t-Boc-Aminooxy-PEG3-thiol is a crosslinker containing a t-Boc-aminooxy group and a thiol group. The thiol group reacts with maleimide, OPSS, vinylsulfone and transition metal surfaces including gold, The protected aminoxy can be deprotected under mild acidic conditions. The hydrophilic PEG spacer increases solubility in aqueous media.