DNA-Linked Metal Nanosphere Materials: Structural Basis for the Optical Properties

Distribution of Single-Particle Resonances Determines the Plasmonic Response of Disordered Nanoparticle Ensembles

Understanding how colloidal soft materials interact with light is crucial to the rational design of optical metamaterials. Electromagnetic simulations are computationally expensive and have primarily been limited to model systems described by a small number of particles-dimers, small clusters, and small periodic unit cells of superlattices. In this work we study the optical properties of bulk, disordered materials comprising a large number of plasmonic colloidal nanoparticles using Brownian dynamics simulations and the mutual polarization method. We investigate the far-field and near-field optical properties of both colloidal fluids and gels, which require thousands of nanoparticles to describe statistically. We show that these disordered materials exhibit a distribution of particle-level plasmonic resonance frequencies that determines their ensemble optical response. Nanoparticles with similar resonant frequencies form anisotropic and oriented clusters embedded within the otherwise isotropic and disordered microstructures. These collectively resonating morphologies can be tuned with the frequency and polarization of incident light. Knowledge of particle resonant distributions may help to interpret and compare the optical responses of different colloidal structures, correlate and predict optical properties, and rationally design soft materials for applications harnessing light.

Surface plasmon coupling between wide-field SPR microscopy and gold nanoparticles

The coupling behavior of the wide field surface plasmon microscopy (WF-SPRM) with single-, two-, and multiple-gold nanoparticles (AuNPs) with different AuNPs sizes is investigated using theoretical, simulation, and experimental approaches. The signal intensity of a single AuNP increases from 208 a.u. to 583 a.u. as particle size increases from 40 to 80 nm, which evidences the signal-building mechanism of Rayleigh scattering theory. A discrete particle model of SPR is used to understand the interaction between an Au-layer and a single AuNP. The calculated intensity profile of the single AuNP from the discrete particle model is accepted with the experimental data. In addition, the superposition between 2-AuNPs surface plasmon waves is studied using the finite element method as well as experimental data from WF-SPRM. The surface plasmon waves around the two particles generate an interference pattern. Finally, it is demonstrated that plasmonic multiple particles scattering can be represented by an effective media, which is described by Maxwell-Garnet equations.

Plasmonic Response of Complex Nanoparticle Assemblies

Optical properties of nanoparticle assemblies reflect distinctive characteristics of their building blocks and spatial organization, giving rise to emergent phenomena. Integrated experimental and computational studies have established design principles connecting the structure to properties for assembled clusters and superlattices. However, conventional electromagnetic simulations are too computationally expensive to treat more complex assemblies. Here we establish a fast, materials agnostic method to simulate the optical response of large nanoparticle assemblies incorporating both structural and compositional complexity. This many-bodied, mutual polarization method resolves limitations of established approaches, achieving rapid, accurate convergence for configurations including thousands of nanoparticles, with some overlapping. We demonstrate these capabilities by reproducing experimental trends and uncovering far- and near-field mechanisms governing the optical response of plasmonic semiconductor nanocrystal assemblies including structurally complex gel networks and compositionally complex mixed binary superlattices. This broadly applicable framework will facilitate the design of complex, hierarchically structured, and dynamic assemblies for desired optical characteristics.

Development of RNA-based assay for rapid detection of SARS-CoV-2 in clinical samples

Introduction

The ongoing spread of pandemic coronavirus disease-19 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is of growing concern. Rapid diagnosis and management of SARS-CoV-2 are crucial for controlling the outbreak in the community. Here, we report the development of a first rapid-colorimetric assay capable of detecting SARS-CoV-2 in the human nasopharyngeal RNA sample in less than 30 min.

Method

We utilized a nanomaterial-based optical sensing platform to detect RNA-dependent RNA polymerase gene of SARS-CoV-2, where the formation of oligo probe-target hybrid led to salt-induced aggregation and change in gold-colloid color from pink to blue visibility range. Accordingly, we found a change in colloid color from pink to blue in assay containing nasopharyngeal RNA sample from the subject with clinically diagnosed COVID-19. The colloid retained pink color when the test includes samples from COVID-19 negative subjects or human papillomavirus-infected women.

