Controllable Shell Thickness Research Articles

Synthesis of Monodispersed Hollow Mesoporous Organosilica and Silica Nanoparticles with Controllable Shell Thickness Using Soft and Hard Templates

Hollow mesoporous nanoparticles with controllable size (less than 100 nm) are desired as drug-delivery carriers. Herein, we report the synthesis of monodispersed hollow mesoporous organosilica (HMOS) and hollow mesoporous silica (HMS) nanoparticles using soft and hard templating methods. HMOS shells, with 1,2-bis(triethoxysilyl)ethane (BTEE) as the precursor and hexadecyltrimethylammonium bromide and sodium dodecyl sulfate (SDS) as the soft templates, were formed on monodispersed silica nanoparticles (SNPs), which were used as the hard templates. HMOS and HMS nanoparticles were obtained by removing the SNPs after three rounds of ammonia dialysis. The hollow size of HMOS can be tuned by changing the size of the SNPs. By using SNPs with a size of 36.5 nm, hollow spaces of approximately 20 nm connected the surface through narrow pores (<5 nm). Mesopores of approximately 12 nm were formed by the surfactant micelles. Additionally, the interparticle space in HMOS and HMS was approximately 12 nm. The shell thicknesses of HMOS and HMS could be tuned in the range of 5-9 nm by changing the BTEE amount. Moreover, the amount of surfactant used varied the porous structure. The HMOS with a thickness of 5 nm exhibited a Brunauer-Emmett-Teller (BET) surface area of 268 m2/g and a total pore volume of 1.14 cm3/g. Meanwhile, HMS demonstrated a BET surface area of 553 m2/g and a total pore volume of 1.82 cm3/g while maintaining a hollow structure. HMOS displayed a high loading capacity for ibuprofen (3009 mg/g), and its drug release system showed a sustained-release property. Therefore, the HMOS preparation using hard and soft templates proposed herein can control the hollow size and shell thickness for drug-delivery applications.

Highly resistant and sensitive colorimetric immunochromatographic assay for sibutramine (SBT) illegally adulterated into diet food based on PDA/AuNP labelling.

A gold nanoparticle (AuNP) based immunochromatographic assay strip is a valuable tool for monitoring chemicals in foods. However, the sensitive ICA strip for SBT is rarely reported due to the fact that monoclonal antibodies (mAbs) against SBT with high affinity are commercially unavailable. Herein, a monoclonal antibody against SBT was prepared through a designed hapten with a carboxyl end-capped space arm. The obtained mAb showed high affinity for SBT and N-desmethylsibutramine, a metabolite of SBT. Furthermore, a series of core-shell NPs, polydopamine (PDA) coated AuNPs (PDA/AuNPs) with controlled shell thickness and packing density were synthesized. The obtained PDA/AuNP-mAb conjugate demonstrated high tolerance to salt and good stability in a wide pH range, which is beneficial for improving the matrix interference common in ICA. As a result, PDA/AuNP-based ICA could quantify SBT in the range of 3.39-69.60 ng mL-1 with a limit of detection (LOD) of 0.98 ng mL-1. This novel ICA improved the sensitivity of the traditional AuNP-based ICA by nearly 12 times. Method validation was conducted with spiked samples of slimming food and human serum and compared with HPLC-MS/MS. Consistent results indicated that high sensitivity, accuracy, and reliability of the PDA/AuNP-based ICA approach were achieved. To the best of our knowledge, this study reported the most sensitive immunoassay for SBT thus far.

NIR light-propelled bullet-shaped carbon hollow nanomotors with controllable shell thickness for the enhanced dye removal.

