Synthesis of nano-bowls with a Janus template

Polymeric Bowl-Shaped Nanoparticles: Hollow Structures with a Large Opening on the Surface

Polymeric bowl-shaped nanoparticles (BNPs) are anisotropic hollow structures with large openings on the surface, which have shown advantages such as high specific area and efficient encapsulation, delivery and release of large-sized cargoes on demand compared to solid nanoparticles or closed hollow structures. Several strategies have been developed to prepare BNPs based on either template or template-free methods. For instance, despite the widely used self-assembly strategy, alternative methods including emulsion polymerization, swelling and freeze-drying of polymeric spheres, and template-assisted approaches have also been developed. It is attractive but still challenging to fabricate BNPs due to their unique structural features. However, there is still no comprehensive summary of BNPs up to now, which significantly hinders the further development of this field. In this review, the recent progress of BNPs will be highlighted from the perspectives of design strategies, preparation methods, formation mechanisms, and emerging applications. Moreover, the future perspectives of BNPs will also be proposed.

Enzymatic and Cellular Degradation of Carbon-Based Biconcave Nanodisks

The assessment of the biodegradability of nanomaterials is of pragmatic importance for understanding the interactions between nanomaterials and biological systems and for the determination of ultimate fate of these materials as well as their potential use. We recently developed carbon-based biconcave nanodisks (CBBNs) serving as a versatile nanocarrier for enhanced accumulation in tumors and combined photothermal-chemotherapy. Here, we investigate both the enzymatic and cellular degradation of CBBNs by monitoring their cellular response with electron microscopy, near-infrared absorbance spectroscopy, and cell viability and oxidative stress assessments. Our results show that CBBNs underwent significant degradation in solutions catalyzed by horseradish peroxidase (HRP) and hydrogen peroxide (H₂O₂), or in the presence of macrophage cells. The ability of CBBNs to be degraded in biological systems provides suitability for their future biomedical applications.

Lipid-Encapsulated Silica Nanobowls as an Efficient and Versatile DNA Delivery System

Nonmesoporous Janus silica nanobowls (NBs) are unique in that they possess two different nonporous surfaces per particle for loading biological molecules and can thus be designed with multifunctional properties. Although silica NBs have been successfully employed for both targeted therapeutic and diagnostic applications, their ability to deliver DNA has not yet been fully explored. The purpose of this study was to design and develop an in vitro transfection agent that would exploit the distinct characteristics of the silica NB. First, we determined that the NB surface can be linked to either supercoiled cDNA plasmids or vectorless, linear cDNA constructs. Additionally, the linearized cDNA can be functionalized and chemisorbed on NBs to obtain a controlled release. Second, the successful transfection of cells studied was dependent on lipid coating of the NB (LNBs). Although both NBs and LNBs were capable of undergoing endocytosis, NBs appeared to remain within vesicles as shown by transmission electron microscopy (TEM). Third, fluorescence microscopy and Western blotting assays revealed that transfection of four different cell lines and acutely isolated rat sensory neurons with LNBs loaded with either linear or supercoiled cDNA constructs coding for the fluorescent protein, clover and tdTomato, resulted in protein expression. Fourth, two separate opioid receptor-ion channel signaling pathways were functionally reconstituted in HEK cells transfected with LNBs loaded with three separate cDNA constructs. Overall, these results lay the foundation for the use and further development of LNBs as in vitro transfection agents.

Dumbbell-Like Silica Coated Gold Nanorods and Their Plasmonic Properties

Silica coated gold nanorods (GNRs@SiO₂) with dumbbell-like morphology allowing dual functionalization in an individual nanostructure have attracted great attention for applications such as sensing and biological imaging. We report a detailed study on the feasibility of controlling the morphology of silica coating on GNRs. The morphology of the silica shell can be either cylindrical or dumbbell shaped. With constant GNR concentration, the ratio of hexadecyltrimethylammonium bromide (CTAB) and tetraethylorthosilicate (TEOS) concentrations is the key to determine the amount of available TEOS for silica deposition on the GNR since the TEOS will diffuse toward the surface of GNRs. The effect of morphologies on surface-enhanced Raman scattering (SERS) performance was also investigated, and we found that the dumbbell morphology of silica coated gold nanorods has the most significant SERS enhancement. Our study is significant in terms of the capability to control the dumbbell morphology of silica coated gold nanorods, which can eventually broaden the application of these plasmonic nanomaterials.