Results

The results were validated using nasopharyngeal RNA samples from positive COVID-19 subjects (n = 136). Using real-time polymerase chain reaction as gold standard, the assay was found to have 85.29% sensitivity and 94.12% specificity. The optimized method has detection limit as little as 0.5 ng of SARS-CoV-2 RNA.

Conclusion

We found that the developed assay rapidly detects SARS-CoV-2 RNA in clinical samples in a cost-effective manner and would be useful in pandemic management by facilitating mass screening.

Development of RNA-Based Assay for Rapid Detection of SARS-CoV-2 in Clinical Samples

INTRODUCTION

The ongoing spread of pandemic coronavirus disease-19 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is of growing concern. Rapid diagnosis and management of SARS-CoV-2 are crucial for controlling the outbreak in the community. Here, we report the development of a first rapid-colorimetric assay capable of detecting SARS-CoV-2 in the human nasopharyngeal RNA sample in less than 30 min.

METHOD

We utilized a nanomaterial-based optical sensing platform to detect RNA-dependent RNA polymerase gene of SARS-CoV-2, where the formation of oligo probe-target hybrid led to salt-induced aggregation and change in gold-colloid color from pink to blue visibility range. Accordingly, we found a change in colloid color from pink to blue in assay containing nasopharyngeal RNA sample from the subject with clinically diagnosed COVID-19. The colloid retained pink color when the test includes samples from COVID-19 negative subjects or human papillomavirus-infected women.

RESULTS

The results were validated using nasopharyngeal RNA samples from positive COVID-19 subjects (n = 136). Using real-time polymerase chain reaction as gold standard, the assay was found to have 85.29% sensitivity and 94.12% specificity. The optimized method has detection limit as little as 0.5 ng of SARS-CoV-2 RNA.

CONCLUSION

We found that the developed assay rapidly detects SARS-CoV-2 RNA in clinical samples in a cost-effective manner and would be useful in pandemic management by facilitating mass screening.

Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review

Gold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The potential catalytic applications and their enhancement upon modification of Au nanostructures have also been discussed in detail. The present analysis also offers brief summaries of the major Au nanomaterials synthetic procedures, such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapor deposition, sonochemical deposition, electrochemical deposition, microwave and laser pyrolysis. Among the various strategies used for improving the catalytic performance of nanostructured Au, the modification and functionalization of nanostructured Au produced better results. Therefore, various synthesis, modification and functionalization methods employed for better catalytic outcomes of nanostructured Au have been summarized in this review.

Size dependency of gold nanoparticles interacting with model membranes

The rapid development of nanotechnology has led to an increase in the number and variety of engineered nanomaterials in the environment. Gold nanoparticles (AuNPs) are an example of a commonly studied nanomaterial whose highly tailorable properties have generated significant interest through a wide range of research fields. In the present work, we characterise the AuNP-lipid membrane interaction by coupling qualitative data with quantitative measurements of the enthalpy change of interaction. We investigate the interactions between citrate-stabilised AuNPs ranging from 5 to 60 nm in diameter and large unilamellar vesicles acting as a model membrane system. Our results reveal the existence of two critical AuNP diameters which determine their fate when in contact with a lipid membrane. The results provide new insights into the size dependent interaction between AuNPs and lipid bilayers which is of direct relevance to nanotoxicology and to the design of NP vectors.

