Assembly and Healing: Capacitive and Conductive Plasmonic Interfacing via a Unified and Clean Wet Chemistry Route.

Solution-based nanoparticle assembly represents a highly promising way to build functional metastructures based on a wealth of synthetic nanomaterial building blocks with well-controlled morphology and crystallinity. In particular, the involvement of DNA molecular programming in these bottom-up processes gradually helps the ambitious goal of customizable chemical nanofabrication. However, a fundamental challenge is to realize strong interunit coupling in an assembly toward emerging functions and applications. Herein, we present a unified and clean strategy to address this critical issue based on a H2O2-redox-driven "assembly and healing" process. This facile solution route is able to realize both capacitively coupled and conductively bridged colloidal boundaries, simply switchable by the reaction temperature, toward bottom-up nanoplasmonic engineering. In particular, such a "green" process does not cause surface contamination of nanoparticles by exogenous active metal ions or strongly passivating ligands, which, if it occurs, could obscure the intrinsic properties of as-formed structures. Accordingly, previously raised questions regarding the activities of strongly coupled plasmonic structures are clarified. The reported process is adaptable to DNA nanotechnology, offering molecular programmability of interparticle charge conductance. This work represents a new generation of methods to make strongly coupled nanoassemblies, offering great opportunities for functional colloidal technology and even metal self-healing.

DNA-Condensed Plasmonic Supraballs Transparent to Molecules.

DNA nanotechnology offers an unrivaled programmability of plasmonic nanoassemblies based on encodable Watson-Crick basepairing. However, it is very challenging to build rigidified three-dimensional supracolloidal assemblies with strong electromagnetic coupling and a self-confined exterior shape. We herein report an alternative strategy based on a DNA condensation reaction to make such structures. Using DNA-grafted gold nanoparticles as building blocks and metal ions with suitable phosphate affinities as abiological DNA-bonding agents, a seedless growth of spheroidal supraparticles is realized via metal-ion-induced DNA condensation. Some governing rules are disclosed in this process, including kinetic and thermodynamic effects stemming from electrostatic and coordinative forces with different interaction ranges. The supraballs are tailorable by adjusting the volumetric ratio between DNA grafts and gold cores and by overgrowing extra gold layers toward tunable plasmon coupling. Various appealing and highly desirable properties are achieved for the resulting metaballs, including (i) chemical reversibility and fixation ability, (ii) stability against denaturant, salt, and molecular adsorbates, (iii) enriched and continuously tunable plasmonic hotspots, (iv) permeability to small guest molecules and antifoulingness against protein contaminates, and (v) Raman-enhancing and photocatalytic activities. Innovative applications are thus foreseeable for this emerging class of meta-assemblies in contrast to what is achieved by DNA-basepaired ones.

Steering DNA Condensation on Engineered Nanointerfaces.

DNA has received increasing attention in nanotechnology due to its ability to fold into prescribed structures. Different from the commonly adopted base-pairing strategy, an emerging class of amorphous DNA materials are formed by DNA's abiological interactions. Despite the great successes, a lack of nanoscale nucleation/growth control disables more advanced considerations. This work aims at harnessing the heterogeneous nucleation of metal-ion-glued DNA condensates on nanointerfaces. Upon unveiling key orthogonal factors including solution pH, ionic cross-linkers, and surface functionalities, chemically programmable DNA condensation on nanoparticle seeds is achieved, resembling a famous Stöber process for silica coating. The nucleation rules discovered on individual nanoseeds can be passed on to their dimeric assemblies, where broken spherical symmetry and the existence of interparticle gaps help a regiospecific DNA gelation. The steerable DNA condensation, and the multifunctions from DNA, metal ions, and nanocores, hold a great promise in noncanonical DNA nanotechnology toward novel applications.

Sub-1.5 nm-gapped heterodimeric plasmonic nanomolecules.

