Thin Silica Shell Research Articles

Controlling Silicification on DNA Origami with Polynucleotide Brushes.

DNA origami has been used as biotemplates for growing a range of inorganic materials to create novel organic-inorganic hybrid nanomaterials. Recently, the solution-based silicification of DNA has been used to grow thin silica shells on DNA origami. However, the silicification reaction is sensitive to the reaction conditions and often results in uncontrolled DNA origami aggregation, especially when growth of thicker silica layers is desired. Here, we investigated how site-specifically placed polynucleotide brushes influence the silicification of DNA origami. Our experiments showed that long DNA brushes, in the form of single- or double-stranded DNA, significantly suppress the aggregation of DNA origami during the silicification process. Furthermore, we found that double-stranded DNA brushes selectively promote silica growth on DNA origami surfaces. These observations were supported and explained by coarse-grained molecular dynamics simulations. This work provides new insights into our understanding of the silicification process on DNA and provides a powerful toolset for the development of novel DNA-based organic-inorganic nanomaterials.

Soccer Ball‐like Assembly of Edge‐to‐edge Oriented 2D‐silica Nanosheets: A Promising Catalyst Support for High‐Temperature Reforming

AbstractControlled assembly of nanoparticles into well‐defined assembled architectures through precise manipulation of spatial arrangement and interactions allows the development of advanced mesoscale materials with tailored structures, hierarchical functionalities, and enhanced properties. Despite remarkable advancements, the controlled assembly of highly anisotropic 2Dnanosheets is significantly challenging, primarily due to the limited availability of selective edge‐to‐edge connectivity compared to the abundant large faces. Innovative strategies are needed to unlock the full potential of 2D‐nanomaterialsin self‐assembled structures with distinct and desirable properties. This research unveils the discovery of controlled self‐assembly of 2D‐silica nanosheets (2D‐SiNSs) into hollow micron‐sized soccer ball‐like shells (SA‐SiMS). The assembly is driven by the physical flexibility of the 2D‐SiNSs and the differential electricdouble‐layer charge gradient creating electrostatic bias on the edge and face regions. The resulting SA‐SiMS structures exhibit high mechanical stability, even at high‐temperatures, and exhibit excellent performance as catalyst support in the dry reforming of methane. The SA‐SiMS structures facilitate improved mass transport, leading to enhanced reaction rates, while the thin silica shell prevents sintering of small catalyst nanocrystals, thereby preventing coke formation. This discovery sheds light on the controllable self‐assembly of 2D nanomaterials and provides insights into the design and synthesis of advanced mesoscale materials with tailored properties.

Soccer Ball-like Assembly of Edge-to-edge Oriented 2D-silica Nanosheets: A Promising Catalyst Support for High-Temperature Reforming.

Controlled assembly of nanoparticles into well-defined assembled architectures through precise manipulation of spatial arrangement and interactions allows the development of advanced mesoscale materials with tailored structures, hierarchical functionalities, and enhanced properties. Despite remarkable advancements, the controlled assembly of highly anisotropic 2Dnanosheets is significantly challenging, primarily due to the limited availability of selective edge-to-edge connectivity compared to the abundant large faces. Innovative strategies are needed to unlock the full potential of 2D-nanomaterialsin self-assembled structures with distinct and desirable properties. This research unveils the discovery of controlled self-assembly of 2D-silica nanosheets (2D-SiNSs) into hollow micron-sized soccer ball-like shells (SA-SiMS). The assembly is driven by the physical flexibility of the 2D-SiNSs and the differential electricdouble-layer charge gradient creating electrostatic bias on the edge and face regions. The resulting SA-SiMS structures exhibit high mechanical stability, even at high-temperatures, and exhibit excellent performance as catalyst support in the dry reforming of methane. The SA-SiMS structures facilitate improved mass transport, leading to enhanced reaction rates, while the thin silica shell prevents sintering of small catalyst nanocrystals, thereby preventing coke formation. This discovery sheds light on the controllable self-assembly of 2D nanomaterials and provides insights into the design and synthesis of advanced mesoscale materials with tailored properties.

