Surface Plasmon Resonance Frequency Research Articles

Анизотропия оптических свойств металлических нанодисков

Expressions for the diagonal components of the polarizability tensor, absorption cross sections, and dimensional dependences of the surface plasmon resonance frequencies of metal nanodisks are obtained in the work in the classical approximation. Calculations of the frequency and size dependences of these characteristics for disks of different metals and with different aspect ratios are presented. The influence of the aspect ratio on the evolution of the frequency dependences of the components of the polarizability tensor and absorption cross sections is analyzed. The most significant factors influencing the splitting of the surface plasmon resonance in metal nanodisks with a small asect ratio have been determined.

In Ukrainian

In recent years, interest in studying the optical properties of metallic nanostructures has grown. This interest is primarily related to the possibility of practical application of such nanostructures in quantum optical computers, micro- and nanosensors. These applications are based on the fundamental optical effect of surface plasmon excitation. The consequence of this phenomenon is surface plasmon resonance (SPR) - an increase in the cross section of energy absorption by a metal nanoparticle as the frequency of incident light (laser radiation) approaches the SPR frequency of the nanoparticle. Plasmon structures are used to improve the efficiency of thin-film SC. In such structures, metal nanoparticles can primarily act as additional scattering elements for the long-wavelength component of sunlight illuminating SC. As a collective phenomenon, SPR can be described using kinetic approaches, ie using the Boltzmann kinetic equation for the conduction electrons of metal nanoparticles. In this work, the theory of SPR based on the kinetic equation for the conduction electrons of nanoparticles is constructed. to the well-known results derived from the Drude-Sommerfeld theory. Second, the kinetic method makes it possible to study metal nanoparticles with sizes larger or ptical conductivity tensor for spheroidal metal nanoparticles. It is shown that the effect of nanoparticle asymmetry on the ratio of the components of the optical conductivity tensor differs not only smaller than the average electron free path length. The developed theory is used to calculate the oquantitatively but also qualitatively in high-frequency and low-frequency surface scattering. It was found that in metal nanoparticles in a dielectric matrix, under SPR conditions, the full width of the SPR line in a spherical metal nanoparticle depends on both the radius of the particle and the frequency of the electromagnetic (laser) radiation exciting this SPR. It is shown that oscillations of the SPR line width with a change in the dielectric constant of the medium in which they are located can be observed in metal nanoparticles. The magnitude of these oscillations is greater the smaller the size of the nanoparticle and increases significantly with increase. As the radius of the spherical nanoparticle increases, the width of the SPR line decreases significantly and prevails around a certain constant value in media with a higher value of dielectric constant.

On the nature of plasmon-induced photocurrent enhancement in Bacteriochlorophyll c sensitized solar cells: Towards red light harvesting

Bacteriochlorophyll c (BChl c) is a naturally occurring pigment which, as a monomer, exhibits strong absorption in the red region (600–700 nm), where the dyes used in the most efficient solar cells absorb only weakly. Herein, we investigate the plasmonic enhancement of photoconversion efficiencies in BChl c sensitized solar cells using gold nanoparticles of different morphologies. Using cyclic voltammetry, a favourable band offset (~0.72 eV) between the lowest unoccupied molecular orbital of BChl c and the conduction band edge of titania photoanode was established. Further, gold nanorods with a localized surface plasmon resonance (SPR) frequency overlapping the absorption maxima of BChl c at ~670 nm were used, and compared with gold nanospheres with a SPR maximum in a region (~525 nm) where BChl c has no absorption. Gold nanorod incorporated solar cells displayed the highest photoconversion efficiency with more than 30% increase in photocurrent, compared to devices containing nanospheres and only BChl c. The results are explained using boundary element method simulations, which show a significantly enhanced scattering cross-section and local electric field in the vicinity of gold nanorods compared to the nanospheres. Electrochemical impedance spectroscopy studies indicate reduced charge transport resistance in both gold nanorod and nanosphere incorporated devices.

