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This study explores the surface plasmon resonance (SPR) and the electromagnetic field responses of multi-layer structures with incident light to enhance the sensitivity and range for measurement of nanoscale thin liquid film thickness. We assess the effect of metal layer type and its corresponding thickness on the optical responses. Notably, the silver (Ag) layer exhibits a more acute reflectance curve with a thickness of 50 nm, which is attributable to the minimization of non-radiative losses and a substantial real component of the dielectric constant of the Ag layer. Furthermore, a correlation between liquid film thickness and reflectance has been established across different metal layer types at specified thicknesses. The Ag layer demonstrates the broadest measurement range for liquid film thickness due to its extensive penetration depth into the dielectric material. Conversely, the sodium (Na) layer presents the narrowest measurement range, albeit with the highest SPR sensitivity. [ABSTRACT FROM AUTHOR]

The present study investigated the impact of incorporating copper nanoparticles (CuNPs) on the optical properties of erbium-doped borate glasses. Through melt-quenching and heat treatment techniques, glasses with varying Cu 2 O concentrations (x = 0–5 mol%) were synthesized. Physical and structural analyses revealed that Cu ions serve as effective network modifiers. They foster the formation of a greater proportion of BO 4 tetrahedra and thus enhancing glass homogeneity. Optical absorption spectra demonstrate a distinct modulation of Er3+ absorption bands with Cu 2 O embedding, indicating the formation of CuNPs, as validated by the emergence of surface plasmon resonance bands. This structural evolution results in a noticeable reduction in the bandgap energy, signifying improved semiconducting behavior. Judd-Ofelt analysis highlighted the profound influence of CuNPs on hypersensitive transitions, thereby affecting oscillator strength. Photoluminescence measurements revealed amplified emission in the visible red and near infrared (NIR) region, attributed to the synergistic effects of CuNPs and Er3+ ions, with 5 mol % Cu 2 O exhibiting the highest emission intensity. Analysis of the radiative properties validates the enhancement of the emission cross-section, gain bandwidth, optical gain and radiative transitions. These enhancements contribute to a notable increase in the branching ratio from 0.91 % to 5.41 % accompanied by an increase in the quantum efficiency from ∼79 % to ∼90 %. Moreover, decay analysis revealed a notable enhancement in lifetime from 3.03 ms to 15.74 ms, which is indicative of enhanced radiative transitions. Overall, the incorporation of CuNPs into erbium-doped borate glasses facilitates significant enhancements in physical, structural, and optical properties. This positions them as promising materials for a wide array of optoelectronic applications. This comprehensive study sheds light on the complex interplay between CuNPs and erbium-barium borate glasses, offering valuable insights for the development of advanced optoelectronic materials with enhanced performance and functionality. [Display omitted] [ABSTRACT FROM AUTHOR]

2-Furaldehyde (2-FAL) is one of the main by-products of the degradation of hemicellulose, which is the solid material of the oil–paper insulating system of oil-filled transformers. For this reason, it has been suggested as a marker of the degradation of the insulating system; sensing devices for 2-FAL analysis in a wide concentration range are of high interest in these systems. An optical sensor system is proposed; this consists of a chemical chip, able to capture 2-FAL from the insulating oil, coupled with a surface plasmon resonance (SPR) probe, both realized on multimode plastic optical fibers (POFs). The SPR platform exploits gold nanofilm or, alternatively, a double layer of gold and silicon oxide to modulate the sensor sensitivity. The capturing chip is always based on the same molecularly imprinted polymer (MIP) as a receptor specific for 2-FAL. The system with the SPR probe based on a gold nanolayer had a higher sensitivity and a lower detection limit of fractions of μg L−1. Instead, the SPR probe, based on a double layer (gold and silicon oxide), has a lower sensitivity with a worse detection limit, and it is suitable for the detection of 2-FAL at concentrations of 0.01–1 mg L−1. [ABSTRACT FROM AUTHOR]

The cytokine interleukin-6 (IL-6) plays a crucial role in autoimmune and inflammatory diseases. Understanding the precise mechanism of IL-6 interaction at the amino acid level is essential to develop IL-6-inhibiting compounds. In this study, we employed computer-guided drug design tools to predict the key residues that are involved in the interaction between IL-6 and its receptor IL-6R. Subsequently, we generated IL-6 mutants and evaluated their binding affinity to IL-6R and the IL-6R − gp130 complex, as well as monitoring their biological activities. Our findings revealed that the R167A mutant exhibited increased affinity for IL-6R, leading to enhanced binding to IL-6R − gp130 complex and subsequently elevated intracellular phosphorylation of STAT3 in effector cells. On the other hand, although E171A reduced its affinity for IL-6R, it displayed stronger binding to the IL-6R − gp130 complex, thereby enhancing its biological activity. Furthermore, we identified the importance of R178 and R181 for the precise recognition of IL-6 by IL-6R. Mutants R181A/V failed to bind to IL-6R, while maintaining an affinity for the IL-6 − gp130 complex. Additionally, deletion of the D helix resulted in complete loss of IL-6 binding affinity for IL-6R. Overall, this study provides valuable insights into the binding mechanism of IL-6 and establishes a solid foundation for future design of novel IL-6 inhibitors. [ABSTRACT FROM AUTHOR]

Over the past years, Surface Plasmon Resonance (SPR) has been used in various domains including medical diagnostics, chemical and biological sensing, and environmental monitoring. SPR-based biosensors have more advantages than other optical biosensors due to their rapid, label-free, and targeted detection capabilities. There have been challenges to designing SPR biosensors with enhanced performance and improved environmental adaptability, including considerations such as prism-metal bonding, biomolecule adhesion, and oxidation protection. This paper presents sensitivity and performance enhancement in an SPR biosensor based on Kretschmann configuration while using a low refractive index CaF2 glass prism, a zinc oxide (ZnO) layer, a gold-silver alloy (Au10Ag90), and a single layer of 2D graphene. Theoretical analysis shows that the use of a CaF2 prism and the alloy gives a good sensitivity of 280 ∘ / RIU . The sole addition of a ZnO layer improves this sensitivity to 320 ∘ / RIU . Further addition of a graphene layer to make the final proposed structure CaF2/ZnO/Au10Ag90/graphene/SM, improves sensitivity to 340 ∘ / RIU , giving a figure of merit value of 60.28 / RIU and a quality factor value of 102.48 / RIU . Despite supporting the SPR mode and enhancing sensitivity, ZnO improves prism-alloy bonding while graphene promises better biomolecule adhesion and improved oxidation protection. Overall, our proposed structure has better sensing performance compared to other designs in the literature. The high sensitivity makes our proposed biosensor suitable for the detection of tiny cancer bio-markers in body fluids, enabling early medical interventions. [ABSTRACT FROM AUTHOR]

Silver-based grating structures offer means for implementing low-cost, efficient grating couplers for use in surface plasmon resonance (SPR) sensors. One-dimensional grating structures with a fixed periodicity are confined to operate effectively within a single planar orientation. However, two-dimensional grating structures as well as grating structures with variable periodicity allow for the plasmon excitation angle to be seamlessly adjusted. This study demonstrates silver-based grating designs that allow for the plasmon excitation angle to be adjusted via rotation or beam position. The flexible angle adjustment opens up the possibility of developing SPR sensor designs with an expanded dynamic range and increased flexibility in sensing applications. The results demonstrate that efficient coupling into two diffraction orders is possible, which ultimately leads to an excitation angle range from 16° to 40° by rotating a single structure. The findings suggest a promising direction for the development of versatile and adaptable SPR sensing platforms with enhanced performance characteristics. [ABSTRACT FROM AUTHOR]

