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

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.