Controlling Structure and Porosity in Catalytic Nanoparticle Superlattices with DNA

Tunable crystalline assemblies using surface-engineered protein cages

Assembly of nanoparticles into superlattices yields nanomaterials with novel properties. We have recently shown that engineered protein cages are excellent building blocks for the assembly of inorganic nanoparticles into highly structured hybrid materials, with unprecedented precision. In this study, we show that the protein matrix, composed of surface-charged protein cages, can be readily tuned to achieve a number of different crystalline assemblies. Simply by altering the assembly conditions, different types of crystalline structures were produced, without the need to further modify the cages. Future work can utilize these new protein scaffolds to create nanoparticle superlattices with various assembly geometries and thus tune the functionality of these hybrid materials.

Principles of Photocatalysts and Their Different Applications: A Review

Human existence and societal growth are both dependent on the availability of clean and fresh water. Photocatalysis is a type of artificial photosynthesis that uses environmentally friendly, long-lasting materials to address energy and environmental issues. There is currently a considerable demand for low-cost, high-performance wastewater treatment equipment. By changing the structure, size, and characteristics of nanomaterials, the use of nanotechnology in the field of water filtration has evolved dramatically. Semiconductor-assisted photocatalysis has recently advanced to become among the most promising techniques in the fields of sustainable energy generation and ecological cleanup. It is environmentally beneficial, cost-effective, and strictly linked to the zero waste discharge principle used in industrial effluent treatment. Owing to the reduction or removal of created unwanted byproducts, the green synthesis of photoactive nanomaterial is more beneficial than chemical synthesis approaches. Furthermore, unlike chemical synthesis methods, the green synthesis method does not require the use of expensive, dangerous, or poisonous ingredients, making it a less costly, easy, and environmental method for photocatalyst synthesis. This work focuses on distinct greener synthesis techniques utilized for the production of new photocatalysts, including metals, metal doped-metal oxides, metal oxides, and plasmonic nanostructures, including the application of artificial intelligence and machine learning to the design and selection of an innovative photocatalyst in the context of energy and environmental challenges. A brief overview of the industrial and environmental applications of photocatalysts is also presented. Finally, an overview and recommendations for future research are given to create photocatalytic systems with greatly improved stability and efficiency.

Inspired Beyond Nature: Three Decades of Spherical Nucleic Acids and Colloidal Crystal Engineering with DNA

The conception, synthesis, and invention of a nanostructure, now known as the spherical nucleic acid, or SNA, in 1996 marked the advent of a new field of chemistry. Over the past three decades, the SNA and its analogous anisotropic equivalents have provided an avenue for us to think about some of the most fundamental concepts in chemistry in new ways and led to technologies that are significantly impacting fields from medicine to materials science. A prime example is colloidal crystal engineering with DNA, the framework for using SNAs and related structures to synthesize programmable matter. Herein, we document the evolution of this framework, which was initially inspired by nature, and describe how it now allows researchers to chart paths to move beyond it, as programmable matter with real-world significance is envisioned and created.

A Review on Self-Assembly of Colloidal Nanoparticles into Clusters, Patterns, and Films: Emerging Synthesis Techniques and Applications

The colloidal synthesis of functional nanoparticles has gained tremendous scientific attention in the last decades. In parallel to these advancements, another rapidly growing area is the self-assembly or self-organization of these colloidal nanoparticles. First, the organization of nanoparticles into ordered structures is important for obtaining functional interfaces that extend or even amplify the intrinsic properties of the constituting nanoparticles at a larger scale. The synthesis of large-scale interfaces using complex or intricately designed nanostructures as building blocks, requires highly controllable self-assembly techniques down to the nanoscale. In certain cases, for example, when dealing with plasmonic nanoparticles, the assembly of the nanoparticles further enhances their properties by coupling phenomena. In other cases, the process of self-assembly itself is useful in the final application such as in sensing and drug delivery, amongst others. In view of the growing importance of this field, this review provides a comprehensive overview of the recent developments in the field of nanoparticle self-assembly and their applications. For clarity, the self-assembled nanostructures are classified into two broad categories: finite clusters/patterns, and infinite films. Different state-of-the-art techniques to obtain these nanostructures are discussed in detail, before discussing the applications where the self-assembly significantly enhances the performance of the process.

