Tumor Necrosis Factor Interaction with Gold Nanoparticles
De-Hao D. Tsai, Sherrie R. Elzey, Frank W. DelRio, Robert I. MacCuspie, Suvajyoti S. Guha, Michael R. Zachariah, Athena M. Keene, Jeffrey D. Clogston, Vincent A. Hackley
We report on a systematic investigation of molecular conjugation of tumor necrosis factor protein-α (TNF) onto gold nanoparticles (AuNPs) and the subsequent binding behavior to its antibody (anti-TNF). We employ a combination of physical and spectroscopic characterization methods, including electrospray-differential mobility analysis, dynamic light scattering, polyacrylamide gel electrophoresis, attenuated total reflectance-Fourier transform infrared spectroscopy, fluorescence assay, and enzyme-linked immunosorbent assay. The native TNF used in this study exists in the active homotrimer configuration prior to conjugation. After binding to AuNPs, the maximum surface density of TNF is (0.09 ± 0.02) nm-2 with a binding constant of 3×106 L/mol. Dodecyl sulfate ions induce desorption of monomeric TNF from the AuNP surface, indicating a relatively weak intermolecular binding within the bound TNF trimers. Anti-TNF binds to both TNF-conjugated and citrate-stabilized AuNPs, showing that non-specific binding exists. Based on the number of anti-TNF molecules adsorbed, a substantially higher binding affinity was observed for the TNF-conjugated surface. The presence of thiolated polyethylene glycol (SH-PEG) on the AuNPs inhibits the binding of anti-TNF, and the amount of inhibition is proportional to the number ratio of surface bound SH-PEG to TNF and the way in which the ligands are introduced.