Anisotropic Nanoparticles Research Articles

Nanosupernova: a new anisotropic nanostructure for SERS.

Gold and/or silver nanostars are interesting anisotropic nanoparticles that have been used in surface-enhanced Raman scattering (SERS). In particular SERS nanotags consisting of gold nanostars and Raman reporter molecules have been widely utilised in biosensing and bioimaging. To improve the SERS activity of gold/silver nanostars, this paper details the development of a simple synthesis method that results in the formation of quasi-spherical SERS nanotags and larger highly anisotropic nanoparticles with a novel structure, which we have designated nanosupernova. The resulting SERS nanotags and nanosupernova contain gold/silver nanostars at their core, a self-assembled monolayer of Raman reporter molecules, and a final silver coating. The silver coating is the essential step responsible for the formation of the two types of particles, with incubation time, and type of Raman reporter molecule, the defining factor as to which forms. We discovered that the Raman reporter molecule, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), plays a crucial role in controlling the morphology of nanosupernova. We believe the larger highly anisotropic nanoparticles will open new applications in material sciences and in optical and electronic devices in the future.

Uniform and Length-Tunable, Paramagnetic Self-Assembled Nitroxide-Based Nanofibers for Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a widely used non-invasive medical imaging tool. Nanoparticle-based MRI contrast agents have received considerable attention due to their high loading capability for magnetic species, enhanced accumulation in lesions, and versatile surface functionalization. Anisotropic nanoparticles such as nanofibers can exhibit significant advantages over their well-explored spherical counterparts in terms of their pharmacokinetic and biodistribution profiles. Herein, we report the retrosynthetic design, synthesis, and characterization of uniform and length-tunable paramagnetic core-shell nanofibers for MRI through the use of the seeded-growth “living” crystallization-driven self-assembly (CDSA) approach. Triblock copolymer (TriBCP) precursors with a crystallizable polycarbonate core-forming segment, a nitroxide-bearing central region, and a hydrophilic poly(ethylene glycol) (PEG) terminal corona-forming segment were prepared via sequential living organocatalytic ring-opening polymerization (ROP). Low dispersity nanofibers of length ca. 80 nm relevant for biomedical applications were prepared for detailed studies by living CDSA and these possessed an average number of nitroxides per nanofiber of >8000. Subsequent evaluation of the water-proton relaxivities demonstrated that tuning the hydrophilicity of the central segment in the TriBCP allowed access to nanofibers with impressive performance compared to most existing polymer-based nitroxide-based contrast agents. As a result of their 1D morphology, the synthetic nanofibers therefore represent promising organic radical contrast agents (ORCAs) for MRI applications.

Polarized emission from unidirectionally oriented semiconductor nanorods in light-emitting devices

Unidirectional ordering of colloidal semiconductor nanorods (NRs) is key to taking advantage of anisotropic optical properties of NRs in solid-state devices. In this study, we report long-range orientation of colloidal CdSe/CdS heterostructure NRs by spin coating a mixture of NRs and poly(9-vinylcarbazole) (PVK) molecules on an off-center position of a substrate. Addition of 1,2-dichlorobenzene slows the evaporation of solvent resulting in better orientation with contrast ratio of 2.5 in linear photoluminescence polarization and 2.0 in electroluminescence. Our calculation reveals that the stabilization of the NR assembly is likely a result of depletion energy during spin coating. The retarded evaporation enables the depletion interaction to come into play in the process of NR stacking, hence highly oriented and closely packed NR films. Our findings on unidirectionally assembled NRs in uniform film offer an insight for ordering of anisotropic colloidal nanoparticles.

