Asymmetric Nanoparticles Research Articles

Engineering of Asymmetric Hollow Carbon Nanoparticles with Tunable Architecture via Flowable Colloidal Polymer‐Emulsion Assembly Strategy

Engineering of Asymmetric Hollow Carbon Nanoparticles with Tunable Architecture via Flowable Colloidal Polymer‐Emulsion Assembly Strategy

Symmetry-breaking-induced off-resonance second-harmonic generation enhancement in asymmetric plasmonic nanoparticle dimers

Abstract The linear and nonlinear optical properties of metallic nanoparticles have attracted considerable experimental and theoretical research interest. To date, most researchers have focused primarily on exploiting their plasmon excitation enhanced near-field and far-field responses and related applications in sensing, imaging, energy harvesting, conversion, and storage. Among numerous plasmonic structures, nanoparticle dimers, being a structurally simple and easy-to-prepare system, hold significant importance in the field of nanoplasmonics. In highly symmetric plasmonic nanostructures, although the odd-order optical nonlinearity of the near-surface region will be improved because of the enhanced near-fields, even-order nonlinear processes such as second-harmonic generation (SHG) will still be quenched and thus optically forbidden. Under this premise, it is imperative to introduce structural symmetry breaking to realize plasmon-enhanced even-order optical nonlinearity. Here, we fabricate a series of nanoparticle dimers each composed of two gold nanospheres with different diameters and subsequently investigate their structural asymmetry dependent linear and nonlinear optical properties. We find that the SHG intensities of gold nanosphere dimers are significantly enhanced by structural asymmetry under off-resonance excitation while the plasmonic near-field enhancement mainly affects SHG under on-resonance excitation. Our results reveal that symmetry breaking will play an indispensable role when designing novel coupled plasmonic nanostructures with enhanced nonlinear optical properties.

Tunable Plasmonic Properties of Spatially Overlapping Asymmetric Nanoparticle Dimers

Tunable Plasmonic Properties of Spatially Overlapping Asymmetric Nanoparticle Dimers

On the Synthesis, Microstructure, and Thermoelectric Properties of the Composite Material Bi2Te2.7Se0.3/Teδ Obtained from Asymmetric Nanoparticles

On the Synthesis, Microstructure, and Thermoelectric Properties of the Composite Material Bi2Te2.7Se0.3/Teδ Obtained from Asymmetric Nanoparticles

Preparation of Asymmetric Al2O3-SiO2 Janus Nanoparticles in Aqueous Phase and Its Interfacial Property.

In this study, asymmetric Al2O3-SiO2 Janus nanoparticles with a dumbbell-like structure were synthesized by a facile chemical process in the aqueous phase. Prior to synthesis, Al2O3 nanoparticles in hydrosol were amino-modified using 3-aminopropyl triethoxysilane (KH550) and then carboxyl acid-functionalized using a ring-opening reaction of the amine functions with succinic anhydride, imparting unique anionic properties to the Al2O3 end. SiO2 nanoparticles were rendered hydrophobic through modification with hexamethyldisilazane (HMDS) and further functionalized with 3-chloropropyl triethoxysilane (KH230). The two nanoparticle hydrosols were then mixed, and the asymmetric Al2O3-SiO2 Janus nanoparticles were synthesized via the reaction between the -NH2 and -CH2Cl groups. The prepared Janus nanoparticles were primarily characterized by dynamic light scattering (DLS), Zeta potential (ZP), and transmission electron microscopy (TEM). The results indicated that about 90% of the modified Al2O3 and SiO2 nanoparticles were covalently coupled in a one-to-one manner to form the dominant dumbbell-like structure. These Janus nanoparticles exhibit amphiphilic properties, making them highly promising surfactants for emulsifying oil-water mixtures.

