Hi Akram Etemadi

Using an electrochemical scanning probe microscopy (EC-SPM) could work, this should give you the local information you need to determine if the alkanethiol is only on the gold, rather than the usual global view you would get from standard bulk electrochemistry. EC-SPM encompasses a range of different techniques from certain AFMs, to Scanning ElectroChemical Microscopy (SECM), to Scanning Vibrating Electrode Technique (SVET), and a variety of others.

Presumably the alkanethiol will act to reduce the activity of the gold structures, so if you ran an initial EC-SPM experiment prior to functionalizing the gold structures you should be able to pick out the gold versus the silicon. A second experiment after functionalization should still show a difference between gold and silicon, however if the gold has been functionalized I would expect its activity to have dropped.

The best EC-SPM technique for your work would probably be limited by the resolution require. SVET has been used to measure alkanethiols on a variety of metals (as an example: Laffineur et al, Langmuir, 2004, 20 (8), pp 3240–3245). However the resolution of this technique could be too low for what you want to achieve (10s of microns). On the other hand, SECM, which ahs also been used to investigate, and even functionalize a wide variety of SAMs (as an example: Rianasari et al, Langmuir, 2008, 24 (16), pp 9110–9117) could be a better option. This can have a resolution similar to the probe size, so measurement of micron, and sub-micron features isn't out of question. SECM should allow you to very clearly determine gold and silicon features based on their differing activities, and then investigate the change in activity of the gold after the SAM has been formed.

Hope this helps,

Sam

Dear Akram Etemadi ,

You may find the following thesis from a prior student of my PhD supervisor interesting: Label-Free Detection of Nucleic Acids by their Intrinsic Molecular Charge [Simon D. Keighley].

The thesis covers the characterisation of different SAMs on gold.

The following articles are also interesting:

https://pubs.acs.org/doi/10.1021/la00041a015

Article Comparison of self-assembled monolayers on gold: Coadsorptio...

Jules