Quadrupole Plasmon Resonance Research Articles

Quadrupole mode plasmon resonance enabled dual-band metamaterial for refractive index sensing application

In this paper, design and fabrication of a dual-band near-zero index metamaterial (MTM) structure using copper on an epoxy resin fiber (FR-4) dielectric substrate is reported for refractive index sensing applications. The primary objective is to achieve dual-band operation spanning a 1–15 GHz frequency range, with a specific focus on achieving a broad bandwidth in the C-band. The resonance of the MTM structure was ascribed to the coupling of plane electromagnetic waves with surface plasmon polaritons on the structure, resulting in a quadrupole plasmon resonance mode. Furthermore, transmission characteristics of the fabricated MTM structure were experimentally measured and found to align closely with the simulated results obtained through the finite element method in COMSOL Multiphysics. The designed MTM structure demonstrates negative and near-zero permittivity at resonance frequencies, enabling left-handed and near-zero index behavior in dual microwave frequency bands. Under room temperature conditions, the MTM sensor exhibited sensitivities of 1 GHz/RIU and 3 GHz/RIU at resonance frequencies of 2.7 and 7.3 GHz, respectively. Consequently, the MTM structure exhibits significant potential for diverse applications, serving as a valuable component in sensors, detectors, and optoelectronic devices operating in the GHz region.

Synthesis, Characterization, Acute Dermal Toxicity, Anti-inflammatory, and Wound Healing Potential of Biogenic Silver Nanoparticles in Balb C Mice.

The current study aimed to develop an economic plant-based therapeutic agent to improve the treatment strategies for diseases at the nano-scale. In the current research, silver nanoparticles were synthesized using Trillium govanianum aqueous extract. Characterizations were done using UV-visible spectrophotometer, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. In vivo biological activities such as acute dermal toxicity, wound healing, and anti-inflammatory were done on Balb C mice. Absorbance at 295 nm corresponds to the out-of-plane quadrupole Plasmonresonance while at 350 nm corresponds to in-plane dipole resonance. SEM images showed the morphology of TGAgNPs is not exactly spherical while XRD analysis shows that highly crystalline TGAgNPs with an average size of 27.94 nm. The FTIR spectrum represents sharp peaks of aldehyde, amide I, aromatic rings, and polysaccharides. The microscopic assessment did not find any epidermal and dermal layer abnormalities in Blab C mice when exposed to TGAgNPs during acute dermal toxicity. Results revealed that 1000 mg/kg is not a lethal dose. In the wound healing activity, no mortality and no abnormal signs were observed when petroleum jelly, nitrofuranose, TGaqu, and TGAgNPs-based ointments were applied. Enhanced epithelization was recorded in TGaqu and TGAgNPs treated mice (p≤0.001). The wound contraction percentage was higher in nitrofuranose-treated mice (74%) followed by TGAgNPs (71%), and TGaqu (69%) compared to vehicle-treated and open-wounded mice. The paw edema model proved the potential use of TGAgNPs and TGaqu as anti-inflammatory agents. Hence, the results proved that both TGaqu and TGAgNPs are not toxic and possessed strong anti-inflammatory and wound-healing effects due to the presence of phytochemical constituents and could be used in various drug production as a therapeutic agent.

Cylindrical Al Nano-Dimer Induced Polarization in Deep UV Region

The polarization properties of asymmetric plasmonic nanostructures originating from optical anisotropy show great application prospects in many fields, such as display, sensing, filtering, and detection. Here, we report the realization of polarization control in the deep ultraviolet (UV) region using Al nano-dimer structures. The simulation results indicated that the polarization effect was generated by the modulation of inter-coupling between the quadrupole plasmon resonances of the asymmetric dimer. By further optimizing the size and gap of the dimer, the extinction in the 200-nm deep UV region obtained a polarization ratio of 18%. This research is helpful for understanding the resonance hybridization of high-order surface plasmons in UV region and is of great significance to the emerging polarized micro-nano photonics fields, such as spin optoelectronics and deep UV optoelectronic devices.Graphical

Генерация второй гармоники монослоем сферических двухслойных наночастиц

A model is proposed for calculating the intensity of the second harmonic (SH) when light is reflected from a monolayer consisting of a dielectric core and a plasmon shell of spherical nanoparticles located near the interface of two optically transparent media. The nonlinear polarization of the interface created by nanoparticles, which is the source of SH, is calculated. An increase in the intensity of the reflected SH caused by dipole and quadrupole plasmon resonances in nanoparticles was found. It is shown that the spectral positions of the SH intensity maxima depend significantly on the particle core size and its dielectric permittivity