A highly sensitive D-shaped microfluidic channel (MFC) incorporated in a single-mode fiber (SMF) equipped with a tungsten trioxide ( W O 3 ) layer coated with gold (Au) or silver (Ag) on the base of the MFC is designed and investigated utilizing a finite element method (FEM) to obtain the sensing performance of the optical fiber surface plasmon resonance (SPR) structure. The proposed sensor is appropriate for both bimetallic layers and analytes. With the sizeable cladding diameter of SMF, the fluidic channel size can be changed following demand, making fabrication more accessible and applicable. The hollow D-section above the core deposited a bimetallic structure of silver (Ag) or gold (Au) as plasmonic materials, followed by a tungsten trioxide ( W O 3 ) nanolayer. This optical fiber biochemical monitors the changes in the refractive index (RI) by measuring the transmission spectral shifts of the fiber at their resonance wavelengths. The W O 3 layer protects the plasmonic material from oxidation and effectively enhances the surface plasmon wave (SPW) while interacting with free electrons. Upon achieving the optimum structural parameters, the numerical investigation results showed that the maximum wavelength sensitivity of 6.0 μ m//RIU and 5.0 μ m//RIU for Au/ W O 3 and Ag/ W O 3 were obtained, with the coefficient of performance of 50.12 R I U - 1 and 134.84 R I U - 1 , respectively, for ultra-wide sensing ranges from 1.28 to 1.38. Also, the simulation outcomes revealed that the tungsten trioxide-coated with Ag or Au layers significantly enhanced the sensor. Finally, the numerical results of this study showed that the proposed sensor has substantial possibilities for large sensing RI applications such as biology and chemistry analytes, and it is also valid for other lower RI analyte sensing requirements as a consequence of its features such as high sensitivity, simple design, cost-effective design, and promising linear sensing performance. [ABSTRACT FROM AUTHOR]

We propose a dual-core, highly sensitive PCF SPR biosensor with C-shaped grooves based on a fusion of graphene and gold film. The performance of our sensor is enhanced by our circular fibre lattice with perforated air holes. We evaluate the biosensor's sensitivity to variations in refractive index (RI) in cancer cells numerically using the Finite Element Method (FEM) in COMSOL Multiphysics. After enhancing fiber parameters and using numerical results from amplitude method and spectral interrogation methods, we found that the biosensor demonstrates the highest sensitivity for MCF7 cells, 2142.86 nm/RIU under spectral interrogation. With HeLa cells, the biosensor shows a sensitivity of – 1058.039 1/RIU under the amplitude interrogation approach. Moreover, for MCF7, the biosensor reaches a resolution of 04.60 × 1E–5 RIU. [ABSTRACT FROM AUTHOR]

This article presents a highly sensitive plasmonic sensor with a focus on enhancing its capabilities through innovative design and simple geometric structure. A hexagonal-shaped photonic crystal fiber (PCF) based surface plasmon resonance sensor is designed and proposed for external sensing applications. The plasmonic material is made of gold and positioned on the outer side of the designed PCF. For detection purposes, the flow of the testing analyte is introduced on the exterior section of the PCF. The sensing capability of this innovative sensor is meticulously examined using the finite element technique facilitated by the COMSOL Multiphysics software. The suggested sensor, with a refractive index of 1.38, has a maximum amplitude sensitivity and wavelength sensitivity of 765.86 RIU−1 and 8,000 nm/RIU respectively. At the same refractive index, the sensing resolution of the sensor is 1.31 × 10–5 for amplitude sensitivity and 1.25 × 10–5 for wavelength sensitivity. Additionally, the sensing capability of the sensor lies in the range of the analyte refractive indices from 1.33 to 1.39. Furthermore, the sensing performance of the designed sensor is analyzed by optimizing the values of several design parameters including air-hole diameter, pitch, and gold layer thickness. The suggested sensor can recognize biological analytes with high sensitivity, improved sensing resolution, and appropriate linearity. [ABSTRACT FROM AUTHOR]

Photothermal therapy (PTT) is recognized as an effective tool for the treatment of cancer and it has attracted considerable attention of scientists. In this work, gold nanospheres (AuNSs) and gold nanorods (AuNRs) stabilized using poly(N‐vinylpyrrolidone) (PVP), pristine gellan gum (PGG), and poly(2‐ethyl‐2‐oxazoline)‐grafted gellan gum (GG‐g‐PEtOx) are synthesized and evaluated as PTT agents in Ehrlich cancer cells. The physicochemical characteristics of these AuNSs and AuNRs, including their surface plasmon resonance absorption spectra, size, zeta potential, and aspect ratio are studied using UV–vis‐spectroscopy, dynamic light scattering, zeta potential, transmission electron microscopy, and optical microscopy techniques. The polymer‐protected AuNSs exhibit light‐to‐heat conversion, raising the temperature from 37 to 43 °C when irradiated using a visible light source. In the case of AuNSs, considerable damage to Ehrlich cancer cells is observed following irradiation and 40 days of examination. However, with regard to AuNSs, the damage to Ehrlich cancer cells is slightly lower than observed in AuNRs. In vivo experiments demonstrate that laser irradiation of tumors in mice after injecting AuNSs leads to a statistically significant decrease in tumor size as compared to those not irradiated and the control samples. [ABSTRACT FROM AUTHOR]

The high affinity of the biotin–streptavidin interaction has made this non-covalent coupling an indispensable strategy for the immobilization and enrichment of biomolecular affinity reagents. However, the irreversible nature of the biotin–streptavidin bond renders surfaces functionalized using this strategy permanently modified and not amenable to regeneration strategies that could increase assay reusability and throughput. To increase the utility of biotinylated targets, we here introduce a method for reversibly immobilizing biotinylated thrombin-binding aptamers onto a Ni-nitrilotriacetic acid (Ni-NTA) sensor chip using 6xHis-tagged streptavidin as a regenerable capture ligand. This approach enabled the reproducible immobilization of aptamers and measurements of aptamer–protein interaction in a surface plasmon resonance assay. The immobilized aptamer surface was stable during five experiments over two days, despite the reversible attachment of 6xHis-streptavidin to the Ni-NTA surface. In addition, we demonstrate the reproducibility of this immobilization method and the affinity assays performed using it. Finally, we verify the specificity of the biotin tag–streptavidin interaction and assess the efficiency of a straightforward method to regenerate and reuse the surface. The method described here will allow researchers to leverage the versatility and stability of the biotin–streptavidin interaction while increasing throughput and improving assay efficiency. [ABSTRACT FROM AUTHOR]

Cu-PMMA nanocomposite films have been prepared via ex-situ chemical route by reduction of cupric chloride dissolved in aqueous CTAB solution with hydrazine and then incorporated the prepared Cu nanoparticles in a solution of Polymethylmethacrylate (PMMA) in chloroform and cast into thin films. Optical and structural characterizations of resulting nanocomposite films were performed using UV-visible spectroscopy and Transmission Electron Microscopy (TEM). Characteristic Surface Plasmon Resonance (SPR) peak of Cu nanoparticles was observed at about 2.14 eV (577 nm) in absorption spectra of Cu-PMMA nanocomposite films. From the observation of absorption spectra, the optical band gap and Urbach's energy values have been calculated. Band gap values of Cu-PMMA nanocomposite films were found to decrease from 3 eV to 2.4 eV, while Urbach's energy values increased with the increase in the concentration of Cu nanoparticles in PMMA. The decrease in the optical band gap and increase in Urbach's energy values indicated the modifications in the optical band structure of the PMMA matrix on the incorporation of Cu nanoparticles. TEM micrograph revealed spherical Cu nanoparticles embedded in PMMA with an average diameter of 6.5+ 2.5 nm. [ABSTRACT FROM AUTHOR]

