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Colloidal metal nanocrystals (NCs) show great potential in plasmon-enhanced spectroscopy owing to their attractive and structure-depended plasmonic properties. Herein, unique Au rod-cup NCs, where Au nanocups are embedded on the one or two ends of Au nanorods (NRs), are successfully prepared for the first time via a controllable wet-chemistry strategy. The Au rod-cup NCs possess multiple plasmon modes including transverse and longitudinal electric dipole (TED and LED), magnetic dipole (MD), and toroidal dipole (TD) modulated LED resonances, producing large extinction cross-section and huge near-field enhancements for plasmon-enhanced spectroscopy. Particularly, Au rod-cup NCs with two embedded cups show excellent surface-enhanced Raman spectroscopy (SERS) performance than Au NRs (75.6-fold enhancement excited at 633 nm) on detecting crystal violet owing to the strong electromagnetic hotspots synergistically induced by MD, LED, and TED-based plasmon coupling between Au cup and rod. Moreover, the strong TD-modulated dipole-dipole double-resonance and MD modes in Au rod-cup NCs bring a 37.3-fold enhancement of second-harmonic generation intensity compared with bare Au NRs, because they can efficiently harvest photoenergy at fundamental frequency and generate large near-field enhancements at second-harmonic wavelength. These findings provide a strategy for designing optical nanoantennas for plasmon-enhanced applications based on multiple plasmon modes., Electronic Supplementary Material: Supplementary material (SEM image of Au rod-one-cup NCs; TEM image of Au/PbS hybrids; SEM image of Au rod-two-cup NCs; low-amplification SEM image of Au rod-two-cup NCs; experimental extinction and calculated electric field distributions of Au NR excited at different wavelengths; calculated absorption and scattering spectra of Au rod-one-cup NCs; schematic illustration of the cut plane and the corresponding magnetic field distribution under L3 excitation; Raman spectra of CV (10 -6 M) adsorbed on Au rod-cup NCs with different cup sizes; calculated magnetic field distribution of Au rodcup NCs excited at 532 and 633 nm; calculated electric field distributions of Au rod-one-cup NC excited at 600 nm along TE and LE; the models of Au rod-cup NCs used in the simulations) is available in the online version of this article at 10.1007/s12274-022-4562-5., (© Tsinghua University Press 2022.)

The cooperation of magnetic and electric plasmon resonances in cup-shaped metallic nanostructures exhibits significant capability for second-harmonic generation (SHG) enhancement. Herein, we report an approach for synthesizing Au open nanoshells with tunable numbers and sizes of openings on a template of six-pointed PbS nanostars. The morphology of Au nanoshells is controlled by adjusting the amount of HAuCl 4 , and the characteristic shapes of pointed nanocaps, open nanoshells, and hollow nanostars are obtained. Owing to the collaboration of electric and magnetic plasmon resonance modes, the Au nanoshells exhibit significantly broadened and highly tunable optical responses. Furthermore, the morphology-dependent SHG of the Au nanoshells shows two maximal SHG intensities, corresponding to four-opening and one-opening Au nanoshells with appropriate opening sizes. Ag/Au and AuAg/Ag/Au open nanoshells were further investigated to achieve enhanced SHG. By adjusting the thickness of the Ag shell, the SHG intensity of Ag/Au open nanoshells reaches a maximum due to the gradient field at the AuAg bimetallic interface. After replacing the Ag shells with Au shells, the SHG intensity of AuAg/Ag/Au open nanoshells reaches a maximum due to further symmetry breaking. These findings provide a strategy to prepare colloidal metal nanocrystals with prospective applications ranging from nonlinear photonic nanodevices to biospectroscopy and photocatalysis.

A phase junction fabricated by two crystalline phases of the same semiconductor is a promising photocatalyst with efficient charge transfer and separation. However, the weak light absorption and uncontrolled phase junction interface limit the generation and separation of photogenerated carriers. Herein, a two-dimensional (2D)/2D phase junction was prepared by growing orthorhombic WO 3 ultrathin nanosheets on hexagonal WO 3 nanosheets through a one-step hydrothermal method. The orthorhombic/hexagonal WO 3 possesses large-area phase junction interfaces, rich reactive sites, and built-in electric field, which greatly accelerate the photogenerated charge separation and transfer. Thus, the orthorhombic/hexagonal WO 3 displayed excellent photocatalytic hydrogen generation activity from water splitting under light irradiation (λ > 420 nm), which is 2.16 and 2.85 times those of orthorhombic and hexagonal WO 3 phase components. Furthermore, Au nanoparticles (about 4.5 nm in diameter) were deposited on both orthorhombic and hexagonal WO 3 nanosheets to form a plasmon-mediated phase junction. The hybrids exhibit prominent visible-light absorption and efficient charge transfer, leading to a further improved photocatalytic hydrogen generation activity. Further characterization studies demonstrate that superior photoactivity arises from the excellent visible-light-harvesting ability, appropriate band structure, and high-efficiency and multichannel transferring processes of photogenerated carriers.

