An aminopropylsilane would be the way to go, but you may need to be cautious about when and how it is added (depending on how concerned you are about the thickness of the aminopropylsiloxane layer that is deposited). The amines in the silane will catalyze their own hydrolysis and condensation, so any residual water will lead to reactions of the silanes. A little of this is good because it will cause them to react with the surface of the silica. Too much may lead to formation of poly(aminopropyl)siloxane polymers which may or may not be attached to the surface of the particles. Long-term stability of the amines in an aqueous environment is also a potential problem.

To avoid these problems, it may be helpful to:

1) Limit the amount of water on the silica surface prior to functionalization (e.g. by heating in vacuum to remove bound water)

2) Avoid water during functionalization (use dried solvent during the process)

3) Cure the aminosilane prior to further use

The suggestion above to cap remaining silanols on the silica surface is a good idea too to help to stabilize the amine groups.

Try with aminopropyl trimethoxysilene (APTMS) and trihydroxylsilyl propyl methyl phosphonateb (THPM). The first one will provide the amine group and the second one contains an inert stabilizing group (methylphosphonate) blocking the aggregation of the nanoparticles.

Hi Ivan, Thank you for your views. Can you provide the procedure for APTMS.

You can functionalize the SiO2 with APTES(aminopropyl triethoxysilene ) or APTMS(aminopropyl trimethoxysilene ).

You can see the detailed procedure in my recent publication [RSC Adv. DOI: 10.1039/c3ra41966e]

The Chemistry of Silica : Solubility, Polymerization, Colloid and Surface Properties and Biochemistry of Silica by Ralph K. Iler (1979, Hardcover)

Ralph K. Iler | ISBN-10: 047102404X | ISBN-13: 9780471024040

Hi Avinash, the procedure is the following one: you prepare the SiO2 by hydrolisis of the TEOS and, when you think that the process is finished, add 80 uL of APTMS and 30 uL of THPM. Then let to stir for 24 h (without changing the solution reaction used during the synthesis of your silica nanospheres). It's a really easy procedure.

An aminopropylsilane would be the way to go, but you may need to be cautious about when and how it is added (depending on how concerned you are about the thickness of the aminopropylsiloxane layer that is deposited). The amines in the silane will catalyze their own hydrolysis and condensation, so any residual water will lead to reactions of the silanes. A little of this is good because it will cause them to react with the surface of the silica. Too much may lead to formation of poly(aminopropyl)siloxane polymers which may or may not be attached to the surface of the particles. Long-term stability of the amines in an aqueous environment is also a potential problem.

To avoid these problems, it may be helpful to:

1) Limit the amount of water on the silica surface prior to functionalization (e.g. by heating in vacuum to remove bound water)

2) Avoid water during functionalization (use dried solvent during the process)

3) Cure the aminosilane prior to further use

The suggestion above to cap remaining silanols on the silica surface is a good idea too to help to stabilize the amine groups.