A simple two-step seed-mediated synthesis of monodisperse quasi-spherical silver nanoparticles by citrate and ascorbic acid reduction is presented. Control over monodispersity is achieved by a variety of compounds with hydroxyl groups such as glycerol, ethylene glycol, agarose, or sucrose. The latter can also be used as a matrix for storage.

A biocompatible, seed-mediated synthesis of monodisperse ~60 nm gold nanostars, followed by hydrophilic stabilization with ethylene glycol-modified Raman reporter molecules, is presented. Their application as SERS labels for imaging of the tumor suppressor p63 in prostate biopsies by immuno-SERS microscopy is demonstrated.

The synthesis of 3D self-assembled plasmonic superstructures of gold nanospheres as well as the characterization of their structural and optical properties at the single-particle level is presented. This experimental work is complemented by FEM (finite element method) simulations of elastic scattering spectra and the spatial |E|(4) distribution for establishing structure-activity correlations in these complex 3D nanoclusters.

Immuno-SERS microscopy is a novel imaging technique in nano-biophotonics, which employs antibodies labeled with SERS-active nanoparticles in conjunction with Raman microscopy. Rapid data acquisition is of central importance for screening large areas of tissue specimens. Here, we first discuss the role of SERS labels with single-particle sensitivity in immuno-SERS microscopy, in particular with respect to false-negative results. In combined single-particle experiments (SERS microscopy/dark-field microscopy/HR-SEM), we then demonstrate that small glass-coated clusters (dimers and trimers) of gold nanospheres exhibit the desired single-particle SERS sensitivity, even at acquisition times as short as 30 msec per pixel, while monomers do not. The proof-of-concept for rapid immuno-SERS microscopy with 30 msec acquisition time per pixel for selective imaging of the p53 family member p63 in prostate tissue sections is demonstrated.

Dimers of metal nanospheres are well-known for their characteristic anisotropic optical response. Here, we demonstrate in single-particle SERS experiments that individual gold trimers and 3D superstructures exhibit a polarization-independent SERS response. This optical behavior of single particle clusters provides constant SERS signals, independent of the mutual orientation of the incident laser polarization and the plasmonic nanostructure, which is desired or even required in many SERS applications.