I would like to coat AFM tip with APTES and found that 10% APTES is the solution in which tips are placed and incubated for 2hrs. I have seen papers mentioning the usage of solvents like acetone, toluene, water, PBS and ethanol. Which of them gives monolayer of APTES on AFM tip and what properties of the solvent decide the efficiency of coating?
The best solvent is one where hydrolysis and self-ondensation do not occur. The preference is to have the silane to react with the hydroxyls on the solid surface instead of with the solvent, water in the solvent, or itself.
Anhydrous toluene fulfills this role well. Water, by comparison, is likely the worst solvent in the list. The others will have their differing advantages and disadvantages depending on how dry they can be maintained and how low their preference to promote self-condensation is. In practice, I would also avoid low vapor pressure solvents, e.g. acetone, entirely.
Vapor deposition has been recommended in many cases as the absolute best to obtain a consistent monolayer. It has its own practical disadvantages, especially that it must be done in dry gas environments.
Hi Dr. Jeffrey,
I have read that vapor deposition of APTES is done in Argon gas environment in a dessicator. Would it make any difference to do vapor deposition in vacuum? as moisture is the main issue and we don't have it either in vacuum or in Argon environment. Are there any issues other than moisture?
Would the dielectric constant of solvent decide the thickness of silane coating?
The key requirement is to avoid residual moisture in the gas phase and on the sample itself during vapor deposition.
Thickness is determined by the extent of self-condensation reactions that occur. It is chemistry, not solid state physics.
Hi Dr. Jeffrey,
Do I have to cure the APTES coated surface at higher temperature for few hours? Later I would like to treat the surface with glutaraldehyde and then with streptavidin protein.
Dear Jeffrey,
If anhydrous solvents are used, then how does initial hydrolysis of "Alkoxy" groups will occur to further from silanol and then oxane bonds with substrate?
We propose the first step in the chemistry is physisorption followed by surface reaction. See the references in my silane project. This does not require silanols. Granted halide silanes will behave differently than alkoxy silanes for the surface reaction.
Does anybody knows why in some papers the APTES or any other amine group binds to biomolecules such as antibodies without add EDC step ?
Dear Jeffrey,
I found better results when I used ethanol/water system for coating the magnetic nanoparticles than using anhydrous toluene. When I check the zeta potential after MNPs functionalization with ethanol/water and anhydrous toluene, I found higher positive zeta potential value for MNPs synthesized by ethanol/water system.
The APTES can cross-link in solution and that cross-linked layer can coat the surface. I imagine this will occur even more so when water is present in the solution phase. Have you washed the nanoparticles thoroughly after coating? Does this change the results?
@Pradyumma Waifalkar: Your question is unrelated to this topic. In respect to this, can you start a new discussion.
Yes, I have thoroughly washed the MNPs after coating. I could not see better results from non-aqueous toluene anhydrous synthesis. I think when you use APTES to coat directly onto the MNPs without TEOS functionalization, then anhydrous toluene might play major role. But in case of TEOS functionalized MNPs, APTES functionalization is not affected by anhydrous synthesis or aqueous synthesis because APTES upon contact with water gets hydrolyzed and binds to silica surface.
I want to use APTES to functionalise the surface of plasma cleaned PCL films, but all of the recommended solvents (acetone, toluene) dissolve or warp my PCL. Can I use a solvent such as ethanol, which doesn't do this?
dear Nicola Foster cola Foster concerning the surface modification you may find some solutions in the publications of Waldi MUNief and me (it’s a different Question)
Following the reactivity of the silane to siloxane reaction not only the water but also the condition ”””pH””” which is influenced by APTES have to be considered.
Article Analysis of silanes and of siloxanes formation by Raman spectroscopy
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