Tunable Molecular Logic Gates Designed for Imaging Released Neurotransmitters

Fluorescent probes for the simultaneous detection of multiple analytes in biology

This review identifies and discusses fluorescent sensors that are capable of simultaneously reporting on the presence of two analytes for biological application.

Turn-On Near-Infrared Fluorescent Sensor for Selectively Imaging Serotonin

A molecular imaging tool that provides for the direct visualization of serotonin would significantly aid in the investigation of neuropsychiatric disorders that are attributed to its neuronal dysregulation. Here, the design, synthesis, and evaluation of NeuroSensor 715 (NS715) is presented. NS715 is the first molecular sensor that exhibits a turn-on near-infrared fluorescence response toward serotonin. Density functional theory calculations facilitated the design of a fluorophore based on a coumarin-3-aldehyde scaffold that derives from an electron-rich 1,2,3,4-tetrahydroquinoxaline framework, which provides appropriate energetics to prevent the hydroxyindole moiety of serotonin from quenching its fluorescence emission. Spectroscopic studies revealed that NS715 produces an 8-fold fluorescence enhancement toward serotonin with an emission maximum at 715 nm. Accompanying binding studies indicated NS715 displays a 19-fold selective affinity for serotonin and a modest affinity for catecholamines over other primary-amine neurotransmitters. The utility of NS715 toward neuroimaging applications was validated by selectively labeling and directly imaging norepinephrine within secretory vesicles using live chromaffin cells, which serve as a model system for specialized neurons that synthesize, package, and release only a single, unique type of neurotransmitter. In addition, NS715 effectively differentiated between cell populations that express distinct neurotransmitter phenotypes.

Dual enzyme-responsive “turn-on” fluorescence sensing systems based on in situ formation of 7-hydroxy-2-iminocoumarin scaffolds

We herein report a novel class of dual enzyme-responsive fluorogenic probes based on two orthogonal deprotection reactions via the “covalent assembly” principle. Sensing of two different enzymes (hydrolase and nitroreductase) through domino reactions, producing the push–pull backbone of a fluorescent 3-substituted 7-hydroxy-2-iminocoumarin dye, is reported.