Investigation of a new graphene strain sensor based on surface plasmon resonance

The high confinement of surface plasmon polaritons in graphene nanostructures at infrared frequencies can enhance the light-matter interactions, which open up intriguing possibilities for the sensing. Strain sensors have attracted much attention due to their unique electromechanical properties. In this paper, a surface plasmon resonance based graphene strain sensor is presented. The considered sensing platform consists of arrays of graphene ribbons placed on a flexible substrate which enables efficient coupling of an electromagnetic field into localized surface plasmons. When the strain stretching is applied to the configuration, the localized surface plasmon resonance frequency sensitively shift. The strain is then detected by measuring the frequency shifts of the localized plasmon resonances. This provides a new optical method for graphene strain sensing. Our results show that the tensile direction is the key parameter for strain sensing. Besides, the sensitivity and the figure of merit were calculated to evaluate the performance of the proposed sensor. The calculated figure of merit can be up to two orders of magnitude, which could be potentially useful from a practical point of view.

Tailoring the Spectral Absorption Coefficient of a Blended Plasmonic Nanofluid Using a Customized Genetic Algorithm

Recently, plasmonic nanofluids (i.e., a suspension of plasmonic nanoparticles in a base fluid) have been widely employed in direct-absorption solar collectors because the localized surface plasmon supported by plasmonic nanoparticles can greatly improve the direct solar thermal conversion performance. Considering that the surface plasmon resonance frequency of metallic nanoparticles, such as gold, silver, and aluminum, is usually located in the ultraviolet to visible range, the absorption coefficient of a plasmonic nanofluid must be spectrally tuned for full utilization of the solar radiation in a broad spectrum. In the present study, a modern design process in the form of a genetic algorithm (GA) is applied to the tailoring of the spectral absorption coefficient of a plasmonic nanofluid. To do this, the major components of a conventional GA, such as the gene description, fitness function for the evaluation, crossover, and mutation function, are modified to be suitable for the inverse problem of tailoring the spectral absorption coefficient of a plasmonic nanofluid. By applying the customized GA, we obtained an optimal combination for a blended nanofluid with the desired spectral distribution of the absorption coefficient, specifically a uniform distribution, solar-spectrum-like distribution, and a step-function-like distribution. The resulting absorption coefficient of the designed plasmonic nanofluid is in good agreement with the prescribed spectral distribution within about 10% to 20% of error when six types of nanoparticles are blended. Finally, we also investigate how the inhomogeneous broadening effect caused by the fabrication uncertainty of the nanoparticles changes their optimal combination.

Computational Investigation of Antifouling Property of Polyacrylamide Brushes.

Antifouling materials and coatings have broad fundamental and practical applications. Strong hydration at polymer surfaces has been proven to be responsible for their antifouling property, but molecular details of interfacial water behaviors and their functional roles in protein resistance remain elusive. Here, we computationally studied the packing structure, surface hydration, and protein resistance of four poly(N-hydroxyalkyl acrylamide) (PAMs) brushes with different carbon spacer lengths (CSLs) using a combination of molecular mechanics (MM), Monte Carlo (MC), and molecular dynamics (MD) simulations. The packing structure of different PAM brushes were first determined and served as a structural basis for further exploring the CSL-dependent dynamics and structure of water molecules on PAM brushes and their surface resistance ability to lysozyme protein. Upon determining an optimal packing structure of PAMs by MM and optimal protein orientation on PAMs by MC, MD simulations further revealed that poly(N-hydroxymethyl acrylamide) (pHMAA), poly(N-(2-hydroxyethyl)acrylamide) (pHEAA), and poly(N-(3-hydroxypropyl)acrylamide) (pHPAA) brushes with shorter CSLs = 1-3 possessed a much stronger binding ability to more water molecules than a poly(N-(5-hydroxypentyl)acrylamide) (pHPenAA) brush with CSL = 5. Consequently, CSL-induced strong surface hydration on pHMAA, pHEAA, and pHPAA brushes led to high surface resistance to lysozyme adsorption, in sharp contrast to lysozyme adsorption on the pHPenAA brush. Computational studies confirmed the experimental results of surface wettability and protein adsorption from surface plasmon resonance, contact angle, and sum frequency generation vibrational spectroscopy, highlighting that small structural variation of CSLs can greatly impact surface hydration and antifouling characteristics of antifouling surfaces, which may provide structural-based design guidelines for new and effective antifouling materials and surfaces.

