Fiber surface modification technology for fiber-optic localized surface plasmon resonance biosensors

Microfluidic immunosensor based on a graphene oxide functionalized double helix microfiber coupler for anti-Müllerian hormone detection

A label-free microfluidic immunosensor based on the double helix microfiber coupler (DHMC) coated with graphene oxide (GO) was proposed for the specific detection of anti-Müllerian hormone (AMH). Two single-mode optical fibers were twisted in a parallel direction, the coning machine was used to fuse and taper them, and the high-sensitivity DHMC was obtained. To make a stable sensing environment, it was immobilized in a microfluidic chip. And then, the DHMC was modified by GO and bio-functionalized by the AMH monoclonal antibodies (anti-AMH MAbs) for the specific detection of AMH. The experimental results showed that the detection range of the immunosensor for AMH antigen solutions was 200 fg/mL∼50 µg/mL, the detection of limit (LOD) was ∼235.15 fg/mL, and the detection sensitivity and the dissociation coefficient were ∼3.518 nm/(log(mg/mL)) and ∼1.85 × 10 ^{- 12} M, respectively. The alpha fetoprotein (AFP), des-carboxy prothrombin (DCP), growth stimulation expressed gene 2 (ST2) and AMH serum were used to confirm the excellent specific and clinical properties of the immunosensor, showing that the proposed immunosensor was easy-made and can be potentially applied in the biosensing field.

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

Fiber-optic biosensors based on localized surface plasmon resonance (LSPR) have the advantages of great biocompatibility, label-free, strong stability, and real-time monitoring of various analytes. LSPR fiber-optic biosensors have attracted extensive research attention in the fields of environmental science, clinical medicine, disease diagnosis, and food safety. The latest development of LSPR fiber-optic biosensors in recent years has focused on the detection of clinical disease markers and the detection of various toxic substances in the environment and the progress of new sensitization mechanisms in LSPR fiber-optic sensors. Therefore, this paper reviews the LSPR fiber-optic sensors from the aspects of working principle, structure, and application fields in biosensors. According to the structure, the sensor can be divided into three categories: traditional ordinary optical fiber, special shape optical fiber, and specialty optical fiber. The advantages and disadvantages of existing and future LSPR fiber-optic biosensors are discussed in detail. Additionally, the prospect of future development of fiber-optic biosensors based on LSPR is addressed.

Quantifiable Effect of Interparticle Plasmonic Coupling on Sensitivity and Tuning Range for Wavelength-Mode LSPR Fiber Sensor Fabricated by Simple Immobilization Method

Herein a gold nanosphere (AuNS)-coated wavelength-mode localized surface plasmon resonance (LSPR) fiber sensor was fabricated by a simple and time-saving electrostatic self-assembly method using poly(allylamine hydrochloride). Based on the localized enhanced coupling effect between AuNSs, the LSPR spectrums of the AuNS monolayer with good dispersity and high density exhibited a favourable capability for refractive index (RI) measurement. Based on the results obtained from the optimization for AuNS distribution, sensing length, and RI range, the best RI sensitivity of the fiber modified by 100 nm AuNS reached up to about 2975 nm/RIU, with the surrounding RI range from 1.3322 to 1.3664. Using an 80 nm AuNS-modified fiber sensor, the RI sensitivity of 3953 nm/RIU was achieved, with the RI range increased from 1.3744 to 1.3911. The effect of sensing length to RI sensitivity was proven to be negligible. Furthermore, the linear relationship between the RI sensitivity and plasma resonance frequency of the bulk metal, which was dependent on the interparticle plasmon coupling effect, was quantified. Additionally, the resonance peak was tuned from 539.18 nm to 820.48 nm by different sizes of AuNSs-coated fiber sensors at a RI of 1.3322, which means the spectrum was extended from VIS to NIR. It has enormous potential in hypersensitive biochemistry detection at VIS and NIR ranges.

