Seed-mediated Process Research Articles

From Structure to Function: Understanding Synthetic Conditions in Relation to Magnetic Properties of Hybrid Pd/Fe-Oxide Nanoparticles.

Heterostructured magnetic nanoparticles show great potential for numerous applications in biomedicine due to their ability to express multiple functionalities in a single structure. Magnetic properties are generally determined by the morphological characteristics of nanoparticles, such as the size/shape, and composition of the nanocrystals. These in turn are highly dependent on the synthetic conditions applied. Additionally, incorporation of a non-magnetic heterometal influences the final magnetic behavior. Therefore, construction of multifunctional hybrid nanoparticles with preserved magnetic properties represents a certain nanotechnological challenge. Here, we focus on palladium/iron oxide nanoparticles designed for combined brachytherapy, the internal form of radiotherapy, and MRI-guided hyperthermia of tumors. The choice of palladium forming the nanoparticle core is envisioned for the eventual radiolabeling with 103Pd to enable the combination of hyperthermia with brachytherapy, the latter being beyond the scope of the present study. At this stage, we investigated the synthetic mechanisms and their effects on the final magnetic properties of the hybrid nanoparticles. Thermal decomposition was applied for the synthesis of Pd/Fe-oxide nanoparticles via both, one-pot and seed-mediated processes. The latter method was found to provide better control over morphology of the nanoparticles and was therefore examined closely by varying reaction conditions. This resulted in several batches of Pd/Fe-oxide nanoparticles, whose magnetic properties were evaluated, revealing the most relevant synthetic parameters leading to promising performance in hyperthermia and MRI.

Synthesis of stable core-shell perovskite based nano-heterostructures

Despite having exceptional optical and photoelectric properties, the application of organometal halide perovskites (OHP) is restricted due to the limited penetration depth of the UV excitation light and poor stability. Attempts have been made to make composite materials by mixing other materials such as upconversion nanoparticles (UCNP) with OHP. In contrast to linear absorption and emission of OHP, the nonlinear upconversion of UCNP offers numerous advantages such as deep penetration depth of the near-infrared (NIR) excitation light, minimal photodamage to biological tissues, and negligible background interference, which offer great potential in various applications such as multiplexed optical encoding, three-dimensional displays, super-resolution bioimaging, and effective solar spectrum conversion. However, it is challenging to synthesize hybrid OHP-UCNP nanocrystals due to the inherent difference in crystal structures of hexagonal phase UCNP and cubic phase OHP. In this work, we report OHP-UCNP heterostructured nanocrystals synthesized via growing cubic phase NaGdF4 UCNP over cubic phase CsPbBr3 OHP in a seed-mediated process based on a very small lattice mismatch and then converting cubic phase UCNP to hexagonal phase through heating. The juxtaposition of UCNP over OHP in a single nanocrystal facilitates efficient energy transfer from UCNP to OHP under NIR excitation and acts as a protective layer improving the stability. The stability is further enhanced by coating an inert UCNP shell on the OHP-UCNP nano-heterostructures with the same UCNP material earlier used in the heterostructures. The coating demonstrated greater stability under continuous UV exposure and in harsh environments such as high temperatures and polar solvents. These NIR excitable perovskite-UCNP nano-heterostructures with improved stability have great potential for use in new optoelectronic and biological applications.

Bottom-up microwave-assisted seed-mediated synthesis of gold nanoparticles onto nanocellulose to boost stability and high performance for SERS applications

The development of accurate, reliable, inexpensive and fully recyclable analytical platforms is of utmost relevance to several fields from medical diagnosis to environmental screening. Surface-enhanced Raman spectroscopy (SERS) is a compelling detection method with high specificity and sensitivity. In this work, a microwave-assisted synthesis method was used for fast and uniform in situ growth of gold nanoparticles (AuNPs) onto nanocellulose (NC) membranes, through a seed-mediated process. The as-prepared membranes were fully optimized and its application as SERS platforms was demonstrated. A direct comparison with other cellulose-based substrates showed the superior characteristics of NC such as high mechanical strength, high surface area and lower porous content. An Enhancement Factor (EF) up to ~106 was obtained using rhodamine 6G (R6G) 10−6 M as probe molecule and a remarkable shelf life of at least 7 months was achieved, with no special storage requirements. Preliminary results on the label-free detection of spike protein from SARS-CoV-2 virus are shown, through direct measurements on the optimized SERS membrane. We believe that this work evidences the effectiveness of in situ seed-mediated microwave-assisted synthesis as a fabrication method, the high stability of AuNPs and the superior characteristics of NC substrates to be used as SERS platforms.

