Reactions were set up on a 750 µg scale for monobodies and a 100 µg scale for VHH and IgGs. 1 equivalent of the target protein was used and 1-3 equivalents of siRNA in a buffer containing 50 mM Trizma® base at pH 8.0. The bTG enzyme was added last at 1.5 equivalents. Reactions were stirred at 500 rpm and 37°C overnight. For monobody and VHH conjugation, reaction mixtures were analyzed using anSEC (Superdex 75 5/150 Increase, buffer PBS and a 0.3 mL/min isocratic elution). Purification of the monobodies were performed on an ÄKTA pure system with Superdex75 or HiLoad Superdex75 columns for monobody, the final conjugate was analyzed by SEC-MS. For IgG conjugation, reaction mixtures were analyzed using anlEX (Propac SAX 10 column, Buffer A: 10 mM Tris buffer, 20% EtOH pH 8, Buffer B: 10 mM Tris buffer, 20% EtOH + 1.5M NaCl pH 8. Gradient: 3 min at 10% B, 14 min to 100% B, 4 min at 100% B, 1 min to 10% B, 8 min at 10%B at a 0.75 mL/min flow rate) LCMS analysis 10 min method LCMS analysis was carried out on a Waters Acquity UPLC system and a 10 min method with 5% to 60% B in 8.0 min. Mass spectra over a mass range from 120 m/z to 3000 m/z are acquired using positive-ion Electrospray Ionization (ESI). Deconvolution range from 10 -150 kDa using Maximum Entropy (MaxEnt). Lipofection studies 15000 HEPA1-6 cells per well (150 uL of media) were plated and the cells were recovered overnight. The lipoplex was prepared and incubated for 20 minutes. In the meantime, the compounds were diluted to 8 µM in DPBS and a serial dilution 1:2 from 100 nM to 0.39 nM was performed. A negative control containing only lipofectamine in PBS was set up. 50 uL of media was then removed from the plates and 50 µL of optimum containing the diluted siRNA was added, in order to have a final volume of 150 uL of media containing lipoplex. This was let in the hood 20 min before being incubated at 37°C for 24h. The cells were lysed and RT-PCR was performed.