Bottom‐Up Single‐Electron Transistors

As the downscaling of conventional semiconductor electronics becomes more and more challenging, the interest in alternative material systems and fabrication methods is growing. A novel bottom‐up approach for the fabrication of high‐quality single‐electron transistors (SETs) that can easily be contacted electrically in a controllable manner is developed. This approach employs the self‐assembly of Au nanoparticles forming the SETs, and Au nanorods forming the leads to macroscopic electrodes, thus bridging the gap between the nano‐ and microscale. Low‐temperature electron‐transport measurements reveal exemplary single‐electron tunneling characteristics. SET behavior can be significantly changed, post‐fabrication, using molecular exchange of the tunnel barriers, demonstrating the tunability of the assemblies. These results form a promising proof of principle for the versatility of bottom‐up nanoelectronics, and toward controlled fabrication of nanoelectronic devices.     

Magnetic Plasmon Networks Programmed by Molecular Self‐Assembly

Nanoscale manipulation of magnetic fields has been a long‐term pursuit in plasmonics and metamaterials, as it can enable a range of appealing optical properties, such as high‐sensitivity circular dichroism, directional scattering, and low‐refractive‐index materials. Inspired by the natural magnetism of aromatic molecules, the cyclic ring cluster of plasmonic nanoparticles (NPs) has been suggested as a promising architecture with induced unnatural magnetism, especially at visible frequencies. However, it remains challenging to assemble plasmonic NPs into complex networks exhibiting strong visible magnetism. Here, a DNA‐origami‐based strategy is introduced to realize molecular self‐assembly of NPs forming complex magnetic architectures, exhibiting emergent properties including anti‐ferromagnetism, purely magnetic‐based Fano resonances, and magnetic surface plasmon polaritons. The basic building block, a gold NP (AuNP) ring consisting of six AuNP seeds, is arranged on a DNA origami frame with nanometer precision. The subsequent hierarchical assembly of the AuNP rings leads to the formation of higher‐order networks of clusters and polymeric chains. Strong emergent plasmonic properties are induced by in situ growth of silver upon the AuNP seeds. This work may facilitate the development of a tunable and scalable DNA‐based strategy for the assembly of optical magnetic circuitry, as well as plasmonic metamaterials with high fidelity.     

Nanowire‐Intensified Metal‐Enhanced Fluorescence in Hybrid Polymer‐Plasmonic Electrospun Filaments

Hybrid polymer‐plasmonic nanostructures might combine high enhancement of localized fields from metal nanoparticles with light confinement and long‐range transport in subwavelength dielectric structures. Here, the complex behavior of fluorophores coupling to Au nanoparticles within polymer nanowires, which features localized metal‐enhanced fluorescence (MEF) with unique characteristics compared to conventional structures, is reported. The intensification effect when the particle is placed in the organic filaments is remarkably higher with respect to thin films of comparable thickness, thus highlighting a specific, nanowire‐related enhancement of MEF effects. A dependence on the confinement volume in the dielectric nanowire is also indicated, with MEF significantly increasing upon reduction of the wire diameter. These findings are rationalized by finite element simulations, predicting a position‐dependent enhancement of the quantum yield of fluorophores embedded in the fibers. Calculation of the ensemble‐averaged fluorescence enhancement unveils the possibility of strongly enhancing the overall emission intensity for structures with size twice the diameter of the embedded metal particles. These new, hybrid fluorescent systems with localized enhanced emission, and the general nanowire‐enhanced MEF effects associated to them, are highly relevant for developing nanoscale light‐emitting devices with high efficiency and intercoupled through nanofiber networks, highly sensitive optical sensors, and novel laser architectures.     

