Selective attachment of antibodies to the edges of gold nanostructures for enhanced localized surface plasmon resonance biosensing.

Here we demonstrate control over the location of anti-immunoglobulin G (anti-IgG) proteins bound to Au nanoplates formed on glass and silicon samples. Preferential attachment to edge and vertex sites occurs by performing a thiol place-exchange reaction between mercaptoethanol (ME) attached to the Au nanostructures and mercaptoundecanoic acid (MUA) in solution, which localizes the carboxylic acid groups of MUA on the edge sites for subsequent amide linkage to anti-IgG. In contrast, anti-IgG attaches randomly onto the terrace regions of Au nanostructures functionalized directly in pure MUA or 1:10 MUA/ME solutions. Importantly, Au nanostructures with anti-IgG selectively bound to the edge sites exhibit significantly larger changes in the absorbance and wavelength of maximum absorbance (lambda(max)) of their localized surface plasmon resonance (LSPR) response upon binding than those with anti-IgG randomly attached to terrace regions. This leads to at least 500 times more sensitive detection of IgG down to 0.1 ng/mL.