DNA-Mediated Morphological Control of Pd–Au Bimetallic Nanoparticles

Customized Self-Assembled Gold Nanoparticle-DNA Origami Composite Templates for Shape-Directed Growth of Plasmonic Structures

The metal plasmonic nanostructure has the optical property of plasmon resonance, which holds great potential for development in nanophotonics, bioelectronics, and molecular detection. However, developing a general and straightforward method to prepare metal plasmonic nanostructures with a controllable size and morphology still poses a challenge. Herein, we proposed a synthesis strategy that utilized a customizable self-assembly template for shape-directed growth of metal structures. We employed gold nanoparticles (AuNPs) as connectors and DNA nanotubes as branches, customizing gold nanoparticle-DNA origami composite nanostructures with different branches by adjusting the assembly ratio between the connectors and branches. Subsequently, various morphologies of plasmonic metal nanostructures were created using this template shape guided strategy, which exhibited enhancement of surface-enhanced Raman scattering (SERS) signals. This strategy provides a new approach for synthesizing metallic nanostructures with multiple morphologies and opens up another possibility for the development of customizable metallic plasmonic structures with broader applications.

Colloidal SERS measurement of enrofloxacin with petaloid nanostructure clusters formed by terminal deoxynucleotidyl transferase catalyzed cytosine-constituted ssDNA

We developed petal-like plasmonic nanoparticle (PLNP) clusters-based colloidal SERS method for enrofloxacin (EnFX) detection. PLNPs were synthesized by the regulation of single-stranded DNA composed of homo-cytosine deoxynucleotides (hC) catalyzed by terminal deoxynucleotidyl transferase. SERS hot spots were created via the agglomeration process of PLNPs by adding an inorganic salt potassium iodide solution, in which EnFX molecules were attached to the negatively charged PLNPs surface by electrostatic interactions. This approach enabled direct in situ detection of antibiotic residues, achieving a limit of detection (LOD) of 1.15 μg/kg for EnFX. The spiked recoveries of the SERS method were approximately 92.7% to 107.2% and the RSDs ranged from 1.05% to 7.8%, indicating that the method can be applied to actual sample detection. This colloidal SERS measurement platform would be very promising in various applications, especially in real-time and on-site food safety screening owing to its rapidness, simplicity, and sensitivity.

Recent Advances of Tumor Microenvironment-Responsive Nanomedicines-Energized Combined Phototherapy of Cancers

Photodynamic therapy (PDT) has emerged as a powerful tumor treatment tool due to its advantages including minimal invasiveness, high selectivity and thus dampened side effects. On the other side, the efficacy of PDT is severely frustrated by the limited oxygen level in tumors, thus promoting its combination with other therapies, particularly photothermal therapy (PTT) for bolstered tumor treatment outcomes. Meanwhile, nanomedicines that could respond to various stimuli in the tumor microenvironment (TME) provide tremendous benefits for combined phototherapy with efficient hypoxia relief, tailorable drug release and activation, improved cellular uptake and intratumoral penetration of nanocarriers, etc. In this review, we will introduce the merits of combining PTT with PDT, summarize the recent important progress of combined phototherapies and their combinations with the dominant tumor treatment regimen, chemotherapy based on smart nanomedicines sensitive to various TME stimuli with a focus on their sophisticated designs, and discuss the challenges and future developments of nanomedicine-mediated combined phototherapies.

DNA-Encoded Bidirectional Regulation of the Peroxidase Activity of Pt Nanozymes for Bioanalysis

Rational regulation of nanozyme activity can promote biochemical sensing by expanding sensing strategies and improving sensing performance, but the design of effective regulatory strategies remains a challenge. Herein, a rapid DNA-encoded strategy was developed for the efficient regulation of Pt nanozyme activity. Interestingly, we found that the catalytic activity of Pt nanozymes was sequence-dependent, and its peroxidase activity was significantly enhanced only in the presence of T-rich sequences. Thus, different DNA sequences realized bidirectional regulation of Pt nanozyme peroxidase activity. Furthermore, the DNA-encoded strategy can effectively enhance the stability of Pt nanozymes at high temperatures, freezing, and long-term storage. Meanwhile, a series of studies demonstrated that the presence of DNA influenced the reduction degree of H₂PtCl₆ precursors, which in turn affected the peroxidase activity of Pt nanozymes. As a proof of application, the sensor array based on the Pt nanozyme system showed superior performance in the accurate discrimination of antioxidants. This study obtained the regulation rules of DNA on Pt nanozymes, which provided theoretical guidance for the development of new sensing platforms and new ideas for the regulation of other nanozyme activities.

Metal Nanoparticles as Novel Agents for Lung Cancer Diagnosis and Therapy

Lung cancer is one of the most common malignancies worldwide and contributes to most cancer-related morbidity and mortality cases. During the past decades, the rapid development of nanotechnology has provided opportunities and challenges for lung cancer diagnosis and therapeutics. As one of the most extensively studied nanostructures, metal nanoparticles obtain higher satisfaction in biomedical applications associated with lung cancer. Metal nanoparticles have enhanced almost all major imaging strategies and proved great potential as sensor for detecting cancer-specific biomarkers. Moreover, metal nanoparticles could also improve therapeutic efficiency via better drug delivery, improved radiotherapy, enhanced gene silencing, and facilitated photo-driven treatment. Herein, the recently advanced metal nanoparticles applied in lung cancer therapy and diagnosis are summarized. Future perspective on the direction of metal-based nanomedicine is also discussed. Stimulating more research interests to promote the development of metal nanoparticles in lung cancer is devoted.

Poly-thymine DNA templated MnO2 biomineralization as a high-affinity anchoring enabling tumor targeting delivery

Manganese oxide nanomaterials (MONs) are emerging as a type of highly promising nanomaterials for diseases diagnosis, and surface modification is the basis for colloidal stability and targeting delivery of the nanomaterials. Here, we report the in-situ functionalization of MnO₂ with DNA through a biomineralization process. Using adsorption-oxidation method, DNA templated Mn²⁺ precursor to biomineralize into nano-cubic seed, followed by the growth of MnO₂ to form cube/nanosheet hybrid nanostructure. Among four types of DNA homopolymers, poly-thymine (poly-T) was found to stably attach on MnO₂ surface to resist various biological displacements (phosphate, serum, and complementary DNA). Capitalized on this finding, a di-block DNA was rationally designed, in which the poly-T block stably anchored on MnO₂ surface, while the AS1411 aptamer block was not only an active ligand for tumor targeting delivery, but also a carrier for photosensitizer (Ce6) loading. Upon targeting delivery into tumor cells, the MnO₂ acted as catalase-mimic nanozyme for oxygenation to sensitize photodynamic therapy, and the released Mn²⁺ triggered chemodynamic therapy via Fenton-like reaction, achieving synergistic anti-tumor effect with full biocompatibility. This work provides a simple yet robust strategy to functionalize metal oxides nanomaterials for biological applications via DNA-templated biomineralization.