Contrastive Study of In Situ Sensing and Swabbing Detection Based on SERS-Active Gold Nanobush-PDMS Hybrid Film.

Surface-enhanced Raman scattering (SERS) with fast and intuitive property has been extensively utilized in the field of food safety. Here, we demonstrated a novel noble metal-polymer hybrid film as a SERS substrate for food fungicide analysis. Benefiting from its transparency and flexibility, poly(dimethylsiloxane) (PDMS) film was chosen as a versatile supporting matrix to grow gold nanobushes (Au NBs) through a seed-mediated process. The as-prepared AuNB-PDMS hybrid film performed satisfactorily in testing 4-nitrothiophenol (4NTP) and exhibited an enhancement factor (EF) of 2.56 × 106. Moreover, the high sensitivity and elastic properties make the hybrid film a promising substrate in practical detection. Hence, the in situ sensing of TBZ, carbaryl, and their mixture was finally realized using the developed hybrid film, which exhibited higher sensitivity than that obtained by the swabbing method. This high-performance SERS substrate based on the flexible and transparent AuNB-PDMS hybrid film has great potential applications in the fast in situ monitoring of biochemical molecules.

Coupling magnetic and plasmonic anisotropy in hybrid nanorods for mechanochromic responses

Mechanochromic response is of great importance in designing bionic robot systems and colorimetric devices. Unfortunately, compared to mimicking motions of natural creatures, fabricating mechanochromic systems with programmable colorimetric responses remains challenging. Herein, we report the development of unconventional mechanochromic films based on hybrid nanorods integrated with magnetic and plasmonic anisotropy. Magnetic-plasmonic hybrid nanorods have been synthesized through a unique space-confined seed-mediated process, which represents an open platform for preparing next-generation complex nanostructures. By coupling magnetic and plasmonic anisotropy, the plasmonic excitation of the hybrid nanorods could be collectively regulated using magnetic fields. It facilitates convenient incorporation of the hybrid nanorods into polymer films with a well-controlled orientation and enables sensitive colorimetric changes in response to linear and angular motions. The combination of unique synthesis and convenient magnetic alignment provides an advanced approach for designing programmable mechanochromic devices with the desired precision, flexibility, and scalability.

Preparation of Cu2O nanocubes with different sizes and rough surfaces by a seed-mediated self-assembly process and their application as a non-enzymatic glucose sensor

In this study, ultrafine and uniform cuprous oxide (Cu2O) nanocubes with different sizes and rough surfaces were prepared via a seed-mediated process.

Tuning adhesion forces between functionalized gold colloidal nanoparticles and silicon AFM tips: role of ligands and capillary forces.

Adhesion forces between functionalized gold colloidal nanoparticles (Au NPs) and scanning probe microscope silicon tips were experimentally investigated by atomic force microscopy (AFM) equipped with PeakForce QNM (Quantitative Nanoscale Mechanics) module. Au NPs were synthesized by a seed-mediated process and then functionalized with thiols containing different functional groups: amino, hydroxy, methoxy, carboxy, methyl, and thiol. Adhesion measurements showed strong differences between NPs and silicon tip depending on the nature of the tail functional group. The dependence of the adhesion on ligand density for different thiols with identical functional tail-group was also demonstrated. The calculated contribution of the van der Waals (vdW) forces between particles was in good agreement with experimentally measured adhesive values. In addition, the adhesion forces were evaluated between flat Au films functionalized with the same molecular components and silicon tips to exclude the effect of particle shape on the adhesion values. Although adhesion values on flat substrates were higher than on their nanoparticle counterparts, the dependance on functional groups remained the same.

Continuous Synthesis of Monodisperse Ag Nanocubes

The precise control of both the size and shape of Ag nanoparticles strongly influences their optical properties. Although the synthesis of Ag nanocubes with sharp corners and edges has been demonstrated, the ability to scale these approaches with high selectivity remains elusive. In this study, a continuous flow microwave-assisted reactor was used to separate nucleation from growth events, which provides a method to synthesize very uniform single crystalline Ag nanocubes. Nucleation in the microwave zone was enhanced through seed-mediated processes by sulfide formation, and a chemical regulator was used in the growth zone to further improve the sharpness of the edges of the nanocubes. Transmission electron microscopy and optical properties were used to optimize the reaction conditions and Ag nanocubes with edge lengths of 28 and 45 nm were readily synthesized with narrow particle size distributions and high selectivities (>70%). Nanocubes with 28 nm edge lengths were used to prepare films to demonstrate t...

