Localized Surface Plasmon Resonance Peak Research Articles

Experimental and Theoretical Screening of Core Gold Nanoparticles and Their Binding Mechanism to an Anticancer Drug, 2-Thiouracil.

This study demonstrated the capability of two readily available optical spectroscopy tools, namely UV-Vis absorption spectrophotometry and Raman/surface-enhanced Raman spectroscopy, to select in a rapid and noninvasive manner the most homogenous gold nanoparticle (AuNP) models and to identify their chemical binding mechanism to 2-thiouracil (2-TU). 2-TU is an anticancer drug of great promise in the antiproliferative and photothermal therapies of cancer. The citrate-capped AuNPs emerged as the most stable as well as time- and cost-effective AuNP model out of the three widely used colloidal nanocores (citrate-, borohydride-citrate-, and sodium dodecyl sulfate (SDS)-capped AuNPs) that were examined. 2-TU chemically attached to the relatively monodispersed AuNPs via a chemisorption mechanism. The 2-TU-AuNPs complex formed through the covalent bonding of the S atom of 2-TU to the nanosurface in a vertical orientation. The spectroscopic results were then confirmed with the help of density functional theory (DFT) calculations and other physicochemical characterization tools for nanomaterials such as transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential. Overall, the purified 2-TU-AuNPs were found to be spherical, had an average diameter of 25 ± 2 nm, a narrow size distribution (1-30 nm), a sharp localized surface plasmon resonance (LSPR) peak at 525 nm, and a negative surface charge (-14 mV).

A dual-signal output plasmonic sensor based on glucose oxidase-triggered etching of triangular silver nanoprism for sensitive detection of fumonisins

A dual-signal output plasmonic sensor based on glucose oxidase (GOx)-triggered etching of triangular silver nanoprisms (TAgNPRs) was developed for detecting fumonisins (FBs). In the sensor, glucose oxidase (GOx)-FB1 conjugation was used as competitive antigens that compete with FBs to bind with anti-FBs monoclonal antibody (McAb) coated in microplate well. GOx catalyzed glucose to produce hydrogen peroxide (H2O2) which acted as an oxidant to etch TAgNPRs. As a result, the wavelength of localized surface plasmon resonance (LSPR) peak blue shifted along with a color change of the solution. The amount of FBs was correlated to the wavelength shift of LSPR peak and the color change of the solution from light blue to violet in a linear range of 0.1–500 ng/mL. The colorimetric and LSPR detection limits were 0.1 ng/mL and 0.06 ng/mL respectively. The sensitivity of the dual-signal output sensor is better than those of aggregation plasmonic sensor and magnetoimmunosensor.

Construction of the fiber optic LSPR sensor for highly sensitive detection of miR-103 by a dual signal enhancement strategy based on the hot-spot effect and HexSG4 catalysis

MicroRNAs are important tumor biomarkers. How to effectively detect them by sensors is a challenge because of their extremely low concentrations. We proposed a dual signal enhancement strategy to develop the fiber optic (FO) localized surface plasmon resonance (LSPR) sensor for the highly sensitive detection of miR-103. It included two stages, one was to obtain the hot-spot by constructing the multimer structure, AuNP-spacer- AuNPs, and another was the combination of capturing miR-103 by the probe and catalytic amplification by Hexagonal star G-quadruplex catalyzing 4-chloro-1-naphthol to generate benzo-4-chlorohexadienone, which deposited on the AuNPs, resulting in the generation of LSPR peak redshift. The parameters of the preparation and detection application were systematically optimized. The redshift values had a good linear relationship with the logarithms of miR-103 concentrations, with high R2 0.9973, wide detection range 102 - 107 fM, and low LOD 6.4 fM. The method had high specificity, repeatability, and reproducibility, and was also successfully validated with real samples. Therefore, the dual signal strategy for constructing FO LSPR sensors can achieve the high sensitivity detection of extremely low concentration of MicroRNAs, which will have great application prospects in medicine and life science.

Tuning Chemical Interface Damping: Competition between Surface Damping Pathways in Amalgamated Gold Nanorods Coated with Mesoporous Silica Shells.

