Engineering In Situ Activatable Integrated Polymer Dots with a Defined Chiral Microenvironment for In Vivo Enantioselective Monitoring of D-Noradrenaline in Brains with Alzheimer’s Disease

Enantioselective discrimination of enantiomers is very important to reveal the function and concentration fluctuation of chiral isomers in biological processes and disease pathogenesis. It remains challenging to distinguish D/L-enantiomers because they possess identical chemical composition and very similar physicochemical properties. Norepinephrine (NE) is a chiral monoamine neurotransmitter that shows extensive physiological effects on both the peripheral and central nervous systems of mammals and plays significant roles in the pathogenesis of Alzheimer's disease (AD). However, specific fluorescent probes for direct enantioselective discrimination of D/L-NE have rarely been reported so far, although gold standard methods such as chiral high-performance liquid chromatography (HPLC) and circular dichroism (CD) spectroscopy have been established. In this study, we present an integrated and in situ activatable chiral D-NE probe, BTTD polymer dots (Pdots) derived from a chiral fluorescent conjugated polymer, for distinguishing D-NE from L-NE based on the defined chiral microenvironment. BTTD Pdots exhibited high selectivity over other amino neurotransmitters, including dopamine and epinephrine, fast response within 2 s, good biocompatibility, and favorable penetrating efficiency of 37.02% across the blood-brain barrier (BBB). BTTD Pdots were successfully applied to fluorescence imaging of the NE exocytosis process induced by a high concentration of K⁺, and also used to monitor D-NE levels in the brains of AD mice. The results reveal that the D-NE level is substantially lower in the brain with AD than in normal mice. This study provides a distinctive avenue for designing a chiral fluorescent probe for differentiating enantiomers through engineering a defined chiral microenvironment with clew-like polymer-derived Pdots.