Self-assembly Of Silica Nanoparticles Research Articles

Self-assembled degradable iron-doped mesoporous silica nanoparticles for the smart delivery of prochloraz to improve plant protection and reduce environmental impact

Herein, a degradable silicon-based iron-doped nanoparticle (Fe-MSN) was prepared as a porous carrier. After loading the pesticide prochloraz (Pro), tannic acid (TA) was used to seal the pores and stabilize the nanocarrier structure. Due to the enough pore surface areas, the loading rate of Pro@Fe-MSNs/TA nanoparticles (Nps) was up to 31%. Nps possessed an excellent acid-responsive controlled-release of Pro and degradation behavior of the silica wall. Nanocarrier could effectively protect Pro against photodegradation and improve the storage stability of Pro. Pesticide deposition was enhanced by good wettability and Nps possessed better inhibitory efficacy against Rhizoctonia solani. The biosafety of Nps was evaluated and showed no obvious toxicological influence on cells and zebrafish. Furthermore, the pot experiment showed that nanocarriers could effectively promote the growth of wheat plants due to the rich supply of metal trace element. This study provides a promising strategy for sustainable crop disease management to reduce environmental risk. • Nanoparticles possessed an excellent acid-responsive controlled-release of prochloraz and degradation behavior of the silica wall. • The loading rate of nanoparticle was up to 31%. • Nanocarriers improved the stability and wettability of prochloraz. • Nanoparticles possessed better inhibitory efficacy against Rhizoctonia solani . • Iron-doped nanocarriers could effectively promote the growth of wheat plants.

Shape memory photonic gels enable reversible regulation of photoluminescence: Towards multiple anti-counterfeiting

Rampant counterfeit products have seriously threatened worldwide public security. It is highly desirable yet challenging to develop advanced encryption and anti-counterfeiting strategies. Herein, a fluorophore-doped shape memory photonic gel (SMPG) for high-end multi-mode anti-counterfeiting purposes is developed by synergistically utilizing two collaborative optical signals of structural color and photoluminescence (PL). The SMPG is prepared by polymerizing mixed monomers of poly(ethylene glycol) methacrylate (PEGMA) and trimethylolpropane ethoxylate triacrylate (ETPTA) in the presence of self-assembled silica nanoparticles (NPs) array, followed by doping Rhodamine B (RhB) in the polymeric matrix and selectively etching the silica NPs. The regular macroporous structures of RhB-doped SMPG can be destroyed temporarily after drying and restored after solvent triggering, and such a variation is reversible, repeatable, and stable. We show that dry RhB-doped SMPG is highly transparent under natural light and exhibits PL under UV light, while wet RhB-doped SMPG exhibits vivid and angle-dependent structural color under natural light and a depressed PL under UV light because of the inhibition of the appearance of photonic bandgap (PBG). As a proof-of-concept, various shapes of anti-counterfeiting tags can be prepared by laser engraving technology, significantly improving the security of anti-counterfeiting tags and shows great potential in the high-end anti-counterfeiting fields.

UV-Assisted Multiscale Superhydrophobic Wood Resisting Surface Contamination and Failure.

In the modern forestry, the demand for renewable and environmentally friendly wood protection is increasing. This paper reports a green method for preparing stable and self-cleaning superhydrophobic coating for wood protection by dripping polyvinyl alcohol cross-linked hollow silica nanoparticles on the surface of wood in combination with polydimethylsiloxane modification. The coating is based on a laminated structure with layers stacked on the surface of the wood and cured quickly with the assistance of UV. The coatings obtained on wood substrates with appropriate ratios have excellent superhydrophobic properties, with an optimum water contact angle of up to 160.4 ± 0.2°. The coating also exhibits good transparency in the UV–visible spectrum and a maximum transmittance of 91%. With transmission electron microscopy, the microscopic morphology of the self-assembled hollow silica nanoparticles was observed. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction were also applied to investigate the morphology and chemical composition of the coatings. A water contact angle of 151.5 ± 0.7° was maintained even after the abrasion tests with sandpaper at a distance of 300 cm. Meanwhile, the resultant coatings exhibit good self-cleaning properties apart from mechanical durability and chemical stability, which enables effective resistance to contamination. Evidenced by the abovementioned data, this composite coating is capable of optimizing the surface wettability of wood, offering a new dimension to the extensive and prolonged application of wood and wood-based products. Furthermore, considering the advantages of this method, it could also be used in other areas in the future, such as glass, solar substrates, and optical devices.

