Preparation And Application Of SERS Substrate Based On Plasmonic Nanoanterina

Plasmonic nanoantennas act as a bridge of the optical far field and near field.During the energy transfer process, plasmonic nanoantennas enable an efficienttransfer of electromagnetic energy from near to far field. Plasmonic nanoantennasexploit the unique properties of metal nanostructures. They represented the forms ofthe strongly coupled plasmons at optical frequencies. The purpose of this paper is toenhance Raman signals with a plasmonic nanoantenna based on a long-range surfaceplasmon resonance/probe/silver nanoparticle (LRSPR-P-NP) sandwich configuration.This plasmonic nanoantenna was also applied for pH sensing.(1) We employed the incident angle-dependent spectroscopy to optimize thecoupling efficiency of this plasmonic nanoantenna. The strongest SERS intensity onthe LRSPR-P-NP nanoantenna was obtained when the incident angle was64.40°,which presents a cocontribution for SERS from both the LRSPR and localized SPR.(2) FDTD simulation shows that the electromagnetic field at the gap between thesilver film and a silver nanoparticle increases by a factor of about2.1×10~4, whichproves that stronger SERS was caused by the electromagnetic enhancement.(3) In this LRSPR-P-NP configuration, the value of G was calculated as5.62×10~7. It seems that not too much increase (only2.8times) in the LRSPR-P-NPconfiguration was observed relative to the LRSPR configuration (G=2.0×10~7).However, it should be noted that the G represents an average EF. If we consider theloading of silver NPs, which supports the LRSPRP-NP configuration, the G will bedifferent. So, the modified G from the LRSPR-P-NP configuration was calculated ashigh as9.2×10~8, which is comparable to the SERS enhancement level of “hottestsites”(the G is larger than10~9). (4) We detected the SERS spectra of4-Mpy with different pH under thisconfiguration. We plotted Log (A1206/A1221) vs. pH value and found it had a goodlinear relationship in the pH range of2.2-7.0. The correlation coefficient of the fittedline is0.9929. The adsorption orientation of4-Mpy also changed.