Fiber-optic localized surface plasmon resonance sensor excited with ambient light through a fluorescent fiber

In this study, a localized surface plasmon resonance sensor using an optical fiber was fabricated and experimentally proven for the possibility of achieving a biosensor by detecting a combination of peptides using the reaction of transglutaminase. To enhance the performance of a fiber-optic localized surface plasmon resonance (FO LSPR) sensor, we propose to improve the surface condition of an etched optical fiber. A process condition that is able to control the diameter and surface density ratio of gold nanoparticles on the etched optical fiber was established and the sensor with optimized sensitivity was fabricated through optical analysis of varying diameters and surface density ratios of gold nanoparticles. The proposed FO LSPR sensor is expected to measure various biological reactions, and it can be applied to various biological applications.

Real-time detection of prostate-specific antigens using a highly reliable fiber-optic localized surface plasmon resonance sensor combined with micro fluidic channel

Sensitive fiber-optic localized surface plasmon resonance sensor for early pancreatic cancer detection via carbohydrate antigen 19-9 and supplementary biomarkers.

Fiber-optic localized surface plasmon resonance (LSPR) sensors realized by depositing metallic nanoparticles on various fiber structures have captured intensive research attention in recent years due to their high degree of integration, high sensitivity, flexibility, and remote sensing capability. Modified with macrocyclic molecules, metallic nanoparticles possess improved biocompatibility and highly efficient biomolecule immobilization and recognition via host-guest interaction. As a macrocyclic molecule, β-cyclodextrin (β-CD) has a cavity structure and can form stable complexes with various guest molecules. In this thesis, high-quality and monodisperse β-CD-capped gold nanoparticles (AuNPs) are synthesized in a one-step facile and eco-friendly process, where β-CDs serve as both reductants and capping agents without introducing harsh reagents. The β-CD-capped AuNPs are integrated with a microfiber through electrostatic interaction. Owing to the host-guest interaction between β-CD and cholesterol, the fabricated fiber-optic LSPR sensor delivers an ultralow detection limit of cholesterol molecules of 5 aM. The selective recognition of the proposed biosensor to cholesterol is further verified by interference study. The recovery experiments in human serum samples also show credible results. Next, different from conventional LSPR sensors that are typically based on the sensing mechanism that the resonance peak variation is induced by the ambient refractive index change on the immobilized metal nanoparticles. In this thesis, a dynamic “react-and-cut” sensing mechanism that actively tailors the quantity of AuNPs on a fiber surface is proposed, in which supramolecular chemistry and organic chemistry are combined in fiber-optic LSPR sensors. Also, the proposed sensor is demonstrated with glutathione detection. To be specific, a compound with a triethoxysilyl (TES) and an adamantane group connected by a disulfide bond is synthesized. The molecules are then functionalized on the surface of a microfiber by silicon-oxygen bonds, and β-CD-capped AuNPs are decorated on the microfiber by the host-guest interaction between β-CD and adamantane. The dynamic sensing is based on the fact that the sulfhydryl groups on glutathione first react with and then break the disulfide bonds. As a result, AuNPs are detached from the fiber surface, introducing the change of plasmonic behavior. This integrated fiber-optic LSPR sensor delivers a unique mechanism by cutting off AuNPs rather than the adsorption of analytes, providing more design space to achieve vast sensing platforms. In addition to the aforementioned silica fibers adopted in LSPR sensors, elastic and stretchable optical fibers have received extensive attention due to their high flexibility, dynamic bending elasticity and mechanical toughness. Recently, self-healing materials that can recover their physical properties after being subjected to external damage have been used to fabricate elastic and stretchable optical fibers. In this thesis, a transparent thermoplastic polyurethane (TPU) elastomer with high tensile strength and toughness is synthesized through step-growth polymerization. The synthetic TPU achieves superior self-healing capability by facile aromatic disulfide metathesis. After being shaped into a preform with an appropriate shape, the self-healing TPU optical fiber is manufactured via thermal drawing technique. This is the first time self-healing fibers have been prepared by thermal drawing technique with large-scale production capacity. Subsequently, the self-healing speed of TPU optical fiber is investigated through the transmission spectrum variation during the whole healing process. This provides a novel method to characterize self-healing materials, and it is expected to provide a unified standard for quantitatively studying the speed and efficiency of self-healing behaviors. Last, TPU optical fibers with different peak absorption are obtained by doping with organic dyes. Harness the self-healing and stretchable properties of TPU, dye-doped fibers are spliced together to fabricate a distributed strain sensor.