Three-dimensional visualization of nanoparticle lattices and multimaterial frameworks

Advances in nanoscale self-assembly have enabled the formation of complex nanoscale architectures. However, the development of self-assembly strategies toward bottom-up nanofabrication is impeded by challenges in revealing these structures volumetrically at the single-component level and with elemental sensitivity. Leveraging advances in nano-focused hard x-rays, DNA-programmable nanoparticle assembly, and nanoscale inorganic templating, we demonstrate nondestructive three-dimensional imaging of complexly organized nanoparticles and multimaterial frameworks. In a three-dimensional lattice with a size of 2 micrometers, we determined the positions of about 10,000 individual nanoparticles with 7-nanometer resolution, and identified arrangements of assembly motifs and a resulting multimaterial framework with elemental sensitivity. The real-space reconstruction permits direct three-dimensional imaging of lattices, which reveals their imperfections and interfaces and also clarifies the relationship between lattices and assembly motifs.

Programmable Matter: The Nanoparticle Atom and DNA Bond

Colloidal crystal engineering with DNA has led to significant advances in bottom-up materials synthesis and a new way of thinking about fundamental concepts in chemistry. Here, programmable atom equivalents (PAEs), comprised of nanoparticles (the "atoms") functionalized with DNA (the "bonding elements"), are assembled through DNA hybridization into crystalline lattices. Unlike atomic systems, the "atom" (e.g., the nanoparticle shape, size, and composition) and the "bond" (e.g., the DNA length and sequence) can be tuned independently, yielding designer materials with unique catalytic, optical, and biological properties. In this review, nearly three decades of work that have contributed to the evolution of this class of programmable matter is chronicled, starting from the earliest examples based on gold-core PAEs, and then delineating how advances in synthetic capabilities, DNA design, and fundamental understanding of PAE-PAE interactions have led to new classes of functional materials that, in several cases, have no natural equivalent.

Spherical Nucleic Acids: Integrating Nanotechnology Concepts into General Chemistry Curricula

Nanoscience and technology research offer exciting avenues to modernize undergraduate-level General Chemistry curricula. In particular, spherical nucleic acid (SNA) nanoconjugates, which behave as "programmable atom equivalents" (PAEs) in the context of colloidal crystals, are one system that one can use to reinforce foundational concepts in chemistry including matter and atoms, the Periodic Table, Lewis dot structures and the octet rule, valency and valence-shell electron-pair repulsion (VSEPR) theory, and Pauling's rules, ultimately leading to enriching discussions centered on materials chemistry and biochemistry with key implications in medicine, optics, catalysis, and other areas. These lessons connect historical and modern concepts in chemistry, relate course content to current professional and popular science topics, inspire critical and creative thinking, and spur some students to continue their science, technology, engineering, and mathematics (STEM) education and attain careers in STEM fields. Ultimately, and perhaps most importantly, these lessons may expand the pool of young students interested in chemistry by making connections to a broader group of contemporary concepts and technologies that impact their lives and enhance their view of the field. Herein, a way of teaching aspects of General Chemistry in the context of modern nanoscience concepts is introduced to instructors and curricula developers at research institutions, primarily undergraduate institutions, and community colleges worldwide.

Noncovalent Self-Assembly of Protein Crystals with Tunable Structures

Engineering noncovalent interactions for assembling nonspherical proteins into supramolecular architectures with tunable morphologies and dynamics is challenging due to the structural heterogeneity and complexity of protein surfaces. Herein, we employed an anisotropic building block l-rhamnulose-1-phosphate aldolase (RhuA) to control supramolecular polymorphism in highly ordered protein assemblies by introducing histidine residues. Histidine-based π-π stacking interactions enabled thermodynamically controlled self-organization of RhuA to form three-dimensional (3D) nanoribbons and crystals. Self-assembly of different 3D crystal phases was kinetically modulated by the strong metal ion-histidine chelation, and double-helical protein superstructures were formed by engineering increased histidine interactions at the RhuA binding surface. Their structural properties and dynamics were determined via fluorescence microscopy, transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering. This work is aimed at expanding the toolbox for the programming of tunable, highly ordered, protein superstructures and increasing the understanding of the mechanisms of protein interfacial interactions.

The Effects of Temperature on the Assembly of Gold Nanoparticle by Interpolymer Complexation

Using synchrotron-based small-angle X-ray scattering techniques, we demonstrate that poly(ethylene glycol)-functionalized gold nanoparticles (PEG-AuNPs) are assembled into close-packed structures that include short-range order with face-centered cubic structure, where crystalline qualities are varied by controlling the electrolyte concentration, pH, and temperature of the suspensions. We show that interpolymer complexation with poly(acrylic acid) (PAA) is induced by lowering the pH level of the PEG-AuNPs suspensions, and furthermore, increasing the temperature of the suspension strengthens interparticle attraction, leading to improved supercrystal structures. Our results indicate that this strategy creates robust nanoparticle superlattices with high thermal stability. The effects of PAA and PEG chain lengths on the assemblies are also investigated, and their optimal conditions for creating improved superlattices are discussed.