Magnetic particle spectroscopy and magnetic particle imaging of zinc and cobalt ferrite nanoparticles: Distinct relaxation mechanisms

Magnetic particle imaging (MPI) is an emerging imaging method based on the nonlinear response of superparamagnetic tracers to a sinusoidal AC magnetic field. Higher harmonics obtained by the Fourier transform of acquired signals form a so-called magnetic particle spectrum, whereby straightforward evaluation of different nanoparticles as potential MPI tracers can be carried out. The shape of the spectra is largely dictated by the combined Néel and Brownian relaxation of superspins, whose relative contributions vary significantly depending on the tracer properties. The present study is focused on the comparison of several Zn ferrite and Co ferrite samples, selected for their different magnetic behaviors, together with the commercial tracer Resovist® (SH U 555 A). A new custom-made magnetic particle spectrometer and a commercial MPI system (Bruker) with comparable AC field amplitudes (∼14 mT) and frequencies (∼25 kHz) are used. Magnetic nanoparticles of Zn and Co ferrites have been synthesized by the thermal decomposition method and by the solvothermal/hydrothermal route, achieving four different samples of magnetic cores with the mean crystallite size in the range of 8–16 nm. From all of them, well-comparable silica-coated particles with a shell thickness of 5–6 nm have been prepared. To analyse the effect of the coating layer and hydrodynamic size, three additional samples have been supplemented: solvothermal Zn ferrite nanoparticles stabilized with a citrate monolayer, the same particles coated with 17 nm thick silica shell, and silica-coated Zn ferrite particles from the thermal decomposition with a higher degree of agglomeration. Fundamental characterizations of the nanomaterials by XRD, XRF, TEM, and DLS are followed by detailed investigations of their magnetic properties and structural peculiarities by SQUID magnetometry and 57Fe Mössbauer spectroscopy. Magnetic particle spectroscopy and subsequent MPI study demonstrate: (i) superior properties of Zn ferrite nanoparticles compared to their Co ferrite counterparts, (ii) only negligible to weak effect of the type/thickness of the coating on signal of Zn ferrite nanoparticles, (iii) comparable performance of the solvothermal Zn ferrite particles with a thin silica shell and of the Resovist® tracer, and importantly, (iv) that suitable choice of the magnetic phase enables to separate the contributions of the Néel and Brownian relaxation on the timescale of MPI.

Slippery Au Nanosphere Monolayers with Analyte Enrichment and SERS Enhancement Functions.

Slippery surfaces can enrich analytes from solutions into tiny dots after solvent evaporation for surface-enhanced Raman scattering (SERS) detection. Here, we make the self-assembled Au nanosphere monolayers slippery, which can not only behave as SERS substrates but also enrich the analytes during solvent evaporation. A thin silica shell was used to wrap the Au nanosphere monolayer to allow the functionalization of a slippery polydimethylsiloxane brush monolayer onto it. These slippery Au nanosphere monolayers could be easily cleaned and reused many times. When Au nanospheres were introduced into the analyte solution droplet on the slippery Au nanosphere monolayer, a 3D Au nanoparticle/analyte aggregate was formed after solvent evaporation. Both the Au nanoparticle aggregate and the underneath slippery Au nanosphere monolayer could contribute to SERS enhancement. We endow the self-assembled Au nanosphere monolayer SERS substrates with an analyte enrichment function, greatly strengthening their SERS enhancement.

One-Shot Laser-Pulse Modification of Bare and Silica-Coated Gold Nanoparticles of Various Morphologies.