Anisotropic Nanoparticle Arrays Guided by Ordered Nanowire Films Enhance Surface‐Enhanced Raman Scattering

AbstractDesigning high‐efficiency surface‐enhanced Raman scattering (SERS) substrates has attracted explosive attention in recent decades for their novel and potential applications. Great achievements have been made to optimize the intrinsic activity of nanomaterial in SERS substrates, while little attention has been paid to the unique structural design of the nanomaterial building blocks. Herein, a new strategy is provided for assembling Au nanoparticles into well‐defined ordered structures by using a highly ordered arrangement nanowires template to explore the ordering effect on the SERS performance. The highly ordered Au nanoparticle arrays show a detection limit of 10−9 m that exceeds disordered Au particles by two orders of magnitude, as well as over treble enhancement factor at the same detection concentration. Importantly, this novel scientific discovery can be further confirmed in various probed molecules or nanoparticles with different diameters, which means SERS substrate design can be pushed forward further combined with traditional intrinsic activity design.

A Comprehensive Study of Synthesis and Analysis of Anisotropic Iron Oxide and Oxyhydroxide Nanoparticles.

One-dimensional anisotropic nanoparticles are of great research interest across a wide range of biomedical applications due to their specific physicochemical and magnetic properties in comparison with isotropic magnetic nanoparticles. In this work, the formation of iron oxides and oxyhydroxide anisotropic nanoparticles (ANPs) obtained by the co-precipitation method in the presence of urea was studied. Reaction pathways of iron oxide and oxyhydroxide ANPs formation are described based on of X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and pulse magnetometry studies. It is shown that a nonmonotonic change in the Fe3O4 content occurs during synthesis. The maximum content of the Fe3O4 phase of 47.4% was obtained at 12 h of the synthesis. At the same time, the reaction products contain ANPs of α-FeOOH and submicron isotropic particles of Fe3O4, the latter formation can occur due to the oxidation of Fe2+ ions by air-oxygen and Ostwald ripening processes. A subsequent increase in the synthesis time leads to the predominant formation of an α-FeOOH phase due to the oxidation of Fe3O4. As a result of the work, a methodological scheme for the analysis of iron oxide and oxyhydroxide ANPs was developed.

Magnetic Systems for Regenerative Medicine

Magnetic Systems for Regenerative Medicine

Site-Selective Assembly of Centimeter-Scale Arrays of Precisely Oriented Magnetic Nanoellipsoids.

The precise organization and orientation of anisotropic nanoparticles (NPs) on substrates over a large area is key to the application of NP assemblies in functional optical, electronic, and magnetic devices, but achieving such high-precision NP assembly still remains challenging. Here, we demonstrate the site-selective assembly of magnetic nanoellipsoids into large-area precisely positioned, orientationally controlled arrays via a combination of chemical patterning and magnetic manipulation. Magnetic ellipsoidal NPs are selectively positioned on predetermined chemical patterns with high fidelity through electrostatic interactions and aligned uniformly in line with an applied magnetic field. The position, orientation, and interparticle spacing of the ellipsoids can be precisely tuned by controlling the chemical patterns and magnetic field. This approach is simple to implement and can generate centimeter-scale arrays in high yield (up to 99%). The arrays exhibit collective magnetic responses that are dependent on the orientation of the ellipsoids. This work offers a tool for the fabrication of precisely engineered arrays of anisotropic NPs for applications such as metasurface and artificial spin ice.

Directional growth of quasi-2D Cu2O monocrystals on rGO membranes in aqueous environments.

The preparation technology of unconventional low-dimensional Cu2O monocrystals, which exhibit specific crystal planes and present significantly unique interfacial and physicochemical properties, is attracting increasing attention and interest. Herein, by integrating a high-temperature oxidation process under vacuum and a pure-water incubation process under ambient conditions, we propose the self-assembled growth and synthesis of quasi-two-dimensional Cu2O monocrystals on reduced graphene oxide (rGO) membranes. The prepared Cu2O crystals have a single (110) crystal plane, regular rectangular morphology, and potentially well conductivity. Experimental and theoretical results suggest that this assembly is attributed to the pre-nucleation clusters aggregation and directional attachment of Cu and O on the rGO membranes in aqueous environment and cation-π interactions between the (110) crystal plane of Cu2O and rGO surface. Our findings offer a potential avenue for the discovery and design of advanced low-dimensional single-crystal materials with specific interfacial properties in a pure aqueous environment.

