Plasmon Resonance Of Nanoparticles Research Articles

Spatial Distributions of Single-Molecule Reactivity in Plasmonic Catalysis.

Plasmonic catalysts have the potential to accelerate and control chemical reactions with light by exploiting localized surface plasmon resonances. However, the mechanisms governing plasmonic catalysis are not simple to decouple. Several plasmon-derived phenomena, such as electromagnetic field enhancements, temperature, or the generation of charge carriers, can affect the reactivity of the system. These effects are convoluted with the inherent (nonplasmonic) catalytic properties of the metal surface. Disentangling these coexisting effects is challenging but is the key to rationally controlling reaction pathways and enhancing reaction rates. This study utilizes super-resolution fluorescence microscopy to examine the mechanisms of plasmonic catalysis at the single-particle level. The reduction reaction of resazurin to resorufin in the presence of Au nanorods coated with a porous silica shell is investigated in situ. This allows the determination of reaction rates with a single-molecule sensitivity and subparticle resolution. By variation of the irradiation wavelength, it is possible to examine two different regimes: photoexcitation of the reactant molecules and photoexcitation of the nanoparticle's plasmon resonance. In addition, the measured spatial distribution of reactivity allows differentiation between superficial and far-field effects. Our results indicate that the reduction of resazurin can occur through more than one reaction pathway, being most efficient when the reactant is photoexcited and is in contact with the Au surface. In addition, it was found that the spatial distribution of enhancements varies, depending on the underlying mechanism. These findings contribute to the fundamental understanding of plasmonic catalysis and the rational design of future plasmonic nanocatalysts.

Ultraviolet Exposure Improves SERS Activity of Graphene-Coated Ag/ZrO2 Substrates

This study reveals a significant improvement in surface-enhanced Raman scattering (SERS) activity of Ag/ZrO2 substrates covered with a few-layer graphene preliminary exposed to ultraviolet (UV) light. The SERS-active substrates are formed by the “silver mirror” deposition of Ag nanoparticles on annealed zirconia blocks. The film composed of ~3 graphene layers is grown on copper foil by a chemical vapor deposition and then wet-transferred to the SERS-active substrates. The graphene-free Ag/ZrO2 samples are found to provide an enhancement of the Raman scattering from rhodamine 6G (R6G) at a micromolar concentration, which is associated with combined effects from the surface plasmon resonance in the Ag nanoparticles and a charge transfer facilitated by zirconium dioxide. It is revealed that the SERS signal from the analyte molecules can be suppressed by a UV exposure of the Ag/ZrO2 samples due to photocatalytic activity of the wide band gap semiconductor. However, if the samples are covered with a few-layer graphene (Gr/Ag/ZrO2) it prevents the dye molecule decomposition upon the UV treatment and improves SERS activity of the substrates. The 365 nm treatment leads to a 40% increase in the 10–6 M R6G SERS spectrum intensity, while the 254 nm irradiation causes it to rise by 47%, which is explained by different responses from the surface and bulk zirconia crystals to the short and long UV wavelengths. This enhancement is attributed to the distinct responses of surface and in-depth zirconia crystals to varied UV wavelengths and underscores the pivotal role of graphene as a protective and enhancing layer.

A novel simulador for agile and graphical modeling of surface plasmon resonance based sensors

Surface plasmon resonance (SPR) sensor is a consolidated technology for analysis of biomolecular interaction, largely applied in biology and pharmaceutical research. The simulation of the surface plasmon optical excitation response is an important step in the development process of SPR based sensors. The structure, design and configuration of the desired sensor benefits from a previous simulated analyses of the generated responses, defining operational conditions and feasibility of the selected materials to composed the optical coupling layers. Here an online web-based SPR sensor’s simulator is presented. With a visual-oriented interface, enable drag & drop actions to easily and quickly model a variety of sensor arrangements. Presenting an embedded materials database for metals, glasses, 2D materials, nanoparticles, polymers, and custom substances, the simulator enables flexible configuration for sensors operating in angular and spectral modes, as well as localized SPR. The light propagation through the multilayer of materials is presented in terms of Fresnel coefficients, which are graphically displayed. The so-called SPR morphology parameters can be visualized. Moreover, sensor dynamic behavior could be knowledge by a Sensorgram simulation. Localized surface plasmon resonance (LSPR) in homogeneous and spherical nanoparticles is also present in the simulator. Simulated scenario’s in various configurations, designs and excitation were performed and compare with other simulator. The proposed simulator guarantees comparable results with low-code, agile, and intuitive flow of execution.