Gold nanoparticles are widely used in laser biomedical applications due to their favorable properties, mainly localized plasmon resonance. However, laser radiation can cause a change in the shape and size of plasmonic nanoparticles, thus resulting in an unwanted reduction of their photothermal and photodynamic efficiency due to a drastic alteration of optical properties. Most previously reported experiments were carried out with bulk colloids where different particles were irradiated by different numbers of laser pulses, thus making it difficult to accurately evaluate the laser power photomodification (PM) threshold. Here, we examine the one-shot nanosecond laser-pulse PM of bare and silica-coated gold nanoparticles moving in a capillary flow. Four types of gold nanoparticles, including nanostars, nanoantennas, nanorods, and SiO2@Au nanoshells, were fabricated for PM experiments. To evaluate the changes in the particle morphology under laser irradiation, we combine measurements of extinction spectra with electron microscopy. A quantitative spectral approach is developed to characterize the laser power PM threshold in terms of normalized extinction parameters. The experimentally determined PM threshold increases in series were as follows: nanorods, nanoantennas, nanoshells, and nanostars. An important observation is that even a thin silica shell significantly increases the photostability of gold nanorods. The developed methods and reported findings can be useful for the optimal design of plasmonic particles and laser irradiation parameters in various biomedical applications of functionalized hybrid nanostructures.

Thin silica shell on Ag3PO4 nanoparticles augments stability and photocatalytic reusability.

Semiconductor photocatalysts are promising cost-effective materials for degrading hazardous organic contaminants in water. Ag3PO4 is an efficient visible-light photocatalyst for the oxidation of water and dye degradation. The excited Ag3PO4 photocatalyst uses a hole to oxidise water or organic contaminants except the electron, which reduces Ag+ to Ag0. In the present study, the inherited disadvantage was overcome by a thin silica shell overcoating on Ag3PO4 nanoparticles. The silica-coated Ag3PO4 nanoparticles retain the photocatalytic activity even after five cycles of photodegradation, while the bare Ag3PO4 nanoparticles show a photocatalytic activity declined to half. The study demonstrates that the thin silica shell enhances the photostability, keeping the photocatalytic activity unaffected, even after several cycles of photodegradation of dyes. XPS analysis showed that the Ag0 formation on the surface of bare Ag3PO4 is greater than that on silica-coated Ag3PO4, which declines the photocatalytic activity of Ag3PO4 after five cycles of photodegradation. Electrochemical studies identified that the intermediates, such as OH˙ and O2-, formed during water oxidation play a crucial role in the photodegradation of dyes. This study can provide insights into the design of core-shell semiconductor nanostructures for reusable photocatalytic applications.

Amikacin@SiO2 core@shell nanocarriers to treat pulmonal bacterial infections.

AMC@SiO2 core@shell nanocarriers (AMC: amikacin) are realized and contain an exceptionally high drug load of 0.8 mg mg-1 (i.e. 80% AMC of total nanocarrier mass). They are prepared via a solvent-antisolvent approach with AMC nanoparticles formed in a first step, which are then covered and stabilised by a thin silica shell in a one-pot synthesis. In total, the core@shell nanocarriers exhibit a mean diameter of 240 nm with an inner AMC core of 200 nm and an outer silica shell of 20 nm. Subsequent to synthesis, the nanocarriers can be stored in frozen dimethylsulfoxide (DMSO) and applied directly after warming to room temperature with particle contents of 5 mg mL-1. Size, structure, and composition of the AMC@SiO2 core@shell nanocarriers are evidenced by electron microscopy (SEM, TEM), spectroscopic methods (EDXS, FT-IR, UV-Vis), as well as X-ray powder diffraction and elemental analysis. As proof-of-concept, the AMC release and the activity of the novel nanocarriers are tested against two relevant, difficult-to-treat and notoriously multidrug resistant, bacterial pathogens: Mycobacterium tuberculosis (M.tb.) and Mycobacterium abscessus (M.abs.). Colloidal stability, storage stability, high drug load, and activity of the AMC@SiO2 core@shell nanocarriers are promising for, e.g., aerosol-type pulmonal application.