Efficient Photodegradation of Eriochrome Black-T by a Trimetallic Magnetic Self-Synthesized Nanophotocatalyst Based on Zn/Au/Fe-Embedded Poly(vinyl alcohol)

This study presents a novel photocatalytic system for photocatalytic degradation of Eriochrome black-T (EBT) dye via green light-emitting diode (LED) light exposure. This photocatalyst is comprised of nanoscale components, i.e., poly(vinyl alcohol) (PVA), magnetic iron oxide nanoparticles (Fe₃O₄ NPs), gold NPs (Au NPs), and zinc oxide nanorods (ZnO NRs), rendering an active high surface area. The most highlighted property from the structural facet is the superparamagnetic behavior of Fe₃O₄ NPs, which provides a facile collection of magnetic photocatalyst NPs from the reaction flask and is successfully recycled eight times without considerable reduction in catalytic behavior. Briefly, the photocatalytic degradation at its highest efficiency reached 51.4% (10 ppm dye solution, 5.0 mL) and 64.75% (8 ppm dye solution, 5.0 mL) utilizing 10 mg of the designed photocatalyst (formulated as Fe₃O₄@PVA-Au/ZnO), a magnetic photocatalytic system under green LED light (7 W, 526 nm) exposure for 60 min. Besides, the photocatalytic degradation mechanism of the EBT dye by the as-prepared photocatalyst was proposed. Based on the obtained results, the presented photocatalytic method was recommended for scaling up and large-scale exploitation for the purification of the water resources.

A Review of Optical Fibre Ethanol Sensors: Current State and Future Prospects

A range of optical fibre-based sensors for the measurement of ethanol, primarily in aqueous solution, have been developed and are reviewed here. The sensing approaches can be classified into four groups according to the measurement techniques used, namely absorption (or absorbance), external interferometric, internal fibre grating and plasmonic sensing. The sensors within these groupings can be compared in terms of their characteristic performance indicators, which include sensitivity, resolution and measurement range. Here, particular attention is paid to the potential application areas of these sensors as ethanol production is globally viewed as an important industrial activity. Potential industrial applications are highlighted in the context of the emergence of the internet of things (IoT), which is driving widespread utilization of these sensors in the commercially significant industrial and medical sectors. The review concludes with a summary of the current status and future prospects of optical fibre ethanol sensors for industrial use.

A multiplexed phospholipid membrane platform for curvature sensitive protein screening

The curvature of lipid membranes plays a key role in many relevant biological processes such as membrane trafficking, vesicular budding and host-virus interactions. In vitro studies on the membrane curvature of simplified biomimetic models in the nanometer range are challenging, due to their complicated nanofabrication processes. In this work, we propose a simple and low-cost platform for curvature sensitive protein screening, prepared through scanning probe lithography (SPL) methods, where lipid bilayer patches of different compositions can be multiplexed onto substrate areas with tailored local curvature. The curvature is imposed by anchoring nanoparticles of the desired size to the substrate prior to lithography. As a proof of principle, we demonstrate that a positive curvature membrane sensitive protein derived from the BAR domain of Nadrin2 binds selectively to lipid patches patterned on substrate areas coated with 100 nm nanoparticles. The platform opens up a path for screening curvature-dependent protein-membrane interaction studies by providing a flexible and easy to prepare substrate with control over lipid composition and membrane curvature.

Portable and field-deployed surface plasmon resonance and plasmonic sensors

Plasmonic sensors are ideally suited for the design of small, integrated, and portable devices that can be employed in situ for the detection of analytes relevant to environmental sciences, clinical diagnostics, infectious diseases, food, and industrial applications. To successfully deploy plasmonic sensors, scaled-down analytical devices based on surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) must integrate optics, plasmonic materials, surface chemistry, fluidics, detectors and data processing in a functional instrument with a small footprint. The field has significantly progressed from the implementation of the various components in specifically designed prism-based instruments to the use of nanomaterials, optical fibers and smartphones to yield increasingly portable devices, which have been shown for a number of applications in the laboratory and deployed on site for environmental, biomedical/clinical, and food applications. A roadmap to deploy plasmonic sensors is provided by reviewing the current successes and by laying out the directions the field is currently taking to increase the use of field-deployed plasmonic sensors at the point-of-care, in the environment and in industries.

