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In this paper, we propose a Fano-resonance-based refractive index sensor with ultra-high sensitivity. The sensor comprises a metal–insulator-metal (MIM) waveguide with two rectangular stubs coupled with a circular resonator embedded with a defective metal nanocube (CRMN). The transmission characteristics of the structure are simulated using the 2D finite element method. This analysis reveals that the Fano resonance mode splitting is affected by the geometry of the sensor. In addition, the modulation depth and position of the Fano resonance can be tuned by adjusting the width and length of the stub on the CRMN. Optimizing the structural parameters results in a peak sensing sensitivity of 10200 nm∙RIU−1 under the ultra-compact sensor size. This sensitivity allows the sensor to be used in the detection of hemoglobin concentration (HC). By processing simulation data, the linear relationship between the refractive index of three different blood groups (A, B, and O) and HC is obtained. Based on the sensing principle of the designed device, HC can be calculated from measuring the shift of the Fano resonance wavelength. These results provide critical developments for the application of nanoscale refractive index sensors in the biomedical field.

The present study reports on the investigation carried out on a newly designed photonic crystal fiber (PCF) based plasmonic biosensor for label-free hemoglobin concentration detection. In the first part, a new approach is proposed to avail external sensing mechanism by introducing the solid core at fiber periphery and nanoscale gold film coating outside the fiber. By analyzing modal characteristics using finite element method (FEM), the wavelength sensitivity is found to be varied nonlinearly up to 34,800 nm/RIU within the analyte detection range of 1.34 − 1.41 RIU (refractive index unit). In later study, the proposed fiber is investigated as hemoglobin concentration sensor (HbCS) to detect unknown hemoglobin concentration. From the detail study, to calculate sensitivity of HbCS, a nonlinear equation as a function of hemoglobin concentration has been proposed to detect unknown concentration and a maximum sensitivity of 31.2 nm/g/dL is achieved. Moreover, the minimum measurable deviation of the sensor is found to be lies of the order of 10−6 with a high figure of merit (FOM) up to 229 RIU−1 representing an overall good sensing performance. The proposed plasmonic sensor provides high sensitivity, good specificity, environmental stability along with high resolution compare to other existing technologies. Therefore, this study opens an easy and reliable window for hemoglobin concentration detection in biomedical applications. • New approach is proposed to avail external sensing mechanism by introducing the solid core at fiber periphery. • Sensitivity is varied nonlinearly up to 34,800 nm/RIU within the analyte detection range 1.34 − 1.41 RIU. • Proposed fiber is investigated as hemoglobin concentration sensor (HbCS). • A numerical solution is reported to detect unknown hemoglobin concentration. • As HbCS, maximum sensitivity of 31.2 nm/g/dL is achieved. [ABSTRACT FROM AUTHOR]

• A Fano-resonance-based refractive index sensor with ultra-high sensitivity is proposed. • The proposed sensor design combines excellent sensitivity with ultra-compact size. • The maximum sensing sensitivity of the sensor is 10200 nm·RIU−1. In this paper, we propose a Fano-resonance-based refractive index sensor with ultra-high sensitivity. The sensor comprises a metal–insulator-metal (MIM) waveguide with two rectangular stubs coupled with a circular resonator embedded with a defective metal nanocube (CRMN). The transmission characteristics of the structure are simulated using the 2D finite element method. This analysis reveals that the Fano resonance mode splitting is affected by the geometry of the sensor. In addition, the modulation depth and position of the Fano resonance can be tuned by adjusting the width and length of the stub on the CRMN. Optimizing the structural parameters results in a peak sensing sensitivity of 10200 nm∙RIU−1 under the ultra-compact sensor size. This sensitivity allows the sensor to be used in the detection of hemoglobin concentration (HC). By processing simulation data, the linear relationship between the refractive index of three different blood groups (A, B, and O) and HC is obtained. Based on the sensing principle of the designed device, HC can be calculated from measuring the shift of the Fano resonance wavelength. These results provide critical developments for the application of nanoscale refractive index sensors in the biomedical field. [ABSTRACT FROM AUTHOR]