Plasmonic molecules are discrete assemblies of similar/dissimilar nanomaterials (atomic equivalents) with efficient inter-unit coupling toward electromagnetic hybridization. Albeit fundamentally and technologically very important, these structures are rare due to the lack of a general way to manipulate the structure, composition, and coupling of the nanoassemblies. While DNA nanotechnology offers a precious chance to build such structures, the weak coupling of DNA-bonded materials and the very limited material building blocks are two obstacles. This work aims to remove the bottlenecking barriers on the road to dimeric (and possibly more complicated) plasmonic molecules. After solving key synthetic issues, DNA-guided, solvo-driven Ag ion soldering is utilized to build a whole set (10 combinations of 4 metals) of homo/heterodimeric plasmonic nanomolecules with prescribed compositions. Importantly, strong in-solution electric-dipole coupling mediated by a sub-1.5 nm interparticle dielectric gap is achieved for materials with strong (Au, Ag) or damped (Pt, Pd) plasmonic responses. The involvement of Pt/Pd materials is of great value for plasmon-mediated catalysis. The broken dimeric symmetry is desirable for Fano-like resonance and photonic nanodiode devices, as well as lightening-up of plasmon dark states. The generality and reliability of the method would allow excitonic, nonlinear-optical, and magnetic units to be involved toward correspondingly enhanced functions.

DNA-Programmable AgAuS-Primed Conductive Nanowelding Wires-Up Wet Colloids.

Self-assembly of nanomaterials, directed by molecular or supramolecular interactions, is a powerful strategy to build nanoscale devices. Despite many advantages of such solution-based processes, a big challenge is to realize interparticle ohmic contacts toward facilitated charge transport over a long distance. We report a new concept of primed nanowelding to thread solution-borne nanoparticles in prescribed assemblies. The process starts with a gap-specific deposition of Ag2 E (E=S, Se) materials in pre-assembled gold structures, which spontaneously transform into AgAuE semiconductors via directional gold diffusion. Treatment with tributylphosphine generates alloyed Au/Ag welding spots that conductively wire-up nanoparticles into discrete "molecules" and micron-long "polymers". This method is compatible with DNA programming and delivers a possible way to solve the problem of the carrier-transport dilemma in solution-processed nanostructures for better-functioning nanodevices.

Evaporative Drying: A General and Readily Scalable Route to Spherical Nucleic Acids with Quantitative, Fully Tunable, and Record-High DNA Loading.

Nanoparticles (NPs) grafted with highly dense DNA strands are termed as spherical nucleic acids (SNAs), which have important applications benefiting from various unique properties unpossessed by naturally occurring nucleic acids. To overcome existing challenges toward an ideal SNA synthesis, herein, a very simple, while highly effective evaporative drying strategy featuring various long-desired advantages, is reported. This includes record-high DNA loading, generality for more NP materials, fully and quantitatively tunable DNA density, and readiness toward bulk production. The process requires almost zero care and the solid products are especially suitable for a long-time storage without quality degradation. The research reveals a quick and highly efficient packing of thiol-tagged DNA on the NP surface at the critical moment of drying, which refreshes previous knowledge on DNA conjugation chemistry. Based on this advancement, practical applications of SNAs in various fields may become possible.

Decoupled Roles of DNA-Surfactant Interactions: Instant Charge Inversion, Enhanced Colloidal and Chemical Stabilities, and Fully Tunable DNA Conjugation of Shaped Plasmonic Nanocrystals.

Surfactant-dictated syntheses of nanomaterials with well-defined shapes offer an extra dimension of control beyond nanoparticle size and chemical composition on the properties and self-assembly behaviors of colloidal materials. However, the surfactant bilayers on nanocrystals often cause great difficulty toward DNA grafting due to their unfavorable electrostatic charges and dense surface packing. Herein a revisit to this dilemma unveils a rapid charge inversion and enhanced colloidal/chemical stabilities of cationic-bilayer-covered nanocrystals upon DNA adsorption. Decoupling this hidden scenario provides a rationale to significantly improve DNA functionalization of surfactant-capped nanocrystals. Accordingly, fully tunable DNA conjugation (via Au-S bonding) on up to seven classes of surfactant-coated metal nanounits is easily and consistently achievable. The DNA-nanocrystal complexes featuring a continuously variable DNA density function well in DNA-guided nanoassembly. Our method opens the door to a wealth of material building blocks derived by surfactant-directed nanosyntheses toward DNA-programmable, extremely diversified, and highly complicated structures and functions.