Facile synthesis and upconversion luminescence of β-NaYF4:Yb, Tm nanocrystals with highly tunable and uniform β-NaYF4 shells

Homogeneous core-shell nanocrystals (NCs) with highly tunable and uniform thickness shells were synthesized with a one-step, seed-mediated process. It was determined that the quantity of ligand oleic acid (OA) directly affects the uniformity of shell precursor epitaxial growth on core NCs. The optimum quantity of ligand OA was experimentally determined. Based on this finding, NaYF4:Yb, Tm/NaYF4 core-shell NCs with shell thicknesses tuned to 1 nm, 3 nm, 5 nm, 10 nm, and 15 nm were synthesized. TEM and EDS analysis confirmed the successful synthesis of core-shell NCs with the aforementioned specifications. Under 980 nm excitation, the upconversion (UC) fluorescence intensity of the core-shell NCs is enhanced exponentially with shell thickness (d) in the form of (1−0.9exp (−d/d0)). For the 800 nm emission intensity of our core-shell NCs, the d0 was determined as about 5.8 nm, corresponding to an enhancement of about 13 times. When the shell thickness is beyond d0, the UC fluorescence intensity increase becomes quite slow.

Modelling the Optical Properties of Metal Nanoparticles: Analytical vs Finite Elements Simulation

Metal nanoparticles are an important research field for their broad and various application. The modeling of their chemical and physical properties is essential for the correct design of innovative materials. In this study the analytical simulation, based on the bare Mie theory, is directly compared with the measured absorbance spectra of gold colloids, prepared through a seed-mediated process. The goodness in the prediction of the particles dimension gives an indication on the level of precision of the model to simulate the optical behavior of the sample. Then, a discrete simulation is performed, which implements finite element analysis; a good level of agreement with the analytical model is obtained for single isolated nanoparticles, and additional properties like electromagnetic behavior of the particles is modeled. At last the discrete simulation is used to explore complex particle structures, whose analytical simulation is not possible, like dimer, nanoparticles chain and planar distribution. For these configurations, the electric field is analyzed, with particular attention to the best configuration for the field enhancement, and the trend of the absorption spectrum is studied as a function of the relative distance among the particles. The results indicate that the plasmon resonance shifts to the red when array of particles are considered since 10 and 30nm shift has been observed for a chain of closely spaced nanoparticles and for a planar ordered nanoparticles, respectively.

Electrocrystallization of Tetrathiafulvalene Charge-Transfer Salt Nanorods on Gold Nanoparticle Seeds

This paper describes electrochemical synthesis of nanorods of tetrathiafulvalene (TTF) charge-transfer salt on gold nanoparticle (GNP) seeds. The seed-mediated process was monitored by cyclic voltammetry, AFM, and field-emission SEM. The electrodeposition of GNPs (nucleation seeds) on highly oriented pyrolytic graphite (HOPG) electrodes was studied as a function of the electrolytic conditions. The GNP size increases with increasing HAuCl4 concentration and decreasing applied overpotential. A morphological transition from quasi-spherical particles to dendritic aggregates occurs when the HAuCl4 concentration increases from 0.5 to 1 mM. The electrocrystallization of (TTF)Br0.76 on the GNP-decorated HOPG was investigated as a function of TTF concentration and GNP morphology. We observed a preferential nucleation of (TTF)Br0.76 on the GNP seed. The seed-mediated (TTF)Br0.76 crystals display a confined crystal morphology in comparison to those nucleated on bare HOPG. (TTF)Br0.76 nanorods as small as 7 nm in hei...