Ablation and Fragmentation of Gold Nanoparticles under Intense Laser Irradiation in the Spectral Regions of the Dipole and Quadrupole Plasmon Resonances

Methods of vacuum deposition and subsequent thermal treatment of thin gold films that allow obtaining both ultimately small gold nanoparticles exhibiting spectrally narrow dipole plasmon resonances and larger nanoparticles sustaining quadrupole oscillations are proposed. The influence of high-power laser radiation on both small and large metal nanoparticles in the regions of the dipole and quadrupole resonances, respectively, is investigated experimentally. High-power laser irradiation causes ablation of small particles, while large particles experience fragmentation into particles of smaller size.

Screening of Antibacterial, Anti-Biofilm, Cell Proliferation Inhibition, and Synergistic Effects of Biogenic Synthesized Silver Nanostructures Using Trillium govanianum with Antibiotics

The aim of study is to develop the economic plant-based antibacterial agents to improve the treatment strategies for bacterial infections at nano-scale. In current research silver nanostructures synthesis was carried out using Trillium govanianum aqueous extract. Characterizations were done using UV–Visible spectrophotometer, scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. Antibacterial efficacy of green-synthesized silver nanostructures and aqueous extract was evaluated via agar well diffusion method, crystal violet assay (antibiofilm analysis), tetrazolium salt assay (cell viability assay), Direct agar overlay technique, and TLC- spot screening against clinical bacterial pathogens. Synergistic effect of synthesized nanostructures, aqueous extract along with antibiotics was determined by agar disc diffusion method. Minimum inhibitory concentration was also evaluated using agar well diffusion method. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) method was used for screening of antioxidant potential effect at various concentrations (0.5, 1 and 1.5 and#181;l). The indication of major phytochemical constituents was determined using both qualitative methods and Thin Layer Chromatography (TLC). Absorbance in UV region (295 nm) corresponds to the out of plane quadrupole Plasmon-resonance while at 350 nm corresponds to in-plane dipole resonance. SEM images shows prepared the morphology of Ag nanostructures TGAgNSs is not exactly spherical while XRD analysis shows that highly crystalline TGAgNSs have been prepared with average crystallite size of 27.94 nm. The FTIR spectrum represents sharp peaks of aldehyde, amide I, aromatic rings, and polysaccharides. Minimum inhibitory concentration showed the increased bactericidal effect with increase in concentration of silver nanostructures. Maximum inhibition of E. coli, S. epidermidis, S. pyogenes, and K. pneumonia was recorded at 0.12 mg/ml concentration of TGAgNSs with 7.6.0and#177;0.0 mm, 7.6and#177;0.0 mm, 6.6and#177;0.0 mm, and 7.0and#177;0.0 mm zones of inhibition. Similarly, TGAgNSs showed maximum inhibition of E. coli, S. pyogenes, and S. marcesscens at 0.14 mg/ml concentration (8.3and#177;0.0 mm, 7.0and#177;0.0 mm, 7.0and#177;0.0 mm), respectively. Cell viability, antibiofilm assay, TLC-spot screening, and TLC-bio-autography proves the potential antibacterial effect of TGAgNSs. Synergistic effect showed greater antibacterial effect. Glycosides, saponins, flavonoids, proteins, terpenoids, alkaloids, phenols, and tannins were detected. The scavenging potential of TGAgNSs was calculated as 74% at 1.5 and#181;l. It was concluded that green synthesized nanostructures have efficient antibacterial potential and would be used in medical devices to cure infections in near future.

