A Novel Class of Organic SERS-Active Materials from Bioinspired Supramolecular Frenkel Excitonic Nanoassemblies

While Surface-enhanced Raman Spectroscopy (SERS) is one of the most sensitive techniques for non-destructive analysis for molecular analytes at ultra-low concentrations, the development of SERS-based devices operating in real-life conditions have been restricted by current SERS substrates. Here, we overcome these limitations by providing proof-of- concept for an entirely new class of SERS-active materials: aqueous solution-based supramolecular Frenkel excitonic nanoassemblies. We found inter-molecular photon- induced charge-transfer from a model analyte—Rhodamine 6G (R6G)—adsorbed to cyanine dye based supramolecular nanotubes (b-NTs). Near-field Scanning Optical Microscopy (NSOM), time-resolved fluorescence spectroscopy and SERS revealed that the energy-level alignment between R6G and b-NT’s exciton band led to efficient Herzberg- Teller coupling, resulting in high degree of charge-transfer ( ρ =0.72) and significant plasmon-free SERS enhancement factor (3.0x104). Our results demonstrate how Frenkel excitonic nanoassemblies can serve as breakthrough materials allowing for rational design of efficient, tunable, and flexible substrates for charge-transport and resonant, aqueous solution-based plasmon-free SERS substrates.