Black coating of quartz sand towards low-cost solar-absorbing and thermal energy storage material for concentrating solar power

Solid particles based direct solar absorbing heat transfer fluid (HTF) and thermal energy storage (TES) material is gaining increasing interests for high-temperature concentrating solar power (CSP). However, there is no particulate material that simultaneously possesses the performance and cost metrics needed to achieve the target levelized cost of electricity of future CSP, including high solar absorptance, high thermal conductivity, good mechanical and thermal stability, and importantly, low cost. In this work, we demonstrate a facile and scalable method to turn low-cost quartz sand into a direct solar-absorbing HTF and TES material by coating a thin silica shell containing black spinel nanoparticles (Cu0.5Cr1.1Mn1.4O4and CuCr2O4). The black coating increases the solar absorptances of the sand from ∼0.43 to ∼0.89. The coated quartz sand also shows excellent stability and nearly unchanged optical properties after 100-hr of isothermal annealing at 800 °C and up to 24-hr ball mixing with Yttria Stabilized Zirconia (YSZ) grinding balls. The measured effective thermal conductivity of the coated quartz sand increases 0.30 W m−1 K−1 to 0.65 W m−1 K−1 from 20 °C to 700 °C and is comparable to that of uncoated sand as well as Carbo ceramic particle beds currently used in CSP plants. The coating process could represent a cost-effective and generic strategy to enhance the solar absorptance of solid particles, and when applied on low-cost sand, could turn them into low-cost and high-performance HTF and TES media for future CSP systems.

An emulsion swelling route to surface-wrinkled polystyrene-silica colloidal nanocomposite particles

There is increasing interest in the fabrication of surface-wrinkled colloidal particles. This paper reports a facile emulsion swelling route to prepare surface-wrinkled polymer-silica core-shell nanocomposite particles. Submicrometer-sized polystyrene-silica (PS–SiO 2 ) nanocomposite particles were first prepared by emulsion polymerization of styrene using glycerol-functionalized ultrafine aqueous silica sols, and then surface-wrinkled PS−SiO 2 particles were obtained by swelling the PS−SiO 2 particles with a toluene/water emulsion and subsequent drying. The key to success is simply the use of the PS-SiO 2 core-shell nanocomposite particles prepared by emulsion polymerization, in which the SiO 2 shell was composed of individual and discrete ultrafine SiO 2 sols. The influence of various swelling parameters including toluene/particle ratio, surfactant concentration, swelling temperature and swelling time on the formation of the wrinkled nanocomposite particles was studied. Furthermore, hollow wrinkled silica thin shells composed of silica nanoparticles could be obtained by calcination of the wrinkled nanocomposite particles. This method represents a new paradigm in the preparation of surface-wrinkled polymer colloids. This paper reports a facile route to prepare surface-wrinkled polymer-silica nanocomposite particles with a thin silica shell through the judicious combination of emulsion polymerization and emulsion swelling. • A facile emulsion swelling route to prepare surface-wrinkled polymer-silica core-shell nanocomposite particles is reported. • The protocol involves judicious combination of emulsion polymerization and emulsion swelling. • Hollow wrinkled silica thin shells composed of silica nanoparticles could be obtained by calcination. • This method represents a new paradigm in the preparation of surface-wrinkled polymer colloids.

Electron-phonon effects on the photoacoustic response of gold core-silica shell nanoparticles: From the linear regime to nanocavitation.

Coating gold nanostructures with a silica shell has been long considered for biomedical applications, including photoacoustic imaging. Recent experimental and modeling investigations reported contradicting results concerning the effect of coating on the photoacoustic response of gold nanostructures. Enhanced photoacoustic response is generally attributed to facilitated heat transfer at the gold/silica/water system. Here, we examine the photoacoustic response of gold core-silica shell nanoparticles immersed in water using a combination of the two temperature model and hydrodynamic phase field simulations. Here, of particular interest is the role of the interfacial coupling between the gold electrons and silica shell phonons. We demonstrate that as compared to uncoated nanoparticles, photoacoustic response is enhanced for very thin silica shells (5nm) and short laser pulses, but for thicker coatings, the photoacoustic performance are generally deteriorated. We extend the study to the regime of nanocavitation and show that the generation of nanobubbles may also play a role in the enhanced acoustic response of core-shell nanoparticles. Our modeling effort may serve as guides for the optimization of the photoacoustic response of heterogeneous metal-dielectric nanoparticles.

