This article reports formulation of remarkably stable macromolecule capped silver nanoparticles for the instant naked eye assay of extremely hazardous environmental pollutant, picric acid. We have established a simple and sensitive colorimetric technique for the assay of picric acid using spherical FCC silver nanoparticles modified with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT). In this context, highly stable AHMT capped silver nanoparticles (Ag@AHMT) are developed and optimized via UV-vis, IR and zeta potential. The designed Ag@AHMT nanoparticles of 4-10 nm size range are symmetrically distributed, regularly arranged and utilized for the ultra-trace assay of picric acid. It is found that picric acid encourages the aggregation of modified Ag nanoparticles through charge transfer complex formation, leading to color varies from light yellow to brownish yellow. This variation can be visualized by naked eyes. Further it was examined through UV-vis spectra and the limit of detection was obtained as 0.13 nM with sensitivity 0.045 ng/mL. The new approach lightens scope for fabrication of naked eye sensing devices of environmental pollutants. (C) 2018 Elsevier B.V. All rights reserved.