DNA Polymer Nanoparticles Programmed via Supersandwich Hybridization for Imaging and Therapy of Cancer Cells

Spherical nucleic acid (SNA) constructs are promising new single entity materials, which possess significant advantages in biological applications. Current SNA-based drug delivery system typically employed single-layered ss- or ds-DNA as the drug carriers, resulting in limited drug payload capacity and disease treatment. To advance corresponding applications, we developed a novel DNA-programmed polymeric SNA, a long concatamer DNA polymer that is uniformly distributed on gold nanoparticles (AuNPs), by self-assembling from two short alternating DNA building blocks upon initiation of immobilized capture probes on AuNPs, through a supersandwich hybridization reaction. The long DNA concatamer of polymeric SNA enables to allow high-capacity loading of bioimaging and therapeutics agents. We demonstrated that both of the fluorescence signals and therapeutic efficacy were effectively inhibited in resultant polymeric SNA. By further modifying with the nucleolin-targeting aptamer AS1411, this polymeric SNA could be specifically internalized into the tumor cells through nucleolin-mediated endocytosis and then interact with endogenous ATP to cause the release of therapeutics agents from long DNA concatamer via a structure switching, leading to the activation of the fluorescence and selective synergistic chemotherapy and photodynamic therapy. This nanostructure can afford a promising targeted drug transport platform for activatable cancer theranostics.

M13 bacteriophage spheroids as scaffolds for directed synthesis of spiky gold nanostructures

The spherical form (s-form) of a genetically-modified gold-binding M13 bacteriophage was investigated as a scaffold for gold synthesis. Repeated mixing of the phage with chloroform caused a 15-fold contraction from a nearly one micron long filament to an approximately 60 nm diameter spheroid. The geometry of the viral template and the helicity of its major coat protein were monitored throughout the transformation process using electron microscopy and circular dichroism spectroscopy, respectively. The transformed virus, which retained both its gold-binding and mineralization properties, was used to assemble gold colloid clusters and synthesize gold nanostructures. Spheroid-templated gold synthesis products differed in morphology from filament-templated ones. Spike-like structures protruded from the spherical template while isotropic particles developed on the filamentous template. Using inductively coupled plasma-mass spectroscopy (ICP-MS), gold ion adsorption was found to be comparatively high for the gold-binding M13 spheroid, and likely contributed to the dissimilar gold morphology. Template contraction was believed to modify the density, as well as the avidity of gold-binding peptides on the scaffold surface. The use of the s-form of the M13 bacteriophage significantly expands the templating capabilities of this viral platform and introduces the potential for further morphological control of a variety of inorganic material systems.

Human serum albumin corona on functionalized gold nanorods modulates doxorubicin loading and release

Human serum albumin corona around functionalized gold nanorods can modulate doxorubicin loading and release.

Magneto-Optical Response of Cobalt Interacting with Plasmonic Nanoparticle Superlattices

The magneto-optical Kerr effect is a striking phenomenon whereby the optical properties of a material change under an applied magnetic field. Though promising for sensing and data storage technology, these properties are typically weak in magnitude and are inherently limited by the bulk properties of the active magnetic material. In this work, we theoretically demonstrate that plasmonic thin-film assemblies on a cobalt substrate can achieve tunable transverse magneto-optical (TMOKE) responses throughout the visible and near-infrared (300-900 nm). In addition to exhibiting wide spectral tunability, this response can be varied in sign and magnitude by changing the plasmonic volume fraction (1-20%), the composition and arrangement of the assembly, and the shape of the nanoparticle inclusions. Of particular interest is the newly discovered sensitivity of the sign and intensity of the TMOKE spectrum to collective metallic plasmonic behavior in silver, mixed silver-gold, and anisotropic superlattices.

