The highlight of day two of ABRF, for me, was the talk by Robert Campbell on fluorescent reporters. He started off by saying that existing fluorescent proteins were quite good and unlikely to get dramatically better. He spent the rest of his talk discussing his labs work to improve fluorescent protein reporters, where there is a lot of work still to be done. One of his guiding principles is “redder is better”.
He first discussed a wide range of new variants of his GECO series of calcium sensors , including red variants that allow simultaneous imaging and optogenetic stimulation. The paper is forthcoming in ACS Chemical Neuroscience (accepted preprint). They have even made a photoconvertible GECO based on their photoconvertible protein mMaple  that can been switched from green to red and responds to calcium in both states . I’m not sure what this is good for, but I hope someone comes up with a very clever experiment with it.
He then discussed work on voltage indicators. There is a consortium website from a number of other labs, fluorogenetic-voltage-sensors.org, which contains information on much of what has been previously developed (reviewed in ). One of the best current proteins is Arclight , which is GFP based and has a ΔF/F of about 35%. They’ve made an unpublished variant where they replace the GFP with a circularly permuted RFP, and can roughly double the ΔF/F. They’ve also been working on improved version of the archeal rhodopsin sensor Arch  ; they currently have an improved Arch that’s about 3-fold brighter than the original and has a ΔF/F about 4x better than Arclight.
Other things that came up in discussion: two ultrabright luciferases, which are both supposed to be bright enough for microscopy: Nano-lantern  and NanoLuc. Life Technologies mentioned that they recommend Pacific Blue for 405 nm imaging with small molecule dyes (although see our wiki page on 405 nm dyes).
That’s the summary of the ABRF meeting. It was a nice small meeting – about 500 total and 50 or so people in the microscopy track, and I got to meet a number of other core directors. It’s definitely a good meeting to attend if you want to talk to other core directors and see how they do things. Plus, they seem to like to hold it in sunny places – next year it’s in Albuquerque.