We show that sum-frequency generation spectroscopy performed in the total internalreflection configuration (TIR–SFG) combined with a dense gold nanoparticles monolayerallows us to study, with an excellent signal to noise ratio and high signal to backgroundratio, the conformation of adsorbed molecules. Dodecanethiol (DDT) was used as probemolecules in order to assess the potentialities of the approach. An enhancement of morethan one order of magnitude of the SFG signals arising from the adsorbed species isobserved with the TIR geometry compared to the external reflection one whilethe SFG non-resonant contribution remains the same for both configurations.Although further work is required to fully understand the origin of the SFG processon nanoparticles, our work opens new possibilities for studying nanostructures.