Tunable longitudinal modes in extended silver nanoparticle assemblies

Nanostructured materials with tunable properties are of great interest for a wide range of applications. The self-assembly of simple nanoparticle building blocks could provide an inexpensive means to achieve this goal. Here, we generate extended anisotropic silver nanoparticle assemblies in solution using controlled amounts of one of three inexpensive, widely available, and environmentally benign short ditopic ligands: cysteamine, dithiothreitol and cysteine in aqueous solution. The self-assembly of our extended structures is enforced by hydrogen bonding. Varying the ligand concentration modulates the extent and density of these unprecedented anisotropic structures. Our results show a correlation between the chain nature of the assembly and the generation of spectral anisotropy. Deuterating the ligand further enhances the anisotropic signal by triggering more compact aggregates and reveals the importance of solvent interactions in assembly size and morphology. Spectral and morphological evolutions of the AgNPs assemblies are followed via UV-visible spectroscopy and transmission electron microscopy (TEM). Spectroscopic measurements are compared to calculations of the absorption spectra of randomly assembled silver chains and aggregates based on the discrete dipole approximation. The models support the experimental findings and reveal the importance of aggregate size and shape as well as particle polarizability in the plasmon coupling between nanoparticles.

Facile synthesis of optical pH-sensitive molybdenum disulfide quantum dots

An effective fabrication of MoS2 quantum dots (QDs) has been developed using alkali metal-intercalation and exfoliation. The obtained MoS2 QDs are monolayers with a uniform lateral size of 4.26 ± 0.96 nm, which exhibit distinct blue fluorescence with a quantum yield of 2.28%, robust dispersibility, storage stability and pH dependent optical properties.

Plasmonic Metallurgy Enabled by DNA

Mixed silver and gold plasmonic nanoparticle architectures are synthesized using DNA-programmable assembly, unveiling exquisitely tunable optical properties that are predicted and explained both by effective thin-film models and explicit electrodynamic simulations. These data demonstrate that the manner and ratio with which multiple metallic components are arranged can greatly alter optical properties, including tunable color and asymmetric reflectivity behavior of relevance for thin-film applications.

[The Increase of Oligonucleotides--Gold Nanoparticles Conjugates Stability]

For today the reagents based on oligonucleotides--gold nanoparticles conjugates and used for specific nucleic acids detection are actively being developed. Such molecular structures are stabilized through the bonds between thiol group in oligonucleotides and gold atoms in nanoparticle. The durability of oligonucleotides--gold nanoparticles binding affects directly on the stability of conjugates and on the possibility of further manipulations. In this paper, a method for the strengthening of oligonucleotides attachment on the gold nano-particles surface by means of anchor groups with dithiolane residues is proposed. A comparative study of the anchors molecular structure influence on the conjugates stability at conditions that typical for oligonucleotide probes was carried out.

Synthesis and Overall Photophysical Characterization of SiO2:(Ag/SiO2) Nanostructured Sonogel Hybrid Glasses

Bulk SiO 2-based inorganic–inorganic sonogel (SG) hybrid glasses were fabricated with Ag / SiO 2 supported metal nanoparticles (MNPs). The catalyst-free SG route was implemented to produce these optically active nanostructured composites by doping the liquid sol-phase with Ag / SiO 2 synthesized according to the deposition–precipitation method. As prepared Ag / SiO 2-MNPs exhibited particle diameters below 10 nm and homogeneous size distribution. The easy and homogeneous Ag / SiO 2 loading within the micro/mesoporous SiO 2-SG network has evidenced the guest–host chemical affinity of these systems. This fact allowed us to fabricate outstanding chemically, photo-physically and mechanically stable bulk hybrid monoliths with controllable geometry and doping rates, suitable for linear and nonlinear optical (NLO)–spectroscopic characterizations. Indeed, the hosting SG matrix provided an elevated thermal and mechanical stability protecting the reactive Ag nanoparticles from environment conditions, diminishing their tendency to from aggregates and, above all, preserving their pristine photophysical properties. Comprehensive morphological, structural, spectroscopic and NLO characterizations were performed on the obtained SiO 2:( Ag / SiO 2) hybrid composites. Results have shown that the nanocrystalline (NC) properties, multipolar nature and small sizes of the implemented Ag / SiO 2-nanoparticles, together with the bulk guest–host mechanical interactions, play a crucial role for the observation of outstanding spectroscopic and quadratic NLO properties of the developed hybrid systems.