Spontaneous Formation of Highly Stable Nanoparticle Supercrystals Driven by a Covalent Bonding Interaction

Nanoparticle supercrystals (NPSCs) are of great interest as materials with emergent properties. Different types of intermolecular forces, such as van der Waals interaction and hydrogen bonding, are present in the NPSCs fabricated to date. However, the limited structural stability of such NPSCs that results from the weakness of these intermolecular forces is a challenge. Here, we report a spontaneous formation of NPSCs driven by covalent bonding interactions, a type of intramolecular force much stronger than the above-mentioned intermolecular forces. A model solution-phase anhydride reaction is used to form covalent bonds between molecules grafted on the surface of gold nanoparticles, resulting in three-dimensional NPSCs. The NPSCs are very stable in different solvents, in dried conditions, and at temperatures as high as 160 °C. In addition to this, the large library of covalent-bond-forming reactions available and the low cost of reactants make the covalent bonding approach highly versatile and economical.

Mie-Resonant Three-Dimensional Metacrystals

Optical metamaterials, engineered to exhibit electromagnetic properties not found in natural materials, may enable new light-based applications including cloaking and optical computing. While there have been significant advances in the fabrication of two-dimensional metasurfaces, planar structures create nontrivial angular and polarization sensitivities, making omnidirectional operation impossible. Although three-dimensional (3D) metamaterials have been proposed, their fabrication remains challenging. Here, we use colloidal crystal engineering with DNA to prepare isotropic 3D metacrystals from Au nanocubes. We show that such structures can exhibit refractive indices as large as ∼8 in the mid-infrared, far greater than that of common high-index dielectrics. Additionally, we report the first observation of multipolar Mie resonances in metacrystals with well-formed habits, occurring in the mid-infrared for submicrometer metacrystals, which we measured using synchrotron infrared microspectroscopy. Finally, we predict that arrays of metacrystals could exhibit negative refraction. The results present a promising platform for engineering devices with unnatural optical properties.

Pulmonary toxicity of synthetic amorphous silica - effects of porosity and copper oxide doping

Materials can be modified for improved functionality. Our aim was to test whether pulmonary toxicity of silica nanomaterials is increased by the introduction of: a) porosity; and b) surface doping with CuO; and whether c) these modifications act synergistically. Mice were exposed by intratracheal instillation and for some doses also oropharyngeal aspiration to: 1) solid silica 100 nm; 2) porous silica 100 nm; 3) porous silica 100 nm with CuO doping; 4) solid silica 300 nm; 5) porous silica 300 nm; 6) solid silica 300 nm with CuO doping; 7) porous silica 300 nm with CuO doping; 8) CuO nanoparticles 9.8 nm; or 9) carbon black Printex 90 as benchmark. Based on a pilot study, dose levels were between 0.5 and 162 µg/mouse (0.2 and 8.1 mg/kg bw). Endpoints included pulmonary inflammation (neutrophil numbers in bronchoalveolar fluid), acute phase response, histopathology, and genotoxicity assessed by the comet assay, micronucleus test, and the gamma-H2AX assay. The porous silica materials induced greater pulmonary inflammation than their solid counterparts. A similar pattern was seen for acute phase response induction and histologic changes. This could be explained by a higher specific surface area per mass unit for the most toxic particles. CuO doping further increased the acute phase response normalized according to the deposited surface area. We identified no consistent evidence of synergism between surface area and CuO doping. In conclusion, porosity and CuO doping each increased the toxicity of silica nanomaterials and there was no indication of synergy when the modifications co-occurred.

Applications of Photoinduced Phenomena in Supramolecularly Arranged Phthalocyanine Derivatives: A Perspective

This review focuses on the description of several examples of supramolecular assemblies of phthalocyanine derivatives differently functionalized and interfaced with diverse kinds of chemical species for photo-induced phenomena applications. In fact, the role of different substituents was investigated in order to tune peculiar aggregates formation as well as, with the same aim, the possibility to interface these derivatives with other molecular species, as electron donor and acceptor, carbon allotropes, cyclodextrins, protein cages, drugs. Phthalocyanine photo-physical features are indeed really interesting and appealing but need to be preserved and optimized. Here, we highlight that the supramolecular approach is a versatile method to build up very complex and functional architectures. Further, the possibility to minimize the organization energy and to facilitate the spontaneous assembly of the molecules, in numerous examples, has been demonstrated to be more useful and performing than the covalent approach.