Droplet‐Directed Anisotropic Assembly of Semifootball‐Like Carbon Nanoparticles with Multimodal Pore Architectures

AbstractHierarchical porous carbon nanoparticles, with tailored asymmetric morphologies and pore structures, have great implications in high‐performance electrode materials. However, the controlled synthesis of anisotropic carbon nanoparticles with tailored multimodal pore structures remains a challenge. Herein, a droplet‐directed anisotropic assembly approach to synthesize asymmetric carbon nanoparticles with macro/mesopores is demonstrated. This synthesis relies on the anisotropic growth of mesoporous polydopamine (PDA) seeds on the emulsion interfaces and the subsequent immersion of 1,3,5‐trimethylbenzene (TMB) droplets into the seeds. The obtained carbon nanoparticles present a semifootball‐shaped morphology with a high surface area (383 m2 g−1), well‐controlled macropores (≈105 nm), and mesopores (≈3.8 nm). By tuning the polarity of the oil phase, the morphologies transform from non‐porous spheres to semifootball‐like architectures and finally to nano‐ellipsoid with meso‐channels. The pore structures are further optimized by ZnCl2 activation, and the semifootball‐like carbon nanoparticles with modulated pore compositions deliver a high reversible capability, excellent rate performance (215 F g−1 at 0.05 A g−1 and 143 F g−1 at 20 A g−1 in organic electrolyte), and enhanced energy density (53.4 Wh Kg−1). Simulation results elucidate the structure–activity relationship between the multistage pore structure and electrochemical performance, i.e., pore hierarchy enhances ion diffusion flux, and large‐mesopore structure facilitates rate performance.

Spatially Asymmetric Nanoparticles for Boosting Ferroptosis in Tumor Therapy.

Despite its effectiveness in eliminating cancer cells, ferroptosis is hindered by the high natural antioxidant glutathione (GSH) levels in the tumor microenvironment. Herein, we developed a spatially asymmetric nanoparticle, Fe3O4@DMS&PDA@MnO2-SRF, for enhanced ferroptosis. It consists of two subunits: Fe3O4 nanoparticles coated with dendritic mesoporous silica (DMS) and PDA@MnO2 (PDA: polydopamine) loaded with sorafenib (SRF). The spatial isolation of the Fe3O4@DMS and PDA@MnO2-SRF subunits enhances the synergistic effect between the GSH-scavengers and ferroptosis-related components. First, the increased exposure of the Fe3O4 subunit enhances the Fenton reaction, leading to increased production of reactive oxygen species. Furthermore, the PDA@MnO2-SRF subunit effectively depletes GSH, thereby inducing ferroptosis by the inactivation of glutathione-dependent peroxidases 4. Moreover, the SRF blocks Xc- transport in tumor cells, augmenting GSH depletion capabilities. The dual GSH depletion of the Fe3O4@DMS&PDA@MnO2-SRF significantly weakens the antioxidative system, boosting the chemodynamic performance and leading to increased ferroptosis of tumor cells.

Asymmetric nanoparticle oxidation observed in-situ by the evolution of diffraction contrast

The use of transmission electron microscopy (TEM) to observe real-time structural and compositional changes has proven to be a valuable tool for understanding the dynamic behavior of nanomaterials. However, identifying the nanoparticles of interest typically require an obvious change in position, size, or structure, as compositional changes may not be noticeable during the experiment. Oxidation or reduction can often result in subtle volume changes only, so elucidating mechanisms in real-time requires atomic-scale resolution or in-situ electron energy loss spectroscopy, which may not be widely accessible. Here, by monitoring the evolution of diffraction contrast, we can observe both structural and compositional changes in iron oxide nanoparticles, specifically the oxidation from a wüstite-magnetite (FeO@Fe3O4) core–shell nanoparticle to single crystalline magnetite, Fe3O4 nanoparticle. The in-situ TEM images reveal a distinctive light and dark contrast known as the ‘Ashby-Brown contrast’, which is a result of coherent strain across the core–shell interface. As the nanoparticles fully oxidize to Fe3O4, the diffraction contrast evolves and then disappears completely, which is then confirmed by modeling and simulation of TEM images. This represents a new, simplified approach to tracking the oxidation or reduction mechanisms of nanoparticles using in-situ TEM experiments.