Confining the Nucleation and Overgrowth of Rh to the {111} Facets of Pd Nanocrystal Seeds: The Roles of Capping Agent and Surface Diffusion

This article describes a systematic study of the spatially confined growth of Rh atoms on Pd nanocrystal seeds, with a focus on the blocking effect of a surface capping agent and the surface diffusion of adatoms. We initially used Pd cuboctahedrons as the seeds to illustrate the concept and to demonstrate the capabilities of our approach. Because the Pd{100} facets were selectively capped by a layer of chemisorbed Br(–) or I(–) ions, we were able to confine the nucleation and deposition of Rh atoms solely on the {111} facets of a Pd seed. When the synthesis was conducted at a relatively low temperature, the deposition of Rh atoms followed an island growth mode because of the high Rh–Rh interatomic binding energy. We also facilitated the surface diffusion of deposited Rh atoms by increasing the reaction temperature and decreasing the injection rate for the Rh precursor. Under these conditions, the deposition of Rh on the Pd{111} facets was switched to a layered growth mode. We further successfully extended this approach to a variety of other types of Pd polyhedral seeds that contained Pd{111} and Pd{100} facets in different proportions on the surface. As expected, a series of Pd–Rh bimetallic nanocrystals with distinctive elemental distributions were obtained. We could remove the Pd cores through selective chemical etching to generate Rh hollow nanoframes with different types and degrees of porosity. This study clearly demonstrates the importance of facet capping, surface diffusion, and reaction kinetics in controlling the morphologies of bimetallic nanocrystals during a seed-mediated process. It also provides a new direction for the rational design and synthesis of nanocrystals with spatially controlled distributions of elements for a variety of applications.

Synthesis and characterisation of organic-modified inorganic nanorods

Gold and cadmium sulphide nanorods with aspect ratios ≈5 were synthesised in quantities of several hundred milligrams via surfactant-driven seed-mediated processes. Such nanorods then underwent surface-modification processes in which the surfactant coating was at least partially replaced with both commercially available alkanethiols and synthesised organic molecules with the intention of forming hybrid organic–inorganic nanorods capable of exhibiting liquid crystalline-like ordering. An increase in the localised alignment of functionalised nanorods was observed in transmission electron microscope images. Additional characterisation of these novel hybrid molecules has been performed using polarised optical microscopy, differential scanning calorimetry, energy dispersive X-ray spectroscopy, nuclear magnetic resonance and UV-Visible absorption spectroscopy.

Synthesis of Pd/Fe3O4 Hybrid Nanocatalysts with Controllable Interface and Enhanced Catalytic Activities for CO Oxidation

Palladium is an important catalyst for many industrial processes and chemical reactions. The conjunction of Pd and a metal oxide is of particular interest for improving catalytic performance in heterogeneous catalysis. Here we report the synthesis of Pd/Fe3O4 hybrid nanoparticles with controllable interface and the evaluation of their catalytic activities for CO oxidation. The synthesis involves a seed-mediated process in which Pd nanoparticles serve as seeds, followed by the deposition of the Fe3O4 layer in the solution phase. The adhesion of the oxide layer to the metal surface is through the reduced form of Fe. Upon thermal annealing, the Fe3O4 layer evolved from complete to partial coverage on the Pd core surface. This process is accompanied by increased crystallinity of Fe3O4. The resultant Pd–Fe3O4 nanoparticles with a partial Fe3O4 shell significantly lower the light-off temperature of CO oxidation.

H2O2‐Aided Seed‐Mediated Synthesis of Silver Nanoplates with Improved Yield and Efficiency

H₂O₂‐Aided Seed‐Mediated Synthesis of Silver Nanoplates with Improved Yield and Efficiency

The morphology and evolution of bipyramidal gold nanoparticles

We examine the growth and evolution with time of bipyramidal gold nanoparticles grownby a seed-mediated process. The nanoparticles are characterized both by their physicaldimensions determined by transmission electron microscopy and by the wavelength positionof their localized surface plasmon resonance. Each growth’s physical dimensionscorrespond to particular initial conditions, and we observe two distinct modes oftemporal evolution during growth. The effects of varying silver nitrate concentrationand growth time are also explored. We observe a linear relationship between thetip radius of curvature and the wavelength of the longitudinal localized surfaceplasmon resonance (LSPR) peak. Critical parameters for synthesizing bipyramidalnanoparticles with sharp tips and correct length to width ratio are determined.

