Large-area metamaterial nanostructures of a Janus gold nanoparticle (AuNP) film decorated with thiol-terminated polymers have been fabricated and tuned at an oil/water interface by a facile and innovative process. The results show that AuNPs had been arrayed with ultrasmall gaps between neighboring particles laminated with polymer which is called a Janus film. This film exhibits a sensitive property for surface-enhanced Raman scattering (SERS) for determination of both hydrophilic methylene blue and hydrophobic thiram. The structure-dependent SERS of the Janus AuNP film has also been confirmed by a finite-difference time domain (FDTD) method
