Recently developed alternative procedures involving the use of a mass spectrometer allowed for very precise measuring of the chemical compositions of nanoparticles of specific sizes inside a gas.

http://copublications.greenfacts.org/en/nanotechnologies/l-2/7-exposure-nanoparticles.htm

First of all that depends on the nanoparticle or better the material of the nanoparticle. You always can try to lyse the plant or parts of it and then detect the nanoparticles with a specific reaction which shows the presense of the material your NPs are made of. Plus you probably can use the optical properties to quantify them. 

Recently developed alternative procedures involving the use of a mass spectrometer allowed for very precise measuring of the chemical compositions of nanoparticles of specific sizes inside a gas.

http://copublications.greenfacts.org/en/nanotechnologies/l-2/7-exposure-nanoparticles.htm

Agree with Lala - ICP-MS is considered a gold standard to quantify a presence of NPs in various tissues. Destructive however...

thank  you all for sharing your valuable knowledge...

The best way to detect nanoparticles in plant tissue is either ICP-MS or by TEM analysis.

Also, you can go for SEM and AAS also. But, for ICP-MS and AAS you need to digest the plant material by nitric acid.

Also, you can go for SEM and AAS also. But, for ICP-MS and AAS you need to digest the plant material by nitric acid.

Dear Sudip Mukherjee let me know that after acidic digestion of plant material, do  nanoparticles  remain in the final maintained volume for AAS analysis or change into Elemental forms of their constituent elements.

or could the  corresponding elements detected through AAS correspond to the concentration of Nanoparticles.