Localized Surface Plasmon Resonance Research Articles

Plasmonic Biosensors for Health Monitoring: Inflammation Biomarker Detection.

Surface plasmon resonance (SPR) and localized SPR (LSPR) biosensors have emerged as viable technologies in the clinical detection of biomarkers for a wide array of health conditions. The success of SPR biosensors lies in their ability to monitor in real-time label-free biomarkers in complex biofluids. Recent breakthroughs in nanotechnology and surface chemistry have significantly improved this feature, notably from the incorporation of advanced nanomaterials including gold nanoparticles, graphene, and carbon nanotubes providing better SPR sensor performance in terms of detection limits, stability, and specificity. Recent progress in microfluidic integration has enabled SPR biosensors to detect multiple biomarkers simultaneously in complex biological samples. Taken together, these advances are closing the gap for their use in clinical diagnostics and point-of-care (POC) applications. While broadly applicable, the latest advancements in plasmonic biosensing are overviewed using inflammation biomarkers C-reactive protein (CRP), interleukins (ILs), tumor necrosis factor-α (TNF-α), procalcitonin (PCT), ferritin, and fibrinogen for a series of conditions, including cardiovascular diseases, autoimmune disorders, infections, and sepsis, as a key example of plasmonic biosensors for clinical applications. We highlight developments in sensor design, nanomaterial integration, surface functionalization, and multiplexing and provide a look forward to clinical applications by assessing the current limitations and exploring future directions for translating SPR biosensors for diagnostics and health monitoring. By enhancement of diagnostic accuracy, reproducibility, and accessibility, particularly in POC settings, SPR biosensors have the potential to significantly contribute to personalized healthcare and bring real-time, high-precision diagnostics to the forefront of clinical practice.

Self-referenced Digital Spectral Chromatic Local Surface Plasmon Resonance in Ultrasensitive Severe Sepsis Interleukin-6 Detection.

Clinical monitoring of cytokines, such as interleukin-6 (IL-6), enables a timely diagnosis and can significantly improve patient prognosis. In this study, we developed a rapid, label-free, ultrasensitive, and low matrix-effect method called chromatic digital nanoplasmon-metry (cDiNM) to detect IL-6 in human blood plasma. Utilizing a multiple filter configuration, two nonadjacent specific transmission wavelength bands are extracted. One is centered within the full-width-at-half-maximum (fwhm) range where the local surface plasmon resonance (LSPR) response of the 80 nm gold nanoparticles (AuNPs) is strongest, while the other band is narrowed and blue-shifted from the peak to a region with minor intensity change. Scattering images of AuNPs passing through these two bands are then captured simultaneously and independently via the red and green channels of a color scientific complementary metal-oxide-semiconductor (sCMOS) camera. This configuration allows every AuNPs' spectral chromatic image contrast to be a self-referenced subtractive analysis LSPR and facilitates evaluation of their changes induced by the IL-6 binding across numerous individual AuNPs. This method achieves IL-6 detection in blood plasma within 45 min, requiring only 0.5 mL of a 10-fold diluted, label-free sample, with a limit of detection and quantification (LOD and LOQ) of less than 19.2 and 87.8 fg/mL, respectively, and a recovery rate of 96%. In summary, cDiNM provides rapid and accurate IL-6 monitoring with promising potential for clinical application in sepsis patient care.

Machine Learning-Integrated Numerical Simulation for Predicting Photothermal Conversion Performance of Metallic Nanofluids.

Photothermal conversion in metallic nanofluids, driven by localized surface plasmon resonances, is essential for applications in biomedicine, such as cancer treatment and biosensing. However, accurately predicting photothermal conversion performance, particularly the spatial temperature distribution, remains challenging due to the complex interplay of nanoparticle properties. Existing experimental methods are labor-intensive and often insufficient in providing detailed thermal profiles. Here, a novel approach that integrates machine learning is presented with numerical simulations to predict the photothermal conversion efficiency and spatial temperature distribution in gold nanorod nanofluid. The method employs Discrete Dipole Approximation for optical property calculations, Monte Carlo simulations for light transport, and finite element methods for temperature distribution modeling. The machine learning model, trained on 1,024 cases of photothermal conversion efficiency and 2,016 cases of temperature fields, achieves rapid and accurate predictions with a high correlation coefficient (R2 = 0.972) to simulation results. This approach not only streamlines the prediction process but also provides an accessible tool for optimizing nanoparticle design, with significant implications for advancing biomedicine, energy, and sensor technologies.

