Spherical Polyelectrolyte Brushes as Templates to Prepare Hollow Silica Spheres Encapsulating Metal Nanoparticles

Colloidal Polymer-Templated Formation of Inorganic Nanocrystals and their Emerging Applications

Inorganic nanocrystals possess unique physicochemical properties compared to their bulk counterparts. Stabilizing agents are commonly used for the preparation of inorganic nanocrystals with controllable properties. Particularly, colloidal polymers have emerged as general and robust templates for in situ formation and confinement of inorganic nanocrystals. In addition to templating and stabilizing inorganic nanocrystals, colloidal polymers can tailor their physicochemical properties such as size, shape, structure, composition, surface chemistry, and so on. By incorporating functional groups into colloidal polymers, desired functions can be integrated with inorganic nanocrystals, advancing their potential applications. Here, recent advances in the colloidal polymer-templated formation of inorganic nanocrystals are reviewed. Seven types of colloidal polymers, including dendrimer, polymer micelle, stare-like block polymer, bottlebrush polymer, spherical polyelectrolyte brush, microgel, and single-chain nanoparticle, have been extensively applied for the synthesis of inorganic nanocrystals. Different strategies for the development of these colloidal polymer-templated inorganic nanocrystals are summarized. Then, their emerging applications in the fields of catalysis, biomedicine, solar cells, sensing, light-emitting diodes, and lithium-ion batteries are highlighted. Last, the remaining issues and future directions are discussed. This review will stimulate the development and application of colloidal polymer-templated inorganic nanocrystals.

Self-Assembly of Shark Scale-Patterned Tunable Superhydrophobic/Antifouling Structures with Visual Color Response

The stacked riblet-like shark scales, also known as dermal denticles, allow them to control the boundary layer flow over the skin and to reduce interactions with any biomaterial attached, which guide the design of antifouling coatings. Interestingly, shark scales are with a wide variation in geometry both across species and body locations, thereby displaying diversified antifouling capabilities. Inspired by the multifarious denticles, a stretchable shark scale-patterned silica hollow sphere colloidal crystal/polyperfluoroether acrylate-polyurethane acrylate composite film is engineered through a scalable self-assembly approach. Upon stretching, the patterned photonic crystals feature different short-term antibacterial and long-term anti-biofilm performances with a distinguished color response under varied elongation ratios. To gain a better understanding, the dependence of elongation ratio on antiwetting behaviors, antifouling performances, and structural color changes has also been investigated in this research.

Temperature Responsive Diblock Polymer Brushes as Nanoreactors for Silver Nanoparticles Catalysis

Metal nanoparticles are widely used in catalysis. Loading metal nanoparticles into polymer brushes has aroused wide attention, but regulation of catalytic performance still needs to be improved. The novel diblock polymer brushes, polystyrene@sodium polystyrene sulfonate-b-poly (N-isopropylacrylamide) (PSV@PSS-b-PNIPA) and PSV@PNIPA-b-PSS with reversed block sequence, were prepared by surface initiated photoiniferter-mediated polymerization (SI-PIMP) and used as nanoreactors to load silver nanoparticles (AgNPs). The block sequence caused the difference of conformation and further affected the catalytic performance. PSV@PNIPA-b-PSS@Ag was found to be able to control the amount of AgNPs exposed to external reactant of 4-nitrophenol at different temperatures to achieve regulation of the reaction rate due to the hydrogen bonds and further physical crosslinking between PNIPA and PSS.

Bifunctional Polymer Brush Reactor for In Situ Synthesis of Hollow Silica-Supported Gold Nanocatalysts

Gold nanoparticles (AuNPs) on carriers have received wide attention as catalysts as a result of their excellent stability and catalytic performance. Herein, we report the design and synthesis of hollow silica-supported gold nanocatalysts (SNPs@AuNPs) composed of highly dispersed AuNPs with approximately 4.30 nm using an in situ colloidal polyelectrolyte template strategy. The monodisperse polystyrene nanospheres accompanied by poly[(2-methacryloyloxyethyl)trimethylammonium chloride] brushes were first synthesized. Subsequently, the facile polymer-brush-engaged strategy for the synthesis of hollow SNPs@AuNPs involves in situ reduction of AuNPs, hydrolytic condensation of silica, and a chemical etching process. In combination with dynamic light scattering, transmission electron microscopy, small-angle X-ray scattering, X-ray powder diffraction, and Fourier transform infrared spectroscopy, the as-obtained polymer brushes were proven as effective versatile nanoreactors for the synthesis of AuNPs and silica nanoparticles without any catalysts. Benefiting from the structural advantages, the resultant hollow SNPs@AuNPs manifested superior catalytic activity and reusability for the reduction of p-nitrophenol by sodium borohydride in aqueous solution. With a delicate design, we believe that this synthetic strategy can be extended to fabricate multifunctional nanomaterials with diverse compositions, which would be of great interest in catalysis, energy, and many other important domains.