Immobilization and plasmon-enhanced fluorescence of EGFP on Al nanohole arrays

Enhanced Green Fluorescent Protein has been covalently immobilized on thin perforated Al films with short-order nanohole arrays using (3-Glycidyloxypropyl)trimethoxysilane and native aluminum oxide layer. The nanoholes’ diameter varied in range 60–120 nm, allowing to tune the surface plasmon resonance frequency. The fluorescence intensity enhancement up to factor 2.75 for the nanohole arrays with the largest overlap between EGFP fluorescence band and surface plasmon resonance.

The Simulation of a Surface Plasmon Resonance Metallic Grating for Maximizing THz Sensitivity in Refractive Index Sensor Application

Nowadays, the simplicity of both designing and fabrication process of a terahertz (THz) resonator-based sensing technique leads to its ongoing development. The consumable THz resonator needs to be easily integrated into an existing terahertz time domain spectroscopy (THz TDS) measurement system. It should also be able to be fabricated in a mass scale with a low production cost. In this work, a metal-coated surface plasmon resonance- (SPR-) based sensor is simulated and designed as a low-cost refractive index sensor utilizing rigorous coupled wave analysis (RCWA). To demonstrate our methodology, we design a gold-coated grating with a polydimethylsiloxane (PDMS) as a substrate, in order to perform quantitative analysis of gasoline-toluene mixture composition, which has a refraction index variation of 0.1 at THz frequency. The grating period is tuned such that its surface plasmon resonance (SPR) frequency matches with the peak frequency of the THz TDS system. Moreover, other grating parameters, i.e., a filling factor and a grating depth, are optimized to increase the sensor sensitivity and sharpen the resonance dip. High sensitivity up to 500 GHz/RIU with a refractive index resolution up to 0.01 is numerically revealed. The H-field of the designed grating is then evaluated to indicate a strong SPR excitation. The well-developed designed grating introduces a promising, low-cost, and easily fabricated THz refractive index sensor.

Use of laser-triggered gold nanoparticle-grafted dual light and temperature-responsive polymeric sensor for the recognition of thioguanine as anti-tumor agent

Objective(s): Today, there is an urgent need for improved sensor materials for drug sensing and effective monitoring and interventions in this area are highly required to struggle drug abuse. The present study aimed to synthesize a thioguanine-responsive sensor based on a nanocomposite consisting of AuNP-grafted light- and temperature-responsive poly butylmethacrylate-co-acrylamide-co-methacrylic acid ([P(BMA-co-AAm-co-MAA)] with an On/Off switching property in the presence and absence of light radiation.Materials and Methods: The incorporation of AuNPs into the structure of a polymer as the sensing moiety allows the detection of thiol-containing drug based on established gold-sulfur chemistry. The prepared nanocomposite sensor was characterized using transmission electron microscopy, scanning electron microscopy, and Fourier-transform infrared spectroscopy. In addition, the thermal sensitivity and thermal and optical switching properties of the nanocomposite were investigated. The sensor could be triggered by laser radiation at the wavelengths matched with the surface plasmon resonance (SPR) frequency of the AuNPs, providing it with an On/Off switching property.Results: The sensor was observed to have high binding ability indicating its promising sensing applications with the wide linear responsive range of 20-250 µM and low limit of detection (0.1 µM) toward thioguanine.Conclusion: The prepared sensor could be used to detect the analyte in biological and pharmaceutical samples, while it is also efficient in the detection of thioguanine in actual samples.

