Fiber-optic Localized Surface Plasmon Resonance Research Articles

Construction of the fiber optic LSPR sensor for highly sensitive detection of miR-103 by a dual signal enhancement strategy based on the hot-spot effect and HexSG4 catalysis

MicroRNAs are important tumor biomarkers. How to effectively detect them by sensors is a challenge because of their extremely low concentrations. We proposed a dual signal enhancement strategy to develop the fiber optic (FO) localized surface plasmon resonance (LSPR) sensor for the highly sensitive detection of miR-103. It included two stages, one was to obtain the hot-spot by constructing the multimer structure, AuNP-spacer- AuNPs, and another was the combination of capturing miR-103 by the probe and catalytic amplification by Hexagonal star G-quadruplex catalyzing 4-chloro-1-naphthol to generate benzo-4-chlorohexadienone, which deposited on the AuNPs, resulting in the generation of LSPR peak redshift. The parameters of the preparation and detection application were systematically optimized. The redshift values had a good linear relationship with the logarithms of miR-103 concentrations, with high R2 0.9973, wide detection range 102 - 107 fM, and low LOD 6.4 fM. The method had high specificity, repeatability, and reproducibility, and was also successfully validated with real samples. Therefore, the dual signal strategy for constructing FO LSPR sensors can achieve the high sensitivity detection of extremely low concentration of MicroRNAs, which will have great application prospects in medicine and life science.

Fiber Optic Localized Surface Plasmon Resonance Sensor Based on Carboxymethylated Dextran Modified Gold Nanoparticles Surface for High Mobility Group Box 1 (HMGB1) Analysis

Rapid, sensitive, and reliable detection of high mobility group box 1 (HMGB1) is essential for medical and diagnostic applications due to its important role as a biomarker of chronic inflammation. Here, we report a facile method for the detection of HMGB1 using carboxymethyl dextran (CM-dextran) as a bridge molecule modified on the surface of gold nanoparticles combined with a fiber optic localized surface plasmon resonance (FOLSPR) biosensor. Under optimal conditions, the results showed that the FOLSPR sensor detected HMGB1 with a wide linear range (10-10 to 10-6 g/mL), fast response (less than 10 min), and a low detection limit of 43.4 pg/mL (1.7 pM) and high correlation coefficient values (>0.9928). Furthermore, the accurate quantification and reliable validation of kinetic binding events measured by the currently working biosensors are comparable to surface plasmon resonance sensing systems, providing new insights into direct biomarker detection for clinical applications.

Ω-shaped fiber optic LSPR biosensor based on mismatched hybridization chain reaction and gold nanoparticles for detection of circulating cell-free DNA

Circulating cell-free DNA (cfDNA) is a promising biomarker of liquid biopsy, but it still faces some difficulties in achieving sensitive and convenient detection. Herein, an Ω-shaped fiber optic localized surface plasmon resonance (FO-LSPR) biosensor based on hybridization chain reaction (HCR) coupled with gold nanoparticles (AuNPs) was developed, and applied in simple and sensitive detection of cfDNA. Specifically, one-base mismatch was designed in HCR hairpins (H1 and H2) to obtain high reaction efficiency, and AuNPs was introduced onto H1 through poly-adenine to construct HCR coupled with AuNPs strategy. Meanwhile, target cfDNA was designed into two domains: one could trigger HCR to generate dsDNA concatemer carrying numerous AuNPs, and the other could hybridize with capture DNA on the surface of Ω-shaped fiber optic (FO) probes. Thus, the presence of target cfDNA would initiate HCR, and bring the formed dsDNA concatemer and AuNPs to approach the probe surface, resulting in dramatically amplified LSPR signal. Besides, HCR required simple isothermal and enzyme-free condition, and Ω-shaped FO probe with high refractive index sensitivity just needed to be immersed into HCR solution directly for signal monitoring. Benefiting from the synergetic amplification of mismatched HCR and AuNPs, the proposed biosensor exhibited high sensitivity with a limit of detection of 14.0 pM, and therefore could provide a potential strategy for biomedical analysis and disease diagnosis.

