Opto-Electronic Refractometric Sensor Based on Surface Plasmon Resonances and the Bolometric Effect

Abstract

The bolometric effect allows us to electrically monitor spectral characteristics of plasmonic sensors; it provides a lower cost and simpler sample characterization compared with angular and spectral signal retrieval techniques. In our device, a monochromatic light source illuminates a spectrally selective plasmonic nanostructure. This arrangement is formed by a dielectric low-order diffraction grating that combines two materials with a high-contrast in the index of refraction. Light interacts with this structure and reaches a thin metallic layer, that is also exposed to the analyte. The narrow absorption generated by surface plasmon resonances hybridized with low-order grating modes, heats the metal layer where plasmons are excited. The temperature change caused by this absorption modifies the resistance of a metallic layer through the bolometric effect. Therefore, a refractometric change in the analyte varies the electric resistivity under resonant excitation. We monitor the change in resistance by an external electric circuit. This optoelectronic feature must be included in the definition of the sensitivity and figure of merit (FOM) parameters. Besides the competitive value of the FOM (around 400 RIU −1 , where RIU means refractive index unit), the proposed system is fully based on opto-electronic measurements. The device is modeled, simulated and analyzed considering fabrication and experimental constrains. The proposed refractometer behaves linearly within a range centered around the index of refraction of aqueous media, n≃1.33 , and can be applied to the sensing for research in bio-physics, biology, and environmental sciences.