An Ag-graphene layers-coated H-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor with a U-shaped grooves open structure for refractive index (RI) sensing is proposed and numerically simulated by the finite element method (FEM). The designed sensor could solve the problems of air-holes material coating and analyte filling in PCF. Two big air-holes in the x-axis produce a birefringence phenomenon leading to the confinement loss and sensitivity of x-polarized light being much stronger than y-polarized. Graphene is deposited on the layer of silver in the grooves; its high surface to volume ratio and rich π conjugation make it a suitable dielectric layer for sensing. The effect of structure parameters such as air-holes size, U-shaped grooves depth, thickness of the silver layer and number of graphene layers on the sensing performance of the proposed sensor are numerical simulated. A large analyte RI range from 1.33 to 1.41 is calculated and the highest wavelength sensitivity is 12,600 nm/RIU. In the linear RI sensing region of 1.33 to 1.36; the average wavelength sensitivity we obtained can reach 2770 nm/RIU with a resolution of 3.61 × 10−5 RIU. This work provides a reference for developing a high-sensitivity; multi-parameter measurement sensor potentially useful for water pollution monitoring and biosensing in the future.
With
the advanced development of miniaturized Raman spectroscopy,
surface-enhanced Raman spectroscopy (SERS) has extended its applications
into the field of point-of-care testing (POCT) and demonstrated its
great significance by virtue of its noninvasive property and capability
of fingerprint identification. In the SERS-based analysis and/or sensing
system, the preparation of a low-cost, high-performance SERS substrate
is critically important. In this manuscript, vacuum filtration is
utilized to fabricate the silver nanoparticles (AgNPs)-embedded nylon
filter membrane (ANFM) as flexible paper-based SERS chips. By characterizing
the typical analytes with a miniaturized smartphone-based Raman analyzer,
the proposed SERS chips have successfully demonstrated good sensitivity,
repeatability, and stability. The lowest concentration as detected
can approach 1 pmol for rhodamine 6G (RH6G) and 10 pmol for both crystal
violet (CV) and malachite green (MG), respectively. With the help
of the microporous structure of the membrane, the ANFM-based SERS
chips can implement the separation of small molecules from a complex
mixture and can achieve “purified” SERS signals of targeted
molecules. Besides, with the function of antifriction resistance and
flexibility, the ANFM can serve as SERS papers to preconcentrate the
contaminates by multiple swapping and further enhance the SERS signals
for point-of-care analysis. Therefore, we demonstrate multifunctions
of the flexible ANFM-based SERS chips, which provide a promising solution
for the POCT analysis with the SERS technique on account of their
flexibility and low fabrication cost.
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