Used in solid-phase oligonucleotide synthesis to introduce a biotin label via a triethylene glycol (TEG) spacer. The biotin tag enables strong binding to streptavidin, making it ideal for applications like affinity purification, nucleic acid detection, and immobilization on streptavidin-coated surfaces such as beads or biosensors. The TEG spacer enhances solubility and reduces steric hindrance, improving binding efficiency. Commonly used in diagnostic probes, gene expression studies, and functional genomics.