We do not have a protein-oligo kit made specifically for protein[cysteine]-oligo conjugations, but your planned strategy is exactly right. You would want to use the S-4FB crosslinker to modify your oligonucleotide, which has an amino group at the 3’ or 5’ end, and crosslink that product to an antibody (or protein) modified with HyNic. The way to conjugate your protein (at a Cys residue instead of a Lys residue) to HyNic is with our MHPH reagent, then react the two modified biomolecules together to get your conjugate. It is recommended to add TCEP (tricarboxyethylphosphine) to the MHPH modification reaction, which reduces any disulfide bonds, but does not react with the maleimido group. Recommended conditions are adding 3-5 mol equiv of TCEP/mol protein during the modification step. We also recommend conjugating the HyNic modified protein immediately.