Plasmonic Micro-Channel Assisted Photonic Crystal Fiber Based Highly Sensitive Sensor for Multi-Analyte Detection

Abstract

A dual-channel propagation controlled photonic crystal fiber (PCF)-based plasmonic sensor was presented to detect multiple analytes simultaneously. Plasmonic micro-channels were placed on the outer surface of the PCF, which facilitates an easy sensing mechanism. The sensor was numerically investigated by the finite element method (FEM) with the perfectly matched layer (PML) boundary conditions. The proposed sensor performances were analyzed based on optimized sensor parameters, such as confinement loss, resonance coupling, resolution, sensitivity, and figure of merit (FOM). The proposed sensor showed a maximum wavelength sensitivity (WS) of 25,000 nm/refractive index unit (RIU) with a maximum sensor resolution (SR) of 4.0 × 10^-6 RIU for channel 2 (Ch-2), and WS of 3000 nm/RIU with SR of 3.33 × 10^-5 RIU for channel 1 (Ch-1). To the best of our knowledge, the proposed sensor exhibits the highest WS compared with the previously reported multi-analyte based PCF surface plasmon resonance (SPR) sensors. The proposed sensor could detect the unknown analytes within the refractive index (RI) range of 1.32 to 1.39 in the visible to near infrared region (550 to 1300 nm). In addition, the proposed sensor offers the maximum Figure of Merit (FOM) of 150 and 500 RIU^-1 with the limit of detection (LOD) of 1.11 × 10^-8 RIU²/nm and 1.6 × 10^-10 RIU²/nm for Ch-1 and Ch-2, respectively. Due to its highly sensitive nature, the proposed multi-analyte PCF SPR sensor could be a prominent candidate in the field of biosensing to detect biomolecule interactions and chemical sensing.

Keywords: multi-analyte detection; optical fiber sensors; photonic crystal fiber; surface plasmon resonance.

Figure 1

(a) 2D cross-sectional view of the proposed sensor, and (b) stack preform.

Figure 2

The typical sensing mechanism of the proposed sensor.

Figure 3

EM field distribution of the core guided mode and the SPP mode for (a,b) Ch-1 at RI 1.32 and (c,d) Ch-2 at RI 1.36.

Figure 4

(a) The dispersion relationship of the proposed sensor for n_a = 1.32 & 1.36 and (b) analyte channels dependency behavior at analyte RI of 1.32 and 1.36.

Figure 5

(a) CL spectra, (b) Amplitude sensitivity, and (c) normalized 2D map of CL intensity of the proposed sensor when the analyte RI of Ch-1 and Ch-2 varies simultaneously.

Figure 6

(a,c) CL spectra and (b,d) amplitude sensitivity of the proposed sensor when the analyte RIs of Ch-1 varies with constant Ch-2 and Ch-2 varies with fixed Ch-1, respectively.

Figure 7

(a) CL spectrum while the same analyte RI is infiltrated in both channels, (b) AS for the variation of analyte RI from 1.33 to 1.38, and (c) normalized 2D map of CL intensity when the same analyte RIs are used in both channels.

Figure 8

(a) Sensor length and (b) resonance wavelength shift and loss curve fitting of the proposed sensor as a function of analyte RI from 1.32 to 1.39.

Figure 9

Impact of gold layer thickness variation (t = 35 nm, 40 nm, and 45 nm) on (a) CL spectra and (b) light sensitivity alteration with the change of t when RI 1.35 is used in both channels.

Figure 10

CL spectra with the structural parameter variation of (a) pitch, Λ, (b–d) air-hole diameters dc, d, ds up to ±10% from the optimum value when same analyte RI 1.35 used in both channels.