DNA-Programmed Tuning of the Growth and Enzyme-Like Activity of a Bimetallic Nanozyme and Its Biosensing Applications

Nanozymes, which combine the merits of both nanomaterials and natural enzymes, have aroused tremendous attention as new representatives of artificial enzyme mimics. However, it still remains to be a great challenge to rationally engineer the morphologies and surface properties of nanostructures that lead to the desired enzyme-like activities. Here, we report a DNA-programming seed-growth strategy to mediate the growth of platinum nanoparticles (PtNPs) on gold bipyramids (AuBPs) for the synthesis of a bimetallic nanozyme. We find that the preparation of a bimetallic nanozyme is in a sequence-dependent manner, and the encoding of a polyT sequence allows the successful formation of bimetallic nanohybrids with greatly enhanced peroxidase-like activity. We further observe that the morphologies and optical properties of T15-mediated Au/Pt nanostructures (Au/T15/Pt) change over the reaction time, and the nanozymatic activity can be tuned by controlling the experimental conditions. As a concept application, Au/T15/Pt nanozymes are used to establish a simple, sensitive, and selective colorimetric assay for the determination of ascorbic acid (AA), alkaline phosphatase (ALP), and the inhibitor sodium vanadate (Na₃VO₄), demonstrating excellent analytical performance. This work provides a new avenue for the rational design of bimetallic nanozymes for biosensing applications.

Identifying and Differentiating Topological G-Quadruplex Structures with DNA-Encoded Plasmonic Gold Nanoparticles

DNA G-quadruplexes (G4s) have been identified as critical elements in modulating genomic functions and many other biological processes. Their functions are highly dependent on the primary nucleotides and secondary folding structures. Therefore, to understand their functions, methods to identify and differentiate structures of G4 with speed and accuracy are required but limited. In this report, we have applied a synthetic G4 DNA-encoded nanoparticle approach to identify and differentiate G4 DNA molecules with different topologies and nucleotide residues. We found that the resulting plasmonic properties of the gold nanoparticles, monitored by UV/Vis spectroscopy, are quite sensitive to different G4 structures, including stacking layers, loop sequences, capping bases on G4s, and topological structures. Through these systematic investigations, we demonstrate that this G4-encoded gold nanoparticle approach can be used to profile the G4 structures and distinguish G4s from human telomeres. Such a method may have wide applications in G4 research.

Preparation, applications, and challenges of functional DNA nanomaterials

As a carrier of genetic information, DNA is a versatile module for fabricating nanostructures and nanodevices. Functional molecules could be integrated into DNA by precise base complementary pairing, greatly expanding the functions of DNA nanomaterials. These functions endow DNA nanomaterials with great potential in the application of biomedical field. In recent years, functional DNA nanomaterials have been rapidly investigated and perfected. There have been reviews that classified DNA nanomaterials from the perspective of functions, while this review primarily focuses on the preparation methods of functional DNA nanomaterials. This review comprehensively introduces the preparation methods of DNA nanomaterials with functions such as molecular recognition, nanozyme catalysis, drug delivery, and biomedical material templates. Then, the latest application progress of functional DNA nanomaterials is systematically reviewed. Finally, current challenges and future prospects for functional DNA nanomaterials are discussed.

Adenine oligomer directed synthesis of chiral gold nanoparticles

Precise control of morphology and optical response of 3-dimensional chiral nanoparticles remain as a significant challenge. This work demonstrates chiral gold nanoparticle synthesis using single-stranded oligonucleotide as a chiral shape modifier. The homo-oligonucleotide composed of Adenine nucleobase specifically show a distinct chirality development with a dissymmetric factor up to g ~ 0.04 at visible wavelength, whereas other nucleobases show no development of chirality. The synthesized nanoparticle shows a counter-clockwise rotation of generated chiral arms with approximately 200 nm edge length. The molecular dynamics and density functional theory simulations reveal that Adenine shows the highest enantioselective interaction with Au(321)R/S facet in terms of binding orientation and affinity. This is attributed to the formation of sequence-specific intra-strand hydrogen bonding between nucleobases. We also found that different sequence programming of Adenine-and Cytosine-based oligomers result in chiral gold nanoparticles' morphological and optical change. These results extend our understanding of the biomolecule-directed synthesis of chiral gold nanoparticles to sequence programmable deoxyribonucleic acid and provides a foundation for programmable synthesis of chiral gold nanoparticles.

Methionine-Controlled Impediment of Secondary Nucleation Leading to Nonclassical Growth within Self-Assembled De Novo Gold Nanoparticles

The conventional key steps for seed-mediated growth of noble metal nanostructures involve classical and nonclassical nucleation. Furthermore, the surface of the seed catalytically enhances the secondary nucleation involving Au⁺ to Au⁰ reduction, thus providing in-plane growth of the seed. In contrast to this well-established growth mechanism, herein, we report the unique case of a methionine (Met)-controlled seed-mediated growth reaction, which rather proceeds via impeding secondary nucleation in the presence of citrate-stabilized gold nanoparticles (AuNPs). The interaction between the freshly generated Au⁺ and the thioether group of Met in the medium restricts the secondary nucleation process of further seed-catalyzed Au⁺ reduction to Au⁰. This incomplete conversion of Au⁺, as confirmed by X-ray photoelectron spectroscopy, results in a significant enhancement of the zeta (ζ) potential even at low Met concentrations. Nucleation of in situ generated small-sized particles (nAuNPs) takes place on the parent seed surface followed by their segregation from the seed. The self-assembly process of these nAuNPs arises from the aurophilic interaction among the Au⁺. Furthermore, the time-dependent growth of smaller particles to larger-sized particles through assembly and merging within the same self-assembly validates the nonclassical growth. This strategy has been successfully extended toward the seed-mediated growth reaction of AuNPs in the presence of three bio-inspired decameric peptides having varying numbers of Met residues. The study confirms the nucleation strategy even in the presence of a single Met residue in the peptide and also the self-assembly of nucleated particles with increasing Met residues within the peptide.