Self-assembly of anisotropic nanoparticles into functional superstructures

Self-assembly of colloidal nanoparticles (NPs) into superstructures offers a flexible and promising pathway to manipulate the nanometer-sized particles and thus make full use of their unique properties. This bottom-up strategy builds a bridge between the NP regime and a new class of transformative materials across multiple length scales for technological applications. In this field, anisotropic NPs with size- and shape-dependent physical properties as self-assembly building blocks have long fascinated scientists. Self-assembly of anisotropic NPs not only opens up exciting opportunities to engineer a variety of intriguing and complex superlattice architectures, but also provides access to discover emergent collective properties that stem from their ordered arrangement. Thus, this has stimulated enormous research interests in both fundamental science and technological applications. This present review comprehensively summarizes the latest advances in this area, and highlights their rich packing behaviors from the viewpoint of NP shape. We provide the basics of the experimental techniques to produce NP superstructures and structural characterization tools, and detail the delicate assembled structures. Then the current understanding of the assembly dynamics is discussed with the assistance of in situ studies, followed by emergent collective properties from these NP assemblies. Finally, we end this article with the remaining challenges and outlook, hoping to encourage further research in this field.

Electron microscopy of nanoparticle superlattice formation at a solid-liquid interface in nonpolar liquids

Nanoparticle superlattice films form at the solid-liquid interface and are important for mesoscale materials, but are notoriously difficult to analyze before they are fully dried. Here, the early stages of nanoparticle assembly were studied at solid-liquid interfaces using liquid-phase electron microscopy. Oleylamine-stabilized gold nanoparticles spontaneously formed thin layers on a silicon nitride (SiN) membrane window of the liquid enclosure. Dense packings of hexagonal symmetry were obtained for the first monolayer independent of the nonpolar solvent type. The second layer, however, exhibited geometries ranging from dense packing in a hexagonal honeycomb structure to quasi-crystalline particle arrangements depending on the dielectric constant of the liquid. The complex structures formed by the weaker interactions in the second particle layer were preserved, while the surface remained immersed in liquid. Fine-tuning the properties of the involved materials can thus be used to control the three-dimensional geometry of a superlattice including quasi-crystals.

Embedding Ultrasmall Au Clusters into the Pores of a Covalent Organic Framework for Enhanced Photostability and Photocatalytic Performance

Gold clusters loaded on various supports have been widely used in the fields of energy and biology. However, the poor photostability of Au clusters on support interfaces under prolonged illumination usually results in loss of catalytic performance. Covalent organic frameworks (COFs) with periodic and ultrasmall pore structures are ideal supports for dispersing and stabilizing Au clusters, although it is difficult to encapsulate Au clusters in the ultrasmall pores. In this study, a two-dimensional (2D) COF modified with thiol chains in its pores was prepared. With -SH groups as nucleation sites, Au nanoclusters (NCs) could grow in situ within the COF. The ultrasmall pores of the COF and the strong S-Au binding energy combine to improve the dispersibility of Au NCs under prolonged light illumination. Interestingly, Au-S-COF bridging as observed in this artificial Z-scheme photocatalytic system is deemed to be an ideal means to increase charge-separation efficiency.

Light-Responsive Colloidal Crystals Engineered with DNA

A novel method for synthesizing and photopatterning colloidal crystals via light-responsive DNA is developed. These crystals are composed of 10-30 nm gold nanoparticles interconnected with azobenzene-modified DNA strands. The photoisomerization of the azobenzene molecules leads to reversible assembly and disassembly of the base-centered cubic (bcc) and face-centered cubic (fcc) crystalline nanoparticle lattices. In addition, UV light is used as a trigger to selectively remove nanoparticles on centimeter-scale thin films of colloidal crystals, allowing them to be photopatterned into preconceived shapes. The design of the azobenzene-modified linking DNA is critical and involves complementary strands, with azobenzene moieties deliberately staggered between the bases that define the complementary code. This results in a tunable wavelength-dependent melting temperature (Tm ) window (4.5-15 °C) and one suitable for affecting the desired transformations. In addition to the isomeric state of the azobenzene groups, the size of the particles can be used to modulate the Tm window over which these structures are light-responsive.