Large scale synthesis of self-assembled shuttlecock-shaped silica nanoparticles with minimized drag as advanced catalytic nanomotors

• Large scale synthesis of shuttlecock-shaped silica nanoparticles (SSNs) were reported. • Assembly behavior of two surfactants were finely controlled to direct the growth. • SSNs exhibited minimized drag force in motion in fluid. • SSNs based nanomotors showed high diffusibility and lipid degradation activity. The catalytic performance of nanomotors is highly dependent on their interaction with substrates, for which the motion dynamics of the nanomotors needs to be carefully manipulated via materials design. Herein, we report a facile one-step self-assembly strategy for hundred-gram scale synthesis of shuttlecock-shaped silica nanoparticles as advanced catalytic nanomotors. These asymmetric nanoparticles have a streamline conical morphology with ultra-large opening in one side. The shuttlecock-mimetic morphology endows the nanoparticles with minimized drag force during fluid motion and consequently high diffusibility, while the large open cavity ensures efficient encapsulation of lipase (a model enzyme) to provide propulsive force. These unique features collectively result in superior diffusibility, leading to significantly improved catalytic performance compared with conventional large pore mesoporous silica nanoparticles with a spherical morphology. This research provides a new conceptual design and synthetic strategy to develop high-performance nanomotors.

Dual response to pH and chiral microenvironments for the release of a flurbiprofen-loaded chiral self-assembled mesoporous silica drug delivery system

This study examined the effects of pH and chirality on the release of flurbiprofen (FP)-loaded chiral (L/D) self-assembled mesoporous silica nanoparticles (CSA-L/D-MSNs), which were synthesized using cationic cetyltrimethyl ammonium bromide (CTAB) as a template and chiral modified using L/D-tartaric acids. The morphology and physicochemical properties of the CSA-L/D-MSNs were systemically determined and compared with those of non-functionalized mesoporous silica nanoparticles (MSN). The results showed that the CSA-L/D-MSNs were spherical nanoparticles, and the chirality in the L/D-tartaric acids was successfully imparted to the CSA-L/D-MSNs. FP could be loaded into the CSA-L/D-MSNs and was effectively transformed from the crystalline state to an amorphous state after drug loading due to the finite size effect. The release of FP@CSA-L/D-MSNs was faster than that of FP in a pH 1.2 medium and slower in a pH 6.8 medium, and it was better than that of FP@MSNs in both release mediums. Meanwhile, the FP@CSA-L/D-MSNs exhibited a clearly enhanced pH response because the negatively charged carboxyl groups on their surface induced stronger electrostatic repulsion between FP and CSA-L/D-MSNs. Moreover, the effect of the chiral environment on the release of FP@CSA-L/D-MSNs was further studied by introducing small-molecule chiral additives (L/D-alanine). It was found that the release of FP was inhibited in a chiral environment. Particularly, the CSA-L/D-MSNs began to exert the chiral recognition function, in which the CSA-L-MSN responded to chiral stimuli and enhanced the cumulative release amount from 84.25 %–89.11 % in a pH 6.8-L medium, while the CSA-D-MSN showed a suppressed release in the pH 6.8-L medium. Notably, the CSA-L/D-MSNs exhibited intelligent drug release by both chirality response and pH response, and will provide valuable guidance for the design of drug delivery systems.

Fabrication of quasi-hexagonal Si nanostructures and its application for flexible crystalline ultrathin Si solar cells

Optimally designed Si nanostructures can serve as effective light trapping structures for flexible crystalline ultrathin Si solar cells. In this study, we develop a unique quasi-hexagonal inverted nano-pyramid in a hexagonal array, fabricated by a combined process of nanosphere lithography and wet etching. Self-assembled silica nanoparticles were deposited on Si wafers by spin coating, followed by deposition of triangular metal nanodisks in a hexagonal array. The metal nanodisks were used as a wet etch mask in an alkaline solution to create the quasi-hexagonal Si nanostructures. We investigated a temporal evolution of the Si nanostructures with increasing the etch time to optimize optical performances. The newly developed nanostructures take a quasi-hexagonal inverted pyramid, which provides geometrically high compatibility with the self-assembled monolayers in a hexagonal array. We incorporated these quasi-hexagonal nanostructures to the flexible crystalline ultrathin Si solar cells, and the novel nanostructures exhibited optical performances comparable to conventional micro-pyramid textures while showing the enhanced mechanical flexibility of the ultrathin Si-based solar cells.