Kinetic Reconstruction of DNA-Programed Plasmonic Metal Nanostructures with Predictable Shapes and Optical Properties

It is desirable to rationally engineer plasmonic metal nanostructures with sets of structural parameters that lead to specific functions. However, it is still challenging to predict the nanostructured outcome of a synthesis reaction by design because not only the exact kinetic path for the structural evolution is very complicated but also the relationships among various functional and structural parameters are often tangled. It is necessary to deconvolute the structure-function relationships and understand the co-evolution of structural and functional parameters as the nanostructures grow. DNA is a programable biomolecular capping ligand that was shown to be capable of precisely controlling the evolution of metal nanostructures. In this study, we systematically analyzed the evolution of two structural parameters and several functional parameters in the growth of Au-Ag nanostructures controlled by two DNA sequences. We deconvoluted the contributions from the two structural parameters in affecting the plasmonic properties in different kinetic and geometric domains. We further designed new nanostructures by exchanging DNA sequences in the growth environment, which also changed their evolution pathways. The resulting structural and functional parameters could be predictively tuned by the timing of the exchange. This study demonstrates the powerful toolbox provided by programable biomolecules in producing novel nanostructures in a predictable manner. It also shows that by understanding the kinetic evolution of the structural parameters and their relationships with the function parameters, it is possible to design the precise combinations of structural and functional parameters in the nanostructured products.

DNA Nanotechnology-Enabled Fabrication of Metal Nanomorphology

In recent decades, DNA nanotechnology has grown into a highly innovative and widely established field. DNA nanostructures have extraordinary structural programmability and can accurately organize nanoscale materials, especially in guiding the synthesis of metal nanomaterials, which have unique advantages in controlling the growth morphology of metal nanomaterials. This review started with the evolution in DNA nanotechnology and the types of DNA nanostructures. Next, a DNA-based nanofabrication technology, DNA metallization, was introduced. In this section, we systematically summarized the DNA-oriented synthesis of metal nanostructures with different morphologies and structures. Furthermore, the applications of metal nanostructures constructed from DNA templates in various fields including electronics, catalysis, sensing, and bioimaging were figured out. Finally, the development prospects and challenges of metal nanostructures formed under the morphology control by DNA nanotechnology were discussed.

Biomimetic recognition strategy for efficient capture and release of circulating tumor cells

Efficient capture and release of circulating tumor cells play an important role in cancer diagnosis, but the limited affinity of monovalent adhesion molecules in existing capture technologies leads to low capture efficiency, and the captured cells are difficult to be separated. Inspired by the phenomenon that the long tentacles of jellyfish contain multiple adhesion domains and can effectively capture moving food, we have constructed a biomimetic recognition strategy to capture and release tumor cells. In details, gold-coated magnetic nanomaterials (Au@Fe₃O₄ NPs) were first prepared and characterized by scanning electron microscopy, UV-vis absorption spectra, and Zeta potential. Then, the DNA primers modified on Au@Fe₃O₄ nanoparticles can be extended to form many radialized DNA products by rolling circle amplification. These long DNA products resemble jellyfish tentacles and contain multivalent aptamers that can be extended into three dimensions to increase the accessibility of target cells, resulting in efficient, simple, rapid, and specific cells capture. The capture efficiencies are no less than 92% in PBS buffer and 77% in blood. Subsequently, DNase I was selected to degrade biomimetic tentacles to release the captured tumor cells with high viability. This release strategy can not only improve cell viability, but also reduce a tedious release process and unnecessary costs. We believe that the proposed method can be expanded for the capture and release of various tumor cells and will inspire the development of circulating tumor cells analysis. A biomimetic recognition strategy for capture and release of circulating tumor cells has been developed. This method modified specific P1 DNA primers on Au@Fe₃O₄ NPs to form many radialized DNA products by rolling circle amplification. These products can efficiently capture CTCs since it contains multiple aptamers with a multivalent binding capacity. This make it a promising tool to capture and release of other tumor cells, and will inspire the development of CTC analysis.

In vitro and in vivo osteogenesis up-regulated by two-dimensional nanosheets through a macrophage-mediated pathway

Two-dimensional (2D) nanomaterials are attracting more and more interest in regenerative medicine due to their unique properties; however 2D biomimetic calcium mineral has not yet been developed and demonstrated application for bone tissue engineering. Here we described a novel calcium phosphate material with a 2D nanostructure that was synthesized using collagen and sodium alginate as the template. In vitro performance of the nanocrystalline material was evaluated, and we found that 2D CaP nanoparticles (NPs) enhanced the in vitro osteogenic differentiation of rat mesenchymal stem cells (rMSCs) through a macrophage-mediated signal pathway, when co-cultured with RAW 264.7 cells, rather than direct NP/stem cell interaction. A 2D topology structured surface was constructed by encapsulating the CaP nanomaterials in a gelatin hydrogel, which was demonstrated to be able to mediate in vivo ossification through a macrophage polarization related pathway in a femur defect rat model, and allowed the optimal therapeutic outcome compared to normal CaP counterparts. Our current work may have enlightened a new mechanism regarding NP-induced stem cell differentiation through immunoregulation, and the 2D CaP encapsulated hydrogel scaffold may serve as a potential alternative to autograft bone for orthopedic applications.

DNA-encoded bimetallic Au-Pt dumbbell nanozyme for high-performance detection and eradication of Escherichia coli O157:H7

Infectious Escherichia coli O157:H7 threatens the health of millions people each year. Thus, it is important to establish a simple and sensitive method for bacterial detection and eradication. Herein, a DNA-programming strategy is explored to synthesize anisotropic dumbbell-like Au-Pt nanoparticles with excellent catalytic and anti-bacterial activities, which were applied in the simultaneous detection and eradication of pathogenic bacteria. The DNA sequence-dependent growth of bimetallic nanoparticles is firstly studied and polyT20 has the tendency to form dumbbell-like Au-Pt bimetallic structures based on gold nanorods seeds. PolyA20 and polyC20 can also form similar structures but only at much lower DNA concentrations, which can be explained by their much higher affinity to the metal surfaces than T20. The as-prepared nanoparticles exhibit high nanozyme catalytic activity resulting from the synergistic effect of Au and Pt. Under light irradiation, the Au-Pt nanoparticles show high photothermal conversion efficiency and enhanced catalytic activity, which can be applied for the eradication and detection of E. coli O157:H7 with a robust efficacy (95%) in 5 min and provides excellent linear detection (10-10⁷ CFU/mL), with a detection limit of 2 CFU/mL. This study offered new insights into DNA-directed synthesis of nanomaterials with excellent biosensing and antibiotic applications.