Flower-like metallic nanocrystals have shown great potential in the fields of nanophononics and energy conversion owing to their unique optical properties and particular structures. Herein, colloid Au nanoflowers with different numbers of petals were prepared by a steerable template process. The structure-adjustable Au nanoflowers possessed double plasmon resonances, tunable electric fields, and greatly enhanced SERS and photocatalytic activity. In the extinction spectra, Au nanoflowers had a strong electric dipole resonance located around 530 to 550 nm. Meanwhile, a longitudinal plasmon resonance (730~760 nm) was obtained when the number of petals of Au nanoflowers increased to two or more. Numerical simulations verified that the strong electric fields of Au nanoflowers were located at the interface between the Au nanosphere and Au nanopetals, caused by the strong plasmon coupling. They could be further tuned by adding more Au nanopetals. Meanwhile, much stronger electric fields of Au nanoflowers with two or more petals were identified under longitudinal plasmon excitation. With these characteristics, Au nanoflowers showed excellent SERS and photocatalytic performances, which were highly dependent on the number of petals. Four-petal Au nanoflowers possessed the highest SERS activity on detecting Rhodamine B (excited both at 532 and 785 nm) and the strongest photocatalytic activity toward photodegrading methylene blue under visible light irradiation, caused by the strong multi-interfacial plasmon coupling and longitudinal plasmon resonance.

The quantum behavior of surface plasmons has received extensive attention, benefiting from the development of exquisite nanotechnology and the diverse applications. Blueshift, redshift, and nonshift of localized surface plasmon resonances (LSPRs) have all been reported as the particle size decreases and enters the quantum size regime, but the underlying physical mechanism to induce these controversial size dependences is not clear. Herein, we propose an improved semiclassical model for modifying the dielectric function of metal nanospheres by combining the intrinsic quantized electron transitions and surface electron injection or extraction to investigate the plasmon shift and LSPR size dependence of the charged Au nanoparticles. We experimentally observe that the nonmonotonic blueshift of LSPRs with size for Au nanoparticles is turned into an approximately monotonic blueshift by increasing the electron donor concentration in the reduction solution, and it can also be transformed to an approximately monotonic redshift after surface passivation by ligand molecules. Moreover, we demonstrate controlled blueshift and redshift for the electron and hole plasmons in Cu_{2-x}S@Au core-shell nanoparticles by injecting electrons. The experimental observations and the theoretical calculations clarify the controversial size dependences of LSPR reported in the literature, reveal the critical role of surface electron injection or extraction in the transformation between the different size dependences of LSPRs, and are helpful for understanding the nature of surface plasmons in the quantum size regime.

The self-assembly process of metal nanoparticles has aroused wide attention due to its low cost and simplicity. However, most of the recently reported self-assembly systems only involve two or fewer metals. Herein, we first report a successful synthesis of self-assembled Ag@AuCu trimetal nanoplates in aqueous solution. The building blocks of multibranched AuCu alloy nanocrystals were first synthesized by a chemical reduction method. The growth of Ag onto the AuCu nanocrystals in the presence of hexadecyltrimethylammonium chloride (CTAC) induces a self-assembly process and formation of Ag@AuCu trimetal nanoplates. These nanoplates with an average side length of over 2 μm show a porous morphology and a very clear boundary with the branches of the as-prepared AuCu alloy nanocrystals extending out. The shape and density of the Ag@AuCu trimetal nanoplates can be controlled by changing the reaction time and the concentration of silver nitrate. The as-assembled Ag@AuCu nanoplates are expected to have the potential for wide-ranging applications in surface-enhanced Raman scattering (SERS) and catalysis owing to their unique structures.

A simple method for the controllable synthesis of Au nanocrystals-metal selenide hybrid nanostructures via amino acid guiding strategy is proposed. The results show that the symmetric overgrowth mode of PbSe shells on Au nanorods can be precisely manipulated by only adjusting the initial concentration of Pb 2+ . The shape of Au-PbSe hybrids can evolve from dumbbell-like to yolk-shell. Interestingly, the plasmonic absorption enhancement could be tuned by the symmetry of these hybrid nanostructures. This provides an effective pathway for maneuvering plasmon-induced energy transfer in metal-semiconductor hybrids. In addition, the photoactivities of Au-PbSe nanorods sensitized TiO 2 electrodes have been further evaluated. Owing to the synergism between effective plasmonic enhancement effect and efficient interfacial charge transfer in these hybrid nanostructures, the Au-PbSe yolk-shell nanorods exhibit an outstanding photocurrent activity. Their photocurrent density is 4.38 times larger than that of Au-PbSe dumbbell-like nanorods under light irradiation at λ > 600 nm. As a versatile method, the proposed strategy can also be employed to synthesize other metal-selenide hybrid nanostructures (such as Au-CdSe, Au-Bi 2 Se 3 and Au-CuSe).

Optical excitation, subsequent energy transfer, and emission are fundamental to many physical problems. Optical antennas are ideal candidates for manipulating these processes. We extend energy transfer to second- and third-harmonic (SH and TH) fields through the collaborative susceptibility χ ( n ) ( n = 1, 2, 3) resonances of nonlinear optical antennas. Hollow gold stars, with a broadband response covering the fundamental, SH, and TH frequencies, are synthesized as nonlinear antennas. Harmonic resonance energy transfer through a χ (3) → χ (1) collaboration is revealed. A χ (3) → χ (2) collaboration is uncovered, with largely enhanced SH radiation demonstrated by exciting the three resonances at the fundamental, SH, and TH frequencies. A theoretical model of the effective nonlinear susceptibilities is proposed to calculate the efficiencies of the two nonlinear energy transfer processes.