Materials with asymmetric nanostructures have attracted tremendous research attention due to their unique structural characteristics, excellent physicochemical properties, and promising prospects. However, it is still difficult to design and fabricate bullet-shaped nanostructure due to its structural complexity. Herein, for the first time, we successfully constructed NIR light-propelled bullet-shaped hollow carbon nanomotors (BHCNs) with an open mouth on the bottom of nano-bullet for the enhanced dye removal, by employing bullet-shaped silica nanoparticles (B-SiO2 NPs) as a hard template. BHCNs were formed by the growth of polydopamine (PDA) layer on the heterogeneous surface of B-SiO2 NPs, followed by the carbonization of PDA and subsequent selective etching of SiO2. The shell thickness of BHCNs was able to be facilely controlled from ≈14 to 30nm by tuning the added amount of dopamine. The combination of streamlined bullet-shaped nanostructure with good photothermal conversion efficiency of carbon materials facilitated the generation of asymmetric thermal gradient field around itself, thus driving the motion of BHCNs by self-thermophoresis. Noteworthily, the diffusion coefficient (De) and velocity of BCHNs with shell thickness of 15nm (BHCNs-15) reached to 43.8μm⋅cm-2 and 11.4μm⋅s-1, respectively, under the illumination of 808nm NIR laser with the power density of 1.5 W⋅cm-2. The NIR laser propulsion caused BCHNs-15 to enhance the removal efficiency (53.4% vs. 25.4%) of methylene blue (MB) as a typical dye because the faster velocity could produce the higher micromixing role between carbon adsorbent and MB. Such a smart design of the streamlined nanomotors may provide a promising potential in environmental treatment, biomedical and biosensing applications.

Molecularly imprinted polymer (MIP) based core-shell microspheres for bacteria isolation

Molecularly imprinted polymers (MIPs) have been utilized as biorecognition elements in various fields such as separation, sensing and imaging due to their easy accessibility and high binding capacity to target molecular analytes. To expand the application scope of MIPs and widen their range of targets to microorganisms, we have developed a methodology for the synthesis of MIP shells on the surface of polystyrene microparticles (MPs) with a binding affinity towards E. coli OP50 as a bacterial surrogate. Monodisperse MIP-based core–shell microparticles (MIP-MPs) with controllable shell thickness ranging from 0.25 μm to nearly 3.5 μm were produced using a stepwise polymerization method. Optical and fluorescence microscopy as well as scanning electron microscopy were used for characterization of MIP-MPs and MPs coated with non-imprinted polymers (i.e., NIP-MPs) under various timing and temperature settings. E. coli OP50 imprinting and rebinding experiments were conducted using the MIP-MPs with a suitable MIP shell thickness of 2–3 μm. Capturing experiments were carried out with different concentrations of NIP- and MIP-MPs (i.e., 10 2 , 10 3 and 10 4 particles/mL) to investigate the uptake ratio of bacteria (10 4 cells/mL) and its particle dose-dependency. The optimum uptake ratio of E. coli was approximately 74%, which was achieved using 10 3 MIP-MPs/mL. NIP-MPs had reduced bacteria recovery and results were statistically lower than MIP-MPs, showing the affinity of our MIP shells towards microorganisms. The results reported here provide a new fabrication methodology and binding efficiency of core–shell MIP-MPs to bacteria, and can create the basis for the fabrication of various imprinted coating layers on spherical substrates with potential applications in bioseparation and point-of-care sensing. • Polystyrene microparticles (MPs) with molecularly imprinted polymer (MIP) shells. • MIPs composed of four monomers for enhanced imprinting of bacteria cells on MPs. • Two-step temperature-dependent polymerization to control MIP shell thicknesses. • Optimum MIP-MPs to bacteria ratio of 1–10, showing high-level MIP imprinting. • MIP-MPs reached 74% bacteria capturing efficacy improving the state of the art.

Exploring the Effect of Pd on the Oxygen Reduction Performance of Pt by In Situ Raman Spectroscopy.

