Halotag-thiol-O4 is widely used in biochemical and cellular research for protein labeling and imaging. It enables specific covalent attachment of fluorescent dyes, affinity tags, or other functional groups to Halotag fusion proteins, facilitating real-time visualization and tracking of proteins in live cells. This technology is particularly valuable in studying protein-protein interactions, localization, and dynamics within complex biological systems. Additionally, it supports high-throughput screening and targeted drug delivery applications by allowing precise and efficient modification of proteins. Its versatility and specificity make it a powerful tool in molecular biology and drug discovery.