Two‐Dimensional Self‐Organization of an Ordered Au Silicide Nanowire Network on a Si(110)‐16 × 2 Surface

A well‐ordered two‐dimensional (2D) network consisting of two crossed Au silicide nanowire (NW) arrays is self‐organized on a Si(110)‐16 × 2 surface by the direct‐current heating of ≈1.5 monolayers of Au on the surface at 1100 K. Such a highly regular crossbar nanomesh exhibits both a perfect long‐range spatial order and a high integration density over a mesoscopic area, and these two self‐ordering crossed arrays of parallel‐aligned NWs have distinctly different sizes and conductivities. NWs are fabricated with widths and pitches as small as ≈2 and ≈5 nm, respectively. The difference in the conductivities of two crossed‐NW arrays opens up the possibility for their utilization in nanodevices of crossbar architecture. Scanning tunneling microscopy/spectroscopy studies show that the 2D self‐organization of this perfect Au silicide nanomesh can be achieved through two different directional electromigrations of Au silicide NWs along different orientations of two nonorthogonal 16 × 2 domains, which are driven by the electrical field of direct‐current heating. Prospects for this Au silicide nanomesh are also discussed.     

Simulation‐Experimental Approach to Investigate the Role of Interfaces in Self‐Replenishing Composite Coatings

To investigate self‐replenishing on surface‐structured composite coatings a dual simulation‐experimental approach is employed to study the decisive role of polymer‐air and polymer‐particle interfaces. Experimentally, the composite system consists of a cross‐linked polymer network with fluorinated‐dangling chains, embedding colloidal SiO₂ nanoparticles which are incorporated in the network via covalent bonding. These particles provide the desired surface structure at the air‐interface before and after damage. Any damage replicates the rough surface, while the polymer layer on top of the particles serves as source of low surface energy groups which are able to reorient towards the new air‐interfaces. Using coarse‐grained simulations details of these self‐replenishing composite systems are revealed such as the minimum thickness of the polymer layer necessary for providing optimal self‐replenishing ability and the distribution profile of the dangling chains at the various interfaces. The principles and dual approach reported here may be applied to other self‐healing composite systems with applications in self‐cleaning, anti‐fouling or low adhesion materials.     

DNA‐Driven Two‐Layer Core–Satellite Gold Nanostructures for Ultrasensitive MicroRNA Detection in Living Cells

It is a significant challenge to achieve controllable self‐assembly of superstructures for biological applications in living cells. Here, a two‐layer core–satellite assembly is driven by a Y‐DNA, which is designed with three nucleotide chains that hybridized through complementary sequences. The two‐layer core–satellite nanostructure (C₃₀S₅S₁₀ NS) is constructed using 30 nm gold nanoparticles (Au NPs) as the core, 5 nm Au NPs as the first satellite layer, and 10 nm Au NPs as the second satellite layer, resulting in a very strong circular dichroism (CD) and surface‐enhanced Raman scattering. After optimization, the yield is up to 85%, and produces a g‐factor of 0.16 × 10^?2. The hybridization of the target microRNA (miRNA) with the molecular probe causes a significant drop in the CD and Raman signals, and this phenomenon is used to detect the miRNA in living cells. The CD signal has a good linear range of 0.011–20.94 amol ng_RNA^?1 and a limit of detection (LOD) of 0.0051 amol ng_RNA^?1, while Raman signal with the range of 0.052–34.98 amol ng_RNA^?1 and an LOD of 2.81 × 10^?2 amol ng_RNA^?1. This innovative dual‐signal method can be used to quantify biomolecules in living cells, opening the way for ultrasensitive, highly accurate, and reliable diagnoses of clinical diseases.     

Thermoreversible Self‐Assembly of Perfluorinated Core‐Coronas Cellulose‐Nanoparticles in Dry State

Self‐assembly of nanoparticles (NPs) forming unique structures has been investigated extensively over the past few years. However, many self‐assembled structures by NPs are irreversible, because they are generally constructed using their suspensions. It is still challenging for NPs to reversibly self‐assemble in dry state, let alone of polymeric NPs with general sizes of hundreds of nm. Herein, this study reports a new reversible self‐assembly phenomenon of NPs in dry state, forming thermoreversible strip‐like supermolecular structures. These novel NPs of around 150 nm are perfluorinated surface‐undecenoated cellulose nanoparticles (FSU‐CNPs) with a core‐coronas structure. The thermoreversible self‐assembled structure is formed after drying in the air at the interface between FSU‐CNP films and Teflon substrates. Remarkably, the formation and dissociation of this assembled structure are accompanied by a reversible conversion of the surface hydrophobicity, film transparency, and anisotropic properties. These findings show novel feasibility of reversible self‐assembly of NPs in dry state, and thereby expand our knowledge of self‐assembly phenomenon.     

