Localized Surface Plasmon Resonance Biosensor Research Articles

Multi-channel prismatic localized surface plasmon resonance biosensor for real-time competitive assay multiple COVID-19 characteristic miRNAs

A multi-channel prismatic localized surface plasmon resonance (LSPR) biosensor was developed for quantitative and real-time detection of multiple COVID-19 characteristic miRNAs. The well-dispersed and dense gold nanoparticles (AuNPs) arrays for LSPR biosensing were fabricated through a nano-thickness diblock copolymer template (BCPT). Both theoretical and experimental analyses were conducted to investigate the effects of particle size, interparticle spacing, and surface coverage on LSPR sensing spectrum and intensity sensitivity of varied AuNPs sizes. A competitive assay strategy was proposed and used for non-amplification miRNA detection with a low limit detection of 3.41 nM, while a four-channel prismatic LSPR system enables parallel detection of multiple miRNAs. Furthermore, this sensing strategy can effectively and specifically identify target miRNA, distinguish mismatched miRNA and interfering miRNA, and exhibit low non-specific adsorption. This BCPT-based LSPR biosensor demonstrates the practicality and potential of a multi-channel, adaptable, and integrated prismatic sensor in medical testing and diagnostic applications.

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.

Gold Nanoparticle-Based Colorimetric Biosensing for Foodborne Pathogen Detection.

Ensuring safe high-quality food is an ongoing priority, yet consumers face heightened risk from foodborne pathogens due to extended supply chains and climate change in the food industry. Nanomaterial-based assays are popular and have recently been developed to ensure food safety and high quality. This review discusses strategies for utilizing gold nanoparticles in colorimetric biosensors. The visible-signal biosensor proves to be a potent sensing technique for directly measuring targets related to foodborne pathogens in the field of food analysis. Among visible-signal biosensors, the localized surface plasmon resonance (LSPR) biosensor has garnered increasing attention and experienced rapid development in recent years. This review succinctly introduces the origin of LSPR theory, providing detailed insights into its fundamental principles. Additionally, this review delves into the application of nanotechnology for the implementation of the LSPR biosensor, exploring methods for utilizing gold nanoparticles and elucidating the factors that influence the generation of visible signals. Several emerging technologies aimed at simple and rapid immunoassays for onsite applications have been introduced in the food industry. In the foreseeable future, field-friendly colorimetric biosensors could be adopted in food monitoring systems. The onsite and real-time detection of possible contaminants and biological substances in food and water is essential to ensure human health and safety.

Investigation of Performance Parameters of Spherical Gold Nanoparticles in Localized Surface Plasmon Resonance Biosensing.

In this paper, we present numerical and experimental results on Localized Surface Plasmon Resonance (LSPR) refractive index (RI) sensitivity, Figure of Merit (FoM), and penetration depth (dp) dependence on spherical gold nanoparticles (AuNPs) size, and the effects of AuNP dimer interparticle distance (ds) studied numerically. These parameters were calculated and observed for d = 20, 40, 60, 80, and 100 nm diameter spherical AuNPs. Our investigation shows d = 60 nm AuNPs give the best FoM. The AuNP dimer interparticle distance can significantly influence the RI sensitivity. Therefore, the effect of distances between pairs of d = 20 nm and 60 nm AuNPs is shown. We discuss the importance of penetration depth information for AuNPs functionalized with aptamers for biosensing in the context of aptamer size.

An ultrasensitive J-shaped optical fiber LSPR aptasensor for the detection of Helicobacter pylori

The development of label-free and sensitive detection of pathogenic bacteria is of great significance for disease prevention and public health protection. In this study, an originally bent structure, named as J-shaped optical fiber probe, was first designed to engineer a localized surface plasmon resonance (LSPR) aptamer biosensor for the rapid and ultrasensitive detection of Helicobacter pylori (H. pylori). The J-shaped optical fiber probe exhibited a significant improvement in refractive index sensitivity (RIS) and LSPR signal response. Meantime, the original sequence of aptamer was truncated in order to effectively capture H. pylori on the optical fiber surface. Besides, a spacer nucleic acid with short stem-loop structure was adopted to control the aptamer density on gold nanoparticles (AuNPs) on the surface of the J-shaped optical fiber probe, which displayed a further enhancement in LSPR signal response. Benefitting from these creative designs, the proposed LSPR biosensor can realize label-free and sensitive detection of H. pylori with a detection limit as low as 45 CFU/mL and a wide linear range from 1.0 × 102 CFU/mL to 1.0 × 108 CFU/mL. At the same time, the sensing strategy can detect the pathogenic bacteria from actual water samples in one step just in 30 min without any sample pretreatment. Due to the advantages of ease-to-preparation, high sensitivity, and rapid analysis, this proposed J-shaped optical fiber LSPR aptasensor can provide a potential strategy for point-of-caring detection of pathogenic bacteria in environmental monitoring and disease diagnosis.