The mechanism of mercury (Hg) amalgamation in gold nanorods coated with a mesoporous silica shell (AuNRs@mSiO2) and the effect of chemical treatments on the localized surface plasmon resonance (LSPR) spectral changes in single amalgamated AuNRs@mSiO2 remains unclear. In this study, we investigated Hg amalgamation and inward Hg diffusion in single AuNRs@mSiO2 without structural deformation via dark-field scattering spectroscopy and X-ray photoelectron spectroscopy. Then, we investigated the chemisorption of thiol molecules on single amalgamated AuNRs@Hg-mSiO2. Unlike previous studies on single AuNRs, the thiolation on single AuNRs@Hg-mSiO2 resulted in a redshift and line width narrowing of the LSPR peak within 1 h. To determine the chemical effect, we investigated the competition between two surface damping pathways: metal interface damping (MID) and chemical interface damping (CID). When we exposed amalgamated AuNRs@Hg-mSiO2 to 1-alkanethiols with three different carbon chain lengths for 1 h, we observed an increase in the line width broadening with longer chain lengths owing to enhanced CID, demonstrating the tunability of CID and LSPR properties upon chemical treatments. We also investigated the competition between the two surface damping pathways as a function of the time-dependent Au-Hg surface properties in AuNRs@Hg-mSiO2. The 24-h Hg treatment resulted in increased line width broadening compared to the 1-h treatment for the same thiols, which was attributed to the predominance of CID. This was in contrast to the predominance of MID under the 1-h treatment, which formed a core-shell structure. Therefore, this study provides new insights into the Hg amalgamation process, the effect of chemical treatments, competition between surface decay pathways, and LSPR control in AuNRs@mSiO2.

Green synthesis of silver nanoparticles (AgNPs) by Lallemantia royleana leaf Extract: Their Bio-Pharmaceutical and catalytic properties

The study of the silver nanoparticles (AgNPs) synthesis based-green methods become more interesting recently due to their low-cost preparation, eco-friendly and non-toxic precursors. The present study approved the ability of the Lallemantia royleana (Benth. in Wall.) Benth. leaf extract for the synthesis of AgNPs for the first time. The synthesized AgNPs were physico-chemical characterized using ultraviolet–visible spectroscopy (UV–Vis), X-ray diffraction (XRD), Fourier Transform-Infrared Spectroscopy (FT-IR), zeta potential and transmission electron microscopy (TEM) analysis. The total phenols, flavonoids, anthocyanin, tannin contents, antioxidant, antimicrobial, anti-inflammatory, anti-arthritic and cytotoxic activities of L. royleana leaf extract and the synthesized AgNPs were investigated. The biocatalytic activity of prepared AgNPs was assessed on methylene blue as a pollutant organic dye. The TEM examination showed that the synthesized AgNPs were predominantly spherical with some mixed shapes and crystalline with average size 34.47 ± 1.6 nm, and showed a localized surface plasmon resonance (LSPR) peak at 425 nm. The zeta potential value was −24.1 mV indicating the stability of produced AgNPs. The new prepared AgNPs have lower total phenols, flavonoids, anthocyanin, tannin contents than L. royleana leaf extract. In addition, the new prepared AgNPs demonstrated the higher DPPH radical scavenging activity (87 %) and the ABTS radical scavenging activity (77 %) at the maximum prepared concentration of 250 μg mL−1 as compared to the L. royleana leaf extract (62 % and 58 %, respectively). The produced AgNPs also exhibited the higher antimicrobial activity against both the Gram-positive (Staphylococcus aureus and Bacillus cereus) and the Gram-negative (Escherichia coli and Shigella flexneri) bacteria and the Candida strains (Candida glabrata and Candida albicans) as compared to the L. royleana leaf extract. The resulting AgNPs indicated a dose-dependent anti-inflammatory effect on human red-blood cell (RBC) membrane stabilization assay and had more activity (72 %) compared to the L. royleana leaf extract (61 %) at 250 µg mL−1. The prepared AgNPs showed promising in vitro anti-arthritic activity evaluated by 73 % compared to 58 % in case of L. royleana leaf extract. The new produced AgNPs showed the higher cytotoxic effect against the human hepatoma (Hep-G2) and the human breast (MCF-7) cancer cells compared to the L. royleana leaf extract with 79.3 % and 77.2 % at 250 µg/mL, respectively. The obtained results revealed also that the green synthesized AgNPs were capable to catalyze MB dye. Therefore, the obtained results provide a promising route of the green synthesis of AgNPs using L. royleana leaf extract with considerable biopharmaceuticals and catalytic applications.