Directly monitoring the oxygen reduction reaction (ORR) process in situ is very important to deeply understand the reaction mechanism and is a critical guideline for the design of high-efficiency catalysts, but there is still lack of definite in situ evidence to clarify the effect between adsorbed intermediates and the strain/electronic effect for enhanced ORR performance. Herein, in situ surface-enhanced Raman spectroscopy (SERS) was employed to detect the intermediates during the ORR process on the Au@Pd@Pt core/shell heterogeneous nanoparticles (NPs). Direct spectroscopic evidence of the *OOH intermediate was obtained, and an obvious red shift of the *OOH frequency was identified with the controllable shell thickness of Pd. Detailed experimental characterizations and density functional theory (DFT) calculations demonstrated that such improved ORR activity after inducing Pd into Au@Pt NPs can be attributed to the optimized adsorbate-substrate interaction due to the strain and electronic effect, leading to a higher Pt-O binding energy and a lower O-O binding energy, which was conducive to O-O dissociation and promoted the subsequent reaction. Notably, this work illustrates a relationship between the performance and strain/electronic effect via the intermediate detected by SERS and paves the way for the construction of ORR electrocatalysts with high performance.

Shell-thickness control of hollow SiO2 nanoparticles through post-treatment using sol–gel technique toward efficient water confinement

Hollow structures possess a confinement function, which enables the handling and use of functional liquids. In this study, we focus on the confinement of water in the inner spaces of hollow SiO 2 nanoparticles (HSNPs). Water is introduced into the hollow spaces passing through the mesopores of the shells. The introduced water is then confined by thickening the shell through a post-treatment using silicon alkoxides. HSNPs with a variety of shell thicknesses are prepared by tuning the synthetic conditions of the reaction media and the alkoxides. It is found that the amount of water retained in a hollow space is increased with shell thickness. The resultant water–HSNP nanocomposites exhibit effective far-infrared absorption. The facile confinement approach reported in this study will lead to highly functional complex nanocomposites, such as isolated metal nanoparticles–water–silica.

Deformable and Robust Core–Shell Protein Microcapsules Templated by Liquid–Liquid Phase‐Separated Microdroplets

AbstractMicrocapsules are a key class of microscale materials with applications in areas ranging from personal care to biomedicine, and with increasing potential to act as extracellular matrix (ECM) models of hollow organs, tissues, or biomolecular condensates. Such capsules are conventionally generated from non‐ECM materials including synthetic polymers. Here, robust microcapsules with controllable shell thickness from physically‐ and enzymatically‐crosslinked gelatin are fabricated, and a core–shell architecture is achieved by exploiting a liquid–liquid phase‐separated aqueous system in a one‐step microfluidic process. Microfluidic mechanical testing reveals that the mechanical robustness of thicker‐shell capsules could be controlled through modulation of the shell thickness. Furthermore, the microcapsules demonstrate environmentally‐responsive deformation, including buckling driven by osmosis and external mechanical forces. A sequential release of cargo species is obtained through the degradation of the capsules. Stability measurements show the capsules are stable at 37 °C for more than 2 weeks. Finally, through gel–sol transition, microgels function as precursors for the formation of all‐aqueous liquid–liquid phase‐separated systems that are two‐phase or multiphase. These smart capsules that can undergo phase transition are promising models of hollow biostructures, microscale drug carriers, and building blocks or compartments for active soft materials and robots.

P‐14.2: Optimizing the Performance of Inkjet Printed Green QLED by Precisely Control of Shell Thickness

The quantum dot light‐emitting diodes (QLEDs) by inkjet printing are promising candidates for lighting and display applications of the industry. The external quantum efficiency of devices by inkjet printing have gap with that of devices by spin coating, so achieving high efficiency in such inkjet printed devices remains challenging. Herein, we report an inkjet printed green QLED capable of achieving a 21.0% external quantum efficiency.