Polymer Stereocomplexation as a Scalable Platform for Nanoparticle Assembly

DNA-mediated assembly of inorganic particles has demonstrated to be a powerful approach for preparing nanomaterials with a range of interesting optical and electrical properties. Building on this inspiration, we describe a generalizable gram-scale method to assemble nanoparticles through the formation of poly(methyl methacrylate) (PMMA) triple-helices. In this work, alkene-terminated syndiotactic (st-) and isotactic (it-) PMMA polymers were prepared and subsequently functionalized to afford nanoparticle ligands. Nanoparticles with complementary st- and it-PMMA ligands could then be spontaneously assembled upon mixing at room temperature. This process was robust and fully reversible through multiple heating and cooling cycles. The versatility of PMMA stereocomplexation was highlighted by assembling hybrid structures composed of nanoparticles of different compositions (e.g., Au and quantum dots) and shapes (e.g., spheres and rods). These initial demonstrations of nanoparticle self-assembly from inexpensive PMMA-based materials present an attractive alternative to DNA-based nanomaterials.

Inorganic Perovskite-Induced Synergy on Highly Selective Pd-Catalyzed Hydrogenation of Cinnamaldehyde

The transformation of various organic molecules into value-added chemicals has been driven by the success in development of highly active catalytic systems. Heterogeneous catalysts have found use in many industrial processes by virtue of their ease of separation and high activities in various reactions. However, many processes employing heterogeneous catalysts in the transformation of organic molecules suffer significantly when it comes to product selectivity. Herein, we report on the synthesis of highly selective palladium nanoparticle (Pd NP)-containing catalysts. The heterogeneous catalysts reported herein consist of active mixed-metal oxides, in the form of perovskites as catalysts, and as catalytic supports for Pd NPs. The activity of pure perovskites when applied as catalysts in the hydrogenation of cinnamaldehyde is 3 factors lower compared with Pd NPs immobilized on them. However, considering the fact that perovskites achieved percentage conversions between 18 and 25% in a short period of time makes them perfect candidates to replace platinum group metals in the future. In addition to being earmarked as the future of catalysis, perovskites induced a synergistic effect on the conversion of the substrate compared to when Pd NPs are immobilized on the silica support. Furthermore, these catalysts are 100% selective to hydrocinnamaldehyde and stable for up to five catalytic cycles. With regard to reusability of the catalysts, Pd/LaFeO₃ was used as a benchmark catalyst and revealed the need for surface restructuring of the catalyst for optimum activity.

Mesoporous gold nanospheres via thiolate-Au(i) intermediates

This manuscript reports a facile yet effective surfactant-templated synthesis methodology to grow in situ metallic gold mesoporous nanospheres for methanol electrooxidation.

Mesoporous gold (mesoAu) nanospheres support enhanced (electro)catalytic performance owing to their three-dimensional (3D) interior mesochannels that expose abundant active sites and facilitate electron/mass transfers. Although various porous Nanostructured Au has been fabricated by electrochemical reduction, alloying–dealloying and hard/soft templating methods, successful synthesis of mesoAu nanospheres with tailorable sizes and porosities remains a big challenge. Here we describe a novel surfactant-directed synthetic route to fabricate mesoAu nanospheres with 3D interconnected mesochannels by using the amphiphilic surfactant of C₂₂H₄₅N⁺(CH₃)₂–C₃H₆–SH (Cl^–) (C₂₂N–SH) as the mesopore directing agent. C₂₂N–SH can not only self-reduce trivalent Au(iii)Cl₄^– to monovalent Au(i), but also form polymeric C₂₂N–S–Au(i) intermediates via covalent bonds. These C₂₂N–S–Au(i) intermediates facilitate the self-assembly into spherical micelles and inhibit the mobility of Au precursors, enabling the crystallization nucleation and growth of the mesoAu nanospheres via in situ chemical reduction. The synthetic strategy can be further extended to tailor the sizes/porosities and surface optical properties of the mesoAu nanospheres. The mesoAu nanospheres exhibit remarkably enhanced mass/specific activity and improved stability in methanol electrooxidation, demonstrating far better performance than non-porous Au nanoparticles and previously reported Au nanocatalysts. The synthetic route differs markedly from other long-established soft-templating approaches, providing a new avenue to grow metal nanocrystals with desirable nanostructures and functions.