Synthesis of poly (N-isopropyl acrylamide-co-2-acrylamido methylpropane sulfonic acid) hydrogel containing copper and nickel nanoparticles with easy recycling and efficient catalytic potential

Poly(N-isopropyl acrylamide-co-2-acrylamido methyl propane sulfonic acid) hydrogel was prepared and used as matrix for the fabrication of nickel and copper nanoparticles. Nickel and copper nanoparticles were fabricated via in situ reduction of Ni (II) and Cu (II) ions within the hydrogel matrix. The manufactured hydrogel and its corresponding composites with Ni and Cu nanoparticles were characterized by FTIR, XRD, EDX, TEM, and TGA. Thermal stability of hydrogel was found to be increased upon fabricating with metal nanoparticles. The hydrogel showed ability to absorb water 63 times of its weight in dried form. The Ni and Cu nanoparticles were observed to be well dispersed, spherical in shape and most of them were having diameters in the range of 12.5 to 38.8 nm and 58 to 102 nm, respectively. The as-prepared hydrogel-nickel and hydrogel-Cu nanocomposite were used as catalysts for the reduction of a toxic pollutant 4-nitrophenol. At 25 °C, the reduction of 4-NP was found to proceed with apparent rate constant (k app) of 0.107 and 0.122 min−1 in the presence of composite containing Ni and Cu nanoparticles, respectively. However, k app was increased with corresponding increase in temperature and its maximum value was found to be 0.815 min−1 at 88 °C with catalyst containing Ni nanoparticles. The formation of well dispersed Ni and Cu nanoparticles in the prepared hydrogel reflected that this hydrogel system can act as efficient stabilizing agent along with acting as a reactor medium. Recycling potential of catalysts was studied for five successive cycles.

Hollow Silica Nano and Micro Spheres with Polystyrene Templating: A Mini-Review

Synthesis of monodisperse hollow silica nanospheres, especially using a hard template route, has been shown to be successful, but a high yield is needed for this strategy to be used on an industrial scale. On the other hand, there is a research gap in the synthesis of hollow silica microspheres due to the popularity and easiness of the synthesis of silica nanospheres despite the larger spheres being beneficial in some fields. In this review, current trends in producing hollow silica nanospheres using hard templates, especially polystyrene, are briefly presented. Soft templates have also been used to make highly polydisperse hollow silica spheres, and complex designs have improved polydispersity. The effect of the main parameters on the coating is presented here to provide a basic understanding of the interactions between the silica and template surface in the absence or presence of surfactants. Surface charge, surface modification, parameters in the sol-gel method and interaction between the silica and templates need to be further improved to have a uniform coating and better control over the size, dispersity, wall thickness and porosity. As larger organic templates will have lower surface energy, the efficiency of the micro sphere synthesis needs to be improved. Control over the physical structure of hollow silica spheres will open up many opportunities for them to be extensively used in fields ranging from waste removal to energy storage.

Transport of Magnetic Polyelectrolyte Capsules in Various Environments

Microcapsules consisting of eleven layers of polyelectrolyte and one layer of iron oxide nanoparticles were fabricated. Two types of nanoparticles were inserted as one of the layers within the microcapsule’s walls: Fe2O3, ferric oxide, having a mean diameter (Ø) of 50 nm and superparamagnetic Fe3O4 having Ø 15 nm. The microcapsules were suspended in liquid environments at a concentration of 108 caps/mL. The suspensions were pumped through a tube over a permanent magnet, and the accumulation within a minute was more than 90% of the initial concentration. The design of the capsules, the amount of iron embedded in the microcapsule, and the viscosity of the transportation fluid had a rather small influence on the accumulation capacity. Magnetic microcapsules have broad applications from cancer treatment to molecular communication.

Immobilization of Gold Nanoparticles in Spherical Polymer Brushes Observed by Small-Angle X-ray Scattering

Nanosized gold nanoparticles (AuNPs) are of great interest in areas such as catalysts or imaging but are easy to aggregate due to high surface activity. To stabilize AuNPs, two approaches were employed to immobilize AuNPs in spherical polymer brushes (SPBs), namely, the in situ preparation of AuNPs within the brush layer of SPBs and external addition of preprepared citrate-capped AuNPs. The distribution and stability of AuNPs in SPBs were studied by small-angle X-ray scattering (SAXS). SAXS results demonstrated that the in situ-prepared AuNPs were mainly located on the inner layer and their amount decreased from inside to outside. In the case of external addition of preprepared AuNPs, the cationic SPB showed obvious immobilization, while almost no AuNPs were immobilized in the anionic SPB. The stable immobilization of the AuNPs in SPBs was the result of multiple interactions including complexation and electrostatic interaction. SAXS was validated to be a distinctive and powerful characterization method to provide theoretical guidance for the stable immobilization of AuNPs.

