Your plant extract may not be a strong enough reducing agent to be able to reduce copper or zinc. As you have not provided information about what the plant extract is, why you think that it might be able to reduce metal salts, anything else that you have put in your reaction to try and make nanoparticles, it is difficult to help. You may need to add additional reducing agents, leave the reaction for a long time (days or weeks) or try other metals that it is easier for the plant extract to reduce (e.g. silver, gold, platinum, etc). We recently explored a range of biotemplated materials synthesis in a highlight (http://pubs.rsc.org/en/content/articlelanding/2012/jm/c2jm31620j#!divAbstract) and concept articles (http://onlinelibrary.wiley.com/doi/10.1002/chem.201300721/abstract) and there are a lot of different methods discussed in these articles, some of them may be appropriate to your problem. I hope this helps

Your plant extract may not be a strong enough reducing agent to be able to reduce copper or zinc. As you have not provided information about what the plant extract is, why you think that it might be able to reduce metal salts, anything else that you have put in your reaction to try and make nanoparticles, it is difficult to help. You may need to add additional reducing agents, leave the reaction for a long time (days or weeks) or try other metals that it is easier for the plant extract to reduce (e.g. silver, gold, platinum, etc). We recently explored a range of biotemplated materials synthesis in a highlight (http://pubs.rsc.org/en/content/articlelanding/2012/jm/c2jm31620j#!divAbstract) and concept articles (http://onlinelibrary.wiley.com/doi/10.1002/chem.201300721/abstract) and there are a lot of different methods discussed in these articles, some of them may be appropriate to your problem. I hope this helps

The compound which i am using is gallic acid and i've already synthesized silver and iron it has shown good results

Dear Dinesh please go through this link

http://www.sciencedirect.com/science/article/pii/S1319610312000506

Also, do you know if biomaterial is able to bind to your metal ions of choice? There is evidence from protein crytallography that some iron binding proteins (e.g. apoferritin) do not bind zinc. It may be that your material only binds/interacts with some metal ions and not others - you might need to try and do some metal ion binding assays to see how much it can bind, and if this is important for the templating of your metal nanoparticles.

Producing nanoparticles via green routes, involve (1) choosing of a reaction medium (solvent) (2) reducing agents; plant extracts (3) nontoxic substances as reagents use for the synthesis of NPs (e.g., gold and silver salts)

Gold and silver have an unfilled conduction band but a filled valence shell

Dear Friend....

I suggest you to choose any plant extract and mix with the metal salt solution which you want to reduce and expose it to microwave radiation (Microwave Owen).... and wait,,, If change in color,,, Sure... You will get the nano particles... There are many papers on silver and gold nanoparticles synthesis by same route..... I doubt about zinc,, But ,,We loose nothing in Trying :-)

I don't understand why do anyone use a cocktail of plant extract to make any nanoparticles. It will be meaningful and useful if you handle stuffs which you know are pure and characterizable. You can use different sugars or carbohydrate polymers. After making the nanoparticle, functionalize the polymer and use it to a meaningful end.

Easy Synthesis of Nanoparticles by Leaf Extract,

http://www.instanano.com/nanomaterial-synthesis/metal-nanoparticles/synthesis-copper-nanoparticles-2/