In Situ Activatable NIR‐II Polymer Dot Emitted at 1100 nm for Fluorescence Imaging of Norepinephrine Fluctuations in Live Neural Cell and Brain with Alzheimer's Disease

Aberrant levels of norepinephrine (NE) expression in brains with Alzheimer's disease (AD) are implicated in disease states, and monitoring the fluctuations of NE levels in brains can present a unique opportunity to inspire new treatment avenues. Fluorescence imaging in NR‐II region is a particularly favorable approach for real‐time monitoring in brain. Currently, the fluorescent probes for in vivo brain imaging of NE in AD mice are rarely available. Herein, an NE‐activatable NIR‐II polymer dots (Pdots)‐based fluorescent probe is developed with the longest emission wavelength and largest Stokes shift so far, DTBD Pdots derived from newly designed polymer, for recognizing NE through nucleophilic substitution and intramolecular nucleophilic cyclization. This study shows that NE level in brain of AD mouse is significantly lower than that in a normal mouse and also decreases with the progression of AD. This study unveils the correlation of NE levels in the brain with AD, and may provide new insights to assess pathology and degeneration process of AD by designing novel NE fluorophores.