Screening of Antibacterial, Anti-Biofilm, Cell Proliferation Inhibition, and Synergistic Effects of Biogenic Synthesized Silver Nanostructures Using Trillium govanianum with Antibiotics

The aim of study is to develop the economic plant-based antibacterial agents to improve the treatment strategies for bacterial infections at nano-scale. In current research silver nanostructures synthesis was carried out using Trillium govanianum aqueous extract. Characterizations were done using UV–Visible spectrophotometer, scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. Antibacterial efficacy of green-synthesized silver nanostructures and aqueous extract was evaluated via agar well diffusion method, crystal violet assay (antibiofilm analysis), tetrazolium salt assay (cell viability assay), Direct agar overlay technique, and TLC- spot screening against clinical bacterial pathogens. Synergistic effect of synthesized nanostructures, aqueous extract along with antibiotics was determined by agar disc diffusion method. Minimum inhibitory concentration was also evaluated using agar well diffusion method. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) method was used for screening of antioxidant potential effect at various concentrations (0.5, 1 and 1.5 and#181;l). The indication of major phytochemical constituents was determined using both qualitative methods and Thin Layer Chromatography (TLC). Absorbance in UV region (295 nm) corresponds to the out of plane quadrupole Plasmon-resonance while at 350 nm corresponds to in-plane dipole resonance. SEM images shows prepared the morphology of Ag nanostructures TGAgNSs is not exactly spherical while XRD analysis shows that highly crystalline TGAgNSs have been prepared with average crystallite size of 27.94 nm. The FTIR spectrum represents sharp peaks of aldehyde, amide I, aromatic rings, and polysaccharides. Minimum inhibitory concentration showed the increased bactericidal effect with increase in concentration of silver nanostructures. Maximum inhibition of E. coli, S. epidermidis, S. pyogenes, and K. pneumonia was recorded at 0.12 mg/ml concentration of TGAgNSs with 7.6.0and#177;0.0 mm, 7.6and#177;0.0 mm, 6.6and#177;0.0 mm, and 7.0and#177;0.0 mm zones of inhibition. Similarly, TGAgNSs showed maximum inhibition of E. coli, S. pyogenes, and S. marcesscens at 0.14 mg/ml concentration (8.3and#177;0.0 mm, 7.0and#177;0.0 mm, 7.0and#177;0.0 mm), respectively. Cell viability, antibiofilm assay, TLC-spot screening, and TLC-bio-autography proves the potential antibacterial effect of TGAgNSs. Synergistic effect showed greater antibacterial effect. Glycosides, saponins, flavonoids, proteins, terpenoids, alkaloids, phenols, and tannins were detected. The scavenging potential of TGAgNSs was calculated as 74% at 1.5 and#181;l. It was concluded that green synthesized nanostructures have efficient antibacterial potential and would be used in medical devices to cure infections in near future.

Theoretical design of twelve-band infrared metamaterial perfect absorber by combining the dipole, quadrupole, and octopole plasmon resonance modes of four different ring-strip resonators.

Multiband metamaterial perfect absorbers (MPAs) have promising applications in many fields like microbolometers, infrared detection, biosensing, and thermal emitters. In general, the single resonator can only excite a fundamental mode and achieve single absorption band. The multiband MPA can be achieved by combining several different sized resonators together. However, it's still challenging to design the MPA with absorption bands of more than four and average absorptivity of more than 90% due to the interaction between differently sized resonators. In this paper, three absorption bands are successfully achieved with average absorptivity up to 98.5% only utilizing single one our designed ring-strip resonator, which can simultaneously excite a fundamental electric dipole mode, a higher-order electric quadrupole mode, and a higher-order electric octopole mode. As the biosensor, the sensing performance of the higher-order modes is higher than the fundamental modes. Then we try to increase the absorption bands by combining different sized ring-strip resonators together and make the average absorptivity above 90% by optimizing the geometry parameters. A six-band MPA is achieved by combining two different sized ring-strip resonators with average absorptivity up to 98.8%, which can excite two dipole modes, two quadrupole modes, and two octopole modes. A twelve-band MPA is achieved by combining four different sized ring-strip resonators with average absorptivity up to 93.7%, which can excite four dipole modes, four quadrupole modes, and four octopole modes.

Multipolar Nanocube Plasmon Mode-Mixing in Finite Substrates.