Plasmonic Graphene-Gold Nanostar Heterojunction for Red-Light Photoelectrochemical Immunosensing of C-Reactive Protein.

The development of red-light photoelectrochemical (PEC) nanoimmunosensors offers new avenues for detecting clinically relevant biomarkers with high sensitivity and specificity. Herein, the first PEC nanoimmunosensor based on a plasmonic graphene and gold nanostar (AuNS) heterojunction excited with 765 nm red light is presented for label-free detection of C-reactive protein (CRP), a key biomarker of inflammation. This platform leverages the unique localized surface plasmon resonance effect of AuNSs in combination with in situ generated graphene to enhance photoelectrical conversion efficiency under 765 nm monochromatic light. This wavelength minimizes photodamage and interference from biological samples. By optimizing the nanoarchitecture and utilizing a bifunctional photoactive transduction platform, a linear detection range of 25-800 pg/mL is achieved, with a limit of detection as low as 13.3 pg/mL. The low-energy red-light activation, effective electron-hole pair separation, and signal amplification allow CRP's rapid, selective, and sensitive detection in real clinical samples from patients with low-grade chronic inflammation. The nanoimmunosensor demonstrated consistent analytical performance across multiple samples, showing potential for accurate biomarker monitoring in inflammatory disorders. This work highlights plasmonic nanomaterials to develop robust PEC immunosensors that provide scalable, noninvasive, automated, low-background noise as a highly sensitive alternative for clinical diagnostics.

Multiscale Biomimetic Evaporators Based on Liquid Metal/Polyacrylonitrile Composite Fibers for Highly Efficient Solar Steam Generation

Solar steam generation (SSG) offers a cost-effective solution for producing clean water by utilizing solar energy. However, integrating effective thermal management and water transportation to develop high-efficiency solar evaporators remains a significant challenge. Here, inspired by the hierarchical structure of the stem of bird of paradise, a three-dimensional multiscale liquid metal/polyacrylonitrile (LM/PAN) evaporator is fabricated by assembling LM/PAN fibers. The strong localized surface plasmon resonance of LM particles and porous structure of LM/PAN fibers with interconnected channels lead to efficient light absorption up to 90.9%. Consequently, the multiscale biomimetic LM/PAN evaporator achieves an outstanding water evaporation rate of 2.66kgm-2h-1 with a solar energy efficiency of 96.5% under one sun irradiation and an exceptional water rate of 2.58kgm-2h-1 in brine. Additionally, the LM/PAN evaporator demonstrates a superior purification performance for seawater, with the concentration of Na+, Mg2+, K+ and Ca2+ in real seawater dramatically decreased by three orders to less than 7mgL-1 after desalination under light irradiation. The multiscale LM/PAN evaporator with hierarchical structure regulates the water transportation as well as thermal management for highly effective solar-driven evaporation, providing valuable insight into the structural design principles for advanced SSG systems.

Ultra-Sensitive Nanoplatform for Detection of Brain-Derived Neurotrophic Factor Using Silica-Coated Gold Nanoparticles with Enzyme-Formed Quantum Dots

A fluorescence-based detection platform was developed for brain-derived neurotrophic factor (BDNF), a key biomarker of Alzheimer’s disease (AD). This platform utilizes localized surface plasmon resonance effects resulting from the interactions between silica-coated gold nanoparticles (Au@SiO2) and enzymatically synthesized quantum dots (QDs). The gold nanoparticles were silica coated via the hydrolysis of tetraethyl orthosilicate, which allowed for precise control over the distance between the nanoparticles and QDs and refined the dynamics of fluorescence quenching and enhancement. Antibody conjugation was performed via sequential amination and carboxylation, followed by EDC/NHS coupling. BDNF was detected across a range of concentrations, from 1 ng/mL to 1 ng/mL, using an alkaline phosphatase (ALP)-conjugated polyclonal antibody targeting a secondary epitope of BDNF. The enzymatic hydrolysis of p-nitrophenyl phosphate by immobilized ALP led to the formation of cadmium sulfide QDs, with the fluorescence intensity correlating directly with the BDNF concentration. This platform offers a refined and precise method for detecting BDNF and is a reliable tool for the early diagnosis of AD.