Asymmetric Pt nanoparticles with high lattice strain grown onto 3D graphene film as efficient integrated catalyst layer for proton exchange membrane fuel cells

Reducing Pt loading in proton exchange membrane fuel cells (PEMFCs) with improved performance is highly demanded for their wide adoption.Herein, asymmetric Pt nanoparticles (NPs) onto 3D graphene porous film (3D-GF) as integrated electrode was developed for ultra-low Pt loading PEMFCs. The 3D-GF featuring highly graphitic degree and rich macro-porosity as the framework of constructing catalyst layer was prepared by arc-discharge method and Pt NPs were grown onto 3D-GF via atomic layer deposition. The Pt NPs prefer to grow along the surface of graphene, presenting unique characteristics of high lattice strain with extended contact interface with 3D-GF. The specific structure is completely distinguished from Pt based NPs with symmetric structures synthesized by wet chemical methods. The cell with Pt/3D-GF at 100 μgPt cm−2 as the cathode exhibits outstanding activity and durability, in which its maximum power density (MPD) is 2.07 W cm−2 and 0.88 W cm−2 under H2/O2 and H2/Air at 150.0 kPa respectively, much higher than that of the cell with Pt/C at 200 μgPt cm−2, as the mass activity (MA) of Pt/3D-GF is 3.0 times higher than that of commercial Pt/C catalysts, and its performance suffers from the MPD loss of 25 % and 7.6 % after accelerated durability tests (ADTs) with 30 K cycles at 0.6–0.95 V and 5 K cycles at 1.0–1.5 V respectively, which is also significantly lower than that of commercial Pt/C catalyst. The asymmetric Pt NPs on 3D-GF provides a new concept for achieving ultra-low Pt loading PEMFCs.

Light absorption enhancement in organic solar cell using non-concentric Ag:SiO2 core-shell nanoparticles

Low solar energy conversion efficiency prevents the widespread of organic solar cells; hence, metal nanoparticles have been used to overcome this problem without increasing cell thickness. We investigated light absorption enhancement in view of the embedment of Ag:SiO2 core-shell nanoparticles of different shell thicknesses, core offsets, offset orientation angles, and vertical mismatches between neighboring particles. The simulations were carried out using the finite element method. This is the first investigation in the use of asymmetric nanoparticles. At optimized conditions, absorption enhancement up to 345% compared to the one without the nanoparticles could be achieved. The enhancement was found much higher than that of the published values. The enhancement results were mainly from the increase of near-field localization and scattering in the active layer of solar cells due to the excitation of Fano resonances. The resonance occurred due to the non-symmetric nature of the core-shell nanoparticles.

Tetrazole Linkages as Photoactivated Fuels for Light‐Regulated Photothermal/Photocatalytic Propulsion of Versatile Polymer Nanoplatforms

AbstractColloidal motors with multimode propulsion have attracted considerable attention because of enhanced transportability. It is a great challenge to fabricate colloidal motors powered by a single engine for multimode synergistic propulsion. Herein, we report on Janus versatile polymer nanoplatforms integrating various functionalities via tetrazole linkages for light‐regulated multimode synergistic propulsion in the liquid. The presence of tetrazole linkages in the polymers endows the nanoparticles with various photoresponsive capabilities. A sole energy source (ultraviolet or visible light) simultaneously activates photocatalytic N2 release and photothermal conversion within the tetrazole‐containing polymer phase at one side of asymmetric nanoparticles for converting light energy into photothermal/photocatalytic propulsion independent of the surrounding chemical medium. The photoactivated locomotion using tetrazoles as light‐triggered fuels highly corresponds to light wavelengths, light powers and tetrazole contents. The tetrazole linkages capable of incorporating various functionalities to the polymer nanoparticles allow on‐demand customizing of the colloidal motors, showing great potential in bio‐applications.

