Localized Surface Plasmon Resonance Properties Research Articles

Plasmoelectronic-Based Ultrasensitive Assay of Tumor Suppressor microRNAs Directly in Patient Plasma: Design of Highly Specific Early Cancer Diagnostic Technology.

It is becoming understood that microRNAs hold great promise for noninvasive liquid biopsies for screening for different types of cancer, but current state-of-the-art RT-PCR and microarray techniques have sensitivity limitations that currently restrict their use. Herein, we report a new transduction mechanism involving delocalization of photoexcited conduction electrons wave function of gold triangular nanoprism (Au TNP) in the presence of -ssDNA/microRNA duplexes. This plasmoelectronic effect increases the electronic dimension of Au TNPs and substantially affects their localized surface plasmon resonance (LSPR) properties that together allow us to achieve a sensitivity for microRNA assay as low as 140 zeptomolar concentrations for our nanoplasmonic sensors. We show that the position of a single base-pair mismatch in the -ssDNA/microRNA duplex dramatically alters the LSPR properties and detection sensitivity. The unprecedentedly high sensitivity of nanoplasmonic sensors has allowed us to assay four different microRNAs (microRNA-10b, -182, -143, and -145) from bladder cancer patient plasma (50 μL/sample). For the first time, we demonstrate the utility of a label-free, nanoplasmonic sensor in quantification of tumor suppressor microRNAs, the level of tumor suppressor microRNAs goes down in a cancer patient as compared to normal healthy individuals, in metastatic and nonmetastatic bladder cancer patient plasma. Our statistical analysis of patient samples unequivocally suggests that the tumor suppressor microRNAs are more specific biomarkers ( p-value of <0.0001) than oncogenic microRNAs for differentiation between metastatic and nonmetastatic bladder cancer, and nonmetastatic cancer from healthy individuals. This work demonstrating the electron wave functions delocalization dependent ultrasensitive LSPR properties of noble metal nanoparticles has a great potential for fabrication of miniaturized and extremely powerful sensors to investigate microRNA properties in other cancers (for example breast, lung, and pancreatic) through liquid biopsy.

A microscale spectrophotometric method for quantification of doxorubicin in exhaled breath condensate

This study presents a microscale spectrophotometric method for the determination of doxorubicin, one of the most important anticancer drugs in the clinic, based on the localized surface plasmon resonance property of silver nanoparticles.

"Green" Synthesis of Cytotoxic Silver Nanoparticles Based on Secondary Metabolites of Lavandula Angustifolia Mill.

In this study, we used “green” synthesis to prepare silver nanoparticles (NPs) from aqueous plant and callus extracts of the narrow-leaved lavender Lavandula angustifolia Mill. 35.4 ± 1.6 nm and 56.4 ± 2.4 nm nanoparticles, colloidally stable in phosphate-buffered saline, were synthesized using the plant extract and the callus extract, respectively. NPs were characterized by spectrophotometry, dynamic light scattering, and scanning electron microscopy. We studied the dynamics of the nanoparticle synthesis and evaluated the cytotoxic properties of the plant extract-based NPs. Modification of NPs with bovine serum albumin demonstrated that blockage of the nanoparticle surface completely suppressed NP cytotoxic activity in vitro. The synthesized NPs possess localized surface plasmon resonance properties and are of small sizes, and their surface can be modified with protein molecules, which makes them promising agents for cancer theranostics.

Complex coloration and antibacterial functionalization of silk fabrics based on noble metal nanoparticles

Noble metal nanoparticles and traditional dyes jointly colorate silk fabrics. Gold and silver nanoparticles were in situ synthesized on silk fabrics, and the complex coloration was realized by the integration of traditional dyes into the treated silk. The localized surface plasmon resonance properties of gold and silver nanoparticles were not affected by the coloration of dyed-on silk fabrics. The combined optical properties of nanoparticles and dyes extended the color range and enhanced the color strength (K/S) of silk fabrics. Ultraviolet–visible diffuse absorption spectroscopy and scanning electron microscopy demonstrated the in situ synthesis of gold and silver nanoparticles on silk fabrics. The coloration of traditional dyes influenced the morphologies of gold and silver nanoparticles on fiber surface slightly. The silk fabrics with complex coloration showed significant antibacterial property. The complex coloration based on particular nanoparticles and dyes provides a promising strategy to develop multifunctional textiles.