Label-free and specific detection of soluble programmed death ligand-1 using a localized surface plasmon resonance biosensor based on excessively tilted fiber gratings

Programmed death ligand-1 (PD-L1) plays an important role in tumor evasion from the host immune system. The level of soluble PD-L1 (sPD-L1) in serum is closely related to tumor aggressiveness and outcomes. This study aimed to propose a localized surface Plasmon resonance (LSPR) biosensor based on excessively tilted fiber grating (ExTFG) coated with large-sized (∼160 nm) gold nanoshells for label-free and specific detection of sPD-L1. The experimental results showed that the limit of detection (LOD) of the immunosensor for sPD-L1 in buffer solutions was ∼1 pg/mL due to the enhanced LSPR effect resulting from the interaction between sPD-L1 molecules and anti-sPD-L1 monoclonal antibodies. The detection of sPD-L1 in complex serum media, such as fetal bovine serum, confirmed that the label-free immunosensor was extremely specific to sPD-L1 and could identify it at a concentration as low as 5 pg/mL. Therefore, it can be potentially applied in clinic for the fast and early diagnosis of cancer.

Polymer-Templated Gold Nanoparticles on Optical Fibers for Enhanced-Sensitivity Localized Surface Plasmon Resonance Biosensors

Dense arrays of well-dispersed gold nanoparticles (AuNPs) on optical fibers are shown to bridge the gap in sensitivity and sensing performance between localized surface plasmon resonance (LSPR) and classical SPR sensing. A simple self-assembly method relying on a poly(styrene- b-4-vinylpyridine) (PS- b-P4VP) block copolymer brush layer was used to immobilize AuNPs of different diameters from 10 to 92 nm on optical fibers. In comparison with standard AuNP deposition methods using (3-aminopropyl)trimethoxysilane (APTMS) and polyelectrolytes, the sensitivity with the PS- b-P4VP templating method was found to be 3-fold better, a consequence of the smaller gap between particles and the presence of fewer AuNP aggregates. Hence, the sensitivity of the LSPR sensor for IgG was comparable to a classical SPR, also on optical fibers, and about 68% of that for a prism-based wavelength-interrogation SPR instrument. The reproducibility and the detection limit of the LSPR sensor were about the same as the SPR sensor. The enhanced performance of the LSPR sensors using the PS- b-P4VP block copolymer fabrication method paves the way for use of these LSPR biosensors in a smaller and more cost-effective platform.

A novel immunosensor based on excessively tilted fiber grating coated with gold nanospheres improves the detection limit of Newcastle disease virus

A novel immunosensor for detecting Newcastle disease virus (NDV) was developed using excessively tilted fiber grating (Ex-TFG) coated with gold nanospheres (AuNs). AuNs were coated on the Ex-TFG surface via Au-S bonds using 3-mercaptopropyltrimethoxysilane (MPTMS), and the activated staphylococcal protein A (SPA) was linked to AuNs by covalent bonds via cysteamine. AuNs greatly enhanced the impact of the analyte on the fiber cladding mode through the local surface Plasmon resonance (LSPR) effect, thus improving the detection limit and sensitivity of the immunosensor. Meanwhile, SPA enhanced the bioactivity of anti-NDV monoclonal antibodies (MAbs), thus promoting the effectiveness of specific binding events on the fiber surface. Immunoassays were performed by monitoring the resonance wavelength shift of the proposed sensor under NDV samples containing different particle amounts. Specificity was assessed, and clinical tests for NDV were performed by contrast experiments. Experimental results showed that the detection limit for NDV was about 5~10 times improved compared to that of reference Ex-TFG without AuN treatment. Moreover, the novel biosensor was reusable and could potentially be applied in clinic.

Optical Microfibre Based Photonic Components and Their Applications in Label-Free Biosensing

Optical microfibre photonic components offer a variety of enabling properties, including large evanescent fields, flexibility, configurability, high confinement, robustness and compactness. These unique features have been exploited in a range of applications such as telecommunication, sensing, optical manipulation and high Q resonators. Optical microfibre biosensors, as a class of fibre optic biosensors which rely on small geometries to expose the evanescent field to interact with samples, have been widely investigated. Due to their unique properties, such as fast response, functionalization, strong confinement, configurability, flexibility, compact size, low cost, robustness, ease of miniaturization, large evanescent field and label-free operation, optical microfibres based biosensors seem a promising alternative to traditional immunological methods for biomolecule measurements. Unlabeled DNA and protein targets can be detected by monitoring the changes of various optical transduction mechanisms, such as refractive index, absorption and surface plasmon resonance, since a target molecule is capable of binding to an immobilized optical microfibre. In this review, we critically summarize accomplishments of past optical microfibre label-free biosensors, identify areas for future research and provide a detailed account of the studies conducted to date for biomolecules detection using optical microfibres.

