I have SERS microsphere sensors that have been silica coated, I have been coating them in APTES for further protein crosslinking.
In order to get a good and even coating of APTES a lot of papers use Piranha solution, to clean all contaminants from the silica surface, however my samples have organic underlayers, and any exposed parts of this will undergo oxidation in that solution, it's also quite harsh to be using frequently.
I've been using fluorescamine analysis for amine detection, but have had varying results.
What I would like to know is, if there are milder alternatives to Piranha that I can use to ensure the surface is prepared for silanization with organosilanes.
Thank in advance for any that take their time to help.
Pirahna treatment before bonding silanes to silica seems like going too far. Of course, no organic material may survive. This protocol might be good for ultraclean facilities. Normally, when typical silica (for chromatographic purposes) is bonded with APTES, it is boiled and pre-treated with 1 M HCl in water. This is followed by washing with ultrapure water and drying. The purpose is to generate more surface silanols groups and remove metal impurities, if any.
The suggestion for a cleaning solvent will completely depend on what organic layers you have underneath. Why don't you try "no pretreatment" option and see if APTES binds or not. It would be a good control experiment anyway and it might work.
Rinsing with pure solvents might be a good idea.
I think a lower amount of surface attached APS might also be okay for your application.
we have published a number of works in which we coated surfaces even only after rinsing the surface.
We habe also analysed the siloxane formation kineti.
This contribution also contains a nice overview about possible pretreatments.
K. Hermansson, U. Lindberg, B. Hök, and G. Palmskog, Wetting properties of silicon surfaces, International Conference on Solid-State Sensors and Actuators, 1991.
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