Gold Nanostar Characterization by Nanoparticle Tracking Analysis.

We demonstrate the application of nanoparticle tracking analysis (NTA) for the quantitative characterization of gold nanostars (GNSs). GNSs were synthesized by the seed-mediated growth method using triblock copolymer (TBP) gold nanoparticles (GNPs). These GNPs (≈ 10 nm) were synthesized from Au3+ (≈ 1 mM) in aqueous F127 (w/v 5%) containing the co-reductant ascorbic acid (≈ 2 mM). The GNS tip-to-core aspect ratio (AR) decreased when higher concentrations of GNPs were added to the growth solution. The AR dependency of GNSs on Au3+/Au(seed) concentration ratio implies that growth is partly under kinetic control. NTA measured GNS sizes, concentrations, and relative scattering intensities. Molar absorption coefficients ∼ 109-1010 M-1 cm-1 (ε400nm) for each batch of GNSs were determined using the combination of extinction spectra and NTA concentrations for heterogeneous samples. NTA in combination with UV-vis was used to derive the linear relationships: (1) hydrodynamic size versus localized surface plasmon peak maxima; (2) ε400nm versus localized surface plasmon peak maxima; (3) ε400nm versus hydrodynamic size. NTA for quantitative characterization of anisotropic nanoparticles could lead to future applications, including heterogeneous colloidal catalysis.

DNA Nanostructure-Guided Plasmon Coupling Architectures

DNA Nanostructure-Guided Plasmon Coupling Architectures

Unraveling the Seedless Growth of Gold Nanostars through Fractional Factorial Design

Gold nanostars (AuNSs) are anisotropic nanoparticles that display morphology-tunable optical properties. Most AuNS synthetic methods require a two-step procedure and the use of cytotoxic and/or strongly bound surfactants, which complicate biomedical application. The seedless synthesis of AuNSs overcomes those limitations by using biocompatible Good’s buffers, such as HEPES, as reducing and stabilizing agents. However, the simplicity of this one-pot protocol (i.e., two reagents and one solution) can result in high batch-to-batch variability, as several factors are thought to affect the growth of the nanostars. In this paper, we used a fractional factorial design of experiments to identify five factors (i.e., HEPES concentration, Au3+ concentration, temperature, pH, and stirring) that control the growth, morphology, and optical properties of AuNSs. Notably, we identified several secondary interactions, most prominently, temperature–Au3+ concentration and pH–HEPES concentration, for which simultaneous changes of both factors induced larger effects than the sum of effects of each factor alone. These results provide new insights into the growth of AuNSs, explaining some of the discrepancies in the literature regarding the impact of certain factors and highlighting the importance of characterizing secondary interaction effects to improve the synthesis of gold nanoparticles with desired properties.

Concave gold nano-arrows (AuCNAs) for efficient catalytic reduction of 4-nitrophenol

Anisotropic gold nanostructures have attracted great attention in different fields including catalysis. Thermodynamically driven selective surface growth offers a reliable and reproducible method for anisotropic gold nanoparticle synthesis with specific morphologies. Herein, monocrystalline concave gold nano-arrows (AuCNAs) are prepared by the over-growth method using Au nanorods (AuNRs) as seeds. The as-prepared AuCNAs consist of a biconical head and four concave structures. Interestingly, silver ions (Ag+) concentration significantly affects the product morphology by tuning the peak positions of surface plasmon resonance (SPR), aspect ratio, arrow, and concave morphology of AuCNAs. The position of longitudinal SPR peaks is observed at 810, 805 and 782 nm at [Ag+]/[Au3+] molar ratios of 1:2, 1:1, and 2:1, respectively. Diameters and lengths of AuCNAs varied from 25 nm to 36 nm; 104 nm, 78 nm, and 120 nm, respectively. Additionally, the AuCNAs are applied for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in presence of excess NaBH4. Compared to gold nanorods (AuNRs), the prepared AuCNAs catalyst shows excellent catalytic activity, demonstrating that concave structures and sharp corners significantly enhance the catalytic activity. The value of pseudo-first-order reaction kinetic constants (kapp) increased from 0.0051 to 0.0195 s−1 with increasing catalyst valume from 7.5 to 37.5 μL. The highest normalized reaction rate constant (Knor) and turnover frequency (TOF) reach 5.84 × 104 min−1 mmol−1 and 443.47 h−1, respectively, at [Ag+]/[Au3+] ratio of 1:1 in AuCNAs catalyst. This study expands catalytic applications of anisotropic gold nanostructures and widens their potential application areas, such as surface plasmon exciton photonics, biomedical photonics, and photocatalysis.

