Researchers at Peking University, China, are studying a new generation of sensors based on extraordinary optical transmission (EOT) because these nanostructures support the unusual phenomenon of EOT. The scientists add metal lids to conventional periodic nanoholes to build up novel quasi-3D structured, periodic arrays of two-layer coupled quadrate-holes and squares for SERS applications.

According to calculations, the top metal layer's job appears to be the collection and transport of energy to the gap between the edges of the structure by coupling with the bottom metal square. Both experiment and simulation show the advantages of the quasi-3D structure over the structure of one-layer nanoholes for SERS enhancement.

More details can be found in the journal Nanotechnology.