ABSTRACT
From the point of view of classical electrodynamics, nano-optical and enantioselective tweezers for single biomolecules have been routinely investigated using achiral and chiral localized surface plasmons, respectively. In this work, we propose the use of interference of collective plasmons (Fano-type plasmon) that exist in densely hexagonal plasmonic oligomers to design a high-efficiency nano-optical tweezer to trap individual biomolecules with a radius of 2 nm. For this purpose, we fabricated and simulated 2D hexagonal arrays of Au nanoparticles (AuNPs) with sub-wavelength lattice spacing which support collective plasmons by near-field coupling. Our full-field simulations show that densely hexagonal plasmonic oligomers can enhance the Fano-like resonances arising from the interference of superradiant and subradiant modes. This interference of collective plasmons results in a strong intensification and localization of the electric near-field in the interstice of the AuNPs. The methodology can also be extended to collective chiral near-fields for all-optical enantioseparation of chiral biomolecules with a small chirality parameter (±0.001) with the hypothesis of the existence of strong magnetic near-fields.
ABSTRACT
This work deals with a portable device system applied to detect and classify different metallic ions as proposed and developed, aiming its application for hydrological monitoring systems such as rivers, lakes and groundwater. Considering the system features, a portable colorimetric system was developed by using a multispectral optoelectronic sensor. All the technology of quantification and classification of metallic ions using optoelectronic multispectral sensors was fully integrated in the embedded hardware FPGA ( Field Programmable Gate Array) technology and software based on virtual instrumentation (NI LabView®). The system draws on an indicative colorimeter by using the chromogen reagent of 1-(2-pyridylazo)-2-naphthol (PAN). The results obtained with the signal processing and pattern analysis using the method of the linear discriminant analysis, allows excellent results during detection and classification of Pb(II), Cd(II), Zn(II), Cu(II), Fe(III) and Ni(II) ions, with almost the same level of performance as for those obtained from the Ultravioled and visible (UV-VIS) spectrophotometers of high spectral resolution.
ABSTRACT
Enhanced upconversion (UC) emission was experimentally demonstrated using gold double antenna nanoparticles coupled to nanoslits in gold films. The transmitted red emission from UC ytterbium and erbium co-doped sodium yttrium fluoride (NaYF4:Yb(3+)/Er(3+)) nanoparticles (UC NPs) at â¼665 nm (excited with a 980 nm diode laser) was enhanced relative to the green emission at â¼550 nm. The relatively enhanced UC NP emission could be tuned by the different polarization-dependent extraordinary optical transmission modes coupled to the gold nanostructures. Finite-difference time-domain calculations suggest that the preferential enhanced UC emission is related to a combination of different surface plasmon mode excitation coupling to cavity Fabry-Perot interactions. A maximum UC enhancement of 6-fold was measured for nanoslit arrays in the absence of the double antennas. In the presence of the double nanoantennas inside the nanoslits, the UC enhancement was between 2- and 4-fold, depending on the experimental conditions.
ABSTRACT
The surface plasmons that are enabled by grating coupling in two-dimensional gold nano-particle arrays (AuNPAs) affected the spectral characteristics of the up-conversion (UC) emission from Yb(3+)-Er(3+)-Gd(3+) co-doped sodium yttrium fluoride (NaYF4:Yb/Er/Gd) nano-rods. The red emission of NaYF4:Yb/Er/Gd nano-rods at 660 nm (excited with a 980 nm diode laser) was significantly enhanced by the interaction with the AuNPAs. The geometric characteristics of the gold nanoparticles influenced the position of the surface plasmon resonance, and their near field strengths. The intensity of the red emission normalized versus the green emission reached 1.4, measured against a reference film in the absence of the metallic nanostructures. The lifetime for the green and red emission decreased steadily as the periodicity decreased (relative to the reference), reaching about 6% reduction for the 350 nm AuNPA. A qualitative agreement was obtained between the experimental results and finite difference time domain (FDTD) calculations.
