Localized Surface Plasmon Resonance Sensor Research Articles

Recent advance on fiber optic SPR/LSPR-based ultra-sensitive biosensors using novel structures and emerging signal amplification strategies

Biomarkers with ultralow concentration in the actual samples play a vital role in the clinical disease diagnosis, infectious disease screening, food security, and environmental monitoring. Fiber optic (FO)-based surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) biosensors attract immense attention for in situ, and rapid detection due to their merits of miniaturized devices, easy integration, and low cost, showing great promising for point of care point-of-caring test. In order to achieve ultrasensitive detection of biomarkers, great effort focused on design of a sensitive FO-based biosensor on the aspect of novel FO probes and signal amplification strategies. Firstly, novel FO probes, including gating and new structure-based, were develop to adjust the light propagation and allow intensely interaction between the light and metal film or nanoparticles, which excites strong SPR or LSPR for sensitive biosensor. Then, nanomaterials on FO surface improved the intensity of electromagnetic fields or provided a good scaffold to modify with more recognition element for signal amplification. Nucleic acid circuits get rid of the limitation of the signal-to-target ratio of 1:1 and exhibited high efficiency to amplify the signal. These efforts have also led to the application of FO-SPR and LSPR sensors for detection of various targets, such as cells, nucleic acids, proteins, and small molecules. In the review, we summarized the important progress of the ultrasensitive FO-based biosensor about emerging FO probes and signal amplification strategies, also discussed its opportunities and challenges for the point-of-caring test. The review aims to promote the application of the FO-SPR and LSPR from experiments to real samples.

Plasmonic sensing: FDTD calculations to interpret experimental LSPR water adsorption isotherms

Finite-Difference Time-Domain (FDTD) calculations are widely used to interpret experimental Localized Surface Plasmon Resonance (LSPR) spectra. With FDTD it is possible to predict the physical parameters of the nanostructures that will theoretically give the best experimental LSPR signals. This information is crucial for optimizing sample fabrication and saving significant time. FDTD is also essential to control and calibrate various parameters of the nanostructures and to understand effects such as a Cr adhesion layer and LSPR sensor size distribution. Finally, for water adsorption sensing, FDTD confirms that the LSPR peak shift strictly follows Campbell’s model, even at submonolayer coverage.

Development of Liquid-Phase Plasmonic Sensor Platforms for Prospective Biomedical Applications.

Localized Surface Plasmon Resonance (LSPR) is an optical method for detecting changes in refractive index by the interaction between incident light and delocalized electrons within specific metal thin films' localized "hot spots". LSPR-based sensors possess advantages, including their compact size, enhanced sensitivity, cost-effectiveness, and suitability for point-of-care applications. This research focuses on the development of LSPR-based nanohole arrays (NHAs) as a platform for monitoring probe/target binding events in real time without labeling, for low-level biomolecular target detection in biomedical diagnostics. To achieve this objective, this study involves creating a liquid-phase setup for capturing target molecules. Finite-difference time-domain simulations revealed that a 75 nm thickness of gold (Au) is ideal for NHA structures, which were visually examined using scanning electron microscopy. To illustrate the functionality of the liquid-phase sensor, a PDMS microfluidic channel was fabricated using a 3D-printed mold with a glass slide base and a top glass cover slip, enabling reflectance-mode measurements from each of four device sectors. This study shows the design, fabrication, and assessment of NHA-based LSPR sensor platforms within a PDMS microfluidic channel, confirming the sensor's functionality and reproducibility in a liquid-phase environment.

