I am generating self assembling monolayers of thiol-modified DNA strands on a gold surface, and I'd like to clean and reuse the gold surfaces. From what I've seen, folks typically use either piranha solution or oxygen plasma to remove gold-thiol bound monolayers. Is one method known to be better/more effective than the other? The gold surfaces will also come into contact with silicone gaskets. I've heard that silicone can potentially contaminate surfaces, but I'm not sure that will actually have an effect on monolayer formation, or if silicone contamination is mostly a concern when it comes to performing surface analysis (i.e. XPS analysis). Is it known whether piranha solution or plasma cleaning can remove silicone contamination from gold surfaces?
For those interested in more specific details, I'm using 1000 Å gold deposited onto borosilicate glass microscope slides using electron beam evaporation. The slides have a thin 2-7 nm layer of chromium (99.99%) as an adhesion promoter for the gold coating. The monolayers are made from variable length double-stranded DNA with a 5' C6 S-S modification. The thiol group is reduced in TCEP and the surface is backfilled with 6-mercapto-1-hexanol for 1 hour after letting the DNA monolayer form overnight. The slides are then washed with DI water and a buffer solution, and dried with argon before use.
Not sure of which is better. I used a UV/ozone cleaning method (supposedly like plasma cleaning) which is known to break CC bonds (turns organic layers into CO2 and water?) and on glass you get a good hydrophobic surface back. On gold I found that I could not get a packed monolayer of hexadecane thiol to form after that cleaning. It would seem that oxygen binds to the surface and the sulfur can't bind to the gold after that. I had to use freshly prepared gold surfaces to get the experiment to work correctly.
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