Dear Antonios

Thanks a billion for your answer, but in this case, I coated iron oxide nanoparticles with dextran so that I have free OH group and I am going to conjugate it to the amine group in one peptide and one protein. EDC/Sulfo-NHS couple COOH group to the primary amine and I am confused now whether I can use this method to conjugate OH free group of dextran to amine group in peptide and protein or not? in addition, I do not know that it is possible to conjugate two different proteins at the same time to my nanoparticle or it should be in separate steps?

I would be so much appreciative of you to give me some comments.

EDC/NHS linker chemistry cannot be used to couple hydroxyl groups to amines. it only works for carboxylic groups to be coupled to amines. For hydroxylic groups you need harsher chemistry as the reactivity in water of hydroxyl groups is relatively low. Ideally you would introduce the functional groups into your dextran before you coat the nanoparticles with it, so you can avoid organic solvents with your particles.

Dear Robert

Thanks a lot for the comment and then how I can carboxylate my dextran before conjugation?

Have a look at the literature:

like http://onlinelibrary.wiley.com/doi/10.1002/pol.1985.170230513/abstract

people use phosphate derivatives to connect something on the surface - the OH group may be not be nucleophile enough to react.

another option, I think easier would be to use carbonyldiimidazole (CDI). It will allow you to couple OH and NH2, without EDC use.

Check this book; http://www.sciencedirect.com/science/book/9780123705013

Dear Rozita Nasiri

Salam

Another suggestion, you can change the Hydroxyl groups to Carboxylic groups using Chloroacetic acid and then conjunction of COOH- with NH2 using EDC NHS.

Hydroxyl group has not enough activity to go trough reaction with amine group. At first should activated -OH group with addition a homo/hetro bifunctional crosslinker. Specially N,N'-Carbonyl diimidazole (CDI) is best for you. CDI is a crosslinker  regarding to attache -OH group in first molecule to -NH2 group of another molecule. 

Another crosslinker reagent is N, N -Disuccinimidyl Carbonate (DSC) or N-Hydroxysuccinimidyl Chloroformate.

Hope its be useful. 

Dear Rozita,

Another method is by the use succinic anhydride which links to OH group providing a 4 chain linker.The carboxlate end can then be linked to NH2 group of the enzyme

https://www.google.com.hk/search?q=Nadia+M.+Mahfouz%E2%80%9D*%2C+Tarek+Aboul-Fadl%E2%80%9D%2C+Ahmed+K.+Diabb&oq=Nadia+M.+Mahfouz%E2%80%9D*%2C+Tarek+Aboul-Fadl%E2%80%9D%2C+Ahmed+K.+Diabb&aqs=chrome..69i57.1392j0j7&sourceid=chrome&es_sm=93&ie=UTF-8