Localized Surface Plasmon Resonance Field Research Articles

Gold nanoparticles decorated MoS[formula omitted] nanosheets for sensing and degradation of carbamazepine in environmental wastewater

Trace pharmaceuticals and personal care products (PPCPs) have led to environmental contaminant and health risk. In this work, by in-situ reduction method, gold nanoparticles are loaded on the surface of the ultrathin MoS2 nanosheets to prepare AuNPs/MoS2 nanocomposites. AuNPs/MoS2 nanocomposites generate the superior localized surface plasmon resonance field due to the presence of nanogap between neighboring AuNPs and electron transfer within boundary of metal and semiconductor, which contributing great surface enhanced Raman scattering (SERS) effect. AuNPs/MoS2 nanocomposites-based SERS protocol is developed and successfully utilized to detect carbamazepine (CBZ) in wastewater. It presented a linear concentration ranging from 10−3 to 10−9 mol/L (R2=0.985) and a limit of detection about 1.36 × 10−10 mol/L, which foreboded the possibility for trace analysis. In addition, AuNPs/MoS2 nanocomposites with topological effect providing Mo4+ active sites and many defects present peroxidase-like activity to catalyze H2O2, forming radical oxide species (ROS) including ⋅OH, O2⋅− and 1O2. Herein, AuNPs/MoS2 nanocomposites as nanozyme with durability in environment are firstly used to catalytically degrade CBZ in wastewater by H2O2, showing high efficiency. Application of AuNPs/MoS2 nanocomposites as nanozyme to deal with pollution problems paves a promising paradigm for promoting the environmental and health safeties.

Enhancing Photocatalysis of Ag Nanoparticles Decorated BaTiO3 Nanofibers through Plasmon-Induced Resonance Energy Transfer Turned by Piezoelectric Field

Revealing the charge transfer path is very important for studying the photocatalytic mechanism and improving photocatalytic performance. In this work, the charge transfer path turned by the piezoelectricity in Ag-BaTiO3 nanofibers is discussed through degrading methyl orange. The piezo-photocatalytic degradation rate of Ag-BaTiO3 is much higher than the photocatalysis of Ag-BaTiO3 and piezo-photocatalysis of BaTiO3, implying the coupling effect between Ag nanoparticle-induced localized surface plasmon resonance (LSPR), photoexcited electron-hole pairs, and deformation-induced piezoelectric field. With the distribution density of Ag nanoparticles doubling, the LSPR field increases by one order of magnitude. Combined with charge separation driven by the piezoelectric field, more electrons in BaTiO3 nanofibers are excited by plasmon-induced resonance energy transfer to improve the photocatalytic property.

Metal-Organic Framework Membranes Encapsulating Gold Nanoparticles for Direct Plasmonic Photocatalytic Nitrogen Fixation.

Photocatalytic nitrogen fixation reaction can harvest the solar energy to convert the abundant but inert N2 into NH3. Here, utilizing metal-organic framework (MOF) membranes as the ideal assembly of nanoreactors to disperse and confine gold nanoparticles (AuNPs), we realize the direct plasmonic photocatalytic nitrogen fixation under ambient conditions. Upon visible irradiation, the hot electrons generated on the AuNPs can be directly injected into the N2 molecules adsorbed on Au surfaces. Such N2 molecules can be additionally activated by the strong but evanescently localized surface plasmon resonance field, resulting in a supralinear intensity dependence of the ammonia evolution rate with much higher apparent quantum efficiency and lower apparent activation energy under stronger irradiation. Moreover, the gas-permeable Au@MOF membranes, consisting of numerous interconnected nanoreactors, can ensure the dispersity and stability of AuNPs, further facilitate the mass transfer of N2 molecules and (hydrated) protons, and boost the plasmonic photocatalytic reactions at the designed gas-membrane-solution interface. As a result, an ammonia evolution rate of 18.9 mmol gAu-1 h-1 was achieved under visible light (>400 nm, 100 mW cm-2) with an apparent quantum efficiency of 1.54% at 520 nm.

Enhanced Photochromism of Diarylethene Induced by Excitation of Localized Surface Plasmon Resonance on Regular Arrays of Gold Nanoparticles.

Localized surface plasmon resonance (LSPR) excitation on the photochromic reaction of a diarylethene derivative (DE) was studied by surface enhanced Raman scattering (SERS). UV and visible light irradiations transform reversibly DE between open-form (OF) and closed-form (CF) isomers, respectively. A mixture of PMMA and DE (either OF or CF isomer) was spin-coated onto gold nanorods (GNRs) arrays, designed by electron beam lithography, with two localized surface plasmon resonances (LSPR) at distinct wavelengths, due to their anisotropy. The photochromic reaction rates from CF to OF isomers, under LSPR excitation, were monitored from SERS spectral changes under different polarizations, on the same GNR substrate to compare the effect of LSPR field strength. It appears that the photoisomerization rate was faster when LSPR was excited with the polarization parallel to the GNR long axis. The present results highlight a potential genuine mechanism, from near field LSPR excitation, involved in the photochromic enhancement of diarylethene photochromes.