Hybrid polymeric therapeutic microcarriers for thermoplasmonic-triggered release of resveratrol

Diabetic retinopathy (DR) is a severe ocular complication that causes retinal damage, being one of the leading causes of blindness globally, thus the development of new strategies to prevent and treat DR as well as other degenerative diseases is highly desired. This work is focused on the design and fabrication of an ingenious model of polymeric microcapsules (MC) for controlled drug delivery in human retina cells able to carry therapeutic resveratrol (RSV) molecules in tandem with active anisotropic gold bipyramidal nanoparticles (AuBPs) as efficient photothermal agents. Specifically, MC were developed via a Layer-by-Layer deposition technique, by successively adding oppositely charged polyelectrolytes on a RSV-conjugated calcium carbonate (CaCO3) core. For the monitorization and localization of the as-formed spherical fluorescent MC inside human retina pigmented epithelial (RPE) D407 cells, fluorescein isothiocyanate, a Food and Drug Administration approved fluorophore, was attached between the polyelectrolytes layers. High-performance liquid chromatography analysis revealed a loading efficiency of over 90% of RSV on the CaCO3 core and demonstrates its release upon NIR irradiation as a consequence of the thermoplasmonic effect of MC. The cytotoxicity of the RSV-carrying MC inside human retina cells was assessed by WST-1 assay. Finally, cellular internalization and localization of the MC inside living RPE cells were monitored via Conventional Fluorescence and Re-Scanning Confocal Fluorescence Microscopy. This research seeks to take use of the novel MC and implement them as potential intraocular RSV delivery vehicles for the therapy of DR.

Exploitation of N-Gene of SARS-CoV-2 to Develop a New Rapid Assay by ASOs@AuNPs.

A naked-eye (equipment-free), label-free (cost-effective), and RNA extraction-free (to speed up) method for SARS-CoV-2 (as a case study of RNA viruses) detection is developed. Here, the DNA is being used as a template for in situ formation of anisotropic gold nanoparticles (AuNPs) without any chemical modification or DNA labeling. In this study, synthesized AuNPs for the direct detection of N-gene (nucleocapsid phosphoprotein) of SARS-CoV-2 are exploited. To this aim, antisense oligonucleotides (ASOs) with an extra poly guanine tail (G12) were designed. Thus, in the presence of its viral target RNA gene and ASOs@AuNPs-RNA hybridization, there was a red shift in its localized surface plasmon resonance (LSPR), and the intensity of the LSPR peak at 690 nm of throat swab samples was compared to the threshold cycle (Ct) of a reverse-transcriptase real-time polymerase chain reaction (RT-qPCR) (as a gold standard). Results suggested that the plasmonic biosensor can detect a very low amount of SARS-CoV-2 with a detection limit close to RT-qPCR. Simplicity of the new conjugation method with hybridization and annealing without amplification and denaturation steps enabled it to perform in a microfluidic paper-based analytical device.