Bifunctional Diblock DNA-Mediated Synthesis of Nanoflower-Shaped Photothermal Nanozymes for a Highly Sensitive Colorimetric Assay of Cancer Cells

The activity of a nanozyme is closely related to its surface area-to-volume ratio and the surrounding temperature. To acquire highly active nanozymes, one-pot metallization-like synthesis of novel nanoflower-shaped photothermal nanostructures was conducted using polyadenine-containing diblock DNA as the scaffold. The nanoflower-shaped structures with a high surface area-to-volume ratio and photothermal performance exhibited excellent peroxidase-mimicking activity, and the biorecognition capability was retained by the capping agent of diblock DNA. The functionalized nanostructures were used for a proof-of-concept colorimetric assay of cancer cells in vitro. Upon incorporation of 808 nm laser irradiation, high sensitivity and selectivity for the cancer cell assay were achieved with the lowest detection level of 10 cells/mL. Relative to spherical gold nanostructures, the nanoflower-shaped photothermal nanozyme exhibited higher assay sensitivity, paving the way for the construction of nanozyme-based colorimetric sensors for point-of-care testing.

One-Step Synthesis of Single-Stranded DNA-Bridged Iron Oxide Supraparticles as MRI Contrast Agents

Despite progress on DNA-assembled nanoparticle (NP) superstructures, their complicated synthesis procedures hamper their potential biomedical applications. Here, we present an exceptionally simple strategy for the synthesis of single-stranded DNA (ssDNA) assembled Fe₃O₄ supraparticles (DFe-SPs) as magnetic resonance contrast agents. Unlike traditional approaches that assemble DNA-conjugated NPs via Watson-Crick hybridization, our DFe-SPs are formed with a high yield through one-step synthesis and assembly of ultrasmall Fe₃O₄ NPs via ssDNA-metal coordination bridges. We demonstrate that the DFe-SPs can efficiently accumulate into tumors for sensitive MR imaging. By virtue of reversible DNA-metal coordination bridges, the DFe-SPs could be disassembled into isolated small NPs in vivo, facilitating their elimination from the body. This work opens a new avenue for the ssDNA-mediated synthesis of superstructures, which expands the repertoire of DNA-directed NP assembly for biomedical applications.

Controllable Synthesis of Bimetallic Nanostructures Using Biogenic Reagents: A Green Perspective

Bimetallic nanostructures are emerging as a significant class of metal nanomaterials due to their exceptional properties that are useful in various areas of science and technology. When used for catalysis and sensing applications, bimetallic nanostructures have been noted to exhibit better performance relative to their monometallic counterparts owing to synergistic effects. Furthermore, their dual metal composition and configuration can be modulated to achieve optimal activity for the desired functions. However, as with other nanostructured metals, bimetallic nanostructures are usually prepared through wet chemical routes that involve the use of harsh reducing agents and hazardous stabilizing agents. In response to intensifying concerns over the toxicity of chemicals used in nanomaterial synthesis, the scientific community has increasingly turned its attention toward environmentally and biologically compatible reagents that can enable green and sustainable nanofabrication processes. This article aims to provide an evaluation of the green synthetic methods of constructing bimetallic nanostructures, with emphasis on the use of biogenic resources (e.g., plant extracts, DNA, proteins) as safe and practical reagents. Special attention is devoted to biogenic synthetic protocols that demonstrate controllable nanoscale features, such as size, composition, morphology, and configuration. The potential use of these biogenically prepared bimetallic nanostructures as catalysts and sensors is also discussed. It is hoped that this article will serve as a valuable reference on bimetallic nanostructures and will help fuel new ideas for the development of more eco-friendly strategies for the controllable synthesis of various types of nanostructured bimetallic systems.

Functional Nucleic Acid Nanomaterials: Development, Properties, and Applications

Functional nucleic acid (FNA) nanotechnology is an interdisciplinary field between nucleic acid biochemistry and nanotechnology that focuses on the study of interactions between FNAs and nanomaterials and explores the particular advantages and applications of FNA nanomaterials. With the goal of building the next-generation biomaterials that combine the advantages of FNAs and nanomaterials, the interactions between FNAs and nanomaterials as well as FNA self-assembly technologies have established themselves as hot research areas, where the target recognition, response, and self-assembly ability, combined with the plasmon properties, stability, stimuli-response, and delivery potential of various nanomaterials can give rise to a variety of novel fascinating applications. As research on the structural and functional group features of FNAs and nanomaterials rapidly develops, many laboratories have reported numerous methods to construct FNA nanomaterials. In this Review, we first introduce some widely used FNAs and nanomaterials along with their classification, structure, and application features. Then we discuss the most successful methods employing FNAs and nanomaterials as elements for creating advanced FNA nanomaterials. Finally, we review the extensive applications of FNA nanomaterials in bioimaging, biosensing, biomedicine, and other important fields, with their own advantages and drawbacks, and provide our perspective about the issues and developing trends in FNA nanotechnology.

A brief note on the potential of homo-oligo-dsDNA and hetero-oligo-dsDNA based on their binder-free electrochemical characteristics on gold electrode

In this fundamental research, we found that homo-oligo based dsDNA holds potential electrochemical characteristics in comparison to hetero-oligo based dsDNA which can be exploited in voltammetric and impedimetric biosensors. We prepared a homo-oligo based dsDNA from 20 deoxyribonucleotides of adenine, guanine, cytosine, and thymine (A20, G20, C20, and T20 respectively) and a hetero-oligo based dsDNA from two partially complementary oligos (5'-TTT TTT CAT CTA TCA ACA TCA GTC TGA TAA GCT ATA GAA GC-3' and 5'-TTT TTT ATA GCT TTG ATA GA-3'. Electrochemical impedance spectroscopy in 1 mM 0.1 M K₃[Fe(CN)₆]/KCl showed that Au working electrode modified with hetero-oligo based dsDNA (Au/hetero-oligo-dsDNA) was more resistive toward charge transfer of Fe(CN)₆^3-/4- compared to Au working electrode modified with homo-oligo based dsDNA (Au/homo-oligo-dsDNA). Additionally, cyclic voltammetry and linear sweep voltammetry showed that Au/homo-oligo-dsDNA produced quantifiable anodic and cathodic peak currents which were not observed for Au/hetero-oligo-dsDNA. Nyquist and Bode plots derived from electrochemical impedance spectroscopy on three different electroactive areas (0.0705, 0.0747 and 0.0837 cm²) of Au working electrode showed no significant change in the capacitive behavior of Au/homo-oligo-dsDNA and Au/hetero-oligo-dsDNA in a linear range of frequency (10-100 Hz).

Cl−-Induced selective fabrication of 3D AgCl microcrystals by a one-pot synthesis method

Cl⁻ induces the shape evolution of AgCl crystals with different morphologies.