Imparting multi-functionality to covalent organic framework nanoparticles by the dual-ligand assistant encapsulation strategy

The potential applications of covalent organic frameworks (COFs) can be further developed by encapsulating functional nanoparticles within the frameworks. However, the synthesis of monodispersed core@shell structured COF nanocomposites without agglomeration remains a significant challenge. Herein, we present a versatile dual-ligand assistant strategy for interfacial growth of COFs on the functional nanoparticles with abundant physicochemical properties. Regardless of the composition, geometry or surface properties of the core, the obtained core@shell structured nanocomposites with controllable shell-thickness are very uniform without agglomeration. The derived bowl-shape, yolk@shell, core@satellites@shell nanostructures can also be fabricated delicately. As a promising type of photosensitizer for photodynamic therapy (PDT), the porphyrin-based COFs were grown onto upconversion nanoparticles (UCNPs). With the assistance of the near-infrared (NIR) to visible optical property of UCNPs core and the intrinsic porosity of COF shell, the core@shell nanocomposites can be applied as a nanoplatform for NIR-activated PDT with deep tissue penetration and chemotherapeutic drug delivery.

78511 Synthesis of Novel Core/Shell Polymeric Nanoparticles for Controlled Drug Release

ABSTRACT IMPACT: This work will develop a novel drug delivery system that has improved biocompatibility and controlled release than current systems and allow for customizable loading and drug delivery to unique patient and treatment requirements. OBJECTIVES/GOALS: The goal of my project is a novel hybrid core/shell nanoparticle system for controlling in vivo chemotherapeutic concentration. The current goal is to confirm core and shell polymeric nanoparticle formation via emulsion technique and validate predictive model developed to optimize shell formation efficiency and control shell thickness. METHODS/STUDY POPULATION: Though early results are promising, they are not proof that the desired core/shell structure is being formed via my novel process. I constructed a theoretical model to use to optimize and control the process for precise shell thicknesses. Therefore, the current experimental plan focus is to not only visually confirm the predicted formation of my core/shell design but use these experiments to validate the model. 1.Gel-Suspended SEM: nanoparticles suspended in gel matrix, bisected to reveal inner structure2.Fluorescent Conjugation Microscopy: visually-distinct dyes used to show polymer distribution and validated against the theoretical model predictions.3.Modified Hydrophobic Dye Release: different mixtures of polymers with release showing if previous promising results due to core/shell structure RESULTS/ANTICIPATED RESULTS: As stated, the experiments will confirm the core/shell nanoparticle structure, validate the developed theoretical model, or provide direct evidence against any formation. This core/shell structure is key to the current design for controlling payload release rate and thus in vivo drug concentration. For the gel-suspension experiment, the interior core will be labeled with ultrasmall SPIONs and thus any layers within the particles will be distinct. While this result is qualitative, high magnification fluorescent microscope images will be analyzed using image processing software to determine core/shell formation efficiency and compared to estimated efficiencies from the model. Finally, the mixed release will clarify previous experiments’ release mechanism and either support or disprove shell influence. DISCUSSION/SIGNIFICANCE OF FINDINGS: The significance of this work is twofold: core/shell particles have been proven to provide variable control of release on the micron scale but not yet at the nanoscale, allowing for a circulating, targeted system that can finely control release. The process is also novel for producing this type of structure, at highly consistent quality and size.

Preparation of Core-Shell Silica Microspheres with Controllable Shell Thickness for Fast High Performance Liquid Chromatography Separation of Alkyl Benzenes and Intact Proteins.

As it is difficult to prevent secondary nucleation and agglomeration during the preparation of core-shell silica microspheres, these issues have been successfully resolved in this study using template-dissolution-induced redeposition. The non-porous particles are transformed into core-shell silica microspheres (CSSMs) in the presence of cetyltrimethylammonium bromide and octyltrimethylammonium bromide under basic conditions. The shell thickness and pore sizes of the CSSMs are controlled by adjusting the etching time and molar ratio of the template, respectively. The CSSMs are modified using octadecyltrimethylammonium chloride to separate the mixture of alkyl benzenes, and a high column separation efficiency is achieved within two minutes. The CSSMs are used for the separation and analysis of proteins and the digests of bovine serum albumin. The chromatographic column packed with core-shell particles affords a significantly higher separation efficiency than the commercial column. Therefore, as a chromatographic stationary phase, these core-shell particles can potentially be used for the fast separation of proteins, small solutes, and complex samples.

