2-Heptyl-3-hydroxyquinolin-4(1H)-one, commonly known as Pseudomonas quinolone signal (PQS), is a bacterial quorum sensing molecule produced by Pseudomonas aeruginosa. It regulates key processes such as virulence factor expression, biofilm formation, and iron homeostasis in this pathogen. Due to its strong fluorescence emission in the visible range, PQS serves as a valuable fluorescent probe in biochemical, microbiological, and analytical applications. Its quinoline core enables selective chelation of metal ions, particularly iron, rendering it useful in sensors for detecting trace metals in environmental and biological samples. PQS and its derivatives have been explored in antimicrobial studies, demonstrating inhibitory activity against certain bacterial and fungal strains by interfering with quorum sensing pathways or enzymatic functions. The lipophilic heptyl side chain facilitates cell membrane penetration, enhancing its utility in cellular imaging, bioassays, and investigations of bacterial pathogenesis. Additionally, research has examined its potential in antioxidant applications and as a lead for anticancer agents targeting DNA replication or cell division in malignant cells.