis can be used to assess the stability as well. Qualitative accordance was found between DLS and spectrophotofluorimetry proving that this latter technique can indeed be used when switching from in vitro to ex vivo analysis to overcome opacity of the biological samples. These stability evaluation procedures should be therefore adopted for any new NP formulation before attempting in vivo studies.

http://link.springer.com/article/10.1007/s11051-012-0920-7

3-A study conducted by our group on the stability of ODTMA clay-micelles complex and SLS-Charcoal micelles complex revealed that these nanoparticles will be stable in their solid state for about one year if kept in closed containers. No study was done on their stability in solutions.

4-When nanoparticles are exposed to high salt solutions such as those present in most biologically compatible media, agglomeration can occur. Depending on the nanoparticle material, size, and surface, the agglomeration can happen instantaneously or over a period of days. Once the particles agglomerate, they behave like much larger particles and can have rapid settling rates, and the optical properties of the aggregated particles are typically dramatically different that those of individually dispersed particles.

http://nanocomposix.com/pages/salt-stability-of-nanoparticles

Hoping this will be helpful,

Rafik

Dear Biswal ,its very difficult to generalize the stability of NP's because it's varies with nature, size , morphology,reaction  environment,precursor nature its concentration,etc as Rafik explain very well,but in my experience its difficult to explain stability or destabilization rate of NP's ,as I prepared many types of nanoparticles I observed,Some time Ag nanoparticles are more stable than Au,while Cr more stable than Ni nanoparticles but on other hand when I prepared these same NP's  in different ways and conditions ,situation completely reversed( because i prepared these all in various ways,methods and environments),rate of destabilization or aggregation not same always ,stablity time can be extended or reduced by tuning or changing capping agents even their concentrations ,stability time observed few hours,few days,few weeks even few months,in my experience bi-metallic,tri-metallic nanoparticles are more stable and remains stable for long time.,hope it may help YOU to understand 

Regard 

Muhammad imran khattak 

Thanks all for your comments.