Highly sensitive silver-based localized surface plasmon resonance (LSPR) biosensor for microRNA-21 detection: Discrete dipole approximation together with molecular polarizability method

In this research, a highly sensitive gastric cancer biosensor based on the (LSPR) properties of silver nanoparticles has been produced to identify the microRNA-21. This biosensor has been analyzed by UV–Visible spectrophotometer (UV) and Field Emission Scanning Electron Microscopy (FESEM). The obtained results show that our optimized synthesis process leads to the creation of approximately zig-zag chain structures consisting of 4 or 5 nanoparticles which can sense the cancer agent by a maximum shift in the plasmonic peak position. In addition, the mentioned results were confirmed by a comprehensive simulation of the biosensors using discrete dipole approximation (DDA) modified by the molecular polarizability method. The simulation process has been made by considering the effects of the actual molecular structures for both the receptor and target microRNAs on the surface of nanoparticles. The mentioned approach led to approximately accurate results that were matched with experimental achievements. This comparison indicates that the presented method is a suitable way for deep analysis of (LSPR)-based cancer biosensors.

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.

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.

Wearable Localized Surface Plasmon Resonance-Based Biosensor with Highly Sensitive and Direct Detection of Cortisol in Human Sweat

Wearable biosensors have the potential for developing individualized health evaluation and detection systems owing to their ability to provide continuous real-time physiological data. Among various wearable biosensors, localized surface plasmon resonance (LSPR)-based wearable sensors can be versatile in various practical applications owing to their sensitive interactions with specific analytes. Understanding and analyzing endocrine responses to stress is particularly crucial for evaluating human performance, diagnosing stress-related diseases, and monitoring mental health, as stress takes a serious toll on physiological health and psychological well-being. Cortisol is an essential biomarker of stress because of the close relationship between cortisol concentration in the human body and stress level. In this study, a flexible LSPR biosensor was manufactured to detect cortisol levels in the human body by depositing gold nanoparticle (AuNP) layers on a 3-aminopropyltriethoxysilane (APTES)-functionalized poly (dimethylsiloxane) (PDMS) substrate. Subsequently, an aptamer was immobilized on the surface of the LSPR substrate, enabling highly sensitive and selective cortisol capture owing to its specific cortisol recognition. The biosensor exhibited excellent detection ability in cortisol solutions of various concentrations ranging from 0.1 to 1000 nM with a detection limit of 0.1 nM. The flexible LSPR biosensor also demonstrated good stability under various mechanical deformations. Furthermore, the cortisol levels of the flexible LSPR biosensor were also measured in the human epidermis before and after exercise as well as in the morning and afternoon. Our biosensors, which combine easily manufactured flexible sensors with sensitive cortisol-detecting molecules to measure human stress levels, could be versatile candidates for human-friendly products.

Constructing the Au nanoparticle multimer on optical fiber end face to enhance the signal of localized surface plasmon resonance biosensors: A case study for deoxynivalenol detection

Localized surface plasmon resonance (LSPR) based optical fiber end-face biosensors have the advantages of convenience, fast, accuracy, and high sensitivity. Because the sensor area (optical fiber end face)) is small, how to improve its signal strength is a challenge faced by researchers. In this study, an Au nanoparticle (AuNP) multimer structure was designed to enhance the LSPR signal by the hot spots effect produced by the AuNP multimers. The fiber end face was coupled with the first batch of AuNPs, on which the second batch of AuNPs was coupled using 3-aminopropyl triethoxysilane as a spacer, then deoxynivalenol (DON) aptamer was coupled on to complete the biosensor. Also, the preparation parameters were optimized. The results showed that this biosensor with the AuNP multimers had a higher signal strength, its LSPR absorbance was 2.1 fold of that of the biosensor with AuNPs. It had a high performance for DON detection, furthermore, the LSPR peak shift value and LOD of this developed biosensor was 3.4 fold and 1/8 of that of LSPR the biosensor with AuNPs. Therefore, it is a good strategy to enhance the signal of the optical fiber LSPR biosensors by constructing the AuNP multimers on the fiber end face.