Structural Colors Go Active.

Structural colors find wide applications for color printing, intelligent display, filtering imaging, etc., owing to their benefits, including high resolution, stable properties, and dynamic tunability. This review first illustrates the mechanisms of structural color generation, such as surface plasmon resonances, localized surface plasmon resonances, Fabry-Perot resonances, Mie resonances, etc. It then proposes the recent technological strategies employed to realize dynamic structural colors. The integration of structural colors with functional materials like phase-change, along with the development of color dynamic control mechanisms such as microfluidic chips, micro-electro-mechanical system drivers, and microheaters, represents key approaches for spectrum regulation. Furthermore, the review assesses the performance, advantages, and limitations of various technologies for dynamic structural colors. Finally, this review concluded with a section on the future challenges and prospects in large-area fabrication, practical applications, and performance improvement. It explains the current typical applications, including smart windows, adaptive camouflage, sensors, etc., and explores the processing methods that can achieve large-area, high-fidelity preparation of structural colors, such as nanoimprint, deep ultraviolet lithography, immersion lithography, laser printing, etc. This field promises advancements in high-density data storage, information encryption, and broader market applications.

Plasmonic Light Emission by Inelastic Charge Transport in Ultrathin Zinc Oxide/Metal Heterostructures.

Controlling light emission from plasmonic nanojunctions is crucial for developing tunable nanoscale light sources and integrated photonic applications. It requires precise engineering of plasmonic nanocavity electrodes and a detailed understanding of electrically driven light emission. Using scanning tunneling microscopy-induced luminescence (STML), we studied plasmonic light emission from ultrathin ZnO/Ag(111) inside a silver nanocavity. At positive bias, plasmonic luminescence, caused by radiative decay of localized surface plasmons (LSP), is spectrally low-pass filtered by the ZnO layers. The emission of photon energies above the conduction band edge energy (ECB) of ZnO is suppressed, while the spectral distribution below ECB resembles the LSP resonance on Ag(111). This spectral filtering is absent at negative bias and depends on the local electronic structure, as confirmed by spatial STML mapping. Our findings demonstrate that the ZnO conduction band serves as the initial state for plasmonic luminescence driven by inelastic electron transport across the ZnO/Ag(111) interface.

Wide index optical fiber sensor based on localized surface plasmon resonance

Abstract A wide refractive index (RI) photonic crystal fiber (PCF) sensor based on localized surface plasmon resonance (LSPR) was used to detect the RI of unknown analytes, and the modified sensor was numerically analyzed. The design features a D-type fiber structure with gold nanorods as the sensing layer, which enhances the mode matching between the core mode and the plasmon, thereby effectively promoting the LSPR effect. The results of the full-vector finite element method (FEM) analysis present that the displacement of core mode constraint loss peak is more obvious in Y-polarized mode. The wavelength sensitivity and figure of merit (FOM) are used to better and more accurately evaluate and analyze the output characteristics of the sensor. The results present that the sensor has a maximum wavelength sensitivity (WS) of 26,000 nm/RIU, a resolution of 3.85×10-6 RIU, a maximum FOM of 123.6, a sensor RI range of 1.02~1.39, and excellent transmission characteristics. The sensor has a simple structure and low cost, and its wide RI range has great application potential in molecular biology detection, environmental pollution detection, food safety detection, and drug research.

Gold nanoparticles for theranostic treatment of cancer

The chemical stability, low toxicity, and relative simplicity of methods for the synthesis and modification of gold nanoparticles open up wide possibilities for their use as theranostic agents for the diagnosis and treatment of cancer. The unique properties of gold nanoparticles, known as localized surface plasmon resonance, make it possible to create theranostic agents based on these nanoparticles, combining the capabilities of both in vitro diagnostics and targeted drug delivery. The high surface-area-to-volume ratio of gold nanoparticles significantly facilitates the creation of complex nanoplatforms, which can be used in several therapeutic and diagnostic areas at once.

