Refractive index sensing using the metal layer in DVD-R discs

In recent years, grating based bio-sensors have received much attention due to their promising applications in integrated sensing devices. However, production of high quality, large scale and low cost metal gratings is still challenging. Here, we introduce an extremely simple and low cost method to fabricate metal gratings by peeling off the metal layer from a DVD-R disc. An atomic force microscope image shows that the metal layer is a high quality grating, the period and depth of which are 740 nm and 86 nm, respectively. Based on the fabricated metal grating, refractive index sensing is experimentally achieved using two configurations, where either the resonant wavelength or the modulated laser power is measured. The sensitivity of the sensor by wavelength modulation reaches as high as 637 nmRIU^-1, which is comparable with or even higher than that of the existing grating coupled sensors. Our method largely reduces the cost to fabricate high quality metal gratings and will promote the development of grating based SPR sensors.