Application of Anisotropic Gold Nanomaterials in Plasmonic Sensors for Detection of Glyphosate

The trend of using agrochemicals is increasing, especially glyphosate-based herbicides (GBH). The application of toxic chemicals as pest control in food crops carries a risk to human safety. Therefore, it is important to create a sensor for detection through Localized Surface Plasmon Resonance (LSPR) by utilizing anisotropic gold nanoparticles (AGN) to detect the presence of GBH contaminants in the form of malathion and temephos, with a detection level as low as three-part per million (ppm). AGN-based LSPR is successfully synthesized through an experimental technique using the Seed Mediated Growth Method (SMGM). The UV-Vis response showed two strong absorbances with a peak occurring around 500 to 600 nm, the peak within the transverse surface plasmon resonance range (t-SPR) corresponds to one aspect, while the peak within the spectral range extending from 700 nm to 900 nm corresponds to another aspect, namely Longitudinal Surface Plasmon Resonance (l-SPR). Anlysis of the FESEM photograph shows a structure consisting of two particles with different shapes, pentagonal pyramids and a bone shape. Pentagonal pyramids joined with a surface density of 64.43 ± 1,53 % and bone shape of 32,46 ± 1.53 %. This characterization shows strong and distinctive optical resonance in the near-infrared visible light spectrum, which is very suitable for LSPR sensors. It is necessary to fabricate an LSPR sensor device capable of detecting the presence of GBH by testing sensitivity, stability and repeatability. The sensitivity test results were evaluated by varying the synthesis time and concentration of contaminants in the AGN growth solution. It confirmed that the AGN-based LSPR sensor has a promising potential for GBH residue detection.

The Refractive Index Sensing Performance of Au and Ag Nanoparticles Under Different Surrounding Environment

AbstractBenefiting from the sensitive response to the change of surrounding environment, localized surface plasmon resonance sensors have wide applications for the detection of bio‐/chemical species. Traditionally, the sensitivity research of localized surface plasmon resonance sensors mainly focused on the morphologies and materials of sensor structures. Instead, the effect of environmental refractive index on sensitivity of a gold (Au) nanoparticle sensor is theoretically investigated in this work. The results show that when few free targets are adjacent to the sensor, a better sensing performance can be achieved as the refractive index increases from 1.00 to 1.10. However, when a target layer is closely covered on the Au nanoparticle, a 0.1 decrease in environmental refractive index can lead to a significant improvement in sensitivity. The similar results can be also obtained on a silver (Ag) nanoparticle. This work provides new understandings for advanced sensing applications of surface plasmon resonance sensors.

WaveFlex Biosensor: MXene-Immobilized W-shaped Fiber-Based LSPR sensor for highly selective tyramine detection

Tyramine is generally produced via decarboxylation of tryptophan, and its long-term exposure can induce severe symptoms in humans like brain stroke and hypertensive crisis. It also served as an important factor to check the food quality, as its increased level is frequently found in rotten food products. Thus, more precise, practical, quick, and easy methods have been required for the detection of tyramine in various samples. In the present study, a localized surface plasmon resonance (LSPR) optical fiber-based, highly sensitive, and selective method for tyramine detection has been proposed. The fiber surface has been functionalized with MXene and gold nanoparticles to provide increased surface area for enzyme immobilization as well as enhance the performance of the sensor. The results showed that the developed sensor efficiently detects tyramine with high specificity due to the presence of the tyrosinase enzyme. Further studies revealed the stability, repeatability, and reusability of the proposed biosensor with a 6.96 µM detection limit and a sensitivity of 0.0385 nm/µM. As a result, the proposed optical fiber-based sensor has significant potential for application in the detection of the presence of tyramine in a wide variety of agricultural and food samples.

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.