Core-Shell Interface-Oriented Synthesis of Bowl-Structured Hollow Silica Nanospheres Using Self-Assembled ABC Triblock Copolymeric Micelles

Hollow porous silica nanospheres (HSNs) are emerging classes of cutting-edge nanostructured materials. They have elicited much interest as carriers of active molecule delivery due to their amorphous chemical structure, nontoxic nature, and biocompatibility. Structural development with hierarchical morphology is mostly required to obtain the desired performance. In this context, large through-holes or pore openings on shells are desired so that the postsynthesis loading of active-molecule onto HSNs via a simple immersion method can be facilitated. This study reports the synthesis of HSNs with large through-holes or pore openings on shells, which are subsequently termed bowl-structured hollow porous silica nanospheres (BHSNs). The synthesis of BHSNs was mediated by the core-shell interfaces of the core-shell corona-structured micelles obtained from a commercially available ABC triblock copolymer (polystyrene- b-poly(2-vinylpyridine)- b-poly(ethylene oxide) (PS-P2VP-PEO)). In this synthesis process, polymer@SiO₂ composite structure was formed because of the deposition of silica (SiO₂) on the micelles' core. The P2VP block played a significant role in the hydrolysis and condensation of the silica precursor, i.e., tetraethylorthosilicate (TEOS) and then maintaining the shell's growth. The PS core of the micelles built the void spaces. Transmission electron microscopy (TEM) images revealed a spherical hollow structure with an average particle size of 41.87 ± 3.28 nm. The average diameter of void spaces was 21.71 ± 1.22 nm, and the shell thickness was 10.17 ± 1.68 nm. According to the TEM image analysis, the average large pore was determined to be 15.95 nm. Scanning electron microscopy (SEM) images further confirmed the presence of large single pores or openings in shells. These were formed as a result of the accumulated ethanol on the PS core acting to prevent the growth of silica.

Gold-Embedded Hollow Silica Nanogolf Balls for Imaging and Photothermal Therapy

Hybrid nanocarriers with multifunctional properties have wide therapeutic and diagnostic applications. We have constructed hollow silica nanogolf balls (HGBs) and gold-embedded hollow silica nanogolf balls (Au@SiO₂ HGBs) using the layer-by-layer approach on a symmetric polystyrene (PS) Janus template; the template consists of smaller PS spheres attached to an oppositely charged large PS core. ζ Potential measurement supports the electric force-based template-assisted synthesis mechanism. Electron microscopy, UV-vis, and near-infrared (NIR) spectroscopy show that HGBs or Au@SiO₂ HGBs are composed of a porous silica shell with an optional dense layer of gold nanoparticles embedded in the silica shell. To visualize their cellular uptake and imaging potential, Au@SiO₂ HGBs were loaded with quantum dots (QDs). Confocal fluorescent microscopy and atomic force microscopy imaging show reliable endocytosis of QD-loaded Au@SiO₂ HGBs in adherent HeLa cells and circulating red blood cells (RBCs). Surface-enhanced Raman spectroscopy of Au@SiO₂ HGBs in RBC cells show enhanced intensity of the Raman signal specific to the RBCs' membrane specific spectral markers. Au@SiO₂ HGBs show localized surface plasmon resonance and heat-induced HeLa cell death in the NIR range. These hybrid golf ball nanocarriers would have broad applications in personalized nanomedicine ranging from in vivo imaging to photothermal therapy.

Protecting patches in colloidal synthesis of Au semishells

Protecting groups are commonly applied in multi-step molecular syntheses to protect one or multiple functional groups from reacting. After the reaction, they are removed from the molecule. In full analogy to this concept, we report the practical and scalable colloidal synthesis of Au semishells using polyphenylsiloxane protecting patches to prevent part of the surface of polystyrene nanoparticles from being covered with Au. After Au deposition, the patches are removed yielding Au semishells. We anticipate that this strategy can be extended to the synthesis of other types of non-centrosymmetric nanoparticles.

Dual-Functionalized Theranostic Nanocarriers

Nanocarriers with the ability to spatially organize chemically distinct multiple bioactive moieties will have wide combinatory therapeutic and diagnostic (theranostic) applications. We have designed dual-functionalized, 100 nm to 1 μm sized scalable nanocarriers comprising a silica golf ball with amine or quaternary ammonium functional groups located in its pits and hydroxyl groups located on its nonpit surface. These functionalized golf balls selectively captured 10-40 nm charged gold nanoparticles (GNPs) into their pits. The selective capture of GNPs in the golf ball pits is visualized by scanning electron microscopy. ζ potential measurements and analytical modeling indicate that the GNP capture involves its proximity to and the electric charge on the surface of the golf balls. Potential applications of these dual-functionalized carriers include distinct attachment of multiple agents for multifunctional theranostic applications, selective scavenging, and clearance of harmful substances.