Facile control of the radiative and nonradiative properties of plasmonic nanostructures is of practical importance to a wide range of applications in the biological, chemical, optical, information, and energy sciences. For example, the ability to easily tune not only the plasmon spectrum but also the degree of coupling to light and/or heat, quality factor, and optical mode volume would aid the performance and function of nanophotonic devices and molecular sensors that rely upon plasmonic elements to confine and manipulate light at nanoscopic dimensions. While many routes exist to tune these properties, identifying new approaches-especially when they are simple to apply experimentally-is an important task. Here, we demonstrate the significant and underappreciated effects that substrate thickness and dielectric composition can have upon plasmon hybridization as well as downstream properties that depend upon this hybridization. We find that even substrates as thin as ∼10 nm can nontrivially mix free-space plasmon modes, imparting bright character to those that are dark (and vice versa) and, thereby, modifying the plasmonic density of states as well as the system's near- and far-field optical properties. A combination of electron energy-loss spectroscopy (EELS) experiment, numerical simulation, and analytical modeling is used to elucidate this behavior in the finite substrate-induced mixing of dipole, quadrupole, and octupole corner-localized plasmon resonances of individual silver nanocubes.

Quadrupole mode plasmon resonance enabled subwavelength metal-dielectric grating optical reflection filters.

A metal-dielectric subwavelength grating structure was investigated for making single-peak narrow linewidth optical reflection filters in the near-infrared region. The subwavelength grating filter structure consists of a one-dimensional periodic array of metal (gold) and dielectric (Al2O3) elements on a dielectric substrate. Optimized reflection filters have a single reflection peak with ~10 nm linewidth in the infrared region over a wide spectral band. Finite-difference time-domain (FDTD) simulations and multipole analysis show that the narrow linewidth reflection is due to the coupling of the Rayleigh anomaly wave to the quadrupole plasmon resonance mode of the subwavelength metal-dielectric grating. Additionally, it was found that the contrast of the indices of refraction of two dielectric materials in the subwavelength structure is critical for realizing optical filter effect.

Fabrication and laser-assisted modification of the Ag particles ensembles supporting quadrupole plasmon oscillations

A combination of physical vapour deposition, thermal annealing and laser irradiation was used to tailoring of the silver nanoparticles array on a quartz substrate. This method for control of optical properties is exploit 355-nm pulsed laser irradiation. Experimental separation of three main overlapped plasmonic modes, dipoles that correspond to parallel and perpendicular oscillations and quadrupole with maximum wavelength at 355 nm, in extinction spectrum of Ag nanoparticles ensembles was demonstrated. It was shown that the laser post-processing of the nanoparticles array in spectral vicinity of the quadrupole band leads to selective ablation of nanometer particles. This process resulted to close-packing of the nanoparticles ensemble on top of the substrate causing, in turn, formation of ‘hot-spots’ and absorptive bands in the near IR range. Using the laser post-processing as persistent spectral hole burning technique, a dephasing time of quadrupole plasmon resonances was experimentally defined for the first time.

Highly Wavelength-Selective Enhancement of Responsivity in Ag Nanoparticle-Modified ZnO UV Photodetector.

We proposed and demonstrated Ag nanoparticles (NPs)-decorated ZnO photodetectors for UV light sensing. After decoration of their surface with random Ag NPs, the dark current density of ZnO UV photodetectors decreases obviously. Moreover, the device exhibits an obvious increase in peak responsivity at around 380 nm, which can be attributed to the narrow-band quadrupole plasmon resonance of Ag NPs in the UV range. Meanwhile, the responsivity at the other wavelengths decreases a lot. As a result, the response peak becomes more significant, and the response of the devices presents an excellent wavelength selectivity after covering with Ag NPs. The detailed mechanism for this phenomenon was explained. We believe that our findings would open a way to harness the high-order plasmon modes in the field of UV optoelectronic devices.

Polarization bremsstrahlung of fast electrons on metal nanospheres in a dielectric matrix in view of plasmon interference effects

The paper is devoted to the theoretical analysis of polarization bremsstrahlung (PB) [1] due to scattering of fast electrons by a metal nanosphere embedded in a dielectric matrix in a frequency region in the vicinity of dipole and quadrupole plasmon resonances. Here we take into account plasmon interference effects that arise in the frequency-angular distribution of PB. These effects are a consequence of interrelation between contributions to PBs due to a plasmon on the sphere surface of different multipolarity. Our approach is based on the Fermi method of equivalent photons [2] and the Mie theory of radiation scattering by small metal particles [3]. It is shown that taking into account plasmon interference in the PB differential cross-section results in specific features in the spectral distribution of an emitted photon that depend strongly on the radiation angle and nanosphere radius.

Localized Surface Plasmon Resonance of Silver Nanotriangles Synthesized by a Versatile Solution Reaction.