Flash Synthesis of Spherical Nucleic Acids with Record DNA Density.

Nanoparticles (NPs) decorated with a high density of DNA strands, also known as spherical nucleic acids (SNAs), are widely used in DNA-programmable assembly, sensing, imaging, and therapeutics. A regular SNA synthesis is very time-consuming, which requires great caution to avoid NP aggregation. Herein we report an extremely simple, efficient, and scalable process to realize instant (in seconds) synthesis of SNAs with record-high DNA density. Our method relies on a rapid water removal from a DNA/NP mixture in contact with a butanol phase. This process generates a dehydrated "solid solution" that greatly accelerates DNA anchorage on NPs via Au-S bonding. Compared to a state-of-the-art DNA conjugation strategy in the literature, up to 3-time increase of DNA density is achieved by the instant dehydration in butanol (INDEBT). The ultradense DNA grafting is accomplished in a few seconds, which is highly hybridizable to form core-satellite assemblies. Our work turns SNA synthesis into an easy job, and enables future explorations of physical, chemical, and biological effects of SNAs with ultrahigh DNA density.

Antibody responses to SARS-CoV-2 in healthy individuals returning to Shenzhen.

To verify reliability of antibody detection and investigate population immunity to severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) in the local Chinese population. A cross-sectional study was conducted in Shenzhen to detect anti-coronavirus antibodies including, immunoglobulin G (IgG), immunoglobulin M (IgM), and immunoglobulin A (IgA). In the COVID-19 group, nine patients were enrolled after diagnosis. In the control group, 1589 individuals without clinical symptoms (cough, fever, and fatigue) and returning from outside Shenzhen were enrolled. The first study enrollment occurred at the end of February 2020; the final study visit was 18 March 2020. In the COVID-19 group, the seven of nine patients were positive for IgM, IgG, and IgA. Meanwhile, six of the 1589 healthy individuals were found to be weakly positive for IgG. According to SARS-CoV-2 nucleic acid tests, the six individuals were all negative. Strong supplemental support for clinical information can be provided by antibody detection, especially for IgA. According to comparison with overseas reports, the infection rate of the Chinese population outside Shenzhen, China, is significantly low, so most of the population in China is still susceptible. Hence, social distancing measures are still inevitable until a vaccine is developed successfully.

Preparation of a Ti0.7W0.3O2/TiO2 nanocomposite interfacial photocatalyst and its photocatalytic degradation of phenol pollutants in wastewater.

A Ti0.7W0.3O2/TiO2 nanocomposite interfacial photocatalyst was designed and prepared for the photocatalytic degradation of phenol pollutants in wastewater. The detailed properties of the Ti0.7W0.3O2/TiO2 nanocomposite interface (NCI) were analyzed by XRD, SEM, EDX, DRS, UPS and XPS technologies, showing that anatase TiO2 nanospheres (NSs) were uniformly dispersed on the surface of rutile Ti0.7W0.3O2 nanoparticles (NPs) and formed the nanocomposite interface. The DRS and UPS results of 5 wt% Ti0.7W0.3O2/TiO2 NCI indicated a greatly broadened light response range with a wavelength shorter than 527 nm and a shorter band gap energy of 2.37 eV. The conduction band of TiO2 NSs, Ti0.7W0.3O2 NPs and 5 wt% Ti0.7W0.3O2/TiO2 NCI were measured based on the results of the valence band and band gap energy obtained via XPS and DRS, and then the energy level diagram of Ti0.7W0.3O2/TiO2 NCI was proposed. The photocatalytic degradation of phenol at Ti0.7W0.3O2/TiO2 NCI with different loading ratios of Ti0.7W0.3O2 NPs was investigated under optimum conditions (i.e., pH of 4.5, catalyst dosage of 0.45 g L-1 and phenol initial concentration of 95 ppm) under the illumination of ultraviolet visible light. Also, 5 wt% Ti0.7W0.3O2/TiO2 NCI exhibited the highest photocatalytic activity, with the initial rate constant (k) calculated as 0.09111 min-1. After recycling six times, Ti0.7W0.3O2/TiO2 NCI showed good stability and recyclability. The involvement of superoxide radicals in the initial reaction at Ti0.7W0.3O2/TiO2 NCI was evidenced by the use of a terephthalic acid (TA) fluorescent probe. Besides, UV-Vis spectroscopy, UHPLC-MS and GC-MS technologies were used to analyze the main intermediates in the photocatalytic degradation of phenol. The probable photocatalytic degradation mechanism of phenol at Ti0.7W0.3O2/TiO2 NCI was also proposed.

