<p>Gold nanoparticles (AuNPs) coated with disodium ethylenediaminetetraacetic acid (Na₂EDTA) have been created as a highly sensitive, selective, and simple colorimetric test for the detection of Cd²⁺. In this case, Na₂EDTA serves as a stabilizing and reducing agent. When Cd²⁺ coordinates with Na₂EDTA capped-AuNPs in a colorimetric sensing method, the interparticle distances decrease, leading to aggregation. As a result, the color shifts significantly from red wine to blue. The Na₂EDTA-AuNPs/Cd complex is created when the color changes from red-wine to purple and finally blue as the concentration of Cd²⁺ increases. The Na₂EDTA-AuNPs/Cd blue solution turns yellow when Na₂S is added. By comparing these color changes to various metal ions (Hg²⁺, Mg²⁺, Ni²⁺, Co²⁺, Ca²⁺, K⁺, Ba²⁺, and Bi²⁺), selective Cd²⁺ detection can be achieved. This provided a simple and effective colorimetric sensor (no enzyme or DNA) for on-site, real-time Cd²⁺ detection. With a linear fit coefficient of R² = 0.93929, this shows a sensitive linear relationship between 1/R values and [Cd²⁺]. Using a cotton probe based on Na₂EDTA-AuNPs, the estimated detection limit of Cd was 280&#xa0;nM.</p>