For the sake of public safety and citizen health, the development of efficient and portable detection devices to nerve agents is critical. In this investigation, a naphthalimide-rhodamine based dual-chromophore, RNI-P, was synthesized and applied to detect nerve-agent mimic diethyl chlorophosphate (DCP) and real nerve agents. The probe exhibits inherently weak fluorescence due to the PET processes from both piperazine and rhodamine units to the naphthalimide unit. It shows rapid fluorescence enhancement to DCP in aqueous solution, demonstrating exceptional sensitivity and selectivity. Furthermore, the probe-inked paper strip can also rapidly respond to DCP vapor when integrated into a lab-made portable sensing platform. The detection limit to DCP vapor can be as low as 130 ppb. Most notably, the probe is capable of quickly and effectively detecting real nerve agents such as sarin and soman in aqueous solution, highlighting its significant potential for practical use. The turn-on responses are attributed to the prohibition of PET processes through protonation of the probe. This study reveals that not only the usual nucleophilic groups but also a second fluorophore can cause effective PET process to the core chromophore and empowers the probe with strong potential for efficient detection of nerve agents.