Improved control on the morphology and LSPR properties of plasmonic Pt NPs through enhanced solid state dewetting by using a sacrificial indium layer.

Platinum (Pt) nanoparticles (NPs) are important nano-material components in various catalytic, photonic and electronic applications, yet face challenges in the fabrication of desired morphology and uniformity with the conventional solid-state dewetting approach. Specifically, the necessity of high annealing temperatures, typically above 800 °C due to the low diffusivity of Pt atoms, limits the morphological and functional tunability of Pt NPs. In this work, the fabrication of Pt NPs with an improved configuration, spacing and uniformity is demonstrated through the enhancement of solid state dewetting by using a sacrificial indium (In) layer on sapphire (0001). The well-defined Pt NPs demonstrate the dynamic localized surface plasmon (LSPR) bands in the visible range between ∼400 and 700 nm depending on the size and spacing of NPs. The LSPR peak intensity and width are also varied depending on the uniformity of Pt NPs. The overall dewetting magnitude is significantly enhanced through the inter-mixing of In and Pt atoms at the In/Pt interface that eventually results in the formation of an In–Pt alloy. During the dewetting process the In atoms desorb from the NP matrix by atomic sublimation, which gives rise to pure Pt NP fabrication. In sharp contrast to the pure Pt film dewetting, the Pt NPs in this approach demonstrate significantly improved spatial arrangement with well-defined configuration and uniformity. In addition, the ratio of In can be readily controlled along with the thickness of the Pt layer to alter the dewetting kinetics and thereby the surface morphology of Pt NPs. Specifically, large hexagonal, semi-spherical and small hexagonal Pt NPs are obtained through the dewetting of In75 nm/Pt25 nm, In20 nm/Pt20 nm and In2.5 nm/Pt7.5 nm bilayers respectively.

Plasmonic Pt Nanocrystals by Using a Sacrificial In Component via the Enhanced Dewetting on Sapphire (0001): Improvement on Morphological and Localized Surface Plasmon Resonance Properties

Modulation of functional metallic nanoparticles (NPs) in terms of their size, configuration, and dimension can offer a promising route to control the optical, catalytic, magnetic, and sensing properties for a wide range of applications. Herein, the platinum (Pt) nanostructures of improved morphological and localized surface plasmon resonance properties are demonstrated via the enhanced solid-state dewetting by using a sacrificial indium (In) layer on sapphire (0001). Upon annealing, the concurrent occurrence of intermixing between In and Pt atoms, formation of In–Pt alloy and sublimation of In atoms plays major roles in accelerating the dewetting process, which results in the formation of definite Pt nanostructures. The alteration in the In and Pt ratio readily varies the shape, size, and areal density of the resulting Pt NPs. The optical characteristics reveal that the localized surface plasmon resonance (LSPR) response is sensitively affected by the resulting surface morphology of Pt NPs. Specifically, ...

Synergistic Nanozymetic Activity of Hybrid Gold Bipyramid-Molybdenum Disulfide Core@Shell Nanostructures for Two-Photon Imaging and Anticancer Therapy.

In recent years, the concept of combined therapy using gold hybrid nanomaterials has been broadly adopted to pioneer new anticancer treatments. However, their synergistic anticancer effects have yet to be thoroughly investigated. Herein,a hybrid gold nanobipyramid nanostructure coated with molybdenum disulfide (MoS2) semiconductor (AuNBPs@MoS2) was proposed as a smart nanozyme for anticancer therapy and two-photon bioimaging. The hybrid material showed dramatically enhanced localized surface plasmon resonance property under excitation owing to its anisotropic nature, coupled with the rich electron density in MoS2, resulting in the superior in situ photogeneration of reactive oxidative species (ROS - 1O2, •OH). We demonstrated that the synergistic effect of enhanced photothermal conversion and generation of ROS could increase the anticancer effect of AuNBPs@MoS2. Two-photon luminescence imaging confirmed that AuNBPs@MoS2 was successfully internalized in cancer cells and that simultaneous anticancer treatments based on catalytic and photothermal therapy could be achieved. This study highlighted, for the first time, a novel approach of plasmon-mediated powerful anticancer therapy and imaging via the unprecedented combination of anisotropic AuNBPs and two-dimensional MoS2 material.