Ordered Arrangement and Optical Properties of Silica‐Stabilized Gold Nanoparticle–PNIPAM Core–Satellite Clusters for Sensitive Raman Detection

Gold–polymer hybrid nanoparticles attract wide interest as building blocks for the engineering of photonic materials and plasmonic (active) metamaterials with unique optical properties. In particular, the coupling of the localized surface plasmon resonances of individual metal nanostructures in the presence of nanometric gaps can generate highly enhanced and confined electromagnetic fields, which are frequently exploited for metal‐enhanced light–matter interactions. The optical properties of plasmonic structures can be tuned over a wide range of properties by means of their geometry and the size of the inserted nanoparticles as well as by the degree of order upon assembly into 1D, 2D, or 3D structures. Here, the synthesis of silica‐stabilized gold–poly(N‐isopropylacrylamide) (SiO₂‐Au‐PNIPAM) core–satellite superclusters with a narrow size distribution and their incorporation into ordered self‐organized 3D assemblies are reported. Significant alterations of the plasmon resonance are found for different assembled structures as well as strongly enhanced Raman signatures are observed. In a series of experiments, the origin of the highly enhanced signals can be assigned to the interlock areas of adjacent SiO₂‐Au‐PNIPAM core–satellite clusters and their application for highly sensitive nanoparticle‐enhanced Raman spectroscopy is demonstrated.     

A General and Straightforward Route to Noble Metal‐Decorated Mesoporous Transition‐Metal Oxides with Enhanced Gas Sensing Performance

Controllable and efficient synthesis of noble metal/transition‐metal oxide (TMO) composites with tailored nanostructures and precise components is essential for their application. Herein, a general mercaptosilane‐assisted one‐pot coassembly approach is developed to synthesize ordered mesoporous TMOs with agglomerated‐free noble metal nanoparticles, including Au/WO₃, Au/TiO₂, Au/NbO_x, and Pt/WO₃. 3‐mercaptopropyl trimethoxysilane is applied as a bridge agent to cohydrolyze with metal oxide precursors by alkoxysilane moieties and interact with the noble metal source (e.g., HAuCl₄ and H₂PtCl₄) by mercapto (? SH) groups, resulting in coassembly with poly(ethylene oxide)‐b‐polystyrene. The noble metal decorated TMO materials exhibit highly ordered mesoporous structure, large pore size (≈14–20 nm), high specific surface area (61–138 m² g^?1), and highly dispersed noble metal (e.g., Au and Pt) nanoparticles. In the system of Au/WO₃, in situ generated SiO₂ incorporation not only enhances their thermal stability but also induces the formation of ε‐phase WO₃ promoting gas sensing performance. Owning to its specific compositions and structure, the gas sensor based on Au/WO₃ materials possess enhanced ethanol sensing performance with a good response (R_air/R_gas = 36–50 ppm of ethanol), high selectivity, and excellent low‐concentration detection capability (down to 50 ppb) at low working temperature (200 °C).     

Self‐Assembled Au/CdSe Nanocrystal Clusters for Plasmon‐Mediated Photocatalytic Hydrogen Evolution

Plasmon‐mediated photocatalytic systems generally suffer from poor efficiency due to weak absorption overlap and thus limited energy transfer between the plasmonic metal and the semiconductor. Herein, a near‐ideal plasmon‐mediated photocatalyst system is developed. Au/CdSe nanocrystal clusters (NCs) are successfully fabricated through a facile emulsion‐based self‐assembly approach, containing Au nanoparticles (NPs) of size 2.8, 4.6, 7.2, or 9.0 nm and CdSe quantum dots (QDs) of size ≈3.3 nm. Under visible‐light irradiation, the Au/CdSe NCs with 7.2 nm Au NPs afford very stable operation and a remarkable H₂‐evolution rate of (10× higher than bare CdSe NCs). Plasmon resonance energy transfer from the Au NPs to the CdSe QDs, which enhances charge‐carrier generation in the semiconductor and suppresses bulk recombination, is responsible for the outstanding photocatalytic performance. The approach used here to fabricate the Au/CdSe NCs is suitable for the construction of other plasmon‐mediated photocatalysts.     