Investigating Adsorption of Cellulose Nanocrystals at Air–Liquid and Solid–Liquid Interfaces in the Presence of Hydrotropes

AbstractCoating a substrate with anisotropic nanoparticles such as cellulose nanocrystals (CNCs) confers some of their desirable physicochemical properties, such as strength, wettability, and barrier properties. The formation of monolayer coatings of CNCs via dip coating is affected by the enrichment of CNCs at both air–liquid and substrate–liquid interfaces. In this work, a surfactant‐free method for dip coating CNCs is presented through use of the hydrotrope tetraethylammonium chloride. Hydrotropes demonstrate a different mechanism for facilitating interfacial enrichment, adsorbing to CNCs and rendering them weakly hydrophobic, causing them to adsorb to both solid–liquid and air–liquid interfaces without affecting the surface tension of the system. This new coating mechanism may be more robust as adsorption onto the substrate from the bulk dispersion is less sensitive to the air–liquid interface. Adsorption at the solid–liquid interface showed two distinct CNC layers, with a tightly bound, close‐packed CNC layer at the interface, and a loosely associated outer layer. Adsorption of both layers is shown to be fully reversible after washing with ultra pure water, highlighting the potential of hydrotropes for facilitating new coating mechanisms.

Tuning the thermodynamic, optical, and rheological properties of thermoresponsive polymer solutions via silica nanoparticle shape and concentration

HypothesisThe shape and quantity of hydrophilic silica nanoparticles (NPs) can be used to tune the microstructure, rheology, and stability of phase-separating polymer solutions. In thermoresponsive polymer systems, silica nanospheres are well-studied whereas anisotropic NPs have little literature precedent. Here, we hypothesize that NP shape and concentration lower the onset of rheological and turbidimetric transitions of aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions. ExperimentsDifferential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), turbidimetry, and oscillatory rheology are utilized to examine interactions between NPs, PNIPAM, and water and to track changes in phase separation and rheological properties due to NP concentration and shape. FindingsNP addition reduces phase separation enthalpy due to PNIPAM-NP hydrogen bonding interactions, the degree to which depends on polymer content. While NP addition minorly impacts thermodynamic and optical properties, rheological transitions and associated rheological properties are dramatically altered with increasing temperature, and depend on NP quantity, shape, and polymer molecular weight. Thus NP content and shape can be used to finely tune transition temperatures and mechanical properties for applications in stimuli-responsive materials.

TiB2 derived nanosheets co-immobilized with triangular gold nanoparticles elicit fast and stable photocatalytic hydrogen evolution

Transition metal diborides are recently being revisited from the viewpoint of yielding 2D nanostructures owing to their layered topology and the inherent presence of boron honeycomb planes. In this report, we show that nanosheets derived from titanium diboride (TiB2), when co-immobilized with anisotropic gold nanoparticles, demonstrate an impressive photocatalytic behavior towards hydrogen evolution. We found that this novel nano construct could achieve H2 evolution rates of up to 1.13 mmol g−1h−1 at neutral pH and simulated light irradiation. This production rate is significant considering the fact that we neither employed any co-catalyst or electron/hole scavenging chemical species nor applied any external bias. In addition, the catalyst could continuously produce H2 for at least 30 h. We also found that the construct was active under direct sunlight exposure. The co-immobilized construct also showed photocatalytic activity under UV and NIR irradiations. This is the first report wherein TiB2 derived nanosheets have been employed towards catalyzing the HER. We attribute the mechanism of photocatalytic H2 evolution to either better electron/hole pair separation or direct electron transfer from the photosensitive gold nanoparticles to the nanosheets (through the formation of a Schottky barrier). This report showcases the rich potential of functionalized metal diboride nanosheets and their constructs for next-generation photocatalysts.

Anisotropic CdSe Tetrapods in Vortex Flow for Removing Non-Specific Binding and Increasing Protein Capture.