Egg-yolk core-shell mesoporous silica nanoparticles for high doxorubicin loading and delivery to prostate cancer cells.

Mesoporous silica-based nanoparticles (MSNs) have gained rapid interest as a drug delivery system (DDS) and demonstrated their versatility in delivering drugs for the treatment of various cancers. However, the drug loading efficiency of MSNs is low and is usually improved by improving textural properties through complicated synthesis methods or by post synthesis modification of the surface that can result in the loss of surface area and modify its drug release properties. In this study, we report a direct single-step synthesis of MSNs with a unique egg-yolk core-shell morphology, large pore volume and a hydrophilic surface, decorated with nitrogen rich surface functionalities for increasing its drug loading capacity. This combination of excellent textural properties and surface functionalisation was achieved by a simple soft templating method using dual surfactants and the silica sources assisted by employing either triethylamine (TEA) or triethanolamine (TEO) as the hydrolysis agent. The morphology and well-ordered mesoporous structure can simply be tuned by changing the pH of the synthesis medium that affects the self-assembly mechanism of the micelles. HRTEM image of samples clearly revealed an egg-yolk core-shell morphology with a thin mesoporous silica shell. The optimised MSN samples synthesized at a pH of 11 using either TEA or TEO depicted a higher doxorubicin (Dox) loading capacity of 425 μg mg-1 and 481 μg mg-1 respectively, as compared to only 347 μg mg-1 for MSN samples due to the uniform distribution of nitrogen functionalities. The anticancer activity of Dox loaded MSNs evaluated in two different prostate cancer cell lines (PC-3 and LNCaP) showed a higher cytotoxicity of the drug loaded on optimised MSN samples as compared to pristine MSNs without affecting the cellular uptake of the particles. These results suggest that the unique single-step synthesis and functionalisation method resulted in successfully achieving higher drug loading in egg-yolk core-shell nitrogen functionalised MSNs and could be implemented as an effective carrier of chemotherapeutic drugs.

Preparation and fluorescence characterization of monodisperse core-shell structure SiO2 @SiO2 :Tb(1,2-BDC)3 phen microspheres by a sol-seed method.

The SiO2 @SiO2 :Tb(1,2-BDC)3 phen microspheres with monodispersed core-shell structure, are kind of fluorescent particles, which are prepared by a seeded growth method under the catalysis of glacial acetic acid (1,2-BDC,1,2-benzenedicarboxylic acid; phen,1,10-phenanthroline). Firstly, silica seed was fabricated by the hydrolysis of ethyl orthosilicate, and the Tb(1,2-BDC)3 phen was prepared by using 1,2-BDC and phen. Then, a thin mesoporous silica shell doped with Tb(1,2-BDC)3 phen was grown on the prepared monodisperse silica colloids. The prepared phosphor was analyzed by Fourier-transform infrared spectroscopy, X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, thermogravimetric and fluorescence spectroscopy. The experimental results showed that the diameter of the SiO2 @SiO2 :Tb((1,2-BDC)3 phen microsphere was about 200 nm with a typical core-shell structure, among which the diameter of the silica core was 180 nm, and that of the mesoporous silicon shell doped with terbium complex was about 10nm. The fluorescence intensity of SiO2 @SiO2 :Tb((1,2-BDC)3 phen microsphere is nearly three times higher than that of Tb((1,2-BDC)3 phen complexes. The prepared microspheres could be widely used in bio-imaging, optoelectronic appliances and medical diagnosis.

A Silica Coating Approach to Enhance Bioconjugation on Metal-Encoded Polystyrene Microbeads for Bead-Based Assays in Mass Cytometry.

