Configuring Au and Ag nanorods for sensing applications (original) (raw)
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Different Plasmon Sensing Behavior of Silver and Gold Nanorods
The Journal of Physical Chemistry Letters, 2013
Silver nanorods (AgNRs) of ∼20 nm diameter and different lengths, which were increased up to ∼100 nm by increasing the reduction time, were prepared by a seedless synthetic approach. A linear relationship between the AgNRs aspect ratios and the LSPR peak position was observed experimentally and confirmed theoretically. The Raman signal enhancement by silver nanorods is more efficient than by gold nanorods (AuNRs) because the plasmon field intensity of AgNRs is stronger than that of AuNRs, as shown by the discrete dipole approximation calculation. The Rayleigh scattering by AuNRs is stronger than that by the AgNRs. Therefore, AuNRs are recommended for optical plasmon imaging, while AgNRs are more efficient in plasmon sensing. SECTION: Physical Processes in Nanomaterials and Nanostructures T he optical properties of the plasmonic nanoparticles can be tuned by changing their shape, 1,2 size, 3 composition, and structure (solid or hollow). 4 Common applications of the plasmonic metallic nanoparticles are based on the presence of the localized surface plasmon resonance (LSPR), 5 the electromagnetic plasmon field, 6 and the electron scavenging capability. 7,8 Plasmonic nanoparticles have been widely used as sensors because their LSPR frequency is greatly affected by the change of the dielectric function of the surrounding medium. 5,9 The LSPR extinction spectrum consists of two accumulated parts: absorption and scattering spectra. 5,10 The ratio between the scattering spectrum and absorption spectrum depends on the shape, size, and composition of the plasmonic nanoparticle; 11 this ratio increases by increasing the particle size. The absorption part of LSPR extinction spectrum was used for the photothermal applications (biological 12 and chemical systems 13 ) or in the plasmonic energy transfer to other electronic systems, which bound to the nanoparticles surface, 14 while the LSPR scattering has been used to enhance the optical properties of different chemical, photochemical, and photoelectrochemical systems by light focusing. The electromagnetic field of the plasmonic nanoparticles is useful in enhancing different electromagnetic signals such as Raman, 17 fluorescence, 16 and Rayleigh scattering. 18 Because of their broad applications, plasmonic nanoparticles with different shapes have been prepared by, various methods, such as spheres, 3 cubes, 4 octahedrons, prisms, 19 rods, 2 wires, 20,21 stars, 22,23 cages, 4 and so on. The new designation of the plasmonic nanoparticles aims to control the following: (1) the LSPR extinction peak position to fit the application requirement, (2) the ratio between LSPR absorption and scattering spectra (some applications require strong absorption spectrum, while strong scattering is needed in certain applications), and (3) obtaining the highest possible electromagnetic plasmon field.
Plasmonics, 2012
The localized surface plasmon resonance dependence on surrounding medium refractive index of Ag, Al, Au, and Cu nanoparticles is examined by electrodynamic approach. The refractive index sensitivity and sensing figure of merit (FOM) dependence of selected metal nanoparticles with similar geometry shows that although, sensing relevant parameters are shape (i. e., aspect ratio), and material dependent below the width 20 nm, but above this size these parameters are material independent under similar geometrical conditions. We have concluded that at optimum size, however, Al shows much higher refractive index sensitivity (RIS) in comparison to Au, Cu, and Ag, but FOM is higher for Ag in comparison to other metals. The observed sensing behavior is expected due to parameters like surface scattering, dynamic depolarization, radiation damping, and interband transitions, which may influence the nanorod plasmons.
Optimal Dimensions of Gold Nanorod for Plasmonic Nanosensors
Plasmonics, 2011
Localized surface plasmon resonance (LSPR) for longitudinal mode of gold nanorod is simulated by using Gans theory. The parameters like surface scattering, radiation damping, and dynamic depolarization of radiation across the surface of nanorod affecting response of free electrons towards optical excitation are considered. Simulation results show that refractive index sensitivity linearly rises with size and aspect ratio, whereas this leads to the broadening of resonant line width also. Therefore, to optimize the size of nanorod, figure of merit (FOM) is calculated and observed that optimized width is 15 nm for an aspect ratio of 2, whereas it is 12 nm for aspect ratios 3 and 4. Further, optimization by using newly modified figure of merit (MFOM) shows that optimized width is 39 nm for aspect ratio of 2 and 24 nm for 3 and 4 aspect ratios. It is also found that at aspect ratio 2, both FOM and MFOM are higher than the aspect ratios 3 and 4. The quality factor calculation for LSPR response of nanorod explains its dependence with aspect ratio and optimized dimensions.
Effect of nanoparticle geometry on sensitivity of metal nanoparticle based sensor
IOP conference series, 2019
Bio chemical detection using metal nanoparticles has been intensively investigated due to availability of robust nanoparticle synthesis methods whether chemically or using lithographic approach. SPR based sensor employs the shift of plasmonic resonance wavelength when local surrounding medium of metal nanoparticles change even slightly. The shift of the resonance wavelength depends sensitively on geometry and size of nanoparticle. The resonance wavelength and its shift were calculated numerically using boundary element method. Here, we compare the sensitivity of gold and silver nanoparticles to sense small change in refractive index of medium. Four different geometries (spherical, ellipsoidal, cylindrical, and donut-like nanoparticles) of different size were investigated to find the highest sensor sensitivity.