Studying the Potential of Copper Nanoparticles Synthesized from Staphylococcus aureus against Drug-Resistant Bacteria

Copper nanoparticles (CuNPs) have gained a lot of interest due to their tendency to combat various bacterial strains, making them potential candidates against antibiotic resistant bacteria. Green synthesis of CuNPs eradicates the potential drawbacks of other traditional methods such as high cost, toxic chemicals and adverse conditions. The objectives of current study include the preparation of CuNPs from the culture supernatant of Staphylococcus aureus and the analysis of antibacterial potential of prepared CuNPs. The synthesis of CuNPs from the culture supernatant of Staphylococcus aureus was carried out under various optimization conditions including pH, temperature, incubation time, and concentration of salt. This research study focuses on the preparation of fine and well defined CuNPs by the reduction of Cu2+ ions using the culture supernatant of clinical isolate of Staphylococcus aureus as the feasible and cost effective method. The prepared nanoparticles were characterized through various techniques including Ultraviolet Visible Spectrophotometry, Dynamic Light Scattering and Scanning electron microscopy. The prepared copper nanoparticles were studied for their antibacterial potential by the Agar Well Method against drug resistant and drug sensitive bacteria. The surface plasmon resonance of copper nanoparticles was maximum around the visible range wavelength of 380 nm which is the characteristic absorbance peak of copper nanoparticles while the dynamic light scattering analysis recorded the maximum percentage intensity of particle size distribution around 295 nm. SEM analysis showed the amorphous nature of particles with no distinct size and shape. CuNPs showed significant antibacterial potential against drug resistant Salmonella typhimurium with 29mm zone of inhibition and against drug sensitive Bacillus subtillis with 25mm zone of inhibition. The antibacterial potential of copper nanoparticles was found to be appreciable against drug resistant Salmonella typhimurium, Staphylococcus epidermis and Staphylococcus aureus.

Integration of ohmic junction and step-scheme heterojunction for enhanced photocatalysis

A novel and efficient photocatalyst, Cu2WS4/MoS2-Au plasmonic Step-scheme (S-scheme) heterojunction, was constructed for the first time and applied to remove environmental pollutants. Among all the prepared photocatalysts, the.Cu2WS4/MoS2-Au-5 exhibited the highest catalytic activity with an 89.1% reduction efficiency for Cr6+ and a 98.7% oxidation efficiency for Benzophenone-1 (BP-1) under visible light irradiation. The Cu2WS4/MoS2-Au photocatalyst exhibits stable performance and efficient photocatalytic activity due to effective charge separation, enhanced light absorption from localized surface plasmon resonance (LSPR) of gold nanoparticles, and the formation of an S-scheme heterojunction with strong oxidation–reduction capabilities. In addition, through analysis of experiments and theoretical calculations, it is speculated that the Cu2WS4/MoS2-Au follows a typical S-scheme photogenerated carrier transferring mechanism, which is verified by the finite difference time domain simulation, the free radical quenching experiments, the electron paramagnetic resonance analysis and the simulated charge density distribution. More importantly, the simulations of the work function and charge density distribution confirm the built-in electric field and the ohmic junction have been established at the interfaces between the Cu2WS4 and MoS2 (Cu2WS4/MoS2) as well as the interface between MoS2 and Au (MoS2-Au), respectively. The built-in electric field and ohmic junction enable efficient separation of photogenerated electrons and holes, ensuring the superior catalytic oxidation and reduction activities of the Cu2WS4/MoS2-Au photocatalyst. Finally, we propose a photocatalytic mechanism for the Cu2WS4/MoS2-Au plasmonic S-scheme heterojunction based on experimental results and simulated calculations. The research results of this study are significance for the development of the plasmonic S-scheme photocatalytic system.

