Simultaneous Monitoring of Intracellular Temperature and Norepinephrine Variation by Fluorescent Probes during Norepinephrine Reuptake

A long-standing challenge has been the simultaneous sensing of intracellular temperature and norepinephrine (NE) variations to explore signaling pathways and depression pathogeny. Here, we designed a fluorescent probe using poly(N-isopropylacrylamide) and 1-[4-(7-nitro-benzo [1,2,5]oxadiazol-4-yl)-piperazin-1-yl]-propenone (PNIPAm–AANBD) and (E)-1-(4-boronobenzyl)-2-(2-(1,3-dioxo-1H,3H-benzo[de]isochromen-6-yl)vinyl)pyridin-1-ium bromide (PHE) for simultaneously measuring the temperature and NE with high selectivity. The fluorescence intensity of the PNIPAm–AANBD moiety exhibited a good response to temperature changes. The PHE moiety could selectively sense NE due to the naphthalic anhydride group in PHE, which formed naphthalimide upon bonding with the primary amino group of NE. The hydroxyl-terminated ligand recognized the phenolic hydroxyl group of NE through the formation of hydrogen bonds. Using the proposed fluorescent probe, variations in the intracellular temperature and NE during NE reuptake could be simultaneously measured. It was first discovered that with the inhibition of antidepressant drugs, the intracellular temperature increased by 1.2–2.1 °C, and the NE reuptake decreased by about 21.5 μM. The measured variations in intracellular temperature and NE during neurotransmitter reuptake can shed light on the underlying mechanism of neurotransmitter signaling pathways, which may facilitate the treatment of depression.