Assembly Of Nanorods Research Articles

An Interesting Nanoparticle‐Ligand Interaction Between Porphyrins and Gold Nanorods Leads to Luminescent Mesostructures

AbstractIn this study, we aim to investigate the family of porphyrins from a novel perspective. In particular, we focus on their role in controlling the assembly of gold nanorods (AuNRs) through a synthetic approach. Using a seed‐mediated growth method, AuNRs were first synthesized. Then, the surfaces of the AuNRs were functionalized with four different types of porphyrins to explore their unique influence on the assembly process. Two pairs of porphyrins were synthesized: the metal‐free porphyrins 1 and 2 and the two corresponding zinc complexes Zn(1) and Zn(2). Compounds 1 and Zn(1) bind to the nanoparticle surface via an amine group, 2 and Zn(2) via a carbon‐carbon triple bond. A careful photophysical and morphological characterization has been carried out on the different samples, and interestingly, we observed that metal‐free porphyrins 1 and 2 promote nanoparticle assembly, forming luminescent mesostructures. Porphyrin 2 preferentially organizes nanorods by end‐to‐end assembly, whereas porphyrin 1 does not confer a preferential organization.

Surfactant molecules and nano gold on HOPG: Experiment and theory

Excessive surfactant molecules within the solution adhere to highly ordered pyrolytic graphite (HOPG) when a droplet containing gold nanorods evaporates, leading to the emergence of a unique coffee-ring pattern. The combination of surface hydrophobicity and evaporation of the aqueous phase results in a stick-slip motion, which enhances the convective hydrodynamics of suspended particles. This phenomenon initiates interactions that influence the deposition and flow dynamics inside the droplet. High-resolution scanning electron microscopy (HRSEM) does not provide significant insights into regions potentially linked to cetyltrimethylammonium bromide (CTAB) molecules, whereas the atomic force microscope (AFM) displays the presence of gold nanoparticles arranged by CTAB within specific CTAB patches. The layers forms with varying heights and gaps between them, indicating diverse adhesion of CTAB. The analytical focus lies on the quantitative assessment of CTAB molecules, stripe dimensions, and energy profiles influenced by concentration and the effective positioning of CTAB-coated gold nanorods in CTAB-covered regions. AFM examination reveals CTAB molecular stripes on HOPG, showing a binding energy of −20 kJ/mol with the surface, −10 kJ/mol for nitrogen bonding with HOPG, and a total binding energy (BE) of −60 kJ/mol, considering various contributing factors. Completely parallel aligned molecules (CPAM) exhibit higher binding energy than non-perfectly aligned molecules (NPAM) due to maximum Van der Waals (VdW) interactions, ideal electrostatic interactions, and minimal steric repulsion. The difference in binding energy between perfectly and non-perfectly aligned molecules is around 20kJ/mol, emphasizing the importance of molecular orientation. As temperature rises from 298 K to 348 K, the likelihood of NPAM desorption increases significantly, with the binding energy shifting from 2.5kJ/mol to 4.1kJ/mol. Temperature significantly influences the equilibrium of molecules on HOPG surfaces. The emphasis is on elucidating the alterations in energy levels during nanorod aggregation on CTAB areas compared to bare HOPG surfaces, underscoring the impact of nanorods on CTAB micelle deformation energy. Observations on the variation in CTAB desorption rates with temperature changes underscore the dynamic nature of molecular binding energy associated with surface properties, underscoring the importance of molecular configuration and energy transfers in nanoscale systems.

Coupling of Spectrin Repeat Modules for the Assembly of Nanorods and Presentation of Protein Domains.

Modular protein engineering is a powerful approach for fabricating high-molecular-weight assemblies and biomaterials with nanoscale precision. Herein, we address the challenge of designing an extended nanoscale filamentous architecture inspired by the central rod domain of human dystrophin, which protects sarcolemma during muscle contraction and consists of spectrin repeats composed of three-helical bundles. A module of three tandem spectrin repeats was used as a rigid building block self-assembling via coiled-coil (CC) dimer-forming peptides. CC peptides were precisely integrated to maintain the spectrin α-helix continuity in an appropriate frame to form extended nanorods. An orthogonal set of customizable CC heterodimers was harnessed for modular rigid domain association, which could be additionally regulated by metal ions and chelators. We achieved a robust assembly of rigid rods several micrometers in length, determined by atomic force microscopy and negative stain transmission electron microscopy. Furthermore, these rigid rods can serve as a scaffold for the decoration of diverse proteins or biologically active peptides along their length with adjustable spacing up to tens of nanometers, as confirmed by the DNA-PAINT super-resolution microscopy. This demonstrates the potential of modular bottom-up protein engineering and tunable CCs for the fabrication of functionalized protein biomaterials.