Recent Advances in the Synthesis of Intra-Nanogap Au Plasmonic Nanostructures for Bioanalytical Applications

Plasmonic nanogap-enhanced Raman scattering has attracted considerable attention in the fields of Raman-based bioanalytical applications and materials science. Various strategies have been proposed to prepare nanostructures with an inter- or intra-nanogap for fundamental study models or applications. This report focuses on recent advances in synthetic methods to fabricate intra-nanogap structures with diverse dimensions, with detailed focus on the theory and bioanalytical applications. Synthetic strategies ranging from the use of a silica layer to small molecules, the use of polymers and galvanic replacement, are extensively investigated. Furthermore, various core structures, such as spherical, rod-, and cube-shaped, are widely studied, and greatly expand the diversity of plasmonic nanostructures with an intra-nanogap. Theoretical calculations, ranging from the first plasmonic hybridization model that is applied to a concentric Au-SiO2 -Au nanosphere to the modern quantum corrected model, have evolved to accurately describe the plasmonic resonance property in concentric core-shell nanostructures with a subnanometer nanogap. The greatly enhanced and uniform Raman responses from the localized Raman reporter in the built-in nanogap have made it possible to achieve promising probes with an extraordinary high sensitivity in various formats, such as biomolecule detection, high-resolution cell imaging, and an in vivo imaging application.

Synthesis and applications of anisotropic nanoparticles with precisely defined dimensions

Shape and size play powerful roles in determining the properties of a material; controlling these aspects with precision is therefore an important, fundamental goal of the chemical sciences. In particular, the introduction of shape anisotropy at the nanoscale has emerged as a potent way to access new properties and functionality, enabling the exploration of complex nanomaterials across a range of applications. Recent advances in DNA and protein nanotechnology, inorganic crystallization techniques, and precision polymer self-assembly are now enabling unprecedented control over the synthesis of anisotropic nanoparticles with a variety of shapes, encompassing one-dimensional rods, dumbbells and wires, two-dimensional and three-dimensional platelets, rings, polyhedra, stars, and more. This has, in turn, enabled much progress to be made in our understanding of how anisotropy and particle dimensions can be tuned to produce materials with unique and optimized properties. In this Review, we bring these recent developments together to critically appraise the different methods for the bottom-up synthesis of anisotropic nanoparticles enabling exquisite control over morphology and dimensions. We highlight the unique properties of these materials in arenas as diverse as electron transport and biological processing, illustrating how they can be leveraged to produce devices and materials with otherwise inaccessible functionality. By making size and shape our focus, we aim to identify potential synergies between different disciplines and produce a road map for future research in this crucial area.

Quantitative Analysis of DNA-Mediated Formation of Metal Nanocrystals

The predictive synthesis of metal nanocrystals with desired structures relies on the precise control of the crystal formation process. Using a capping ligand is an effective method to affect the reduction of metal ions and the formation of nanocrystals. However, predictively synthesizing nanostructures has been difficult to achieve using conventional capping ligands. DNA, as a class of the promising biomolecular capping ligands, has been used to generate sequence-specific morphologies in various metal nanocrystals. However, mechanistic insight into the DNA-mediated nanocrystal formation remains elusive due to the lack of quantitative experimental evidence. Herein, we quantitatively analyzed the precise control of DNA over Ag+ reduction and the structures of resulting Au-Ag core-shell nanocrystals. We derived the equilibrium binding constants between DNA and Ag+, the kinetic rate constants of sequence-specific Ag+ reduction pathways, and the percentage of active surface sites remaining on the nanocrystals after DNA passivation. These three synergistic factors influence the nucleation and growth process both thermodynamically and kinetically, which contributed to the morphological evolution of Au-Ag nanocrystals synthesized with different DNA sequences. This study demonstrates the potential of using functional DNA sequences as a versatile and tunable capping ligand system for the predictable synthesis of metal nanostructures.

Good's buffers have various affinities to gold nanoparticles regulating fluorescent and colorimetric DNA sensing

Citrate-capped gold nanoparticles (AuNPs) are highly important for sensing, drug delivery, and materials design. Many of their reactions take place in various buffers such as phosphate and Good's buffers. The effect of buffer on the surface properties of AuNPs is critical, yet this topic has not been systematically explored. Herein, we used halides such as fluoride, chloride, and bromide as probes to measure the relative adsorption strength of six common buffers. Among them, HEPES had the highest adsorption affinity, while MES, citrate and phosphate were weakly adsorbed with an overall ranking of HEPES > PIPES > MOPS > MES > citrate, phosphate. The adsorption strength was reflected from the inhibited adsorption of DNA and from the displacement of pre-adsorbed DNA. This conclusion is also supported by surface enhanced Raman spectroscopy. Furthermore, some buffer molecules did not get adsorbed instantaneously, and the MOPS buffer took up to 1 h to reach equilibrium. Finally, a classic label-free AuNP-based colorimetric sensor was tested. Its sensitivity increased by 15.7-fold when performed in a MES buffer compared to a HEPES buffer. This study has articulated the importance of buffer for AuNP-based studies and how it can improve sensors and yield more reproducible experimental systems.

Aside from maintaining pH, Good's buffers can be adsorbed on gold nanoparticles with different affinities, affecting the stability and its fluorescent and colorimetric sensing performance.

Capping Ligand Size-Dependent LSPR Property Based on DNA Nanostructure-Mediated Morphological Evolution of Gold Nanorods for Ultrasensitive Visualization of Target DNA

Systematically tuning the structures and properties of noble-metal nanoparticles through biomolecule-mediated overgrowth is of significant importance for their applications in biosensing and imaging. Herein thiolated biomolecules with different concentrations and sizes (molecular weight and spatial structure) were used as a class of capping ligands to control the longitudinal surface plasmon resonance (LSPR) property of gold nanorods (GNRs). The LSPR peaks were red-shifted by increasing the capping agent concentration. The size effect could be divided to two aspects: (1) When the ligands are small molecules, the LSPR peak is blue-shifted as the size of the capping ligand increases. (2) When the ligands are macromolecular proteins, the LSPR property is similar to that of the overgrown nanoparticle (Au@gap@GNR) without thiolated biomolecules as capping agents. Interestingly, thiol-free and nonhomooligomeric DNA strands as capping agents present a similar influence in shaping the overgrowth of GNRs by varying their concentrations and sizes. In addition, the size effect of a DNA nanostructure was used to construct a Δλ_LSPR-based catalytic nucleic acid biosensor using a DNA dendritic nanostructure as a capping agent combined with LSPR signals generated from the Au@gap@GNRs with morphological evolution. More importantly, the Δλ_LSPR-based biosensor possesses three advantages in nucleic acid biosensing: (1) It is completely label- and wash-free, (2) it has an ultrahigh sensitivity and signal-to-noise ratio, and (3) it can be visualized without any instrumental aid, indicating a significant potential for ultrasensitive biosensing.