Dual signal AA detection based on fluorescence and local surface plasmon resonance absorption technology

The core/shell Au@MnO2 nanoparticles (Au@MnO2 NPs) were prepared and characterized by UV–vis spectrum, transmission electron microscopy (TEM) and X-ray photoelectron spectrum (XPS). It was found that MnO2 in the shell of Au@MnO2 NPs could oxidize thiamine (VB1) into blue fluorescent thiochrome (TC). The reduction of MnO2 in the shell layer could lead to a decrease of Au@MnO2 NPs size along with a blue shift of the localized surface plasmon resonance (LSPR) peak. Once ascorbic acid (AA) was introduced, MnO2 in the shell was rapidly reduced to Mn2+ ions. Accordingly, the oxidation of VB1 was inhibited and the fluorescence of TC was weakened. Based on these phenomena, we have established a dual signal method for AA determination with the help of UV–vis and fluorescence spectrophotometer. Under the optimum conditions, the LSPR absorption peak shift (Δλ) of Au@MnO2 NPs and the decrease in fluorescence of TC correlated well with AA concentration ranging from 0.75 to 17.5 μM. The detection limits of LSPR absorption assay and fluorescence assay were 0.18 and 0.47 μM, respectively. More importantly, this dual-signal detection method has been used for the determination of AA in vitamin C tablets with high accuracy and precision, indicating its promising potential applications.

Tightly focused linearly and radially polarized beam effect on the LSPR peak with varying particle size

Interactions of gold and silver spherical nanoparticles (NPs) of a wide range of radius size with tightly focused beams are investigated for a wide range of wavelengths. The scattering of tightly focused beams with a single NP of varying size is examined using a generalized Mie theory and average intensity enhancement in the near-field due to localized surface plasmons is examined for different tightly focused beams. A multipole expansion approach is used to observe the contribution of modes in shaping the scattered light intensity. Influence of particle size and tightly focused beam on intensity enhancement factor is investigated and a shift in localized surface plasmon resonance (LSPR) peak towards higher wavelength is observed with increasing particle size. Maximum intensity enhancement factor due to scattering of different incident beams by a metallic NP is theoretically examined and reported. Gold and silver NP having radius size ranging from 30–60 nm and 1–15 nm respectively showed a maximum intensity enhancement factor in different media. A significant enhancement for the tightly focused radially polarized beam is observed for gold and silver NPs of radius size between 50 nm and 100 nm. Variation towards higher wavelength in LSPR peak due to involvement of higher order of multipoles, and the surrounding medium are also examined in detail.

Elevating Second Near-Infrared Photothermal Conversion Efficiency of Hollow Gold Nanorod for a Precise Theranostic of Orthotopic Bladder Cancer.

The second near-infrared (NIR-II) window laser-activated agents have attracted broad interest in an orthotopic cancer theranostic. However, developing NIR-II photothermal agents (PTAs) with advanced photothermal conversion efficiency (PTCE) and tumor-specific response elevation remains a crucial challenge. Herein, a hollow gold nanorod (AuHNR) with a strong localized surface plasmon resonance (LSPR) peak in the NIR-II window was coated with MnO2 and chitosan to obtain AuHNR@MnO2@CS (termed AuMC) by a one-step method. Upon exposure to the tumor microenvironment (TME), the overexpressed GSH triggered degradation of the MnO2 layer to release Mn2+ and resulted in the PTCE elevation owing to exposure of the AuHNR. Consequently, photoacoustic and magnetic resonance imaging for accurate diagnosis, Mn2+-mediated chemodynamic therapy, and AuHNR elevating PT therapy for precise treatment could be achieved. Both in vitro and in vivo experiments confirmed the good performance of the AuMC on an orthotopic bladder cancer precise theranostic. This study provided NIR-II activated, TME-response PT conversion efficiency enhanced PTAs and offered a tumor-selective theranostic agent for orthotopic bladder cancer in clinical application.