Flow Microreactor Synthesis of Zeolitic Imidazolate Framework (ZIF)@ZIF Core-Shell Metal-Organic Framework Particles and Their Adsorption Properties.

Metal-organic frameworks (MOFs) with core-shell structures enable to enhance intrinsic properties of constituent MOFs and impart additional functional activities. Although shell thickness is a key factor for regulating the properties of core-shell MOF particles, controlling it has been challenging. The widely used batch reactor synthesis cannot produce core-shell particles with uniform shell thickness because of poor reactant mixing. A microreactor could ensure excellent mixing, and that would allow to control shell thickness. In this study, we synthesized zeolitic imidazolate framework-8 (ZIF-8)@ZIF-67 and ZIF-67@ZIF-8 core-shell particles using a microreactor and investigated the effects of the mixing performance on the shell thickness of the obtained particles. Our results demonstrated that rapid mixing was critical for the uniformity of the synthesized particles. The concentration of core particles is another key factor that can preferentially induce heterogeneous nucleation on the surface of the core particles without inducing self-nucleation in the bulk solution, particularly when the self-nucleation rate of the shell MOF is high. The N2 adsorption isotherms of the synthesized particles revealed their unique adsorption properties, which were ascribed to the core-shell structures obtained at low shell formation rates. Our simple and versatile synthesis technique not only allowed the preparation of ZIF@ZIF particles with novel functionalities but also can be extended to synthesize core-shell MOF particles with different combinations of core particles and shells.

Core-shell Co-MOF-74@Mn-MOF-74 catalysts with Controllable shell thickness and their enhanced catalytic activity for toluene oxidation

A series of core-shell Co-MOF-74@Mn-MOF-74 samples with different shell thicknesses were prepared by the seed growth method, which were characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy, nitrogen adsorption-desorption and scanning electron microscopy (SEM). The shell thickness of these MOF samples were successfully controlled by adjusting the mass ratio between MnCl2·4H2O and Co-MOF-74. On this basis, these MOFs were applied to the catalytic oxidation of toluene. The results showed that with the growth of Mn-MOF-74 in the outer layer of Co-MOF-74, the oxidative selectivity of the substrate to benzaldehyde was greatly improved for the synergy between the core layer and shell layer. The conversion of toluene was 22.4%, and the selectivity of benzaldehyde was 98.1%. In addition, the catalyst can transform various substituted toluene into the corresponding aldehydes in highly selectivity and still keep good stability after four catalytic cycles. The selectivity of the corresponding aldehyde is generally above 80%.

Facile preparation of core-shell Ag@SiO2 nanoparticles and their application in spectrally splitting PV/T systems

Several researchers have demonstrated that plasmonic nanofluids based filters can potentially enhance hybrid solar photovoltaic/thermal (PV/T) systems performance. In this work, we report a facile process for achieving silica-coated silver (Ag) nanoparticles using dimethylamine (DMA) as a basic solvent to induce tetraethyl orthosilicate (TEOS) hydrolysis. Then, the prepared Ag@SiO2 nanoparticles which have a controllable silica shell thickness are suspended in propylene glycol-CoSO4 hybrid fluid. Finally, the characteristics of the PV/T system filtered by the Ag@SiO2/CoSO4-PG nanofluids are evaluated based on the indoor test and photo-thermal conversion model. The results show that the nanoparticles prepared under optimized conditions, i.e., pH value of 8–9, water: ethanol volume ratio of 1:4, temperature of 25 °C, TEOS volume of 0.05 mL, and reaction time of 12 h, exhibit an absorption peak at 474 nm. Further, this study reveals that Ag@SiO2/CoSO4-PG nanofluid filter with concentration of 25.4 mg/L gives a reasonable spectral match with silicon concentrator solar cell according to the measured optical transmittance and the calculated filtering efficiency of 39.3%. The use of 25.4 mg/L Ag@SiO2/CoSO4-PG nanofluid filter produces a higher total efficiency of 63.3% and yields economic value enhancement of 67.8% compared to the PV only system when worth factor (w) is 3.