DNA-Modulated Plasmon Resonance: Methods and Optical Applications

The near-field effects in the vicinity of metallic nanoparticle surfaces, as induced by electromagnetic radiation with specific wavelength, give rise to a variety of novel optical properties and attractive applications because of surface plasmons, which are the coherent oscillations of conduction electrons on a metal surface. The interdisciplinary field of plasmonics has witnessed vigorous growth, promoting research on the modulation of plasmon resonance by constructing advanced plasmonic nanoarchitectures with controllable size, morphology, or interparticle coupling. Among diversified tools, deoxyribonucleic nucleic acid (DNA) possesses prominent superiority as a result of its designability, programmability, addressability, and ease of nanomaterial modification. In this review, we focus on the methods and optical applications of plasmon resonance modulation accomplished by DNA nanotechnology. Recent developments in the construction of DNA-mediated plasmonic nanoarchitecture and key ongoing research directions utilizing unique optical features are highlighted. Obstacles and challenges in this field are pointed out, followed by preliminary suggestions on some areas of opportunity that deserve attention.

One-step fabrication of trimetallic alloy nanozyme catalyzer for luminol-H2O2 chemiluminescence and its application for miRNA-21 detection coupled with miRNA walking machine

PtCuCo trimetallic alloys (PtCuCo-TAs) are synthesized by one-step reduction. The chemiluminescence (CL) properties of PtCuCo-TAs are studied systemically. PtCuCo-TAs show good catalyzing for luminol-H₂O₂ system. A CL platform is developed for the detection of miRNA-21 using PtCuCo-TAs as nanozyme catalyzer. In the CL detection platform, H1 (Hairpin DNA1) is immobilized onto magnetic beads (MBs) firstly. In the presence of miRNA-21, H1 is opened. H2 (Hairpin DNA2) then hybridizes with H1. Meanwhile, a "cleat" in the end of miRNA-21 with a fewer bases complementary is formed to prevent miRNA-21 dissociating from H1. This miRNA-21 hybridizes to another H1. When cpDNA-PtCuCo-TAs which consisted with cDNA (Complementary strand of probe DNA) and pDNA-PtCuCo-TAs (PtCuCo-TAs labeled with probe DNA) are added, the ssDNA region of H1 reacts with the toehold domain of probe DNA and cDNA is released resulting pDNA-PtCuCo-TAs being captured. With this process repeatedly, a lot of pDNA-PtCuCo-TAs are captured onto MBs. After separation and washing, the precipitate and H₂O₂ are put into the 96-well and luminol solution is injected. The CL signal is produced by PtCuCo-TAs catalyzing luminol-H₂O₂ system. The amount of miRNA-21 is detected with CL signal. This CL platform performs with limit of detection 0.167 fM and has good selectivity over other RNA.

Orthogonal deposition of Au on different facets of Ag cuboctahedra for the fabrication of nanoboxes with complementary surfaces

We report the fabrication of Ag-Au cuboctahedral nanoboxes enclosed by {100} and {111} facets, respectively, through the orthogonal deposition of Au on two different facets of Ag cuboctahedra. Specifically, we titrate aqueous HAuCl₄ into an aqueous mixture containing Ag cuboctahedra, ascorbic acid, and NaOH (under basic conditions), in the presence of poly(vinylpyrrolidone) (PVP) and cetyltrimethylammonium chloride (CTAC), respectively. In the case of PVP, the oxidation of Ag was initiated from the {111} facets of the cuboctahedra through the galvanic replacement reaction between Au(iii) and Ag, accompanied by the deposition of Au onto the {100} facets. Because the dissolved Ag(i) ions could react with NaOH to form Ag₂O on the {111} facets and thus terminate the galvanic reaction, the Au(iii) ions would be further reduced by the ascorbate monoanion (HAsc^-) to generate Au atoms for their continuing deposition on the {100} facets, converting Ag cuboctahedra to Ag@Au_{100} cuboctahedra. Upon the etching of Ag from the core, we obtained Ag-Au cuboctahedral nanoboxes enclosed by {100} facets. In contrast, when CTAC was present, the oxidation of Ag through a galvanic reaction could continuously proceed on {100} facets as the dissolved Ag(i) ions would react with the excessive amount of Cl^- ions derived from CTAC to produce soluble AgCl₂^- ions rather than insoluble Ag₂O. As a result, the dissolved Ag(i) and Au(iii) ions would be co-reduced by HAsc^- for the generation of Ag and Au atoms, followed by their co-deposition onto {111} facets for the generation of Ag@Au_{111} concave cuboctahedra. After the removal of Ag from the core by etching, we obtained Ag-Au_{111} cuboctahedral nanoboxes enclosed by {111} facets. Both samples of cuboctahedral nanoboxes exhibited strong optical absorption in the infrared region. Interestingly, the cuboctahedral nanoboxes enclosed by {111} facets showed significantly enhanced catalytic activity toward the reduction of 4-nitrophenol by NaBH₄ relative to their counterparts encased by {100} facets.

Pd@Au Bimetallic Nanoplates Decorated Mesoporous MnO2 for Synergistic Nucleus-Targeted NIR-II Photothermal and Hypoxia-Relieved Photodynamic Therapy

Bimetallic nanoparticles have received considerable attention owing to synergistic effect and their multifunctionality. Herein, new multifunctional Pd@Au bimetallic nanoplates decorated hollow mesoporous MnO₂ nanoplates (H-MnO₂ ) are demonstrated for achieving not only nucleus-targeted NIR-II photothermal therapy (PTT), but also tumor microenvironment (TME) hypoxia relief enhanced photodynamic therapy (PDT). The Pd@Au nanoplates present a photothermal conversion efficiency (PTCE) as high as 56.9%, superior to those PTAs activated in the NIR-II region such as Cu₉ S₅ nanoparticles (37%), Cu₃ BiS₃ nanorods (40.7%), and Au/Cu_{2- x} S nanocrystals (43.2%). They further functionalize with transactivator of transcription (TAT) moiety for cell nuclear-targeting and biodegradable hollow mesoporous MnO₂ (≈100 nm) loaded with photosensitizer Ce6 (TAT-Pd@Au/Ce6/PAH/H-MnO₂ ) to construct a hierarchical targeting nanoplatform. The as-made TAT-Pd@Au/Ce6/PAH/H-MnO₂ demonstrates good premature renal clearance escape ability and increased tumor tissue accumulation. It can be degraded in acidic TME and generate O₂ by reacting to endogenous H₂ O₂ to relieve the hypoxia for enhanced PDT, while the released small TAT-Pd@Au nanoplates can effectively enter into the nucleus to mediate PTT. As a result, a remarkable therapeutic effect is achieved owing to the synergistic PTT/PDT therapy. This hierarchical targeting, TME-responsive, cytoplasm hypoxia relief PDT, and nuclear NIR-II PTT synergistic therapy can pave a new avenue for nanomaterials-based cancer therapy.

