Two-photon (2P) in vivo functional imaging of genetically encoded fluorescent Ca2+indicators (GECIs) for neuronal activity has become a broadly applied standard tool in modern neuroscience, because it allows simultaneous imaging of the activity of many neurons at high spatial resolution within living animals.

Unfortunately, the most commonly used light-sources, tunable femtosecond pulsed Ti:sapphire lasers, can be prohibitively expensive for many labs and fall short of delivering sufficient powers for some new ultrafast 2P microscopy modalities. Inexpensive homebuilt, or industrial light sources such as Ytterbium fiber lasers (YbFLs) show great promise to overcome these limitations as they are becoming widely available at costs orders of magnitude lower and power outputs of up to many times higher than conventional Ti:sapphire lasers. However, these lasers are typically bound to emitting a single wavelength (are not tunable) centered around 1020-1060 nm, which fails to efficiently excite state-of-the-art green GECIs such as jGCaMP7 or 8.

To this end, we designed and characterized spectral variants (yellow CaMP = YCaMP) of the ultrasensitive genetically encoded calcium indicator jGCaMP7, that allows for efficient 2P-excitation at wavelengths above 1010nm.

In this talk, I will give a brief overview of some of the reasons why using a fiber laser for 2P excitation might be right for you. I will talk about the development of jYCaMP and some exciting new experimental avenues that it has opened while touching on the prospect that shifting biosensors to yellow could have for the  2P imaging community.