Abstract
In this paper, a reconfigurable sensing platform based on an asymmetrical metal-insulator-metal stacked structure integrating an indium tin oxide (ITO) ultrathin film is proposed and investigated numerically. The epsilon-near-zero (ENZ) mode and antisymmetric mode can be resonantly excited, generating near-perfect absorption of over 99.7% at 1144 and 1404 nm, respectively. The absorptivity for the ENZ mode can be modulated from 90.2% to 98.0% by varying the ENZ wavelength of ITO by applying different voltages. To obtain a highly sensitive biosensor, we show that the proposed structure has a full-width at half-maximum (FWHM) of 8.65 nm and a figure-of-merit (FOM) of 24.7 with a sensitivity of 213.3 nm/RI (refractive index) for the glucose solution. Our proposed device has potential for developing tunable biosensors for real-time health monitoring.
Highlights
Refractive index (RI) sensors, as bio-optical sensors that can detect tiny refractive indexes (RIs) changes, have attracted considerable research interest due to their extensive application in biological and chemical sensing, including pH value measurement, detection of the solution concentration, environmental monitoring, and molecular structure determination [1,2,3,4,5,6,7]
With RI sensors, the label-free detection of molecule concentrations depends on the detection of variation in the refractive index, which does not require the sample to be marked with fluorescent dyes due to bonding events
We addressed the modulation of the absorptivity by applying electric field gate bias
Summary
Refractive index (RI) sensors, as bio-optical sensors that can detect tiny RI changes, have attracted considerable research interest due to their extensive application in biological and chemical sensing, including pH value measurement, detection of the solution concentration, environmental monitoring, and molecular structure determination [1,2,3,4,5,6,7]. The ITO ultra-thin film taken as an ENZ material is integrated into the device between the grating and SiO2 dielectric layer, which is able to excite the ENZ mode by coupling the energy of the incident light guiding via nano-grating.
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