High-performance plasmonic oblique sensors for ions detection.

Efficient optical sensing is desirable for wide applications. For the sensors, the spectral factors of the sensitivity (S) and the figure of merit (FoM) and the intensity change related figure of merit (FOM*) are all the key points for sensing measurement. In this work, we propose and demonstrate a novel high-performance plasmonic sensor platform via using a resonant cavity array grating under the oblique excitation. Ultra-sharp absorption mode with the bandwidth down to 1.3 nm is achieved when the oblique angle is 7.5o. During the sensing of the Na+ (Cl-) ions in the solution, the spectral S and FoM factors reach 568 nm/RIU (refractive index unit) and 436, respectively. The minimum detection limit is as low as 3.521 x 10-6 RIU. The FOM* factor is simultaneously up to 907. Moreover, the spectral intensity change is up to 57% when only 1% concentration change is introduced for the solution. The detection limit of the ions' concentration can be as low as 0.002%. The sensor has great potential applications due to its ultrahigh S, FoM and FOM*.