Localized surface plasmon resonance (LSPR) occurs when nanoparticles are bound to the surface of a sensor which is sensitive to the refractive index of the surrounding medium. The sensitivity of the sensor is highly dependent on the type of nanoparticles and their size, density and shape. Using an optical fiber as a sensor has various advantages, such as guided signal delivery and low energy loss. In this study, a Fiber-optic localized surface plasmon resonance (FO-LSPR) sensor was developed and the sizes of the gold nanoparticles (Au NPs) used therein were controlled by reduction with chloroauric acid. The extinction cross-section was calculated by the Mie theory to examine the dependence of the resonance intensity and sensitivity of the fabricated FO-LSPR sensor on the size and density of the Au NPs situated on its end-face. In order to use it as a biosensor, the fabricated FO-LSPR sensor was used to detect the biotin-streptavidin interaction.

A fast and facile method of fabricating fiber-optic localized surface plasmon resonance sensors based on spherical gold nanoparticles was introduced in this study. The gold nanoparticles with an average diameter of 55 nm were synthesized via the Turkevich method and were then immobilized onto the surface of an uncladded sensor probe using a polydopamine layer. To obtain a sensor probe with high sensitivity to changes in the refractive index, a set of key optimization parameters, including the sensing length, coating time of the polydopamine layer, and coating time of the gold nanoparticles, were investigated. The sensitivity of the optimized sensor probe was 522.80 nm per refractive index unit, and the probe showed distinctive wavelength shifts when the refractive index was changed from 1.328 6 to 1.398,7. When stored in deionized water at 4 °C, the sensor probe proved to be stable over a period of two weeks. The sensor also exhibited advantages, such as low cost, fast fabrication, and simple optical setup, which indicated its potential application in remote sensing and real-time detection.

A tip-based fiber-optic localized surface plasmon resonance (LSPR) sensor is reported for sensing of acetone. It is designed by coating the tip of multi-mode optical fiber with gold nanoparticles (size: ~ 40 nm) via a chemisorption process and further functionalization with a metal-organic framework (MOF) HKUST-1 via a layer-by-layer process. Two sensors with a different number of layers (80 and 120) corresponding to different thicknesses are reported. Both sensors show a redshift of resonance wavelength to acetone as a result of an increase in local refractive index induced by acetone adsorption into the HKUST-1 thin film. Sensors gradually saturate as acetone concentration increases and are fully reversible when the concentration decreases. The sensor with a thicker film exhibits slightly higher sensitivity to acetone than the thinner film with a wavelength shift of 5.27 nm for the concentration of 3.4 %.

Fiber optic localized surface plasmon resonance hydrogen sensor based on gold nanoparticles capped with palladium

Supercapacitors with high power density, ultralong lifespan and wide range operating temperature have drawn significant attention in recent years. However, monitoring the state of charge in supercapacitors in a cost-effective and flexible way is still challenging. Techniques such as transmission electron microscopy and X-ray diffraction can analyze the characteristics of supercapacitor well. But with large size and high price, they are not suitable for daily monitoring of the supercapacitors’ operation. In this paper, a low cost and easily fabricated fiber-optic localized surface plasmon resonance (LSPR) probe is proposed to monitor the state of charge of the electrode in a supercapacitor. The Au nanoparticles were loading on the fiber core as LSPR sensing region. In order to implant the fiber in the supercapacitor, a reflective type of fiber sensor was used. The results show that this tiny fiber-optic LSPR sensor can provide online monitoring of the state of charge during the charging and discharging process in situ. The intensity shift in LSPR sensor has a good linear relationship with the state of charge calculated by standard galvanostatic charging and discharging test. In addition, this LSPR sensor is insensitive to the temperature change, presenting a great potential in practical applications.

Fiber-optic refractive index (RI) sensors have the advantages of low cost, simple optical setup, remote sensing, and simple fabrication. A cone-based round structure, which is the combined structure of the cone structure and the round structure, is successively fabricated by using a cleaving method, a chemical glass etching method, and an electrical arc discharge method. In order to examine the possibility of the RI sensor, the fabricated cone-based round structure is used for the detection of various RIs by measuring the reflected intensities in the target sensing media. In addition, a fiber-optic localized surface plasmon resonance (LSPR) sensor based on the cone-based round structure is fabricated to enhance the sensitivity regarding RI changes. The fabricated fiber-optic LSPR sensor is used to detect the change of the RIs using the shift of peak wavelengths, as well as the change of reflected resonance intensities, by measuring LSPR spectra for gold nanoparticles on it.