Plasmonic fiber-optic sensing system for in situ monitoring the capacitance and temperature of supercapacitors.

Compared with ex situ measurement, the in situ measurement is more suitable for inspecting complex electrochemical reactions and improving the intelligent energy storage management. However, most of the in situ investigation instruments are bulky and expensive. Here we demonstrate a miniaturized, portable, and low-cost fiber-optic sensing system for in situ monitoring the capacitance and temperature. It can help evaluate the self-discharge rate in supercapacitors (SCs). The fiber-optic sensing system with two probes are implanted inside the SCs to monitor the capacitance and temperature, respectively. The dual fiber-optic probes can work independently and avoid cross-interference through structure design. The fiber-optic localized surface plasmon resonance (LSPR) probe near the electrode surface can detect the capacitance in real-time by monitoring ion aggregation on the opposite electrode. The fiber-optic surface plasmon resonance (SPR) probe encapsulated in the thermosensitive liquid can independently detect the temperature change. The measurement uncertainties of the two sensing probes are 5.6 mF and 0.08 ℃, respectively. The proposed tiny and flexible fiber-optic sensing system provides a promising method for in situ monitoring the critical parameters. It is also a powerful tool for investigating electrochemical reactions in various energy storage devices.

High-performance biosensor using a sandwich assay via antibody-conjugated gold nanoparticles and fiber-optic localized surface plasmon resonance

For real-time and high-sensitivity analysis of low-concentration targets, a sandwich immunoassay using second antibody-second gold nanoparticle (2nd Ab-2nd AuNP) conjugates was combined with fiber-optic localized surface plasmon resonance (FO LSPR). An FO LSPR format was constructed by immobilizing AuNPs on a fiber-optic cross-section for compactness, portability, and ease of handling. In addition, it was combined with a microfluidic system to ensure reproducibility and reliability of measurements. A detection limit of 97.6 fg/mL (148 aM) was obtained for thyroglobulin (Tg) without a sandwich assay. The detection limit was enhanced by approximately 15 times (6.6 fg/mL, 10 aM) when a sandwich strategy was performed with a 2nd Ab-2nd AuNP signal amplifier to further improve the responsivity. Additionally, the good selectivity of the proposed method was confirmed against the unpaired antigen. To evaluate its practical applicability in the field, an FO LSPR biosensor boosted with a sandwich assay using antibody-functionalized AuNPs was applied to detect Tg contained in patient serum, and the results were compared and verified with those of a commercial radioimmunoassay kit. Based on the above results, the signal-enhancing immunoassay with FO LSPR will contribute to the development of optical biosensors for early diagnosis and preventive applications.

D-shape optical fiber probe dimension optimization for LSPR based bio-sensor

The evanescent wave absorption based photonic sensing platform has been developed using D-shaped fiber optic probes for refractive index (RI) mediated bio-sensors. The RI sensitivity of this bare probe was established using different sucrose solutions by optimizing the active de-cladded surface area of the fiber. A linear correlation between probe sensing area and RI sensitivity was observed for different probe lengths. Further, these bare probes have been functionalized using amine (–NH2) functional groups on the air-exposed core using the standard silane treatment process. This probe was demonstrated as a localized surface plasmon resonance (LSPR) monitoring platform by immobilizing the spherical gold nanoparticles (AuNPs). The effect of D-shaped length/area on absorption sensitivity was compared with bare and LSPR probes. The biosensing property of this LSPR probe was tested using Immunoglobulin antibody (HIgG). An exponential bimolecular binding kinetic has been observed during this antigen–antibody conjugation and the limit of detection was measured (0.6 µg/mL) by varying concentrations of antigen (GaHIgG). These fiber optic LSPR probes can be integrated into an optical system to develop an evanescent wave absorption-based biosensor.