Fabrication of Metal Nanostructures on DNA Templates

Metal nanoarchitectures fabrication based on DNA assembly has attracted a good deal of attention. DNA nanotechnology enables precise organization of nanoscale objects with extraordinary structural programmability. The spatial addressability of DNA nanostructures and sequence-dependent recognition allow functional elements to be precisely positioned; thus, novel functional materials that are difficult to produce using conventional methods could be fabricated. This review focuses on the recent development of the fabrication strategies toward manipulating the shape and morphology of metal nanoparticles and nanoassemblies based on the rational design of DNA structures. DNA-mediated metallization, including DNA-templated conductive nanowire fabrication and sequence-selective metal deposition, etc., is briefly introduced. The modifications of metal nanoparticles (NPs) with DNA and subsequent construction of heterogeneous metal nanoarchitectures are highlighted. Importantly, DNA-assembled dynamic metal nanostructures that are responsive to different stimuli are also discussed as they allow the design of smart and dynamic materials. Meanwhile, the prospects and challenges of these shape-and morphology-controlled strategies are summarized.

Micelle-Assisted Formation of Nanoparticle Superlattices and Thermally Reversible Symmetry Transitions

Nanoparticle superlattices (NPSLs) are of great interest as materials with designed emerging properties depending on the lattice symmetry as well as composition. The symmetry transition of NPSLs depending on environmental conditions can be an excellent ground for making new stimuli-responsive functional materials. Here, we report a spherical micelle-assisted method to form exceptionally ordered NPSLs which are inherently sensitive to environmental conditions. Upon mixing functionalized gold nanoparticles (AuNPs) with a nonionic surfactant spherical micellar solution, NPSLs of different symmetries such as NaZn₁₃, MgZn₂, and AlB₂-type are formed depending on the size ratio between micelles and functionalized AuNPs and composition. The NPSLs formed by the spherical micelle-assisted method show thermally reversible order-order (NaZn₁₃-AlB₂) and order-disorder (MgZn₂-isotropic) symmetry transitions, which are consistent with the Gibbs free energy calculations for binary hard-sphere model. This approach may open up new possibilities for NPSLs as stimuli-responsive functional materials.

Templated Growth of Crystalline Mesoporous Materials: From Soft/Hard Templates to Colloidal Templates

Mesoporous non-siliceous materials, in particular mesoporous transition metal oxides (m-TMOs), are of interest due to their fascinating electronic, redox, and magnetic properties for a wide range of applications in catalysis and energy storage. Control of the porosity (e.g., pore size, wall thickness, and surface area) and the crystalline degree (e.g., phase composition, crystallinity, and crystal grain size) of m-TMOs are critical for those applications. To crystallize TMOs, high temperature annealing is often needed to remove the amorphous defects and/or tune the compositions of different crystalline phases. This has brought many challenges to surfactant or block copolymer templates used in the process of evaporation-induced-self-assembly to prepare m-TMOs. In this review, we summarize the most recent achievements including the findings in our own laboratory on the use of organosilicate-containing colloids for the templated growth of mesoporous materials. We review a few key examples of preparing crystalline mesoporous oxides using different templating methods. The colloidal templating method by which mesoporous nanostructures can be stabilized up to 1,000°C is highlighted. The applications of m-TMOs and meso metal-oxide hybrids synthesized using organosilicate-containing colloidal templates in photocatalysis and high-temperature catalysis are also discussed.

Stabilization of Colloidal Crystals Engineered with DNA

A postsynthetic method for stabilizing colloidal crystals programmed from DNA is developed. The method relies on Ag⁺ ions to stabilize the particle-connecting DNA duplexes within the crystal lattice, essentially transforming them from loosely bound structures to ones with very strong interparticle links. Such crystals do not dissociate as a function of temperature like normal DNA or DNA-interconnected superlattices, and they can be moved from water to organic media or the solid state, and stay intact. The Ag⁺ -stabilization of the DNA bonds is accompanied by a nondestructive ≈25% contraction of the lattice, and both the stabilization and contraction are reversible with the chemical extraction of the Ag⁺ ions, by AgCl precipitation with NaCl. This synthetic tool is important, since it allows scientists and engineers to study such crystals in environments that are incompatible with structures made by conventional DNA programmable methods and without the influence of a matrix such as silica.

Peptide-Programmable Nanoparticle Superstructures with Tailored Electrocatalytic Activity

Biomaterials derived via programmable supramolecular protein assembly provide a viable means of constructing precisely defined structures. Here, we present programmed superstructures of AuPt nanoparticles (NPs) on carbon nanotubes (CNTs) that exhibit distinct electrocatalytic activities with respect to the nanoparticle positions via rationally modulated peptide-mediated assembly. De novo designed peptides assemble into six-helix bundles along the CNT axis to form a suprahelical structure. Surface cysteine residues of the peptides create AuPt-specific nucleation site, which allow for precise positioning of NPs onto helical geometries, as confirmed by 3-D reconstruction using electron tomography. The electrocatalytic model system, i.e., AuPt for oxygen reduction, yields electrochemical response signals that reflect the controlled arrangement of NPs in the intended assemblies. Our design approach can be expanded to versatile fields to build sophisticated functional assemblies.

