Dansyl-L-leucine is primarily used as a fluorescent probe in biochemical and biophysical research. Its application includes studying protein-ligand interactions, enzyme activity, and conformational changes in proteins due to its strong fluorescence properties. It is also employed in fluorescence spectroscopy and microscopy to track and visualize biological processes at the molecular level. Additionally, it serves as a marker in chromatographic techniques for the separation and identification of amino acids and peptides. Its unique fluorescence characteristics make it valuable in assays for detecting and quantifying biomolecules in complex mixtures.