The metal-semiconductor heterostructure is an important candidate for photocatalysis due to its efficient charge transport and separation. A controllable morphology and ideal interfaces are critically significant for improving the heterostructure photocatalytic performance. By controlling the concentration of Cd 2+ to control the reaction environment (pH value) and reaction rate, the CdSe nanocrystal is overgrown on the side or tip of the Au nanorods, which leads to a strong interaction between the excitons of CdSe nanocrystals and the plasmons of Au nanorods. Both kinds of Au-CdSe heterorods exhibit good hydrogen productivity. Particularly, the lateral Au-CdSe heterorods exhibit excellent photocatalytic efficiency due to the larger contact interface of Au and CdSe and the strong local field of the CdSe nanocrystals grown on one side of the Au nanorods being enhanced by the transverse plasmon resonance in the visible region. We provide an approach to modulate the combination of the asymmetric metal nanoparticle and the semiconductor shell; these core-semishell heterostructures have potential applications ranging from photocatalysis to photonic nanodevices.

Metal-semiconductor heterostructures integrate multiply functionalities beyond those of their individual counterparts. Great efforts have been devoted to synthesize heterostructures with controlled morphologies for the applications ranging from photocatalysis to photonic nanodevices. Beyond the morphologies, the interface between two counterparts also significantly influences the performance of the heterostructures. Here, we synthesize Au/CdSe Janus nanostructures consisting of two half spheres of Au and CdSe separated by a flat and high-quality interface. Au/CdSe with other morphologies could also be prepared by adjusting the overgrowth conditions. The photocatalytic hydrogen generation of the Au/CdSe Janus nanospheres is measured to be 3.9 times higher than that of the controlled samples with CdSe half-shells overgrown on the Au nanospheres. The highly efficient charge transfer across the interface between Au and CdSe contributes to the improved photocatalytic performance. Our studies may find the applications in the design of heterostructures with highly efficient photocatalytic activity.

Strong couplings between molecular excitons and metal plasmons bring advantages to effectively manipulate the optical properties of hybrid systems, including both absorption and fluorescence. In contrast to absorption behaviours, which have been quite well understood and can be categorized into different regimes such as Fano dip and Rabi splitting, the characteristics of fluorescence in strongly coupled hybrids remain largely unexplored. Quenching instead of the enhancement of fluorescence is usually observed in the corresponding experiments, and a theoretical model to deal with this phenomenon is still lacking. Herein, we demonstrate a largely enhanced fluorescence in a hybrid system with Cy5 dye molecules strongly coupled to Ag nanoparticle films, signified by the huge Rabi splitting absorption spectra. The plexciton Rabi splitting of the hybrids can be tuned from 320 meV to as large as 750 meV by adjusting both plasmon strength and molecular concentration. Moreover, when the excitation and emission wavelengths are respectively tuned to be resonant with the two Rabi peaks, the hybrid acting as a plexcitonic dual resonant antenna exhibits an enhanced fluorescence 44 times larger than that of the free dye molecule. We also develop a theoretical model to simultaneously study the characteristics of both the absorption and emission spectra, including the peak shifting and strength. These findings offer a new strategy to design and fabricate plexcitonic devices with tunable optical responses and efficient fluorescence.

We theoretically demonstrate that pure magnetic quadrupole (MQ) scattering is achieved via the excitation of anapole modes and Fano resonance in noble metal (Au or Ag) and high refractive index dielectric (AlGaAs) hybrid nano-antennas. In Au-AlGaAs hybrid nano-antennas, electric anapole and magnetic anapole modes are observed, leading to the suppressions of electric and magnetic dipoles. Introducing gain material to AlGaAs nanodisk to increase the strength of electric quadrupole (EQ) Fano resonance leads to the suppression of EQ scattering. Then, ideal MQ scattering is achieved at the wavelength of total scattering cross-section dip. The increase of signal-to-noise ratio of MQ results in the great enhancement of near-field inside AlGaAs nanodisk. Additionally, the strong MQ resonance exhibits great capability for boosting second-harmonic generation by proper mode matching. These findings achieved in subwavelength geometries have important implications for functional metamaterials and nonlinear photonic nanodevices.

Metallic nanocavities exhibit extremely high spectral sensitivity to geometrical variations and are promising for sensing applications. Here, the sensitivity of a cubic dimer cavity, to picometer gap variation, is analysed in a model, which takes into account the phase shift of scattering at the boundaries and the quantum tunnelling effect in the small gap limit. The resonance wavelengths are expressed in terms of the plasmon frequency, the medium dielectric function, and the geometry of the gap. The sensitivity of the resonance wavelength to the gap width variation is found to be as high as 1 nm pm-1. While the resonance wavelengths depend on the materials' dielectric functions, the sensitivity is found to scale universally as a function of gap distance. In the sub-nanometer regime, electron tunnelling across the gap starts to suppress the plasmonic field, setting the limit of sensitivity of such a dimer cavity. The results given by the analytical model are complemented by numerical simulations using Comsol. Our model reveals the origin and universal behaviours of the sensitivity of the cavity plasmon and provides guidance for the design of new sensitive rulers at the picometer scale.

