In this work, authors have developed a portable, sensitive, and quick-response fiber optic sensor that is capable of detection of Aflatoxins B1 (AFB1) quantitatively and qualitatively. Using multi-mode fiber (MMF) and multi-core fiber (MCF), the MMF-MCF-MCF-MMF fiber structure based on symmetric transverse offset splicing and waist-expanded taper is fabricated. The evanescent waves are enhanced to form a strong evanescent field by etching the fiber surface with hydrofluoric acid. To successfully excite the localized surface plasmon resonance phenomenon, gold nanoparticles are deposited on the optical fiber probe's surface. Further, to modify the fiber optic probes, Niobium carbide (Nb2CTx) MXene and AFB1 antibodies are functionalized. Nb2CTx MXene is employed to strengthen the biocompatibility of the sensor and increase the specific surface area of the fiber probe, while AFB1 antibody is used to identify AFB1 micro-biomolecules in a specific manner. The reproducibility, reusability, stability, and selectivity of the proposed fiber probe are tested and validated using various concentration of AFB1 solutions. Finally, the linear range, sensitivity, and limit of detection of the sensing probe are determined as 0 - 1000 nM, 11.7 nm/µM, and 26.41 nM, respectively. The sensor offers an indispensable technique, low-cost solution and portability for AFB1-specific detection in agricultural products and their byproducts with its novel optical fiber structure and superior detecting capability. It is also useful for marine species like fish and consequently affecting health of human body.

Plasmonic sensor based on offset-splicing and waist-expanded taper using multicore fiber for detection of Aflatoxins B1 in critical sectors.

/pdf/recent-advancements-of-lspr-fiber-optic-biosensing-2b3fk79g.pdf

Recent Advancements of LSPR Fiber-Optic Biosensing: Combination Methods, Structure, and Prospects

Presently, plasmonic sensors are widely employed for the detection of numerous biomolecules found in the human body, owing to their high sensitivity and selectivity even in complex media (e.g., serum, urine, saliva). The most advanced plasmonic sensing technique for real-time screening and monitoring of analyte interactions is surface plasmon resonance (SPR)/localized surface plasmon resonance (LSPR). In recent years, the advancement of signal amplification tags such as gold/silver thin films (nanoparticles) and diverse sensing substrates such as 2D materials (e.g., graphene/MXene) has accelerated the development of SPR/LSPR sensors. This review of the literature focuses on 2D materials-based plasmonic sensors for the detection of various biomolecules, including creatinine, cardiac troponin I, alanine aminotransferase, acetylcholine, cholesterol, glucose, uric acid, and p-cresol. The review concludes with an overview of the advantages and disadvantages of 2D diagnostic materials. 

(Invited) Advances in 2D nanomaterials-assisted plasmonics optical fiber sensors for biomolecules detection

Biochemical Sensor Based on Functional Material Assisted Optical Fiber Surface Plasmon Resonance: A Review

/pdf/advances-in-tapered-optical-fiber-sensor-structures-from-27jyqa85.pdf

Advances in Tapered Optical Fiber Sensor Structures: From Conventional to Novel and Emerging

Localized surface plasmon resonance (LSPR) optical fiber biosensing is an advanced and powerful label-free technique which gets great attention for its high sensitivity to refractive index change in surroundings. However, the pursuit of a higher sensitivity is still challenging and should be further investigated. In this paper, based on a monolayer graphene/gold nanoparticles (Grm/Au NPs) three-dimensional (3D) hybrid structure, we fabricated a D-shaped plastic optical fiber (D-POF) LSPR sensor using a facile two-step method. The coupling enhancement of the resonance of this multilayer structure was extremely excited by the surface plasmon property of the stacked Au NPs/Grm layer. We found that the number of plasmonic structure layers was of high importance to the performance of the sensor. Moreover, the optimal electromagnetic field enhancement effect was found in three-layer plasmonic structure. Besides, the n*(Grm/Au NPs)/D-POF sensor exhibited outstanding performance in sensitivity (2160 nm/RIU), linearity (linear fitting coefficient R2 = 0.996) and reproducibility. Moreover, the sensor successfully detected the concentration of glucose, achieving a sensitivity of 1317.61 nm/RIU, which suggested a promising prospect for the application in medicine and biotechnology.

LSPR optical fiber sensor based on 3D gold nanoparticles with monolayer graphene as a spacer.