Conformal, macroscopic crystalline nanoparticle sheets assembled with DNA

A novel method for preparing conformal silica-embedded crystalline nanoparticle sheets via DNA programmable assembly provides independent control over nanoparticle size, nanoparticle spacing, and film thickness. The conformal materials retain the nanoparticle crystallinity and spacing after being transferred to flat or highly curved substrates even after being subjected to various mechanical, physical, and chemical stimuli.

Nanoscale form dictates mesoscale function in plasmonic DNA-nanoparticle superlattices

The nanoscale manipulation of matter allows properties to be created in a material that would be difficult or even impossible to achieve in the bulk state. Progress towards such functional nanoscale architectures requires the development of methods to precisely locate nanoscale objects in three dimensions and for the formation of rigorous structure-function relationships across multiple size regimes (beginning from the nanoscale). Here, we use DNA as a programmable ligand to show that two- and three-dimensional mesoscale superlattice crystals with precisely engineered optical properties can be assembled from the bottom up. The superlattices can transition from exhibiting the properties of the constituent plasmonic nanoparticles to adopting the photonic properties defined by the mesoscale crystal (here a rhombic dodecahedron) by controlling the spacing between the gold nanoparticle building blocks. Furthermore, we develop a generally applicable theoretical framework that illustrates how crystal habit can be a design consideration for controlling far-field extinction and light confinement in plasmonic metamaterial superlattices.

Small-molecule detection in thiol-yne nanocomposites via surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is generally performed on planar surfaces, which can be difficult to prepare and may limit the interaction of the sensing surface with targets in large volume samples. We propose that nanocomposite materials can be configured that both include SERS probes and provide a high surface area-to-volume format, i.e., fibers. Thiol-yne nanocomposite films and fibers were fabricated using exposure to long-wave ultraviolet light after the inclusion of gold nanoparticles (AuNPs) functionalized with thiophenol. A SERS response was observed that was proportional to the aggregation of the AuNPs within the polymers and the amount of thiophenol present. Overall, this proof-of-concept fabrication of SERS active polymers indicated that thiol-yne nanocomposites may be useful as durable film or fiber SERS probes. Properties of the nanocomposites were evaluated using various techniques including UV-vis spectroscopy, μ-Raman spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, and transmission electron microscopy.

Using nanoscale and mesoscale anisotropy to engineer the optical response of three-dimensional plasmonic metamaterials

The a priori ability to design electromagnetic wave propagation is crucial for the development of novel metamaterials. Incorporating plasmonic building blocks is of particular interest due to their ability to confine visible light. Here we explore the use of anisotropy in nanoscale and mesoscale plasmonic array architectures to produce noble metal-based metamaterials with unusual optical properties. We find that the combination of nanoscale and mesoscale anisotropy leads to rich opportunities for metamaterials throughout the visible and near-infrared. The low volume fraction (<5%) plasmonic metamaterials explored herein exhibit birefringence, a skin depth approaching that of pure metals for selected wavelengths, and directionally confined waves similar to those found in optical fibres. These data provide design principles with which the electromagnetic behaviour of plasmonic metamaterials can be tailored using high aspect ratio nanostructures that are accessible via a variety of synthesis and assembly methods.

Gelatin-templated gold nanoparticles as novel time-temperature indicator

Gold nanoparticles (AuNPs) were generated by mixing of gelatin solution and gold precursor (HAuCl(4,) 1 mM) under isothermal condition (80 °C). The effects of gelatin concentration (1% to 6%) and pH (3, 5, and 9) on the color signal of gelatin-templated AuNPs were examined. The λ(max) of AuNPs shifted from 535 to 552 nm at 1% gelatin, and the color intensity of the AuNPs was a maximum at 2% gelatin. The speed of color development was accelerated at pH 3, and the AuNPs prepared at pH 3 were bigger (45 to 162 nm) and more irregular in shape than those prepared at pH 5 or 9. When the performance of gelatin nanoreactor as time-temperature indicator (2%, pH 5) was evaluated in a simulated frozen storage, clear color signals developed as little as 6 h of exposure at 30 °C and the intensity of the color signal was proportional to duration of exposure.

