Au Core Research Articles

Elucidating the stabilities and properties of the thiolate-protected Au nanoclusters with detaching the staple motifs.

Thiolate-protected Au nanoclusters (AuNCs) have been widely studied in areas of catalysis, biosensors, and bioengineering. In real applications, e.g., catalytic reactions, the thiolate groups are normally partially detached. However, which of the thiolate groups are easily detached and how the detachment of the ligands affects the geometries and electronic structures of the Au nanoclusters have been rarely studied. In this work, we employed the density functional theory calculations as well as the molecular orbital analysis to explore the detachment effect of the ligands using nine thiolate-protected AuNCs as examples. Our results showed that there existed a nearly linear relationship between the averaged detachment energies and the numbers of Au atoms in the motifs. Detaching longer motifs normally required more energies owing to the stronger aurophilic effects. For detaching a full motif, based on the structure decomposition via the grand unified model, analysis on the inner Au core indicated that the change in Au-Au bond length was more sensitive for the inter-block compared to the intra-block. The detachment of the -SH fragment generally needs less energy and brings less structural deformations when compared to the removal of a full motif. Molecular orbital analysis showed that the relative energies of the HOMO orbitals were elevated, which led to the narrow down of the HOMO-LUMO gap. This work provides a primary description of the correlation of the ligands' detachment with the relative stabilities and structures of the AuNCs, which would be beneficial for establishing the structure-property relationship of AuNCs in real applications.

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Design of Plasmonic Catalysts Utilizing Nanostructures

This review describes the design of nanostructured plasmonic catalysts, such as nanoparticles and nanosheet morphologies, that strongly absorb visible light over a wide range of the solar spectrum due to localized surface plasmon resonance (LSPR) and application to enhanced hydrogen evolution. A new method for the synthesis of Ag nanoparticles, with color dependent on the particle size and morphology, combined microwave heating and the use of mesoporous silica materials. Further combination with Pd nanoparticles significantly enhanced the catalytic activities for hydrogen production from ammonia borane (NH3BH3) compared with the inherent Ag catalysts under both dark and visible-light irradiation conditions. We also describe the synergistic catalysis activities of plasmonic Au(core)–Pd(shell) nanoparticles supported on amine-functionalized metal-organic frameworks (MOFs) for boosting room-temperature hydrogen production from formic acid (HCOOH) under visible light irradiation. Our search for plasmonic materials based on earth abundant elements found that reduced molybdenum oxide (HxMoO3−y) nanosheet with oxygen defects and doped hydrogen displayed intense absorption in a wide range from the visible to the near-infrared region. This unique plasmonic HxMoO3−y nanosheet can enhance dehydrogenation from ammonia borane under visible light irradiation.

Au@Ag Dendritic Nanoforests for Surface-Enhanced Raman Scattering Sensing.

The effects of Au cores in Ag shells in enhancing surface-enhanced Raman scattering (SERS) were evaluated with samples of various Au/Ag ratios. High-density Ag shell/Au core dendritic nanoforests (Au@Ag-DNFs) on silicon (Au@Ag-DNFs/Si) were synthesized using the fluoride-assisted Galvanic replacement reaction method. The synthesized Au@Ag-DNFs/Si samples were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, reflection spectroscopy, X-ray diffraction, and Raman spectroscopy. The ultraviolet-visible extinction spectrum exhibited increased extinction induced by the addition of Ag when creating the metal DNFs layer. The pure Ag DNFs exhibited high optical extinction of visible light, but low SERS response compared with Au@Ag DNFs. The Au core (with high refractive index real part) in Au@Ag DNFs maintained a long-leaf structure that focused the illumination light, resulting in the apparent SERS enhancement of the Ag coverage.

