I did a literature search and a brief review on gold nanoparticles (GNPs) as an assignment. So, I was lucky enough to read about them. When I first learned that some reactions take a few minutes to prepare the GNPs, I was so surprised. At first, I couldn't understand and asked to myself how is it possible to build a structure like that in a few minutes. Obviously, as I read more, I saw what's happening there. Making them is not the problem. Making them at the size you want, characterizing and making them function is the problem as far as I can understand.
I want to let some of the readers (who are not in chemistry) know that GNPs are not high-tech compounds of the 21st century. If you read some review papers, you will see that they go back to a few thousand years ago. People used them as therapeutics without knowing that the solutions they drank had GNPs. Now, the area that we can use them expanded. Because of their chemical inertness and photophysical properties they are excellent tools for imaging, delivery etc. Of course they have other issues.
So, I read this paper today and I skipped the experimental section. In this article, being inspired by the surfaces of most proteins (they tend to be charged, polar), the researchers capped the GNPs with a peptide sequence that consists of three parts. Obviously the part that binds to Gold is made of prolines and a cysteine (sulfur-hard/soft acid base theory). Then they tested the stability of the GNPs.