Objective·To establish various in vitro screening systems for the discovery of peptide inhibitors targeting the interaction between small ubiquitin-like modifier (SUMO)-activating enzyme subunit 1 (SAE1) and subunit 2 (SAE2), as well as to evaluate their advantages, disadvantages, and applicability to this research. Methods·The DNA fragments encoding human SAE1 and SAE2 were cloned into vector pET-28a, respectively, to generate protein SAE1 and SAE2. Purified proteins were used to establish screening assays, including isothermal calorimetry (ITC), fluorescence polarization (FP), surface plasmon resonance (SPR) and a fluorescence assay based on the SAE enzyme activity. The inhibitory activity of peptide candidates in different screening systems was examined, and their performance in terms of sensitivity, robustness, throughput and cost was evaluated. Results·The dissociation constant (Kd) of in vitro SAE1 and SAE2 interaction was determined to be 0.96 μmol/L by ITC, and PEPT7 was identified as the most potent peptide. However, the tracer of FP, which was derived from PEPT7, was not up to snuff due to its low affinity with SAE2. In the SPR assay, the Kd value (=1.13 μmol/L) of SAE1 and SAE2 interaction was in line with the results from ITC. The SAE enzyme activity-based screening assay revealed that HP1B, the most effective peptide, inhibited SAE with an halfmaximal inhibitory concentration (IC50) of 15.72 μmol/L. The affinity of HP1B for SAE1 was determined to be 34.4 μmol/L by SPR. Conclusion·Several common screening systems for protein-protein interation (PPI) inhibitors are established and compared. Among them, ITC does not allow for high-throughput screening and it is difficult to accurately evaluate the low-affinity polypeptides with insignificant binding heat. The feasibility of FP relies heavily on the strong affinity between a tracer peptide and the protein target, making it unsuitable for the screening and optimization of low-affinity peptides. SPR is highly sensitive but the cost is high. The SAE enzyme activity-based assay stands out because it is a combination of high sensitivity, robustness, throughput and acceptable cost. [ABSTRACT FROM AUTHOR]

Given the medical and social significance of Helicobacter pylori infection, timely and reliable diagnosis of the disease is required. The traditional invasive and non-invasive conventional diagnostic techniques have several limitations. Recently, opportunities for new diagnostic methods have appeared based on the recent advance in the study of H. pylori outer membrane proteins and their identified receptors. In the present study we assess the way in which outer membrane protein–cell receptor reactions are applicable in establishing a reliable diagnosis. Herein, as well as in other previous studies of ours, we explore the reliability of the binding reaction between the best characterized H. pylori adhesin BabA and its receptor, the blood antigen Leb. For the purpose we developed surface plasmon resonance (SPR) and double resonance long period grating (DR LPG) biosensors based on the BabA–Leb binding reaction for diagnosing H. pylori infection. In SPR detection, the sensitivity was estimated at 3000 CFU/mL—a much higher sensitivity than that of the RUT test. The DR LPG biosensor proved to be superior in terms of accuracy and sensitivity—concentrations as low as 102 CFU/mL were detected. [ABSTRACT FROM AUTHOR]

In this paper, we have proposed a new multilayer structure and investigated its performance as a chemical sensor utilizing surface plasmon resonance. Our proposed design consists of a black phosphorus layer sandwiched between a metal layer and a graphene layer, blue phosphorene/MoS2 heterostructure layers placed over it, and the sensing layer containing the analyte placed on top. A CaF2 prism in the Kretschmann configuration is employed to excite surface plasmon resonance (SPR), and the angle interrogation method is used for analysis. Sellmeier equations calculate the reflectivity and other parameters of the multilayer design. We also study the effect of the combination of BP and metal interlayer. Analysis of the proposed design shows significantly improved sensitivity compared to recent SPR-based sensors. In this paper, the sensitivity of 466°/RIU is obtained with silver metal, BP, graphene, and BlueP/MoS2 layers SPR sensor. [ABSTRACT FROM AUTHOR]

The confinement of electrons in gold nanoparticles results in Surface Plasmon Resonance (SPR), which is characterized by electric field enhancement in the vicinity of these nanoparticles. This property has been extensively studied and applied in various fields. In our research, we conduct a detailed investigation of plasmonic coupling in spherical gold nanoparticles. Specifically, we use the Discrete Dipole Approximation (DDA) method implemented in DDSCAT to simulate the coupling of electric fields in a doublet of nanoparticles as a function of the distance between them. Our simulations show that the coupling of SPR between two nanoparticles occurs up to a separation of 12 nm. Moreover, we extend our simulations to study the coupling of nanoparticles in linear chains consisting of up to five nanoparticles and in clustered forms. Our results indicate that the SPR coupling in a linear chain occurs, and as the number of nanoparticles increases, the field enhancement also increases. However, we observe that this effect saturates after four nanoparticles in a line. Our study provides insights into the plasmonic coupling in gold nanoparticles, which can aid in the design and optimization of plasmonic devices for various applications. [ABSTRACT FROM AUTHOR]

A dual-channel surface plasmon resonance (SPR) sensor, based upon a multimode-single mode-multimode-single mode- multimode (MSMSM) fiber structure, is reported for the simultaneous measurement of temperature and refractive index. One channel is coated with an indium tin oxide-silver layer for refractive index sensing, and the channel is coated with Au and cyclohexane layer for temperature sensing. The experiments show that the sensor provides high sensitivity with values of 3379 nm/RIU across the refractive index range from 1.333 to 1.3699 and −3.163 nm/°C from 40 °C to 90 °C. The cross-sensitivity problem is resolved by the dual-wavelength matrix method. Moreover, the proposed sensor has good stability, low cost, and a compact structure and may be employed in biology, chemistry, and environmental testing. [ABSTRACT FROM AUTHOR]

Toll-like receptor 4 (TLR4) is a crucial inflammatory signaling pathway that can serve as a potential treatment target for various disorders. A number of inhibitors have been developed for the TLR4 pathway, and although no inhibitors have been approved for clinical use, most have been screened against the TLR4-MD2 conformation. The venom gland is the organ of venomous snakes that secretes substances that are toxic to other animals. The level of gene transcription in venom glands is different from that in other tissues, includes a large number of biologically active ingredients, and is an important natural resource for the development of new drugs. We constructed a T7 phage display library using the cobra (Naja atra) venom gland from the Guangdong Snake Breeding Plant and performed three rounds of screening with TLR4 as the target, randomly selecting monoclonal phage spots for PCR followed by Sanger sequencing. The obtained sequences were subjected to length analysis, molecular docking, solubility prediction, and stability prediction, and a peptide containing 39 amino acids (NA39) was finally screened out. The BLAST results indicated that NA39 was a sequence in RPL19 (Ribosomal Protein L19). After peptide synthesis, the binding ability of NA39 to TLR4 was verified by the surface plasmon resonance (SPR) technique. In this study, a new peptide that can specifically bind TLR4 was successfully screened from the cobra venom gland cDNA library, further demonstrating the effectiveness of phage display technology in the field of drug discovery. [ABSTRACT FROM AUTHOR]