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

We propose an optical fiber-based localized surface plasmon resonance sensor to overcome limitations with hydrogen gas explosions in various types of hydrogen sensors and minimize human damage caused by exposure to hazardous environments. For selective detection of hydrogen, a simple palladium-capping process was applied on a fiber-optic localized surface plasmon resonance. After the palladium-capping, the sensor was exposed to various refractive index solutions to confirm the linearity of the response. Hydrogen gas reactivity was measured at concentrations from 0.8% to 4%; the reaction time at each concentration was observed as 116 s until the signal stabilized. The coefficient of variation (CV) and limit of detection (LOD) were calculated based on the results obtained through repeated measurements. The reproducibility was verified with an average CV of 11%. In addition, the developed sensor showed a low LOD of 0.086%. The hysteresis characteristic was observed within 1% in the output change, which was similar to the fluctuation range allowed by the light source per time. The proposed sensor based on the optical principle is expected to reduce the risk of explosions and has advantages in a simple configuration and low-cost production based on optical fiber.

Performance improvement of a glucose sensor based on fiber optic localized surface plasmon resonance and anti-aggregation of the non-enzymatic receptor

The performance of glucose sensors based on non-enzymatic receptors is often limited because of the aggregation of receptors and the resulting lowered binding efficiency. To improve the limit of detection (LOD) in glucose sensors, a polyoligomeric silsesquioxane (POSS) is introduced as a support to enhance the binding efficiency between glucose and non-enzymatic receptor. POSS support reduces the aggregation and partially grants orientation to ensure that non-enzymatic receptors can productively react with targets. The synthesized amine@POSS-aminophenylboronic acid (APBA) conjugate was immobilized on the surface of gold nanoparticles, which were fastened on the optical fiber. Optical fiber-based sensors using localized surface plasmon resonance (LSPR) enabled rapid detection, ease of handling, and remote sensing. After confirming the response characteristics to the refractive index, a suitable concentration of amine@POSS-APBA receptor was selected for the fabricated fiber optic sensor. Glucose detection was performed at various concentrations using non-enzymatic receptors with and without POSS support. The experimental results demonstrated that increased responses were observed in the designed method than when only the non-enzymatic receptor was applied. The LOD for glucose was quantified as 25.0 μM. We believe that improved glucose sensors based on fiber optic LSPR and POSS support has the potential to be applied to field detection in various fields, such as medicine, food safety, and the environment.

MoS2 Functionalized Multicore Fiber Probes for Selective Detection of Shigella Bacteria Based on Localized Plasmon

Present study demonstrates the fiber-optic localized surface plasmon resonance (LSPR) based sensitive biosensor for detection of Shigella bacterial species. The proposed sensor is comprised of multi-core fiber (MCF) having seven cores arranged in a hexagonal shape and spliced with single-mode fiber (SMF) for efficient detection. An increase in evanescent waves (EWs) and coupling of modes between MCF cores was achieved by etching process in a controlled manner. The etching process also increases the refractive index sensitivity (RIS) of the proposed sensor. Further, coating with nanomaterials like gold nanoparticles (AuNPs) and molybdenum disulfide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) helps in the excitation of localized plasmons. Here, Shigella specific oligonucleotide probes are used as a recognition element. The results demonstrate that the proposed sensor can successfully and efficiently detect the Shigella bacterial species with high sensitivity. Shigella in the range of 10 - 100 CFU/mL (colony-forming unit/mL) can cause serious intestinal infection and therefore, its detection in this range is critical. The proposed sensor demonstrates a linearity range from 1 to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> CFU/mL with a detection time of 5 min and a limit of detection (LoD) of 1.56 CFU/mL. The proposed sensing methodology can be a potential alternative to the commercially existing ones in the near future.