Bead-based assays in flow cytometry are multiplexed analytical techniques that allow rapid and simultaneous detection and quantification of a large number of analytes from small volumes of samples. The development of corresponding bead-based assays in mass cytometry (MC) is highly desirable since it could increase the number of analytes detected in a single assay. The microbeads for these assays have to be labeled with metal isotopes for MC detection. One must also be able to functionalize the bead surface with affinity reagents to capture the analytes. Metal-encoded polystyrene microbeads prepared by multi-stage dispersion polymerization can produce effective isotopic signals in MC with relatively small bead-to-bead variations. However, functionalizing this microbead surface with bioaffinity agents remains challenging, possibly due to the interference of the steric-stabilizing PVP corona on the microbead surface. Here, we report a systematic investigation of a silica coating approach to coat Eu-encoded microbeads with thin silica shells, to functionalize the surface with amino groups, and to introduce bioaffinity agents. We examine the effect of silica shell roughness on the bioconjugation capacity and the effect of silica shell thickness on signal quality in MC measurements. To limit non-specific binding, we converted the amino groups on the microbead surface to carboxylic acid groups. Antibodies were effectively attached to microbead by first conjugating NeutrAvidin to the carboxyl-modified bead surface and then attaching biotinylated antibodies to the NeutrAvidin-modified bead surface. The antibody-modified microbeads can specifically capture antigens, which were marked with isotopic labels, and generate strong signals in MC. These are promising results for the development of bead-based assays in MC.

Highly Sensitive Detection and Rapid Removal of Picric Acid Using Fe2O3-CdSe Nanocomposite As Fluorescent Probe

Detection of the nitro-fragrant compound at trace level is critical in combating terrorism, for keeping up homeland security, accompanying environmental and clinical safety. Among various nitroaromatics compounds (NACs), the importance of picric acid (PA), also known as 2,4,6-Trinitrophenol (TNP), due to its extensive usage in the production of deadly explosives, fireworks, rocket fuels, leather processing and sensitizers in photographic emulsions. Moreover, it is an odorless, colorless pale yellow solid which profoundly contaminant to soil due to high solvency in an aqueous medium, ends up in adverse effects. The ecological contamination caused by this results in respiratory problems, intense irritation to the skin and eyes, high doses may cause prospective harms in organs and causes cancer, sensitization, destruction, kidney damage, acute hepatitis and diarrhea, etc.[1] The metabolism of these explosive nitro-aromatic compounds end up in generation of reactive nitrogen oxide species, that promptly react with biological macromolecules and cause formation of potent genotoxic and mutagenic metabolites.[2] Therefore, detection and quantitative estimation of those hazardous chemicals are highly indispensable.In the past, there are a number of reports on multifunctional sensors for the detection of NACs, given the appreciable sensitivity and selectivity. As of now, many fluorescence chemosensors/probes have been effectively applied for the detection of PA with functional specificity based on its characteristic properties, particularly resonance energy transfer and electron-deficient nature of the nitro group (-NO2), yet only a few appeared closer to the practical applications.[3] Recent reports on nanoparticle and quantum dot (QD) probes exhibited remarkable chemosensory response towards NACs compared with the conventional organic small molecules, polymers and metal-organic frameworks (MOFs) because of their unique optical properties and thanks to the confinement of electronic states of quantum dots.[4] Recently, thiols capped semiconductor NPs, synthesize through water treatment, has given a fascinating and alternate methodology to synthesize semiconductor NPs. Among these, CdSe nanoparticles are the extensively examined semiconductor NPs primarily attributable to their well-tuned emissive properties process and moderately mature synthetic methods. Late reports on CdSe nanoparticles and expedient to surface modification showed its fate in the detection of NACs.[3] Quantum dots have a clear advantage over molecule-based emitters; however, these multi-model sensors are inexpedient for the evacuation of the earmark species, which might be a source of secondary contamination. From this perspective, the fuse of a fluorescent and magnetic functionality in a solitary nanocomposite molecule would be a promising alternative. This study aimed to focus on the development of this kind nanocomposite, serving a challenge that magnetic NPs possess a strong photoluminescence quenching in the merely fluorescent moiety. Various reports reveal that this undesirable photoluminescence quenching in heterodimer structures comprised of immediate contact between the semiconductor and magnetic domain can be caused by strong electronic coupling.[5] Reasoning from this fact, extra care must be taken to suppress undesirable preventive interactions within the nanocomposite that would revoke the unwelcome properties.In this work, we reported a hybrid nanostructure, comprises a magnetic core of Fe2O3 NPs encapsulated inside a thin silica shell, electrostatically adsorbed with a positively charged spacer arm of florescent Cysteamine-capped CdSe quantum dots (QDs). This promising novel hybrid nanostructure, namely magneto-fluorescent nanosensor (particle size ≈ 12.7 nm), stabilized through strong electrostatic attraction between 3-((Triethoxylsilyl)propylcarbamoyl) butyric acid-anchored Fe2O3@SiO2 NPs and Cysteamine-capped CdSe QDs, electrostatically attached to the free anionic carboxyl group in the spacer arm of Fe2O3@SiO2 NPs. This multimodal nanosensor probe showed a strong specific response to Picric Acid over a number of other explosive (NACs) in DMSO, making them promising fluorescence probes for PA detection and removal, simultaneously, for real-time application. The quenching constant (KPA) of nanosensor with PA was obtained to be 4.3×104 M-1 in DMSO with a limit of detection (LOD) up to 2.2 µM as a consequence of turn off sensing.[6] The sensing mechanism is probed via UV–Vis spectroscopy, steady-state and time-resolved fluorescence spectroscopy. In addition to solution-phase sensing, this nanosensor also showed an excellent ability for the removal of detected PA molecules with the use of an external magnet, staging as a possibility for the potential application of low-cost and stand-off sensor.