Plasmon-tunable Au@Ag core-shell spiky nanoparticles for surface-enhanced Raman scattering

A facile synthetic approach has been developed to prepare uniform and size-tunable spiky Au@Ag core-shell nanoparticles (NPs) to tailor the localized surface plasmon resonance (LSPR) properties. The gradual assembly of small Au nanocrystals allows the size of spiky Au NPs to be modulated from tens to several hundreds of nanometers by tuning the concentration of initial Au seeds and Au source; and the thickness of the Ag shell can be adjusted with stepwise reduction of Ag(I) ions. The LSPR bands of such spiky Au@Ag core-shell NPs resemble those of pure spiky Au NP cores of similar sizes in near-infrared region, and increasing the Ag shell thickness results in a blue shift and broadening of the LSPR band in the near-infrared region. Additionally, the spiky Au@Ag core-shell NPs exhibit improved surface-enhanced Raman scattering (SERS) activity as compared to the bare spiky Au NPs and spherical Ag@Au NPs. This work has offered a facile route to synthesize plasmonic metal NPs with LSPR band in 650 to 800 nm that show strong enhancement of localized electromagnetic field, which provides an effective SERS substrate for SERS imaging and detection in biological fluids and tissues.

Ag Nanocrystals with Nearly Ideal Optical Quality: Synthesis, Growth Mechanism, and Characterizations.

Though Ag nanocrystals are predicted to be the best material for localized surface plasmon resonances (LSPR) in the visible light region, realization of their ideal LSPR properties is hindered by the stringent requirements: i.e., simultaneous control of their size, shape, crystallinity, and surface structure. To achieve this goal, a synthetic scheme in non-polar solvent coupled with mild oxidative etching by H+ ions has been established. With a trace amount of Cl- ions as catalysts, H+ ions (in the form of carboxylic acids) become active for selectively etching the nuclei (and small nanocrystals) with imperfect crystal structure, which results in a new growth mechanism for formation of monodisperse nanocrystals, namely "self-focusing of size/crystallinity distribution". H+ ions, ligands, and other reagents in the scheme are confirmed to possess negligible effects on the surface dielectric properties of Ag nanocrystals. To eliminate radiative damping of LSPR, single-crystalline and monodisperse spherical Ag nanocrystals in the size range between 7 and 20 nm are synthesized using this one-pot scheme. With excellent control of all related structural parameters, the full width at half-maximum of LSPR spectra of single-crystalline Ag nanocrystals match theoretical predictions in the entire size range, and the maximum quality factor (∼20) of LSPR predicted by theory is realized. The Raman enhancement factor of the single-crystalline Ag nanocrystals for crystal violet (excitation at 514 nm) is 5 times higher than that of the typical multi-twinned nanocrystals with the same size.

PH and Temperature Dual-Responsive Plasmonic Switches of Gold Nanoparticle Monolayer Film for Multiple Anticounterfeiting.