Study of the Application of Recycled Gold Nanoparticles in Coatings for Eyewear Lenses

The surface plasmon resonance of gold nanoparticles causes visible light absorption and scattering effects that may be used in optical coatings for eliminating blue light emission from display monitors, for blocking UV light, and for decorative applications. This study examines the achievement of functional properties provided by gold nanoparticles in a commercially established C60 fullerene-coated eyewear product. The gold nanoparticles used were sourced from recycling rapid lateral flow tests (LFIA), which use gold nanoparticles as test markers. After the gold’s recovery, Ultrasonic Spray Pyrolysis (USP) with freeze-drying was used for the synthesis of new gold nanoparticles, to be used in optical coatings. The gold nanoparticles were examined with SEM, TEM, DLS, zeta potential, BET, and Vis-NIR for characterising their shapes and sizes, as is required for determination of the surface plasmon resonance effect. After applying the newly produced gold nanoparticles with fullerene C60 in a combined coating for eyewear lenses, the absorption and transmission of the lenses were determined for establishing changes in the coating’s functionality. The results show that enhancing the fullerene C60 coating with gold nanoparticles improves light absorption and reflectance for blue and UV light further, which may be evaluated as beneficial for the eyewear user, as the reduction in eye strain is increased due to the coating.

Leveraging Coupling Effect-Enhanced Surface Plasmon Resonance of Ruthenium Nanocrystal-Decorated Mesoporous Silica Nanoparticles for Boosted Photothermal Immunotherapy.

Photothermal immunotherapy (PTI) has emerged as a promising approach for cancer treatment, while its efficacy is often hindered by the immunosuppressive tumor microenvironment (TME). Here, this work presents a multifunctional platform for tumor PTI based on ruthenium nanocrystal-decorated mesoporous silica nanoparticles (RuNC-MSN). By precisely regulating the distance between RuNC on MSN, this work achieves a remarkable enhancement in surface plasmon resonance of RuNC, leading to a significant improvement in the photothermal efficiency of RuNC-MSN. Furthermore, the inherent catalase-like activity of RuNC-MSN enables effective modulation of the immunosuppressive TME, thereby facilitating an enhanced immune response triggered by the photothermal effect-mediated immunogenic cell death (ICD). As a result, RuNC-MSN exhibits superior PTI performance, resulting in pronounced inhibition of primary tumor and metastasis. This study highlights the rational design of PTI agents with coupling effect-enhanced surface plasmon resonance, enabling simultaneous induction of ICD and regulation of the immunosuppressive TME, thereby significantly boosting PTI efficacy.

Preparation and characterization of ZnO composite nanomaterials in chitosan oligosaccharide iodine solution

AbstractComposite nanomaterials of ZnO/chitosan oligosaccharide (ZnO/COS) and ZnO/chitosan oligosaccharide iodine (ZnO/CTS‐I2) were expected to have effective antimicrobial effects due to the synergistic effects of the components. In this work, we present a method to synthesize ZnO nanoparticles with size of 12.3‐15.0 nm stabled in COS with low molecular weight (Mw) 3,321 g/mol and COS‐I2 complex by precipitation of Zn2+ with NaOH at pH 9, and then ultrasonic treatment to form ZnO nanoparticles. The UV‐Vis spectra of ZnO/COS and ZnO/COS‐I2 composite nanomaterials both appeared absorption peaks typical for surface plasmon resonances of ZnO nanoparticles in solution at 372 and 370 nm, respectively. X‐ray diffraction (XRD) patterns confirmed the formation of ZnO/COS‐I2 with wurtzite crystal structure characterized in both materials. The FT‐IR spectra of COS, COS‐I2, nano ZnO/COS, and nano ZnO/COS‐I2 were measured. The characteristic peaks for the bonding vibrations of –OH and –NH2 groups of ZnO/COS and ZnO/COS‐I2 shifted to a larger wavenumber than that of COS. The prepared ZnO/COS and ZnO/COS‐I2 nanocomposite materials may have potential for application as antibacterial agents used in medicine, food, and agricultural product preservation, control of harmful microorganisms on plants, and plant growth promotion.

