Thiol-PEG4-Thiol is a bifunctional polyethylene glycol (PEG) derivative. Its molecular structure consists of two thiol groups (-SH) connected by a tetraethylene glycol (PEG4) chain, with a molecular weight of approximately 248.33. The production process involves precisely controlling the polymerization degree of the PEG chain and introducing active thiol groups at both ends to ensure a product purity of ≥95%. This reagent exhibits high reactivity; the thiol groups can undergo specific reactions with maleimides, alkenes, etc., or form disulfide bonds through oxidation for cross-linking. It is commonly used for surface modification of gold nanoparticles to enhance stability, preparation of PEG hydrogels, and as a cross-linker to construct biosensors or drug delivery systems, with extensive applications in the fields of biomedicine and nanomaterials.