In Ukrainian

A characteristic feature of metal nanoparticles is the dependence of their absorption of light (laser radiation) on the polarization of the wave and the shape of the particles, especially in the ultraviolet frequency range. Under the same conditions, the power absorbed by nanoparticles, equal in volume but different in shape, can differ by several orders of magnitude. In addition, surface plasmon resonance (SPR) takes place in metal nanoparticles — an increase in the absorption cross section of the energy of the nanoparticle as the frequency of incident laser radiation approaches the SPR frequency of the nanoparticle. The appearance of surface plasmons in the Drude-metal model and the absorption of laser radiation in metal nanoparticles at frequencies close to SPR are analyzed. Nanoparticles whose linear dimensions are much smaller than the wavelength of laser radiation are considered. It is shown that in this case the metal nanoparticle is in spatially homogeneous, but time-oscillating electric and magnetic fields. The geometric factors for elongated and flattened spheroids are calculated. It is shown that the shape of a flattened spheroid changes from a disk (e = 1) to a ball (e = 0), and an elongated spheroid changes from a needle (e = 1) to a ball (e = 0). The relationship between the transverse and longitudinal components of the width of the SPR line on the ratio of the axes of the spheroid is considered. It was found that the widths of the absorption lines of external radiation at the SPR frequencies, in addition to the shape of the particles, are also determined by the diagonal components of the nanoparticle conductivity tensor. The aim of this work is to consider the plasmon vibrations of electrons in metal nanoparticles of various shapes and to determine the frequencies at which resonant absorption of laser radiation energy can occur and to calculate the plasmon resonance line width.

Modeling of highly improved SPR sensor for formalin detection

Consumption of formalin with food is a worldwide concern and has become a serious social problem in recent years, especially in the developing societies, which are at a higher risk of danger because of the lack of satisfactory monitoring and policies. The Frequent consumption of formalin causes severe health issues that lead to critical and fatal diseases like chronic cancer. Formalin detection in food is an urgent concern, which is becoming a national issue in developing countries. In this article, a graphene-MoS2 composite 2D sheets with a TiO2-SiO2 nano-layered surface plasmon resonance (SPR) based sensor is presented for formalin detection. Analytical analysis is carried out on the performance parameters of the sensor using MATLAB commercial software. The effect of amalgamation of Graphene-MoS2 with TiO2-SiO2 layers has been studied. The sensitivity and quality factor of the sensor are found to be 98 deg. RIU−1 and 88.89 RIU−1, respectively. This sensor detects the existence of formalin by using attenuated total reflection (ATR) and evaluating the reflectance vs SPR angle and transmittance vs surface plasmon resonance frequency (SPRF) attributes. It is found that, the sensitivity of the traditional SPR based sensor is 70°/RIU, on the other hand, the graphene-MoS2 based sensor improves this sensitivity to 76°/RIU. Finally, a comparative performance study of the traditional SPR sensors and the proposed sensor is also presented.

Theoretical Investigation of Plasmonic Properties of Quantum-Sized Silver Nanoparticles

Plasmonic nanoparticles (NPs) like silver (Ag) strongly absorb the incident light and produce enhanced localized electric field at the localized surface plasmon resonance (LSPR) frequency. Enormous theoretical and experimental research has focused on the plasmonic properties of the metallic nanoparticles with sizes greater than 10 nm. However, such studies on smaller sized NPs in the size range of 3 to 10 nm (quantum-sized regime) are sparse. In this size regime, the conduction band of the metal particles discretizes, thus altering plasmon properties of the NPs from classical to the quantum regime. In this study, plasmonic properties of the spherical Ag NPs in size range of 3 to 20 nm were investigated using both quantum and classical modeling to understand the importance of invoking quantum regime to accurately describing their properties in this size regime. Theoretical calculations using standard Mie theory were carried out to monitor the LSPR peak shift and electric field enhancement as a function of the size of the bare plasmonic nanoparticle and the refractive index (RI) of the surrounding medium. Comparisons were made with and without invoking quantum regime. Also, the optical properties of metallic NPs conjugated with a chemical ligand using multi-layered Mie theory were studied, and interesting trends were observed.

A Tunable Polymer-Metal Based Anti-Reflective Metasurface.