Functional Macromolecule-Enabled Colloidal Synthesis: From Nanoparticle Engineering to Multifunctionality

The synthesis of well-defined inorganic colloidal nanostructures using functional macromolecules is an enabling technology that offers the possibility of fine-tuning the physicochemical properties of nanomaterials and has contributed to a broad range of practical applications. The utilization of functional reactive polymers and their colloidal assemblies leads to a high level of control over structural parameters of inorganic nanoparticles that are not easily accessible by conventional methods based on small-molecule ligands. Recent advances in polymerization techniques for synthetic polymers and newly exploited functions of natural biomacromolecules have opened up new avenues to monodisperse and multifunctional nanostructures consisting of integrated components with distinct chemistries but complementary properties. Here, the evolution of colloidal synthesis of inorganic nanoparticles is revisited. Then, the new developments of colloidal synthesis enabled by functional macromolecules and practical applications associated with the resulting optical, catalytic, and structural properties of colloidal nanostructures are summarized. Finally, a perspective on new and promising pathways to novel colloidal nanostructures built upon the continuous development of polymer chemistry, colloidal science, and nanochemistry is provided.

Functional DNA Molecules Enable Selective and Stimuli-Responsive Nanoparticles for Biomedical Applications

Nanoparticles (NPs) have enormous potential to improve disease diagnosis and treatment due to their intrinsic electronic, optical, magnetic, mechanical, and physiological properties. To realize their full potential for nanomedicine, NPs must be biocompatible and targetable toward specific biomolecules to ensure selective sensing, imaging, and drug delivery in complex environments such as living cells, tissues, animals, and human bodies. In this Account, we summarize our efforts to impart specific biocompatibility and biorecognition functionality to NPs by developing strategies to integrate inorganic and organic NPs with functional DNA (fDNA), including aptamers, DNAzymes, and aptazymes to create fDNA-NPs. These hybrid NPs take advantage of fDNA's ability to either bind targets or catalyze reactions in the presence of targets selectively and utilize their unique physicochemical properties including small size, low immunogenicity, and ease of synthesis and chemical modification in comparison with other molecules such as antibodies. By integrating inorganic NPs such as gold NPs, quantum dots, and iron oxide nanoparticles with fDNA, we designed stimuli-responsive fDNA-NPs that exhibit target induced assembly and disassembly of NPs, resulting in a variety of colorimetric, fluorescent, and magnetic resonance imaging (MRI)-based sensors for diagnostic of a broad range of analytes. To impart both biocompatibility and selectivity on inorganic NPs for targeted bioimaging, we have demonstrated DNA-mediated surface functionalization, shape-controlled synthesis, and coordinative assembly of such NPs as specific bioprobes. A highlight is provided on the construction of fDNA-based nanoprobes with light-activatable sensing and imaging functions, which provides precise control of recognition properties of fDNA with high spatiotemporal resolution. To explore the potential of organic NPs for biosensing applications, we have developed an enzyme-responsive fDNA-liposome as a universal sensing platform compatible with diverse biological targets as well as different detection methods including fluorescence, MRI, or temperature, making possible point-of-care diagnostics. To expand the application regime of organic NPs, we collaborated with the Zimmerman group to prepare single-chain block copolymer-based NPs and incorporated it with a variety of functions, including monovalent DNA for assembly, tunable surface chemistry for cellular imaging, and coordinative Cu(II) sites for catalyzing intracellular click reactions, demonstrating the potential of using organic NPs to create promising fDNA-NP systems with programmable functionalities. Furthermore, we survey our recent endeavor in integration of cell-specific aptamers with different NPs for targeted drug delivery, showing that introducing stimuli-responsive properties into NPs that target tumor microenvironments would enable safer and more effective therapy for cancers. Finally, current challenges and future perspectives in fDNA-mediated engineering of NPs for biomedical applications are discussed.

Bioapplications of DNA nanotechnology at the solid-liquid interface

DNA nanotechnology engineered at the solid-liquid interface has advanced our fundamental understanding of DNA hybridization kinetics and facilitated the design of improved biosensing, bioimaging and therapeutic platforms. Three research branches of DNA nanotechnology exist: (i) structural DNA nanotechnology for the construction of various nanoscale patterns; (ii) dynamic DNA nanotechnology for the operation of nanodevices; and (iii) functional DNA nanotechnology for the exploration of new DNA functions. Although the initial stages of DNA nanotechnology research began in aqueous solution, current research efforts have shifted to solid-liquid interfaces. Based on shape and component features, these interfaces can be classified as flat interfaces, nanoparticle interfaces, and soft interfaces of DNA origami and cell membranes. This review briefly discusses the development of DNA nanotechnology. We then highlight the important roles of structural DNA nanotechnology in tailoring the properties of flat interfaces and modifications of nanoparticle interfaces, and extensively review their successful bioapplications. In addition, engineering advances in DNA nanodevices at interfaces for improved biosensing both in vitro and in vivo are presented. The use of DNA nanotechnology as a tool to engineer cell membranes to reveal protein levels and cell behavior is also discussed. Finally, we present challenges and an outlook for this emerging field.

Plasmonic ELISA based on DNA-directed gold nanoparticle growth for Cronobacter detection in powdered infant formula samples

The traditional gold nanoparticle (AuNP) growth-based plasmonic ELISA (pELISA) strictly and directly controlled by reducing reagents can achieve high sensitivity, but it remains fragile toward the surrounding environment. This work developed a sandwich pELISA for Cronobacter detection in powdered infant formula samples by mediating AuNP growth through DNA. In this assay, DNA adsorbed on the surface of gold nanoseeds guided the anisotropic crystal growth with hydroxylamine as a reducing reagent, and the catalase-hydrogen peroxide (Cat-H₂O₂) system was introduced to bridge the DNA-directed AuNP growth and pELISA, as such DNA can be cleaved into fragments by the hydroxyl radical generated from oxidation of H₂O₂ through Fenton reagents. Under optimized conditions, the proposed pELISA can qualitatively detect Cronobacter species (Cronobacter muytjensii ATCC 51329) by the naked eye with a cut-off limit of 3 × 10⁵ cfu/mL. This method also revealed a good linear range (3 × 10² to 3 × 10⁷ cfu/mL) for quantitative detection of C. muytjensii ATCC 51329 with a limit of detection of 1.6 × 10² cfu/mL, which is approximately 162.5 times lower than that of horseradish peroxidase-based conventional ELISA (2.6 × 10⁴ cfu/mL). By taking advantage of highly stable DNA-directed AuNP growth, the proposed method shows a good performance in powdered infant formula samples spiked with different concentrations of C. muytjensii ATCC 51329 with average recoveries ranging from 90.79 to 119.09% and coefficient of variation ranging from 4.24 to 9.55%. These values corresponded to an acceptable accuracy and precision for the proposed method. In brief, this work shows potential for screening other analytes in food safety, clinical diagnostics, and environmental monitoring.

