I pre-coated the chips with 11-mercaptoundecanoic acid (MUA). Since, MUA self-assembly monolayer is a dense film, I wonder how to regenerate the chip . Is there anyone who deal with this before?
Hi Lie,
The best way is to put the chips in a UV Ozone cleaner and irradiate it for 40-60 mins. The ozone will clean away all the organic matter on the gold substrate. You can reuse QCM chips this way. Check out this link for more details
http://www.jelight.com/uv-ozone-cleaning.html
Good luck!
Sir,
In recommendation to Kumar sir, I would suggest the same to irridiate the chips in UV- ozone cleaner, to ensure reusability of QCM chips on gold substrate
Hi Ramya,
Thank you for your answer. I just wonder whether ozone could oxidize such a long alkyl chain molecule. MUA has 12 carbon long chain and form a dense monolayer. Acturally, i firstly treated the chip with UV Ozone cleaner for 30min, and then boil the chip in H2O/NH3H2O/H2O2 5/1/1 for 10 min in 70℃。 However, the regenerated chip fails to give the same result as fresh new chip. Thus, i ascribe this failure to the unclean surface of regenerated chip.
By the way, is there any method to assess the quality of clean protocol?
I've cleaned even 100nm thick coatings using uvo. The monolayer should be easy. Maybe you can do Ftir to check the absence of the Sam. Also the reason for not being able to reproduce result is chip damage. Most manufacturers say you can't reuse more than 3 cycles. Maybe use a new chip? The old one may have cracks or scratches despite being cleaned
Plasma or chemical cleaning damages gold film. It is may be OK, but the qcm electrode will withstand 1-3 cleaning. The better way may be electrochemical. Just use it as a working electrode in an organic solvent supporting electrolyte and apply positive potential ~+1.1 v vs AgCl pseudoreference electrode. The mercapto-compound will desorb from gold surface. It may be required to chemically clean traces of the compound from the surface.
Hi Ramya,
Yes, i also consider the possibility of chip damage. FTIR fails to detect monolayer MUA SAM, and the au film on the chip absorbs nearly all the IR irradiation. I asked the manufacturer about how to remove the MUA SAM. They said the protocols they provided may fail to clean a long chain thio-alcohol modified chip.
Hi, Lie,
Have you dealt with this problem? I met the same problem recently. Could you please tell me how you solve it finally?
Hi Lie, sorry for the late answer, hopefully, it will help. Here are some articles on electrochemical desorption of thiols from gold electrodes:
http://pubs.acs.org/doi/abs/10.1021/la960365q
http://pubs.acs.org/doi/pdf/10.1021/ja00079a021
http://www.sciencedirect.com/science/article/pii/002207289185271P
You may find something newer in google scholar by searching something like "electrochemical reductive desorption thiol gold".
Piranha solution is a standard method to clean the gold sensing surface of a QCM. However, it deteriorates the chromium adhesion layer and can only be done a few times before the chip needs replaced.
I have found O2 plasma cleaning to be most effective at cleaning the QCM and have repeated the process more than 50 times on a sensor with no issue.
Hi, Michael Milgie
Thank you for your answer. Piranha solution and O2 plasma cleaning are suitable to regenerate chips that modified with short chain thioalcohol. Unfortunately, for long chain thioalcohol, i found it hard to remove these thioalcohol at a acceptable level (since the results are not repeatable for cleaned chips). I guess that the monolayer formed from long chain thioalcohol is so dense that ions and O2 plasma are hardly penetrate through the layer to interacted with Au-S bond, leading to a relative low remove ratio. I also contact the Biolin, they also think that for long chain thioalcohol modification such as 11-mercaptoundecanoic acid (MUA),Piranha solution and O2 plasma cleaning may not give a acceptable results.
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