Colloidal Synthesis of Giant Shell PbSe-Based Core/Shell Quantum Dots in Polar Solvent: Cation Exchange versus Epitaxial Growth

Shell thickness control of core/shell quantum dots (QDs) plays an importance role in determining their optical properties as well as the corresponding device performance. PbSe-based core/shell QDs ...

Tuning Microcapsule Shell Thickness and Structure with Silk Fibroin and Nanoparticles for Sustained Release.

Microcapsules have attracted widespread interest for their unique properties in encapsulation, protection, and separation of active ingredients from the surrounding environment. However, microcapsule carriers with controllable shell thickness, permeability, good mechanical properties, and thermostability are challenging to obtain. Herein, robust and versatile composite microcapsules were fabricated using SiO2 nanoparticle-stabilized (Pickering) oil emulsions as core templates, while silk fibroin (SF) was assembled at the oil/water interface. This process resulted in the formation of physically and chemically stable microcapsules with a thick (∼800 nm) shell that protected the encapsulated ingredient from high shear forces and high temperatures during spray-drying. SiO2 nanoparticles were randomly distributed in the shell matrix after preparation, making the microcapsules mechanically robust (4.48 times higher than control samples prepared using surfactant Tween 80 instead of the SiO2 nanoparticles), as well as thermostable (retained shape to 900 °C). The microcapsules displayed tunable drug release by adjusting the SF content in the shell. Under optimal conditions (weight ratio of SiO2/SF = 7:10, corn oil content about 55 wt %), a model drug (curcumin) was encapsulated in the SF microcapsules with an encapsulation efficiency up to 95%. The in vitro drug release from these SF microcapsules lasted longer than control microcapsules, demonstrating the capability of these novel microcapsules in sustaining drug release.

Core-Shell Fe/FeS Nanoparticles with Controlled Shell Thickness for Enhanced Trichloroethylene Removal.

Zero-valent iron nanoparticles (nZVI) treated by reduced sulfur compounds (i.e., sulfidated nZVI, S-nZVI) have attracted increased attention as promising materials for environmental remediation. While the preparation of S-nZVI and its reactions with various groundwater contaminants such as trichloroethylene (TCE) were already a subject of several studies, nanoparticle synthesis procedures investigated so far were suited mainly for laboratory-scale preparation with only a limited possibility of easy and cost-effective large-scale production and FeS shell property control. This study presents a novel approach for synthesizing S-nZVI using commercially available nZVI particles that are treated with sodium sulfide in a concentrated slurry. This leads to S-nZVI particles that do not contain hazardous boron residues and can be easily prepared off-site. The resulting S-nZVI exhibits a core–shell structure where zero-valent iron is the dominant phase in the core, while the shell contains mostly amorphous iron sulfides. The average FeS shell thickness can be controlled by the applied sulfide concentration. Up to a 12-fold increase in the TCE removal and a 7-fold increase in the electron efficiency were observed upon amending nZVI with sulfide. Although the FeS shell thickness correlated with surface-area-normalized TCE removal rates, sulfidation negatively impacted the particle surface area, resulting in an optimal FeS shell thickness of approximately 7.3 nm. This corresponded to a particle S/Fe mass ratio of 0.0195. At all sulfide doses, the TCE degradation products were only fully dechlorinated hydrocarbons. Moreover, a nearly 100% chlorine balance was found at the end of the experiments, further confirming complete TCE degradation and the absence of chlorinated transformation products. The newly synthesized S-nZVI particles thus represent a promising remedial agent applicable at sites contaminated with TCE.