Plasma enhanced label-free immunoassay for alpha-fetoprotein based on a U-bend fiber-optic LSPR biosensor

A simple, label-free and cost-effective localized surface plasmon resonance (LSPR) immunosensing method was developed for detection of alpha-fetoprotein (AFP).

All-fiber hybrid photon-plasmon circuits: integrating nanowire plasmonics with fiber optics

We demonstrate all-fiber hybrid photon-plasmon circuits by integrating Ag nanowires with optical fibers. Relying on near-field coupling, we realize a photon-to-plasmon conversion efficiency up to 92% in a fiber-based nanowire plasmonic probe. Around optical communication band, we assemble an all-fiber resonator and a Mach-Zehnder interferometer (MZI) with Q-factor of 6 × 10(6) and extinction ratio up to 30 dB, respectively. Using the MZI, we demonstrate fiber-compatible plasmonic sensing with high sensitivity and low optical power.

Diverse applications of electronic-nose technologies in agriculture and forestry

Electronic-nose (e-nose) instruments, derived from numerous types of aroma-sensor technologies, have been developed for a diversity of applications in the broad fields of agriculture and forestry. Recent advances in e-nose technologies within the plant sciences, including improvements in gas-sensor designs, innovations in data analysis and pattern-recognition algorithms, and progress in material science and systems integration methods, have led to significant benefits to both industries. Electronic noses have been used in a variety of commercial agricultural-related industries, including the agricultural sectors of agronomy, biochemical processing, botany, cell culture, plant cultivar selections, environmental monitoring, horticulture, pesticide detection, plant physiology and pathology. Applications in forestry include uses in chemotaxonomy, log tracking, wood and paper processing, forest management, forest health protection, and waste management. These aroma-detection applications have improved plant-based product attributes, quality, uniformity, and consistency in ways that have increased the efficiency and effectiveness of production and manufacturing processes. This paper provides a comprehensive review and summary of a broad range of electronic-nose technologies and applications, developed specifically for the agriculture and forestry industries over the past thirty years, which have offered solutions that have greatly improved worldwide agricultural and agroforestry production systems.

Tapered optical fiber sensor based on localized surface plasmon resonance

A tapered fiber localized surface plasmon resonance (LSPR) sensor is demonstrated for refractive index sensing and label-free biochemical detection. The sensing strategy relies on the interrogation of the transmission intensity change due to the evanescent field absorption of immobilized gold nanoparticles on the tapered fiber surface. The refractive index resolution based on the interrogation of transmission intensity change is calculated to be 3.2×10⁻⁵ RIU. The feasibility of DNP-functionalized tapered fiber LSPR sensor in monitoring anti-DNP antibody with different concentrations spiked in buffer is examined. Results suggest that the compact sensor can perform qualitative and quantitative biochemical detection in real-time and thus has potential to be used in biomolecular sensing applications.

Sensors Based on Plasmonic-Photonic Coupling in Metallic Photonic Crystals

An optical sensor based on the coupling between the plasmonic and photonic resonance modes in metallic photonic crystals is investigated. Large-area metallic photonic crystals consisting of periodically arranged gold nanostructures with dimensions down to sub-100 nm are fabricated using solution-processible gold nanoparticles in combination with interference lithography or interference ablation, which introduces a variety of fabrication techniques for the construction of this kind of sensor device. Sensitivity of the plasmonic response of the gold nanostructures to the changes in the environmental refractive index is enhanced through the coupling between the narrow-band photonic resonance mode and the relatively broad-band plasmon resonance, which is recognized as a Fano-like effect and is utilized to explore sensors. Theoretical modeling shows the characterization and the optimization of the sensitivity of this kind of sensor device. Theoretical and experimental results are demonstrated for the approaches to improve the sensitivity of the sensor device.