We synthesize Au@WS2 hybrid nanobelts and investigate their third-order nonlinear responses mediated by a strong anti-Stokes effect. By using the femtosecond Z-scan technique and tuning the excitation photon energy (Eexc), we find the sign reversals of both nonlinear absorption coefficient β and nonlinear refractive index γ to be around 1.60 eV, which is prominently higher than the bandgap (1.35 eV) of WS2 bulk owing to the strong anti-Stokes processes around the bandgap of the indirect semiconductors. The saturable absorption and self-defocusing of the WS2 nanobelts are significantly enhanced by the plasmon resonance of the Au nanoparticles when Eexc > 1.60 eV. But the excited state absorption assisted by the anti-Stokes processes and the self-focusing observed at Eexc < 1.60 eV are suppressed by the surface plasmon. Furthermore, by using population rate equations, we theoretically analyze the sign reversals of both β and γ and reveal the physical mechanism of the unique nonlinear responses of the hybrids with the plasmon resonance and anti-Stokes effect. These observations enrich the understanding of the nonlinear processes and interactions between the plasmon and exciton and are helpful for developing nonlinear optical nanodevices.

The magnetic plasmons of three-dimensional nanostructures have unique optical responses and special significance for optical nanoresonators and nanoantennas. In this study, we have successfully synthesized colloidal Au and AuAg nanocups with a well-controlled asymmetric geometry, tunable opening sizes, and normalized depths ( h/ b, where h is depth and b is the height of the templating PbS nanooctahedrons), variable magnetic plasmon resonance, and largely enhanced second-harmonic generation (SHG). The most-efficient SHG of the bare Au nanocups is experimentally observed when the normalized depth h/ b is adjusted to ∼0.78-0.79. We find that the average magnetic field enhancement is maximized at h/ b = ∼0.65 and reveal that the maximal SHG can be attributed to the joint action of the optimized magnetic plasmon resonance and the "lightning-rod effect" of the Au nanocups. Furthermore, we demonstrate for the first time that the AuAg heteronanocups prepared by overgrowth of Ag on the Au nanocups can synergize the magnetic and electric plasmon resonances for nonlinear enhancement. By the tailoring of the dual resonances at the fundamental excitation and second-harmonic wavelengths, the far-field SHG intensity of the AuAg nanocups is enhanced 21.8-fold compared to that of the bare Au nanocups. These findings provide a strategy for the design of nonlinear optical nanoantennas based on magnetic plasmon resonances and can lead to diverse applications ranging from nanophotonics to biological spectroscopy.

Both accurate tumor navigation and nanostructures with high photothermal (PT) conversion efficiency are important but remain challenging to achieve in current biomedical applications. This study reports an anion exchange-based facile and green approach for synthesizing Au@Cu 2- x S core-shell nanoparticles (NPs) in an aqueous system. In addition to the PT effect of the suggested NPs, the surface-enhanced Raman scattering (SERS) is also significantly improved due to the tailored localized surface plasmon resonance coupling between the Au metal core and the Cu 2- x S semiconductor shell. Using an epitaxial strategy, Au@Cu 2 O NPs are first obtained by the in situ reduction of cupric hydroxide on a cresyl violet acetate-coated Au core; then, Au@Cu 2- x S NPs are obtained via anion exchange between the S 2- and Cu 2 O shell. Both the Cu/S atomic ratio and the Cu 2- x S shell thickness can be adjusted conveniently. Hence, the ideal integration of the plasmonic Au core and Cu 2- x S shell into a single unit is conducive not only to highly efficient PT conversion but also to the construction of a SERS-based navigator. This new type of SERS-guided NP, with enhanced photoacoustic signals, is an important candidate for both accurate tumor navigation and nondestructive PT treatment guided in vivo by two modes of optical imaging., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this study, we synthesized CdS/(Au-ReS 2 ) nanospheres that have highly efficient photocatalytic hydrogen production activity induced by dielectric-plasmon hybrid antenna resonance. As the diameter (D) of ReS 2 nanospheres consisting of 2D nanosheets increases from 114 ± 11 to 218 ± 25 nm, the resonance wavelength of the ReS 2 dielectric antenna is tuned from 380 to 620 nm and the hydrogen production rate for the CdS/(Au-ReS 2 ) nanospheres increases by more than 1.85 times and reaches a value as high as 3060 μmol g -1 h -1 , with a 9% weight percentage of Au. Due to the enhancements of the local electromagnetic field and excitation energy transfer by the ReS 2 -Au dielectric-plasmon hybrid antenna, the hydrogen production rate for the CdS/(Au-ReS 2 ) nanospheres (D = 218 ± 25 nm) is 797, 319, 105 and 12 times larger than that for pure ReS 2 , Au-ReS 2 , CdS, and CdS-ReS 2 , respectively. Additionally, the persistence and reusability measurements indicate a favorable stability of CdS/(Au-ReS 2 ). These results provide a strategy to prepare a new class of dielectric-plasmon hybrid antennas consisting of 2D materials and metal nanoparticles, which have promise in applications ranging from photocatalysis to nonlinear optics.