Ag Ion Soldering: An Emerging Tool for Sub-nanomeric Plasmon Coupling and Beyond.

Self-assembly represents probably the most flexible way to construct metastructured materials and devices from a wealth of colloidal building blocks with synthetically controllable sizes, shapes, and elemental compositions. In principle, surface capping is unavoidable during the synthesis of nanomaterials with well-defined geometry and stability. The ligand layer also endows inorganic building blocks with molecular recognition ability responsible for their assembly into desired structures. In the case of plasmonic nanounits, precise positioning of them in a nanomolecule or an ordered nanoarray provides a chance to shape their electrodynamic behaviors and thereby assists experimental demonstration of modern nanoplasmonics toward practical uses. Despite previous achievements in bottom-up nanofabrication, a big challenge exists toward strong coupling and facile charge transfer between adjacent nanounits in an assembly. This difficulty has impeded a functional development of plasmonic nanoassemblies. The weakened interparticle coupling originates from the electrostatic and steric barriers of ionic/molecular adsorbates to guarantee a good colloidal stability. Such a dilemma is rooted in fundamental colloidal science, which lacks an effective solution. During the past several years, a chemical tool termed Ag ion soldering (AIS) has been developed to overcome the above situation toward functional colloidal nanotechnology. In particular, a dimeric assembly of plasmonic nanoparticles has been taken as an ideal model to study plasmonic coupling and interparticle charge transfer. This Account starts with a demonstration of the chemical mechanism of AIS, followed by a verification of its workability in various self-assembly systems. A further use of AIS to realize postsynthetic coupling of DNA-directed nanoparticle clusters evidences its compatibility with DNA nanotechnology. Benefiting from the sub-nanometer interparticle gap achieved by AIS, a conductive pathway is established between two nanoparticles in an assembly. Accordingly, light-driven charge transfer between the conductively bridged plasmonic units is realized with highly tunable resonance frequencies. These situations have been demonstrated by thermal/photothermal sintering of silica-isolated nanoparticle dimers as well as gap-specific electroless gold/silver deposition. The regioselective silver deposition is then combined with galvanic replacement to obtain catalytically active nanofoci (plasmonic nanogaps). The resulting structures are useful for real time and on-site Raman spectroscopic tracking of chemical reactions in the plasmonic hotspots (nanogaps) as well as for study of plasmon-mediated/field-enhanced catalysis. The Account is concluded by a deeper insight into the chemical mechanism of AIS and its adaption to conformation-rich structures. Finally, AIS-enabled functional pursuits are suggested for self-assembled materials with strongly coupled and easily reshapable physicochemical properties.

Chemically modified nanofoci unifying plasmonics and catalysis.

A plasmonic nanofocus, often in the form of a nanogap, is capable of concentrating light in a nanometric volume. The greatly enhanced electromagnetic field offers many opportunities in physics and chemistry. However, the lack of a method to fine-tune the chemical activities of the nanofocus has severely limited its application. Here we communicate an intriguing class of chemically modified nanofoci (CMNFs) that are able to address this challenge. Our results successfully demonstrate a possibility to functionalize the nanosized, mass-transport-restricted nanogap (nanofocus) of a dimeric gold nanoparticle assembly with homo-(Au) and heterogeneous (Ag, Pt, and Pd) materials. The as-produced structures with conductive Au and Ag junctions generate a novel form of charge transfer plasmon (CTP) with continuously tunable frequency covering the visible and near-infrared domains. In addition, the Ag materials can be displaced by catalytic Pt and Pd metals while still maintaining a tightly focused electromagnetic field. These hybrid structures with unified catalytic and plasmonic properties enable real-time, on-site probing of catalytic conversions at the nanofocus by plasmon-enhanced Raman scattering. The chemically/optically engineered CMNFs represent the simplest function-integrated nanodevices for plasmonics, sensing, and catalysis. Our work not only realizes chemical CTP reshaping, but also allows chemical functionalization into an intensified plasmonic near-field. The latter may enable unconventional chemical reactions driven by the catalytically functionalized, strongly boosted light field.