Fluorescent Fe2O3-CdSe nanocomposite probe for selective detection and removal of picric acid

Here, we present a methodology and promising novel hybrid nano-structure that comprises of magnetic core encapsulated inside a thin silica shell, electrostatically adsorbed with a positively charged spacer arm of fluorescent Cysteamine-capped CdSe quantum dots (QDs). This multimodal nanosensor provides an efficient, sensitive and selective detection of Picric Acid (PA) (LOD ≈ 2.2 μM) (Quenching constant KPA ≈ 4.3 × 104 M−1) in solution via photo-induced electron transfer mechanism. The sensing mechanism is probed via UV–Vis spectroscopy, steady-state and time-resolved fluorescence spectroscopy. The removal of PA, attached to the spherical magnetic core-shell particles, is achieved using an external magnet. This elegant architecture results in an ultra-small magneto-fluorescent nanoparticle (particle size ≈ 12.7 nm), offering a novel platform for the development of a field-based PA sensor. This strategy is having the potential for applications in the field of low-cost and stand-off sensor.

Self-Assembly of Plasmonic Nanoantenna-Waveguide Structures for Subdiffractional Chiral Sensing.

Spin-momentum locking is a peculiar effect in the near-field of guided optical or plasmonic modes. It can be utilized to map the spinning or handedness of electromagnetic fields onto the propagation direction. This motivates a method to probe the circular dichroism of an illuminated chiral object. In this work, we demonstrate local, subdiffraction limited chiral coupling of light and propagating surface plasmon polaritons in a self-assembled system of a gold nanoantenna and a silver nanowire. A thin silica shell around the nanowire provides precise distance control and also serves as a host for fluorescent molecules, which indicate the direction of plasmon propagation. We characterize our nanoantenna-nanowire systems comprehensively through correlated electron microscopy, energy-dispersive X-ray spectroscopy, dark-field, and fluorescence imaging. Three-dimensional numerical simulations support the experimental findings. Besides our measurement of far-field polarization, we estimate sensing capabilities and derive not only a sensitivity of 1 mdeg for the ellipticity of the light field, but also find 103 deg cm2/dmol for the circular dichroism of an analyte locally introduced in the hot spot of the antenna-wire system. Thorough modeling of a prototypical design predicts on-chip sensing of chiral analytes. This introduces our system as an ultracompact sensor for chiral response far below the diffraction limit.

