Biotin-PEG4-azide serves as a versatile biotinylation reagent specifically designed for tagging alkyne-containing molecules or biomolecules. It utilizes copper-catalyzed 1,3 dipolar cycloaddition click chemistry or copper-free click chemistry with cyclooctyne derivatives. The azide group within the compound efficiently reacts with alkynes, forming a stable triazole linkage that enables the incorporation of biotin into alkyne-modified systems. Notably, this bioorthogonal reaction is compatible with biological environments, meaning it does not interfere with the biological components present. Additionally, the PEGylated spacer in Biotin-PEG4-azide enhances its hydrophilicity, making it suitable for labeling terminal alkynes in a variety of bioanalytical applications such as non-enzymatic protein tagging, which can be analyzed using SDS-PAGE and Western blot techniques. Furthermore, it has implications in nanostructured biointerfaces, facilitating studies of ligand and receptor interactions amidst diverse signaling molecules.