Localized Surface Plasmon Resonance of Ag-SiO2 Core–Shell Nanowire Tetramers

Localized Surface Plasmon Resonance of Ag-SiO2 Core–Shell Nanowire Tetramers

Cu nanoparticle geometry as the key to bicolor behavior in Oregon sunstones: An application of LSPR theory in nanomineralogy

Abstract The coloration mechanism of Oregon sunstone is a classic and controversial topic in mineralogy because of the unique coexistence of anisotropic (green-red) and isotropic (red) color zones within single feldspar crystals. After nearly 50 years of research, no models proposed to date have satisfactorily accounted for all observed optical phenomena. Here, we present high-resolution transmission electron microscopy analyses of samples prepared by focused ion beam extraction along specific crystal directions. In both the anisotropic and the isotropic color zones, we observed Cu nanoparticles (NPs) included within plagioclase but with different geometries. In the isotropic (red) zone, NPs were randomly distributed nano-spheres or nano-ellipsoids (8.7–12 nm in diameter) with an aspect ratio of 1–1.3. In contrast, in dichroic (green/red) zones, NPs were directionally aligned nano-rods (8.5–21 nm along the long axis) with an aspect ratio of ∼2.5. We applied localized surface plasmon resonance (LSPR) theory to simulate absorption spectra and developed a model to explain the observed optical properties. LA-ICP-MS and polarized UV-Vis spectroscopy were also performed to confirm our conclusions. This study systematically reveals the existence and optical influence of variably shaped metal-NP inclusions in feldspar crystals. Furthermore, it demonstrates the necessity of including LSPR in the canon of mineral coloration mechanisms. Cu-NP-bearing labradorite has been shown to exhibit third-order nonlinear optical properties, and approaches that incorporate NP shapes and sizes will assist in designing NP-embedded optical materials with tailored optical properties.

Self-assembled Cu/Cu2O with LSPR effect complexed with TCPP for inhibiting the self-oxidation process of Cu2O and significantly enhancing the degradation of tetracycline hydrochloride

This research focused on the utilization of non-precious metal copper (Cu) and meso-tetra(4-carboxyphenyl) porphyrin (TCPP), a porphyrin-based compound, to develop a ternary TCPP-Cu/Cu2O heterojunction for the treatment of tetracycline hydrochloride (TCH). The degradation efficiency of TCH by the TCPP-Cu/Cu2O reached 100 % within 30 min under visible light illumination (a 100 W Xenon lamp with 420 nm cutoff filter). The findings indicate that both Cu with localized surface plasmon resonance (LSPR) and porphyrin-based molecules play a role in augmenting the quantity and separation efficiency of photogenerated carriers. Furthermore, the integration of TCPP on the Cu/Cu2O surface also shows two other important roles, 1) preventing the photocorrosion of Cu2O, and 2) improving the hydrophilic properties of Cu2O. LC-MS analysis identified four potential degradation pathways of TCH. This study presents a viable strategy for designing non-precious metal photocatalysts utilizing LSPR and organic molecules to enhance the photocatalytic degradation efficiency of antibiotics.

A multifunctional biosensor for selective identification, sensitive detection and efficient photothermal sterilization of Salmonella typhimurium and Staphylococcus aureus.

The foodborne pathogens, e.g., Salmonella typhimurium (S. typ) and Staphylococcus aureus (S. aureus), pose a serious threat to human health. Accurate identification, rapid detection and efficient inactivation are crucial in the early diagnosis and treatment of S. typ and S. aureus. To date, however, the majority of studies have only concentrated on the construction of single-function biological platform for detection or inactivation of S. typ and S. aureus. Therefore, it is imperative to develop a multifunctional surface-enhanced Raman scattering (SERS) biosensor that can effectively sterilize S. typ and S. aureus while simultaneously achieving sensitive detection and selective identification. Herein, we designed and constructed a multifunctional SERS biosensor based on sandwich structure of "capture probe/bacteria/signal probe" in order to simultaneously identify, detect and kill S. typ and S. aureus. Aptamer-modified ZnO/Ag was used as a capture probe to accurately identify and capture the target bacteria in complex environments. Au@Ag-4-MPBA-Aptamer was employed as signal probe to provide the corresponding bacterial SERS "fingerprint" information. The SERS enhancement mechanism of the sandwich-structure ZnO/Ag-Au@Ag SERS substrate was discussed. The sandwich-type SERS biosensor exhibited the strong localized surface plasmon resonance (LSPR) effect and the detection limit for S. typ and S. aureus was as low as 10cfu/mL. Furthermore, the sandwich-type SERS biosensor offered excellent photothermal conversion efficiency (54.32%), enabling photothermal killing of target bacteria when exposed to laser irradiation. A dual enhancement strategy based on a sandwich structure was proposed to maximize the sensitivity of SERS signals using synergistic action of electromagnetic enhancement and chemical enhancement. SERS enhancement factor (EF) was as high as 4.67×105. In addition, the sandwich-type SERS biosensor not only exhibited negligible cytotoxicity, but also was proved to be a promising tool for photothermally inactivate of S. typ and S. aureus in food samples.