The formation and adsorption of bubbles on electrodes weaken the efficiency of gas evolution reactions such as the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by hindering proton transfer and consuming nucleation energy. Herein, a triphase electrode was fabricated to address this limitation by immobilizing MoS2 nanosheets on a porous gas diffusion layer (GDL). This electrode shows a superior HER and OER ratio, high current density and stable working state in electrocatalytic water splitting. Moreover, by lowering the pressure behind the GDL, we further improved the water-splitting rate (the current density was three times higher than that of a bare MoS2 diphase electrode at -0.37 V for HER and 1.62 V for OER) and stability by eliminating the appearance of bubbles, even under a current density as high as 100 mA cm-2. Our work manifests the significance of constructing a triphase system for water splitting, and the system is also available for other gas evolution reactions.

A yolk/shell composite consisting of an AuNR core and an Nd 2 O 3 shell with a 19 nm gap is synthesized by a multi-step over-growth method. The near-infrared luminescence of AuNR@Nd 2 O 3 is up to 4.6 times higher than that of Nd 2 O 3 hollow nanoparticles. The underlying mechanism of plasmon-induced luminescence enhancement is further investigated., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this paper, we propose a new shape memory polymer (SMP) composite with excellent near-infrared (NIR)-photoresponsive shape memory performance and biodegradability. The composite is fabricated by using piperazine-based polyurethane (PU) as thermo-responsive SMP incorporated with black-phosphorus (BP) sheets as NIR photothermal nanofillers. Under 808 nm light irradiation, the incorporated BP sheets with concentration of only 0.08 wt% enable rapid temperature increase over the glass temperature of PU and trigger the shape change of the composite with shape recovery rate of ∼100%. The in vitro and in vivo toxicity examinations demonstrate the good biocompatibility of the PU/BP composite, and it degrades naturally into non-toxic carbon dioxide and water from PU and non-toxic phosphate from BP. By implanting PU/BP columns into back subcutis and vagina of mice, they exhibit excellent shape memory activity to change their shape quickly under moderate 808 nm light irradiaiton. Such SMP composite enable the development of intelligent implantable devices, which can be easily controlled by the remote NIR light and degrade gradually after performing the designed functions in the body., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

An antenna-reactor hybrid coupling plasmonic antenna with catalytic nanoparticles is a new strategy to optimize photocatalytic activity. Herein, we have rationally proposed a Au/XS 2 /Au (X = Re, Mo) antenna reactor, which has a large Au core as the antenna and small satellite Au nanoparticles as the reactor separated by an ultrathin two-dimensional transition-metal dichalcogenide XS 2 shell (∼2.6 nm). Due to efficient charge transfer across the XS 2 shell as well as energy transfer via coupling of the Au antenna and Au reactor, the photocatalytic activity has been largely enhanced: Au/ReS 2 /Au exhibits a 3.59-fold enhancement, whereas Au/MoS 2 /Au exhibits a 2.66-fold enhancement as compared to that of the sum of the three individual components. The different enhancement in the Au/ReS 2 /Au and Au/MoS 2 /Au antenna-reactor hybrid is related to the competition and cooperation of charge and energy transfer. These results indicate the great potential of the Au/XS 2 /Au antenna-reactor hybrid for the development of highly efficient plasmonic photocatalysts.

Herein, we report a strategy to construct a semi-hollow plasmonic nanocavity and grow ultrathin sulfide nanosheets inside. The competition and cooperation of Au deposition with Ag etching based on flat Ag nanoplates are proposed. For the establishment of the semi-hollow nanocavity, Au shells are grown on Ag nanoplates, which serve as a stable frame, followed by partial etching of the Ag nanoplates. By controlling the thickness of the initial Ag nanoplates or the injected amount of etchant, the nanocavity size is fine-tuned. Significantly, the remaining unetched Ag layers provide a flat platform for the growth of 2D ultrathin sulfides of Ag 2 S and CdS inside the semi-hollow plasmonic nanocavity. Strong plasmon resonance and large local field enhancement are exhibited inside the plasmonic cavity where the ultrathin semiconductor sulfides are grown, indicating strong plasmon-exciton interactions in the hybrids. Furthermore, this synthetic approach is extended to grow other metal sulfides such as Bi 2 S 3 and PbS. The combination of a flat plasmonic cavity with ultrathin semiconductor nanosheets in this study provides a new strategy for the development of unique plasmon-based hybrids with excellent optical properties.

Colloidal disk-like and sphere-like MoS 2 nanoantennas are synthesized. They consist of curly and interlaced 2D nanosheets. The resonance peak of the MoS 2 nanoantennas can be tuned from 500 to 900 nm by adjusting the size and shape. The strong magnetic and electric resonances of the dielectric antennas are revealed by theoretical calculations with Mie theory. The second harmonic generation (SHG) of the exfoliated nanosheets and the synthesized nanodisks and nanospheres is investigated and compared by scanning the excitation laser wavelength. SHG enhancement of 52 fold is observed for the spherical nanoantennas at 400 nm, which is attributed to the nanoantenna-enhanced two-photon resonance excitation of the D exciton of MoS 2 monolayers. Moreover, ReS 2 @Au plasmon-dielectric hybrid nanoantennas are also synthesized. The SHG of Au nanoparticles is enhanced 8.5 times by the coupling of the two types of nanoantennas. This new class of optical nanoantennas consisting of 2D materials and exhibiting unique linear and nonlinear optical responses will bring promising applications ranging from nonlinear photonics to photochemistry.