Two-dimensional (2D) gold nanoparticle (Au NP) monolayer film possesses a lot of fascinating peculiarities, and has shown promising applications in photoelectrical devices, catalysis, spectroscopy, sensors, and anticounterfeiting. Because of the localized surface plasmon resonance (LSPR) property predetermined by the natural structure of metal nanoparticles, it is usually difficult to realize the reversible LSPR transition of 2D film. In this work, we report on the fabrication of a large-area free-standing Au NP monolayer film with dual-responsive switchable plasmonic property using a pH- or thermal-responsive dendronized copolymer as a stimuli-sensitive linker. In this system, an oligoethylene-glycol-based (OEG-based) dendronized copolymer (named PG1A) with pH or temperature sensitivity was first modified onto the surface of a Au NP. Then, polyethylene glycol dibenzyl aldehyde (PEG-DA) was introduced to interact with the amino moieties from PG1A before the process of oil-water interfacial self-assembly of NPs, resulting in an elastic, robust, pH- or temperature-sensitive interpenetrating network among Au NPs in monolayer films. In addition, the film could exhibit reversibly plasmonic shifts of about 77 nm and inherent color changes through varying temperature or pH. The obtained free-standing monolayer film also shows an excellent transferable property, which can be easily transferred onto substrates such as plastic molds, PDMS, copper grids, and silicon wafers. In virtue of these peculiarities of the free-standing property, special plasmonic signal, and homologous macroscopic color, the transferred film was primely applied to an anticounterfeiting security label with clear color change at the designed spots, providing a new avenue to plasmonic nanodevices with various applications.

Design of Gold Hollow Nanorods with Controllable Aspect Ratio for Multimodal Imaging and Combined Chemo-Photothermal Therapy in the Second Near-Infrared Window.

Gold nanoparticles (AuNPs) exhibit great potential for biological applications due to their good biocompatibility and tunable localized surface plasmon resonance (LSPR) properties. Currently, although tuning the aspect ratio of a solid structure or designing a hollow structure has been performed to regulate the LSPR properties of AuNPs, the method of preparing hollow anisotropic AuNPs has rarely been reported. In this study, we designed gold hollow nanorods (AuHNRs) with controllable aspect ratios by a Se-doping Te nanorod-templated method with the assistance of l-cysteine. UV-vis-NIR spectra showed that AuHNRs with an aspect ratio of about 3 could have a LSPR peak in the second near-infrared (NIR-II) window, which is only half of the value required by traditional Au nanorods. Moreover, AuHNRs are nontoxic and capable of loading drugs. In vivo experiment revealed that AuHNRs can be used as contrast agents in multimodal imaging, including photothermal imaging, photoacoustic imaging, and computed tomography imaging, as well as in chemo-photothermal combined therapy of tumor in the NIR-II window. Because light in the NIR-II window has remarkable advantages over that in the first near-infrared (NIR-I) window in biomedical applications, AuHNRs can be used as promising NIR-II-window-responsive multifunctional nanoagents.

High-sensitivity Mercury Ion Detection System Using Unmodified Gold Nanorods

Abstract Hg2+ is one of the most universal and severe toxic metal pollutants. Here we reported a high-sensitivity and rapid method for detection of Hg2+. The technique was based on the localized surface plasmon resonance property of gold nanorods. Neither modification of gold nanorods nor separation of analyte was necessary. The longitudinal absorption peak of gold nanorods presented a linear blue shift as Hg2+ concentration increased. The blue shift of longitudinal absorption peak was due to the changes of both aspect ratio and medium dielectric constant. The sensor had a wide linear interval ranging from 285 nM to 8.00 μM, the detection limit was as low as 112 nM, and the sensitivity was 30.48 nm μMμ1, which were comparable to the performance of the modified sensors.

Multi-functional regenerated cellulose fibers decorated with plasmonic Au nanoparticles for colorimetry and SERS assays

Multi-functional cellulose fiber-Au composites were fabricated through a simple and cost-effective procedure by decorating regenerated cellulose fibers with Au nanoparticles. The cellulose fibers were regenerated from waste paper through the Ioncell-F process, an environmental friendly approach. After grafting positive charge, the surface of the cellulose fibers were decorated with citrate-stabilized plasmonic Au nanoparticles (NPs). X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction, and optical images were used to characterize the regenerated cellulose fibers and fiber-Au NP composites. The fiber-Au composites exhibited different colors as the localized surface plasmon resonance property of Au NPs, which enables visual sensing of the water content in the fiber-Au composites through a colorimetric method. Furthermore, the regenerated cellulose fiber-Au composite was used as an enhanced substrate for the sensing of malachite green via surface-enhanced Raman scattering, in which the limit of detection was lower than 10 ppb. The multi-functional cellulose fibers are potentially suitable for the detection of toxins and the monitoring of water quality.