The surface plasmon resonance (SPR) of silver nanoparticles can be tuned throughout the visible and near-infrared region by their shape and size. Considering SPR applications, an easy and controllable method for preparing the silver nanocrystals with defined shape and size, is necessary. In this work, the triangular silver nanoplates were synthesized by reducing Ag+ ions with ascorbic acid in the presence of silver seeds and poly(vinylpyrrolidone) (PVP) at room temperature. Both the seeds (as the nucleation sites) and PVP (as the capping reagent) played an important role in determining the edge length of the silver nanotriangles. The SPR of silver nanotriangles showed three distinct bands corresponding to the in-plane dipole, quadrupole, and out-plane quadrupole plasmon resonance, and the SPR shifted to shorter wavelengths with the decreased edge length of the silver nanotriangles as the theoretical calculation.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-1058-1) contains supplementary material, which is available to authorized users.

Tunable Dipole Surface Plasmon Resonances of Silver Nanoparticles by Cladding Dielectric Layers.

The tunability of surface plasmon resonance can enable the highest degree of localised surface plasmon enhancement to be achieved, based on the emitting or absorbing wavelength. In this article, tunable dipole surface plasmon resonances of Ag nanoparticles (NPs) are realized by modification of the SiO2 dielectric layer thicknesses. SiO2 layers both beneath and over the Ag NPs affected the resonance wavelengths of local surface plasmons (LSPs). By adjusting the SiO2 thickness beneath the Ag NPs from 5 nm to 20 nm, the dipole surface plasmon resonances shifted from 470 nm to 410 nm. Meanwhile, after sandwiching the Ag NPs by growing SiO2 before NPs fabrication and then overcoating the NPs with various SiO2 thicknesses from 5 nm to 20 nm, the dipole surface plasmon resonances changed from 450 nm to 490 nm. The SiO2 cladding dielectric layer can tune the Ag NP surface charge, leading to a change in the effective permittivity of the surrounding medium, and thus to a blueshift or redshift of the resonance wavelength. Also, the quadrupole plasmon resonances were suppressed by the SiO2 cladding layer because the dielectric SiO2 can suppress level splitting of surface plasmon resonances caused by the Ag NP coupling effect.

Dipole, Quadrupole, and Octupole Plasmon Resonance Modes in Ag Nanoring Structure: Local Field Enhancement in the Visible and Near Infrared Regions

Here, we provide a simulation based on finite-difference time-domain (FDTD) way of the properties of surface plasmons on Ag nanoring and study their electric field distribution in order to identify different multiple surface plasmon resonances. We can obtain the symmetric field distribution that parallels to the orientation of direction of incident light. We find their propagation can be controlled. And we discuss some of the parameters that influence the optical response of the Ag nanoring. Adjustment of nanoring radius (inner radius and outer radius) and height can change the absorption intensity and the resonance peaks. The simulation of the field distribution also displays that the location of the field enhancement is specified by the different resonance patterns. Dipole, quadrupole, and octupole plasmon resonance modes can be found in the Ag nanoring at resonance wavelength. This is an important step toward a thorough understanding of plasmon resonance in Ag nanorings.

Study of strong dipole and quadrupole plasmon resonance in Ag nanorings antenna

Self-organized Ag nanorings antenna were formed on quartz glass wafers by a simple chemistry reaction without any template. By using absorption measurements and three-dimensional finite-difference time-domain (3D-FDTD) calculations, the dipole and quadrupole plasmon resonances of Ag nanorings antenna were investigated experimentally and theoretically. Calculations have shown that large electric fields are confined at the quadrupole of the Ag nanoring, leading to quadrupole plasmon resonances. Compared the electric enhancement factor of the exterior surfaces of Ag nanoring, the electric enhancement factor of the interior surface is about six times excited by an incident light with 514.5 nm wavelength. Furthermore, the highest electric-field intensity of Ag nanorings is around four times larger than that for Ag nanodome with the same condition. These results pave the way to design plasmonic nanostructures for practical applications that require metallic nanoparticles with enhanced electric fields.

Fluorescence enhancement on silver nanoplates at the single- and sub-nanoparticle level.

