Fluorescent biorecognition of gold nanoparticle-IgG conjugates self-assembled on E-beam patterns

A new concept for line patterning of immunoglobulin G (IgG) in nanometer scale using gold nanoparticles (AuNPs) self-assembled in a nanochannel written with an electron beam is proposed and demonstrated. AuNPs are synthesized by reducing KAuCl₄ with NaBH₄, producing AuNPs 40-70 nm in size, where Cl^- ions are capping AuNPs thus making them negatively charged and subsequently stabilized. IgG is conjugated to these AuNPs by simple adsorption. Single or multiple nanochannels are written with an electron beam using a scanning electron microscope (SEM) in a layer of poly(methyl methacrylate) (PMMA), which is spin-coated on a p-doped Si wafer. AuNPs bind into the etched nanochannel where the Si surface is exposed, while the relatively hydrophobic PMMA area repels the particles. The particles with a diameter larger than the channel width are not able to go inside of it. Anti-IgG, conjugated with fluorescein isothiocyanate (FITC), is then exposed to the patterned surface, binding specifically to the IgG-AuNP conjugates within the line patterns. These antibody-antigen bindings can be visualized with a fluorescent microscope, showing the fluorescent signal only along with the nanometer line pattern. These initial steps will lead to the formation of complex protein nanoarrays, based on the size-dependent self-assembly of AuNPs within variously sized nanopatterns.