Research of double emulsion formation and shell-thickness influence factors in a novel six-way junction microfluidic device

The six-way junction microfluidic device has been widely used to prepare thin-shelled double emulsions as templates for liposomes. However, there is little numerical research of double emulsion formation in this device, and the influence factors of shell thickness still need to be further explored. In this paper, numerical simulations based on the VOF method are conducted to investigate double emulsion formation and shell-thickness influence factors in the six-way junction microfluidic device. Moreover, a new concept named relative shell thickness is proposed to intuitively reflect the relationship between the shell thickness and drop size. By the simulations, the double emulsion formation mechanisms at three typical flow regimes are revealed, including dripping, narrowing jetting, and widening jetting. The effects of operation parameters on the flow regime, double-emulsion droplet size and shell thickness are discussed. Results indicate that capillary numbers not only affect the flow regime but also the droplet size and shell thickness. It also finds that the effect of the middle fluid flow rate on the shell thickness is larger than the outer fluid flow rate and that the thin-shelled double emulsions are mainly generated in dripping. This paper reveals the change law of shell thickness with varied operation parameters and can guide for preparing double emulsions with controllable shell thickness in the six-way junction microfluidic device.

Ge Nanocages and Nanoparticles via Microwave-Assisted Galvanic Replacement for Energy Storage Applications

We report a systematic study on the synthesis of highly monodisperse hollow germanium (Ge) nanoparticles (NPs) via galvanic replacement reactions between GeI2 and Ag NPs. By fine-tuning the synthetic parameters such as temperature, precursor molar ratio, ligand concentration, and so forth, the morphology and surface structure of the Ge NPs can be precisely controlled. We also report a method to synthesize solid Ge NPs and Ag@Ge core–shell metal–semiconductor NPs with a controllable uniform shell thickness. An inward diffusion mechanism for galvanic replacement is proposed and supported by imaging the different stages of the reaction and analysis of the products. This mechanism allows the reaction to be self-terminated and achieves nanometer-sized accuracy. The galvanic reaction may be applied to other semiconductors and could serve as a powerful alternative to the classical nucleation-growth mechanism and subsequently advance the scale-up and further energy storage applications.

Multiple Roles of Polyethylenimine during Synthesis of 10 nm Thick Continuous Silver Nanoshells.

Silica@silver core-shell particles (silver nanoshells) present a wide range of applications, owing to their unique optical, chemical, and surface plasmon resonance (SPR) properties. Because SPR properties are mainly determined by shell thickness, precise shell thickness control is required. However, the synthesis of continuous nanoshells less than 10 nm thickness is still a challenge. In this study, we overcame this challenge by using polyethyleneimine (PEI) during the shell growth step of the seed-mediated growth method. We determined that the addition of PEI significantly slowed the shell growth reaction and facilitated the formation of uniform shells, which allowed us to synthesize 9.8 nm thick complete silver nanoshells. The SPR absorptions of the resultant nanoshell suspensions remained almost unchanged for 15 days. Therefore, we demonstrated that PEI molecules played three different roles during the shell growth process: reaction-rate regulators, shell growth facilitators, and resultant suspension stabilizers. The shell thickness was tuned from 9.8 to 29.5 nm by simply varying the silver-ion concentration. A key factor was the amount of added PEI because excess PEI would result in the formation of silver nanoparticles in the bulk solution phase, while too little PEI would produce incomplete shells. The optimum mass ratio of PEI-to-silica particles was determined to be 1.0 for the experimental conditions in this study. The mixing sequence of the reaction solutions was also important because PEI had to be mixed with silica particles first to ensure that the PEI molecules get adsorbed on the surface of silica and accommodated silver ions via the coordination interactions between the amine groups of the PEI molecules and silver ions. The reaction that involves the use of PEI could lead to establishing a simple and robust synthesis technique for silver nanoshells.