Comparison of LSPR-mediated enhanced fluorescence excited by S- and P-polarized light on a two-dimensionally assembled silver nanoparticle sheet

Localized surface plasmon resonance (LSPR) excited by an oblique incidence of S- and P-polarized light to a two-dimensionally assembled silver nanoparticle sheet was investigated via enhanced fluorescence under total internal reflection fluorescence (TIRF) microscopy. The finite-difference-time-domain simulation demonstrated that the S-polarized light induced a strong plasmon coupling at a nanogap between the particles, which eventually led to a highly confined, strong, and “flattened” electric field on the entire surface. In contrast, the LSPR field excited by P-polarized light was located on the individual particles, having a relatively long tail in the axial direction (low confinement). The LSPR-mediated fluorescence appeared stronger under P-polarized light than under S-polarized light in the experiments using cyanine dye solutions, while the opposite result was obtained for the fluorescence bead snapshot (diameter: 200 nm). Magnified images of the single beads taken by a super-resolution digital CMOS camera (65 nm/pixel) revealed improved lateral resolution when S-polarized light was used on both the silver nanoparticle sheet and glass under TIRF microscopy.

Graphene-Oxide Coated Ag-Island-Based Inline LSPR Fiber Sensor

Graphene Oxide (GO) coated silver (Ag) island system based on localized surface plasmon resonance (LSPR) phenomenon have been developed using optical fiber as a sensing probe. The Ag-island is used to excite LSPR field which is responsible for the analyte sensing through a shift in resonance wavelength. The deposition of Ag-islands is confirmed from UV-VIS spectra and Field Emission Scanning Electron Micro-graph (FESEM). The usage of GO helps to protect Ag-island from oxidation along with opening a new window for bio-sensing due to its structural compatibility with the bio-sensing system. We have experientially observed that the GO as a dielectric overlayer on Ag-island shows a refractive index sensitivity of 2217.04 nm/RIU with a resolution of $4.05 \times 10^{-4}$ RIU.

A naturally occurring diatom frustule as a SERS substrate for the detection and quantification of chemicals

Naturally occurring photonic crystal structures play an important role in different fields of application. Herein, we exploit the periodic pore pattern of a diatom frustule and demonstrate surface-enhanced Raman scattering (SERS) using its structure as a template for the SERS substrate. Gold nanoparticles (AuNPs) were initially allowed to self-assemble on the surface and inside the pores of the diatoms. The enhancement in the localized surface plasmon resonance (LSPR) field magnitude for the assembled AuNPs on the diatom frustule were studied using simulation software. For the proposed SERS substrate, an average field enhancement of the order of 108 magnitude was observed. We demonstrate the operation of the designed substrate for the detection and quantification of Raman signals from two Raman active samples, namely malachite green (MG) and fluoride concentrations in drinking water. Using the proposed SERS substrate, an MG concentration as low as 1 nM with a relative standard deviation (RSD) of 7.57% and a fluoride concentration of 100 nM with an RSD of 17.26% could be measured with the Raman spectrometer. We envision that the proposed technique could emerge as an inexpensive alternative fabrication method of SERS substrates which can produce an enhanced LSPR field magnitude and scatter intense Raman signals from Raman active samples.

Periodically Varying Height in Metal Nano-pillars for Enhanced Generation of Localized Surface Plasmon Field

Localized surface plasmon resonance (LSPR) field condition study in metal nanostructure is important for different fields of applications which include chemical and bio-sensing investigations and in surface-enhanced Raman scattering (SERS)-based sensing investigations. Generally, sharp metal nano-tips, metal nano-colloids, nano-pillars and other sharp structures were used to generate different magnitudes of enhanced LSPR conditions, and all such structures usually provide tightly bound LSPR field conditions. In this paper, we demonstrate that with periodically varying height in metal nano-pillars, enhanced LSPR field condition can also be obtained and the enhancement scale of the generated field are found to be more than that of the uniformly structured metal nano-pillars. Different parameters which govern the enhancement factor for LSPR field condition have been thoroughly studied here. Since, periodic pattern of nano-pillars can be fabricated using lithographic tool such as e-beam lithography or focus-ion beam lithography, we envision that our simulation results would be useful in getting desired structure of the proposed nano-pillars for which it provides enhanced LSPR field condition as compared to uniformly structured metal nano-pillars.

