Optimal Size of Gold Nanoparticles for Surface‐Enhanced Raman Spectroscopy under Different Conditions

Abstract

Gold nanoparticles have been used as effective surface-enhanced Raman spectroscopy (SERS) substrates for decades. However, the origin of the enhancement and the effect of the size of nanoparticles still need clarification. Here, gold nanoparticles with different sizes from 17 to 80 nm were synthesized and characterized, and their SERS enhancement toward both 4-aminothiophenol and 4-nitrothiophenol was examined. For the same number of nanoparticles, the enhancement factor generated from the gold nanoparticles increases as the size of nanoparticles increases. Interestingly, when the concentration of gold or the total surface area of gold nanoparticles was kept the same, the optimal size of gold nanoparticles was found out to be around 50 nm when the enhancement factor reached a maximum. The same size effect was observed for both 4-aminothiophenol and 4-nitrothiophenol, which suggests that the conclusions drawn in this study might also be applicable to other adsorbates during SERS measurements.

SERS Nanoparticles in Medicine: From Label-Free Detection to Spectroscopic Tagging

“…[74][75][76]84 These higher order modes decrease the collective motion of electrons leading to wider plasmon band widths 72,77,85,86 and lower EM enhancements. 78,80,81 As particles decrease in size, on the other hand, less area is available to collect the incident light (smaller cross sections). Typically, the highest enhancements for silver and gold nanoparticles with spherical shapes are observed in the size range of 40−60 nm diameter.…”

“…Typically, the highest enhancements for silver and gold nanoparticles with spherical shapes are observed in the size range of 40−60 nm diameter. 80,81,87 Equation 1 would suggest that the optimal condition for maximal SERS intensities is when the LSPR peak has high overlap with the laser line and Raman-scattered frequencies. However, experimental observations have shown that this is not always the case.…”

Application of Gold Nanoseeds in Surface- Enhanced Raman Spectroscopy for Detection of Urea

“…This means that the samples with small size of AuNS and low LSPR peaks are not able to assist urea molecules to produce the Raman scattering signal because smaller nanoparticles will have less surface area and low conductivity of electron for oscillation. Thus, less light is absorbed by the surface which weakens its electromagnetic field and reduces the signal of Raman scattering [7]. From these results, we may concluded that the effective sizes of the AuNS to enhance the Raman scattering are about 15-20 nm.…”

Gallic acid-capped gold nanoparticles inhibit EGF-induced MMP-9 expression through suppression of p300 stabilization and NFκB/c-Jun activation in breast cancer MDA-MB-231 cells

“…Figure 1E shows that the absorption spectra of GA-AuNPs had an absorption maximum at 540 nm. Similarly, the spectra of AuNPs with the mean size of 60 nm showed maximal absorption at 540 nm (Hong and Li, 2013).…”