Nanoplasmonic Au:CuO thin films functionalized with APTES to enhance the sensitivity of gas sensors

Carbon monoxide (CO) is a highly flammable and toxic gas to humans and animals, that’s why its detection and monitoring are crucial. A promising technique to develop a robust and cheap gas sensor, operating at room temperature, is Localized Surface Plasmon Resonance (LSPR) sensing. However, LSPR sensing of inorganic gas molecules, such as CO, is challenging due to their extremely small differences in refractive indices. In this work, a nanoplasmonic thin film, composed of Au NPs semi-embedded in a CuO matrix (Au:CuO) was functionalized with a silane self-assembled monolayer (APTES molecule) that enhanced the sensitivity of the film to a mixture of CO (50 ppm) in Argon. Three different concentrations of APTES (0.1 %, 1.0 %, and 5.0 %) were silanized on Au:CuO thin film surface, and all the functionalized Au:CuO thin films showed better sensing results than bare Au:CuO thin film. The functionalized Au:CuO thin film with 0.1 % of APTES revealed the best sensing characteristics. Its sensitivity was almost 3 times higher than that of the unmodified Au:CuO thin film. Au:CuO thin films functionalized with APTES are potentially relevant to developing sensitive and selective LSPR sensors for the detection of inorganic gases such as CO, in harsh environments.

Antibody binding to plasmonic nanostructure: A validation study using experiment and simulation

Localized surface plasmon resonance (LSPR) sensors allow the label-free detection of molecules in real-time with a high sensitivity, which makes them suitable for the detection of various molecules. However, the experimental characterization of the surface functionalization and the molecular binding on the nanostructured sensor surface represent black boxes. To overcome these uncertainties, this study shows an approach to simulate and experimentally validate the plasmonic response upon molecular binding to a LSPR sensor for the detection of diclofenac (DCF). Assuming homogeneous molecular coverage and averaged parameters such as refractive index and layer thickness through the combination of an iterative experimental validation and electrodynamics simulations a coherent model was formed that includes the uncertainties of molecular binding. This validated model and the obtained parameter for the biochemical assay forms the basis for a future automated optimization of the nanostructure geometry with respect to increased sensitivity to molecular binding.

Growth time dependency on the formation of gold nanobipyramids for efficient detection towards chlorpyrifos-based LSPR sensor

The structure of gold nanobipyramids (GNBPs) is very promising for specific Localized Surface Plasmon Resonance (LSPR) properties, and thus potentially to be used in various applications, especially in sensing. This work reported growth time dependency on the formation of GNBPs for application in LSPR sensors for chlorpyrifos detection. The study on the growth time found that GNBPs formation at the initial stage is dominated by elongation direction and its optimum growth time is 2 h. The optimum GNBPs with 106.32 ± 2.50 in length, 42.17 ± 0.82 in width and an aspect ratio of 2.55 ± 0.08 were implemented as a sensing material for direct and rapid localized surface plasmon resonance (LSPR) sensors to detect chlorpyrifos. The mechanism is based on the change in spectrum intensity and wavelength shift between GNBPs when tested in deionized water and chlorpyrifos solution. The change arises from molecular interaction between the targeted analyte and the sensing material and effectively changes the dielectric features of the medium. The presence of chlorpyrifos in the 1 – 100 mg/mL concentration range has been successfully detected. The proposed sensor offers better sensitivity as high as 1.22 times for transverse LSPR mode and 2.04 for longitudinal LSPR mode than the LSPR sensor based on gold nanosphericals. Moreover, the sensor stability and repeatability response showed a reliable performance for determining chlorpyrifos. Furthermore, this sensor also shows high selectivity towards chlorpyrifos compared to other organophosphate and organochlorine pesticides such as malathion, chlorothalonil, and triclopyr-butotyl.

Uniform Gold Nanostructure Formation via Weakly Adsorbed Gold Films and Thermal Annealing for Reliable Localized Surface Plasmon Resonance-Based Detection of DNase-I.