A proposed surface plasmon resonance (SPR) sensor inclusion of black phosphorus (BP) nanomaterial is presented in this paper. The performance of the sensor is compared with sensors based on graphene, MoS2, MoSe2, WS2, and WSe2. The optimal thickness of the Cu-Ni layer with BP is determined using the angular interrogation method, resulting in the highest sensitivity of 525°/RIU at a wavelength of 633 nm. The results indicate that the proposed sensor outperforms other 2D nanomaterial-based sensors in terms of sensitivity. Furthermore, the sensor is used for detecting glucose levels in urine samples. By optimizing the thickness of the Cu layer, a maximum sensitivity of 430.10°/RIU is achieved for glucose level detection. It is observed that the proposed configuration with other 2D nanomaterials enhances the sensitivity at a lower thickness of Ni. [ABSTRACT FROM AUTHOR]

Programmed death ligand-1 (PD-L1) is highly expressed in a variety of cancer cells and suggests a poorer prognosis for patients. The natural compound isorhamnetin (ISO) shows promise in treating cancers and causing damage to canine mammary tumor (CMT) cells. We investigated the mechanism of ISO in reducing PD-L1 expression in CMT cells. Clustered, regularly interspaced short palindromic repeat-associated protein 9 (CRISPR/Cas9) was used to mediate CD274 knockout in U27 cells. Then, monoclonal cells were screened and cultured. Nucleotide sequencing and expression of PD-L1 were detected. Additionally, we examined cell migration, invasion, and damage. Immunofluorescent staining of PD-L1 was examined in U27 cells. The signaling pathways were measured by Western blotting. Murine xenotransplantation models and murine immunocompetent allograft mammary tumor models were established to evaluate the effect of ISO therapy. Expression of Ki-67, caspase3, and PD-L1 were analyzed by immunohistochemistry. A pull-down assay was used to explore which proteins could bind to ISO. Canine EGFR protein was purified and used to detect whether it directly binds to ISO using a surface plasmon resonance assay. ISO inhibited the EGFR-STAT3-PD-L1 signaling pathway and blocked cancer growth, significantly increasing the survival rate of healthy cells. The cell membrane receptor EGFR was identified as a direct target of ISO. ISO could be exploited as an antineoplastic treatment of CMT by targeting EGFR to suppress PD-L1 expression. [ABSTRACT FROM AUTHOR]

Fluidic and non-fluidic surface plasmon resonance measurements were realized for the same type of sensory layer and using the same mouse IgG antibody and anti-mouse IgG antibody biomolecular system. A comparison of the thicknesses of the anti-mouse IgG antibody layers bound to the ligand at increasing analyte concentrations ranging from 0.0 μg mL−1 to 5.0 μg mL−1 in the non-fluidic and the fluidic variant showed that the thickness of the bound anti-mouse antibody layers in the fluidic variant was approximately 1.5–3 times larger than in the non-fluidic variant. The greater thicknesses of the deposited layers were also reflected in the larger increment of the resonant angle in the fluidic variant compared to the non-fluidic variant in the considered range of analyte concentrations. The choice between fluidic and non-fluidic surface plasmon resonance biosensors may be justified by the availability of analyte volume and the intended modulation technique. When working with limited analyte, non-fluidic biosensors with intensity modulation are more advantageous. For larger analyte quantities, fluidic biosensors with angular modulation are recommended, primarily due to their slightly higher sensitivity in this measurement mode. [ABSTRACT FROM AUTHOR]

Simple Summary: This review significantly contributes to the research community by providing insights into the role of serum-based biomarkers for the diagnosis of ovarian cancer. It also provides a comprehensive overview of recent advancements in immunoassay detection and employing multiplex technology and SPR biosensors to identify CA125 and HE4 biomarkers. Furthermore, it addresses the challenges associated with these diagnostic methods. This valuable information not only enhances our understanding of ovarian cancer diagnosis but also serves as a reference point for researchers and clinicians working in the field, facilitating further advancements and improvements in early detection methods. Epithelial Ovarian Cancer (EOC) is a leading cause of cancer-related deaths among women, mainly due to a lack of early detection and screening methods. Advanced immunoassay techniques, such as Luminex and proximity extension assay (PEA) technology, show promise in improving EOC detection by utilizing highly sensitive and specific multiplex panels to detect multiple combinations of biomarkers. However, these advanced immunoassay techniques have certain limitations, especially in validating the performance characteristics such as specificity, sensitivity, limit of detection (LOD), and dynamic range for each EOC biomarker within the panel. Implementing multiplexing in point-of-care (POC) biosensors can enhance EOC biomarker detection, with Surface Plasmon Resonance (SPR) being a versatile option among optical biosensors. There is no study on multiplex SPR biosensors specifically tailored for diagnosing EOC. Recent studies have shown promising results in the single detection of EOC biomarkers using SPR, with LOD for cancer antigen 125 (CA125) at 0.01 U/mL−1 and human epididymis protein 4 (HE4) at 1pM. This study proposes a potential roadmap for scientists and engineers in academia and industry to develop a cost effective yet highly efficient SPR biosensor platform for detecting EOC. [ABSTRACT FROM AUTHOR]

In this research, metal targets dipped in 3 mL of distilled water (DW) were subjected to pulsed laser ablation. Colloidal dispersions of Fe and Au, and bimetallic Fe@Au core/shell nanoparticles are created. The core/shell structure of these particles was subsequently studied using X-ray diffraction. UV–Vis and HRTEM measurements are used to determine surface Plasmon resonance (SPR) and particle sizes. We also carried out an investigation to gauge the stability in terms of the surface charge of the produced nanoparticles (Zeta-potential). The findings show that maximum absorption value of Fe Nps was 0.45 in the range (200–350) nm, while Au exhibits a surface Plasmon resonance (SPR) peaked at a wavelength of 545 nm in the range (290–1100) nm. Another peak was noticed at (555) nm for the surface Plasmon band of the particles Fe@Au in the range (290–1100) nm, HRTEM measurement was used to check the shape and particle size, and the results showed that the average particle size was less than 50 nm. [ABSTRACT FROM AUTHOR]

Simultaneous measurement of human immunodeficiency virus (HIV) genome DNA hybridization and the DNA melting temperature in a prism-based surface plasmon resonance (SPR) biosensor is modeled theoretically using a simple dual-channel construction. The proposed sensor consists of a BK7 prism coated with silver as a plasmonic material. The metal surface is divided into two channels to detect medium refractive index (RI) and temperature. One half is covered with zinc selenide (ZnSe) semiconductor to enhance the hybridization detection sensitivity and to protect silver from oxidation. The other half is covered with polydimethylsiloxane (PDMS) polymer to detect the temperature variations. The proposed sensor is optimized numerically, and the optimum structure provides an excellent sensitivity of 208 deg/RIU, thanks to the use of the ZnSe layer, which is greater than double the reported dual-channel prism-based sensor in thickness. The polymer channel shows high sensitivity to the temperature variations of − 0.125 deg/°C, which is nearly 10 times the response of the RI channel to temperature variations. The data obtained from the polymer channel is used to compensate for the thermal perturbations of the sensing medium RI, and at the same time, to monitor the increments of the temperature in order to avoid reaching the DNA melting temperature. A mathematical expression is provided to consider the effect of the temperature variations on the RI of the sensing medium to get a better accurate detection process. The DNA hybridization detection of HIV is theoretically discussed in detail starting from the preparation of the sensing medium with the different ingredients until the hybridization between probe and complementary target DNA (ct-DNA) molecules. [ABSTRACT FROM AUTHOR]