Self-Matching Assembly of Chiral Gold Nanoparticles Leads to High Optical Asymmetry and Sensitive Detection of Adenosine Triphosphate.

To achieve chiral amplification, life uses small chiral molecules as building blocks to construct hierarchical chiral architectures that can realize advanced physiological functions. Inspired by the chiral amplification strategy of nature, we herein demonstrate that the chiral assembly of chiral gold nanorods (GNRs) leads to enhanced optical asymmetry factors (g-factors), up to 0.24. The assembly of chiral GNRs, dictated by structural self-matching, leads to g-factors with over 100-fold higher values than those of individual chiral GNRs, as confirmed by numerical simulations. Moreover, the efficient optical asymmetry of chiral GNR assemblies enables their application as highly sensitive sensors of adenosine triphosphate (ATP detection limit of 1.0 μM), with selectivity against adenosine diphosphate and adenosine monophosphate.

DNA Origami Guided Helical Assembly of Gold Nanorods with Tailored Optical Chirality

DNA Origami Guided Helical Assembly of Gold Nanorods with Tailored Optical Chirality

Thermoplasmonic Effect Enables Indirect ON-OFF Control over the Z-E Isomerization of Azobenzene-Based Photoswitch.

Proper formulation of systems containing plasmonic and photochromic units, such as gold nanoparticles and azobenzene derivatives, yields materials and interfaces with synergic functionalities. Moreover, gold nanoparticles are known to accelerate the Z-E isomerization of azobenzene molecules in the dark. However, very little is known about the light-driven, plasmon-assisted Z-E isomerization of azobenzene compounds. Additionally, most of the azobenzene-gold hybrids are prepared with nanoparticles of small, isotropic shapes and azobenzene ligands covalently linked to the surface of nanostructures. Herein, a formulation of an innovative system combining azobenzene derivative, gold nanorods, and cellulose nanofibers is proposed. The system's structural integrity relies on electrostatic interactions among components instead of covalent linkage. Cellulose, a robust scaffold, maintains the material's functionality in water and enables monitoring of the material's plasmonic-photochromic properties upon irradiation and at elevated temperatures without gold nanorods aggregation. Experimental evidence supported by statistical analysis suggests that the optical properties of plasmonic nanometal enable indirect control over the Z-E isomerization of the photochromic component with near-infrared irradiation by triggering the thermoplasmonic effect. The proposed hybrid material's dual plasmonic-photochromic functionality, versatility, and ease of processing render a convenient starting point for further advanced azobenzene-related research and 3D printing of macroscopic light-responsive structures.

Rapid Fingerprinting of Urinary Volatile Metabolites and Point-of-Care Diagnosis of Phenylketonuria on a Patterned Nanorod Sensor Array with Multiplexed Surface-Enhanced Raman Scattering Readouts.

Phenylketonuria (PKU) is one of the most common genetic metabolic diseases, especially among newborns. Traditional clinical examination of newborn blood samples for PKU is invasive, laborious, and limited to hospitals and healthcare facilities. We reported herein a SERS-based sensor array with three thiophenolic nanoreceptors built on a patterned nanorod vertical array for rapid and inexpensive detection of characteristic volatile biomarkers indicative of PKU in the urine and accurate classification of newborn baby patients all performed on a hand-held SERS spectrophotometer. The well-ordered array was generated from the volatility-driven assembly of gold nanorods (AuNRs) into an upright and closely packed hexagonal configuration. The uniformly distributed nanowells between AuNRs offered an intense and aspect-ratio-dependent plasmonic field for the molecular enhancement of SERS outputs. The SERS-based detector was integrated into a test chip for regular monitoring of volatile phenylketone bodies in the spiked solution or patients' urine within 5 min, allowing the quantification of a wide variety of normal or abnormal metabolites at their physiologically relevant concentration range. The detection limits for common biomarkers of PKU, including phenylpyruvic acid, 4-hydroxyphenylacetic acid, and phenylacetic acid, were at a few μM and well below the diagnostic thresholds. Moreover, the volatile headspace mixtures from a given urine sample could be fingerprinted by the sensor array and discriminated using machine-learning algorithms. Ultimately, the discrimination of baby patients among 26 cases of mild and classic PKU phenotypes and 17 cases of healthy volunteers could be realized with an overall accuracy of 97%. This hand-held SERS platform plays a pivotal role in advancing healthcare applications in quick screening of neonatal PKU through a facile urinary vapor test.

