Facile fabrication of truncated octahedral Au nanoparticles and its application for ultrasensitive surface enhanced Raman scattering immunosensing.

Monodispersed truncated octahedral (TOH) Au nanoparticles (NPs) with an average edge-length of about 16 nm were synthesized using poly(diallyldimethylammonium chloride) (PDDA) both as a stabilizing and reducing agent via a one-step reaction. Remarkably, no seeds, surfactants or additional reductant were used in this reaction. In addition, the PDDA molecules on the surface of the TOH AuNPs make them convenient for use in layer-by-layer assembly by electrostatic interactions. Importantly, the TOH AuNPs show a significant surface enhanced Raman scattering (SERS) activity, and can be directly used for building SERS-active substrates and tags. Based on these promising properties, an ultrasensitive SERS-based immunosensing platform was developed. Using human immunoglobulin (h-IgG) as a model target analyte, a detection limit of 36.56 fg ml(-1) was reached.