Anti-reflective surfaces are of great interest for optical devices, sensing, photovoltaics, and photocatalysis. However, most of the anti-reflective surfaces lack in situ tunability of the extinction with respect to wavelength. This communication demonstrates a tunable anti-reflective surface based on colloidal particles comprising a metal core with an electrochromic polymer shell. Random deposition of these particles on a reflective surface results in a decrease in the reflectance of up to 99.8% at the localized surface plasmon resonance frequency. This narrow band feature can be tuned by varying the pH or by application of an electric potential, resulting in wavelength shifts of up to 30 nm. Electrophoretic particle deposition is shown to be an efficient method for controlling the interparticle distance and thereby further optimizing the overall efficiency of the anti-reflective metasurface.

Graphene-MoS2-Au-TiO2-SiO2 Hybrid SPR Biosensor: A New Window for Formalin Detection

In this article, numerically a surface plasmon resonance (SPR) biosensor is developed based on Graphene-M­­­­OS2-Au-TiO2-SiO2 hybrid structure for formalin detection. This developed sensor sensed the presence of formalin by applying attenuated total reflection (ATR). In ATR method, we developed and observed two characteristics curve, one is “SPR angle versus minimum reflectance (Rmin)” and another is “SPR frequency (SPRF) versus maximum transmittance (Tmax). In the proposed sensor, Chitosan is used as probe legend to perform specific reaction with the formalin (40% formaldehyde) as target legend. Here, graphene and MoS2 both are used as biomolecular acknowledgment element (BAE). And TiO2 as well as SiO2 bilayers are used to improve sensor sensitivity and Gold (Au) is to sharp SPR curve. In numerical results, the variation of SPRF and SPR angle for inappropriate sensing of formalin is quiet insignificant which confirms the absence of formalin. On the other hand, these variations for appropriate sensing is considerably significant that confirms the presence of formalin. At the end of this article, a study of variation of sensitivity of the proposed biosensor in corresponding to the increment of refractive index with a refractive index step 0.01 RIU is measured. In inclusion of TiO2-SiO2 bilayers with Graphene-M­­­­OS2, maximum sensitivity of 85.375% more is numerically reported.

The plasmonic nanoparticles with controlled optical properties

The gold and silver plasmon nanoparticles have been synthesized on the c-sapphire and p-silica substrates by the pulsed laser deposition method. It has been demonstrated that the variation of the thickness of as-grown gold and silver films permits producing the plasmon nanoparticles with different size and density. It provides the retuning of the frequency of surface plasmon resonance in wide spectral region.

A Numerical Approach to Design the Kretschmann Configuration Based Refractive Index Graphene-MoS2 Hybrid Layers With TiO2-SiO2 Nano for Formalin Detection

In this paper, a Kretschmann configuration based surface plasmon resonance (SPR) sensor is numerically designed using graphene-MoS2 hybrid structure TiO2-SiO2 nano particles for formalin detection. In this design, the observations of SPR angle versus minimum reflectance and SPR frequency (FSPR) versus maximum transmittance (Tmax) are considered. The chitosan is used as probe legend to perform reaction with the formalin (40% formaldehyde) which acts as target legend. In this paper, both graphene and MoS2 are used as biomolecular acknowledgment element (BAE) and TiO2 as well as SiO2 bilayers is used to improve the sensitivity of the sensor. The numerical results show that the variation of FSPR and SPR angles for inappropriate sensing of formalin is quite insignificant which confirms the absence of formalin. On the other hand, these variations for appropriate sensing are considerably significant that confirm the presence of formalin. At the end of this article, the variation of sensitivity of the proposed biosensor is measured in corresponding to the increment of a refractive index with a refractive index step 0.01 refractive index unit (RIU). In inclusion of TiO2-SiO2 bilayers with graphene-MoS2, a maximum sensitivity of 85.375% is numerically calculated.

Surface Plasmon Resonance Based Temperature Sensors in Liquid Environment.

The aim of this work is to measure the temperature variations by analyzing the plasmon signature on a metallic surface that is periodically structured and immersed in a liquid. A change in the temperature of the sample surface induces a modification of the local refractive index leading to a shift of the surface plasmon resonance (SPR) frequency due to the strong interaction between the evanescent electric field and the metallic surface. The experimental set-up used in this study to detect the refractive index changes is based on a metallic grating permitting a direct excitation of a plasmon wave, leading to a high sensibility, high-temperature range and contactless sensor within a very compact and simple device. The experimental set-up demonstrated that SPR could be used as a non-invasive, high-resolution temperature measurement method for metallic surfaces.