Plasmon-mediated photocatalytic conversion in Au or Ag nanorod aggregates by surface-enhanced Raman spectroscopy

Plasmonic nanoparticles (NPs) hold considerable potential as photocatalysts owing to their robust light–matter interactions across diverse electromagnetic wavelengths, which significantly influence the photophysical characteristics of the adjacent molecular entities. Despite the widespread use of noble-metal NPs in surface-enhanced Raman scattering (SERS) applications, little is known about the kinetics of nanoparticle aggregation and how it affects their configurations. This study investigates the plasmon-driven photochemical conversion of 4-nitrobenzenethiol (NBT) to 4,4′-dimercaptoazobenzene (DMAB) on Au and Ag nanorods (NRs) through SERS. Significantly, photoconversion phenomena were observed on Ag NRs but not on Au NRs upon laser excitation at 633 nm. Finite-difference time-domain simulations revealed the presence of stronger electromagnetic fields on Ag NRs than on Au NRs. The aspect ratios and gaps between individual NPs in dimer configurations were determined to elucidate their effects on electromagnetic fields. The Ag NR dimer with an end-to-end configuration, an aspect ratio of 3.3, and a 1-nm gap exhibited the highest enhancement factor of 1.05 × 1012. Our results demonstrate that the primary contribution from diverse configurations in NR aggregates is the end-to-end configuration. The proposed NP design with adjustable parameters is expected to advance research in plasmonics, sensing, and wireless communications. These findings also contribute to the understanding of plasmon-driven photochemical processes in metallic nanostructures.

Resolving plasmon-mediated high-order multiphoton excitation pathways in dolmen nanostructures using ultrafast nonlinear optical interferometry.

The multiphoton excitation pathways of plasmonic nanorod assemblies are described. By using dolmen structures formed from the directed assembly of three gold nanorods, plasmon-mediated three-photon excitation is resolved. These high-order multiphoton excitation channels were accessed by resonantly exciting a hybrid mode of the dolmen structure that was resonant with the 800-nm carrier wavelength of an ultrafast laser system. Rotation of the exciting field polarization to a non-resonant configuration did not generate third-order responses. Hence, the multiphoton excitation and resultant non-equilibrium electron distributions were generated by structure- and mode-selective excitation. Correlation between high-order and resonant plasmon excitation was achieved through sub-cycle time-resolved interferometric detection of incoherent nonlinear emission signals. The results illustrate the advantages of nonlinear optical interferometry and Fourier analysis for distinguishing plasmon-mediated processes from those that do not require plasmon excitation.

Magnetic Properties of Self-Assemble Naphthalene Diimide Radical Aggregates.

The concept of creating room-temperature ferromagnets from organic radicals proposed nearly sixty years ago, has recently experienced a resurgence due to advances in organic radical chemistry and materials. However, the lack of definitive design paradigms for achieving stable long-range ferromagnetic coupling between organic radicals presents an uncertain future for this research. Here, an innovative strategy is presented to achieve room-temperature ferromagnets by assembling π-conjugated radicals into π-π stacking aggregates. These aggregates, with ultra-close π-π distances and optimal π-π overlap, provide a platform for strong ferromagnetic (FM) interaction. The planar aromatic naphthalene diimide (NDI) anion radicals form nanorod aggregates with a π-π distance of just 3.26 Å, shorter than typical van der Waals distances. The suppressed electron paramagnetic resonance (EPR) signal and emergent near-infrared (NIR) absorption of the aggregates confirm strong interactions between the radicals. Magnetic measurements of NDI anion radical aggregates demonstrate room-temperature ferromagnetism with a saturated magnetization of 1.1 emug-1, the highest among pure organic ferromagnets. Theoretical calculations reveal that π-stacks of NDI anion radicals with specific interlayer translational slippage favor ferromagnetic coupling over antiferromagnetic coupling.

