I am trying to bind gold nanoparticles to functionalized glass surfaces (optical fibers in particular) and the simple protocol I use works GREAT with 3-aminopropyltrimethoxysilanes, but fails regularly with 3-mercaptapropyltrimethoxysilane! The protocol is as follows:
Clean fibers in pirhana (30min)
Rinse with anhydrous ethanol.
Immerse in anhydrous ethanol, add MPTMS/APTMS at 1% by volume for 1 hour.
Remove and rinse with ethanol.
Store fibers in ethanol until use.
The weird part is I've had at least one trial where the MPTMS worked great. (I evaluate the efficacy by monitoring nanoparticles depositing on my fibers in realtime with UV-Vis). I am amenable to any suggestions and really have no idea why this protocol worked really great once, but mostly fails. I have tweaked most parameters such as immersion times, heating vs. non-heating etc.
It's really confusing to me why this doesn't work since the only difference in these molecules is the headgroup.
Here's a reply from a chemical manufacturer:
When the amino functional silane reacts it will orient itself so that the amines are available to react with the gold. The mercapto group will also react with the glass, so you may end up with available alkoxy groups and some mercapto groups available for the gold. It would probably be better to react the mercapto silane to the gold particle and then react the alkoxy groups to the glass. Use a hydrocarbon based solvent when reacting the mercapto to the gold to make sure that there is no water in the system.
This probably won't help me because I don't want to coat my nanoparticles with MPTMS, as they will pretty much be useless for biosensing afterwards.
If you want to coat you glass fiber with MPTMS , you should change your solvent..
Pl refer my any further details. We have clearly demonstrated the binding of gold nanoparticles and surface functionalisation of glass slides with APTMS. ref: Journal of Solid State Electrochemistry
Volume 11, Number 2 (2007), 296-302.
Thanks for your help guys. Turgay, which solvent do you recommend and why is ethanol not suitable?
I will look into the other resources that you guys have shared with me, thanks.
Katrien, thanks for the input. Your protocol is fairly close to mine, so I will try the annealing step. This is promising! Pandian, thanks for the resource. I will look into it soon as I'm sure it's a very good resource.
Is there a known chemical phenomena at play that makes these other solves ideal, or is it sort of black magic?
So I tried new protocols today:
2% h20, 2%MPTMS in ethanol (with and without annealing)
2% MPTMS in Toluene (with and without annealing)
These didn't work. In fact, they had such a small signal that I don't think the problem can be a tweakable parameter such as immersion time etc...
Are there some no-no's associated with these protocols. For example, is it ok to expose the fibers to air after MPTMS immersion for example? I usually expose them to air for 30 sec before storing them in ethanol.
Is it ok to store freshly prepared MPTMS fibers in ethanol? Works fine for my APTMS.
I'm out of ideas.
Is it possible to use a base bath on the fiber? It should etch away the outer most layer of glass slightly leaving behind hydroxyl groups which might be more effective at reacting with the alkoxysilane. If you do this use a concentrated base solution (its thick like syrup at 25C), boil it and submerge your fiber in the boiling liquid for 20 mins then rinse with water. I would also suggest drying with a soft towel then submerge in the silane solution.
The exposure to air should be fine as the silicon oxygen is stable to air and the mercapto groups aren't readily oxidizable at least in the short term in air. The storage in alcohol should also be ok for similar reasons.
As a follow up question what's the optimal protocol you use for the binding of the gold NPs once your surface has been coated with APTMS? and the protocol when it has been coated with MPTMS? assuming your NPs have been made by reduction of HAuCl4 with sodium citrate in water.
Thanks
Check out our publication at Applied Physics Letters 06/2012; 101:053109. DOI:10.1063/1.4739519. MPTMS or APTMS are unreliable and hard to reproduce results, try N1-(3-trimethoxysilylpropyl)diethylenetriamine, works great on glass, fiber, SiO2/Si etc. However, binding efficiency also depends on the particle size, and what sort of capping agents are on top of the particles -- the capping agents probably is the reason why you do not get binding with thiosilanes but you do with aminosilanes.
Thanks Palash. We do have some new particles with a different capping agent so I'll have to try this out!
Adam, did Katrien suggestion of annealing work out for you?
i am also trying to use MPTMS for my glass slides. Let me know.
No, MPTMS is still a no-go for us. We are using the crosslinker that Palash suggested.
http://www.sigmaaldrich.com/catalog/product/fluka/06666?lang=en®ion=US
The problem is the head group. Because of it, MPTMS is far more reluctant to react with glass than APTES does. So under the same conditions, your glass surface is not well dressed with MPTMS, accounting for the failure on AuNPs. To address this problem, you could add some amine into MPTMS/ethanol, which favors the silanezation reaction.
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