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Highly sensitive, simple and multiplex detection capabilities are key criteria of point-of-care (POC) diagnosis in clinical samples. Here, a simple and highly sensitive multi-analyte detection technique is proposed by using photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor that employs both internal and external sensing approaches. The proposed sensor can detect two different analytes simultaneously by the internal and external plasmonic micro-channels. The light propagation through the sensor is controlled by the scaled-down air-holes to excite the free electrons of the plasmonic metal layers. The light-guiding and sensing properties of the sensor is numerically analyzed by using the Finite Element Method (FEM). The proposed sensor shows the maximum wavelength sensitivities (WS) of 12,000 nm/refractive index unit (RIU), and 10,000 nm/RIU, for the internal and external sensing approaches, respectively, and corresponding resolution of 8.33×10-6 RIU and 1.0×10-5 RIU. Moreover, the hybrid sensor is applicable to detect unknown analyte refractive index (RI) in the range of 1.33 to 1.40 which covers extensively investigating analytes such as viruses, different cancer cells, glucose, proteins and DNA/RNA. Due to high sensing performance with multi-analyte detection capability, the proposed sensor can play a significant role to detect bio targets at the POC platform.

Light trapping capability is the key phenomena of the photonic crystal fiber (PCF) which paves the broad range of applications. In this work, we control the light-guiding direction of the proposed PCFs via scaled-down approach to enhance the coupling between core-guided mode and surface plasmon polariton (SPP) mode resulting in the increase of sensitivity. We introduce the scaled-down air-holes in the first and second rings of the proposed PCF which provides the light guiding capability through the desire scaled-down region. A chemically stable plasmonic material gold is used outside the PCF structure to facilitate the detection of unknown analyte externally. Finite element method is used for numerical investigations, and the sensor performance is investigated by following the wavelength and amplitude interrogation methods. The proposed sensor shows the maximum wavelength sensitivities of 30 000 and 22 000 nm/RIU, and the maximum amplitude sensitivities of 1212 RIU−1 and 1506 RIU−1 for $x$ - and $y$ -polarized modes, respectively in the analyte refractive index (RI) range of 1.33 to 1.39. It also shows high sensor wavelength resolution of $3.33\times 10^{-6}$ RIU and $4.54\times 10^{-6}$ RIU, and a figure of merit about 508 and 500 for $x$ - and $y$ -polarized modes, respectively. It should be noted that the proposed PCF SPR sensor shows the significant sensing response for both polarization modes, as a result it will provide more freedom in choosing light source during practical implementation. Furthermore, the finding results indicates the proposed sensor will be effective for the detection of organic chemicals, biomolecules, and medical diagnostics.