Graphene-MoS2 with TiO2[sbnd]SiO2 layers based surface plasmon resonance biosensor: Numerical development for formalin detection

In this article, numerically a surface plasmon resonance (SPR) biosensor is developed based on Graphene-MOS2with TiO2SiO2 hybrid structure for the detection of formalin. Based on attenuated total reflection (ATR) method, we used angular interrogation technique to sense the presence the formalin by observing the change of “minimum reflectance with respect to SPR angle” and “maximum transmittance with respect to surface plasmon resonance frequency (SPRF)”. Here, we used Chitosan as probe analyte to perform chemical reaction with formalin (formaldehyde) which is consider as target analyte. Simulation results show a negligible variation of SPRF and SPR angle for improper sensing of formalin that confirms absence of formalin whereas for proper sensing is considerably countable that confirms the presence of formalin. Thereafter, a comparison of sensitivity for different sensor structure is made. It is observed that the sensitivity without TiO2, SiO2, MoS2 and Graphene (conventional structure) is very poor and 73.67% whereas the sensitivity with graphene but without TiO2, SiO2 and MoS2 layers is 74.67% consistently better than the conventional structure. This is due to the electron loss of graphene, which is accompanying with the imaginary dielectric constant. Furthermore, the sensitivity without TiO2, SiO2 and graphene but with MoS2 layer is 79.167%. After more if both graphene and MoS2 are used and TiO2 and SiO2 layers are not used then sensitivity improves to 80.5%. This greater than before performance is due to the absorption ability and optical characteristics of graphene biomolecules and high fluorescence quenching ability of MoS2. Further again, if TiO2SiO2 composite layer is used with the Graphene-MoS2 then the sensitivity enhances from 80.5% to 82.5%. Finally, the sensitivity for the proposed structure has been carried out, and result is 82.83%, the highest value among all the previous structures to integrate the advantages of graphene, MoS2, TiO2 and SiO2.

Equivalent RLC Ladder Circuit for Scattering by Graphene-Coated Nanospheres

In this paper, an equivalent RLC ladder circuit is derived for a graphene-coated nanosphere. Using this model, it is feasible to tune the resonance frequency of graphene surface plasmons by means of closed-form formulas. To this end, the spherical Bessel and Hankel functions of the modified Mie–Lorenz coefficients are expanded in terms of polynomials and then they are expressed as simple continued fraction forms from which the parameters of the equivalent circuit are derived. It is observed that due to the presence of graphene complex surface conductivity, the impedance of each circuit element is complex, and the real part represents a positive- or negative-valued resistor and the imaginary part modeling an inductor or capacitor. The emergence of the negative resistor which results in the field enhancement is discussed in detail.

One-Pot Synthesis of Multi-Branch Gold Nanoparticles and Investigation of Their SERS Performance.

Gold nanoparticles with multiple branches have attracted intensive studies for their application in sensing of low trace molecules. A large number of the merits found on the gold nanoparticles for the above applications are attributed to the strong localized surface plasmon resonance excited by the incident radiation. However, a facile and flexible way of synthesizing the multi-branch gold nanoparticles with tunable localized surface plasmon resonance frequency is still a challenge for the plasmonic research field. Herein, we report an efficient one-pot synthesis of multi-branch gold nanoparticles method that resembles a seed-medicated approach while using no further chemicals except chloroauric acid, ascorbic acid and 4-(2-Hydroxyethyl)-1-piperazinyl]-ethanesulfonic acid. By controlling the amounts of ascorbic acid volumes in the reaction mixture, the morphology and the localized surface plasmon resonance frequency of the synthesized multi-branch gold nanoparticles can be manipulated conveniently. Moreover, using the 4-Mercaptobenzoic acid as the Raman reporter, the multi-branch gold nanoparticles show superior surface-enhanced Raman spectroscopy characteristics that can be potentially used in chemical and biological sensing.