Recent intense effort has been devoted to exploring different manifestations of resonant excitations of strongly coupled plasmons and excitons, but so far such studies have been limited to situations where the Fano- or Rabi-type spectra are largely symmetric at zero detuning. Using a newly developed full quantum mechanical model, here we reveal the existence of a highly asymmetric spectroscopic regime for both the Rabi splitting and transparency dip. The asymmetric nature is inherently tied to the non-negligible exciton absorbance and is caused by substantial interference-induced energy repartitioning of the resonance peaks. This theoretical framework can be exploited to reveal the quantum behaviors of the two excitation entities with varying mutual coupling strengths in both linear and nonlinear regimes. We also use prototypical systems of rhodamine molecules strongly coupled with AuAg alloyed nanoparticles and well-devised control experiments to demonstrate the validity and tunability of the energy repartitioning and correlated electronic state occupations, as captured by the variations in the asymmetric spectroscopy and corresponding nonlinear absorption coefficient as a function of the Au:Ag ratio. The present study helps to substantially enrich our microscopic understanding of strongly coupled plasmon-exciton systems.

We theoretically study the gain-assisted double plasmonic resonances to enhance second harmonic generation (SHG) in a centrosymmetric multilayered silver-dielectric-gold-dielectric (SDGD) nanostructure. Introducing gain media into the dielectric layers can not only compensate the dissipation and lead to giant amplification of surface plasmons (SPs), but also excite local quadrupolar plasmon which can boost SHG by mode matching. Specifically, as the quadrupolar mode dominates SHG in our nanostructure, under the mode matching condition, the intensity of second harmonic near-field can be enhanced by 4.43 × 10 2 and 1.21 × 10 5 times when the super-resonance is matched only at the second harmonic (SH) frequency or fundamental frequency, respectively. Moreover, the intensity of SHG near-field is enhanced by as high as 6.55 × 10 7 times when the nanostructure is tuned to double super-resonances at both fundamental and SH frequencies. The findings in this work have potential applications in the design of nanosensors and nanolasers.

Three component hybrid (MoS 2 -TiO 2 )/Au substrate is fabricated by loading plasmonic Au nanorods on the MoS 2 nanosheets coated TiO 2 nanorod arrays. It is used for photoelectrochemical (PEC) cell and photocatalyst for hydrogen generation. Owing to the charge transfer between the MoS 2 -TiO 2 hetero-structure, the PEC current density and hydrogen generation of TiO 2 nanoarrays are enhanced 2.8 and 2.6 times. The broadband photochemical properties are further enhanced after Au nanorods loading. The plasmon resonance of Au nanorods provides more effective light-harvesting, induces hot-electron injection, and accelerates photo-excited charges separation. The results have suggested a route to construct nanohybrid by combining one-dimensional arrays and two-dimensional nanosheets, meanwhile have successfully utilized plasmonic nanorods as a sensitizer to improve the photochemical properties of the semiconductor nanocomposite.

The "artificial magnetic" resonance in plasmonic metamolecules extends the potential application of magnetic resonance from terahertz to optical frequency bypassing the problem of magnetic response saturation by replacing the conduction current with the ring displacement current. So far, the magnetic Fano resonance-induced nonlinearity enhancement in plasmonic metamolecule rings has not been reported. Here, we use the magnetic Fano resonance to enhance second-harmonic generation (SHG) in plasmonic metamolecule rings. In the spectra of the plasmonic metamolecule, an obvious Fano dip appears in the scattering cross section, while the dip does not appear in the absorption cross section. It indicates that at the Fano dip the radiative losses are suppressed, while the optical absorption efficiency is at a high level. The largely enhanced SHG signal is observed as the excitation wavelength is adjusted at the magnetic Fano dip of the plasmonic metamolecule rings with stable and tunable magnetic responses. We also compare the magnetic Fano dip with the electric case to show its advantages in enhancing the fundamental and second harmonic responses. Our research provides a new thought for enhancing optical nonlinear processes by magnetic modes.

We report a plasmon-assisted growth of metal and semiconductor onto the tips of Ag nanotriangles (AgNTs) under light irradiation. The site-selective growth of Ag onto AgNTs are firstly demonstrated on the copper grids and amine-coated glass slides. As the irradiation time increases, microscopic images indicate that AgNTs gradually touch with each other and finally "weld" tip-to-tip together into the branched chains. Meanwhile, the redshift of plasmon band is observed in the extinction spectra, which agrees well the growth at the tips of AgNTs and the decrease of the gaps between the adjacent nanotriangles. We also synthesize AgNT-Cu 2 O nanocomposites by using a photochemical method and find that the Cu 2 O nanoparticles preferably grow on the tips of AgNTs. The site-selective growth of Ag and Cu 2 O is interpreted by the local field concentration at the tips of AgNTs induced by surface plasmon resonance under light excitation.

Excitation-dependent fluorophores (EDFs) have been attracted increasing attention owing to their high tunability of emissions and prospective applications ranging from multicolor patterning to bio-imaging. Here, we report tunable fluorescence with quenching dip induced by strong coupling of exciton and plasmon in the hybrid nanostructure of CTAB* EDFs and gold nanoparticles (AuNPs). The quenching dip in the fluorescence spectrum is tuned by adjusting excitation wavelength as well as plasmon resonance and concentration of AuNPs. The observed excitation-dependent emission spectra with quenching dip are theoretically reproduced and revealed to be induced by resonant energy transfer from multilevel EDFs with wider width channels to plasmonic AuNPs. These findings provide a new approach to prepare EDF molecules and a strategy to modulate fluorescence spectrum via exciton-to-plasmon energy transfer.

