Sub‐Second Ratiometric Fluorescence Imaging of Histamine Dynamics in Living Cells via a Supramolecular Probe

ABSTRACT Histamine (HA) is a critical neurotransmitter, yet its intracellular dysregulation remains difficult to monitor due to the slow kinetics and environmental sensitivity of traditional fluorescent probes. Herein, we report a supramolecular ratiometric probe engineered via the host–guest self‐assembly of cationic fluorophores with cucurbit[7]uril (CB[7]). By precisely modulating the cationic locus within the guests, we achieved a 2:1 (host:guest) stoichiometric complex ( CB[7] 2 ⊃GA‐1 ) that displays a distinct 60 nm bathochromic shift. Functioning via a competitive displacement mechanism, this probe demonstrates exceptional selectivity and an ultrafast response time of 0.96 s ( k obs = 3.56 s − 1 ). We successfully utilized this system to visualize real‐time HA fluctuations in living mast cells with sub‐second resolution. Notably, our imaging revealed a quantitative correlation between nigericin‐induced cytoplasmic HA elevation and mast cell rupture. These findings validate the probe's efficacy in tracking cellular inflammatory responses and highlight its potential as an early‐warning indicator for drug‐induced cytotoxicity. Consequently, this work offers a robust tool for dissecting HA‐related pathophysiology and establishes a generalizable design paradigm for the rapid, ratiometric sensing of biologically relevant analytes.