Had no idea it's just a theory. I've lived many years "knowing" that we detect smells due to their shapes.
But while searching, I came across this: https://www.bbc.com/news/science-environment-21150046
I realize that this has long been considered crackpottery, and there has never been a reasonable sense of a mechanism for it. But it did seem to offer at least a stab at a couple of questions that didn't have good answers in the ordinary lock-and-key model of olfaction, such as why sulfur-containing molecules all smell "sulfury" if they all unlock different locks.
As far as I can tell the idea sorta just died out. A lot of work was done trying to make odor molecules with different isotopes, with intriguing but inconclusive results.
Still, I've been kinda curious to see if the theory was finally over and done.
I understand that some kinds exist (and some are even off the shelf) but they tend to be pretty limited in what they can 'sniff'.
This finding recently made a big splash at AChemS 2021 (the annual meeting for the Association for Chemoreception Sciences). And it actually is a really big deal. A protein structure is extremely information rich, telling you where all of the atoms of a given protein are (ish). Before this finding, there were NO structures of any olfactory receptor, and historically the publication of the first structure of a given biomolecule has been a watershed moment for that field (insulin, ribosome, many other examples).
What's more, they used the structural information to rationally engineer their olfactory receptor, expanding the binding pocket and changing how the receptor responds to different odorants. That was pretty much impossible to do before this. So, this is a pretty huge finding, and will definitely encourage more structural work on olfactory receptors in the future.
If I had to poke a hole in this finding, it would be that insect olfactory receptors are substantially different from mammalian olfactory receptors. But in my opinion, it seems that the buzz about this paper is definitely justified. Very cool!