Development of a rapid and ultra-sensitive cytosensor: Ω-shaped fiber optic LSPR integrated with suitable AuNPs coverage

Cytosensor plays a vital role on the cancer diagnosis at early stage. Localized surface plasmon resonance (LSPR)-based fiber optic is a type of emerging cytosensor with the merits of miniaturized devices, real-time and label-free detection, which is, however, limited by its low sensitivity and time-consuming analysis processes. To address those limitations, in this work a one-step LSPR-based cytosensor was constructed featuring Ω-shaped fiber optic with suitable AuNPs coverage. Both refractive index sensitivity (RIS) and density of captured cancer cells increased with a uniform AuNPs, while a sharp decrease of RIS and a plateau of density of captured cancer cells was found when AuNPs coverage increased at aggregation state. Under the same AuNPs coverage, the Ω-shaped fiber optic exhibited an enhanced RIS and efficiency of captured cancer cells, compared to the U-shaped fiber optic, which in hence led to a rapid and ultra-sensitive cytosensor based on Ω-shaped fiber optic cytosensor based on LSPR. The proposed cytosensor with suitable AuNPs coverage has a wide linear range of 5×101 ∼ 1×105 cells/mL with low limit of detection (LOD) of 12 cells/mL for rapid detection of MCF-7 cancer cells just in 37.5 min. Noticeably, an excellent selectivity and anti-inference were achieved by the cytosensor even in fetal bovine serum. Thus, Ω-shaped fiber optic LSPR-based cytosensor has promising application as an analytical method for cancer diagnosis in the further.

Fabrication and Measurement of Fiber Optic Localized Surface Plasmon Resonance Sensor Based on Hybrid Structure of Dielectric Thin Film and Bilayered Gold Nanoparticles

Localized surface plasmon resonance (LSPR) sensor with hybrid structure of dielectric thin film and bilayered gold nanoparticles (AuNPs) on an optical fiber is proposed to enhance the sensitivity. The increased number of nanoparticles per unit plane due to the bilayer structure contributes to the upgrade in the sensitivity by improving the LSPR effect and extending the sensing area. The bilayered AuNPs will be particularly important in the application of fiber optic LSPR (FO LSPR) sensors because the optical fiber has a small cross-sectional area. The Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin film by atomic layer deposition is inserted between the first and second layers of AuNPs. The dielectric spacer can also help to improve the sensitivity by concentrating the electric field due to its high refractive index and ensuring a nanometer gap between nanoparticles. The monolayer and bilayer with AuNPs are prepared on the optical fibers, respectively. In each FO LSPR sensor, refractive index sensitivities are also analyzed and compared. In the sensor with bilayered AuNPs, a sensitivity improvement of approximately 2.3 times is confirmed. This strategy can be a breakthrough to increase the sensing area of the FO LSPR sensor without modifying the structure of the optical fiber.

Direct detection of charge and discharge process in supercapacitor by fiber-optic LSPR sensors

Abstract 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.

Ω-Shaped Fiber-Optic Probe-Based Localized Surface Plasmon Resonance Biosensor for Real-Time Detection of Salmonella Typhimurium.

A novel, Ω-shaped fiber-optic localized surface plasmon resonance (FOLSPR) biosensor was designed for sensitive real-time and label-free bacterial detection. The designed Ω-shaped fiber-optic probe exhibits an outstanding sensitivity, due to the effect of unique geometry on performance. The results show that refractive index (RI) sensitivity of the Ω-shaped fiber-optic probe is 14 times and 2.5 times higher than those of the straight-shaped and the U-shaped FOLSPR, respectively. In addition, the reason for the geometry and the bending radius effects on RI sensitivity was discussed by investigating the relationship between RI sensitivity and the bending area. The results show that RI sensitivity was enhanced with the increase of bending area, and the best RI sensitivity obtained by Ω-shaped FOLSPR was 64.582 (a.u.)/RIU. Combined with this newly designed Ω-shaped FOLSPR biosensor, a real-time, label-free, sensitive, and highly selective bacterial detection method was established. In this work, the aptamers immobilized on the surface of FOLSPR could specifically capture Salmonella Typhimurium, resulting in an intense change of the absorption peak. In line with this principle, the FOLSPR biosensor achieved high detection sensitivity for Salmonella Typhimurium down to 128 CFU/mL within a linear range from 5 × 102 to 1 × 108 CFU/mL and showed good selectivity for Salmonella Typhimurium detection compared to other bacteria. Furthermore, the FOLSPR biosensor was successfully applied to the detection of Salmonella Typhimurium in a chicken sample with the recoveries of 85-123%. With these characteristics, the novel biosensor is a potential alternative tool in food analysis and environmental monitoring.