Silica nanoparticle assists determining liver cancer gene sequence on interdigitated electrode surface.

A high-performance interdigitated electrode (IDE) biosensing surface was reported here by utilizing self-assembled silica nanoparticle (SiNP). The modified surface was used to evaluate the complementation of hairpin forming region from Mitoxantrone resistance gene 7 (MXR7; liver cancer-related short gene). The conjugated SiNPs on 3-aminopropyl triethoxysilane functionalization were captured with probe sequence on IDE biosensing surface. The physical and chemically modified surface was used to quantify MXR7 and an increment in the current response upon complementation was noticed. Limit of target DNA detection was calculated (1-10fM) and this label-free detection is at the comparable level to the fluorescent-based sensing. A linear regression was calculated [y=0.243x-0.0773; R²=0.9336] and the sensitivity was 1fM on the linear range of 1fM to 10pM. With the strong attachment of capture DNA on IDE through SiNP, the surface clearly discriminates the specificity (complementary) versus nonspecificity (complete-, single-, and triple-mismatched sequences). This detection strategy helps to determine liver cancer progression and the similar strategy can be followed for other gene sequence complementation.

Fully Self-Assembled Silica Nanoparticle-Semiconductor Quantum Dot Supra-Nanoparticles and Immunoconjugates for Enhanced Cellular Imaging by Microscopy and Smartphone Camera.

There is a growing need for brighter luminescent materials to improve the detection and imaging of biomarkers. Relevant contexts include low-abundance biomarkers and technology-limited applications, where an example of the latter is the emerging use of smartphones and other nonoptimal but low-cost and portable devices for point-of-care diagnostics. One approach to achieving brighter luminescent materials is incorporating multiple copies of a luminescent material into a larger supra-nanoparticle (supra-NP) assembly. Here, we present a facile method for the preparation and immunoconjugation of supra-NP assemblies (SiO2@QDs) that comprised many quantum dots (QDs) around a central silica nanoparticle (SiO2 NP). The assembly was entirely driven by spontaneous affinity interactions between the constituent materials, which included imidazoline-functionalized silica nanoparticles, ligand-coated QDs, imidazole-functionalized dextran, and tetrameric antibody complexes (TACs). The physical and optical properties of the SiO2@QDs were characterized at both the ensemble and single-particle levels. Notably, the optical properties of the QDs were preserved upon assembly into supra-NPs, and single SiO2@QDs were approximately an order of magnitude brighter than single QDs and nonblinking. In proof-of-concept applications, including selective immunolabeling of breast cancer cells, the SiO2@QDs provided higher sensitivity and superior signal-to-background ratios whether using research-grade fluorescence microscopy or smartphone-based imaging. Overall, the SiO2@QDs are promising materials for enhanced bioanalysis and imaging.

Stealth modified bottom up SERS substrates for label-free therapeutic drug monitoring of doxorubicin in blood serum

Herein, we report the simple and inexpensive approach for the large-scale fabrication of uniform bottom-up Surface Enhanced Raman Spectroscopy (SERS) substrate. SERS substrate was fabricated by controlled sputtering of 10 nm thick gold film on self-assembled silica nanoparticles (SiNPs) of ~120 nm on glass substrates. The SERS detection has been firstly demonstrated using Rhodamine B as a Raman probe molecule with a detection limit of 10−10 M on Au sputtered SiNPs (i.e., Au@SiNPs). The experimental Raman enhancement from 0 to 6 was achieved on Au@SiNPs due to the generation of multiple SERS hotspot. To combat blood serum fouling, the zwitterionic modification of l-cysteine was done on Au@SiNPs substrates which lowered blood serum fouling by 48%. Our SERS-based sensor demonstrated high reproducibility for the detection of Doxorubicin in undiluted blood serum with a limit of detection of 20 nM, which greatly exceeded the detection range of available methodologies. We envision that the translation of this SERS substrate for the detection of chemo-drugs like Doxorubicin will assist clinicians in making rapid and/or early decisions in patients undergoing sustained chemotherapy to lower its side-effects or to incorporate other treatment methodologies as an option for Personalized treatment.

