Effect of Protein Binding Coverage, Location, and Distance on the Localized Surface Plasmon Resonance Response of Purified Au Nanoplates Grown Directly on Surfaces

Here we report the effect of protein binding coverage location, and binding distance on the localized surface Plasmon resonance (LSPR) response of purified Au nanoplates grown directly on surfaces. The response to human anti-IgG binding on the nanoplate surface depends strongly on these variables. The method of anti-IgG attachment Controlled the binding location terrace,, edge; or vertex sites) and the linker coverage and chain length controlled the antibody coverage and binding distance, respectively. The average, Change in lambda(max) (Delta lambda(max)) for binding to terraces at medium coverage, edge sites at low coverage and edge sites at medium Coverage was 21 +/- 5, 44 +/- 2, and 53 +/- 4 nm on nanoplate samples purified by sonication for example. The trend was similar for samples purified by taping, except that the shifts were all smaller due to a smaller initial lambda(max) for those samples. Atomic force microscopy (AFM) images reveal the coverage and binding location of anti-IgG on the nanoplates and, when correlated with the LSPR spectra, confirm that the edge sites are more sensitive to protein binding and Delta lambda(max) increases with increasing anti-IgG coverage. The LSPR response generally increases as the chain length of the linker decreases and matches quite well with that predicted by theory in most cases, although there are some exceptions. Specifically, the LSPR shift increases in the order of mercaptopropionic,acid (MPA) > 11-mercaptoundecanoic acid (MUA) > 16-mercaptohexadecanoic acid (MHDA) as linkers for anti-IgG. The average Delta lambda(max) for anti-IgG attached to the edge sites at high coverage on Au nanoplates purified by sonication Was 61 +/- 5, 53 +/- 4, and 42 +/- 3 nm, for the three linkers, respectively, for example.