The surface plasmon resonance (SPR) of metal nanoparticles exhibits quantum behaviors as the size decreases owing to the transitions of quantized conduction electrons, but most studies are limited to the monotonous SPR blue-shift caused by off-resonant transitions. Here, we demonstrate the nonmonotonous SPR red-shift caused by resonant electron transitions and photocatalytic activity enhanced by the quantum plasmon resonance of colloidal gold nanoparticles. A maximal SPR wavelength and the largest photocatalytic activity are observed in the quantum regime for the first time for the gold nanoparticles with a diameter of 3.6 nm. Theoretical analysis based on a quantum-corrected model reveals the evolution of SPR with quantized electron transitions and well explains the nonmonotonous size-dependencies of the SPR wavelength and absorption efficiency. These findings have profound implications for the understanding of the quantum nature of the SPR of metal nanoparticles and their applications in areas ranging from photophysics to photochemistry.

The transport properties of a single plasmon interacting with a hybrid system composed of a semiconductor quantum dot (SQD) and a metal nanoparticle (MNP) coupled to a one-dimensional surface plasmonic waveguide are investigated theoretically via the real-space approach. We considered that the MNP-SQD interaction leads to the formation of a hybrid exciton and the transmission and reflection of a single incident plasmon could be controlled by adjusting the frequency of the classical control field applied to the MNP-SQD hybrid nanosystem, the kinds of MNPs and the background media. The transport properties of a single plasmon interacting with such a hybrid nanosystem discussed here could find applications in the design of next-generation quantum devices, such as single-photon switching and nanomirrors, and in quantum information processing.

Plasmon-mediated energy transfer is highly desirable in photo-electronic nanodevices, but the direct injection efficiency of "hot electrons" in plasmonic photo-detectors and plasmon-sensitized solar cells (plasmon-SSCs) is poor. On another front, Fano resonance induced by strong plasmon-exciton coupling provides an efficient channel of coherent energy transfer from metallic plasmons to molecular excitons, and organic dye molecules have a much better injection efficiency in exciton-SSCs than "hot electrons". Here, we investigate enhanced light-harvesting of chlorophyll-a molecules strongly coupled to Au nanostructured films via Fano resonance. The enhanced local field and plasmon resonance energy transfer are experimentally revealed by monitoring the ultrafast dynamical processes of the plexcitons and the photocurrent flows of the assembled plexciton-SSCs. By tuning the Fano factor and anti-resonance wavelengths, we find that the local field is largely enhanced and the efficiency of plexciton-SSCs consisting of ultrathin TiO2 films is significantly improved. Most strikingly, the output power of the plexciton-SSCs is much larger than the sum of those of the individual plasmon- and exciton-SSCs. Our observations provide a practical approach to monitor energy and electron transfer in plasmon-exciton hybrids at a strong coupling regime and also offer a new strategy to design photovoltaic nanodevices.

Poly(vinylpyrrolidone)-encapsulated Bi2 Se3 nanosheets with a thickness of 1.7 nm and diameter of 31.4 nm are prepared by a solution method. Possessing an extinction coefficient of 11.5 L g(-1) cm(-1) at 808 nm, the ultrathin Bi2 Se3 nanosheets boast a high photothermal conversion efficiency of 34.6% and excellent photoacoustic performance. After systemic administration, the Bi2 Se3 nanosheets with the proper size and surface properties accumulate passively in tumors enabling efficient photoacoustic imaging of the entire tumors to facilitate photothermal cancer therapy. In vivo biodistribution studies reveal that they are expelled from the body efficiently after 30 d. The ultrathin Bi2 Se3 nanosheets have large clinical potential as metabolizable near-infrared-triggered theranostic agents., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This paper describes a facile method for the synthesis of Au/AuAg/Ag2S/PbS core-multishell nanorods with double trapping layers. The synthesis, in sequence, involved deposition of Ag shells onto the surfaces of Au nanorod seeds, formation of AuAg shells by a galvanic replacement reaction, and overgrowth of the Ag2S shells and PbS shells. The resulting core-multishell nanorod possesses an air gap between the Au core and the AuAg shell. Together with the Ag2S shell, the air gap can efficiently trap light, causing strong field confinement and nonlinear enhancement. The as-prepared Au/AuAg/Ag2S/PbS core-multishell nanorods display distinct localized surface plasmon resonance and nonlinear optical properties, demonstrating an effective pathway for maneuvering the optical properties of nanocavities.

We investigate the nonlinear propagation of surface plasmon polaritons guided on gold nanowires surrounded by silica glass. Based on the Lorentz reciprocity theorem, we derive a formula for the complex nonlinear susceptibility, and study its dependence on waveguide parameters and wavelength for the fundamental mode. Depending on these parameters both positive and negative signs of the real and imaginary parts of the nonlinear coefficient are predicted. This implies that nanowires exhibit the property of saturable absorption or optical limiting as well as positive and negative nonlinear phase shifts. The physical origin of this phenomenon is discussed.

