Size- and shape-dependent plasmonic properties of aluminum nanoparticles for nanosensing applications (original) (raw)
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Progress In Electromagnetics Research M
We engineer Aluminum (Al) based periodic plasmonic nanostructures for enhanced refractive index and thickness sensing, which offer to access complete ultraviolet-visible-near infrared spectral range for surface plasmon resonance sensors. Al-based periodic nanostructures on top of a thin homogeneous Al metal coated on a BK-7 glass substrate were designed by systematic variation of geometrical parameters using Rigorous Coupled Wave Analysis and finite elements full wave solver. The shift in surface plasmon mode excited on the nanostructure-analyte interface was used to measure the variation in refractive index, and the number of waveguide modes with the increase in the thickness of the analyte was used to capture the variation in thickness of the analyte. The proposed nanostructures of period 400 nm and an aspect ratio of 0.1 offered a sensitivity of 400 nm/RIU and full width at half maximum of 18 nm resulting in a figure of merit of 22. These Al-based plasmonic nanostructures have potential to be used as refractive index and thickness sensor due to a high figure of merit, high localization of the field, and very low aspect ratio that is needed to maintain laminar flow of analyte.
Aluminum-based localized surface plasmon resonance for biosensing
Aluminum-based localized surface plasmon resonance (LSPR) exhibits attractive properties including low cost, high natural abundance, and ease of processing by a wide variety of methods including complementary metal oxide semiconductor process, thereby making it superior to conventional LSPR involving noble metals. Moreover, the intrinsic property of the broad plasmon resonances of Al exhibited across the ultraviolet-visible-near-infrared wavelength region can be utilized on demand in refractive index biosensing, surface-enhanced fluorescence, and surface-enhanced Raman scattering. This review focuses on the recent developments of LSPR biosensing with aluminum nanostructures and related areas. Firstly, we introduce LSPR biosensing and the advantages of Al-based plasmonics. Then, we describe the different biosensing strategies employing Al LSPRs in detail. Subsequently, we provide an overview of various well-defined Al nanostructures and their fabrication methods. Finally, the future research trends of Al-based LSPR biosensing are highlighted and a conclusion with perspectives is given.
UV plasmonic-based sensing properties of aluminum nanoconcave arrays
Current Applied Physics, 2014
For several decades the plasmonic behavior of materials has been almost exclusively studied in visible region. Emerging applications require, however, the development of efficient materials operating in UV range. In UV nanoplasmonics aluminum (Al) can play a leading role due to its advantageous electronic properties. Yet, there is still lack of reproducible method to obtain Al nanostructures with desired parameters. Al nanoconcaves can provide a way to overcome these limitations. Here, two different periodicities of the Al nanoconcaves arrays were analyzed. It was observed that the Al concaves can dramatically reduce the optical reflectivity as compared to flat, unstructured Al. At the same time pronounced reflectivity dips were discernible, which were ascribed to (0,1) plasmonic mode. The positions of the dips were at around 250 nm and 350 nm for Al concaves with interpores distance (D c) of 246.3 nm and 456.7 nm, respectively. The refractive index sensitivity (RIS) was:~191 nm/RIU for the Al concaves with D c ¼ 246.3 nm, and~291 nm/RIU for the Al nanoconcaves arrays with D c ¼ 456.7 nm.
Applied Physics Letters, 2012
Localized surface plasmon resonances were controlled at deep-ultraviolet (DUV) wavelengths by fabricating aluminum (Al) nanostructures in a size-controllable manner. Plasmon resonances were obtained at wavelengths from near-UV down to 270 nm (4.6 eV) depending on the fabricated structure size. Such precise size control was realized by the nanosphere lithography technique combined with additional microwave heating to shrink the spaces in a close-packed monolayer of colloidal nanosphere masks. By adjusting the microwave heating time, the sizes of the Al nanostructures could be controlled from 80 nm to 50 nm without the need to use nanosphere beads of different sizes. With the outstanding controllability and versatility of the presented fabrication technique, the fabricated Al nanostructure is promising for use as a DUV plasmonic substrate, a light-harvesting platform for mediating strong light-matter interactions between UV photons and molecules placed near the metal nanostructure. V
Aluminium-Based Plasmonic Sensors in Ultraviolet
Sensors, 2021
We theoretically investigate the surface plasmon polaritons (SPPs) generated on an Al film covered by an Al2O3 layer in the context of their application as refractive index sensors. The calculated reflection spectra indicate SPP resonance excited by ultraviolet light, which was affected by the thickness of both the metal and the oxide layers on the surface. With optimized geometry, the system can work as a tunable sensor with a wide UV wavelength range λ∼ 150–300 nm. We report a quality factor of up to 10 and a figure of merit on the order of 9, and these are comparable to the performance of more complicated UV plasmonic nanostructures and allow for the detection of a 1% change of the refraction index. The sensor can operate on the basis of either the incidence angle or wavelength changes. The effect of oxide surface roughness is also investigated with an emphasis on amplitude-based refraction index sensing.