Deoxyribonuclease-I (DNase-I), a representative endonuclease, is an important biomarker for the diagnosis of infectious diseases and cancer progression. However, enzymatic activity decreases rapidly ex vivo, which highlights the need for precise on-site detection of DNase-I. Here, a localized surface plasmon resonance (LSPR) biosensor that enables the simple and rapid detection of DNase-I is reported. Moreover, a novel technique named electrochemical deposition and mild thermal annealing (EDMIT) is applied to overcome signal variations. By taking advantage of the low adhesion of gold clusters on indium tin oxide substrates, both the uniformity and sphericity of gold nanoparticles are increased under mild thermal annealing conditions via coalescence and Ostwald ripening. This ultimately results in an approximately 15-fold decrease in LSPR signal variations. The linear range of the fabricated sensor is 20-1000ngmL-1 with a limit of detection (LOD) of 127.25 pgmL-1 , as demonstrated by spectral absorbance analyses. The fabricated LSPR sensor stably measured DNase-I concentrations from samples collected from both an inflammatory bowel disease (IBD) mouse model, as well as human patients with severe COVID-19 symptoms. Therefore, the proposed LSPR sensor fabricated via the EDMIT method can be used for early diagnosis of other infectious diseases.

Localized surface plasmon resonance biosensor chip surface modification and signal amplifications toward rapid and sensitive detection of COVID-19 infections

We developed a multi-pronged approach to enhance the detection sensitivity of localized surface plasmon resonance (LSPR) sensor chips to detect SARS-CoV-2. To this end, poly(amidoamine) dendrimers were immobilized onto the surface of LSPR sensor chips to serve as templates to further conjugate aptamers specific for SARS-CoV-2. The immobilized dendrimers were shown to reduce surface nonspecific adsorptions and increase capturing ligand density on the sensor chips, thereby improving detection sensitivity. To characterize the detection sensitivity of the surface-modified sensor chips, SARS-CoV-2 spike protein receptor-binding domain was detected using LSPR sensor chips with different surface modifications. The results showed that the dendrimer-aptamer modified LSPR sensor chip exhibited a limit of detection (LOD) of 21.9 pM, a sensitivity that was 9 times and 152 times more sensitive than the traditional aptamer- or antibody-based LSPR sensor chips, respectively. In addition, detection sensitivity was further improved by combining rolling circle amplification product and gold nanoparticles to further amplify the detection signals by increasing both the target mass and plasmonic coupling effects. Using pseudo SARS-CoV-2 viral particles as detection targets, we demonstrated that this combined signal intensification approach further enhanced the detection sensitivity by 10 folds with a remarkable LOD of 148 vp/mL, making it one of the most sensitive SARS-CoV-2 detection assays reported to date. These results highlight the potential of a novel LSPR-based detection platform for sensitive and rapid detection of COVID-19 infections, as well as other viral infections and point-of-care applications.

Plasmonic Nanopillars-A Brief Investigation of Fabrication Techniques and Biological Applications.

Nanopillars (NPs) are submicron-sized pillars composed of dielectrics, semiconductors, or metals. They have been employed to develop advanced optical components such as solar cells, light-emitting diodes, and biophotonic devices. To integrate localized surface plasmon resonance (LSPR) with NPs, plasmonic NPs consisting of dielectric nanoscale pillars with metal capping have been developed and used for plasmonic optical sensing and imaging applications. In this study, we studied plasmonic NPs in terms of their fabrication techniques and applications in biophotonics. We briefly described three methods for fabricating NPs, namely etching, nanoimprinting, and growing NPs on a substrate. Furthermore, we explored the role of metal capping in plasmonic enhancement. Then, we presented the biophotonic applications of high-sensitivity LSPR sensors, enhanced Raman spectroscopy, and high-resolution plasmonic optical imaging. After exploring plasmonic NPs, we determined that they had sufficient potential for advanced biophotonic instruments and biomedical applications.