Plasmonic S-type Bi/TiO2@C Heterojunction Composites for Efficient Visible-Light Photocatalytic Removal of Multi-Antibiotics and Dyes

In this work, two series of plasmonic S-type heterojunction photocatalysts containing Bi, TiO2, and biochar (Bi/TiO2@C) have been developed through a biomass-assisted hydrothermal-calcination strategy, utilizing grapefruit peel as a reducing agent and C resource. The calcination temperature and the mass ratio of biomass were optimized to obtain the optimal nanocomposite, which shows excellent adsorptive and visible-light photocatalytic performance in the removal of diverse antibiotic and dye pollutants, including tetracycline, oxytetracycline, ciprofloxacin, sulfamethoxazole, sulfisoxazole, malachite green, and rhodamine B. The remarkable performance can be attributed to the enhanced absorption of light absorption resulting from the localized surface plasmon resonance effect of the semimetal Bi, and the formation of heterogeneous interface between Bi and TiO2, which accelerates the transfer of photogenerated charge. Furthermore, trapping tests and electron spin resonance (ESR) analysis reveal that ∙O2- and h+ are the primary active species involved in the removal of tetracycline. A plausible charge transfer mechanism has been proposed.

Bipyramidal gold nanoparticles-assisted plasmonic photothermal therapy for ocular applications.

Gold nanoparticles (AuNPs) play a key role in the field of nanomedicine due to their fascinating plasmonic properties as well as their great biocompatibility. An intriguing application is the use of plasmonic photothermal therapy (PPTT) mediated by anisotropic AuNPs irradiated with a near-infrared (NIR) laser for treating ocular diseases in ophthalmology. For this purpose, bipyramidal-shaped AuNPs (BipyAu), which were surface-functionalized with three different organic ligands (citrate, polystyrene sulphonate (PSS), and cetyltrimethylammonium bromide (CTAB)), were synthesized. The long-term storage stability was assured, in terms of minimal variation in aspect ratio and localized surface plasmon resonance. Better performance was achieved with BipyAu@citrate and BipyAu@PSS NPs. PPTT experiments mediated with the synthesized BipyAu NPs demonstrated that BipyAu@citrate provided the highest value of temperature increase (40 °C at 2.0 W cm-2) after 15 min of 808 nm NIR laser irradiation. The potential future clinical application in ophthalmology was assessed by in vitro cytotoxicity analysis, confirming that BipyAu@citrate NPs were biocompatible for the three major corneal cell types. Furthermore, ex vivo analysis was performed by treating pig corneas with BipyAu@citrate NPs (0.18 μg Au) and subsequent NIR laser irradiation at 808 nm for 15 min, showing distortions in the collagen type I fibrils at the ultrastructural level and promoting the flattening of the corneal surface after treatment, without inducing cell cytotoxicity. This work suggests that a precise control of the fibril distortions can be provoked by PPTT mediated with BipyAu@citrate in the NIR region, paving the way for nanomedicine to correct common deficiencies in corneal diseases.

Solar-Driven Conversion of Nitrogen and Water to Solid Fertilizer in an Outdoor 1 m2 Panel Reactor.