Base-Sequence-Independent Efficient Redox Switching of Self-Assembled DNA Nanocages.

Stimuli responsivity has been extensively pursued in dynamic DNA nanotechnology, due to its incredible application potentials. Among diverse dynamic systems, redox-responsive DNA assembly holds great promise for broad applications, especially considering that redox processes widely exist in various physiological environments. However, only a few studies have been reported on redox-sensitive dynamic DNA assembly. Albeit ingenious, most of these studies are either dependent on the DNA sequence or involve chemical modification. Herein, a facile and universal mechanism to realize redox-responsive self-assembly of DNA nanocages (tetrahedron and cube) driven by the interconversion between cystamine and cysteamine toward dynamic DNA nanotechnology is reported.

Stimuli-Responsive DNA Self-Assembly: From Principles to Applications.

Stimuli-responsive DNA self-assembly shares the advantages of both designed stimuli-responsiveness and the molecular programmability of DNA structures, offering great opportunities for basic and applied research in dynamic DNA nanotechnology. In this minireview, we summarize the most recent progress in this rapidly developing field. The trigger mechanisms of the responsive DNA systems are first divided into six categories, which are then explained with illustrative examples following this classification. Subsequently, proof-of-concept applications in terms of biosensing, in vivo pH-mapping, drug delivery, and therapy are discussed. Finally, we provide some remarks on the challenges and opportunities of this highly promising research direction in DNA nanotechnology.

Nanosecond-Laser-Based Charge Transfer Plasmon Engineering of Solution-Assembled Nanodimers.

The ability to re-engineer self-assembled functional structures with nanometer accuracy through solution-processing techniques represents a big challenge in nanotechnology. Herein we demonstrate that Ag+-soldered nanodimers with a steric confinement coating of silica can be harnessed to realize an in-solution nanosecond laser reshaping to form interparticle conductive pathway with finely controlled conductance. The high structural purity of the nanodimers, the rigid silica coating, and the uniform (but still adjustable) sub-1-nm interparticle gap together determine the success of the laser reshaping process. This method is applicable to DNA-assembled nanodimers, and thus promises DNA-based programming toward higher structural complexity. The resulting structures exhibit highly tunable charge transfer plasmons at visible and near-infrared frequencies dictated by the fluence of the laser pulses. Our work provides an in-solution, rapid, and nonperturbative route to realize charge transfer plasmonic coupling along prescribed paths defined by self-assembly, conferring great opportunities for functional metamaterials in the context of chemical, biological, and nanophotonic applications. The ability to continuously control a subnm interparticle gap and the nanomeric width of a conductive junction also provides a platform to investigate modern plasmonic theories involving quantum and nonlocal effects.

Universal pH-Responsive and Metal-Ion-Free Self-Assembly of DNA Nanostructures.

pH-responsiveness has been widely pursued in dynamic DNA nanotechnology, owing to its potential in biosensing, controlled release, and nanomachinery. pH-triggering systems mostly depend on specific designs of DNA sequences. However, sequence-independent regulation could provide a more general tool to achieve pH-responsive DNA assembly, which has yet to be developed. Herein, we propose a mechanism for dynamic DNA assembly by utilizing ethylenediamine (EN) as a reversibly chargeable (via protonation) molecule to overcome electrostatic repulsions. This strategy provides a universal pH-responsivity for DNA assembly since the regulation originates from externally co-existing EN rather than specific DNA sequences. Furthermore, it endows structural DNA nanotechnology with the benefits of a metal-ion-free environment including nuclease resistance. The concept could in principle be expanded to other organic molecules which may bring unique controls to dynamic DNA assembly.

Freeze the Moment: High Speed Capturing of Weakly Bonded Dynamic Nanoparticle Assemblies in Solution by Ag Ion Soldering.