Tetrazole Linkages as Photoactivated Fuels for Light-Regulated Photothermal/Photocatalytic Propulsion of Versatile Polymer Nanoplatforms.

Colloidal motors with multimode propulsion have attracted considerable attention because of enhanced transportability. It is a great challenge to fabricate colloidal motors powered by a single engine for multimode synergistic propulsion. Herein, we report on Janus versatile polymer nanoplatforms integrating various functionalities via tetrazole linkages for light-regulated multimode synergistic propulsion in the liquid. The presence of tetrazole linkages in the polymers endows the nanoparticles with various photoresponsive capabilities. A sole energy source (ultraviolet or visible light) simultaneously activates photocatalytic N2 release and photothermal conversion within the tetrazole-containing polymer phase at one side of asymmetric nanoparticles for converting light energy into photothermal/photocatalytic propulsion independent of the surrounding chemical medium. The photoactivated locomotion using tetrazoles as light-triggered fuels highly corresponds to light wavelengths, light powers and tetrazole contents. The tetrazole linkages capable of incorporating various functionalities to the polymer nanoparticles allow on-demand customizing of the colloidal motors, showing great potential in bio-applications.

Site-selective growth and plasmonic spectral properties of L-shaped Janus Au-Ag gold nanodumbbells for surface-enhanced Raman scattering

Ligand-mediated interface control has been broadly applied as a powerful tool in constructing asymmetric multicomponent nanoparticles (AMNP), and induces the anisotropic growth with fine-tuning morphology, composition, plasmonic property and functionality. As a new kind of AMNP, the synthesis of Janus Au-Ag nanoparticles with tunable negative surface curvature is still a challenge. Here, we demonstrate that the synergistic surface energy effects between gold nanodumbbells (Au NDs) with a negative surface curvature and 4-mercaptobenzoic acid (4-MBA) can direct the site-selective growth of anisotropic silver domains on gold nanodumbbells (Au NDs@Ag NPs). By adjusting the 4-MBA concentration-dependent interfacial energy, the Au NDs@Ag NPs could be continuously tuned from dumbbell-like core–shell structures, to L-shaped Janus, and then rod-like core–shell structures with directional and asymmetric spatial distributions of resizable Ag domains by site-selective growth. Based on the calculation results of discrete dipole approximation (DDA) method, it has been found that the Au NDs@Ag L-shaped Janus NPs with Ag island domains created polarization orientation-dependent plasmonic extinction spectra and hot spots around the negatively curved waist and Ag domains. The L-shaped Janus Au NDs@Ag NPs exhibited significantly plasmonic spectrum properties with four apparent LSPR peaks that cover from visible to near-infrared range and higher surface-enhanced Raman scattering (SERS) activity compared with the original Au NDs. The best SERS enhancement factor of 1.41 × 107 was achieved. This synergistic surface energy effect-based method involving the asymmetric growth of silver coating on gold nanoparticles with negatively curved surface presents a new method to design and fabricate nanometer optical devices based on asymmetric multicomponent nanoparticles.

PROPERTIES OF NANOSTRUCTURED COMPOSITES OF POLY(VINYLIDENE FLUORIDE) WITH DOPED POLY(3-METHYLTHIOPHENE)