Surface acoustic wave-tuned plasmonic resonances in liquid crystal-covered gold nanostructures

In this work, we propose an acoustically tunable plasmonic device based on liquid crystal (LC)-covered gold nanostructures. By utilizing the standing surface acoustic waves (SSAWs) to realign LC molecules, one can effectively tune the effective refractive index of LCs, and subsequently tune localized surface plasmon resonances (LSPRs) of the gold nanostructures. A 15 nm blue shift of the LSPR peak with the driving voltage of 400 mVpp is experimentally observed. Upon removal of the applied SSAWs, the LC molecules can return to their original orientation, and so does the LSPR peak. Besides the excellent reversibility, this active plasmonic device also features low power consumption and easy integration, which could find many potential applications including switches, modulators, and couplers.

Influence of microstructure on dielectric function and plasmonic properties of silver nanoparticles grown by solid state dewetting: a spectroscopic ellipsometry study

This work reports the microstructure influence on dielectric function and plasmonic properties of silver nanoparticles (Ag NPs). Ag NPs with varying microstructures were grown on corning glass substrate by solid-state dewetting (SSD) of sputtered silver thin films deposited by varying RF power. Dielectric function and plasmonic properties of Ag NPs were investigated from spectroscopic ellipsometry (SE) data using a quite unique model in terms of the combination of different oscillators. Drude–Lorentz model along with two Gauss oscillators was used to account for intraband, interband transitions and different modes of localized surface plasmon resonance (LSPR) of Ag NPs. It was observed that peak of imaginary part of pseudo dielectric function, which is due to LSPR of Ag NPs, shifted towards the lower energy at higher RF power due to increase in thickness of precursor films which subsequently resulted in to increase in particle size. A shift in the LSPR peak in absorbance spectra in UV–Vis-NIR spectroscopy was also observed. No LSPR peak is observed in SE or UV–Vis absorbance spectra for thick films deposited at high RF power due to the presence of continuous silver film even after annealing. This change in microstructure from nanoparticle formation to continuous films is also reflected in the values of void fraction and surface roughness calculated from SE using Bruggeman Effective Medium Approximation (BEMA). Field Emission Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), and X-ray diffraction (XRD) were used to probe the microstructure of Ag NPs. Root mean square (RMS) roughness evaluated from AFM matched well with surface roughness measured from SE.

Detection of NO2- with a colorimetric sensor based on etching Au NBPs

Nitrite (NO2-) in water and food is a potential threat to the environment, human health, and other living organisms. Therefore, the detection of NO2- is highly essential. Herein, a simple and fast colorimetric method for NO2- detection is realized based on the etching of non-modified gold nanobipyramids (Au NBPs), which results in the blue-shift of longitude local surface plasmon resonance (LSPR) peak and obvious color changes. The NO2- was detected through this method with a linear response ranging from 2.0 to 20 μM, a limit of detection (LOD) of 0.17 μM and a naked eye LOD of 6.0 μM under the optimal conditions. The LOD is sufficiently for the detection of NO2- in food in real life applications. During the detection, the morphology of Au NBPs generally changes from the bipyramid shape to the rice shape, and then to the final spheroid shape with increasing NO2- concentration. The feasibility of this method was verified in real samples with good recovery. Compared with other methods, this colorimetric sensor has advantages such as its low cost, excellent sensitivity and selectivity, and the most importantly, it can be applied to visually detect NO2-.

Effect of Postdeposition Heat Treatment on the Nanoplasmonic Behavior of Glancing Angle‐Deposited Silver Nanostructures

Postdeposition heat treatment‐induced modifications of nanoplasmonic response in glancing angle‐deposited (GLAD) Ag nanostructures are systematically investigated. The as‐deposited GLAD Ag thin films are annealed at various temperatures namely 200, 250, 300, and 350 °C in air atmosphere. The reduction in localized surface plasmon resonance (LSPR) absorption peak width is detected with annealing. Morphological characterization of the as‐deposited and annealed films reveals reduction in grain size and shape distributions responsible for narrowing of the LSPR peak width. The refractive index sensitivities of the as‐deposited and annealed films are measured using an in‐house‐developed optical setup and figure of merit (FOM) of the sensors is also estimated. An increase in FOM of the sensors is observed upon annealing while sensitivity is found to be reduced. E‐field profile surrounding the Ag nanoparticles is also simulated to explain the experimental observations on refractive index sensitivity of the films.