The fluorescence intensity of a fluorescent molecule can be strongly enhanced when the molecule is near a metal nanoparticle. Hence, fluorescence enhancement has a lot of applications in the fields of biology and medical science. It is necessary to understand the mechanism for such an attractive effect, if we intend to develop better materials to improve the enhancement. In this paper, we directly image the diverse patterns of fluorescence enhancement on single Ag nanoplates by super-resolution microscopy. The research reveals that the edges or tips of the Ag nanoplate usually show a much higher ability of fluorescence enhancement than the mid part. The spatial distribution of fluorescence enhancement strongly depends on the size of the Ag nanoplate as well as the angle between the Ag nanoplate and the incident light. The experimental results above are essentially consistent with the simulated electric field by the theory of localized surface plasmon resonance (LSPR), but some irregularities still exist. We also find that fluorescence enhancement on small Ag nanoplates is mainly due to in-plane dipole plasmon resonance, while the enhancement on large Ag nanoplates is mainly due to in-plane quadrupole plasmon resonance. Furthermore, in-plane quadrupole resonance of large plates has a higher ability to enhance the fluorescence signal than the in-plane dipole plasmon resonance. This research provides many valuable insights into the fluorescence enhancement at the single- and sub-nanoparticle level, and will be very helpful in developing better relevant materials.

Numerical simulation of light absorption enhancement in microcrystalline silicon solar cells with Al nanoparticle arrays

Metal nanoparticles with low cost and high performance have good potential applications in light-trapping of solar cells. In this paper, a three-dimensional model is proposed to simulate the light absorption of microcrystalline silicon (μc-Si:H) thin film solar cells. The effects of spherical and hemispherical Al nanoparticle arrays located on the front surfaces of solar cells are investigated, and the particle radius and array period are optimized by the finite element method. The results show that the optimal Al nanoparticle arrays can enhance broadband absorption in thin film solar cells. For spherical particle arrays, the key parameter that influences light absorption in solar cells is period/radius ratio (P/R) or particle surface coverage. When P/R=4-5, the optimum integrated absorption enhancement (Eabs) is over 20% under AM1.5 illumination compared with the solar cell without nanoparticles. The value of Eabs is small and decreases with the increase of P/R when P/R>5, and Eabs is less than zero when P/RP=500 nm and R=120 nm, the spectral absorption rate as a function of wavelength shows broadband absorption including four distinct peaks, which are attributed to quadrupole plasmon resonance mode, dipole resonance mode and waveguide mode respectively according to the electric field distribution in the solar cell. For hemispherical particle arrays, the maximum value of Eabs is 24.5%, which is higher than that of the solar cell with optimized spherical particle arrays. This is due to the high coupling efficiencies of the particles, so that most of the scattered light is directly coupled into the substrate. However, the value of Eabs is very sensitive to the hemispherical particle radius. As the radius decreases, the scattering cross-section and scattering efficiency of the particle decrease dramatically. As the radius increases, the dipole plasmon resonance wavelength rapidly shifts towards longer wavelength (red shift). Both of these are detrimental to absorption enhancement of solar cells. Thus we conclude that spherical Al particle arrays are more preferable in actually fabricating the light-trapping of solar cells.

Multipole Surface Plasmon Resonance in Electrodeposited Gold Nanoparticles

Electrodeposition is a convenient, economical and template-free tool to create the gold nanostructures. A two-electrode electrochemical process is used for the deposition process. In this method by controlling the deposition time and electrode potential, nearly spherical and rod-like gold nanostructures were synthesized through the reduction of Chlorauric acid with citric acid as a complexing agent. Spherical gold nanostructures of different size around 2 nm to 30 nm and rod-like nanostructures with an aspect ratio 0.5 were grown directly on fluorine-doped tin oxide (FTO)-coated glass substrate. The growth mechanism of gold nanostructures is explained with the help of oriented attachment process. The contact angle measurement showed the hydrophilic nature of gold nanostructures using water with contact angle of about 56°. The optical properties showed a dipole, quadrupole and an octupole plasmon resonance mode at around 625 nm, 530 nm and 422 nm respectively. The dipole resonance peak extends further to give a broad absorption band in the near infrared region of electromagnetic waves. The refractive index sensitivity of gold nanoparticles in various solvents was investigated by calculating the red shift of surface plasmon resonance (SPR) peaks. The quadrupole plasmon resonance mode showed maximum SPR sensitivity as compared to dipole and octupole plasmon resonance mode. The controlled formation of gold nanoparticles with variation of SPR over wide range of visible region supports the potential applications in biosensors, nanoelectronics and plasmon enhanced light absorption in photovoltaics, etc.