Scalable synthesis of multicomponent multifunctional inorganic core@mesoporous silica shell nanocomposites

Integrating multiple materials with different functionalities in a single nanostructure enables advances in many scientific and technological applications. However, such highly sophisticated nanomaterials usually require complex synthesis processes that complicate their preparation in a sustainable and industrially feasible manner. Herein, we designed a simple general method to grow a mesoporous silica shell onto any combination of hydrophilic nanoparticle cores. The synthetic strategy, based on the adjustment of the key parameters of the sol-gel process for the silica shell formation, allows for the embedment of single, double, and triple inorganic nanoparticles within the same shell, as well as the size-control of the obtained nanocomposites. No additional interfacial adhesive layer is required on the nanoparticle surfaces for the embedding process. Adopting this approach, electrostatically stabilized, small-sized (from 4 to 15 nm) CeO2, Fe3O4, Gd2O3, NaYF4, Au, and Ag cores were used to test the methodology. The mean diameter of the resulting nanocomposites could be as low as 55 nm, with high monodispersity. These are very feasible sizes for biological intervention, and we further observed increased nanoparticle stability in physiological environments. As a demonstration of their increased activity as a result of this, the antioxidant activity of CeO2 cores was enhanced when in core-shell form. Remarkably, the method is conducted entirely at room temperature, atmospheric conditions, and in aqueous solvent with the use of ethanol as co-solvent. These facile and even “green” synthesis conditions favor scalability and easy preparation of multicomponent nanocomposite libraries with standard laboratory glassware and simple benchtop chemistry, through this sustainable and cost-effective fabrication process.

Computational Characterization of the Intermixing of Iron Triade (Fe, Co, and Ni) Surfaces and Sub-nanometric Clusters with Atomic Gold.

Dispersion-corrected density functional theory (DFT-D3) is applied to model iron triade (Fe, Co, and Ni) surfaces upon exchange of surface atoms with atomic gold. One first goal is to analyze the contact problem at the triade surface–Au interface and to correlate our findings with recent observations on iron triade nanoparticles (with diameters of around 5 nm) passivated by a few layers of gold. For this purpose, we analyze: (1) the energies of substitution; (2) the restructuring of the iron triade surfaces upon the atomic exchange; (3) the density of the orbitals bearing the largest projection on d(Au) atomic orbitals and, particularly, their overlap with orbitals from neighboring atoms of the triade surfaces; (4) the modification of the electronic density of states; and (5) the redistribution of the electronic density upon intermixing of Au and triade atoms. Inspite of the similarities between Ni, Co, and Fe in the condensed phase, significant differences are found in the features characterizing the exchange process. In particular, we find a better integration of the Au atom on the substitutional site of the Ni(001) surface than on those of the Fe(001) and Co(001) surfaces. This is in agreement with the fact that the electronic density of states is almost indistinguishable before and after Ni–Au intermixing. This outcome is correlated with the experimental observation on the allowing transition of Ni–Au core–shell nanoparticles before reaching the melting temperature. Our second objective is to explore the Au–triade atom intermixing process in sub-nanometric clusters, finding that it is energetically more favored than at solid surfaces yet endothermic at 0 K. This feature is explained as the result of the structural fluxionality characterizing clusters at the sub-nanometer scale. Entropy contributions make mixed Au–Ni clusters more stable than the unmixed counterpart already at 650 K while unmixed Co clusters remain energetically more favored up to 1295 K and iron clusters are predicted to be stable against intermixing over the experimentally relevant range of temperatures (up to 1100 °C). Remarkably, the net charge donated from the three triade atoms to atomic gold upon intermixing is similar in triade sub-nanometeric clusters and at extended triade surfaces. Gold clusters are prone to host Fe, Co, and Ni atoms at the center of their structures and the exchange process is predicted to be exothermic at 0 K even for a small cluster made of 13 atoms. More generally, our work highlights the importance of the polarity of the chemical bond between unlike metal atoms in alloys.

Microplasma Assembly a High-Efficient and Catalytic Platform Reduction 4-Nitrophenol Based on Reusable Au@Ag Nanoparticle / Cellulose Paper

