Optimal Size of Silver Nanoparticles for Surface-Enhanced Raman Spectroscopy

Abstract

The optimal size of spherical silver nanoparticles (AgNPs) for off-resonance surface-enhanced Raman scattering (SERS) was found to be ∼50 nm based on the equivalent Ag content in AgNP colloids. It is understood that the SERS intensity of adsorbates on the surface of metal nanoparticles is dependent on the size and shape of the particles of interest. Herein, we report a seeded growth mechanism for the formation of silver nanoparticles that allows superior control over the size of the resultant nanoparticles with relatively low polydispersity. The high degree of size control allows for a better understanding of the study of the effect of particle size on SERS intensity. The Raman study performed here employed a long-wavelength excitation (785 nm) so as to avoid photochemical degradation of adsorbed species and photochemical transformation under intense excitation. Under these experimental conditions, it was found that the optimal size of AgNPs for providing a maximum SERS intensity of adsorbed R6G is ∼50−60 nm, a result that is expected to extend to other adsorbates as well.

Synthesis of size tunable monodispersed silver nanoparticles and the effect of size on SERS enhancement

“…For the samples where no aggregation occurred after addition of the analyte as expected [39], the SERS intensity and the G value increases with particle diameter as electromagnetic enhancement increases with size (see table 2) . For TP addition an increase in intensity and G value was also observed however contribution by aggregation for the larger sized nanoparticles affected the SERS intensity.…”

“…The Raman enhancement effect in the SERS experiment was determined by the AEF, which is denoted by G, describes the enhancement of the Raman signal per molecule adsorbed on the surface of a SERS-active species (in this case AgNPs) [39,40]. G is calculated as: [36].…”

Identification of Individual Exosome-Like Vesicles by Surface Enhanced Raman Spectroscopy

“…The 785 nm laser was chosen to limit photodegradation and autofluorescence. [51,52] All spectra were recorded at different locations in the sample. The presence of a gold coated ELV in the focal volume was confirmed by light scattering (figure 3A).…”

Optically Trapped Surface-Enhanced Raman Probes Prepared by Silver Photoreduction to 3D Microstructures

“…Ref. 40) the effect of which was compensated by the increased surface coverage. More detailed analysis of all the parameters affecting the SERS intensity would be needed for satisfactory explanation of the observed dependence, which is beyond the scope of the present work.…”