Abstract: Water is an urgent human need; however, many people have difficulties gaining access to the safe and clean drink water. One of the most innovative techniques to solve this problem is known as biomolecular detection method. This can be followed through monitoring subtle changes in the refraction indices. In the present study, based on synthesis of gold nanoparticles (Au-NPs) on a grating structure sensor is proposed. The proposed structure operates as a refractive index (RI) sensor for detection of waterborne bacteria. Afterwards, we proceed with a cleverly designed RI biosensor optimized for waterborne diseases caused by Escherichia coli (E. coli) pathogen. This bacterial pathogen of various concentrations would be detectable by the proposed biosensor. Hence, the present study would lead to the development of plasmonic sensor with a sensitivity of as high as 467.1 nm/RIU (refractive index unit), in near-infrared region (NIR). In fact, the structure is capable of detecting a single bacterium contamination and determining the concentration level of bacterial spectrum in drinking water, as well. پرونده مقاله