Modeling directed self-assembly of nanoparticles under parallel electric fields

We design and model an experiment to study the effect of electric bias on particle-coverage densities produced during ionic nanoparticle self-assembly. The experiment involves the application of a uniform external electric field parallel to a glass substrate during the self-assembly of silica nanoparticles. We refer to this procedure as directed self-assembly of monolayers (DSAM). In our theoretical analysis, we modify existing cooperative sequential adsorption models to account for diffusion under an applied electric field. We use the mean field approximation to solve for particle-coverage densities. To ascertain the validity of this method, we compare our solutions to Monte Carlo simulations of the system.

Creating Chameleon-like Smart Actuators

Inspired by how chameleons change their skin color, Du and co-workers have developed a general biomimetic strategy for preparing smart photonic crystal actuators with the fast and reversible colorimetric response and programmable shape transformation.

Enhanced scratch resistance of self-assembled silica nanoparticle anti-reflection coatings

With proper pH adjustment, the addition of thermally-crosslinking polyelectrolytes can improve the scratch resistance of silica nanoparticle anti-reflection coatings.

The structural coloration of textile materials using self-assembled silica nanoparticles

The work presented investigates how to produce structural colours on textile materials by applying a surface coating of silica nanoparticles (SNPs). Uniform SNPs with particle diameters in a controlled micron size range (207–350 nm) were synthesized using a Stöber-based solvent varying (SV) method which has been reported previously. Photonic crystals (PCs) were formed on the surface of a piece of textile fabric through a process of natural sedimentation self-assembly of the colloidal suspension containing uniform SNPs. Due to the uniformity and a particular diameter range of the prepared SNPs, structural colours were observed from the fabric surface due to the Bragg diffraction of white light with the ordered structure of the silica PCs. By varying the mean particle diameter, a wide range of spectral colours from red to blue were obtained. The comparison of structural colours on fabrics and on glasses suggests that a smooth substrate is critical when producing materials with high colour intensity and spatial uniformity. This work suggested a promising approach to colour textile materials without the need for traditional dyes and/or pigments.Graphical abstract

Microencapsulation and Stimuli-Responsive Controlled Release of Particles Using Water-in-Air Powders.

In this work, we report a facile, one-step method to encapsulate hydrophilic particles (HP) (micro- or nanosize) using water-in-air powders. Hydrophobic silica nanoparticles were mixed with an aqueous phase containing HP in the presence of air under high shear, resulting in the self-assembly of silica nanoparticles on water droplets to make water-in-air powders with HP encapsulated in the aqueous phase within the silica shell. The encapsulated HP can be released on the basis of an external stimulus such as adding an external aqueous phase of a certain pH or a surfactant solution that alters the wettability of the encapsulating silica nanoparticles. A contact angle study was performed using surface-hydrophobized glass slides, which acted as a proxy for hydrophobic silica nanoparticles, to investigate the effect of these stimuli on surface hydrophobicity. Such encapsulation and a stimuli-responsive controlled release system has promising potential in subsurface petroleum engineering such as the delayed swelling of particles for conformance control and delayed acid stimulation.

Optical properties of cotton and nylon fabrics coated with silica photonic crystals

In this work, colourant-free coloured fabrics have been produced by the self-assembly of silica nanoparticles (SNPs) using a natural sedimentation method. The optical properties of the SNP-coated fabrics were investigated and the spectral reflectance, chromaticity coordinates, and CIE L* a* b* values are reported. The overall colour effect on the fabric can be described by Bragg’s diffraction of the ordered SNP photonic crystal and the Mie scattering of the disordered SNP arrangement. It was found that the structural colour on the tight black woven cotton fabric was more uniform than that from the loose black knitted nylon fabric. Although the structural colour was not easily perceived on a white fabric due to the strong reflection of the white background, the SEM images show that an ordered photonic crystal was formed on the fabric and a small colour difference by the introduction of SNPs was measured using instrumental colour measurement.

One-pot preparation of polymer microspheres having wrinkled hard surfaces through self-assembly of silica nanoparticles.

Polymer microspheres with wrinkled hard surfaces composed of self-assembled silica nanoparticles were prepared via suspension polymerization. The polymer surface morphology could be controlled by changing the silica nanoparticle concentration in the monomer droplets. The wrinkles could trap small polystyrene particles in their grooves, thus demonstrating viability in separation science.