Faraday rotation enhancement due to proximity effect of surface plasmon resonance in magnetoplasmonic colloidal mixtures

The modification of Magneto-optic Faraday Rotation (MFR) based on Surface Plasmon Resonance (SPR) of noble metal nanoparticles (NP) has been an exciting field of research. The underlying physical mechanisms are intriguing and correspond to various observation patterns in composite magnetoplasmonic systems. Exploiting the immense potential of SPR phenomenon for excellent electromagnetic field confinement and energy transfer to a wide variety of dimensionally different nanostructures, we report MFR measurements in typical magnetoplasmonic colloidal mixtures of separately synthesized cobalt ferrite (CoFe2O4) and gold (Au) NP at wavelength of 532 nm where we have observed a spectacular possibility for “proximity effect” based plasmonic enhancement of MFR, for the very first time. The Langevin-type MFR patterns show a strong dependence on the concentrations of participating systems, where a typical optimum concentration produced a significant enhancement in MFR. For both the entities present in the liquid, a mutually dependent optimum concentration was necessary to obtain the Langevin pattern as well as MFR enhancement, confirming the influence from SPR due to the proximity effect. The observations open up exciting possibilities to apply SPR to discover novel magnetoplasmonic phenomena underlined by proximity effects, in addition to eluding constrained procedures to synthesize composite magnetoplasmonic systems.

Tuning the plasmon resonance of Au-Ag core-shell nanoparticles: The influence on the visible light emission for inorganic fluorophores application

In this study, the gold and gold-silver (Au-Ag) core-shell nanoparticles were synthesized via chemical reduction method at different types and quantities of precursor materials. Initially, the gold nanoparticles were prepared with different reducing agents (i.e., sodium borohydride, sodium citrate, and ascorbic acid) and their composites. The optical absorbance, morphology, and size distribution of gold nanoparticles were analyzed to observe the best deposition conditions, used for the Au-Ag core-shell synthesis. Then, the Au-Ag core-shell nanoparticles were grown at four different quantities (i.e., 175 µL, 200 µL, 225 µL, and 250 µL) of silver nitrate precursor to study their effects on the fluorescence property. Optical absorbance, transmission electron microscopy, and laser scanning confocal microscopy were used to characterize the as-synthesized Au-Ag core-shell nanoparticles. From the results of optical absorbance, a single peak is seen for gold nanoparticles while two peaks (major and minor peaks) are observed for Au-Ag core-shell nanoparticles. The sizes of gold and core-shell particles observed from TEM measurement are less than 10 nm, which is typically used in fluorescence applications. The CoSh-2 sample showed a better fluorescence property compared to other core-shell samples. With a rise in exposure time in a laser with a specific wavelength of 405 nm, the intensity of fluorescence declined more for the filter having shorter wavelengths than larger wavelengths. Analyzing these results can be useful to understand the perspective applications of Au-Ag core-shell nanoparticles like synthetic fluorophores application.

Synergistic Enhancement of Photocatalytic CO2 Reduction by Built-in Electric Field/Piezoelectric Effect and Surface Plasmon Resonance via PVDF/CdS/Ag Heterostructure.

Photocatalytic reduction of CO2 using solar energy is an effective means to achieve carbon neutrality. However, the photocatalytic efficiency still requires improvements. In this study, polyvinylidene fluoride (PVDF) ferroelectric/piezoelectric nanofiber membranes are prepared by electrospinning. Cadmium sulfide (CdS) nanosheets are assembled in situ on the surface of PVDF based on coordination between F- and Cd2+ , and then Ag nanoparticles are deposited on CdS. Because of the synergistic effect between localized surface plasmon resonance of Ag nanoparticles and the built-in electric field of PVDF, the CO2 photocatalytic reduction efficiency using PVDF/CdS/Ag under visible light irradiation is significantly higher than that of any combination of CdS, CdS/Ag, or PVDF/CdS. Under micro-vibration to simulate air flow, the CO2 reduction efficiency of PVDF/CdS/Ag is three times higher than that under static conditions, reaching 240.4µmol g-1 h-1 . The piezoelectric effect caused by micro-vibrations helps prevent the built-in electric field from becoming saturated with carriers and provides a continuous driving force for carrier separation.

Relative Humidity Optical Sensor Based on Self-Assembled Gold Nanoparticles Covered with Nafion

The detection of humidity plays a vital role in healthcare, industrial, and scientific areas, and the development of an ideal sensor is in continuous progress. In this work, a relative humidity (RH) optical sensor based on localized surface plasmon resonance of self-assembled gold nanoparticles formed by thermal dewetting and coated with Nafion fluoropolymer is under study. Sensor performance has been found to substantially depend on Nafion layer thickness. The best sensing element—an array of gold nanoparticles covered with a 300 nm-thick Nafion—has been shown to possess a linear response in a wide dynamic range of 0–85% RH with a limit of detection down to 0.12%. Thus, a simple and low-cost method for high-accuracy RH detection has been demonstrated.