In this article, a highly sensitive surface plasmon resonance (SPR) based biosensor is proposed, Kretschmar's configuration with angular interrogation as the most successful and popular technique has been used, a laser with 664 nm is impinged on a device that consists of a stratified medium that includes perovskite (CH3NH3Pbl3), a transfer matrix method for a p-polarized coherent and collimated incident laser beam is used to calculate the reflectivity, and this proposed device is more sensitive for a medium with refractive indices between 1.34 to 1.40. In order to obtain a high enough sensitivity, four different configurations have been brought to the reader's attention. The device has been introduced with the aid of some important quantities to measure the sensitivity, figure of merit (FoM), full width at half-maximum (FWHM) and detection accuracy (DA), their results respectively are ~153.58°/RIU, ~17 RIU-¹, ~10° (at ns = 1.34)and ~0.1 Deg-¹ (at ns = 1.34). Finally, these performances are far better than the first simple configuration, and the simulation results are implemented in Matlab codes. [ABSTRACT FROM AUTHOR]

In order to solve the problem that the optical fiber surface plasmon resonance (SPR) sensor is insufficiently sensitive for biomolecule detection, a novel sensing probe was proposed and designed, where the semiconductor material α-Fe2O3 was introduced for the first time. The α-Fe2O3 with high refractive index enhances the electric field and evanescent field depth at the interface between the α-Fe2O3 film and the ambient medium, resulting a sensitive performance. The characteristics of the sensors with gold film and α-Fe2O3 film at different thicknesses were analyzed and compared by finite element method. The thicker the α-Fe2O3 film, the higher the sensitivity. When the thickness of gold nanofilm is 50 nm and the thickness of α-Fe2O3 nanofilm is 20 nm, the highest figure of merit (FOM) is 50.98 RIU−1, corresponding to a sensitivity of 4800 nm/RIU, which is 2.16 times more sensitive than the traditional SPR sensor. In addition, three α-Fe2O3 film thickness-assisted SPR sensors were successfully prepared with the highest sensitivity of 4173.1 nm/RIU, which is nearly two times higher than without the α-Fe2O3 film. The enhancement after introducing α-Fe2O3 nanofilms and its promising application in the field of biosensing were confirmed through experiments and simulations. [ABSTRACT FROM AUTHOR]

Gastric-lipase (GL) binding to a lipid layer was investigated for the phase of the layer adjusted with the ratio of stigmasterol to the lipid using surface plasmon resonance. While the layer was formed on the hydrophobic surface, more stigmasterol led to lower surface density only in the dipalmitoylphosphatidylcholine (DPPC) layer. The addition of stigmasterol was believed to transform the phase (condensed liquid-phase) of DPPC layer closer to the phase (expanded liquid-phase) of dioleoylphosphatidylcholine (DOPC) layer. At a ratio greater than 15:85, the effect of the stigmasterol on the DPPC was saturated. The adsorption behavior of GL showed the similar trend with the lipid formation. The adsorption increased with the increase in the ratio of stigmasterol to lipid up to 15:85. On the DOPC layer of the expanded liquid-phase, the most adsorption seemed to occur and was indistinguishable from that in the DPPC layer of 15:85. The surface density of the adsorbed GL was interpreted into the fraction of the stigmasterol-dependent DPPC, 0.33, 0.67, and 1.00 for 10:90, 5:95, and 0:100 of DPPC. Furthermore, the equilibrium constant was between 1 × 1013 M−1 and 2 × 1013 M−1 and the kinetics of the adsorption showed an increase in the adsorption rate constant with the increase of the ratio up to 15:85. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) is a popular real-time technique for the measurement of binding affinity and kinetics, and bench-top instruments combine affordability and ease of use with other benefits of the technique. Biomolecular ligands labeled with the 6xHis tag can be immobilized onto sensing surfaces presenting the Ni2+-nitrilotriacetic acid (NTA) functional group. While Ni-NTA immobilization offers many advantages, including the ability to regenerate and reuse the sensors, its use can lead to signal variability between experimental replicates. We report here a study of factors contributing to this variability using the Nicoya OpenSPR as a model system and suggest ways to control for those factors, increasing the reproducibility and rigor of the data. Our model ligand/analyte pairs were two ovarian cancer biomarker proteins (MUC16 and HE4) and their corresponding monoclonal antibodies. We observed a broad range of non-specific binding across multiple NTA chips. Experiments run on the same chips had more consistent results in ligand immobilization and analyte binding than experiments run on different chips. Further assessment showed that different chips demonstrated different maximum immobilizations for the same concentration of injected protein. We also show a variety of relationships between ligand immobilization level and analyte response, which we attribute to steric crowding at high ligand concentrations. Using this calibration to inform experimental design, researchers can choose protein concentrations for immobilization corresponding to the linear range of analyte response. We are the first to demonstrate calibration and normalization as a strategy to increase reproducibility and data quality of these chips. Our study assesses a variety of factors affecting chip variability, addressing a gap in knowledge about commercially available sensor chips. Controlling for these factors in the process of experimental design will minimize variability in analyte signal when using these important sensing platforms. [ABSTRACT FROM AUTHOR]

In this study, for the first time to our knowledge, the effect of silver nano disks on the performance of a transparent wood (TW)–based surface plasmon resonance sensor filled with Polyvinylpyrrolidone (PVP) polymer is designed and analytically studied by a finite element method via COMSOL multiphysics for the crude oil detection with refractive indices ranging from 1.4468 to 1.498860. The simulation results exhibit that the reflectance dip of the transparent wood nanostructure considerably decreases due to more refractive index matching between the PVP polymer and the cellulose compared with the original wood. Also, the proposed organic sensor has the applicability for detecting the crude oil with the average sensitivity of 170.69 deg/RIU and high accuracy based on surface plasmon resonance (SPR). This study is proposing a new method for measuring the refractive index of the low transparent crude oil using combinations of the polymer infiltration into the wood microstructures and embedding of the silver nano disks. [ABSTRACT FROM AUTHOR]

Polymer-based surface plasmon resonance (SPR) sensors can be used to realize simple, small-size, disposable, and low-cost biosensors for application in several fields, e.g., healthcare. The performance of SPR sensors based on optical waveguides can be changed by tuning several parameters, such as the dimensions and the shape of the waveguides, the refractive index of the core, and the metal nanofilms used to excite the SPR phenomenon. In this work, in order to develop, experimentally test, and compare several polymer-based plasmonic sensors, realized by using waveguides with different core refractive indices, optical adhesives and 3D printed blocks with a trench inside have been used. In particular, the sensors are realized by filling the blocks' trenches (with two plastic optical fibers located at the end of these) with different UV-cured optical adhesives and then covering them with the same bilayer to excite the SPR phenomenon. The developed SPR sensors have been characterized by numerical and experimental results. Finally, in order to propose photonic solutions for healthcare, a comparative analysis has been reported to choose the best sensor configuration useful for developing low-cost biosensors. [ABSTRACT FROM AUTHOR]

A hollow-core D-shaped optical fiber-based surface plasmon resonance (SPR) sensor for low-loss and highly sensitive liquid analytes detection is theoretically investigated. The gold (Au) metal nanolayer is coated on the cladding etched D-shaped flat surface to develop the plasmonic effect. The nanolayer coating on the outer flat surface is very easy compared to the inside hollow-core, so our hollow-core sensor manufacturing is too easy compared to other hollow-core refractive indices (RIs) detection sensors. The resonance effect between analytes filled fundamental guided core mode and surface plasmon polariton mode of the D-shaped hollow-core optical fiber sensor is used to obtain the detections of analytes RIs variations. We have found good linear results ( R 2 > 0. 9 9) in analytes RIs versus resonance wavelength for gold layers thicknesses for the analytes RIs range of 1.45–1.52. This hollow-core D-shaped optical fiber sensor achieves the maximum wavelength sensitivity of 23500 nm RIU − 1 and a corresponding resolution of 4. 2 6 × 1 0 − 6 RIU. We have obtained the maximum figure of merit (FOM) of 228 1/RIU. The proposed sensor may be highly active in detecting the biological and chemical liquid analytes. [ABSTRACT FROM AUTHOR]