Combined Facile Synthesis, Purification, and Surface Functionalization Approach Yields Monodispersed Gold Nanorods for Drug Delivery Applications.

Synthesizing gold nanorods (AuNRs) by seed-mediated growth method results in the presence of undesired size and shape particles by-products occupying 10-90% of the population. In this study, AuNRs are synthesized by the seed-mediated growth method using cetyltrimethylammonium bromide (CTAB) as a surfactant. AuNRs with redshifted longitudinal localized surface plasmon resonance (LLSPR) peak, localized in the biological "transparency window" (650-1350nm), are synthesized after optimizing seed solution, silver nitrate solution, and hydrochloric acid solution volumes, based on the published protocols. A two-step purification method, dialysis followed by centrifugation, is applied to remove excess CTAB and collect LLSPR-redshifted AuNRs with high rod purity (>90%). CTAB is subsequently exchanged with polyethylene glycol (PEG) to improve AuNRs biocompatibility. PEGylated AuNRs are confirmed innocuous to both SN4741 cells and B16F10 cells by the modified MTT assay and the modified lactate dehydrogenase (LDH) assay up to 1nm and 24h incubation. In this study, a combined facile synthesis, purification, and surface functionalization approach is proposed to obtain water-dispersible monodispersed AuNRs for drug delivery applications.

Colorimetric and photothermal immunosensor for sensitive detection of cancer biomarkers based on enzyme-mediated growth of gold nanostars on polydopamine

BackgroundDetecting cancer biomarker levels in body fluids is essential for medical diagnosis. Enzyme-linked immunosorbent assay (ELISA) has been broadly used to detect cancer biomarkers. However, colorimetric ELISA based solely on nanoparticles (NPs) are susceptible to environmental influences, which often results in the detection inaccuracy, being limited in clinical applications. In this regard, the dual-mode approach would add signal diversity to the detection, making the results more reliable. ResultsWe present colorimetric and photothermal immunosensor that enables direct reading of the color and temperature of the solution. A core-satellite nanoprobe constructed by polydopamine (PDA) as the core and gold seeds as satellites is rationally designed as the signal reporter. When ascorbic acid is present in the solution, PDA can cooperate with ascorbic acid to reduce chloroauric acid and mediate the growth of gold seeds on the PDA surface, inducing a redshift of the localized surface plasmon resonance peak of the nanosensor and the change in photothermal conversion efficiency. The method is further combined with the sandwiched immunoassay to construct an alkaline phosphatase based colorimetric and photothermal ELISA for the highly sensitive and accurate evaluation and detection of prostate-specific antigen (PSA). The linear range was from 0.05 to 100 ng mL−1 with a detection limit of 6.71 pg mL−1 for the colorimetric detection, while the linear range was from 0.5 to 90 ng mL−1 with a detection limit of 0.13 ng mL−1 in the photothermal analysis. The accurate detection of PSA levels in serum samples was well demonstrated with the dual-mode approach. SignificanceThe presented immunoassay allows straightforward, sensitive, and selective readout by color and temperature without advanced instrumentation. Particularly, the LOD was much lower than the threshold in clinical trials for PSA. Therefore, this method has a great prospect in the early diagnosis of cancer biomarkers based on a dual-mode multifunctional platform.

Elucidating Surface Plasmon Damping and Fano Resonance Induced by Epitaxial Growth of Palladium on Single Gold Nanorods.

