Grating coupled SPR sensors using off the shelf compact discs and sensitivity dependence on grating period
Graphical abstract
Grating coupled surface plasmon resonance (GCSPR) sensors with wavelength modulation are widely used in many fields, but the low sensitivity holds their practical applications. Here we theoretically analyze the sensitivity limit of GCSPR sensors, provide design methods to reach the maximum sensitivity and the way to increase the sensitivity limit. The theoretical analysis shows that metal gratings with periods as large as possible should be used and the incident angle should be set close to 90∘ in order to maximize the sensitivity for a certain detecting wavelength, moreover the sensitivity limit increases as the detecting wavelength increases. Experimentally, we prepare three gratings with periods of 314 nm, 1470 nm and 6733 nm by stripping commercial optical discs or photolithography. The measured sensitivities of the sensors based on these gratings are 319.96 nm/RIU, 1477.74 nm/RIU and 2077.26 nm/RIU, respectively. The sensitivity achieved in this article is much higher than existing ones due to the use of design method following the theoretical analysis. This work paves the way for the optimal design of GCSPR sensors.
Fig. (a-c) are the reflection spectra detected by the GCSPR sensors using metal gratings with periods of (a) 314 nm, (b) 1470 nm and (c) 6733 nm. (d-f) are resonant wavelengths as a function of the refractive index. The data are extracted from (a-c) respectively.