Flower-like SnO2 nanorod aggregates modified with Co3O4 nanoparticles grown on reduced graphene oxide(rGO) sheets for xylene sensing

In this paper, the ternary composite of flower-like SnO2 nanorod aggregates modified with Co3O4 nanoparticles grown on rGO sheets were synthesized by a two-step process of water heating and water bath, and characterized by SEM, TEM, XRD, EDS, and XPS. The gas-sensitive performance test results revealed that the 15-rGO/SnO2/Co3O4 sensor exhibited a higher response value (I0/Ia=24.46) to 100 ppm xylene at the optimal working temperature of 175℃. In addition, the sensor could detect 10 ppb xylene, with a low detection limit. The gas-sensitive properties of 15-rGO/SnO2/Co3O4 were significantly improved due to the large specific surface area of rGO flakes and SnO2 slender nanorods, the catalytic action of p-type semiconductor Co3O4 and the existence of p-n-p double heterojunction. Due to the special nanostructure and synergistic effect of SnO2, rGO and Co3O4, the 15-rGO/SnO2/Co3O4 sensor enabled the efficient and selective detection of xylene.

The Role of the Polyethylene Glycol in the Organization of Gold Nanorods at the Air-Water and Air-Solid Interfaces.

The organization of metallic nanoparticles into assembled films is a complex process. The type of nanoparticle stabilizing ligand and the method for creating an organized layer can profoundly affect the optical properties of the resulting nanoparticle assembly. Investigations of the ligand structure and nanoparticle interactions can provide a greater understanding of the design of the assembly process and the quality of the resulting materials. One of the functionalization methods in the preparation of specific gold nanorods is the utilization of thiol-terminated poly(ethylene glycol). This generates gold nanorods capable of forming stable monolayers at the air-water interface upon dispersion in a suitable organic solvent. Herein, we show that depending on the molecular weight of the poly(ethylene glycol), the structures obtained at the air-water and air-solid interfaces differ in the arrangement. The studied structures were characterized by using spectroscopic and microscopic techniques, and the structural type was correlated with the polymer type. Insoluble and stable Langmuir monolayers composed of higher-molecular-weight gold nanorods with poly(ethylene glycol) were formed only in the presence of an additional stabilizer that prevented the formation of gold nanorods in aqueous solutions. At the air-solid interface, conformational changes in poly(ethylene glycol) induced the aggregation of gold nanorods, which became closely packed under the influence of surface pressure. The presented results suggested that the arrangement of two-dimensional layers of gold nanorods could be tailored using poly(ethylene glycol) of various molecular weights.

Cholesteric Liquid Crystal‐Mediated Chiral Plasmonic Films with Strong Chiroptical Response, Dynamic Tunability, and Reversible Thermal Reconfigurability

AbstractChiral assemblies of plasmonic nanocrystals (NCs) are of immense interest due to their distinctive physicochemical characteristics and promising potential in future optoelectronic applications. Despite recent advances in the construction of chiral NC assemblies, most approaches have led to the formation of static irreversible structures with modest optical responses and limited configurational tunability. Herein, a way to prepare a thermally reconfigurable helical assembly of Au nanorods (AuNRs) with a strong chiroptical response is introduced by employing cholesteric liquid crystals (CLCs) as a chiral template. Circular dichroism (CD) spectroscopy and polarized optical microscopy are used to verify the strong chiroptical activity and dynamic optical tunability of chiral plasmonic film of AuNR–CLC composites and to unveil the interactions between constituents. For the system, chiral dopants are employed to induce strong helical procession along the hierarchical structure of the CLC template, resulting in a strong CD response, which can further be enhanced by increasing the amount of AuNRs. Furthermore, the thermotropic nature of the CLC template leads to the reversible on/off switching of the chiroptical responses of the system at a moderate temperature window with almost complete recovery of the original response, suggesting its feasibility as a promising material for chiral optoelectronic devices.

