A graphene–gold-metasurface sensor is introduced for rapid and accurate detection of heavy metals, specifically Cu²⁺ and Mg²⁺ ions, in water. Using COMSOL simulations, the sensor's performance was analyzed. The sensor achieves optimized sensitivity of 1140 GHz/RIU for Cu²⁺ and 1149 GHz/RIU for Mg²⁺. It also has a minimum figure of merit (FOM) of 2.781 RIU⁻¹ and 2.855 RIU⁻¹ for Cu²⁺ and Mg²⁺ detection, respectively. The highest quality factors (Q factors) are 11.244 for Cu²⁺ and 11.247 for Mg²⁺. The sensor has very low detection limits of 0.466 for Cu²⁺ and 0.485 for Mg²⁺, enabling the detection of trace amounts. The sensor's excellent performance makes it a promising candidate for high-accuracy and high-sensitivity detection of Cu²⁺ and Mg²⁺ ions. These applications are crucial for monitoring environmental cleanliness and other uses. Additionally, the sensor can function as a 2-bit encoder. Keywords: Optical sensor, aqueous solutions, detection accuracy, graphene, metasurface, encoder. Water treatment facilities face congestion due to pollutant inflow, including heavy metals, pathogens, pesticides, and chemicals. Industrial discharge introduces contaminants like mercury, lead, and arsenic, while agricultural runoff adds pesticides and fertilizers, complicating water composition. Contaminated water causes health issues, including severe infections from pathogens like E. coli and Giardia. Heavy metals and persistent organic pollutants affect organs like the liver, kidneys, brain, and central nervous system, potentially causing cancer and neurological disorders. Pollution disrupts ecosystems, reduces biodiversity, and destroys habitats. Pollutant spikes lead to algal blooms and fish deaths, significantly affecting aquatic ecosystems. Soil and groundwater pollution hinder sustainable agriculture and food safety. Safe drinking water requires effective treatment techniques, including filtration, disinfection, and coagulation. Graphene-based sensors have gained interest for their high surface area, electrical conductivity, and chemical reactivity, making them suitable for metal ion detection. These sensors are fabricated using methods like inkjet printing, CVD, and screen printing. The proposed sensor offers a promising solution for detecting heavy metals in water with high accuracy and sensitivity.A graphene–gold-metasurface sensor is introduced for rapid and accurate detection of heavy metals, specifically Cu²⁺ and Mg²⁺ ions, in water. Using COMSOL simulations, the sensor's performance was analyzed. The sensor achieves optimized sensitivity of 1140 GHz/RIU for Cu²⁺ and 1149 GHz/RIU for Mg²⁺. It also has a minimum figure of merit (FOM) of 2.781 RIU⁻¹ and 2.855 RIU⁻¹ for Cu²⁺ and Mg²⁺ detection, respectively. The highest quality factors (Q factors) are 11.244 for Cu²⁺ and 11.247 for Mg²⁺. The sensor has very low detection limits of 0.466 for Cu²⁺ and 0.485 for Mg²⁺, enabling the detection of trace amounts. The sensor's excellent performance makes it a promising candidate for high-accuracy and high-sensitivity detection of Cu²⁺ and Mg²⁺ ions. These applications are crucial for monitoring environmental cleanliness and other uses. Additionally, the sensor can function as a 2-bit encoder. Keywords: Optical sensor, aqueous solutions, detection accuracy, graphene, metasurface, encoder. Water treatment facilities face congestion due to pollutant inflow, including heavy metals, pathogens, pesticides, and chemicals. Industrial discharge introduces contaminants like mercury, lead, and arsenic, while agricultural runoff adds pesticides and fertilizers, complicating water composition. Contaminated water causes health issues, including severe infections from pathogens like E. coli and Giardia. Heavy metals and persistent organic pollutants affect organs like the liver, kidneys, brain, and central nervous system, potentially causing cancer and neurological disorders. Pollution disrupts ecosystems, reduces biodiversity, and destroys habitats. Pollutant spikes lead to algal blooms and fish deaths, significantly affecting aquatic ecosystems. Soil and groundwater pollution hinder sustainable agriculture and food safety. Safe drinking water requires effective treatment techniques, including filtration, disinfection, and coagulation. Graphene-based sensors have gained interest for their high surface area, electrical conductivity, and chemical reactivity, making them suitable for metal ion detection. These sensors are fabricated using methods like inkjet printing, CVD, and screen printing. The proposed sensor offers a promising solution for detecting heavy metals in water with high accuracy and sensitivity.