Magnetically-responsive silica-gold nanobowls for targeted delivery and SERS-based sensing

Composite colloidal structures with multi-functional properties have wide applications in targeted delivery of therapeutics and imaging contrast molecules and high-throughput molecular bio-sensing. We have constructed a multifunctional composite magnetic nanobowl using the bottom-up approach on an asymmetric silica/polystyrene Janus template consisting of a silica shell around a partially exposed polystyrene core. The nanobowl consists of a silica bowl and a gold exterior shell with iron oxide magnetic nanoparticles sandwiched between the silica and gold shells. The nanobowls were characterized by electron microscopy, atomic force microscopy, magnetometry, vis-NIR and FTIR spectroscopy. Magnetically vectored transport of these nanobowls was ascertained by time-lapsed imaging of their flow in fluid through a porous hydrogel under a defined magnetic field. These magnetically-responsive nanobowls show distinct surface enhanced Raman spectroscopy (SERS) imaging capability. The PEGylated magnetically-responsive nanobowls show size-dependent cellular uptake in vitro.

Small is beautiful: Surprising nanoparticles

In the preparation of nanoparticles for drug delivery, it is well known that their size as well as their surface decorations can play a major role in interaction with living media. It is less known that their shape and internal structure can interplay with cellular and in vivo fate. The scientific literature is full of a large variety of surprising terms referring to their shape and structure. The aim of this review is to present some examples of the most often encountered surprising nanoparticles prepared and usable in the pharmaceutical technology domain. They are presented in two main groups related to their physical aspects: 1) smooth surface particles, such as Janus particles, "snowmen", "dumbbells", "rattles", and "onions" and 2) branched particles, such as "flowers", "stars" and "urchins". The mode of preparation and potential applications are briefly presented. The topic has a serious, wider importance, namely in opportunity these structures have to allow exploration of the role of shape and structure on the utility (and perhaps toxicity) of these nanostructures.

Mesoporous Au nanotube-constructed three-dimensional films with excellent SERS performance based on the nanofiber template-displacement reaction strategy

Mesoporous Au nanotube-constructed three-dimensional films with excellent SERS performance are fabricated by the nanofiber template-displacement reaction strategy.

Asymmetric Colloidal Janus Particle Formation Is Core-Size-Dependent

Colloidal particles with asymmetric surface chemistry (Janus particles) have unique bifunctional properties. The size of these particles is an important determinant for their applications in diverse fields from drug delivery to chemical catalysis. The size of Janus particles, with a core surface coated with carboxylate and a partially encapsulating silica shell, depends upon several factors, including the core size and the concentration of carboxylate coating. The role of the carboxylate coating on the Janus particle size is well-understood; however, the role of the core size is not well defined. The role of the carboxylated polystyrene (cPS) core size on the cPS-silica Janus particle morphology (its size and shape) was examined by testing two different silica sizes and five different cPS core sizes. Results from electron microscopy (EM) and dynamic light scattering (DLS) analysis indicate that the composite cPS-silica particle acquires two distinct shapes: (i) when the size of the cPS core is much smaller than the non-cPS silica (b-SiO2) sphere, partially encapsulated Janus particles are formed, and (ii) when the cPS core is larger than or equal to the b-SiO2 sphere, a raspberry-like structure rather than a Janus particle is formed. The cPS-silica Janus particles of ∼100-500 nm size were obtained when the size of the cPS core was much smaller than the non-cPS silica (b-SiO2) sphere. These scalable nanoscale Janus particles will have wide application in a multifunctional delivery platform and catalysis.

Template-assisted synthesis of Janus silica nanobowls

The preparation of anisotropic nanoparticles has drawn much attention in the literature, with most of the efforts being dedicated to convex particles. In this work, instead, we present a reliable method to synthesis silica nanobowls with one well-defined opening, covering a broad range of sizes. The nanobowls have been obtained from asymmetrically functionalized silica-polymer Janus nanodumbbells, used as templates, by removing of the polymer. Polystyrene seeds having different sizes as well as surface chemistry have been used as starting material in a two-step seeded emulsion polymerization, which leads to polymer nanodumbbells. These dumbbells are also asymmetrically functionalized due to the presence of silane groups on only one of their two hemispheres. This allows us to selectively coat the silane-bearing hemisphere of the dumbbells with a silica layer by means of a Stoeber process. The silica nanobowls are eventually obtained after either calcination or dissolution of the polymeric template. Depending on the route followed to remove the polymer, nanobowls made of pure silica (from calcination) or hybrid Janus nanobowls with a silica outer shell and a covalently bound hydrophobic polymer layer inside the cavity (from dissolution) could be prepared. The difference between the two types of nanobowls has been proved by electrostatically binding oppositely charged silica nanoparticles, which adhere selectively only on the outer silica part of the nanobowls prepared by polymer dissolution, while they attach both inside and outside of nanobowls prepared by calcination. We also show that selective functionalization of the outer surface of the Janus nanobowls from dissolution is possible. This work is one of the first examples of concave objects bearing different functionalities in the inner and outer parts of their surface.