UV‐Triggered Optical Asymmetry Modification of Gold Nanorods Helical Assemblies in a Cholesteric Liquid Crystal Host

AbstractThe creation and modulation of chirality innanomaterials is a well‐established and widely applied concept. Nevertheless, the direct approach of dynamically tuning their morphological asymmetry at thenanoscale to reveal their optical asymmetry variations is yet less well‐implemented. The helical templating of nanomaterials within a cholesteric liquidcrystal (CLC) host and the exploitation of their optical asymmetry change inconjunction with the host represent a means of circumventing technological limitations. In this study, a blending approach is employed to investigate the helical assemblies of gold nanorods (Au NRs) within a photo‐tunable CLC host, followed by their morphological asymmetry modulation through the use of UV irradiation. The results demonstrated that the optical asymmetry of the Au NR shelical assemblies increased in response to a reduction in pitch and the distance between the Au NRs, regardless of the azimuthal variations.Furthermore, the Au NRs blended with CLCs exhibited excellent and stable reflective properties comparable to those of conventional CLCs. Additionally,they can modulate the light flux of incident light at NIR wavelengths. The integrated modulation of reflection and transmission by Au NRs helical assemblies and CLC hosts represents a promising avenue for future research inthe field of multi‐level information encryption.

Enhanced oxygen evolution reaction by controlled assembly of Co3O4 nanorods on TiB2 nanosheets

Cobalt oxide (CO) and Titanium boride hybrid composites are synthesized via hydrothermal reaction conditions followed by attentive calcination. Exfoliated Titanium boride (ETB) nanosheet templates are used for the first time to skillfully decorate CO nanorods on it. As-synthesized diverse hybrid composites ETB@CO (1, 3, and 5) are optimized for the electrochemical properties and weight ratios of CO and ETB nanosheets altered accordingly. Various spectroscopic techniques are used to characterize the as-synthesized hybrid composite materials. Standard electrochemical techniques such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and Chronopotentiometry (CP) are used to discover the electro-catalytic behavior of hybrid composites. The composite ETB@CO-3 recorded outstanding performance by exhibiting a lower overpotential of 271 mV, with a cramped Tafel slope of 42.4 mV dec−1 for electrochemical oxygen evolution reaction (OER). The composite ETB@CO-3 clamour a lower overpotential of 271 mV to attain the current density of 10 mA/cm2 than the other composite ratio. Furthermore, the composite ETB@CO-3 displayed remarkable stability over 24 h with continuous OER reaction by maintaining stable voltage at 10 mA/cm2 current density and exhibited no noticeable increase in overpotential, suggesting its feasibility in practical applications.

Nanophotonics with Plasmonic Nanorod Metamaterials

AbstractTaking advantage of their unique and tuneable electromagnetic properties, plasmonic metamaterials constitute a versatile platform for a variety of applications ranging from high‐resolution imaging, sensing and spontaneous emission engineering to ultrafast nonlinear optics and light polarization control. Here, recent advances in the design and applications of plasmonic metamaterials based on aligned metallic nanorod assemblies are reviewed, and the fast‐developing trends in their exploitation in nanophotonics are outlined. The fabrication of the nanorod‐based metamaterials is introduced and their linear and nonlinear optical properties are presented from both microscopic and phenomenological considerations. Multiscale structuring allowing precise engineering of the electromagnetic modes supported by the nanorod metamaterials, as well as nonlocal spatial dispersion effects and their impact on nanophotonic performance are discussed. To illustrate the developing field of practical applications of these metamaterials, some of their main application domains in sensing, photochemistry and nonlinear optics are overviewed and novel designs of anisotropic metamaterials directly derived from the nanorod architecture are introduced.

Active Assembly of CsPbBr3 Nanorods into Microcolumns by Electric Field in Nonpolar Solvent.