Harnessing solar energy to convert molecular N2 into nitrogen-rich chemicals (e.g., ammonia) provides a potential pathway for the manufacture of "solar fertilizers". However, the solar-to-ammonia (STA) efficiency of most solar fertilizer systems developed to date is less than 0.1%. Herein, an outstanding STA efficiency of ≈0.3% using a metallic molybdenum trioxide (metallic MoO3-x) photocatalyst under simulated-solar irradiation is reported, with localized surface plasmon resonance phenomena in the metallic MoO3-x photocatalyst enhancing both light utilization and N2 activation. The potential scalability of the photocatalytic technology is demonstrated in a 1m2 panel reactor system, with a high STA efficiency and good stability demonstrated over 6 days of outdoor testing, yielding a solid (NH4)2SO4 product for easy collection. The as-designed square-meter outdoor reaction system facilitates the integration of solar fertilizer technology with existing agricultural infrastructure.

Hybrid Nanofluids-Based Direct Absorption Solar Collector: An Experimental Approach

In the last years, studies have demonstrated the potential of hybrid nanofluids to enhance the performance of direct absorption solar collectors. These working fluids containing noble metals (gold, silver) are known for their local surface plasmon resonance which is the main cause for the increased absorption within the solar spectrum. In the current paper, new direct absorption solar collectors prototypes using water-ethylene glycol solution and 0.1 wt.% silver nanoparticles + reduced graphene oxide dispersed in water-ethylene glycol mixture were designed, built, and tested under outdoor conditions, at two flow rates (1.0 and 1.5 l·min−1) and two inlet temperatures (20 ∘C and 30 ∘C), over several days in September 2023, at Brasov, Romania. The results suggested that by using silver nanoparticles + reduced graphene oxide nanofluid, the efficiency is improved related to water-ethylene glycol solution. The maximum relative enhancement in efficiency was 16.72% related to the base fluid. Also, at 1.0 l·min−1, the instantaneous and accumulative energies delivered were about 13.51% and 42.91%, respectively, higher than the water-ethylene glycol solution. Finally, the current results were compared to other research carried out on full-scale direct absorption solar collectors tested in outdoor conditions.

Localized surface plasmon resonance-based optical fiber arsenic ion sensor employing Al2O3/GO nanocomposite

A novel optical fiber arsenic (As3+) sensor, to the best of our knowledge, based on a localized surface plasmon resonance (LSPR) technique, is reported in this paper. The sensor employs Al2O3/GO nanocomposite as the sensing film. An experimental investigation demonstrates that the proposed sensor is characterized with a linear response in the range of 0–20 parts per billion (ppb) As3+ concentration, high sensitivity of 0.217 nm/ppb, and remarkably low limit of detection (LOD) of 0.09 ppb, which is significantly lower than the limit set by WHO in drinking water (10 ppb). Additionally, the sensor exhibits a very fast response time of 0.5 s and exhibits high selectivity towards As3+ ions over the other heavy metal ions. Furthermore, the sensor displays a very high degree of repeatability, stability, reversibility, and reliability. To validate the proposed sensor’s real-world applicability, the sensor is employed to detect arsenic in real water samples. The obtained results exhibit strong alignment with the standard inductively coupled plasma mass spectrometry (ICPMS) method, confirming its accuracy for real-world arsenic detection.

Multi-band single bio-molecule detection through inverse-designed graphene-folded spherical particle dimers

The present research employs graphene-coated spherical nano-particles as the basis of optical dimers for multi-frequency refractive index sensing applications. Under parallelly polarized incoming waves, dual operating bands are attained owing to the presence of localized surface plasmon resonances (LSPRs) on graphene shells. Thus, enormous local near-field enrichment is detected at the gap middle as a result of plasmonic hybridization and strong coupling. The potential usage of the proposed dimer as a dual-band high-performance refractive index sensor, with the typical sensitivity of S1 = 2.8143 × 104 nm/RIU and figure of merit of FOM1 = 213.2860 RIU-1 in the first band, and sensitivity of S2 = 1.8070 × 104 nm/RIU and figure of merit of FOM2 = 305.1521 RIU-1 in the second band, is illustrated. Importantly, the enormous near-field enhancement is maintained for particles with different radii, making the element suitable for single bio-molecule recognition of various types by tuning the quality of the graphene layer. The spectral tuning is correspondingly viable after production by imposing a suitable Fermi level on the graphene shells. Finally, machine learning forward and reverse problems based on the random forest (RF), decision tree (DT), and eXtreme Gradient Boosting (XGBoost) algorithms are implemented to propose a method respectively for analysis of the sensor's performance and to design an appropriate sensor for each desired molecule.