Silica-coated gold nanorods biofunctionalization for localized surface plasmon resonance (LSPR) biosensing

We introduce here the engineering of nanobiosensors designed from gold nanorods coated with an ultrathin layer of silica (AuNR@SiO2) and biofunctionalized with antibodies for the Localized Surface Plasmon Resonance (LSPR) biosensing of proteins. Despite the outstanding properties of AuNRs, their use for LSPR biosensing is limited due to the presence of the surfactant cetyltrimethylammonium bromide (CTAB) – mandatory for their synthesis - which forms a strongly-bounded and positively-charged bilayer at their surface and significantly complicates their bio-functionalization. When coated with a thin layer of silica, these nanomaterials exhibit an improved sensitivity to refractive index change which augurs for better analytical performances. Here, we undertook an in-depth investigation of the biofunctionalization of AuNR@SiO2via three different routes to design and test a label-free LSPR biosensor operating in solution. In the first route, we took advantage of the negatively charged external silica shell to immobilize anti-rabbit IgG antibody by electrostatic physisorption. In the second and third routes, the silica surface was reacted with thiol or aldehyde terminated silanes, subsequently utilized to covalently attach anti-rabbit IgG antibody to the surface. The resulting nanoprobes were characterized by a wide range of physical methods (TEM, XPS, DLS, ELS and UV-Visible spectroscopy) then tested for the biosensing of rabbit-IgG. The three nanobiosensors maintain an excellent colloidal stability after analyte recognition and exhibit extremely high analytical performances in terms of specificity and dynamic range, with an LoD down to 12 ng/mL.

Optical Fiber-Based Localized Surface Plasmon Resonance Biosensor Using Gold Nanorods Encapsulated in Graphene Oxide Nanocomposite Film Applied for Immunoassay

In this study, gold nanorods (GNRs) are immobilized on the surface of fiber probe using a self-assembly method for a localized surface plasmon resonance (LSPR)-based optical fiber biosensor. In order to promote the performances of GNRs films, graphene oxide (GO) is used to encapsulate GNRs, which forms the GNRs@GO structure. Furthermore, the GNRs and GNRs@GO fiber probes are used to detect different refractive indices of surrounding environments from 1.33 to 1.38. The results show that the GNRs fiber probes have the sensitivity of 48 nm/RIU with the linearity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}}$ </tex-math></inline-formula> = 0.988. By comparison, for GNRs@GO with 0.2 mg/mL of GO fiber probe, the sensitivity is increased to 218 nm/RIU, and the linearity is improved to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}}$ </tex-math></inline-formula> = 0.991. After that, anti-mouse IgG is immobilized on the GNRs and GNRs@GO fiber probes for immunoassay. The results show that the limit of detection (LOD) of GNRs fiber probe is 147.9 ng/mL, and the sensitivity is 26.5 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{g}$ </tex-math></inline-formula> mL <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula> with the linearity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}}$ </tex-math></inline-formula> = 0.936 in the detecting range of 0.1– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5 \mu \text{g}$ </tex-math></inline-formula> /mL. By comparison, for GNRs@GO with 0.2 mg/mL of GO fiber probe, the LOD is improved to 32.7 ng/mL, and the sensitivity as well as the linearity are increased to 61.1 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{g}$ </tex-math></inline-formula> mL <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{{2}}$ </tex-math></inline-formula> = 0.991, respectively. In addition, the optimal concentration of GO encapsulated with GNRs is 0.2 mg/mL, and the optimal response time is 20 min. The results also show that the GNRs@GO fiber probe has a good selectivity. Finally, the GNRs@GO structure shows the potential for applying in an optical fiber biosensor.