This paper proposes Fiber-Optic Localized Surface Plasmon Resonance (FO LSPR) sensor combined with micro fluidic channel, which enables the continuous supply of fluid for bio-reaction. The proposed method can prevent the degradation of the sensing characteristics due to the change of measurement condition. The feasibility of the FO LSPR sensor with micro fluidic channel is proved by Computational Fluid Dynamics simulation (CFD). Also, the proposed method has been evidenced by measuring the output intensity of the FO LSPR sensor at various refractive index solutions. Finally, Prostate Specific Antigen (PSA) immunoassay was measured to verify the possibility of the fabricated sensor system as a biosensor.

In this work, we have presented a novel local surface plasmon resonance (LSPR) sensor based on the U-bent plastic optical fibre (U-POF). Firstly, a layer of discontinuous silver (Ag) thin film was deposited on the U-POF and then the Ag film was covered by a layer of cladding synthesized by polyvinyl alcohol (PVA), graphene and silver nanoparticles forming the PVA/G/AgNPs@Ag film. The normalized transmittance spectrum of the LSPR sensor have been collected in a range of the refractive index (RI) from 1.330 to 1.3657 in ethanol solution, and 700.3 nm/RIU sensitivity of the developed LSPR sensor has been demonstrated. By experiments, we demonstrated that the graphene could improve the sensitivity of the LSPR sensor and delay the oxidation process of the AgNPs effectively to keep the stability of the LSPR sensor. The LSPR sensor also exhibited good sensitivity and linearity in the detection of glucose solutions. This work shows that the developed LSPR sensor may have promising applications in biosensing.

A comparative analysis of the properties of two optical biosensor platforms: (1) the propagating surface plasmon resonance (SPR) sensor based on a planar, thin film gold surface and (2) the localized surface plasmon resonance (LSPR) sensor based on surface confined Ag nanoparticles fabricated by nanosphere lithography (NSL) are presented. The binding of Concanavalin A (ConA) to mannose-functionalized self-assembled monolayers (SAMs) was chosen to highlight the similarities and differences between the responses of the real-time angle shift SPR and wavelength shift LSPR biosensors. During the association phase in the real-time binding studies, both SPR and LSPR sensors exhibited qualitatively similar signal vs time curves. However, in the dissociation phase, the SPR sensor showed an approximately 5 times greater loss of signal than the LSPR sensor. A comprehensive set of nonspecific binding studies demonstrated that this signal difference was not the consequence of greater nonspecific binding to the LSPR sensor but rather a systematic function of the Ag nanoparticle's nanoscale structure. Ag nanoparticles with larger aspect ratios showed larger dissociation phase responses than those with smaller aspect ratios. A theoretical analysis based on finite element electrodynamics demonstrates that this results from the characteristic decay length of the electromagnetic fields surrounding Ag nanoparticles being of comparable dimensions to the ConA molecules. Finally, an elementary (2 x 1) multiplexed version of an LSPR carbohydrate sensing chip to probe the simultaneous binding of ConA to mannose and galactose-functionalized SAMs has been demonstrated.

LSPR optical fibre sensors based on hollow gold nanostructures

A fiber-optic localized surface plasmon (FO LSPR) sensor was fabricated by gold nanoparticles (Au NPs) immobilized on the end-face of an optical fiber. When Au NPs were formed on the end-face of an optical fiber by chemical reaction, Au NPs aggregation occurred and the Au NPs were immobilized in various forms such as monomers, dimers, trimers, etc. The component ratio of the Au NPs on the end-face of the fabricated FO LSPR sensor was slightly changed whenever the sensors were fabricated in the same condition. Including this phenomenon, the FO LSPR sensor was fabricated with high sensitivity by controlling the density of Au NPs. Also, the fabricated sensors were measured for the resonance intensity for the different optical systems and analyzed for the effect on sensitivity. Finally, for application as a biosensor, the sensor was used for detecting the antibody-antigen reaction of interferon-gamma.