Thiol-modified oligos ordered from IDT are shipped in their oxidized form, with the sulfur atoms protected by an S=S bond. See our Modifications Page under the "Products" tab on the IDT website to view the protecting group. Thus, thiol-modified oligos require a reduction step to remove the protecting group from the oligos before they are used. A protocol for the reduction of Thiol-modified oligonucleotides is available on the web site under SUPPORT & EDUCATION – SUPPORT – User guides and protocols. Access it here.
Note: Once treated, any oligonucleotide that is not used immediately should be stored frozen. Over time, the oligo will oxidize and the below procedure will need to be repeated prior to coupling.