Silver Nanoparticles with Many Sharp Apexes and Edges as Efficient Nanoresonators for Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

One of the tools used for investigations of various interfaces, especially in in situ conditions, is shell-isolated nanoparticle-enhanced Raman spectroscopy - SHINERS. To carry out SHINERS measurements, the surface under analysis is covered with electromagnetic nanoresonators, which locally significantly enhance the electric field of the incident electromagnetic radiation. This leads to a large increase in the Raman signal from molecules in close proximity to the deposited nanoresonators, thus making it possible to determine the composition of the surface phase on the basis of the Raman spectra obtained. We tested silver nanoparticles containing a large number of sharp apexes and edges (such as pentagonal bipyramids and triangular prisms) as surface-enhanced Raman scattering (SERS) and SHINERS nanoresonators. We found that the SERS enhancement factors obtained in the experiments with these anisotropic nanoparticles were 1 order of magnitude larger than in analogous experiments with spherical Ag nanostructures having similar size. Silver pentagonal bipyramids are especially easy to covered with very thin silica layers, and so such silica-covered nanoparticles seem to be very promising nanoresonators for SHINERS measurements. We also present the direct evidence of the significantly higher chemical stability of silica-covered Ag nanoparticles in comparison with bare Ag nanoparticles in the presence of a model biological sample (a suspension of yeasts cells).