Imaging of formaldehyde fluxes in epileptic brains with a two-photon fluorescence probe

Endogenous formaldehyde (FA) generated by a serial of metabolic and epigenetic processes plays vital roles in the physiological and pathological progression of neurodegenerative diseases. However, an in-depth understanding of its functions remains a great challenge due to the lack of direct brain imaging tools for FA monitoring in live animal models. Herein, we report a two-photon (TP) fluorescence probe for imaging endogenous FA fluxes during metabolic and epigenetic processes in animal models, especially in live brains. Functionalization with a four-membered azetidine ring as the electron-donor group and a 2-aza-Cope FA reactive trigger as the receptor unit on the specific quinoline skeleton leads to a highly selective and bright TP probe (FAP-1). FAP-1 is capable of probing the dynamic fluctuations of endogenous FA from live cells to Caenorhabditis elegans and mice, especially in live brains with epileptic behaviors. This work provides a robust imaging tool to trace FA during epileptic physiology and pathology, and further reveals the association between the abnormally elevated endogenous FA and epilepsy.