The combination of properties of intrinsically conducting polymers (ICPs) and functional nanostructured template materials opens up prospects for their use in various fields, ranging from bioelectronics to sensors and energy conversion. Successful combinations solve one of the important drawbacks of many ICPs, created by their insolubility and infusibility, and help to achieve their full potential in thermally processable materials. When developing such hybrid materials, it is necessary to take into account the sensitivity of ICP properties to interphase interactions due to extended π-conjugation in these polymers. However, this aspect of ICP-based nanocomposites has not been sufficiently studied yet. In this paper we investigate the effect of template submicron poly(vinylidene fluoride) (PVDF) particles and the nature of the dopant on properties of poly(3-methylthiophene) (P3MT) precipitated as the shell at the PVDF core surface in the course of the 3MT oxidative polymerization. For this purpose, we compare the properties of P3MT phase of the composites with the properties of the neat P3MT doped with dodecylbenzenesulfonate (DBS), perfluorooctanoate (PFO) and chloride anions. In the formed composite core-shell particles the P3MT is in the form of asymmetric nanoparticles which are localized almost exclusively at the surface of PVDF particles. According to the conjugation length, neat polymers form the following series: P3MT-Cl > P3MT-DBS > P3MT-PFO as evidenced by the IR spectral analysis. In their composites the conjugation length of P3MT doped with Cl- does not change noticeably, while for the DBS and PFO anions cases it increases and for the DBS case it exceeds that of Cl- case. X-ray phase analysis showed an increase in the degree of crystallinity of P3MT-Cl and P3MT-DBS phases in the composition of composites by 1.4 and 1.3 times relative to the corresponding values for the neat doped P3MTs. Such an increase can be caused by the influence of the local electric field of the dipoles of the electroactive part of the crystalline phase of PVDF (β- and γ-phase) on the spatial arrangement of charged P3MT macromolecules formed on the surface of PVDF. Thermogravimetric studies show an increase in the thermal stability of the doped P3MT phase of nanocomposites while conductivity measurements reveal a significant effect of the nature of the dopant anion.

Modular Attachment of Nanoparticles on Microparticle Supports via Multifunctional Polymers.

Nanoparticles are key to a range of applications, due to the properties that emerge as a result of their small size. However, their size also presents challenges to their processing and use, especially in relation to their immobilization on solid supports without losing their favorable functionalities. Here, we present a multifunctional polymer-bridge-based approach to attach a range of presynthesized nanoparticles onto microparticle supports. We demonstrate the attachment of mixtures of different types of metal-oxide nanoparticles, as well as metal-oxide nanoparticles modified with standard wet chemistry approaches. We then show that our method can also create composite films of metal and metal-oxide nanoparticles by exploiting different chemistries simultaneously. We finally apply our approach to the synthesis of designer microswimmers with decoupled mechanisms of steering (magnetic) and propulsion (light) via asymmetric nanoparticle binding, aka Toposelective Nanoparticle Attachment. We envision that this ability to freely mix available nanoparticles to produce composite films will help bridge the fields of catalysis, nanochemistry, and active matter toward new materials and applications.

Impact of plasmonic substrate of different geometries on the enhancement factor of hyper‐Raman scattering process

Effective plasmonic heterotrimers of different geometry have been proposed as an active substrate to substantially enhance the scattered signal of hyper-Raman scattering process. The three-particle systems are constructed independently from asymmetric nanoparticles of spherical, cylindrical, and spheroidal shapes. The interacting metallic characters in each one of the three trimers are arranged collinearly in a J-aggregate configuration and illuminated by a longitudinally polarized light. The finite-difference time-domain electrodynamic simulation tool is employed to simulate optical cross-section and nearfield intensity associated with the excited plasmonic bands. The extinction profile of each one of the three trimers exhibits the excitation of two plasmonic modes. The first is a superradiant mode, which resulted from the in-phase coupling between the dipole moments induced in each one of the three plasmonic elements. The second mode excited at a shorter wavelength, which is a combination between bright and dark modes (Fano interference). The resonance wavelength of the former mode matches the incident one; meanwhile, the resonance energy of the Fano profile is equivalent to the second-order Stokes condition. From the values of the highly enhanced nearfield associated with the observation of these modes, the enhancement factor of the hyper-Raman scattering process is calculated. The simulation results highlight the influence of the selected particle's geometry on both the quality of plasmonic coupling and calculated enhancement factor. The maximum value of the enhancement factor can reach as high as 3.83 × 1017 when the heterotrimer is constructed from spheroids. For nanoparticles of spherical shape, the calculated value of the factor is comparable to the maximum limit; meanwhile, the rod shape demonstrates the minimum limit of the enhancement factor.

