Water-soluble Copper(II) sulfate (CuSO4) is the compound of choice, if click reactions in aqueous media e.g. for experiments with cell culture or sensitive biomolecules that do not accept DMSO-based environment should be performed. To create the click reactive Cu(I), Sodium Ascorbate is needed as reducing agent. Additionally a water-soluble ligand (e.g. THPTA) for protection of your sample has to be used.