Highly sensitive and stable probe refractometer based on configurable plasmonic resonance with nano-modified fiber core

Abstract

A dispersion model is developed to provide a generic tool for configuring plasmonic resonance spectral characteristics. The customized design of the resonance curve aiming at specific detection requirements can be achieved. According to the model, a probe-type nano-modified fiber optic configurable plasmonic resonance (NMF-CPR) sensor with tip hot spot enhancement is demonstrated for the measurement of the refractive index in the range of 1.3332-1.3432 corresponding to the low-concentration biomarker solution. The new-type sensing structure avoids excessive broadening and redshift of the resonance dip, which provides more possibilities for the surface modification of other functional nanomaterials. The tip hot spots in nanogaps between the Au layer and Au nanostars (AuNSs), the tip electric field enhancement of AuNSs, and the high carrier mobility of the WSe 2 layer synergistically and significantly enhance the sensitivity of the sensor. Experimental results show that the sensitivity and the figure of merit of the tip hot spot enhanced fiber NMF-CPR sensor can achieve up to 2995.70 nm/RIU and 25.04 RIU −1 , respectively, which are 1.68 times and 1.29 times higher than those of the conventional fiber plasmonic resonance sensor. The results achieve good agreements with numerical simulations, demonstrate a better level compared to similar reported studies, and verify the correctness of the dispersion model. The detection resolution of the sensor reaches up to 2.00×10 −5 RIU, which is obviously higher than that of the conventional side-polished fiber plasmonic resonance sensor. This indicates a high detection accuracy of the sensor. The dense Au layer effectively prevents the intermediate nanomaterials from shedding and chemical degradation, which enables the sensor with high stability. Furthermore, the terminal reflective sensing structure can be used as a practical probe and can allow a more convenient operation.

Optimally Configured Optical Fiber Near‐Field Enhanced Plasmonic Resonance Immunoprobe for the Detection of Alpha‐Fetoprotein

“…The reflective mirror was fabricated by sputtering an Ag layer of 200 nm and an Au layer of 5 nm on the end face of the fiber core in turn, as seen in Figure S17b in the Supporting Information. A composite layer of hydroxylated WSe 2 @AuNSs (WSe 2 : AuNSs = 5:1, volume ratio) with a thickness of ≈10 nm was coated on the surface of the sensing region by the electrostatic self-assembly, [14] as seen in Figure S17c in the Supporting Information. Due to the saturation of the electrostatic adsorption, the thickness of the composite layer cannot be flexibly adjusted in a large range.…”

“…According to FEA models, the FOM of the optical fiber plasmonic resonance can be preliminarily estimated by the dielectric constant ratio (DCR) of coating materials (especially metallic materials and 2D nanomaterials), rather than the use of the complex spectral calculation. [14] The optimized configuration of the DCR can be achieved by the reasonable selection of coating materials and the modification of coating materials at the atomic level. [16] The FOM of the Ag layer-based fiber plasmonic resonance is the highest due to the DCR of the Ag layer being farthest from 1, as shown in Figure S7d in the Supporting Information.…”

“…In addition, the carrier concentration and the carrier mobility of the WSe 2 layer are 1-2 orders of magnitude higher than those of other transition metal dichalcogenide (TMDC) layers. [14] Compared to other types of metal nanoparticles, AuNSs possess good stability and can produce more significant electric-field enhancement due to the tip hot spot effect. [14,18] Therefore, the composite layer of WSe 2 and AuNSs (WSe 2 @AuNSs layer) is more suitable as the dielectric layer in the development of the immunoprobe.…”

“…This thereby improves the refractive index (RI) sensitivity of the immunoprobe. [14] The designed sensing structure of fiber core/intermediate dielectric layer/metal layer confines the resonance dip within a short wavelength band and narrows the full width at half-maximum (FWHM). This allows a larger amount of dopamine with better biocompatibility to be modified and this thereby further improves the biosensing performance of the immunoprobe.…”

“…b) The mode-field distribution of the tip hot spot obtained by the FEA analysis. The electric field intensity on the upper surface of the Au layer can reach up to 77.38 V m −1 [14].…”