Efficiency Enhancement of Biophotovoltaic Solid‐State Solar Cells

Biophotovoltaic solid‐state solar cells are new environmentally friendly solar cells inspired by photosynthesis phenomena. Photosystem I, a complex protein located in the chloroplast of the plant leaves that has a principal role in light absorption, is the most common light absorber used in biophotovoltaic solid‐state solar cells. Low efficiency and low current density are the main challenges in this kind of solar cell. Herein, to vacillate the motion of electrons and holes, carbon nanotubes and tyrosine are used as transfer layers and to increase light absorbance, a solution of Photosystem I with silver nanoparticles as an absorber layer is used. It is shown that the short circuit current density and the efficiency can be enhanced to 6.61 mA cm−2 and 0.83%, respectively which are the highest values for current density and efficiency reported for this kind of solar cell. These enhancements are due to the high electrical conductivity of carbon nanotubes, proper porosity of tyrosine, and the localized surface plasmon resonance of silver nanoparticles induced under light irradiation. The results can illuminate hopes and dreams for biophotovoltaic solid‐state solar cells with higher current density and higher efficiency.

Nuclear-Electronic Orbital Quantum Dynamics of Plasmon-Driven H2 Photodissociation.

Leveraging localized surface plasmon resonances of metal nanoparticles to trigger chemical reactions is a promising approach for heterogeneous catalysis. First-principles modeling of such processes is challenging due to the large number of electrons and electronic excited states as well as the significance of nuclear quantum effects when hydrogen is involved. Herein, the nonadiabatic nuclear-electronic quantum dynamics of plasmon-induced H2 photodissociation near an Al13- cluster is simulated with real-time nuclear-electronic orbital time-dependent density functional theory (RT-NEO-TDDFT). This approach propagates the nonequilibrium quantum dynamics of both electrons and protons. The plasmonic oscillations are shown to inject hot electrons into the antibonding orbital of H2, thereby inducing H2 dissociation. The quantum mechanical treatment of the hydrogen nuclei leads to faster H2 photodissociation and slightly larger isotope effects. Analysis of the nonequilibrium electronic density suggests that these findings stem from enhanced excited-state electronic coupling between the plasmonic mode and the H2 antibonding orbital due to proton delocalization or zero-point energy effects. Given the low computational overhead for including nuclear quantum effects with the RT-NEO-TDDFT approach, this work paves the way for simulating nonadiabatic nuclear-electronic quantum dynamics in other plasmonic systems.

Thermogalvanic gel patch for self-powered human motion recognition enabled by photo-thermal-electric conversion

Quasi-solid-state electrolytes offer a cheap, leak-free, and scalable way to convert heat directly into electricity for wearable electronics. However, the limited temperature difference with the environment poses a challenge for the extensive application of thermoelectric gels. Currently, photo-thermal-electric (PTE) conversion is an environmentally-friendly technology to exploit the thermogalvanic effect of gels. Here, we report a smart light-driven flexible PTE gel for self-powered human motion monitoring. The whole structure takes advantage of the low thermal conductivity and high output power of poly(vinyl alcohol)/polydimethylsiloxane (PVA-PDMS) gels with Fe2+/3+ as a redox pair, together with the local surface plasmon resonance (LSPR) of Au nanoparticles (AuNPs)@SiO2-PDMS composite film. This enables simultaneous high thermogalvanic and photothermal performance, with an open circuit voltage of up to 12 mV and a short circuit current exceeding 1.25 A m−2 at a temperature difference of up to 9 °C under one sun. The PTE gel is fabricated into a proof-of-concept self-powered patch, which can actively distinguish human motions in real time by recognizing the switching of solar radiation stimulated by arm swing. This work provides thermogalvanic gels with a new opportunity in self-powered wearable sensing that may greatly promote the progress of intelligent medical electronics.

Photocatalysis of Metallic Nanoparticles: Interband vs Intraband Induced Mechanisms.

