Most metal nanoparticles form a protein corona upon interaction with plasma (see http://www.nature.com/nnano/journal/v8/n10/full/nnano.2013.181.html). The nature of the protein corona has a large impact on the biological interactions in vivo. 

it depends on the nature of the particle, meso- porous nano particles are reported in targeted pH based drug delivery. 

Silver nano particles stop replication of cancer cells....

Prakash, I appreciate your answer but I would to differ a bit. I have studied the drug deliveryas well as the mechanism behind the death of cancer cells. But I want to know how the nanoparticles interact with the cells? How they react when they first see the cells?

Most metal nanoparticles form a protein corona upon interaction with plasma (see http://www.nature.com/nnano/journal/v8/n10/full/nnano.2013.181.html). The nature of the protein corona has a large impact on the biological interactions in vivo. 

Nanoparticles release reactive oxygen species in a liquid medium depending on the availability of UV energy, which in turn react with cell wall components. Depending on NP type and pH of the exposure medium, the interaction with cell wall components happens which result in the start of damage of cell membrane.

The interaction of nanoparticles with cells depend on mainly-

1. Size of nanoparticles

2. Shape

3. Surface functionalization,

4. Surface charge etc.

I am attching a good review article. It may help you.

Thank you Dr. Arun. I have a query that how the NP type and pH affect the interaction?? It would be helpful sir, if you could please provide any paper related to this mechanism.

Regards. Shakti

Thank you Dr. Sandra for replying to my query. I found the paper more helpful. But I am already acquainted with the formation of protein corona concept and I have studied the work of Prof. Kenneth Dawson, CBNI, Dublin regarding this corona formation. 

It would be great if you could put some light on the nanoparticle and the cell surface interaction especially based on ligand or receptors. 

Regards. Shakti

As rightly said by Mr. Sudip, it depends on several properties. I would add another factor which is TYPE of nanoparticles. In fact it's not another factor. Rather I'd say the type of nanoparticles in a way describes properties of nanoparticles described by Mr. Sudip. You should specify which kind of nanoparticles you are talking about; whether it is liposomes or protein nanoparticles (even different proteins produce nanoparticles with different properties) or solid lipid nanoparticles, metal nanoparticles or other. and you would find at least one paper on how the said interaction goes for each type of nanoparticle i just described. Even with each type there are several factors which describe their interaction with cells. For example, neutral liposomes interact with cell membranes through their very virtue of structural similarity with cell membrane i.e. through endocytosis, cationic liposomes may enhance cell interaction through binding with negatively charged cell membrane proteins and induced endocytosis, or those with DOPE enhance fusion of liposomes with cell membrane which can occur directly on cell membrane or after endocytosis. There are several other possibilities for just uptake and the same goes for intracellular release of drugs.

I'd suggest you to refer following articles for comprehensive details:

Thorek DL, Tsourkas A: Size, charge and concentration dependent uptake of iron oxide particles by non-phagocytic cells. Biomaterials 29(26), 3583-3590 (2008).

Jiang W, KimBetty YS, Rutka JT, ChanWarren CW. Nanoparticle-mediated cellular response is size-dependent. Nat Nano. 2008, 3(3):145-50.

Geng Y, Dalhaimer P, Cai S, Tsai R, Tewari M, Minko T, et al. Shape effects of filaments versus spherical particles in flow and drug delivery. Nat Nano. 2007, 2(4):249-55.

Some of nanoparticles are not charged. Therefore, they easily pass through cell membrane and membrane of nucleus. We observed small zinc and copper nanpoarticles were observed by EM after 30 second of exposure. We found that small zinc and copper nanoparticles kill cancer cells but spare normal cells. We described this phenomenon in two research articles (attached).