Photoactivatable Biotin, Biotin-LC-ASA , Psoralen-PEG3-Biotin and TFPA-PEG3-Biotin each contain a photoactivatable group. When exposed to UV light, they become activated and insert non specifically into nearby molecules. These reagents may be used to label proteins and peptides, but they are also useful in labeling DNA, RNA and other molecules that do not contain any readily reactive functional groups. Psoralen-PEG3-Biotin contains a reactive psoralen group and is
designed to efficiently label nucleic acids. The psoralen group intercalates into the helix of DNA, allowing it to label efficiently and selectively. The psoralen can also stack along with the bases of single-stranded DNA or RNA increasing labeling efficiency and selectivity.

TFPA-PEG₃-Biotin: For labeling almost any molecule with biotin. Long, PEG-based spacer arm reduces steric hindrance and increases conjugate solubility. TFPA is more efficient than other reactive groups.

Psoralen-PEG₃-Biotin: Water soluble. Much higher coupling yield than achieved with photoactivatable biotin. Psoralen moeity reacts with the 5,6 double bond in thymine- and other pyrimidine-containing bases. Covalent attachment occurs in the presence of UV light (>350 nm) for 10 to 30 minutes. Suitable for biotinylating DNA/RNA probes. Ultrahigh sensitivity relative to radiolabelled probes (<100 femtograms). Does not interfere with hybridisation.