High-sensitive optoelectronic SPR biosensor based on Fano resonance in the integrated MIM junction and optical layers

Development of the miniaturized surface plasmon resonance (SPR) sensors with high sensitivity is required for biomedical sensing applications. In this regard, elimination of the optical detector and enhancement of sensitivity is an important step towards miniaturization of the traditional Kretschmann SPR sensors. In this study, we propose a compact high-sensitivity SPR biosensor with an electrical response based on Fano resonance in the metal–insulator–metal (MIM) junction integrated with the planar waveguide (PWG). The SPR excitation at the top metal of the MIM junction enhances the photoabsorption and hot electrons generation, which can produce photocurrent. We demonstrate that the coupling between the MIM junction SPR and PWG modes can result in modulation of output photocurrent by variation of analyte refractive index. The response of this sensor was calculated in detail and the results showed that the Fano-like profile appears in the photocurrent curve as well as the reflectivity curve. To evaluate the sensing performance of the proposed structure, the figure of merit (FOM) for the bulk sensitivity is predicated as 3.4×103 RIU−1, which is translated to change in the photocurrent of 33.5 μA by introducing the variation of 0.0001 in the refractive index of the analyte. Our results are highly useful for designing an integrated multi-function detector for future diagnoses and sensing applications.