Spin-Coated Amino-Terminated Monolayers to Immobilize Gold Nanorods for Surface-Enhanced Raman Scattering-Active Substrate

Silane-based self-assembled monolayers (SAMs) are widely used to control the surface properties of materials. The spin coating technique is an interesting alternative to the conventional immersion solution for organosilane deposition owing to its speed and ease of use under ambient conditions. In this work, we study the impact of the drying step following organosilane deposition by spin coating. We investigated the influence of the temperature and duration of the drying step on the quality of the monolayers. Two trimethoxysilanes bearing a phthalimide end group with an alkyl chain or a urea moiety as a spacer were used to prepare amino-terminated SAMs. The structural information on SAMs was provided by polarization modulation infrared reflection-adsorption spectroscopy (PM-IRRAS), time-of-flight secondary-ion mass spectrometry (ToF-SIMS), and X-ray photoelectron spectroscopy (XPS). Results showed that the urea group that induced self-assembly by intermolecular hydrogen bonding reduced the drying step duration by half compared with the alkyl chain. In addition, PM-IRRAS and XPS measurements demonstrated the formation by the spin coating with a drying step at RT or 100 °C of a single monolayer. ToF-SIMS analysis showed the strong anchoring of organosilanes by polymerization in the monolayers. The use of spin coating has enabled to achieve homogeneous coverage on a micrometer scale. After deprotection, amino-terminated SAMs were derivatized to afford thiol-terminated SAMs to immobilize gold nanorods and constitute a surface-enhanced Raman scattering (SERS) substrate. An oligonucleotide bearing a terminal thiol immobilized on gold nanorods was identified by SERS, highlighting the potential of this SERS platform to be used as a biosensor in the future.