High-precision, controllable, mass-producible assembly of nanoparticles into complex structures or devices holds immense importance in the application across various fields but it remains challenging. Here a highly controllable and reversible active assembly of colloidal CsPbBr3 nanorods, driven by an external electric field is achieved. This approach enables the nanorods dynamically orient themselves, assemble into chains, aggregate into columns, and eventually form an ordered column array, with the electric field intensity varying from 0 to 50V µm-1 at 100kHz. The nanorods inside the columns align parallel to the electric field, leading to a well-ordered structure. With the analysis of the interactions among the nanorods, a quantitative interpretation of the assembly is proposed. Monte Carlo calculation is also introduced to simulate the assembly process and the results prove to be in great agreement with the experimental observations. This electric field-driven assembly presents an exciting opportunity to pave the way for next-generation sensors and photonic devices based on well-developed colloidal nanoparticles.

An Exploration of Cysteamine as a Subphase Additive for the Fabrication of Uniform Gold Nanorod Arrays using Langmuir-Blodgett Deposition.

Gold nanorods (AuNRs) have attracted significant attention over the past several decades for a variety of applications and there has been steady progress with regards to their synthesis and modification. Despite these advances, the assembly of AuNRs into well-organized hierarchical assemblies remains a formidable challenge. Specifically, there is a need for tools that can fabricate assemblies of nanorods over large length scales at low cost with the potential for high-throughput manufacturing. Langmuir-Blodgettry is a monolayer deposition technique which has been primarily applied to amphiphilic molecules, but which has recently shown promise for the ordering of functionalized nanoparticles residing at the air-water interface. In this work, Langmuir-Blodgett deposition is explored for the formation of AuNR arrays for enhanced surface-enhanced Raman spectroscopy (SERS) sensing. In particular, both surface modification of the AuNRs as well as subphase modification with cysteamine were evaluated for AuNR array fabrication.

Engineering robust ZnO/Au decorated biomass-derived carbonaceous platforms for integrated antibacterial and electromagnetic wave absorbing properties

In consideration of the issues of electromagnetic pollution in medical settings, the function integration of high antibacterial activity and efficient wave absorption is becoming the preferred solution. In this work, spinach-derived carbon coupled with antibacterial assembly of ZnO nanorods decorated by Au nanoparticles were fabricated to form a hierarchical nanocomposite (CS–ZnO/Au) to meet the dual demands. Such an active platform guaranteed a pronounced bactericidal performance upon visible light illumination. 99.9 % of E. coli and 99.7 % of S. aureus were effectively eradicated in a lean period of 30 min, which was attributed to that ZnO/Au nanohybrids promoted the production of reactive oxygen species (ROS) and inhibited the charge recombination. Meanwhile, the anticipated wave attenuation ability was available owing to the multiple loss responses in the hierarchical CS-ZnO/Au. The ternary nanocomposites achieved the maximum absorbing bandwidth of 4.8 GHz and the strongest absorption of −54.61 dB. The mechanisms for wave absorption were ascribed to the improved dielectric loss and optimized impedance matching performance. It proposed an engineering robust platform, in sum, to tackle the dual challenges of antibacterial and wave absorption with these sustainable materials obtained from a green route.

Magnetic Assembly of Eu-Doped NaYF4 Nanorods for Field-Responsive Linearly and Circularly Polarized Luminescence.

Colloidal assembly has emerged as an effective avenue for achieving polarized light emission. Here, we showcase the efficacy and versatility of the magnetic colloidal assembly in enabling both linearly and circularly polarized luminescence. Colloidal europium-doped NaYF4 nanorods with surface-bound Fe3O4 nanoparticles are magnetically assembled into linear or chiral superstructures using corresponding fields created in permanent magnets. In a uniform magnetic field generated by opposing poles, the assemblies exhibit photoluminescence with intensity tunable in response to the magnetic field direction, which is higher when the nanorods are perpendicular to light propagation than when they are parallel. The obtained superstructures display strong linearly polarized luminescence when the nanorods are aligned vertically, exhibiting a high degree of polarization up to 0.61. In a quadrupole chiral field generated by permanent magnets, the assemblies emit left-handed or right-handed polarized light depending on the position of the sample placement, attaining a g-factor of 0.04. Furthermore, the superstructures immobilized in a hydrogel film are found to retain their chirality, exhibiting opposite chiroptical responses depending on the sample orientation. The magnetic colloidal assembly approach facilitates the convenient and efficient generation of polarized light emissions from nonmagnetic luminescent materials, thus creating opportunities for tailoring light behavior in developing innovative optoelectronic devices.