Synthesis and Applications of Perfunctionalized Boron Clusters

This Viewpoint describes major advances pertaining to perfunctionalized boron clusters in synthesis and their respective applications. The first portion of this work highlights key synthetic methods, allowing one to access a wide range of polyhedral boranes (B4 and B6-B12 cluster cores) that contain exhaustively functionalized vertices. The second portion of this Viewpoint showcases the historical developments in using these molecules for applications ranging from materials science to medicine. Last, we suggest potential new directions for these clusters as they apply to both synthetic methods and applications.

Crystalline protein scaffolds as a defined environment for the synthesis of bioinorganic materials

We discuss synthetic strategies and applications of highly ordered bioinorganic materials based on crystalline protein scaffolds.

DNA Grafting and Arrangement on Oxide Surfaces for Self-Assembly of Al and CuO Nanoparticles

DNA-directed assembly of nano-objects as a means to manufacture advanced nanomaterial architectures has been the subject of many studies. However, most applications have dealt with noble metals as there are fundamental difficulties to work with other materials. In this work, we propose a generic and systematic approach for functionalizing and characterizing oxide surfaces with single-stranded DNA oligonucleotides. This protocol is applied to aluminum and copper oxide nanoparticles due to their great interest for the fabrication of highly energetic heterogeneous nanocomposites. The surface densities of streptavidin and biotinylated DNA oligonucleotides are precisely quantified combining atomic absorption spectroscopy with conventional dynamic light scattering and fluorometry and maximized to provide a basis for understanding the grafting mechanism. First, the streptavidin coverage is consistently below 20% of the total surface for both nanoparticles. Second, direct and unspecific grafting of DNA single strands onto Al and CuO nanoparticles largely dominates the overall functionalization process: ∼95% and 90% of all grafted DNA strands are chemisorbed on the CuO and Al nanoparticle surfaces, respectively. Measurements of hybridization efficiency indicate that only ∼5 and ∼10% of single-stranded oligonucleotides grafted onto the CuO and Al surfaces are involved in the hybridization process, corresponding precisely to the streptavidin coverage, as evidenced by the occupancy of 0.9 and 1.2 oligonucleotides per protein. The hybridization efficiency of single-stranded oligonucleotides chemisorbed on CuO and Al without streptavidin coating decreases to only ∼2%, justifying the use of streptavidin despite its poor surface occupancy. Finally, the structure of directly chemisorbed DNA strands onto oxide surfaces is examined and discussed.

A coordination polymer for the site-specific integration of semiconducting sequences into DNA-based materials

Advances in bottom-up material design have been significantly progressed through DNA-based approaches. However, the routine integration of semiconducting properties, particularly long-range electrical conduction, into the basic topological motif of DNA remains challenging. Here, we demonstrate this with a coordination polymer derived from 6-thioguanosine (6-TG-H), a sulfur-containing analog of a natural nucleoside. The complexation reaction with Au(I) ions spontaneously assembles luminescent one-dimensional helical chains, characterized as {Au^I(μ-6-TG)} _n , extending many μm in length that are structurally analogous to natural DNA. Uniquely, for such a material, this gold-thiolate can be transformed into a wire-like conducting form by oxidative doping. We also show that this self-assembly reaction is compatible with a 6-TG-modified DNA duplex and provides a straightforward method by which to integrate semiconducting sequences, site-specifically, into the framework of DNA materials, transforming their properties in a fundamental and technologically useful manner.Integration of semiconducting properties into the basic topological motif of DNA remains challenging. Here, the authors show a coordination polymer derived from 6-thioguanosine that complexes with Au(I) ions to form a wire-like material that can also integrate semiconducting sequences into the framework of DNA materials.

Silica Mineralization of DNA-Inspired 1D and 2D Supramolecular Polymers

The preparation of hybrid materials from supramolecular polymers through the sol‐gel process is presented. Supramolecular polymers are assembled from phosphodiester‐linked pyrene oligomers and act as water‐soluble one‐ or two‐dimensional templates for silicification. The fibrillary and planar morphologies of the assemblies, as well as the excitonic interactions between the chromophores, remain unaffected by the silicification process.