In recent decades, the Surface Plasmon Resonance (SPR) phenomenon has been utilized as an underlying technique in a broad range of application fields. Herein, a new measuring strategy which harnesses the SPR technique in a way that is different from the classical methodology was explored by taking advantage of the characteristics of multimode waveguides, such as plastic optical fibers (POFs) or hetero-core fibers. The sensor systems based on this innovative sensing approach were designed, fabricated, and investigated to assess their ability to measure various physical features, such as magnetic field, temperature, force, and volume, and to realize chemical sensors. In more detail, a sensitive patch of fiber was used in series with a multimodal waveguide where the SPR took place, to alter the mode profile of the light at the input of the waveguide itself. In fact, when the changes of the physical feature of interest acted on the sensitive patch, a variation of the incident angles of the light launched in the multimodal waveguide occurred, and, as a consequence, a shift in resonance wavelength took place. The proposed approach permitted the separation of the measurand interaction zone and the SPR zone. This meant that the SPR zone could be realized only with a buffer layer and a metallic film, thus optimizing the total thickness of the layers for the best sensitivity, regardless of the measurand type. The proposed review aims to summarize the capabilities of this innovative sensing approach to realize several types of sensors for different application fields, showing the high performances obtained by exploiting a simple production process and an easy experimental setup. [ABSTRACT FROM AUTHOR]

In this work, F e 2 O 3 was investigated as a doping agent for poly(methyl methacrylate) (PMMA) in order to enhance the plasmonic effect in sensors based on D-shaped plastic optical fibers (POFs). The doping procedure consists of immerging a premanufactured POF sensor chip in an iron (III) solution, avoiding repolymerization and its related disadvantages. After treatment, a sputtering process was used to deposit a gold nanofilm on the doped PMMA in order to obtain the surface plasmon resonance (SPR). More specifically, the doping procedure increases the refractive index of the POF's PMMA in contact with the gold nanofilm, improving the SPR phenomena. The doping of the PMMA was characterized by different analyses in order to determine the effectiveness of the doping procedure. Moreover, experimental results obtained by exploiting different water–glycerin solutions have been used to test the different SPR responses. The achieved bulk sensitivities confirmed the improvement of the plasmonic phenomenon with respect to a similar sensor configuration based on a not-doped PMMA SPR-POF chip. Finally, doped and non-doped SPR-POF platforms were functionalized with a molecularly imprinted polymer (MIP), specific for the bovine serum albumin (BSA) detection, to obtain dose-response curves. These experimental results confirmed an increase in binding sensitivity for the doped PMMA sensor. Therefore, a lower limit of detection (LOD), equal to 0.04 μM, has been obtained in the case of the doped PMMA sensor when compared to the one calculated for the not-doped sensor configuration equal to about 0.09 μM. [ABSTRACT FROM AUTHOR]

A surface-modified D-type photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is reported for application as a polarization filter and refractive index sensor. The gold film is deposited on the surface of the designed fiber structure to stimulate the SPR effect. Through etching, the upper surface of the designed structure forms an angle of 170°. The etching angle changes the distance between the fiber core and the surface of gold film to enhance the local field SPR effect. The designed optical device is numerically simulated using the finite element method (FEM), the mode distribution is studied, and the coupling phenomenon is analyzed. At a wavelength of 1.31 µm, the y-polarization loss is 1307.90 dB/cm, while the loss of x-polarization is 1.13 dB/cm; at 1.55 µm, the y-polarization loss is 1755.19 dB/cm, while the x-polarization loss is only 1.24 dB/cm. In the case of the same structure parameters as the proposed polarization filter, of which communication window is 1.55 µm, the designed structure also serves as a refractive index sensor from 1.330 to 1.365. The average sensitivity of the refractive index sensor is up to 4857 nm/RIU, and the highest sensitivity is 7588 nm/RIU when the refractive index is 1.365. The results show that the reported SPR-based PCF simultaneously implements dual communication window polarization filtering and refractive index sensing. Hence, the designed device has promising applications with good filtering and sensing performance. [ABSTRACT FROM AUTHOR]

Small gold nanoparticles (GNPs) show special catalytic activity for hydrogen (H2) dissociation reaction, which is essential and important in understanding the hydrogen oxidation reaction in hydrogen energy source. To insight on catalytic properties of GNPs, we simulated H2 dissociation paths on neutral gold clusters (GCs) Aun (n = 1–6) and positively charged GCs Aun+ (n = 3–5), which are possible active sites on GNPs. The calculated results show that H2 dissociation on GCs follows a homolytic cleavage reaction process. Light irradiation and water environment are considered for H2 dissociation on Aunδ+ (n = 3–5, δ = 0 and +1) clusters. The calculated results show that when the incident light has a low energy close to the surface plasmon resonance (SPR) region of GNPs, the light can effectively reduce the H2 dissociation barrier, and an oxidation dissociation process is found for the water‐assisted H2 dissociation reaction. [ABSTRACT FROM AUTHOR]

V-ATPase is an important factor in synaptic vesicle acidification and is implicated in synaptic transmission. Rotation in the extra-membranous V1 sector drives proton transfer through the membrane-embedded multi-subunit V0 sector of the V-ATPase. Intra-vesicular protons are then used to drive neurotransmitter uptake by synaptic vesicles. V0a and V0c, two membrane subunits of the V0 sector, have been shown to interact with SNARE proteins, and their photo-inactivation rapidly impairs synaptic transmission. V0d, a soluble subunit of the V0 sector strongly interacts with its membrane-embedded subunits and is crucial for the canonic proton transfer activity of the V-ATPase. Our investigations show that the loop 1.2 of V0c interacts with complexin, a major partner of the SNARE machinery and that V0d1 binding to V0c inhibits this interaction, as well as V0c association with SNARE complex. The injection of recombinant V0d1 in rat superior cervical ganglion neurons rapidly reduced neurotransmission. In chromaffin cells, V0d1 overexpression and V0c silencing modified in a comparable manner several parameters of unitary exocytotic events. Our data suggest that V0c subunit promotes exocytosis via interactions with complexin and SNAREs and that this activity can be antagonized by exogenous V0d. [ABSTRACT FROM AUTHOR]

This manuscript has analyzed a gold-coated photonic crystal fiber-based single-polarization filter with D-shape for a span of wavelength from 1.408 to 1.652 μm with particular applications in S + U bands. An asymmetric arrangement of air holes has been adopted to allow high birefringence and cross-talk. The filter displays strong filtering characteristics, having a significant confinement loss of 1682.5 dB/cm for the x-direction at a 1.652 μm wavelength while simultaneously possessing a very low intensity in the y-polarization at only 85.89 dB/cm. Additionally, its cross-talk can reach up to 1387 dB, with a 160 dB extinction ratio at a higher wavelength of 1.652 μm for a fiber length of 1000 μm. Thus, the filter can be utilized for both the electromagnetic spectrum's S and U optical bands. [ABSTRACT FROM AUTHOR]