Hollow Gold-Silver Nanoshells Coated with Ultrathin SiO2 Shells for Plasmon-Enhanced Photocatalytic Applications.

This article details the preparation of hollow gold-silver nanoshells (GS-NSs) coated with tunably thin silica shells for use in plasmon-enhanced photocatalytic applications. Hollow GS-NSs were synthesized via the galvanic replacement of silver nanoparticles. The localized surface plasmon resonance (LSPR) peaks of the GS-NSs were tuned over the range of visible light to near-infrared (NIR) wavelengths by adjusting the ratio of silver nanoparticles to gold salt solution to obtain three distinct types of GS-NSs with LSPR peaks centered near 500, 700, and 900 nm. Varying concentrations of (3-aminopropyl)trimethoxysilane and sodium silicate solution afforded silica shell coatings of controllable thicknesses on the GS-NS cores. For each type of GS-NS, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images verified our ability to grow thin silica shells having three different thicknesses of silica shell (~2, ~10, and ~15 nm) on the GS-NS cores. Additionally, energy-dispersive X-ray (EDX) spectra confirmed the successful coating of the GS-NSs with SiO2 shells having controlled thicknesses. Extinction spectra of the as-prepared nanoparticles indicated that the silica shell has a minimal effect on the LSPR peak of the gold-silver nanoshells.

Tuning dipolar effects on magnetic hyperthermia of Zn0.3Fe2.7O4/SiO2 nanoparticles by silica shell

Effects of magnetic dipole interactions on specific loss power (SLP) for Zn0.3Fe2.7O4/SiO2 core/shell nanoparticles (NPs) with identical magnetic core size and varying non-magnetic shell thicknesses were systematically investigated. In the case of thin silica shell, NPs form chain-like structures due to strong dipole interactions between NPs. The chain formation induces additional shape anisotropy. With increasing thickness of the silica shell, the dipole interaction and therefore the anisotropy induced by the dipole interactions decrease. Meanwhile, the hydrodynamic size of the NPs shows a counterintuitive reduction with increasing shell thickness, also due to the decrease in interactions. The magnetic anisotropy and hydrodynamic size affect the SLP through changes in the Néel and Brownian relaxation rates, leading to different field-dependent SLP values for NPs with thin and thick shells.

Silica-coated magnesium ferrite nanoadsorbent for selective removal of methylene blue

This paper demonstrates the adsorption capability of silica-coated magnesium ferrite nanoparticles (MgFe2O4@SiO2 NPs) for the selective adsorption of methylene blue (MB). The MgFe2O4@SiO2 NPs were generated from MgFe2O4 NPs by coating with a thin silica shell. After fully characterizing the MgFe2O4@SiO2 NPs, selective adsorption studies were carefully investigated by using three types of representative dyes: cationic (MB, rhodamine B, and malachite green), anionic (methyl orange and Congo red), and neutral (neutral red) dyes. Efficient removal of MB by the MgFe2O4@SiO2 adsorbents was observed for both individual and mixed dye systems, demonstrating excellent selectivity for MB. To optimize the adsorption capacity for MB removal, several parameters (i.e., initial solution pH, initial dye concentration, and contact time) were carefully investigated. In all cases, the magnetoresponsive adsorbents were easily separated from the solution by using an external magnet. Regeneration of the MgFe2O4@SiO2 NPs for MB removal was also performed to investigate the stability and reusability of the adsorbent. The recycling tests revealed that the MB removal efficiencies remained high after ten adsorption-desorption cycles. On the whole, the MgFe2O4@SiO2 NPs were found to be efficient, selective, and reusable adsorbents for MB removal.