Plasmon damping and Fano resonance induced in the growth of palladium (Pd) on gold nanorods (AuNRs) have been poorly understood. Herein, we investigated the optical properties and morphologies of single AuNRs@Pd (core@shell) synthesized using epitaxial Pd growth at different Pd concentrations. The localized surface plasmon resonance (LSPR) spectra of single AuNRs@Pd showed characteristic subradiant and superradiant peaks as well as Fano resonance as a spectral dip, which was highly influenced by the Pd shell thickness. The occurrence of the Fano resonance during the Pd growth was further verified by in situ real-time observation experiments. We then elucidated time-dependent, real-time variations in LSPR peak wavelength, metal-induced surface damping, and Fano resonance mode of single AuNRs@Pd during Pd shell formation in three successive phases: Pd reduction, nucleation, and growth. Therefore, this study provides new insights into metal interface damping, the Fano resonance, and optical tunability by engineering the Fano resonance energy and Pd shell thickness.

A colorimetric assay for H2O2 and glucose based on the morphology transformation of Au/Ag nanocages to nanoboxes

Herein, we introduced a sensitive colorimetric platform for hydrogen peroxide (H2O2) assay based on gold/silver (Au/Ag) nanocages with porous structure. In the presence of H2O2, the morphology of hollow Au/Ag nanocages was converted to closed nanoboxes, altering their localized surface plasmon resonance (LSPR) peak position and the solution color from light blue to deep blue. The morphology transformation and LSPR peak position of Au/Ag nanocages were proportional to H2O2 concentration at the range of 0.1 to 50 µM. The limit of detection (LOD) was obtained to be 0.02 µM, and the relative standard deviation (RSD, for 0.2, 2.0, and 20 µM) was 2.7, 2.3, and 2.9%, respectively. Moreover, a smartphone-based colorimetric sensor was developed for H2O2 assay at the concentration range of 0.25–4.0 µM, with LOD of 0.2 µM and RSD of 3.2, 2.5, and 2.9% (for 0.5, 1.0, and 3.0 µM, respectively). We exploited the established sensor for glucose assay by measuring the generated H2O2 from the enzymatic reaction between glucose and glucose oxidase. There was a linear relationship between LSPR peak wavelength variations and the amount of glucose from 1.0 to 50 µM, with LOD of 0.4 µM and RSD of 3.2, 3.1, and 3.8% (for 2.0, 10, and 30 µM, respectively). The sensor was successfully applied to determine H2O2 and glucose in food and human serum samples, respectively.

Biomimetic affinity sensor for the ultrasensitive detection of neonicotinoids

Multiple pesticides are often used in combination to protect crops from pests. This makes rapid on-site detection of pesticide contamination challenging. Herein, we describe a method for simultaneous detection of diverse neonicotinoid pesticides using a sensor that combines neonicotinoid-specific odorant-binding protein 2 (OBP2), which was cloned from an insect chemical sensing protein and modified gold nanoparticles with local surface plasmon resonance (LSPR)-based digital nanoplasmonometry (DiNM). When neonicotinoid pesticides bind to OBP2 on gold nanoparticles, the induced LSPR shift peak wavelength is too small to be measured using conventional LSPR immunoassays. DiNM records and compares the scattered image intensity in two adjacent wavelength bands, A and B, centered on the LSPR peak. It considers both the peak shift and the relative intensity change in these two bands, resulting in a significant LSPR signal enhancement. Then the spectral-image contrast was computed as the signal response. Using this approach, we obtained excellent limits of detection (LODs) of 1.4, 1.5, and 4.5 ppb for the neonicotinoids imidacloprid, acetamiprid, and dinotefuran, respectively. Blind tests demonstrated high positive and negative rates for teas, approximately 85 and 100%, respectively. Recombinant OBP2 produced in E. coli offers several advantages over antibodies, including high yield, time savings, and cost effectiveness. Moreover, this method is highly selective and sensitive to neonicotinoids, making it practical for field use.