Functions of 1-Dodecanethiol in the Synthesis and Post-Treatment of Copper Sulfide Nanoparticles Relevant to Their Photocatalytic Applications

Copper-deficient, nonstoichiometric copper sulfide (Cu2–xS, x > 0) nanoparticles (NPs) have been explored as an important hole-based plasmonic material because of their size, morphology, carrier density, and crystal-phase-dependent localized surface plasmon resonance (LSPR) properties. In synthesis of Cu2–xS NPs, alkyl thiols containing sulfur element such as 1-dodecanethiol, C12H25SH (1-DDT), are well-utilized sulfur sources. In addition to the sulfur element in 1-DDT molecules, soft base S2–, linear hydrocarbon chain CH3(CH2)11–, and the proton in the −SH group may provide unique functions in the synthesis and post-treatment of Cu2–xS NPs. Here, we systematically demonstrate the ability of 1-DDT molecules to act as sulfur source and capping ligand for low-chalcocite Cu2S nanodisks (NDs), and size controller for covellite CuS NDs in the process of synthesis. These CuS NDs can be applied as electron donor and hole acceptor to improve the efficiency of photocatalytic reactions. Furthermore, in the post-tre...

Impacts of surface depletion on the plasmonic properties of doped semiconductor nanocrystals.

Degenerately doped semiconductor nanocrystals (NCs) exhibit a localized surface plasmon resonance (LSPR) in the infrared range of the electromagnetic spectrum. Unlike metals, semiconductor NCs offer tunable LSPR characteristics enabled by doping, or via electrochemical or photochemical charging. Tuning plasmonic properties through carrier density modulation suggests potential applications in smart optoelectronics, catalysis and sensing. Here, we elucidate fundamental aspects of LSPR modulation through dynamic carrier density tuning in Sn-doped In2O3 (Sn:In2O3) NCs. Monodisperse Sn:In2O3 NCs with various doping levels and sizes were synthesized and assembled in uniform films. NC films were then charged in an in situ electrochemical cell and the LSPR modulation spectra were monitored. Based on spectral shifts and intensity modulation of the LSPR, combined with optical modelling, it was found that often-neglected semiconductor properties, specifically band structure modification due to doping and surface states, strongly affect LSPR modulation. Fermi level pinning by surface defect states creates a surface depletion layer that alters the LSPR properties; it determines the extent of LSPR frequency modulation, diminishes the expected near-field enhancement, and strongly reduces sensitivity of the LSPR to the surroundings.

The Bi/Bi2WO6 heterojunction with stable interface contact and enhanced visible‐light photocatalytic activity for phenol and Cr(VI) removal

AbstractBACKGROUNDSemiconductor photocatalysis is the most promising green and energy‐saving technology for environmental remediation. Unfortunately, photocatalysis nanotechnology for its practical application is often challenged by the low capturing ability for visible light and use of expensive noble metals. In this work, we report the non‐noble Bi nanoparticles assembled on Bi2WO6 with enhanced visible‐light photocatalytic activity for decontamination of phenol and hexavalent chromium in water.RESULTSThe 3% Bi/Bi2WO6 composite had the highest photocatalytic activity compared to pristine Bi2WO6, which could completely decompose phenol into small products within 120 min. More importantly, the Cr(VI) removal rate of the 3% Bi/Bi2WO6 catalyst in the presence of triethanolamine (TEOA, 2%) after irradiation for 12 min was up to 96.2%.CONCLUSIONSThe improved photocatalytic performance could be due to the fast transfer of photogenerated charge carried by the formation of an anti‐barrier layer at the interface between metal Bi nanoparticles and the n‐type Bi2WO6 semiconductor; the enhancement of electron energy may be attributed to the localized surface plasmon resonance properties of Bi nanoparticles, as well as conspicuously strengthened and broad light‐capturing ability across the whole visible‐light range. This strategy could provide some inspiration for the design of other Bi‐based semiconductor heterostructures for decomposing harmful organic pollutants in wastewater and purifying hazardous gases in the air. © 2018 Society of Chemical Industry

