Peptide synthesis and characterization The FLAG and HA epitopes were synthesized with standard 9fluorenylmethoxycarbonyl (Fmoc protocols on a solid resin support) [35, 36] . Epitope sequences were modified with a linker region comprised of a discrete polyethylene glycol (PEG, purchased as Fmoc-dPEG™ from Quanta Biodesign) and a C-terminal cysteine. PEG was added to attenuate nonspecific binding, while the C-terminal cysteine provided a thiol linkage to the gold surface. PEG formed the link between the cysteine and the rest of the peptide, HA-PEG-C for example. After initial MPC, studies performed without the PEG linker were found to have no binding; all future studies incorporated this linkage. The notations HA-Au, HA-FLAG-Au, and FLAG-Au are assumed to include the incorporation of this linkage. Epitope antigens HA (AYDPVDYPY-(PEG) 6 -C, 1562.6 Da) and FLAG (KDDDDKYD-(PEG) 6 -C, 1451.5 Da) were synthesized on an Apex 396 (Advanced Chemtech) equipped with a 96-well reaction block capable of vortex mixing. 2-Chlorotrityl resin was swollen in dichloromethane (Fisher) prior to synthesis [37] . Fmoc amino acids (Synpep) and Fmoc-dPEG 6 acid (Quanta Biodesign) were coupled using O-benzotriazole-N,N,N′,N′-tetramethyl-uronium-hexafluoro-phosphate (HBTU, 5 eq with respect to resin, Synpep), 1-hydroxybenzatriazole (Hobt, 5 eq, Synpep), and N,N-diisopropylethylamine (DIEA, 10 eq, Advanced Chemtech) in N,N,-dimethylformamide (DMF, Fisher). Peptides were cleaved with 90% (v/v) trifluoroacetic acid, 5% anisole (Sigma), 3% thioanisole (Sigma), and 2% ethanedithiol (Sigma). Final purification was performed on a Waters C18 semi-prep RP HPLC column using a water (0.05% trifluoroacetic acid and acetonitrile) gradient. Peptide identity was confirmed via matrix-assisted laser desorption/ionization-time of flight analysis.