S-acetyl-PEG4-propargyl is a PEG linker containing a sulfur acetyl group and a propargyl moiety. The sulfur acetyl group can be deprotected to produce a thiol compound. The propargyl group can react with azide-bearing compounds or biomolecules via copper catalyzed azide-alkyne Click Chemistry to yield a stable triazole linkage. The hydrophilic PEG linker increases the water solubility of the compounds in the aqueous media.