Photocatalysis induced by localized surface plasmon resonance of metallic nanoparticles has been studied for more than a decade, but photocatalysis originating from direct interband excitations is still under-explored. The spectral overlap and the coupling of these two optical regimes also complicate the determination of hot carriers' energy states and eventually hinder the accurate assignment of their catalytic role in studied reactions. In this Featured Article, after reviewing previous studies, we suggest classifying the photoexcitation via intra- and interband transitions where the physical states of hot carriers are well-defined. Intraband transitions are featured by creating hot electrons above the Fermi level and suitable for reductive catalytic pathways, whereas interband transitions are featured by generating hot d-band holes below the Fermi level and better for oxidative catalytic pathways. Since the contribution of intra- and interband transitions are different in the spectral regions of localized surface plasmon resonance and direct interband excitations, the wavelength dependence of the photocatalytic activities is very helpful in assigning which transitions and carriers contribute to the observed catalysis.

Morphology-Controlled Growth of Crystalline Ag-Pt-Alloyed Shells onto Au Nanotriangles and Their Plasmonic Properties.

The surface plasmon resonance of noble-metal nanoparticles depends on nanoscale size, morphology, and composition, and provides great opportunities for applications in biomedicine, optoelectronics, (photo)catalysis, photovoltaics, and sensing. Here, we present the results of synthesizing ternary metallic or trimetallic nanoparticles, Au nanotriangles (Au NTs) with crystalline Ag-Pt alloyed shells, the morphology of which can be adjusted from a yolk-shell to a core-shell structure by changing the concentration of AgNO3 or the concentration of Au NT seeds, while the shell thickness can be precisely controlled by adjusting the concentration of K2PtCl4. By monitoring the growth process with UV-vis spectra and scanning transmission electron microscopy (STEM), the shells on the Au NT-Ag-Pt yolk-shell nanoparticles were found to grow via a galvanic replacement synergistic route. The plasmonic properties of the as-synthesized nanoparticles were investigated by optical absorbance measurements.

Optical Binding of Metal Nanoparticles Self‐Reinforced by Plasmonic Surface Lattice Resonances

AbstractOptical binding of metal nanoparticles (NPs) provides a promising way to create tunable photonic materials and devices, where the ultrastrong interparticle interaction is generally attributed to the localized surface plasmon resonances of NPs. Here, it is revealed that the optical binding of metal NPs can be self‐reinforced by the plasmonic surface lattice resonances (PSLRs) associated with the discrete NP arrays. Through simulations and experiments, it is demonstrated that PSLRs can spontaneously arise in optically bound gold NP chains with just a few NPs when they are relatively large, e.g., 150 nm in diameter. Additionally, the PSLRs are enhanced by increasing the chain length, leading to stronger optical binding stiffness. These results reveal a previously unidentified factor that contributes to the ultrastrong optical binding of metal NPs. More importantly, this study presents a prospect for building freestanding and reconfigurable NP arrays that naturally support PLSRs for sensing and other applications.

Surface plasmon resonance of gold nanoparticle aggregates induced by halide ions

The localized surface plasmon resonance (LSPR) of metal nanoparticles is strongly dependent on geometrical and environmental factors, as well as the nanoparticle aggregation phenomena, which are exploited in a range of applications. In this work we investigate the LSPR of gold nanoparticles, produced by laser ablation in liquid (LAL), and their agglomeration induced by halides after LAL. We study the aggregation process under a range of factors like bromide concentration, temperature, and different halides. By absorption spectroscopy and electron microscopy we show that increasing bromide concentration leads to longer and more complex aggregates, with consequent red-shift and broadening of the LSPR. Simulations, in agreement with experiments, show that a red-shift of the LSPR is expected as AuNP linear chains become longer and validate this trend for different particle size and gap between particles. By using real-time absorption spectroscopy, we observe immediate growth of nanoparticles after salt addition. We also demonstrate that higher temperatures tend to suppress the aggregation process, while lower temperatures promote it. We then observe that a heavier halide like iodide tends to form a very broad LSPR indicating complex nanoparticle architectures. Finally, we show that the aggregates are disrupted by re-irradiating the colloid. These findings provide an expanded understanding into the factors ruling the aggregation phenomena, and will help developing existing applications while stimulating new ones.

Application of the localized surface plasmon resonance of silver nanoparticles for the determination of ethion in water samples

Application of the localized surface plasmon resonance of silver nanoparticles for the determination of ethion in water samples