Lead is highly toxic. The detection of lead in the environmental bodies is difficult, because it is colourless and odourless. Herein, we report the synthesis of gold nanoparticles (AuNPs) using the interdigitized vesicles formed by N-decanoyltromethamine (NDTM). AuNPs stabilized by NDTM was pink in colour with spherical shape and the size is 29 ± 7 nm. The optical property of the NDTM-AuNPs was explored for the first time to detect toxic chemical, Pb2+. The addition of toxic metal ion Pb2+ to NDTM-AuNPs rapidly (< 1 min) alters the colour from pink to violet due to aggregation, which was confirmed by particle size analyser and TEM. The aggregation induced colour changes were realized via broad spectra in UV–Vis spectroscopy. NDTM-AuNPs showed a selective and sensitive spectrophotometric signal with Pb2+ when compared with other metal ions. The colorimetric change as a function of Pb2+ concentration gave a linear response in the range of 0–30 μM (R2 = 0.9942). The detection limit was found at 10 μM by naked eye and 0.35 μM by spectrophotometry. The proposed method was successfully applied for the determination of Pb2+ ions in tap water and sewage water. Moreover, as a proof of concept, the NDTM-AuNPs sensor system was applied for the detection of lead in commercial paints. The results of the quantitative estimation of lead in paints by NDTM-AuNPs colorimetric sensor were as good as the standard method, atomic absorption spectroscopy. © 2018 Elsevier B.V.