In surface-enhanced Raman scattering (SERS), metal-semiconductor heterostructures have attracted a lot of interest because of their remarkable features. However, the use of organic substances in the fabrication of metal nanoparticles can result in contamination of the SERS substrate, which can negatively impact sensor performance. Here, we introduced new recyclable SERS substrates which include Ag-decorated ZnSe nanowires and hyperbolic metamaterial. The Ag-decorated ZnSe nanowires work as an external coupling structure for hyperbolic metamaterials, due to this structure exhibiting significant plasmonic effects as well as unique optical features. There exists overlapping and physical interaction between metal and semiconductor nanowires, as a result, both resonance energy and hot electron were transferred. Rhodamine 6G (R6G), malachite green (MG), and adenosine were used to assess the SERS performance of synthesized Ag-decorated ZnSe, which showed outstanding stability and a sensitivity limit of 10-12 M. The nanostructure's self-cleaning feature was demonstrated through photocatalytic degradation of R6G and MG molecules under visible light, enabling it to be reused multiple times and showing that it was not limited to a single organic molecule. The bifunctional structure not only offers a unique way of boosting SERS efficiency but is also considerable for photocatalytic behavior. 

Recyclable surface-enhanced Raman spectroscopy (SERS) platform fabricated with Ag-decorated ZnSe nanowires and metamaterial

In this paper, we designed a surface-enhanced Raman scattering (SERS) substrate for graphene/Ag nanoparticles (Ag NPs) bonded multilayer film (MLF) using the hybrid nanostructures composed of graphene and plasmonic metal components with significant plasmonic electrical effects and unique optical characteristics. This paper achieved the advantages of efficient utilization of electromagnetic field and reduction of fluorescence background based on the electromagnetic enhancement activity of Ag NPs and unique physical/chemical properties of graphene with zero gap structures. Au/Al2O3 was stacked periodically to construct MLF. As indicated by the electric field intensity at the Au/Al2O3 interface of the respective layer, bulk plasmon polariton (BPP) in the MLF was excited and coupled with localized surface plasmon (LSP) in the Ag NPs, which enhanced the electromagnetic field on the top-layer of SERS substrate. To measure the performance of the SERS substrate, rhodamine 6G (R6G) and malachite green (MG) were used as the probe molecules, with the detection limits of 10-11 M and 10-8 M, respectively. The SERS substrate had high sensitivity and uniformity, which indicated that it has a broad application prospect in the field of molecular detection.

Composite substrate of graphene/Ag nanoparticles coupled with a multilayer film for surface-enhanced Raman scattering biosensing.

Although the fabrication of controllable three-dimensional (3D) microstructures on substrates has been proposed as an effective solution for SERS, there remains a gap in the detection and manufacturability of 3D substrates with high performance. In this study, photolithography is adopted to obtain a pyramid-like array on a patterned sapphire substrate (PSS), with Al2O3 as the dielectric layer. In addition, silver nanoparticles (AgNPs) are used to decorate Au films to obtain mass-producible 3D SRES substrates. In the case of low fluorescence, the substrate realizes the coupling of localized surface plasmon polaritons (LSPs) and surface plasmon polaritons (SPPs), which is consistent with the simulation results obtained using the finite element method. The performance of the SERS substrate is evaluated using rhodamine 6G (R6G) and toluidine blue (TB) as probe molecules with detection limits of 10−11 M and 10−9 M, respectively. The substrate exhibits high hydrophobicity and excellent light-capturing capability. Moreover, it shows self-cleaning ability and long-term stability in practical applications. Allowing for the consistency of the composite substrate in the preparation process and the high reproducibility of the test results, it is considered to be promising for mass production.

/pdf/lsp-spp-coupling-structure-based-on-three-dimensional-2w8oni7q.pdf

LSP-SPP Coupling Structure Based on Three-Dimensional Patterned Sapphire Substrate for Surface Enhanced Raman Scattering Sensing

Multilayer hyperbolic metamaterial (HMM)-based SERS substrates have received special consideration because they accommodate various propagation modes such as surface plasmonic polaritons (SPP). However, the SPP modes are difficult to generate in HMM due to their weak electric field enhancement. In this article, we designed novel SERS substrates consisting of graphene-covered AgNPs and HMM. The graphene-covered AgNPs work as an external coupling structure for hyperbolic metamaterials due to this structure exhibiting significant plasmonic effects as well as unique optical features. The localized surface plasmonic resonance (LSPR) of the graphene-covered AgNPs excited the SPP and thus formed a strong hot spot zone in the nanogap area of the graphene. The Raman experiment was performed using rhodamine 6G (R6G) and crystal violet (CV), which showed high stability and a maximum enhancement factor of 2.12 × 108. The COMSOL simulation further clarified that enhanced SERS performance was due to the presence of monolayer graphene and provided an atomically flat surface for organic molecules in a more controllable manner. Interestingly, the proposed SERS structure carries out quantitative detection of thiram in soil and can satisfy the basic environmental need for pesticide residue in the soil.

SERS Sensing Using Graphene-Covered Silver Nanoparticles and Metamaterials for the Detection of Thiram in Soil.

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