This work seeks to understand the fundamental chemistry of nanoparticles with lipid bilayers, such that knowledge gained at the molecular level can be applied to design environmentally and biologically sustainable nanomaterials. Nonlinear optical spectroscopies, including sum frequency (SFG) and second harmonic generation (SHG), are employed to study the interactions of nanoparticles with lipid membranes, specifically probing the molecular vibrations, electronic transitions, charge densities, and interfacial potentials at these solid-liquid interfaces in situ. Tracking how nanoparticles influence pure and mixed lipid bilayers will provide key insights necessary to understand, predict, and control molecular interactions between nanomaterials and living systems.