Direct imaging of the near field and dynamics of surface plasmon resonance on gold nanostructures using photoemission electron microscopy

Localized surface plasmon resonance (LSPR) can be supported by metallic nanoparticles and engineered nanostructures. An understanding of the spatially resolved near-field properties and dynamics of LSPR is important, but remains experimentally challenging. We report experimental studies toward this aim using photoemission electron microscopy (PEEM) with high spatial resolution of sub-10 nm. Various engineered gold nanostructure arrays (such as rods, nanodisk-like particles and dimers) are investigated via PEEM using near-infrared (NIR) femtosecond laser pulses as the excitation source. When the LSPR wavelengths overlap the spectrum of the femtosecond pulses, the LSPR is efficiently excited and promotes multiphoton photoemission, which is correlated with the local intensity of the metallic nanoparticles in the near field. Thus, the local field distribution of the LSPR on different Au nanostructures can be directly explored and discussed using the PEEM images. In addition, the dynamics of the LSPR is studied by combining interferometric time-resolved pump-probe technique and PEEM. Detailed information on the oscillation and dephasing of the LSPR field can be obtained. The results identify PEEM as a powerful tool for accessing the near-field mapping and dynamic properties of plasmonic nanostructures. A novel form of microscopy has been used to map the field dynamics of surface plasmon resonances. Hiroaki Misawa and co-workers in Japan used high-resolution (10 nm) multiphoton photoemission electron microscopy (MP-PEEM) to image the field distribution of a variety of metallic nanostructures, such as arrays of gold rods, nanodisks and dimer pairs. MP-PEEM works by recording the electrons emitted from a sample in response to illumination with a series of ultrashort pulses. Illumination with near-infrared pulses caused excited plasmon resonances in the gold nanostructures to show up in the resulting MP-PEEM images as local hot spots, from which the field distribution was determined. The short duration of the pulses made it possible to probe the dynamics of the plasmon resonance field distribution on the femtosecond timescale.

Simultaneous Nanoplasmonic and Quartz Crystal Microbalance Sensing: Analysis of Biomolecular Conformational Changes and Quantification of the Bound Molecular Mass

This paper presents a study of supported lipid bilayer (SLB) formation and subsequent protein binding using a sensor that combines localized surface plasmon resonance (LSPR) and quartz crystal microbalance with dissipation (QCM-D) monitoring. The LSPR activity arises from silicon oxide (SiO x ) coated nanometric apertures in a thin gold film, which also serves as the active electrode of a QCM-D crystal. Both transducer principles provide signatures for the formation of a SLB upon adsorption and subsequent rupture of adsorbed lipid vesicles. However, the two techniques are sensitive over different regions of the sample: LSPR primarily inside and on the rim of the holes and QCM-D primarily on the planar areas between the holes. Although the dimension of the lipid vesicles is on the same order as the dimension of the nanoholes, it is concluded from the response of the combined system that vesicle rupture in the nanoholes and on the planar region between the holes is synchronized. Furthermore, by determining the thickness of the SLB from the QCM-D response, the characteristic decay length of the LSPR field intensity could be determined. This made it possible not only to determine the mass and refractive index of the homogeneous SLB but also to postulate a generic means to quantify the LSPR response in terms of mass-uptake also for nonhomogeneous films. This is exemplified by measuring the adsorbed lipid mass during vesicle adsorption, yielding the critical lipid vesicle coverage at which spontaneous rupture into a planar bilayer occurs. The generic applicability and versatility of the method is demonstrated from specific protein binding to a functionalized SLB. From the absolute refractive index of the protein, provided from the LSPR data alone, it was possible to determine both the effective thickness of the protein film and the molecular mass (or number) of bound protein.

Localized Surface Plasmon Resonance Sensing of Lipid-Membrane-Mediated Biorecognition Events

Supported phospholipid bilayers (SPBs) have emerged as important model systems for studies of the natural cell membrane and its components, which are essential for the integrity and function of cells in all living organisms, and also constitute common targets for therapeutic drugs and in disease diagnosis. However, the preferential occurrence of spontaneous SPB formation on silicon-based substrates, but not on bare noble-metal surfaces, has so far excluded the use of the localized surface plasmon resonance (LSPR) sensing principle for studies of lipid-membrane-mediated biorecognition reactions. This is because the LSPR phenomenon is associated with, and strongly confined to, the interfacial region of nanometric noble-metal particles. This problem has been overcome in this study by a self-assembly process utilizing localized rupture of phospholipid vesicles on silicon dioxide in the bottom of nanometric holes in a thin gold film. The hole-induced localization of the LSPR field to the voids of the holes is demonstrated to provide an extension of the LSPR sensing concept to studies of reactions confined exclusively to SPB-patches supported on SiO2. In particular, we emphasize the possibility of performing label-free studies of lipid-membrane-mediated reaction kinetics, including the compatibility of the assay with array-based reading (approximately 7 x 7 microm2) and detection of signals originating from bound protein in the zeptomole regime.