Micro and Nanosystems, 2021
Background: A relatively narrow LSPR peak and a strong interband transition ranging around 800 nm make Al a strongly plasmonic active material. Usually, Al nanoparticles are preferred for UV-plasmonic as the SPR of small size Al nanoparticles is located in the deep UV-UV region of the optical spectrum. This paper focused on tuning the LSPR of Al nanostructure towards the infrared region by coating the Au layer. The proposed structure has Au as the outer layer, which prevents further oxidation of Al nanostructure. Methods: The Finite Difference Time Domain (FDTD) and Plasmon Hybridization Theory has been used to evaluate the LSPR and field enhancement of single and dimer Al-Al2O3-Au MDM nanostructure. Results: It is observed that the resonance mode shows dependence on the thickness of the Al2O3 layer and also on the composition of the nanostructure. The Au layered MDM nanostructure shows two peaks of equal intensities simultaneously in UV and visible region tuned to the NIR region. T...
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.
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.
2009
Gold nanocrystals in seven different shapes were prepared, including large nanorods, nanobipyramids, oxidized nanobipyramids, oxidized nanorods, dog-bone-like nanorods, peanut-like nanorods, and small nanorods. Their longitudinal plasmon resonance wavelengths were all synthetically controlled to be around 730 nm. Their refractive index sensitivities were measured by dispersing them in water-glycerol mixtures of varying compositions. The index sensitivities were found to be dependent on the shapes of the gold nanocrystals, with the large nanorods exhibiting the highest index sensitivity of 326 nm/RIU (refractive index unit) and the small nanorods exhibiting the lowest sensitivity of 156 nm/RIU. Finite-difference time-domain calculations were performed to obtain the electric field intensity enhancement contours around these gold nanocrystals. The index sensitivity was found to exhibit an approximately linear dependence on the product of the nanocrystal polarizability and end curvature.
Surface Plasmon Resonance Sensing Characteristics of Thin Aluminum Films in Aqueous Solution
IEEE Sensors Journal, 2017
Surface plasmon resonance (SPR) sensors, utilizing thin aluminum (Al) films, are reported. The sensor designs are based in the novel optical trapezoidal prism chip, made from either polymer or BK7 glass. Optimum Al-film thickness was determined to 20 ± 5 nm, and deposited by thermal e-beam evaporation and rf-magnetron sputtering. Upon contact to air, and in de-ionized aqueous solution, a self-limited surface oxide layer forms. Determined by ellipsometric recordings, its thickness grows from 4.6 ± 0.6 nm in air to 12.3 ± 2 nm in the wet interface. A single SP-resonance applies to the dry interface. Unusual spectral broadening, due to the presence of multiple resonances, is predicted and experimentally verified at the wet interface. The Al-oxide adlayer is beneficial in the angular interrogation, where the instrumental response approaches the one exhibited by the noble metals. Under wavelength interrogation conditions, the presence of the Al-oxide adlayer causes severe degradation of the sensor response. Both, angular and wavelength interrogation at the metal-aqueous solution interface were exploited experimentally and compared with theoretical predictions regarding the sensing features of gold (Au), copper (Cu), and silver (Ag) metal films as well. Limitations, cost aspects and alternative routes to overcome degradation and the loss of SPR-activity in the presence of ionic phosphate buffered saline aqueous solutions are outlined for Al-films.