Detection of organophosphorus pesticides (OPPs) is an important challenge in environmental chemistry, because their exposure to humans can cause severe health problems. In the current study, organic nanoparticles of (E)-(4-chlorophenyl)-1,1-diamino-2,3-diazabutadiene were developed using eco-friendly approach which was found to be in the range of 15–20 nm. These synthesized species exhibited both U.V. Visible and “turn-on” fluorescence responses in aqueous media for the selective detection of the extremely hazardous pesticide azinphos-methyl. These organic nanoparticles also exhibit a good linear relationship in the range of 1–100 μM and the limit of detection (LOD) is 7.4 µM. The selective fluorescence response was also observed in RO water, tap water and orange juice. The FT-IR and DFT studies helped in identifying the specific H-bonding interactions responsible for the selective detection of Azinphos-methyl.