The monkeypox outbreak has become a global public health emergency. The lack of valid and safe medicine is a crucial obstacle hindering the extermination of orthopoxvirus infections. The identification of potential inhibitors from natural products, including Traditional Chinese Medicine (TCM), by molecular modeling could expand the arsenal of antiviral chemotherapeutic agents. Monkeypox DNA topoisomerase I (TOP1) is a highly conserved viral DNA repair enzyme with a small size and low homology to human proteins. The protein model of viral DNA TOP1 was obtained by homology modeling. The reliability of the TOP1 model was validated by analyzing its Ramachandran plot and by determining the compatibility of the 3D model with its sequence using the Verify 3D and PROCHECK services. In order to identify potential inhibitors of TOP1, an integrated library of 4103 natural products was screened via Glide docking. Surface Plasmon Resonance (SPR) was further implemented to assay the complex binding affinity. Molecular dynamics simulations (100 ns) were combined with molecular mechanics Poisson–Boltzmann surface area (MM/PBSA) computations to reveal the binding mechanisms of the complex. As a result, three natural compounds were highlighted as potential inhibitors via docking-based virtual screening. Rosmarinic acid, myricitrin, quercitrin, and ofloxacin can bind TOP1 with KD values of 2.16 μM, 3.54 μM, 4.77 μM, and 5.46 μM, respectively, indicating a good inhibitory effect against MPXV. The MM/PBSA calculations revealed that rosmarinic acid had the lowest binding free energy at −16.18 kcal/mol. Myricitrin had a binding free energy of −13.87 kcal/mol, quercitrin had a binding free energy of −9.40 kcal/mol, and ofloxacin had a binding free energy of −9.64 kcal/mol. The outputs (RMSD/RMSF/Rg/SASA) also indicated that the systems were well-behaved towards the complex. The selected compounds formed several key hydrogen bonds with TOP1 residues (TYR274, LYS167, GLY132, LYS133, etc.) via the binding mode analysis. TYR274 was predicted to be a pivotal residue for compound interactions in the binding pocket of TOP1. The results of the enrichment analyses illustrated the potential pharmacological networks of rosmarinic acid. The molecular modeling approach may be acceptable for the identification and design of novel poxvirus inhibitors; however, further studies are warranted to evaluate their therapeutic potential. [ABSTRACT FROM AUTHOR]

The light propagation properties in a D-shaped optical fiber sensor based on the surface plasmon resonance (SPR) effect are investigated and analyzed using the finite element method. A thin gold layer is placed on the flat part of the optical fiber with a detection analyte which is chosen here human blood of refractive index (RI) depending on the excitation wavelength and their oxygenation degree. The RI detection sensitivity of oxygenated blood analyte is investigated for different parameters affecting the plasmonic interactions. We begin with fundamental physical principles, such as the coupling of evanescent and plasmonic wave modes, and discuss the optimization of optical response of biosensor depending on their physical and geometrical parameters and their impact on the sensor performance. The output parameter of the biosensor is the wavelength λ SPR corresponding to the SPR of the gold layer. The sensitivity, detection accuracy, and figure of merit are determined. The obtained results show that the detection efficiency of RI in the vicinity of that of the human blood can be enhanced by modifying the morphological parameters of biosensor such as: the thickness and width of the thin gold layer, the core radius, and volume fraction of SiO2 dopant in the GeO2 core. [ABSTRACT FROM AUTHOR]

A surface plasmon resonance based fiber optic sensor is presented experimentally using silver and nickel oxide layers. The sensitivity analysis of the sensor has been carried out. Also, the influence of the nickel oxide layer thickness upon the sensitivity has been examined. The sensitivity is enhanced with the increase in thickness of nickel oxide layer up to 10 nm and decreased at larger values. The sensor composed of 40 nm silver-10 nm nickel oxide layers provides the highest sensitivity. [ABSTRACT FROM AUTHOR]

A double-sided photonic crystal fiber (PCF) temperature and refractive index (RI) sensor based on surface plasmon resonance (SPR) is reported to simultaneously measure temperature and RI. An arc groove covered with gold is filled with chloroform for temperature detection. The D-shaped plane coated with silver is in direct contact with the analyte to provide the RI. Two independent channels distinguish temperature and RI changes, thus completely solving the cross-sensitivity problem. The sensing characteristics of the plane coating, arc coating, and inner ring coating are discussed. The influence of gold film closure on the optimum RI measurement range was identified, and the best sensing structure of chloroform as a temperature-sensitive material is obtained. The sensing characteristics of different types of metal films are investigated. It is concluded that the band separation may be achieved by plating gold film and silver film in the arc groove and D-plane, respectively. The influence of the central angle of the arc groove on the sensor characteristics was investigated. High-order resonance may be avoided at a 180° center angle. The influence of the thickness of the metal film on the sensitivity of the sensor is studied numerically, and the optimal coating thickness is 50 nm. This work simplifies the selection of the RI range of sensing materials and provides a new approach to solve the high-order resonance and band interference in SPR multi-parameter sensors. [ABSTRACT FROM AUTHOR]

As detection of cancer and diabetes diseases has captured a great attention in the field of biosensing, many ways were introduced to detect these diseases with high accuracy. This paper presents a novel use of zinc selenide (ZnSe) semiconductor material to enhance the sensitivity of a conventional Ag-based surface plasmon resonance biosensor. The proposed sensor structure is simple (BK7 prism/Ag/ZnSe), cost-effective, and easy to design and fabricate. The sensor is tested in the detection of different cancerous cells in human blood, showing an excellent sensitivity of 359 ∘ /RIU. In addiion, it is tested to detect various glucose levels in human urine, and it provides a very high performance with a sensitivity of 366.6 ∘ /RIU, which is 70% better than that of a similar reported work. Thus, the proposed biosensor is capable efficiently to detect various kinds of cancer cells and different glucose concentrations in urine. [ABSTRACT FROM AUTHOR]

Methamphetamine (MA) and cocaine (COC) are among the most abused drugs worldwide. In this study, a portable dual-channel surface plasmon resonance (SPR) biosensor based on an indirect inhibitive immunoassay was developed for the rapid and simultaneous determination of MA and COC in saliva. MA-bovine serum albumin (MA-BSA) and COC-BSA conjugates were prepared as antigens and immobilized on the sensor chip in each channel. Upon contact with the surface-immobilized antigens, MA monoclonal antibody (MA-Ab) or COC monoclonal antibody (COC-Ab) enhanced the SPR signal. The bonding of the antibodies to antigens was inhibited by the presence of MA or COC in the samples. The concentrations of the antigens and antibodies were optimized, and the resulting SPR inhibitive immunoassay exhibited good sensitivity, with limits of detection for MA and COC equal to 0.95 and 3.14 ng·mL−1, respectively. These values are below the legal limits of these drugs for vehicle drivers in China. Furthermore, the suitability of the method was confirmed using saliva from healthy donors, which demonstrated acceptable specificities with satisfactory recoveries. The results indicate that the portable SPR biosensor is facile and rapid for the sensitive determination of abused drugs. [ABSTRACT FROM AUTHOR]