Self‐Assembled Large Au Nanoparticle Arrays with Regular Hot Spots for SERS

The cost‐effective self‐assembly of 80 nm Au nanoparticles (NPs) into large‐domain, hexagonally close‐packed arrays for high‐sensitivity and high‐fidelity surface‐enhanced Raman spectroscopy (SERS) is demonstrated. These arrays exhibit specific optical resonances due to strong interparticle coupling, which are well reproduced by finite‐difference time‐domain (FDTD) simulations. The gaps between NPs form a regular lattice of hot spots that enable a large amplification of both photoluminescence and Raman signals. At smaller wavelengths the hot spots are extended away from the minimum‐gap positions, which allows SERS of larger analytes that do not fit into small gaps. Using CdSe quantum dots (QDs) a 3–5 times larger photoluminescence enhancement than previously reported is experimentally demonstrated and an unambiguous estimate of the electromagnetic SERS enhancement factor of ≈10⁴ is obtained by direct scanning electron microscopy imaging of QDs responsible for the Raman signal. Much stronger enhancement of ≈10⁸ is obtained at larger wavelengths for benzenethiol molecules penetrating the NP gaps.     

Dual pH‐Induced Reversible Self‐Assembly of Gold Nanoparticles by Surface Functionalization with Zwitterionic Ligands

The dual pH‐induced reversible self‐assembly (PIRSA) of Au‐nanoparticles (Au NPs) is reported, based on their decoration with the self‐complementary guanidiniocarbonyl pyrrole carboxylate zwitterion (GCPZ). The assembly of such functionalized Au NPs is found at neutral pH, based on supramolecular pairing of the GCPZ groups. The resulting self‐assembled system can be switched back to the disassembled state by addition of base or acid. Two predominant effects that contribute to the dual‐PIRSA of Au NPs are identified, namely the ionic hydrogen bonding between the GCPZ groups, but also a strong hydrophobic effect. The contribution of each interaction is depending on the concentration of GCPZ on NPs, which allows to control the self‐assembly state over a wide range of different water/solvent ratios.     

Self‐Assembled Ordered Three‐Phase Au–BaTiO3–ZnO Vertically Aligned Nanocomposites Achieved by a Templating Method

Complex multiphase nanocomposite designs present enormous opportunities for developing next‐generation integrated photonic and electronic devices. Here, a unique three‐phase nanostructure combining a ferroelectric BaTiO₃, a wide‐bandgap semiconductor of ZnO, and a plasmonic metal of Au toward multifunctionalities is demonstrated. By a novel two‐step templated growth, a highly ordered Au–BaTiO₃–ZnO nanocomposite in a unique “nanoman”‐like form, i.e., self‐assembled ZnO nanopillars and Au nanopillars in a BaTiO₃ matrix, is realized, and is very different from the random three‐phase ones with randomly arranged Au nanoparticles and ZnO nanopillars in the BaTiO₃ matrix. The ordered three‐phase “nanoman”‐like structure provides unique functionalities such as obvious hyperbolic dispersion in the visible and near‐infrared regime enabled by the highly anisotropic nanostructures compared to other random structures. Such a self‐assembled and ordered three‐phase nanocomposite is obtained through a combination of vapor–liquid–solid (VLS) and two‐phase epitaxy growth mechanisms. The study opens up new possibilities in the design, growth, and application of multiphase structures and provides a new approach to engineer the ordering of complex nanocomposite systems with unprecedented control over electron–light–matter interactions at the nanoscale.     

