Controlling the Fluctuating Tip-Enhanced Raman Spectra of Chloramben on Silver Nanocubes

Tip-enhanced Raman (TER) scattering from molecules residing at plasmonic junctions can be used to detect, identify, and image single molecules. This is most evident for flat molecules interrogated under conditions of extreme temperatures and pressure. It is also the case for (bio)molecular systems that feature preferred orientations/conformations under ambient laboratory conditions. More complex molecules that can adopt multiple conformations and/or feature different protonation or charge states give rise to complex TER spectra. We illustrate how the latter can be controlled in the case of chloramben molecules coated onto plasmonic silver nanocubes. We show that characteristic molecular Raman spectra cannot be obtained when tunneling plasmons are operative, i.e., when the tip is in direct contact with the chemically functionalized plasmonic nanoparticles. We rationalize these observations and propose an approach to less invasive and hence more analytical TER spectral imaging.