This study presents a fluorescence-based microbial sensor for the detection of metal ions as a novel analytical tool for environmental applications. Our results demonstrate the effectiveness of whole-cell sensors in the selective detection of gold ions. Two heavy-metal-tolerant proteobacteria, Cupriavidus metallidurans and Ralstonia eutropha, were examined and showed great specificity. This work highlights the potential of employing engineered microbial strains as robust analytical tools.