Pushing the surface-enhanced Raman scattering analyses sensitivity by magnetic concentration: a simple non core-shell approach.

A simple and accessible method for molecular analyses down to the picomolar range was realized using self-assembled hybrid superparamagnetic nanostructured materials, instead of complicated SERS substrates such as core-shell, surface nanostructured, or matrix embedded gold nanoparticles. Good signal-to-noise ratio has been achieved in a reproducible way even at concentrations down to 5×10(-11) M using methylene blue (MB) and phenanthroline (phen) as model species, exploiting the plasmonic properties of conventional citrate protected gold nanoparticles and alkylamine functionalized magnetite nanoparticles. The hot spots were generated by salt induced aggregation of gold nanoparticles (AuNP) in the presence of those analytes. Then, the aggregates of AuNP/analyte were decorated with small magnetite nanoparticles by electrostatic self-assembly forming MagSERS hybrid nanostructured materials. SERS peaks were enhanced up to 100 times after magnetic concentration in a circular spot using a magnet in comparison with the respective dispersion of the nanostructured material.