PRACTICAL APPLICATION

Gelatin-gold precursor mixture acted as a "nanoreactor" for gold nanoparticle synthesis without need for any additional reactants. When the gelatin-templated AuNPs were exposed to 30 °C, color signals developed with intensities that depended on the duration of exposure. The reaction was irreversible and colors were easily discerned by the naked eye.

Nanoplasmonics for dual-molecule release through nanopores in the membrane of red blood cells

A nanoplasmonics-based opto-nanoporation method of creating nanopores upon laser illumination is applied for inducing diffusion and triggered release of small and large molecules from red blood cells (RBCs). The method is implemented using absorbing gold nanoparticle (Au-NP) aggregates on the membrane of loaded RBCs, which, upon near-IR laser light absorption, induce release of encapsulated molecules from selected cells. The binding of Au-NPs to RBCs is characterized by Raman spectroscopy. The process of release is driven by heating localized at nanoparticles, which impacts the permeability of the membrane by affecting the lipid bilayer and/or trans-membrane proteins. Localized heating and temperature rise around Au-NP aggregates is simulated and discussed. Research reported in this work is relevant for generating nanopores for biomolecule trafficking through polymeric and lipid membranes as well as cell membranes, while dual- and multi-molecule release is relevant for theragnostics and a wide range of therapies.

The golden age: gold nanoparticles for biomedicine

Gold nanoparticles have been used in biomedical applications since their first colloidal syntheses more than three centuries ago. However, over the past two decades, their beautiful colors and unique electronic properties have also attracted tremendous attention due to their historical applications in art and ancient medicine and current applications in enhanced optoelectronics and photovoltaics. In spite of their modest alchemical beginnings, gold nanoparticles exhibit physical properties that are truly different from both small molecules and bulk materials, as well as from other nanoscale particles. Their unique combination of properties is just beginning to be fully realized in range of medical diagnostic and therapeutic applications. This critical review will provide insights into the design, synthesis, functionalization, and applications of these artificial molecules in biomedicine and discuss their tailored interactions with biological systems to achieve improved patient health. Further, we provide a survey of the rapidly expanding body of literature on this topic and argue that gold nanotechnology-enabled biomedicine is not simply an act of 'gilding the (nanomedicinal) lily', but that a new 'Golden Age' of biomedical nanotechnology is truly upon us. Moving forward, the most challenging nanoscience ahead of us will be to find new chemical and physical methods of functionalizing gold nanoparticles with compounds that can promote efficient binding, clearance, and biocompatibility and to assess their safety to other biological systems and their long-term term effects on human health and reproduction (472 references).

Quantifying the nanomachinery of the nanoparticle-biomolecule interface

A study is presented of the nanomechanical phenomena experienced by nanoparticle-conjugated biomolecules. A thermodynamic framework is developed to describe the binding of thrombin-binding aptamer (TBA) to thrombin when the TBA is conjugated to nanorods. Binding results in nanorod aggregation (viz. directed self-assembly), which is detectable by absorption spectroscopy. The analysis introduces the energy of aggregation, separating it into TBA-thrombin recognition and surface-work contributions. Consequently, it is demonstrated that self-assembly is driven by the interplay of surface work and thrombin-TBA recognition. It is shown that the work at the surface is about -10 kJ mol(-1) and results from the accumulation of in-plane molecular forces of pN magnitude and with a lifetime of <1 s, which arises from TBA nanoscale rearrangements fuelled by thrombin-directed nanorod aggregation. The obtained surface work can map aggregation regimes as a function of different nanoparticle surface conditions. Also, the thermodynamic treatment can be used to obtain quantitative information on surface effects impacting biomolecules on nanoparticle surfaces.