Localized Surface Plasmonic Resonance and Sensing Properties of Ag–MgF2 Composite Nanotriangles

Regular nanotriangular (NT) patterns and thin films composed of a mixture of Ag and MgF2 with different composition ratios are prepared by combining nanosphere lithography and electron beam codeposition. The plasmonic property of Ag–MgF2 composites with a high Ag composition CAg (≥90 at. %) are shown to be a function of CAg as well as the size of the NTs, whereas for samples with low CAg (<90 at. %), a nearly constant localized surface plasmon resonance (LSPR) peak appears in all samples, regardless of CAg, NT size, or thin film, which is confirmed to be because of Ag nanoparticles formed during the deposition. Thus, the LSPR property of the composite NTs can be tuned by CAg when CAg ≥ 90 at. %. The resulting LSPR sensor at CAg = 90 at. % with 500 nm diameter polystyrene nanosphere monolayer can achieve a sensitivity of 696 RIU/nm, as compared to 312 RIU/nm for the same NTs with pure Ag. This significantly improved sensitivity is due to the modified dispersion relationship of the dielectric constant by th...

Laser irradiation induced tunable localized surface plasmon resonance of silver thin film

Tunable localized surface plasmon resonance (LSPR) properties of silver thin films were realized by CO2 laser irradiation. The effects of laser irradiation on the structure, morphology and optical property of the samples were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), UV-VIS-NIR double beam spectrometer and Raman system, respectively. XRD patterns show that laser irradiation has the effects of improving grain growth and orientation of Ag thin films. With laser irradiation power increasing, the topography of as-irradiated silver thin films were observed to develop discontinuous nano-ellipsoid structure with a red-shift of the surface plasmon resonance wavelength in visible region. Both the various ellipsoid sizes and the states of aggregation of as-irradiated silver thin films contributed to increase significantly the sensitivity of surface enhanced Raman scattering (SERS). Additionally, the simulation result of Finite-Difference Time-Domain (FDTD) was proved to be in good agreement with that of the experiment.

Colloidal Clusters of Bimetallic Core–Shell Nanoparticles for Enhanced Sensing of Hydrogen in Aqueous Solution

AbstractDeveloping sensitive and stable hydrogen sensors is of great importance for sustainable energy development. Here, a novel hydrogen sensing platform is described based on colloidal clusters of Au@Pd core–shell nanoparticles (Au@Pd NPCs) with characteristic localized surface plasmon resonance (LSPR) properties. Au@Pd NPCs with well‐controlled topologies exhibit highly pronounced sensitivity for LSPR‐based hydrogen sensing in aqueous solution in comparison to their nanoparticle counterparts and previously reported Au–Pd bimetallic nanostructures, which can be attributed to highly promoted plasmonic field resulting from the cluster formation. Furthermore, Au@Pd NPCs show stable sensing capability for repeated hydrogen sensing cycles. The present strategy for devising high‐performance LSPR‐based hydrogen sensors via the controlled assembly of bimetallic nanoparticles can be applied to the development of efficient plasmonic platforms for various sensing applications.

Magneto-plasmonic Au-Coated Co nanoparticles synthesized via hot-injection method

A synthetic procedure is described for the obtaining of superparamagnetic Co nanoparticles (NPs) via hot-injection method in the presence of sodium borohydride. The Co NPs obtained have an average diameter of 5.3 nm and saturation magnetization of 115 emu g−1. A modified Langevin equation is fitted to the magnetization curves using a log-normal distribution for the particle diameter and an effective field to account for dipolar interactions. The calculated magnetic diameter of the Co NPs is 0.6 nm smaller than TEM-derived values, implying a magnetic dead layer of 0.3 nm. The magnetic core is coated with Au to prevent oxidation, resulting in water-stable magneto-plasmonic Co/Au core/shell NPs with saturation of 71.6 emu g−1. The coating adds a localized surface plasmon resonance property with absorbance in the so-called ‘therapeutic window’ (690–900 nm), suitable for biomedical applications. It is suggested that these multifunctional NPs are distinguished as a potential platform for applied and fundamental research.