AHMT functionalized g-C3N4 quantum dots/Au based localized surface plasmon resonance sensors for ultrasensitive and rapid detection of adrenaline

Adrenaline (ADR) is a neurotransmitter/hormone responsible for stress syndrome and the concentration level in blood is an indication of health consequences. Herein, a simple and cost-effective nanosensors based on the interaction between highly fluorescent g-C3N4 quantum dots (CNQDs) and surface plasmon resonance gold nanoparticles (AuNPs) in the presence of 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT) was developed for ultra-sensitive and selective detection of ADR. After functionalization of AHMT onto both CNQDs and AuNPs, AHMT can serve as the recognizer to link with ADR by hydrogen bond, resulting in the non-radiative energy transfer from CNQD to AuNP to quench the fluorescence intensity. The quenching efficiency is highly dependent on ADR concentration and the size of AuNPs. When 45 nm AuNPs is combined with CNQDs, an excellent linear relationship with a wide dynamic range of (10 pM – 100 µM) and a low limit of detection of 7 pM is obtained for ADR detection. Moreover, the developed sensor exhibits high selectivity towards ADR detection over 25 potential interferences. These findings have demonstrated the superiority of AHMT-conjugated CNQD-AuNP sensing probe for ADR detection, which can be applied to design of a newly developed nanosensing platform for the early detection and therapeutic diagnosis of ADR associated diseases in biomedical applications.

Basics of the LSPR Sensors for Soft Matter at Interfaces

An important class of localized surface plasmon resonance (LSPR)–based sensors implies the fabrication of an array of plasmonic metal nanoparticles on the support in combination with a thin protective dielectric layer. If needed, this layer can be covered, e.g., by a suitable thin biological layer, e.g., a lipid bilayer with receptors. The attachment of analyte (e.g., protein molecules or vesicles) to such interfaces is tracked via its indirect optical effect on the LSPR-related peak extinction wavelength. Such sensors have been commercialized and are now used to study biological soft matter. The length scale of the local field able in probing analyte around plasmonic nanoparticles is in this case on the order of 20 nm. Conceptually, these LSPR sensors are similar to the SPR sensors which were developed much earlier. Herein, the similarities and differences in the formalisms used to interpret SPR and LSPR measurements are discussed in detail. In particular, the exponential and power-law attenuation functions employed in these formalisms to describe the drop of the field are compared from various perspectives. The applicability of the power-law attenuation function in the context of LSPR is illustrated by using a generic model describing spherically shaped plasmonic metal nanoparticles. This model is also employed to illustrate the sensitivity of LSPR sensors with respect to various quantities. Among more specific results, the available expressions for the signal reduction factor for analyte nanoparticles of various shapes are collected and complemented by new ones. In addition, the equation describing the LSPR signal related to analyte attachment to a rough surface is presented.

Localized surface plasmon resonance sensing of SO2 and H2S using zeolitic imidazolate framework-8

A localized surface plasmon resonance (LSPR) sensor for SO2 and H2S has been developed by coating a Au nanopattern with zeolitic imidazolate framework-8 (ZIF-8), which is one of the most common metal–organic frameworks. SO2 and H2S were detected by the change in the absorbance at a certain wavelength in the LSPR spectrum. The sensitivity to SO2 and H2S was enhanced by ZIF-8 and with increasing relative humidity, and 0.1–20 ppm SO2 and 0.1–10 ppm H2S could be detected within 5 min at 70% relative humidity. The ZIF-8-coated sensor was more sensitive to SO2. The changes in the absorbance increased during exposure to SO2 and H2S, and only slightly decreased for SO2 and remained almost constant for H2S after stopping exposure. These responses indicate that the sensor can measure the integrated concentrations of SO2 and H2S. If the sensor was not exposed to ≥ 20 ppm SO2 or ≥ 10 ppm H2S, the sensitivity and LSPR spectrum of the sensor could be recovered approximately a dozen times by heating it at 200 °C in air. This study demonstrates the potential of metal–organic-framework-coated LSPR sensors for highly sensitive detection of SO2 and H2S.