Grafting metal nanoparticles (NPs) on flexible platforms is being increasingly attempted to advance their usage in the field of catalysis, sensing, energy storage, etc. However, anchoring NPs on substrates is nontrivial as it involves surface modification of the NPs and/or the substrate, which makes the whole process tedious. On the other hand , Bimetallic nanoparticles, which are composed of two metal elements in a particle, exhibit much higher catalytic activity than respective monometallic ones due to new bi-functional or synergistic effects, so-called a ligand and/or an ensemble effect. Here we present the green, facile, less-time, one-step process fabrication of 3-dimension porous Au(core)@Ag(shell) NP /filter paper by Microplasma-assisted system. The aim of our work is to develop a high efficient catalytic substrate on common filter paper loaded on Au@Ag NPs. In our work, we found Au@Ag NP /filter paper can be synthesized and in a minute time scale. We further extend this technology to fabricated Au@Ag NP /paper and characterized them by SEM, Raman, XRD and UV-Vis spectroscopies. Besides, The as-prepared Au@Ag NP / filter paper is stable, uniform, and exhibits high efficiency and reusability in the catalytic reduction of 4-nitrophenol (4-NP) with a high rate constant as well as an average conversion of 96% in 3 minutes during 6 times. While acting as catalysts, the composites display excellent surface enhanced Raman scattering (SERS) efficiency, allowing the real-time monitoring of chemical reactions. The obtained Au@Ag bimetallic catalysts /filter paper show an exceptional superior catalytic activity for the reduction of 4-nitrophenol (4-NP) which can be completely reduced to 4-aminophenol (4-AP) in a single step within seconds., surpassing most reported noble metal nanoparticle catalysts. The results have not only paved the way for the wide application of Au@Ag NPs / filter paper but also provide a new road for the application of other bimetallic NPs Figure 1

X-Ray Study of Voltage-Tunable 2D-Lattice to Cluster Transition of Nanoparticles at the Interface between Two Immiscible Electrolyte Solutions

Previous X-ray scattering measurements demonstrated the formation of a voltage-tunable 2-dimensional lattice of nanoparticles situated at the liquid-liquid interface between two immiscible electrolyte solutions (Nano Letters 2014, 14, 6816−6822). The nanoparticles had Au cores coated with trimethylammonium terminated ligands and the ITIES consisted of NaCl in water and BTPPATPFB in 1,2-dichloroethane. Here, we present additional measurements on this system which illustrate a transition that occurs at more negative potentials. The transition represents a breakup of the 2D monolayer lattice into a disordered sub-monolayer of nanoparticles that coexists with small nanoparticle clusters in the vicinity of the interface. Grazing Incidence Small Angle X-ray Scattering (GISAXS) provides evidence for the breakup of the lattice and the appearance of clusters. X-ray reflectivity (XR) characterizes the relative location along the interfacial normal of the different types of nanoparticle assemblies.

Small Change, Big Difference: Photoelectrochemical Behavior of Au Nanocluster-Sensitized TiO2 Altered by Core Restructuring

Ultrasmall gold nanoclusters (Au NCs) have recently gained enormous popularity as a newly emerging light harvester, but many fundamental aspects of their photoelectrochemical behavior are still largely unknown. Unlike traditional photoactive nanoparticles, the NC’s core structure, rather than its size, is a key factor that dictates the physical properties of NCs because of a strong quantum confinement effect. Despite this importance, no effort has been made to elucidate the effect of the core structure on the photoelectrochemistry of Au NC-sensitized TiO2 (Au NC–TiO2). Using Au25 NC as a model system, we delicately tailored the icosahedral Au13 core of Au25 NC into a cuboctahedral Au15 core of Au23 NC. This subtle core manipulation has a drastic impact on the entire interfacial behavior of Au NC–TiO2, which in turn significantly affects the photoelectrochemical performance. This new insight highlights the overlooked effect of the core structure on the photoelectrochemistry of Au NC–TiO2.

Directional self-assembly of anisotropic bimetal-poly(aniline) nanostructures for rheumatoid arthritis diagnosis in multiplexing

Anisotropic organic-inorganic hybrid nanoparticles possessing different functionalities and physicochemical properties from each compartment have attracted significant interest for the development of advanced functional materials. Moreover, their self-assembled structures exhibit unique optical properties for photonics-based biosensing. We report herein the fabrication of anisotropic bimetal-polymer nanoparticles (ABPNs) via combination of oxidative polymerization and additional growth of metallic nanoparticles on Au seeds as well as their directional clustering mediated via noncovalent interactions. Polymerization of anilines for poly (aniline) shell was conducted by reducing silver nitrate onto the Au seed in the presence of a surfactant, giving rise to spatially distinct bimetallic Au core and Ag shell compartment and the poly (aniline) counter-one that comprise the ABPNs. Furthermore, ABPNs were directionally clustered in a controlled manner via hydrophobic interaction, when the bimetallic compartment was selectively modified. These nanoclusters showed highly enhanced optical properties owing to the increased electromagnetic fields while the poly (aniline) being used to offer antibody binding capacity. Taking advantages of those properties of the ABPN nanoclusters, surface-enhanced Raman scattering (SERS) intensity-based quantification of two different biomarkers: autoantibodies against cyclic citrullinated peptide and rheumatoid factor was demonstrated using ABPN nanoclusters as SERS nanoprobes. Conclusively, this work has great potential to satisfy a need for multiplexing in diagnosis of early stage of rheumatoid arthritis.

