Carbazole–xanthene-based swab/film fluorescent sensors for on-site visual detection of hydrazine in environmental and agricultural samples

), a highly toxic and carcinogenic industrial chemical, poses severe threats to both the environment and public health due to its extensive use and improper disposal. To address the urgent need for rapid, sensitive, and field-deployable detection tools, we present the design and synthesis of a carbazole-xanthene-based fluorescent probe (CZBX) for visual and selective hydrazine monitoring in environmental and agricultural samples. The probe remains weakly emissive until reacting with hydrazine to form a hydrazone, which produces a distinct "turn-on" fluorescence response. CZBX features rapid response, high selectivity and low detection limits under complex real-world conditions, including contaminated water, soil, and plants. For practical deployment, the probe was integrated into a portable swab-based sensing device and a poly(vinyl alcohol) (PVA) film, enabling convenient detection of hydrazine in both liquid and vapor phases. These portable platforms provide immediate visual feedback for on-site monitoring. Beyond offering a robust tool for real-world hydrazine surveillance, this work establishes a modular design strategy for future fluorescent sensors targeting hazardous environmental pollutants.