Surface Plasmon‐Enhanced Photodetection in Few Layer MoS2 Phototransistors with Au Nanostructure Arrays

2D Molybdenum disulfide (MoS₂) is a promising candidate material for high‐speed and flexible optoelectronic devices, but only with low photoresponsivity. Here, a large enhancement of photocurrent response is obtained by coupling few‐layer MoS₂ with Au plasmonic nanostructure arrays. Au nanoparticles or nanoplates placed onto few‐layer MoS₂ surface can enhance the local optical field in the MoS₂ layer, due to the localized surface plasmon (LSP) resonance. After depositing 4 nm thick Au nanoparticles sparsely onto few‐layer MoS₂ phototransistors, a doubled increase in the photocurrent response is observed. The photocurrent of few‐layer MoS₂ phototransistors exhibits a threefold enhancement with periodic Au nanoarrays. The simulated optical field distribution confirms that light can be trapped and enhanced near the Au nanoplates. These findings offer an avenue for practical applications of high performance MoS₂‐based optoelectronic devices or systems in the future.     

Single‐Step Assembly of Large‐Area,Transparent Conductive Patterns Induced Through Edge Adsorption of Template‐Confined Au‐Thiocyanate

Fabrication of patterned metallic films through chemical means is a primary objective in the emerging field of “bottom‐up” lithography. We present a simple technology for generating large area, highly uniform patterns of conductive gold microwires. The approach is based upon dissolution of a gold complex, Au(SCN)₄⁻, in an organic‐solvent/water mixture and confining the solution underneath polymeric molds. We show that Au(SCN)₄⁻ undergoes spontaneous crystallization/reduction, producing metallic Au microwires tracing the contours of the templates. Importantly, no shape‐directing molecules or reducing agents are required for Au microwire formation, as the thiocyanate ligands both donate the reducing electrons as well as direct the crystallization process of the Au patterns. We demonstrate application of the new technology for creating highly transparent conductive films.     

WO3 Nanofiber‐Based Biomarker Detectors Enabled by Protein‐Encapsulated Catalyst Self‐Assembled on Polystyrene Colloid Templates

A novel catalyst functionalization method, based on protein‐encapsulated metallic nanoparticles (NPs) and their self‐assembly on polystyrene (PS) colloid templates, is used to form catalyst‐loaded porous WO₃ nanofibers (NFs). The metallic NPs, composed of Au, Pd, or Pt, are encapsulated within a protein cage, i.e., apoferritin, to form unagglomerated monodispersed particles with diameters of less than 5 nm. The catalytic NPs maintain their nanoscale size, even following high‐temperature heat‐treatment during synthesis, which is attributed to the discrete self‐assembly of NPs on PS colloid templates. In addition, the PS templates generate open pores on the electrospun WO₃ NFs, facilitating gas molecule transport into the sensing layers and promoting active surface reactions. As a result, the Au and Pd NP‐loaded porous WO₃ NFs show superior sensitivity toward hydrogen sulfide, as evidenced by responses (R_air/R_gas) of 11.1 and 43.5 at 350 °C, respectively. These responses represent 1.8‐ and 7.1‐fold improvements compared to that of dense WO₃ NFs (R_air/R_gas = 6.1). Moreover, Pt NP‐loaded porous WO₃ NFs exhibit high acetone sensitivity with response of 28.9. These results demonstrate a novel catalyst loading method, in which small NPs are well‐dispersed within the pores of WO₃ NFs, that is applicable to high sensitivity breath sensors.     

Self‐Healing of Polarizing Films via the Synergy between Gold Nanorods and Vitrimer

Conventional self‐healing is about the recovery of shape and mechanical properties. In contrast, recovery of functional properties is still a great challenge, especially for optical functional materials, as the known self‐healing methods are incompatible with optical properties. By utilizing the synergistic effect between Au nanorods and vitrimer, the alignment of Au nanorods can be achieved in the crosslinked polymer. The optical properties of the resulting polarizing film, such as light transmittance and polarization degree, can be fully recovered without an external repair agent. With simple laser irradiation to induce the photothermal effect of Au nanorods, the shape‐memory effect of vitrimer returns the Au nanorods to their initial orientation, and the plasticity achieves in situ self‐healing of the cutting area. The self‐healing of polarizing film provides a new research direction and reference for the application of self‐healing systems in functional materials.     