Controllable Core Size of Au@TiO2 through Al(NO3)3 Addition and Its Effects on DSSC Performance

It is known that plasmonic nanoparticles in dye-sensitized solar cells (DSSC) could enhance efficiency through improvement in light absorbance and electron dynamics. Herein we investigated various sizes of AuNP through spontaneous Al(NO3 )3 addition. Core-Shell Au@TiO2 was prepared with various Al(NO3 )3 concentrations of 0.25 mM, 0.5 mM, 0.75 mM and 1 mM. The Au@TiO2 volume fraction of 1% was further added to TiO2 photoanode. Based on the particle size analyzer (PSA) characteristics, the synthesized AuNP’s size was within a range of 34.62 nm – 139.5 nm. The highest efficiency of DSSC was obtained for the sample with the largest AuNP ’s diameter, i.e., 0.0313%, which is about three times higher than pristine DSSC. The increase in efficiency was in accord with Metallic Nanoparticle Boundary Element Method (MNPBEM) simulation, UV-vis spectroscopy, and Incident Photon to Current Conversion Efficiency (IPCE) analysis largest Au core diameter contributes to the strong absorbance and hence the short circuit current

Back Cover

This cover picture describes the graphene‐isolated AuAg nanocrystal (GIAAN) with SERS‐active AuAg core confined in a nanospace of few‐layer graphene shell, possessing unique Raman peaks, high SERS activity and excellent stability, for multiphase SERS analysis and multimodal cellular Raman imaging. More details are discussed in the article by Chen et al. on page 1491–1497.image

Atomic‐Precision Tailoring of Au–Ag Core–Shell Composite Nanoparticles for Direct Electrochemical‐Plasmonic Hydrogen Evolution in Water Splitting

AbstractTraditionally, bandgap materials are a prerequisite to photocatalysis since they can harness a reasonable range of the solar spectrum. However, the high impedance across the bandgap and the low concentration of intrinsic charge carriers have limited their energy conversion. By contrast, metallic nanoparticles possess a sea of free electrons that can effectively promote the transition to the excited state for reactions. Here, an atomic layer of a bimetallic concoction of silver–gold shells is precisely fabricated onto an Au core via a sonochemical dispersion approach to form a core–shell of Au–Ag that exploits the wide availability of excited states of Ag while maintaining an efficient localized surface plasmon resonance (LSPR) of Au. Catalytic results demonstrate that this mix of Ag and Au can convert solar energy to hydrogen at high efficiency with an increase of 112.5% at an optimized potential of −0.5 V when compared to light‐off conditions under the electrochemical LSPR. This outperforms the commercial Pt catalysts by 62.1% with a hydrogen production rate of 1870 µmol g−1 h−1 at room temperature. This study opens a new route for tuning the range of light capture of hydrogen evolution reaction catalysts using fabricated core–shell material through the combination of LSPR with electrochemical means.

Near-Infrared II Thermoplasmonics of Cuprous Selenide Multilayer Nanoshells: The Role of the Plasmonic Core.

We present a numerical investigation of the plasmonic and photothermal properties of two different types of cuprous selenide (Cu2-xSe) concentric multilayer nanoshells (CMNSs), heteroCMNSs and homoCMNSs, comprising an outer Cu2-xSe nanoshell and an intermediate silica layer but with a different nanoparticle core of either Au or Cu2-xSe. Numerical calculations of optical absorption, near-field enhancement, and local temperature increase are performed with varied dimensions. The plasmon modes from both types of CMNSs are interpreted by combining the plasmon hybridization theory with the surface charge distribution. The two CMNSs exhibit remarkable near-infrared II (NIR-II) plasmonic properties tunable by controlling the interaction between the inner core and the Cu2-xSe nanoshell. The distinct temperature increase distributions between the two CMNSs are identified at their NIR-II resonance wavelengths. The correlation between the partial absorption and the temperature increase of the inner core and Cu2-xSe nanoshell suggests the thermal interplay between the components.

