The dual role of a hexaazamacrocyclic ligand L in the effective reduction of Au3+ to Au0 and stabilization of the ensuing gold nanoparticles (AuNPs) is successfully demonstrated. The molar ratio of ligand L to Au3+ is found to be very important for the effective stabilization of the AuNPs. The as-prepared amine-capped AuNPs in the instant visual colorimetric detection of the TNT and 2,4-DNT under easy-to-adopt conditions is established. The naked eye detection of the analytes with an instant color change at concentrations as low as 476 fM is observed. Colorimetric analysis supported the detection of TNT and 2,4-DNT using the nanosensor with the LOD of 1.55 × 10-13 ± 2.02 × 10-13 M and 3.79 × 10-13 ± 3.65 × 10-13 M respectively. © 2014 The Royal Society of Chemistry.