Nature of peptide wrapping onto metal nanoparticle catalysts and driving forces for size control

Colloidal metal nanocrystals find many applications in catalysis, energy conversion devices, and therapeutics. However, the nature of ligand interactions and implications on shape control have remained uncertain at the atomic scale. Large differences in peptide adsorption strength and facet specificity were found on flat palladium surfaces versus surfaces of nanoparticles of 2 to 3 nm size using accurate atomistic simulations with the Interface force field. Folding of longer peptides across many facets explains the formation of near-spherical particles with local surface disorder, in contrast to the possibility of nanostructures of higher symmetry with shorter ligands. The average particle size in TEM correlates inversely with the surface coverage with a given ligand and with the strength of ligand adsorption. The role of specific amino acids and sequence mutations on the nanoparticle size and facet composition is discussed, as well as the origin of local surface disorder that leads to large differences in catalytic reactivity.

Confined Etching within 2D and 3D Colloidal Crystals for Tunable Nanostructured Templates: Local Environment Matters

We report the isotropic etching of 2D and 3D polystyrene (PS) nanosphere hcp arrays using a benchtop O₂ radio frequency plasma cleaner. Unexpectedly, this slow isotropic etching allows tuning of both particle diameter and shape. Due to a suppressed etching rate at the point of contact between the PS particles originating from their arrangement in 2D and 3D crystals, the spherical PS templates are converted into polyhedral structures with well-defined hexagonal cross sections in directions parallel and normal to the crystal c-axis. Additionally, we found that particles located at the edge (surface) of the hcp 2D (3D) crystals showed increased etch rates compared to those of the particles within the crystals. This indicates that 2D and 3D order affect how nanostructures chemically interact with their surroundings. This work also shows that the morphology of nanostructures periodically arranged in 2D and 3D supercrystals can be modified via gas-phase etching and programmed by the superlattice symmetry. To show the potential applications of this approach, we demonstrate the lithographic transfer of the PS template hexagonal cross section into Si substrates to generate Si nanowires with well-defined hexagonal cross sections using a combination of nanosphere lithography and metal-assisted chemical etching.

General Strategy for the Design of DNA Coding Sequences Applied to Nanoparticle Assembly

The DNA-directed assembly of nano-objects has been the subject of many recent studies as a means to construct advanced nanomaterial architectures. Although much experimental in silico work has been presented and discussed, there has been no in-depth consideration of the proper design of single-strand sticky termination of DNA sequences, noted as ssST, which is important in avoiding self-folding within one DNA strand, unwanted strand-to-strand interaction, and mismatching. In this work, a new comprehensive and computationally efficient optimization algorithm is presented for the construction of all possible DNA sequences that specifically prevents these issues. This optimization procedure is also effective when a spacer section is used, typically repeated sequences of thymine or adenine placed between the ssST and the nano-object, to address the most conventional experimental protocols. We systematically discuss the fundamental statistics of DNA sequences considering complementarities limited to two (or three) adjacent pairs to avoid self-folding and hybridization of identical strands due to unwanted complements and mismatching. The optimized DNA sequences can reach maximum lengths of 9 to 34 bases depending on the level of applied constraints. The thermodynamic properties of the allowed sequences are used to develop a ranking for each design. For instance, we show that the maximum melting temperature saturates with 14 bases under typical solvation and concentration conditions. Thus, DNA ssST with optimized sequences are developed for segments ranging from 4 to 40 bases, providing a very useful guide for all technological protocols. An experimental test is presented and discussed using the aggregation of Al and CuO nanoparticles and is shown to validate and illustrate the importance of the proposed DNA coding sequence optimization.

Ordering Gold Nanoparticles with DNA Origami Nanoflowers

Nanostructured materials, including plasmonic metamaterials made from gold and silver nanoparticles, provide access to new materials properties. The assembly of nanoparticles into extended arrays can be controlled through surface functionalization and the use of increasingly sophisticated linkers. We present a versatile way to control the bonding symmetry of gold nanoparticles by wrapping them in flower-shaped DNA origami structures. These "nanoflowers" assemble into two-dimensonal gold nanoparticle lattices with symmetries that can be controlled through auxiliary DNA linker strands. Nanoflower lattices are true composites: interactions between the gold nanoparticles are mediated entirely by DNA, and the DNA origami will fold into its designed form only in the presence of the gold nanoparticles.

Facile synthesis of complex shaped Pt-Cu alloy architectures

Several intricate Pt-Cu alloy architectures have been synthesized including hexapod backbones with stretchers and caved octahedron like hexapods, as well as some other intermediates with complex structures. The mechanistic study indicates that the shape is realized via a competitive effect between etching and growth induced by different chemicals.