Refractive Index Sensitivity Analysis of Ag, Au, and Cu Nanoparticles
Plasmonics, 2011
The localized surface plasmon resonance (LSPR) spectrum of noble metal nanoparticles is studied by quasi-static approximation. Taking the sensitivity of LSPR shape to the size and shape of nanoparticle along with surrounding refractive index, parameters like refractive index sensitivity and sensing figure of merit have been determined. In the present analysis from the sensing relevant parameters, it is concluded that Ag represents a better sensing behavior than Au and Cu over the entire visible to infrared regime of EM spectrum.
The current intense interest in the properties of plasmonic nanostructures for their applications in chemical and biochemical sensors, medical diagnostics and therapeutics, and biological imaging is fundamentally based on their enhanced optical absorption and scattering properties. In this study, the optical extinction, absorption, and scattering efficiencies were calculated as a function of shape definition, aspect ratio, surrounding medium, and material selection. The discrete dipole approximation method was used, which is known to be a very useful and versatile computational tool for particles with any arbitrary shape. Relative contribution of scattering to the total extinction for the longitudinal mode was found to be significantly dependent on the aspect ratio of the nanorod in a somewhat complex manner, different from a typical linear relationship for the resonance wavelength. A slight elongation of Au nanosphere gives rise to a drastic increase in the relative scattering efficiency, which eventually reaches a maximum and begins to decrease with further increase in the aspect ratio. This is ascribed to the increasing absorptive contribution from the larger imaginary dielectric function of the metal particle in the longer wavelength region where the red-shifted excitation of the longitudinal resonance mode occurs. For transverse mode exhibiting the blue-shift in the resonance peak, on the contrary, the absorption efficiency is relatively enhanced compared to the scattering efficiency with increasing aspect ratio. This is thought to result from the dominant effect of the interband transition present in this wavelength region. Besides the dependence of plasmonic characteristics on the aspect ratio of nanorod, the DDA results for a small change of the end-cap shape and the index of the surrounding medium lead us to conclude that there exist two competing key factors: a weighting factor assigned to the shape parameter and the dielectric function of the metal particle, which control the relative enhancement in the scattering and absorption as well as the linearity of resonance wavelength with regard to the aspect ratio.
Gold and Silver nanomaterial based Optical Sensing Systems
1 wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com REVIEW Gold and silver nanomaterials (NMs) such as nanoparticles (NPs) and nanoclusters (NCs) possessing interesting optical properties have become popular sensing materials. With strong surface plasmon resonance (SPR) absorption, extraordinary stability, ease in preparation, conjugation, and biocompatibility, Au NPs are employed to develop sensitive and selective sensing systems for a variety of analytes. However, small sizes of Au and Ag NCs with interesting photoluminescence (PL) properties are used in many PL-based sensing systems for the detection of important analytes. In addition, many bimetallic AuM NMs possessing strong catalytic activity are used to develop highly sensitive fl uorescent sensors. This review article is categorized in four sections based on the NMs used in the sensing systems, including Au NPs, bimetallic AuM NMs, Au NCs, and DNA-Ag NCs. In each section, synthetic strategies and optical properties of the NMs are provided briefl y, followed by emphasis on their analytical applications in the detection of small molecules, metal ions, DNA, proteins, and cells. Current challenges and future prospects of these NMs-based sensing systems will be addressed.
Tunable plasmonic properties of silver nanorods for nanosensing applications
Journal of Materials Science, 2011
Localized surface plasmon resonance (LSPR) sensitivity to the surrounding medium refractive index has been studied for silver nanorods using Gans theory including the effect of retardation and surface scattering. The simulation results show the refractive index sensitivity (eV/RIU) maxima positions at width of 9, 6, and 4 nm for aspect ratios of 2, 3, and 4, respectively. Based on the sensing figure of merit (FOM), 9 nm is found to be a significant nanorod width, where the FOM dependence on width with respect to aspect ratio inverts. However, the optimal nanorod width for both the FOM and the modified figure of merit (MFOM) is about 6 nm for aspect ratios of 2, 3, and 4. A comparison with gold shows that silver nanorods exhibit relatively higher FOM and MFOM and thus, making them potential candidates for biochemical nanosensing applications.
Journal of Optics, 2012
Simulations of absorption spectra using Gans approximation for the prolate shape of gold nanorods are reported. Longitudinal resonance modes are observed for high aspect ratio nanorods by considering that the nanorod size in the range between 10 nm and 20 nm, where both surface scattering and dynamic depolarization are minor and hence, neglected in the present calculations. The LSPR wavelength is found to shift towards higher wavelength with increase in aspect ratio and the surrounding medium dielectric constant. A linear relationship between LSPR wavelength, aspect ratio and surrounding medium dielectric constant is obtained, which is in good agreement with the DDA results, experimental data and experimental linear fit data.