Patterning of Polymer-Functionalized Nanoparticles with Varied Surface Mobilities of Polymers.

The polymers can be either dynamically tethered to or permanently grafted to the nanoparticle to produce polymer-functionalized nanoparticles. The surface mobility of polymer ligands with one end anchored to the nanoparticle can affect the surface pattern, but the effect remains unclear. Here, we addressed the influence of lateral polymer mobility on surface patterns by performing self-consistent field theory calculations on a modeled polymer-functionalized nanoparticle consisting of immobile and mobile brushes. The results show that except for the radius of nanoparticles and grafting density, the fraction of mobile brushes substantially influences the surface patterning of polymer-functionalized nanoparticles, including striped patterns and patchy patterns with various patches. The number of patches on a nanoparticle increases as the fraction of mobile brushes decreases, favored by the entropy of immobile brushes. Critically, we found that broken symmetry usually occurs in patchy nanoparticles, associated with the balance of enthalpic and entropic effects. The present work provides a fundamental understanding of the dependence of surface patterning on lateral polymer mobility. The work could also guide the preparation of diversified nanopatterns, especially for the asymmetric patchy nanoparticles, enabling the fundamental investigation of the interaction between polymer-functionalized nanoparticles.

Selective high-order resonance in asymmetric plasmonic nanostructures stimulated by vortex beams.

Orbital angular momentum (OAM) of light has the potential to induce high-order transitions of electrons in atoms by compensating for the OAM required. However, due to the dark spot situating at the focal center of the OAM beam, high-order transitions are typically weak. In this study, we demonstrate efficient and selective high-order resonances in symmetric and asymmetric plasmonic nanoparticles that are comparable in size to the waist radius of the OAM beam. In a symmetric nanoparticle configured with a complete nanoring lying on the focal center, there is a pure high-order resonance obeying the law of conservation of angular momentum during the interaction between OAM light and the nanosystem. In an asymmetric nanoparticle configured with an complete ring off the beam center or a splitting nanoring, there are multiple resonances whose resonance orders are influenced by the ring's geometry, position, orientation, and photon OAM. Thus, high-order resonances in the symmetric and asymmetric plasmonic nanostructures are selectively stimulated using vortex beams. Our results may help to understand and control OAM-involved light-material interactions of asymmetric nanosystems.

Anisotropic metallic heterotrimer systems for an ultrahigh plasmonic-based improvement of hyper-Raman scattering signal

An anisotropic metallic trimer is proposed as an active plasmonic substrate for an ultrahigh enhancement in the spectroscopic signal of the hyper-Raman scattering (HRS) process. The suggested three-particle system is composed from non-aligned asymmetric nanoparticles of a cubic shape. The interacting resonators are made of gold material and illuminated by a longitudinally polarized light. The non-alignment condition in the heterotrimer is achieved by shifting the intermediate cube transversely away from the interparticle axis. Optical cross-section, nearfield distribution and charge density are calculated by using the finite-difference time-domain electrodynamic simulation tool. The enhancement factor of the HRS is calculated theoretically from the nearfield intensity associated with the resonance phenomenon of the considered trimer. The extinction profile of the illuminated system exhibits the excitation of two plasmonic modes. A superradiant mode observed in the longer wavelength region which resulted from the in-phase coupling between the plasmonic modes excited in each one of the three resonators. The second mode is a subradiant band emerged from the interference between bright and dark modes. The resonance wavelength of these two modes matches the excitation one and the second-order Stockes condition, respectively. After optimizing the value of both the transverse shift and the gap spacing, the enhancement factor of the HRS can reach as high as a value never reported before of 1 × 1018.

Charge transfer plasmon resonances of conductively linked asymmetric gold nanoparticle dimers

Charge transfer plasmon resonances of conductively linked asymmetric gold nanoparticle dimers