Localized surface plasmon resonance biosensing of Mycobacterium tuberculosis biomarker for TB diagnosis

Biosensors offer great advantages over conventional analytical techniques. Specifically, they can provide multiple capabilities such as user-friendly operation, real-time analysis, rapid response, high sensitivity and specificity, portability, label-free detection, and cost-effectiveness. As a result, this diagnostic approach is a point-of-care (POC) diagnostic and monitoring technology. In this study, for the first time, an optical biosensor chip was developed and analyzed using a localized surface plasmon resonance (LSPR) optical biosensing technique to monitor biomolecular interactions between mycolic acid TB antigen and anti-Mycobacterium tuberculosis antibody. Mycolic acid was successfully immobilized on a gold-coated biosensor chip and allowed to react with anti-Mycobacterium tuberculosis antibody. To enhance the detection signal from biomolecular binding events, gold nanoparticles (AuNPs) were used and successfully bioconjugated with goat anti-rabbit IgG H&L secondary antibody and characterized using ultraviolet-visible (UV–vis) spectroscopy, dynamic light scattering (DLS), Fourier-transform infrared (FTIR) spectroscopy, and subsequently introduced on the biosensing layer. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and atomic force microscopy (AFM) were used to characterize the biosensing surface. The optimized biosensor chip was analyzed using a custom-built biosensing transmission spectroscopy setup to perform LSPR biosensing. Our findings showed that mycolic acid was successfully immobilized on the biosensing surface and made it possible to capture anti-Mycobacterium tuberculosis antibodies. The LSPR optical biosensing technique was indeed successful in the detection of anti-Mycobacterium tuberculosis antibodies.

Au Nanoparticle-Based Integrated Microfluidic Plasmonic Chips for the Detection of Carcinoembryonic Antigen in Human Serum

A nanoplasmonic biosensor with merits of label-free and rapid detection provides a key tool for the detection of cancer markers in ultralow concentrations. Herein, a localized surface plasmon resonance (LSPR) biosensor integrated with microfluidics, which has multiple sensing units, was developed by nanomaterial fabrication technology. The performance of the LSPR biosensor was experimentally explored using nine clinical sample tests after the biofunctionalization of Au nanoparticles by biomodification and verified by four characterization methods. The linear detection response of carcinoembryonic antigen (CEA) appeared in the range of 0.5–100 ng/mL, with a detection limit below 1 ng/mL. The results illustrated that the LSPR platform improves the signal-to-noise ratio by about 85 times after adjusting testing system parameters. Furthermore, the simultaneous detection results of the proposed biosensor in nine serum samples of 50 μL from breast cancer patients were proved to be consistent with enzyme-linked immunosorbent assay (ELISA) results (r = 0.94). The low cost and remarkable performance of this LSPR biosensor make it promising to develop a precise clinical detection platform for auxiliary diagnosis, condition monitoring, and efficacy evaluation of cancer.

A Portable Optical Fiber Tip Facet LSPR Aptasensor for Detection of Fumonisin B1

Fumonisin B1 (FB1) is a mycotoxin that mainly contaminates food crops. To avoid the harmful effect of FB1 on the human body, it is necessary to establish a convenient, sensitive, and accurate FB1 detection method. In this study, an optical fiber tip facet biosensor based on the localized surface plasmon resonance (LSPR) that adapts to a general detection platform was developed. An optical fiber end face was assembled with –NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , Au nanoparticles (AuNPs), and aptamer, and the fabricating parameters were optimized. The results showed that the optical fiber LSPR biosensor had a good linear relationship ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{\text {2}}$ </tex-math></inline-formula> = 0.9817) between the logarithmic FB1 concentration and the LSPR peak shifts within the linear range of concentrations of 0.8–200.0 ng/mL and a low limit of detection (LOD) of 0.17 ng/mL, as well as selectivity, recovery rates (96.08%–112.23%), and repeatability relative standard deviation (RSD) of 3.37%. It was validated by corn. Therefore, it was feasible that a tip facet optical fiber LSPR biosensor could be used to detect FB1, with advantages of convenience, renewability, and low cost. It is easy to popularize and apply.

Determination of the Highly Sensitive Carboxyl-Graphene Oxide-Based Planar Optical Waveguide Localized Surface Plasmon Resonance Biosensor.

