Synthesis of DNA–1° Antibody Conjugates.

As-received antibodies (Table S2) were desalted, buffer exchanged to pH 7.4, 1× PBS and concentrated to 0.5 mg/mL using Zeba protein desalting spin columns (Pierce). Succinimidyl 4-hydrazinonicotinate acetone hydrazine (SANH) (Solulink) in N,N-dimethylformamide (DMF) was added to the antibodies at variable molar excess of (300:1) of SANH to antibody. Separately, succinimidyl 4-formylbenzoate (SFB) (Solulink) in DMF was added at 16-fold molar excess to 5′-aminated 30-mer oligomers in 1× PBS. After incubation for 4 h at room temperature, excessive SANH and SFB were removed by buffer exchange of both samples to pH 6.0 citrate buffer using protein desalting spin columns. A 30-fold excess of derivative DNA was then combined with the antibody and allowed to react for 2 h at room temperature followed by overnight incubation at 4 °C. Noncoupled DNAs were removed by FPLC with Pharmacia Superdex 200 gel filtration column (GE) at 0.5 mL/min isocratic flow of 1× PBS. The conjugates were then concentrated to 0.5 mg/mL by Amicon Ultra-4 Centrifugal Filter Unit with Ultracel-10 membrane (Millipore 10 kDa) and stored at 4 °C. The conjugation yield was determined by protein BCA assay with Nanodrop 2000C (Thermo Scientific).