Resonance Quantization in the Absorption Spectra of Concentric Double Gold Nanoshells: A Numerical Study

AbstractConcentric double metallic shells (CDMSs) are strong candidates for photothermal-based therapy, wherein they utilize their tuned plasmon resonance in the near-infrared region via particle coupling factor fitting. Tuning the resonance of CDMSs to the desired near-infrared region is crucial considering the shift caused by variations in their design parameters. In this study, we investigated the effects of these parameters using full-wave electromagnetic analysis to highlight the dominant factors affecting the resonance shift in the absorption spectra of CDMSs. With systematic variations, our simulation data outlined the direct influence of the outer and inner nanoshells’ (NS2 and NS1) aspect ratios r2 and r1, respectively, on the coupling factor (rT) aptitude for resonance tuning. For example, a CDMS with r2 = r1 = 0.8 shows coupling manifestation between NS2 and NS1 with rT as low as 0.2. However, we need the value of rT to be at least 0.6 for a CDMS with r2 = r1 = 0.4. Moreover, the dominant factors of the localized surface plasmon resonance shifts were determined by examining the mismatched parameter values of the same particle and found them to be related to NS2. We demonstrated how these factors are related to the complexity of localized surface plasmon resonance peak shifting and splitting in the absorption spectra of CDMSs. Our findings are expected to greatly improve the design of nanoparticles to optimize their responses in photothermal-based applications.

Hybrid Metal-Ligand Interfacial Dipole Engineering of Functional Plasmonic Nanostructures for Extraordinary Responses of Optoelectronic Properties.

Programmable manipulation of inorganic-organic interfacial electronic properties of ligand-functionalized plasmonic nanoparticles (NPs) is the key parameter dictating their applications such as catalysis, photovoltaics, and biosensing. Here we report the localized surface plasmon resonance (LSPR) properties of gold triangular nanoprisms (Au TNPs) in solid state that are functionalized with dipolar, conjugated ligands. A library of thiocinnamate ligands with varying surface dipole moments were used to functionalize TNPs, which results in ∼150 nm reversible tunability of LSPR peak wavelength with significant peak broadening (∼230 meV). The highly adjustable chemical system of thiocinnamate ligands is capable of shifting the Au work function down to 2.4 eV versus vacuum, i.e., ∼2.9 eV lower than a clean Au (111) surface, and this work function can be modulated up to 3.3 eV, the largest value reported to date through the formation of organothiolate SAMs on Au. Interestingly, the magnitude of plasmonic responses and work function modulation is NP shape dependent. By combining first-principles calculations and experiments, we have established the mechanism of direct wave function delocalization of electrons residing near the Fermi level into hybrid electronic states that are mostly dictated by the inorganic-organic interfacial dipole moments. We determine that both interfacial dipole and hybrid electronic states, and vinyl conjugation together are the key to achieving such extraordinary changes in the optoelectronic properties of ligand-functionalized, plasmonic NPs. The present study provides a quantitative relationship describing how specifically constructed organic ligands can be used to control the interfacial properties of NPs and thus the plasmonic and electronic responses of these functional plasmonics for a wide range of plasmon-driven applications.

Theoretical Modeling of Plasmon Resonance Induced by Hollow Nanoshell Spheres Assisted with a Graphene Shell for Use as an Efficient Narrowband Absorber

We present theoretical modeling of the local surface plasmon resonance (LSPR) induced by hollow nanoshell spheres assisted with a graphene shell, aiming to examine their potential for use as efficient narrowband absorbers in the infrared wavelength region. We investigate two designs of hollow nanoparticles; namely, a hollow graphene nanosphere with a single graphene shell, and a hollow nanosphere with double shells comprising a graphene shell wrapped around a silver shell. The electric field in each region of the nanoshell is determined by solving the Laplace equation of the potential within the electrostatic approximation (the nanoshell radius [Formula: see text]50[Formula: see text]nm). Using the calculated polarizability of nanoshells, we derive analytical expressions for the absorption and scattering cross-sections. We show that in both proposed nanocomposite models, the graphene shell affords an ultra-narrow LSPR with an absorption efficiency significantly higher than the scattering efficiency. In addition, the graphene-assisted LSPR can be tuned through the visible and infrared regions by changing the Fermi energy and thickness of the graphene layer. Another exciting finding is that the use of a silver shell in the hollow bi-shell nanoparticles provides another LSPR peak besides that induced by the graphene shell. Both LSPRs of graphene and silver shells can be overlapped by changing the optical properties of graphene and/or the geometrical parameters of the silver shell. The resulting LSPR is characterized by a dominant absorption cross-section and a significant narrowband. In both proposed nanoshell designs, the properties of LSPRs are promising for use in various optical imaging and phototherapy applications.