Self-Assembly of Monodisperse versus Bidisperse Polymer-Grafted Nanoparticles.

We systematically compare the dispersion and self-assembly of silica nanoparticles (NPs) grafted with either a sparse monomodal long chain length polystyrene (PS) brush or a bimodal brush comprised of a sparse grafting of long PS chains and a dense carpet of short poly(2-vinylpyridine) (P2VP) chains. These two different types of NPs are placed in pure PS matrices of varying molecular weights in a series of experiments. We first show that NP dispersion is generally improved in the case of bimodal brushes. More interestingly, at low PS grafting densities the bimodal brushes give different self-assembled structures relative to the monomodal brushes; we conjecture that the presence of the short P2VP chains in the bimodal brush reduces the effective core-core attractions and thus allows these bidisperse NPs to display self-assembly behavior that is less likely to be kinetically trapped by the strong intercore attractions that control the behavior of monomodal NPs. In this low PS grafting density limit, where we expect the spatial coverage of the brush to be the most nonuniform, we find the formation of "vesicular" structures that are representative of highly asymmetric ("tadpole") surfactants. Our results therefore show that reducing the inter-NP attractions gives rise to a much richer ensemble of NP self-assemblies, apparently with a smaller influence from kinetic traps (or barriers).

Self-assembly of silica nanoparticles into hollow spheres via a microwave-assisted aerosol process

In this work, a simple and efficient strategy for fabrication of silica hollow spheres (SHSs) has been successfully introduced with a one-step microwave-assisted aerosol process using silica nanoparticles (SiO2, 12–50nm) and NH4HCO3 as precursor materials. This approach combines the merits of microwave radiation and the aerosol technique. And the formation of SHSs is ascribed to solvent evaporation and the as-generated gas from NH4HCO3 decomposition in the microwave reactor. The morphology of the SHSs can be easily tuned by varying the residence time, amount of NH4HCO3 and silica sources. The formation mechanism of SHSs was also investigated by structure analysis. In addition, the hollow spheres exhibited remarkable sustained release of potassium persulfate, by loading it into the porous structures. The results provide new sights into the fabrication of inorganic hollow spheres via a one-step process.

Highly Stable Surface Functionalization of Microgas Chromatography Columns Using Layer-by-Layer Self-Assembly of Silica Nanoparticles

A controllable and high-yield surface functionalization of silicon microchannels using layer-by-layer (LbL) self-assembly of SiO2 nanoparticles (SNPs) is presented. The application of SNPs (45 nm average diameter) coating as a stationary phase for chromatographic separation is also demonstrated with surface functionalization using chloroalkylsilanes. This method facilitates a simple, low-cost, and parallel processing scheme that also provides homogeneous and stable nanoparticle-based stationary phases with ease of control over the coating thickness. The SNP-functionalized microfabricated columns with either single capillary channels (1 m long, 150 μm wide, 240 μm deep) or very narrow multicapillary channels (25 cm long, 30 μm wide, 240 μm deep, 16 parallel channels) successfully separated a multicomponent gas mixture with a wide range of boiling points with high reproducibility.

Electrodeposition of CuIn1−xGaxSe2 solar cells with a periodically-textured surface for efficient light collection

The photoresponse of CuIn1−xGaxSe2 (CIGS) solar cells is improved using a periodically-textured structure as an antireflection layer. The CIGS absorber layers were prepared by one-step electrodeposition from an aqueous solution containing 12mM CuSO4, 25mM In2(SO4)3, 28mM Ga2(SO4)3, and 25mM SeO2. The electrodeposited CIGS films exhibit the (112)-preferred orientation of the chalcopyrite structures and feature improved film stoichiometry after the selenization process. In addition, the lower bandgap value of 0.97eV is caused by the discrepancy of the reduction potentials for each constituent, resulting in insufficient Ga content in the deposited films. Using self-assembled silica nanoparticles as the etching mask, periodically-textured structures can be easily formed on an indium tin oxide (ITO)-coated soda lime glass to achieve a low average reflection (<10.5%) in a wide wavelength and incident angle range. With the periodic textured structures suppressing light reflections from the front surface, the photogenerated current in the semi-transparent CIGS solar cells made with transparent conducting electrodes is 1.82 times higher than they otherwise would be.