Figure shows the SERS spectrum of freshly prepared and unpurified C/S particles. The Raman peaks of 4-NTP at 1343 cm -1 , 1100 cm -1 , and 1571 cm -1 are assigned to the symmetric stretch mode of NO2, the C-S stretch mode, and the C-C stretch mode (phenyl ring mode), respectively. In comparison to unpurified C/S particles, the SERS brightness of C/S particles purified by 3-fold centrifugation at 1200 g is increased by 25%. Both samples were prepared from the same colloid, and sample concentrations were normalized regarding the amount of gold in the sample as measured by the absorbance at 400 nm. Therefore, structural differences of C/S particles and concentration differences can be excluded, and the increased SERS intensity is attributed due to the removal of unbound, SERS-inactive AuNP. The latter corresponds to the amount of Au 0 in the sample. The particles were washed with water three times (1200 g, 15 min). Three SERS spectra (10 accumulations with 2 s integration time each) were measured and averaged for each sample. By centrifugation and redispersion, the SERS activity of the particles was increased by 25% due to removing the optically less active unbound satellite particles.