ABSTRACT Due to the increase in agricultural contaminants in tap water and the importance of contaminant detection analysis, we report a sensitive and accurate colorimetric sensor based on the silver nanoparticles (AgNPs) to detect Trifluralin (TFA) in tap water. Silver nanoparticles were modified with 4-mercaptophenylbronic acid (MPBA) and for obtaining better responses from MPBA-AgNPs as a colorimetric sensor, Conditions affecting the reactions were optimised. The surface morphology, chemical structure and size of the MPBA-AgNPs sensor in different conditions were examined by FE-SEM, FT-IR, DLS and TEM analyses. Finally, it was used as a sensor to detect and measure the TFA herbicide with LOD = 3.20 ppm and RSD = %3.30. The recovery was obtained in the range of %87.15–%105.45, which indicated that the presented method is very practical and highly accurate for measuring this herbicide in its real samples.