Antifouling Strategies of Nanoparticles for Diagnostic and Therapeutic Application: A Systematic Review of the Literature

Nanoparticles (NPs) are promising platforms for the development of diagnostic and therapeutic tools. One of the main hurdle to their medical application and translation into the clinic is the fact that they accumulate in the spleen and liver due to opsonization and scavenging by the mononuclear phagocyte system. The “protein corona” controls the fate of NPs in vivo and becomes the interface with cells, influencing their physiological response like cellular uptake and targeting efficiency. For these reasons, the surface properties play a pivotal role in fouling and antifouling behavior of particles. Therefore, surface engineering of the nanocarriers is an extremely important issue for the design of useful diagnostic and therapeutic systems. In recent decades, a huge number of studies have proposed and developed different strategies to improve antifouling features and produce NPs as safe and performing as possible. However, it is not always easy to compare the various approaches and understand their advantages and disadvantages in terms of interaction with biological systems. Here, we propose a systematic study of literature with the aim of summarizing current knowledge on promising antifouling coatings to render NPs more biocompatible and performing for diagnostic and therapeutic purposes. Thirty-nine studies from 2009 were included and investigated. Our findings have shown that two main classes of non-fouling materials (i.e., pegylated and zwitterionic) are associated with NPs and their applications are discussed here highlighting pitfalls and challenges to develop biocompatible tools for diagnostic and therapeutic uses. In conclusion, although the complexity of biofouling strategies and the field is still young, the collective data selected in this review indicate that a careful tuning of surface moieties is a pivotal step to lead NPs through their future clinical applications.

Recent Trends in Noble Metal Nanoparticles for Colorimetric Chemical Sensing and Micro-Electronic Packaging Applications

Noble metal NPs are highly attractive candidates because of their unique combination of physical, chemical, mechanical, and structural properties. A lot of developments in this area are still fascinating the materials research community, and are broadly categorized in various sectors such as chemical sensors, biosensors, Förster resonance energy transfer (FRET), and microelectronic applications. The related function and properties of the noble metals in these areas can be further tailored by tuning their chemical, optical, and electronic properties that are influenced by their size, shape, and distribution. The most widely used Au and Ag NPs in dispersed phase below 100 nm exhibit strong color change in the visible range which alters upon aggregation of the NPs. The chemical sensing of the analyte is influenced by these NPs aggregates. In this article, we have summarized the uniqueness of noble metal NPs, their synthesis methods, nucleation and growth process, and their important applications in chemical sensing, microelectronic packaging, and Förster resonance energy transfer.

Mesoporous Nanostructures Encapsulated with Metallic Nanodots for Smart SERS Sensing

In virtue of uniform mesopores and core-shell nanoarchitectures, metallic nanodot-encapsulated hollow mesoporous nanostructures have shown promising potential in various applications. However, their fabrication with versatile tunability of the encapsulated metallic content has been a challenge. Herein, we have prepared metallic nanodot-encapsulated hollow mesoporous silica nanoparticles (M-HMSNPs) with adjustable inner metallic components. The sacrificial template of polystyrene (PS) nanoparticles precoated with metals (Au/Ag/Pt) is fully wrapped with mesoporous silica (mSiO₂). The metallic nanodots are formed during the template removal process by calcination. The type and content of the encapsulated nanodots can be readily and precisely controlled by the initially deposited metallic layers. We demonstrate the application of the gold (Au) nanodot-loaded HMSNPs (denoted Au-HMSNPs) as smart surface-enhanced Raman spectroscopy (SERS) probes, which can screen between big molecules and small analytes. With the aid of a Raman reporter, the SERS probe can successfully quantify H₂O₂, which is used to distinguish cancer cells in vitro. Further integrated with enzymes, the SERS chips of specificity are prepared and used to detect corresponding substrates of glucose and uric acid, responsively. Besides SERS sensing, the current strategy can inspire future development of many other M-HMSNPs for various applications such as catalysis, energy storage, theranostics, etc.

Nanoparticles in Polyelectrolyte Multilayer Layer-by-Layer (LbL) Films and Capsules—Key Enabling Components of Hybrid Coatings

Originally regarded as auxiliary additives, nanoparticles have become important constituents of polyelectrolyte multilayers. They represent the key components to enhance mechanical properties, enable activation by laser light or ultrasound, construct anisotropic and multicompartment structures, and facilitate the development of novel sensors and movable particles. Here, we discuss an increasingly important role of inorganic nanoparticles in the layer-by-layer assembly—effectively leading to the construction of the so-called hybrid coatings. The principles of assembly are discussed together with the properties of nanoparticles and layer-by-layer polymeric assembly essential in building hybrid coatings. Applications and emerging trends in development of such novel materials are also identified.