Attomolar detection of 4-aminothiophenol by SERS using silver nanodendrites decorated with gold nanoparticles.

In the present work we report a simple, fast, reproducible and cheap methodology for surface enhanced Raman spectroscopy (SERS) substrate fabrication of silver dendritic nanostructures (prepared by electrodeposition) decorated with gold nanospheres by electrophoretic deposition. This is the first report where a metal dendritic nanostructure has been decorated with another type of metal nanoparticles by this technique. The decorated nanostructures were used directly as SERS substrate using 4-aminothiophenol (4-ATP) as analyte. The objective of the decoration is to create more hot-spots in order to detect the analyte in a lower concentration. Decorated nanodendrites had a detection limit one million times lower than bare silver nanodendrites and all the substrates showed an increase in the Raman intensity at concentrations below 1 nM; because this concentration corresponds to the threshold for the formation of a monolayer resulting in a triple mechanism of intensity increase, namely electric field, chemical factor and hot-spots. 4-ATP was detected in attomolar concentration, which is below 1 ppq, corresponding to an analytical enhancement factor in the order of 10.