The limit of microscopes is 200nm, but apparently STED improves this according to this coverage of the Kavil prizes 2014 :
What is the current limit for microscopy ?
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According to Wikipedia, 2.4 nm using STED.
Recently a far field super resolution technique called MINFLUX, Minimal Photon Flux has been introduced by Stefen Hell, the same physicist who came up with STED back then. With this method they could achieve a resolution of 6nm where fluorescence molecules start to interact with each other. So this can be considered as the ultimate limit attainable with fluorophores making further resolution almost impossibe.
So now we can say the next conceptual limit for imaging has been introduced.