Electroless Gold Deposition







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    We eventually succeded in producing electroless (auto catalytic) gold coating on fused silica glass pieces. There are two known methods (there may be more) of depositing electroless gold coating: cyanide based and non-cyanide based. Cyanide based electroless gold coating is done using potassium gold cyanide KAu(CN)2 [chemical name: potassium dicyanoaurate(I)], whereas non-cyanide based electroless gold coating is done using gold(III) chloride trihydrate (HAuCl4.3H2O) [other names: hydrogen tetrachloroaurate(III), tetrachloroauric(III) acid].

Our first attempt was cyanide bath, which didn't work well. So, we switched to the non-cyanide bath. We followed the method described by Jiandong Hu et al with some modifications. Here are the five steps:
  1. Cleaning
  2. Surface hydroxylation
  3. Surface functionalization (-NH2 addition) using APTMS (3-aminopropyltrimethoxysilane)
  4. Preparation of self-assembled monolayers (SAMs) of gold nanoparticles (AuNPs)
  5. Electroless gold deposition using HAuCl4 solution


1. Cleaning
  1. 30 minutes sonication in acetone (CH3COCH3).
  2. 30 minutes sonication in methanol (CH3OH).
  3. 30 minutes sonication in 1:1 :: methanol:HCl.
  4. 30 minutes in concentrated sulfuric acid (H2SO4).
  5. Rinse with DI water, isopropyl alcohol, and dry with N2 gas.


2. Surface hydroxilation (addition of -OH groups on the surface)
  1. 30 minutes immersion in Piranha solution (7:3 :: H2SO4:H2O2) maintained at 70oC.
  2. Rinse with DI water and dry with N2 gas.


3. Surface functionalization (-NH2 addition)
[ using APTMS (3-aminopropyltrimethoxysilane) ]
  1. 16 hours in 9.1% APTMS solution in methanol (i.e., 10 ml APTMS in 100 ml ultra pure methanol).
  2. Rinse with methanol, DI water, and dry with N2 gas.


[Note: All the glassware were cleaned with aqua regia before steps 4 and 5. It is a very crucial step.]

4. Preparation of self-assembled monolayers (SAMs) of gold nanoparticles (AuNPs).
  1. 6 hours immersion in colloidal gold nanoparticles (AuNPs) solution. Click here to read in detail the preparation of gold nanoparticles.
  2. Rinse with DI water (please note that the electroless gold deposition should be done immediately after this step).


5. Electroless gold deposition using HAuCl4 solution
  1. 10 minutes immersion and vigorous agitation in 5 ml 0.01% HAuCl4 solution + 0.25 ml H2O2 (within 2 minutes the color change was observed).
  2. Rinse with DI water, dry with N2 gas, and store it in a clean container until further excercise.
I will write a detailed electroplating procedure as well in future for those who asked about it. For those who asked about gold electroplating kit, there are some on ebay and amazon. For example, check out Goldsmith Gold Plating Kit Brush Plating Kit by Gold Plating Services on Amazon. I am not sure if it comes with cyanide free solution or not as it's not clearly mentioned in the product details. Also, these solutions are mostly proprietary, so you'd have to inquire with the manufacturer.

Please feel free to ask questions in the forum below or directly through the contact page for quicker response. Sorry, I don't sell any products.