Poly(amidoamine) (PAMAM) dendrimers have been identified as potential gene vectors. We are now studying their association with surfactants, dilauroylphospholiponucleosides (DLPN), with a nucleobase polar head that triggers molecular recognition of DNA and RNA. The interactions of DLPN with pre-adsorbed PAMAM monolayers on silica have been investigated with quartz crystal microbalance with dissipation monitoring (QCM-D). Both DLPNs form rigid layers when they interact with the pre-adsorbed dendrimer layer but the viscoelastic properties differ after rinsing. The addition of single stranded DNA affects the surface excess of the PAMAM/DLPN films, but only neutron reflectivity (NR) allows us to determine if DNA interacts with the dendrimer layer and replaces the DLPN or if it interacts with the DLPN layer. We aim to investigate the interactions PAMAM/DLPN on silica using NR to reveal the adsorbed layer structure and composition through the simultaneous fittings of corresponding NR profiles in different isotopic contrasts.