Development of active SERS platform via self-assembly monolayers of AuNRs

Gold Nanorods (AuNRs) have attracted extensive attention and scientific interest due to their special optical properties. In particular, the study of the interaction between electromagnetic radiation and metallic nanostructures is rapidly growing, with analytical applications such as plasmonic devices for Surface- Enhanced Raman spectroscopy (SERS) [1,2]. In this work, we investigated the obtaining of self-assembled monolayers (SAM) of aligned-AuNRs, via supramolecular alignment using cucurbit[7]uril (CB[7]), onto silicon substrates. For this, the silicon substrates were fabricated with submicrometer channels by lithography and etching processes, and then functionalized with (3-mercaptopropyl)trimethoxysilane. Finally, the AuNRs_CB[7] were deposited by immersion in channels. Analysis by UV-vis absorption suggests the inter-rod interaction between AuNRs and CB[7] promoting the self-alignment of AuNRs, which is indicated by the red-shift of the longitudinal surface plasmon resonance band (LSPR) from 735 nm to 762 nm and confirmed by SEM-FEG images. The Raman spectra for the substrates modified with AuNRs_CB[7] were collected using rhodamine 6G as probe molecule and we also investigated the effect of wet and dry states in the Raman analysis. The results indicated that the wet condition shows greater intensity in the spectrum compared to the dry condition, an effect associated with the dielectric component of the analyzed environment. Theoretical data confirmed this effect and also showed that the wet condition is in the resonance region and covers the SERS spectrum. The system has shown to be very effective and promising for SERS sensor applications for molecules at ultralow concentrations.