ATP is related to the occurrence of many diseases, its facile, sensitive and accurate determination in real samples is needed for disease screening and treatment. Although some methods realized the sensitive detection of ATP using the signal amplification of cyclic reactions or nanoparticles, complex experimental processes limit their applications. In this paper, we report a simple surface plasmon resonance (SPR) method based on a single stranded DNA probe. The probe has dual recognition sites of ATP and Ag+; namely the ATP aptamer located in the middle of the probe and five cytosine (C) at both ends of the probe. In the absence of ATP, the probe transforms into a rigid hairpin structure by forming C-Ag+-C structures and produces a large SPR signal. However, once the probe interacts with ATP, three-dimensional structures are formed, and then the Ag+-induced probe configuration change is smaller, resulting in an small SPR signal. The signal difference before and after the probe interacts with ATP is proportional to the analyte concentration. The probe configuration change is in the optimum area for SPR detection, ensuring the sensitive ATP determination. The signal difference has a linear response with the logarithm of ATP concentration from 0.05 to 500 nM with a detection limit of 15 pM. Moreover, the strategy was demonstrated to determine ATP in serum samples with satisfactory recoveries. The results show that this simple and sensitive method has potential applications for clinical ATP determination. [ABSTRACT FROM AUTHOR]

In this work, we propose a surface plasmon resonance (SPR) biosensor based on a hybrid structure of silicon nitride (Si3N4), molybdenum trioxide (MoO3), and graphene oxide (GO) in the Kretschmann configuration. To investigate the performance parameters of the SPR biosensor, we calculate, theoretically, the reflectance spectra of the proposed model and analysed it. The investigation of various performance parameters i.e., sensitivity, detection accuracy, and quality factor, of sensor configuration are theoretically done with the optimized thickness of silver (55 nm), silicon nitride (5 nm), molybdenum trioxide (10 nm), and graphene oxide (2.55 nm) respectively. The sensitivity, detection accuracy, and figure of merit for the proposed SPR structure are found at 301 deg./RIU, 4.01, and 133 RIU−1 respectively for the detection of IgG. Furthermore, the present SPR biosensor shows improved sensitivity as compared to the other reported works. The refractive index of the analyte changes from 1.33 to 1.37 due to adsorption of the analyte at the GO surface. The proposed sensor design can detect the small change in the refractive index of the sensing media doped with the analyte. [ABSTRACT FROM AUTHOR]

An innovative optical-chemical sensor has been used to detect the 2-furaldehyde (2-FAL) in milk. The proposed sensing approach exploits the refractive index changing in a microstructured chip based on a plastic optical fiber (POF) with orthogonal micro-holes containing a specific molecularly imprinted polymer (MIP). This POF-MIP chemical chip modifies the surface plasmon resonance (SPR) phenomena excited in another sensor chip realized in POFs (SPR-POF) and connected in series. The proposed sensor configuration exploits MIP receptors avoiding any modification of the gold film of the SPR platform. This work reports the performance, particularly the high sensitivity and low detection limit, in complex matrices such as buffalo milk fortified with 2-FAL and in different commercial kinds of cow milk thermally treated for pasteurization. The measurements were carried out in about ten minutes by dropping the solution under-test on the planar D-shaped POF surface of the chemical chip. In contrast, on the gold surface of the SPR-POF platform, a water drop is always placed to excite the SPR phenomenon, which is modulated by the chemical chip via MIP-2-FAL binding. Furthermore, the experimental results demonstrated the pros and cons of the proposed sensor system. Thanks to the high sensitivity of the sensor system, the detection of 2-FAL in the diluted milk sample (1:50) was achieved. The dilution is required to reduce the interferent effect of the complex matrix. [ABSTRACT FROM AUTHOR]

A D-shaped photonic crystal fiber (PCF) polarization filter and sensor with a standard hexagonal arrangement of pores is designed. The effects of geometric parameters, metal film thickness, liquid refractive index, and optical material refractive index on polarization filtering and sensing characteristics are analyzed by the finite element method (FEM). The proposed PCF shows single-polarization filtering in communication window and has ultra-high corresponding bandwidth. At the 1.55 µm communication window band, the confinement loss of the y-polarized core mode is 819.27 dB/cm, while the x-polarized core mode is only 3.45 dB/cm. The crosstalk (CT) reached a maximum of 708.6 dB in the communication bands, and the corresponding bandwidth reaches 1000 µm when the fiber length is 1 mm. Meanwhile, the D-type PCF is widely used in sensing because it avoids filling the gold film and analyte in the internal pores. The change in the thickness of the mental coating from 39 nm to 22 nm provides the proposed PCF with sensing properties. By reducing the refractive index of fiber material, the maximum sensitivity is 10,741 nm/RIU. When the refractive index measurement range of the analyte is specified from 1.33 to 1.36, the average sensitivity reaches 7313 nm/RIU. Good performance enables the proposed compatible filtering and sensing PCF may be used in a wide range of scenarios. [ABSTRACT FROM AUTHOR]

A new gold film-molybdenum disulfide (MoS2)-hexagonal boron nitride (h-BN) three-layer sensing structure is reported for sensing applications. The strong photoelectric conversion of MoS2 and the wide forbidden band of h-BN are used to enhance the surface plasmon resonance of the gold film which greatly enhance the sensitivity of the sensor. The Au film was deposited on the optical fiber by controlled vacuum sputtering to monitor the thickness. The MoS2 nanolayer was deposited on the surface of the gold film by electrostatic adsorption and the hexagonal boron nitride nanolayer was subsequently superimposed to complete the preparation. The sensitivity of the prepared sensor was increased to 3803.0 nm/RIU, which is 71.5% higher than for the common gold film sensor. These results confirmed that this approach significantly upgraded the sensor performance. The newly proposed SPR sensor performed well using a simple structure, is low-cost, offers high accuracy and favorable specificity, and may be used for small molecule detection for medical applications. [ABSTRACT FROM AUTHOR]

Although surface plasmon resonance (SPR) methods are frequently employed due to their remarkable advantages such as reduced sample requirements, they confront a significant challenge in terms of sensitivity improvement. GeSe is an appropriate material for resolving this issue. According to the theoretical basis of the research, GeSe is a two-dimensional material which is a direct band gap semiconductor that may be utilized to promote electron transport and stimulate greater SPR phenomena. The first use of GeSe in an optical fiber sensor is reported in this study. A U-shaped optical fiber-GeSe-Au sensor is proposed. As a two-dimensional material with comparable physical characteristics to GeSe, MoS2 is compared to GeSe to characterize its influence upon the sensitivity. The sensitivity of fiber-GeSe-Au sensor is 7398.1 nm/refractive index unit (RIU), which is nearly twice as sensitive as a gold film SPR sensor and 1.5 times as sensitive as a sensor utilizing MoS2 nanosheets with the same structure. This study introduces a novel approach for enhancing the sensitivity, which gives a new option for monitoring biological substances at low concentrations with high sensitivity and stability and demonstrates that GeSe nanosheets have significant promise for future applications. [ABSTRACT FROM AUTHOR]

Temperature sensors have been widely applied in daily life and production, but little attention has been paid to the research on temperature sensors based on surface plasmon resonance (SPR) sensors. Therefore, an SPR temperature sensor with a triple structure of titanium dioxide (TiO2) film, gold (Au) film, and TiO2 nanorods is proposed in this article. By optimizing the thickness and structure of TiO2 film and nanorods and Au film, it is found that the sensitivity of the SPR temperature sensor can achieve 6038.53 nm/RIU and the detection temperature sensitivity is −2.40 nm/°C. According to the results, the sensitivity of the optimized sensor is 77.81% higher than that of the sensor with pure Au film, which is attributed to the TiO2(film)-Au-TiO2(nanorods) structure. Moreover, there is a good linear correlation (greater than 0.99) between temperature and resonance wavelength in the range from 0 °C to 60 °C, which can ensure the detection resolution. The high sensitivity, FOM, and detection resolution indicate that the proposed SPR sensor has a promising application in temperature monitoring. [ABSTRACT FROM AUTHOR]