Non-specific binding (NSB) is one of the important issues in biosensing performance. Herein, we designed a strategy for removing non-specific binding including anti-mouse IgG antibody and bovine serum albumin (BSA) by utilizing anisotropic cadmium selenide tetrapods (CdSe TPs) in a vortex flow. The shear force on the tetrapod nanoparticles was increased by controlling the rotation rate of the vortex flow from 0 rpm to 1000 rpm. As a result, photoluminescence (PL) signals of fluorescein (FITC)-conjugated protein, anti-mouse IgG antibody-FITC and bovine serum albumin (BSA)-FITC, were reduced by 35% and 45%, respectively, indicating that NSB can be removed under vortex flow. In particular, simultaneous NSB removal and protein capture can be achieved even with mixture solutions of target antibodies and anti-mouse IgG antibodies by applying cyclic mode vortex flow on anisotropic CdSe TPs. These results demonstrate successfully that NSB can be diminished by rotating CdSe TPs to generate shear force under vortex flow. This study opens up new research protocols for utilization of anisotropic nanoparticles under vortex flow, which increases the feasibility of protein capture and non-specific proteins removal for biosensors.

High-Throughput Sizing, Counting, and Elemental Analysis of Anisotropic Multimetallic Nanoparticles with Single-Particle Inductively Coupled Plasma Mass Spectrometry.

Nanoparticles (NPs) have wide applications in physical and chemical processes, and their individual properties (e.g., shape, size, and composition) and ensemble properties (e.g., distribution and homogeneity) can significantly affect the performance. However, the extrapolation of information from a single particle to the ensemble remains a challenge due to the lack of suitable techniques. Herein, we report a high-throughput single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS)-based protocol to simultaneously determine the size, count, and elemental makeup of several thousands of (an)isotropic NPs independent of composition, size, shape, and dispersing medium with atomistic precision in a matter of minutes. By introducing highly diluted nebulized aqueous dispersions of NPs directly into the plasma torch of an ICP-MS instrument, individual NPs are atomized and ionized, resulting in ion plumes that can be registered by the mass analyzer. Our proposed protocol includes a phase transfer step for NPs synthesized in organic media, which are otherwise incompatible with ICP-MS instruments, and a modeling tool that extends the measurement of particle morphologies beyond spherical to include cubes, truncated octahedra, and tetrahedra, exemplified by anisotropic Cu NPs. Finally, we demonstrate the versatility of our method by studying the doping of bulk-dilute (<1 at. %) CuAg nanosurface alloys as well as the ease with which ensemble composition distributions of multimetallic NPs (i.e., CuPd and CuPdAg) can be obtained providing different insights in the chemistry of nanomaterials. We believe our combined protocol could deepen the understanding of macroscopic phenomena involving nanoscale structures by bringing about a statistics renaissance in research areas including, among others, materials science, materials chemistry, (nano)physics, (nano)photonics, catalysis, and electrochemistry.

Global Dynamics of a Protein on the Surface of Anisotropic Lipid Nanoparticles Derived from Relaxation-Based NMR Spectroscopy.

The global motions of ubiquitin, a model protein, on the surface of anisotropically tumbling 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG):1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) bicelles are described. The shapes of POPG:DHPC bicelles prepared with high molar ratios q of POPG to DHPC can be approximated by prolate ellipsoids, with the ratio of ellipsoid dimensions and dimensions themselves increasing with higher values of q. Adaptation of the nuclear magnetic resonance (NMR) relaxation-based approach that we previously developed for interactions of ubiquitin with spherical POPG liposomes (Ceccon, A. J. Am. Chem. Soc. 2016, 138, 5789-5792) allowed us to quantitatively analyze the variation in lifetime line broadening of NMR signals (ΔR2) measured for ubiquitin in the presence of q = 2 POPG:DHPC bicelles and the associated transverse spin relaxation rates (R2,B) of bicelle-bound ubiquitin. Ubiquitin, transiently bound to POPG:DHPC bicelles, undergoes internal rotation about an axis orthogonal to the surface of the bicelle and perpendicular to the principal axis of its rotational diffusion tensor on the low microsecond time scale (∼3 μs), while the rotation axis itself wobbles in a cone on a submicrosecond time scale (≤ 500 ns).