This study develops a highly sensitive and low-cost carboxyl-graphene-oxide-based planar optical waveguide localized surface plasmon resonance biosensor (GO-OW LSPR biosensor), a system based on measuring light intensity changes. The structure of the sensing chip comprises an optical waveguide (OW)-slide glass and microfluidic-poly (methyl methacrylate) (PMMA) substrate, and the OW-slide glass surface-modified gold nanoparticle (AuNP) combined with graphene oxide (GO). As the GO has an abundant carboxyl group (–COOH), the number of capture molecules can be increased. The refractive index sensing system uses silver-coated reflective film to compare the refractive index sensitivity of the GO-OW LSPR biosensor to increase the refractive index sensitivity. The result shows that the signal variation of the system with the silver-coated reflective film is 1.57 times that of the system without the silver-coated reflective film. The refractive index sensitivity is 5.48 RIU−1 and the sensor resolution is 2.52 ± 0.23 × 10−6 RIU. The biochemical sensing experiment performs immunoglobulin G (IgG) and streptavidin detection. The limits of detection of the sensor for IgG and streptavidin are calculated to be 23.41 ± 1.54 pg/mL and 5.18 ± 0.50 pg/mL, respectively. The coefficient of variation (CV) of the repeatability experiment (sample numbers = 3) is smaller than 10.6%. In addition, the affinity constants of the sensor for anti-IgG/IgG and biotin/streptavidin are estimated to be 1.06 × 107 M−1 and 7.30 × 109 M−1, respectively. The result shows that the GO-OW LSPR biosensor has good repeatability and very low detection sensitivity. It can be used for detecting low concentrations or small biomolecules in the future.

Site specific biotinylated antibody functionalized Ag@AuNIs LSPR biosensor for the ultrasensitive detection of exosomal MCT4, a glioblastoma progression biomarker

Glioblastoma (GBM) is an incurable brain tumor in which hypoxic GBM cells (GMs) increase the production and release of exosomes, which are 30–200 nm vesicles crossing the blood–brain-barrier, enabling exosomal biomarkers to be promising targets for the tracking of GBM malignancy. Here, a localized surface plasmon resonance (LSPR) sensor chip was developed to detect an infinitesimal amount of exosomal biomarkers. Self-assembly silver nanoparticles decorated on gold nano-islands (Ag@AuNIs) sensor chip was used to provide site-specific bio-conjunction of biotinylated antibodies for detection of exosomal surface biomarkers. The biotinylated antibody functionalized (BAF) Ag@AuNIs LSPR biosensor sensitively detected cluster of differentiation 63, an exosome marker, and monocarboxylate transporter 4 (MCT4), a GBM progression biomarker, in malignant GMs-derived exosomes in the dynamic range of 3.8 × 10−4 to 50 μg/ml with limit of detection (LOD) of 0.38 ng/ml and 1.4 × 10−3 to 500 μg/ml with LOD of 1.4 ng/ml, respectively. Furthermore, it detected the enhanced level of MCT4 in malignant hypoxic GMs-derived exosomes as well as increased MCT4 in the blood serum-derived exosomes of GBM mice in the dynamic range of 4 × 10−4 to 50 μg/ml with LOD of 0.4 ng/ml. Finally, it could quantify MCT4 in the isolated GMs-derived exosomes from the blood of GBM mice by epidermal growth factor receptor variant III-based immunocapture, suggesting its utility for minimally-invasive monitoring of GBM progression as liquid biopsy. With excellent attributes of high sensitivity and selectivity in label-free sensing for exosomal biomarkers, the BAF Ag@AuNIs LSPR biosensor has great potential for early detection of GBM formation and progression.

Immobilization of Streptavidin on a Plasmonic Au-TiO2 Thin Film towards an LSPR Biosensing Platform.

Optical biosensors based on localized surface plasmon resonance (LSPR) are the future of label-free detection methods. This work reports the development of plasmonic thin films, containing Au nanoparticles dispersed in a TiO2 matrix, as platforms for LSPR biosensors. Post-deposition treatments were employed, namely annealing at 400 °C, to develop an LSPR band, and Ar plasma, to improve the sensitivity of the Au-TiO2 thin film. Streptavidin and biotin conjugated with horseradish peroxidase (HRP) were chosen as the model receptor–analyte, to prove the efficiency of the immobilization method and to demonstrate the potential of the LSPR-based biosensor. The Au-TiO2 thin films were activated with O2 plasma, to promote the streptavidin immobilization as a biorecognition element, by increasing the surface hydrophilicity (contact angle drop to 7°). The interaction between biotin and the immobilized streptavidin was confirmed by the detection of HRP activity (average absorbance 1.9 ± 0.6), following a protocol based on enzyme-linked immunosorbent assay (ELISA). Furthermore, an LSPR wavelength shift was detectable (0.8 ± 0.1 nm), resulting from a plasmonic thin-film platform with a refractive index sensitivity estimated to be 33 nm/RIU. The detection of the analyte using these two different methods proves that the functionalization protocol was successful and the Au-TiO2 thin films have the potential to be used as an LSPR platform for label-free biosensors.