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Thin-film fluorescent sensors play critical roles in the gas sensing field. However, fluorescent sensing materials for practical applications are limited, because of the aggregation-caused quenching (ACQ) effect and photobleaching. This study investigates a host–guest thin-film fluorescence sensor by incorporating a fluorescent probe into a metal–organic framework (MOF). The fluorescent molecule Me4BOPHY-1 acts as a recognition probe for the neurotoxin analog diethylchlorophosphite (DCP). The MOF (ZIF-8) provides nanocavities for the confinement of guest molecules, which reduces the self-aggregation of fluorescent molecules and pre-enriches the target gas. By applying ZIF-8 framework to disperse the fluorescent molecules, the ACQ effect of Me4BOPHY-1 can be effectively overcome. The fluorescence quantum efficiency of the molecules is increased from 0.76% to 19.72%, which enables its ability for gas sensing with a fast response time of 3 s and a detection limit as low as 1.13 ppb. Besides, the MOF facilitates selectivity enhancement through the confinement effect, weakening the sensing response to the interference of HCl. Moreover, the confinement effect also ensures high photo-stability as well as thermal stability. It can maintain fluorescence intensity under 4800 s’ laser irradiation. Thus, the host–guest design strategy offers a thin-film fluorescence gas sensor with high 3S (sensitivity, selectivity, and stability) toward neurotoxin analytes. © 2024 Wiley-VCH GmbH.