Stepwise Evolution of AgCl Microcrystals from Octahedron into Hexapod with Mace Pods and their Visible Light Photocatalytic Activity

In this work, we have synthesized hexapods AgCl crystals with mace pods for the first time. Diallyldimethylammonium chloride (DDA)-controlled stepwise evolution of AgCl crystals from octahedron to hexapods with mace pods are achieved by one-pot method. The intermediates have been captured which show the basic process of crystal growth. In this process, octahedra AgCl crystals firstly grow along the <100> direction and then change to grow in the <110> direction. At the same time, the size of AgCl grow from 2 μm to 20 μm. Due to the poor absorption of visible light by AgCl, sodium borohydride(NaBH4) is used to reduce AgCl hexapods with mace pods crystals. By changing the mole ratio(R) of NaBH4 to AgCl, the new structure was reduced to obtain a series of Ag@AgCl microstructures. Visible light catalysis effects of the Ag@AgCl microstructures on degradation of methyl orange (MO) were investigated. The Ag@AgCl microstructures with R = 0.02 have a high photocatalytic performance, which completely degrades MO in 40 minutes.

Discovery of and Insights into DNA "Codes" for Tunable Morphologies of Metal Nanoparticles

The discovery and elucidation of genetic codes has profoundly changed not only biology but also many fields of science and engineering. The fundamental building blocks of life comprises of four simple deoxyribonucleotides and yet their combinations serve as the carrier of genetic information that encodes for proteins that can carry out many biological functions due to their unique functionalities. Inspired by nature, the functionalities of DNA molecules have been used as a capping ligand for controlling morphology of nanomaterials, and such a control is sequence dependent, which translates into distinct physical and chemical properties of resulting nanoparticles. Herein, an overview on the use of DNA as engineered codes for controlling the morphology of metal nanoparticles, such as gold, silver, and Pd-Au bimetallic nanoparticles is provided. Fundamental insights into rules governing DNA controlled growth mechanisms are also summarized, based on understanding of the affinity of the DNA nucleobases to various metals, the effect of combination of nucleobases, functional modification of DNA, the secondary structures of DNA, and the properties of the seed employed. The resulting physical and chemical properties of these DNA encoded nanomaterials are also reviewed, while perspectives into the future directions of DNA-mediated nanoparticle synthesis are provided.

Hierarchical nanomaterials via biomolecular self-assembly and bioinspiration for energy and environmental applications

Bioinspired synthesis offers potential green strategies to build highly complex nanomaterials by utilizing the unique nanostructures, functions, and properties of biomolecules, in which the biomolecular recognition and self-assembly processes play important roles in tailoring the structures and functions of bioinspired materials. Further understanding of biomolecular self-assembly for inspiring the formation and assembly of nanoparticles would promote the design and fabrication of functional nanomaterials for various applications. In this review, we focus on recent advances in bioinspired synthesis and applications of hierarchical nanomaterials based on biomolecular self-assembly. We first discuss biomolecular self-assembly towards biological nanomaterials, in which the mechanisms and ways of biomolecular self-assembly as well as various self-assembled biomolecular nanostructures are demonstrated. Secondly, the bioinspired synthesis strategies including molecule-molecule interaction, molecule-material recognition, molecule-mediated nucleation and growth, and molecule-mediated reduction/oxidation are introduced and discussed. Meanwhile, typical examples and discussions on how biomolecular self-assembly inspires the formation of hierarchical hybrid nanomaterials are presented. Finally, the applications of bioinspired nanomaterials in biofuel cells, light-harvesting systems, batteries, supercapacitors, catalysis, water/air purification, and environmental monitoring are presented and discussed. We believe that this review will be very helpful for readers to understand the self-assembly of biomolecules and the biomimetic/bioinspired strategies for synthesizing hierarchical nanomaterials on the one hand, and on the other hand to design novel materials for extended applications in nanotechnology, materials science, analytical science, and biomedical engineering.

Direct Observation of Early Stages of Growth of Multilayered DNA-Templated Au-Pd-Au Core-Shell Nanoparticles in Liquid Phase

We report here on direct observation of early stages of formation of multilayered bimetallic Au-Pd core-shell nanocubes and Au-Pd-Au core-shell nanostars in liquid phase using low-dose in situ scanning transmission electron microscopy (S/TEM) with the continuous flow fluid cell. The reduction of Pd and formation of Au-Pd core-shell is achieved through the flow of the reducing agent. Initial rapid growth of Pd on Au along <111> direction is followed by a slower rearrangement of Pd shell. We propose the mechanism for the DNA-directed shape transformation of Au-Pd core-shell nanocubes to adopt a nanostar-like morphology in the presence of T30 DNA and discuss the observed nanoparticle motion in the confined volume of the fluid cell. The growth of Au shell over Au-Pd nanocube is initiated at the vertices of the nanocubes, leading to the preferential growth of the {111} facets and resulting in formation of nanostar-like particles. While the core-shell nanostructures formed in a fluid cell in situ under the low-dose imaging conditions closely resemble those obtained in solution syntheses, the reaction kinetics in the fluid cell is affected by the radiolysis of liquid reagents induced by the electron beam, altering the rate-determining reaction steps. We discuss details of the growth processes and propose the reaction mechanism in liquid phase in situ.

Facet-regulated adhesion of double-stranded DNA on palladium surfaces

A better understanding of interactions between metal-nanomaterial surfaces and biomolecules such as DNAs is critical for their biomedical applications. Here we investigated double-stranded DNA (dsDNA) adhering to palladium (Pd) nanosheets with two different exposed facets, {100} and {111}, using a combined computational and experimental approach. Different dsDNA binding modes on the two surfaces were observed, with a surprising "upright" conformation on Pd(100) and a "flat" conformation on Pd(111). Molecular dynamics simulations showed a stronger binding of the dsDNA on Pd(111) than Pd(100), which resulted in significant conformational changes and hydrogen bond breakage in the dsDNA on Pd(111). Further analyses revealed that the different binding strengths were caused by the number and arrangement of water molecules in the first solvation shell (FSS) of the two Pd surfaces. The water hydrogen bond network in the FSS of Pd(100) is compact and resists the embedding of dsDNA, while it is less compact on Pd(111), which allows penetration of dsDNA and its direct contact with Pd(111) surface atoms, thereby exhibiting stronger binding. Further free energy calculations with umbrella sampling supported these observations. Finally, these computational predictions on the adsorption capacity of dsDNA on Pd surfaces were confirmed by gel electrophoresis experiments.