Nb2CTx MXene-assisted double S-tapered fiber-based LSPR sensor with improved features for tyramine detection

Niobium carbide (Nb2CTx), a type of MXene with high optical transparency, large specific surface area, and good electrical conductivity, is expected to perform as an excellent medium in the field of optical fiber biosensing. Here, we fabricated double S-tapered fiber sensors functionalized with gold nanoparticles/graphene oxide/tyrosinase (AuNPs/GO/tyrosinase) and AuNPs/Nb2CTx/tyrosinase, respectively. The double S-tapered structure can provide more evanescent wave leakage and enhance light–matter interaction. By implementing transmittance experiment, the sensitivity of the two probes were tested to be 17 and 34 pm/μM over 0–300 μM tyramine concentrations. The comparative results demonstrate that Nb2CTx-enhanced localized surface plasmon resonance (LSPR) sensor has more excellent performance due to the existence of surface functional groups and large specific surface area of Nb2CTx. Our work provides a research platform for improving the sensitivity of LSPR sensors.

Hybrid structure of u bent optical fiber local surface plasmon resonance sensor based on graphene

<p>In this paper, a fiber optic sensor was designed and implemented to detect the change in refractive index of sodium chloride salt solution based on the local surface plasmon resonance (LSPR) phenomenon. This sensor was manufactured using a plastic optical fiber (POF), this optical fiber was bent in a U-shape with 0.5cm bending diameter, and then the cladding and part from core of the fiber were removed by polishing at the sensor head to become as a D-shape in cross section. The sensor was coated with 30 nm thickness of gold nano particles (GNPs) by DC plasms coating technology and it was tested with sodium chloride solution, the detection sensitivity was 466.66 nm/RIU. To enhancement the sensitivity, the latest sensor was coated with 20nm thickness of graphene nano material and retested with same samples of sodium chloride solutions. It was found that graphene improved the sensitivity by an excellent amount, where shift in wavelength was 20nm and highest sensitivity obtained was 666.666 nm/RIU.</p>

Fabrication of localized surface plasmon resonance sensors with scalable polyvinyltetrazole/copper cluster hybrid ring-array for Cu(II) detection

The bottom of a hole-array photoresist template deposited with a hydrophobic atom-transfer radical polymerization (ATRP) initiator was wetted by treatment with oxygen plasma. After the removal of the photoresist template, ring patterns of the ATRP initiator were formed at the interface between the hydrophobic and wetting regions. Polyacrylonitrile (PAN) was grafted from the initiator ring array to covert to polyvinyltetrazole (PVT) rings via a cyano-to-tetrazole reaction, which could adsorb Cu(II) at various concentrations. The Cu(II) ions within the PVT rings were reduced to form a PVT–copper hybrid ring (VCHR), resulting in a blue-shift of the localized surface plasmon resonance (LSPR) peak as the Cu(II) was adsorbed by the PVT rings. The blue-shift and Cu(II) concentration were linearly correlated, with a detection limit of ∼25 pg mL−1 and a linear range of 25–400 pg mL−1 for Cu(II) detection. Although the PVT rings also chelated Pb(II) and Cr(III), these ions did not exhibit obvious LSPR peaks. The VCHR LSPR sensor exhibited excellent selectivity for Cu(II) detection. Combining lithography and plasma technology provides a versatile platform for developing the scalable ring structure of copper for highly sensitive and selective Cu(II) sensing.

Dual-tapered optical fiber structure-based localized surface plasmon resonance sensor for cholesterol detection in human body

Cholesterol plays an important role in biological systems, and the quantity of cholesterol in the human body serves as a diagnostic marker for a range of disorders. This article presents a localized surface plasmon resonance (LSPR) sensor based on dual-tapered optical fiber (DTOF) that can detect cholesterol levels in the human body. To stimulate the LSPR effect and increase the sensitivity of the sensing probe, gold nanoparticles were fixed on the DTOF’s surface. In this study, the reaction between cholesterol and cholesterol oxidase altered the refractive index near the sensing probe, and the related spectrum was obtained. In addition, the sensor’s performance, including linear range, repeatability, reusability, stability, and selectivity, was examined. The experimental results indicate that the proposed DTOF-based LSPR sensor is capable of reliably measuring cholesterol levels and has promising biomedical applications.