The Role of Bromide Ions in Seeding Growth of Au Nanorods

We report our findings on the important role of bromide ions in the seeding growth process of Au nanorods. The seed-mediated process constitutes a well-developed method for synthesizing gold nanorods in high yield, which is facilitated by a micelle-forming surfactant, cetyltrimethylammonium bromide (CTA-Br). Despite the tremendous work in recent years, the growth mechanism of Au nanorods has not been fully understood. Contrary to the widely accepted mechanism of CTA(+) micelle-templated growth of Au nanorods, we have identified the critical role of bromide ions in the seeding growth of Au nanorods. We found that even when the micelle-forming agent (CTA(+)) concentration is below its critical micelle concentration (cmc), bromide ions added in the form of NaBr can successfully effect the growth of Au nanorods in good yield. By controlling the concentration of externally added bromide ions, the rod shape and dimensions of the resulting Au nanoparticles can be readily controlled in the presence of only a minimum amount of CTABr (as a steric stabilizer for nanorods). High-resolution TEM studies show that the as-formed nanorods are perfectly single crystalline, instead of penta-twinned ones, and are bound by {111} and {100} facets with a [110] direction as the elongation direction. A mechanism is proposed to account for the seeding growth of single crystalline Au nanorods. Overall, this work explicitly demonstrates that Br(-) indeed serves as an important shape-directing agent for gold nanorod formation in the seed-mediated process.

One‐Step Synthesis of Large‐Aspect‐Ratio Single‐Crystalline Gold Nanorods by Using CTPAB and CTBAB Surfactants

Gold nanorods were prepared in high yields by using a one-step seed-mediated process in aqueous cetyltripropylammonium bromide (CTPAB) and cetyltributylammonium bromide (CTBAB) solutions in the presence of silver nitrate. The diameters of the nanorods range from 3 to 11 nm, their lengths are in the range of 15 to 350 nm, and their aspect ratios are in the range of 2 to 70. The diameters of the Au nanorods obtained from one growth batch in CTPAB solutions decrease as their lengths increase, and their volumes decrease as the aspect ratios increase. The diameters of the Au nanorods obtained from one growth batch in CTBAB solutions first decrease and then slightly increase as their lengths increase, and their volumes increase as the aspect ratios increase. These Au nanorods are single-crystalline and are seen to be oriented in either the [100] or [110] direction under transmission electron microscopy imaging, irrespective of their sizes. To the best of our knowledge, this is the first report of the preparation by using wet-chemistry methods of single-crystalline Au nanorods with aspect ratios larger than 15.

Surface Modification of Gold Nanorods with Polymers Synthesized by Reversible Addition−Fragmentation Chain Transfer Polymerization

Herein we describe the surface modification of gold nanorods via the postpolymerization immobilization of polymers prepared by reversible addition−fragmentation chain transfer (RAFT). Gold nanorods have been synthesized via a three-step seed-mediated process and then subsequently modified with RAFT-preformed poly(2-(dimethylamino)ethyl methacrylate), poly(acrylic acid), and polystyrene homopolymers, with and without the use of reducing agents. Transmission electron microscopy has been used to visually monitor nanorod formations and UV−visible spectroscopy has been used to observe the absorption properties of nanorod formations. Both techniques monitored nanorods with and without surface modifications. This research provides a general and versatile technique for the surface modification of gold nanorods utilizing a wide range of polymers. Polymer modification of nanorods will potentially aid in nanorod self-assembly and ordering processes.

ARE POPULATIONS ISLANDS? ANALYSIS OF CHLOROPLAST DNA VARIATION IN AQUILEGIA.

The degree to which conspecific populations are interconnected via ongoing gene flow remains an important focus of evolutionary biology. One major difficulty in distinguishing ongoing gene flow from historical subdivision is that either process can generate similar estimates of apparent gene flow. Thus, gene flow estimates themselves are insufficient to distinguish between these alternatives. However, genetic data coupled with additional information about demography and distribution do allow a distinction to be made. Here we address the specific question, does gene flow link populations of Aquilegia? In a survey of a 525 B.P. chloroplast DNA fragment sampled from 251 individual plants from 18 populations of three taxa, five haplotypes were identified. No significant relationship between geographic distance and apparent gene flow between population pairs existed. Further, the estimated level of gene flow was entirely compatible with a historical subdivision of Aquilegia populations during the late Pleistocene or early Holocene. Therefore, these patterns of variation are due not to ongoing gene flow, but rather to historical association among populations. Thus Aquilegia populations may be considered as distinct evolutionary entities with regard to seed-mediated processes. As a result, comparative analysis of ecological traits undergoing potentially rapid evolution (e.g., life histories, mating systems, inbreeding depression) should be possible in these taxa.