Despite the versatile forms of colloidal aggregates, these spontaneously formed structures are often hard to find a suitable application in nanotechnology and materials science. A determinate reason is the lack of a suitable method to capture the transiently formed and quickly evolving colloidal structures in solution. To address this challenge, a simple but highly efficient strategy is herein reported to capture the dynamic and metastable colloidal assemblies formed in an aqueous or nonaqueous solution. This process takes advantage of a recently developed Ag ion soldering reaction to realize a rapid fixation of as-formed metastable assemblies. This method works efficiently for both solid (3D) nanoparticle aggregates and weakly bonded fractal nanoparticle chains (1D). In both cases, very high capturing speed and close to 100% efficiency are achieved to fully retain a quickly growing structure. The soldered nanochains further enable a fabrication of discrete, uniform, and functionalizable nanoparticle clusters with enriched linear conformation by mechanical shearing, which would otherwise be difficult to make. The captured products are water dispersible and mechanically robust, favoring an exploration of their properties toward possible applications. The work paves a way to previously untouched aspects of colloidal science and thus would create new chances in nanotechnology.

Optimal design for the support structure of a cavity mirror in a chemical oxygen iodine laser resonator.

The dynamic characteristics of the cavity mirror support structure strongly influence the quality of the output beam. However, the contradiction between excellent dynamic performance and light weight make the design process challenging. To cope with the problems encountered in the original design of a chemical oxygen iodine laser system, this paper presents a two-dimensional adjustable support structure based on spherical constraints with large specific stiffness in the initial design phase. Subsequently, a two-level optimization strategy containing a macro design and a detailed design is adopted to optimize the initial structure. At the macro design stage, a two-step topology optimization procedure is introduced, in which the scale of the optimization model is dramatically reduced using the independent continuous mapping algorithm to improve the calculation speed in the first step, and the gray elements are eliminated using the bi-directional evolutionary structural optimization method to clearly obtain the optimal topology in the second step. This method is verified to overcome the defect of low efficiency, while still eliminating gray elements. At the detailed design stage, an adaptive surrogate model and the multi-objective design optimization method are employed to seek the best compromise between the lower weight and higher dynamic performance. The results from the application to the example of the cavity mirror support structure show that the mass is reduced by 41.8%, and the dynamic performance requirement is fulfilled.

Amplification of arsenic genotoxicity by TiO2 nanoparticles in mammalian cells: new insights from physicochemical interactions and mitochondria.

Titanium dioxide nanoparticles (TiO2 NPs) have shown great adsorption capacity for arsenic (As); however, the potential impact of TiO2 NPs on the behavior and toxic responses of As remains largely unexplored. In the present study, we focused on the physicochemical interaction between TiO2 NPs and As(III) to clarify the underlying mechanisms involved in their synergistic genotoxic effect on mammalian cells. Our data showed that As(III) mainly interacted with TiO2 NPs by competitively occupying the sites of hydroxyl groups on the surface of TiO2 NP aggregates, resulting in more aggregation of TiO2 NPs. Although TiO2 NPs at concentrations used here had no cytotoxic or genotoxic effects on cells, they efficiently increased the genotoxicity of As(III) in human-hamster hybrid (AL) cells. The synergistic genotoxicity of TiO2 NPs and As(III) was partially inhibited by various endocytosis pathway inhibitors while it was completely blocked by an As(III)-specific chelator. Using a mitochondrial membrane potential fluorescence probe, a reactive oxygen species (ROS) probe together with mitochondrial DNA-depleted ρ0 AL cells, we discovered that mitochondria were essential for mediating the synergistic DNA-damaging effects of TiO2 NPs and As(III). These data provide novel mechanistic proof that TiO2 NPs enhanced the genotoxicity of As(III) via physicochemical interactions, which were mediated by mitochondria-dependent ROS.

Pt supraparticles with controllable DNA valences for programmed nanoassembly.

Supraparticles are self-limiting nanoparticle ensembles with attractive properties from their unique hierarchical (primary and secondary) structures. Aiming at relieving the bottleneck of the very limited material building blocks in DNA nanotechnology, we herein demonstrate Pt-based supraparticles as catalytic materials for valence-controllable and high density DNA functionalizations toward DNA-programmed nanoassembly.