Pronounced interfacial interaction in icosahedral Au@C60 core-shell nanostructure for boosting direct plasmonic photocatalysis under alkaline condition

The unique hot carrier-driven direct plasmonic photocatalysis of coinage metal nanomaterials (NMs) via energetic localized surface plasmon resonance (LSPR) in visible-light region has been explored in recent years. However, the low photoinduced electron transfer efficiency and insufficient separation of electron-hole pairs would severely preclude their widespread practical applications. Herein, we demonstrate an interesting plasmonic photocatalyst based on the construction of icosahedral (Ih) [email protected]60 core-shell NMs, taking advantage of specific delocalized π electrons structure of a tight C60 shell and enhanced LSPR property of Ih Au core. Then, the pronounced interfacial interaction at junction region endows the obtained [email protected]60 NMs with an outstanding photoinduced hot carrier-transmission during photocatalytic reaction, facilitating a remarkably higher (1.89 times) photocatalytic activity toward visible-light driven degradation of crystal violet (CV) dyes, as compared to bare Au NMs. Impressively, the photocatalytic activity of Ih [email protected]60 NMs can be effectively optimized by changing the pH value of reaction solution, with the kinetic rate constant reaching the maximum value of 0.179 min−1 in pH0 11.4 solution, while 0.005 min−1 at pH0 3.0. Moreover, due to the protection of a tight C60 shell, the Ih [email protected]60 NMs also possess excellent photocatalytic stability/reusability in recycling runs, holding great potential for the design of robust and high-performance plasmonic photocatalysts in repeated practical applications.

Electron Transfer in Films of Atomically Precise Gold Nanoclusters

In applications of monolayer-protected gold clusters, assessing the dynamic behavior of the capping monolayer is crucial, as this determines the cluster’s effective size and electron-transfer (ET) properties. Here, we describe a systematic study on the effect of the monolayer thickness on the ET between molecular Au25(SR)180 nanoclusters in films. The length of the ligands protecting the Au core was varied by using a series of linear-chain thiolate (SCnH2n+1) protected Au25 clusters, where n = 3, 4, 5, 6, 7, 8, and 10. The effect of branching was assessed by using the 2-methyl-1-butanethiolate-protected Au25 cluster. Conductivity measurements were carried out on dry films obtained by drop-casting Au25(SR)180 solutions onto interdigitated gold electrodes. Changing the alkyl chain from C3 to C10 induces a smooth decrease in the film conductivity by 3.5 orders of magnitude. By using electrochemically determined Stokes radii, the conductivity results were transformed into the corresponding ET rate constants (kETs) between neighboring clusters. kET exponentially depends on the distance, and the data show that the average Au center-to-center distance in the film is not larger than the sum of two Stokes radii. This indicates that linear alkyl chains hold a detectable degree of fluidity in films, although not as much as in solution, as shown by the trend of the corresponding heterogeneous standard rate-constant values. For both physical states, these conclusions are precisely confirmed by the much slower ET rate determined for the Au25 cluster protected by the hindered thiolate. ET in films was also studied as a function of temperature, and the results were analyzed in the framework of the ET theory. We found that the outer and inner reorganization energies increase with n. For these ETs, the electronic coupling resonance between the reactant and product states, HRP, ranges from 12 (n = 3) to 0.7 cm–1 (n = 10) and therefore ETs are nonadiabatic. The data also show that 3/4 of the effect of distance on kET is related to HRP, while the rest is associated with the intrinsic barrier and thus the distance dependence of the outer and inner reorganization energies.

Near‐Infrared II Plasmonic Au@Au–Ag Dot‐in‐Cubic Nanoframes for In Vivo Surface‐Enhanced Raman Spectroscopic Detection and Photoacoustic Imaging