Localized surface plasmon resonance biosensor using nanopatterned gold particles on the surface of an optical fiber

Fiber-optic localized surface plasmon resonance (FO LSPR) sensors are fabricated by immobilizing metal nanoparticles on the surface of an optical fiber, and have advantages in their miniaturization, simple optical set-up, low cost, and remote sensing. However, the conventional FO LSPR sensor based on chemically synthesized metal nanoparticles lacks durability and fabrication reproducibility, due to the rearrangement and irregular sizes of metal nanoparticles. In this paper, in order to overcome these problems, focused ion beam (FIB) milling is utilized to pattern nanostructures from a metallic film deposited on the end-face of an optical fiber. We also present a design for the fabrication processes to utilize multi-mode fibers. The proposed method is evidenced by measuring the output intensities of an FO LSPR sensor for various refractive index solutions. To verify fabrication reproducibility, sensors fabricated in different batches are compared. Finally, a prostate-specific antigen (PSA) immunoassay is performed to verify the possibility of the fabricated sensor system as a biosensor. PSA is the most useful biomarker for the screening, early detection, and follow up of prostate cancer. Any change in the low PSA levels is important to detect early diagnosis and recurrence of prostate cancer. We measure the PSA to 0.1 pg/ml using the proposed FO LSPR sensor.

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

Conventional assays using fiber-optic localized surface plasmon resonance (FO LSPR) sensors involve soaking the sensor in solution, which exposes the sensor to air during measurement. Although the exposure time is short, for a small sensor surface area, this can result in drying of biomolecules and rearrangement of nanoparticles caused by the surface tension. To minimize the resulting errors, FO LSPR sensor was combined with a micro fluidic channel. To verify the improved performance of the sensor chip combined with a micro fluidic channel, we conducted real-time detection of various concentrations of prostate-specific antigen (PSA). A calibration method was used to correct nonuniformity among the detected PSA results, arising from differences in sensors because of nonuniform metal nanoparticles on the sensor surface. A micro fluidic channel and calibration increased linearity and improved the sensitivity and dynamic range of PSA measurements. Additionally, the fabricated sensors were applied to detect the test samples and the measured sample concentrations were compared to actual values. Confirming the selectivity towards the target, the proposed system detected the control antigen. Finally, we used our sensor system to detect PSA in patient serum and acquired comparable results to those obtained using a commercialized method.

Fabrication of Localized Surface Plasmon Resonance Sensor Based on Optical Fiber and Micro Fluidic Channel.

This paper proposes Fiber-Optic Localized Surface Plasmon Resonance (FO LSPR) sensor combined with a micro fluidic channel, which enables continuous supply of fluid for bio-reaction. The proposed method prevents degradation of the sensing performance due to changes in measurement conditions. The feasibility of the FO LSPR sensor with a micro fluidic channel was demonstrated by computational fluid dynamics (CFD) simulation. Also, the proposed method was assessed by measuring the output intensity of the FO LSPR sensor at various refractive index solutions. Finally, a prostate-specific antigen (PSA) immunoassay was performed to evaluate the possibility of the fabricated sensor system as a biosensor.

Analysis and Optimization of Antibody Immobilization for Immunoassay Using Fiber-Optic Localized Surface Plasmon Resonance Biosensors

Analysis and Optimization of Antibody Immobilization for Immunoassay Using Fiber-Optic Localized Surface Plasmon Resonance Biosensors

Polydopamine-assisted fabrication of fiber-optic localized surface plasmon resonance sensor based on gold nanoparticles

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.

Fiber-Optic Refractive Index Sensor Based on the Cone-Based Round Structure

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.

Analysis of Fiber-Optic Localized Surface Plasmon Resonance Sensor by Controlling Formation of Gold Nanoparticles and its Bio-Application

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.