By using silver nanoplatelets with a widely tunable localized surface plasmon resonance (LSPR), and their corresponding local field enhancement, here we show large manipulation of plasmonic enhanced upconversion in NaYF4:Yb(3+)/Er(3+) nanocrystals at the single particle level. In particular, we show that when the plasmonic resonance of silver nanolplatelets is tuned to 656 nm, matching the emission wavelength, an upconversion enhancement factor ~5 is obtained. However, when the plasmonic resonance is tuned to 980 nm, matching the nanocrystal absorption wavelength, we achieve an enhancement factor of ~22 folds. The precise geometric arrangement between fluorescent nanoparticles and silver nanoplatelets allows us to make, for the first time, a comparative analysis between experimental results and numerical simulations, yielding a quantitative agreement at the single particle level. Such a comparison lays the foundations for a rational design of hybrid metal-fluorescent nanocrystals to harness the upconversion enhancement for biosensing and light harvesting applications.

We report the development of neurotoxin-mediated upconversion nanoprobes for tumor targeting and visualization in living animals. The nanoprobes were synthesized by preparing polyethylenimine-coated hexagonal-phase NaYF(4):Yb,Er/Ce nanoparticles and conjugating them with recombinant chlorotoxin, a typical peptide neurotoxin that could bind with high specificity to many types of cancer cells. Nanoprobes that specifically targeted glioma cells were visualized by laser scanning upconversion fluorescence microscopy. Good probe biocompatibility was displayed with cellular and animal toxicity determinations. Animal studies were performed using Balb-c nude mice injected intravenously with the nanoprobes. The obtained high-contrast images demonstrated highly specific tumor binding and direct tumor visualization with bright red fluorescence under 980-nm near-infrared irradiation. The high sensitivity and high specificity of the neurotoxin-mediated upconversion nanoprobes and the simplification of the required optical device for tumor visualization suggest an approach that may help improve the effectiveness of the diagnostic and therapeutic modalities available for tumor patients., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Semiconductor quantum dots (QDs) have several photo-physical advantages over organic dyes making them good markers in biomedical application. We used CdSe/ZnS QDs with maximum emission wavelength of 590nm (QD590) linked to alpha-fetoprotein (AFP) monoclonal antibody (Ab) to detect AFP in cytoplasm of human hepatocellular carcinoma (HCC) cell line HCCLM6. For the in vivo studies, we used QD-AFP-Ab probes for targeted imaging of human HCC xenograft growing in nude mice by injecting them into the tail vein. In addition, the cytotoxicity in vitro, the acute toxicity in vivo, the hemodynamics and tissue distribution of these probes were also investigated. The results in vitro and in vivo indicate that our QD-based probes have good stability, specificity and biocompatibility for ultrasensitive fluorescence imaging of molecular targets in our liver cancer model system.

To investigate the influence of surface trapping and dark states on CdSe and CdSe/ZnS quantum dots (QDs), we studied the absorption, fluorescence intensity and lifetime by using one-and two-photon excitation, respectively. Experimental results show that both one- and two-photon fluorescence emission efficiencies of the QDs enhance greatly and the lifetime increase after capping CdSe with ZnS due to the effective surface passivation. The lifetime of one-photon fluorescence of CdSe and CdSe/ZnS QDs increase with increasing emission wavelength in a supralinear way, which is attributed to the energy transfer of dark excitons. On the contrary, the lifetime of two-photon fluorescence of bare and core-shell QDs decrease with increasing emission wavelength, and this indicates that the surface trapping is the dominant decay mechanism in this case.

Objective: To explore in-vivo targeted imaging techniques for liver cancer detection using quantum dots (QDs) labeled probes in a nude mouse model of human hepatocellular carcinoma., Methods: Mercaptoacetic acid (MAA) modified QDs were linked to mouse-anti-human alpha-fetoprotein (AFP) monoclonal antibody to form water soluble QD-AFP-Ab probes, which were validated by spectra analyses and transmission electron microscope. The probes were firstly used to detect AFP antigen in human hepatocellular carcinoma cell line HCCLM6 in-vitro by one-step immunofluorescence method. In-vivo tumor xenografts and lung metastases models were then established by inoculation of HCCLM6 cells subcutaneously and into the tail vein of nude mice, respectively. QD-AFP-Ab probes were injected into the tail vein of the tumor bearing mice for live animal fluorescence imaging. Spectra of tumor and normal tissue were analyzed under illumination of Ti: sapphire laser. Serum levels of alanine amino transferase, aspartate amino transferase, blood urea nitrogen and creatinine were determined by conventional biochemical analysis. The liver, spleen, lungs, kidneys, heart and brain of the experimental nude mice were investigated for nonspecific uptake of the probes by confocal microscope., Results: The QD-AFP-Ab probes had broad excitation spectra and high fluorescence intensity. They could specifically and efficiently recognize AFP antigen in hepatocellular carcinoma cells. Tumor targeting imaging using these probes were successful without any acute toxicity to the experimental animals. Spectra analysis showed that the probes per field were lower in the centre than the periphery of the tumor. Non-specific uptake of QD-AFP-Ab probes occurred mainly in the liver, spleen and lungs., Conclusions: QD-AFP-Ab probes have good optical properties and biocompatibility for in-vivo targeted imaging of hepatocellular carcinoma. Such approach promises to be highly desirable for molecular targeted research of liver cancer.