Core–Shell–Satellite Nanomaces as Remotely Controlled Self‐Fueling Fenton Reagents for Imaging‐Guided Triple‐Negative Breast Cancer‐Specific Therapy

Triple‐negative breast cancer (TNBC) is highly aggressive and insensitive to conventional targeted therapies, resulting in poor therapeutic outcomes. Recent studies have shown that abnormal iron metabolism is observed in TNBC, suggesting an opportunity for TNBC treatment via the iron‐dependent Fenton reaction. Nevertheless, the efficiency of current Fenton reagents is largely restricted by the lack of specificity and low intracellular H₂O₂ level of cancer cells. Herein, core–shell–satellite nanomaces (Au @ MSN@IONP) are fabricated, as near‐infrared (NIR) light‐triggered self‐fueling Fenton reagents for the amplified Fenton reaction inside TNBC cells. Specifically, the Au nanorod core can convert NIR light energy into heat to induce massive production of intracellular H₂O₂, thereby the surface‐decorated iron oxide nanoparticles (IONP) are being fueled for robust Fenton reaction. By exploiting the vulnerability of iron efflux in TNBC cells, such a self‐fueling Fenton reaction leads to highly specific anti‐TNBC efficacy with minimal cytotoxicity to normal cells. The PI3K/Akt/FoxO axis, intimately involved in the redox regulation and survival of TNBC, is demonstrated to be inhibited after the treatment. Consequently, precise in vivo orthotopic TNBC ablation is achieved under the guidance of IONP‐enhanced magnetic resonance imaging. The results demonstrate the proof‐of‐concept of NIR‐light‐triggered self‐fueling Fenton reagents against TNBC with low ferroportin levels.     

Precisely Size‐Tunable Monodisperse Hairy Plasmonic Nanoparticles via Amphiphilic Star‐Like Block Copolymers

In situ precision synthesis of monodisperse hairy plasmonic nanoparticles with tailored dimensions and compositions by capitalizing on amphiphilic star‐like diblock copolymers as nanoreactors are reported. Such hairy plasmonic nanoparticles comprise uniform noble metal nanoparticles intimately and perpetually capped by hydrophobic polymer chains (i.e., “hairs”) with even length. Interestingly, amphiphilic star‐like diblock copolymer nanoreactors retain the spherical shape under reaction conditions, and the diameter of the resulting plasmonic nanoparticles and the thickness of polymer chains situated on the surface of the nanoparticle can be readily and precisely tailored. These hairy nanoparticles can be regarded as hard/soft core/shell nanoparticles. Notably, the polymer “hairs” are directly and permanently tethered to the noble metal nanoparticle surface, thereby preventing the aggregation of nanoparticles and rendering their dissolution in nonpolar solvents and the homogeneous distribution in polymer matrices with long‐term stability. This amphiphilic star‐like block copolymer nanoreactor‐based strategy is viable and robust and conceptually enables the design and synthesis of a rich variety of hairy functional nanoparticles with new horizons for fundamental research on self‐assembly and technological applications in plasmonics, catalysis, energy conversion and storage, bioimaging, and biosensors.     

Decoupling the Effects of Self‐Assembled Monolayers on Gold,Silver, and Copper Organic Transistor Contacts

In bottom‐contact organic field‐effect transistors (OFETs), the functionalization of source/drain electrodes leads to a tailored surface chemistry for film growth and controlled interface energetics for charge injection. This report describes a comprehensive investigation into separating and correlating the energetic and morphological effects of a self‐assembled monolayers (SAMs) treatment on Au, Ag, and Cu electrodes. Fluorinated 5,11‐bis(triethylsilylethynyl) anthradithiophene (diF‐TES‐ADT) and pentafluorobenzenethiol (PFBT) are employed as a soluble small‐molecule semiconductor and a SAM material, respectively. Upon SAM modification, the Cu electrode devices benefit from a particularly dramatic performance improvement, closely approaching the performance of OFETs with PFBT‐Au and PFBT‐Ag. Ultraviolet photoemission spectroscopy, polarized optical microscopy, grazing‐incidence wide‐angle X‐ray scattering elucidate the metal work function change and templated crystal growth with high crystallinity resulting from SAMs. The transmission‐line method separates the channel and contact properties from the measured OFET current–voltage data, which conclusively describes the impact of the SAMs on charge injection and transport behavior.