AbstractNear‐infrared II (NIR‐II) plasmonic noble‐metallic nanostructures are highly desirable for in vivo photodiagnostics because of their multiple functionalities and deep‐tissue optical imaging capability. Herein, a novel class of Au@Au–Ag dot‐in‐cubic nanoframes (DCFs) comprising a solid Au core and a Au–Ag alloy shell with a wall hole on each side face is reported, which exhibit remarkable plasmonic properties spectrally tunable beyond 1400 nm while maintaining a small size. The synthesis of Au@Au–Ag DCFs is principally based on the facet‐selective etching of Ag atoms and co‐deposition of Au and Ag atoms on the edges and corners of Au@Ag dot‐in‐cubes. The geometry (e.g., edge length and wall hole size) can be controllably tailored by simply varying the silver nitrate and chloroauric acid concentrations. Superior in vitro and in vivo NIR‐II photoacoustic imaging performances of Au@Au–Ag DCFs are demonstrated. Additionally, remarkable NIR‐II surface‐enhanced Raman spectroscopy (SERS) activity of Au@Au–Ag DCFs is evidenced with the maximum NIR‐II SERS enhancement occurring at a plasmon resonance wavelength blue‐shifting from the incident laser wavelength and an excellent effective detection depth. Finally, the potential of the developed Au@Au–Ag DCFs is highlighted for in vivo NIR‐II SERS detection of microtumors in animals.

Versatile Graphene‐Isolated AuAg‐Nanocrystal for Multiphase Analysis and Multimodal Cellular Raman Imaging†

Main observation and conclusionSurface‐enhanced Raman spectroscopy (SERS)‐based bioanalytical technique involves the interaction of SERS‐active substrate with complex environment, which has aroused intensive research interests. Compared to the commonly used Au SERS substrates, Ag nanocrystals have larger optical absorption cross section and acceptable price, but they possess poor oxidation resistance and potential biotoxicity, and the occurrence of unnecessary chemical reactions is inevitable due to the direct contact with probe molecules. Herein, we report a graphene‐isolated AuAg nanocrystal (GIAAN) with the SERS‐active AuAg core confined in a nanospace of few‐layer graphene shell, which possesses unique Raman peaks, high SERS activity, excellent stability, superior fluorescence quenching performance and good biocompatibility. Based on the limited solubility of GIAAN in water and organic solvents, it is able to spontaneously generate interfacial self‐assembled GIAAN (ISA‐GIAAN) film at immiscible two‐phase interfaces without any inducer, and multiphase Raman analysis of both water‐ and lipid‐soluble drug model molecules is further achieved. Moreover, the GIAAN is further non‐covalently functionalized with polyoxyethylenestearyl ether (C18‐PEG) to acquire GIAAN@PEG with good water‐solubility for SERS quantitative analysis in homogeneous system and multimodal Raman imaging of MCF‐7 cells. We expect the versatile GIAAN holds great potential to monitor drug metabolism and guide intended drug delivery in clinic trials.

Analysis of Catalytic Activity of Au@Pd Core-shell Nanodendrites for Highly Efficient Ethanol Electrooxidation

Abstract Rational design of efficient Pd-based electrocatalysts is significant for the improvement of their performances for ethanol oxidation reaction (EOR). In this study, core-shell Au@Pd nanodendrites (Au@Pd NDs) were fabricated by a facile and efficient seed-media growth approach at room temperature. The core-shell Au@Pd NDs exhibited better electrocatalytic activity toward EOR in alkaline media, which was 2.34 times higher than that of the commercial Pd/C. The improvement of activity was attributed to the bimetallic synergistic effect and interaction between Pd shell and Au core nanostructure.

Asymmetric Core-Shell Gold Nanoparticles and Controllable Assemblies for SERS Ratiometric Detection of MicroRNA.

Janus nanogap gold nanoparticles (JAuNNPs) with varying proportions of Au shell coverage of (ca. 100/75/50/25 %) are presented. The internal nanogap between the partial Au shell and core caused asymmetric optical behavior; tunability depends on the degree of Au shell coverage and structural asymmetry. The shell-to-shell or core-to-core JAuNNDs(50 %) were self-assembled from amphiphilic JAuNNPs(50 %) by tuning the hydrophilic and hydrophobic polymer brushes on the Au core or shell. The positions of electromagnetic field enhancement of JAuNNDs varied with geometrical configurations because of hybridized plasmonic coupling effects. Furthermore, DNA linkers were utilized to form JAuNND12 (50 %). By combining with Raman molecules, ratiometric SERS signals could be generated, enabling JAuNND12 (50 %) to image the distribution of miR-21 in living cells and tumors. Asymmetric JAuNNPs allowed facile conjugation of various linkage molecules to fabricate dimeric nanostructures.