Alternative materials having higher superparamagnetic properties, such as iron carbides and carbon-coated Fe, were recently explored    . For example, the carbon coated Fe nanoparticles, Fe@C, which exhibit strong su- perparamagnetic properties, have been used as MRI contrast enhancement agents . The presence of carbon shell in the core-shellnanostructures is very important since such shell acts as a protective coating to magnetic cores against chemical components of biological fluids and is inert to pH changes. The carbon shell also facilitates the particles to be stable to chemical environments and treat- ment procedures. The presence of carbon shell provides opportunities to intro- duce functional groups on the carbon surface. A series of methods for functiona- lization of carbon materials and carbon based nanoparticles have been devel- oped. These methods involve either non-covalent functionalization by physical adsorption of chemical compounds, such as polymers, or oxidative route to co- valently introduce functional groups. The oxidative functionalization process is however accompanied by oxidation of Fe core in Fe@C particles and decrease of superparamagnetic properties. Strong chemical interaction between the surface carbon network and the functional groups through a covalent carbon-carbon bonding is preferred. Different functional groups, e.g., amino, hydroxyl, alkyne, or maleimido groups, have been covalently bonded to Fe@C nanoparticles through a two-step reaction with aryl diazonium salts . This process is nevertheless li- mited to bonding only the aryl moieties to carbon shell surface of nanoparticles. Continuing search for simple efficient methods to introduce organic functional groups capable of further modification tailoring the nanoparticle properties to- wards specific applications is an active field of research. In this work, a mild or- ganic reaction based on succinic acid peroxide was used to generate and cova- lently attach carboxyl terminated free alkyl radicals as functional groups to the carbon shell of Fe@C nanoparticles. This technique has previously been effec- tively applied for a non-destructive to the side walls functionalization of carbon nanotubes .
molecules in polymeric core-shellnanostructures where the physico-chemical characteristics of the shell have been designed to interact with lipid membranes, internalization by the tissue macrophage cells can be improved. This reduces transport of free gentamicin to renal tissues and enhances targeting to the liver or spleen. In this research, we utilized an amphiphilic Pluronic F-68 copolymer as the shell, and gentamicin was incorporated into the nanoparticle cores through cooperative electrostatic attractions. To fabricate the nanostructured complexes, a polyanionic PAA - + Na
colloidal form (have high degree of agglomeration). Our study can also be extended to form silica shell over indi- vidual nanoparticles (having high degree of agglomera- tion) which can then be used in various biomedical and catalytic applications. We have also increased the concentration of functional groups on the surface of core-shellnanostructures with the use of organosilane precursors to form the shells. The methodology is an improvement over the commonly used post-grafting or co-condensation method. This point has been proved in this article by carrying out two studies: one with zeta potential and other using a fluorescamine dye. Thus, the methodology described can be used to synthesize core- shellnanostructures with high density of functional groups which can be further used for various analytical purposes such as extraction of trace elements with high specificity. The high density of functional groups will also ensure an increase in the number biomolecules or drugs that can be immobilized on these nanostructures. For this we have carried out a case study using glucose and L-methionine and have shown that the functiona- lized core-shellnanostructures can be used to immobi- lize biomolecules.
In this study, electrospun composite nanofibers containing magnetic core-shellnanostructures were proposedas nanocarrier for the targeted drug delivery of an anticancer drug of daunorubicin. For this purpose, magnetic Fe 3 O 4 nanoparticles were coated with a silica shellusing the stober method and then polyvinyl alcohol composite nanofibers containing these nanoparticles and DAN drug were prepared by electrospining method.The DAN release study from proposed nanocarrier showed that the release rate of the drug at pH= 6 was higher than the release value at pH = 7.4 and the release kinetic was corresponded to the Peppas model. Therefore, it can be concluded that this nanocarrier is capable of responding to pH changes, that is an advantage in the targeted delivery of the drug. Also, this method has the advantages of magnetic sensitivity, high drug loading capacity (due to the hydrogen bonding between the drug groups and the silica layer surrounding the magnetite nanoparticles) and Fig. 6. Release profiles of DOX from nanocarrier in PBS at37˚C (a) pH=6, (b) pH=7.4
Au-Ag alloy nanostructures with various shapes were synthesized using a successive reduction method in this study. By means of galvanic replacement, twined Ag nanoparticles (NPs) and single-crystalline Ag nanowires (NWs) were adopted as templates, respectively, and alloyed with the same amount of Au + ions. High angle annular dark field-scanning TEM (HAADF-STEM) images observed from different rotation angles confirm that Ag NPs turned into AuAg alloy rings with an Au/Ag ratio of 1. The shifts of surface plasmon resonance and chemical composition reveal the evolution of the alloy ring formation. On the other hand, single-crystalline Ag NWs became Ag@AuAg core-shell wires instead of hollow nanostructure through a process of galvanic replacement. It is proposed that in addition to the ratio of Ag templates and Au ion additives, the twin boundaries of the Ag templates were the dominating factor causing hollow alloy nanostructures.
resolution bright and dark TEM images in Figure 3d, e, f, g, h clearly show that most of the nanoparticles are core- shellnanostructures as indicated by arrows in the figures. Meanwhile, some nanoparticles are well-defined core-shell structures as shown by arrows in Figure 3d, e, while some nanoparticles are complete hollow shell structures as shown by arrows in Figure 3f. In addition, there are many nanoparticles with diameters less than 10 nm adsorbed on the side of nanorods as shown in Figure 3e, f. These differ- ent structures of nanoparticles tell us that the replacement process is complex. The Co nanoparticles attached on the tip of nanorods have more opportunities to react with Au 3+ , and they are replaced more absolutely, and, as a
and distorting the original optical properties, which are hard to obtain from the spherical core/shell nanostruc- tures. In addition, the ability of plasmonic material NWs to support strongly localized surface plasmon modes has led to the development of deep subwavelength plas- monic waveguides [19, 40, 41], optical antennas , and surface-enhanced Raman scattering sensors [22, 42, 43]. Rationally designed complex dielectric/metal core/shell or core/multi-shell structures can significantly enhance or suppress the optical responses of nanostructures and allow conventionally inaccessible functionalities such as invisibility cloaking [24–32], super-scattering/super- absorption [33, 34], enhanced luminescence and nonlin- ear optical activities [35–37], and deep subwavelength optical waveguiding [38, 39]. In this review, we introduce various novel plasmonic and metamaterial devices based on 1D subwavelength core/shellnanostructures. We discuss the rational design of core/shell NW structures composed of materials appropriately chosen for targeted functionalities and successful experimental applications using core/shell NW structures. Moreover, we briefly describe the recently developed synthesis/fabrication technologies for realizing 1D subwavelength core/shell nanowires and their practical applications.
(ED) or magnetic dipole (MD), and how the coexistence and interference of the ED and the MD can bring extra ﬂexibility for scattering shaping. Afterwards, we dis- cuss the scattering shaping by core-shellnanostructures through the interferences of electric and magnetic dipoles (Section 4.2), including two examples of broadband unidirectional scattering by core-shell nanospheres (Section 4.2.1) and eﬃcient shap- ing of the scattering pattern for core-shell nanowires (Section 4.2.2). At the end of this chapter we demonstrate polarization-independent Fano resonances in arrays of core-shell nanospheres (Section 4.3.2).
of nanomaterials owing excellent features including enhanced specific surface area, huge void space to accommodate guest molecule, mesoporous channels on outer shell, reduced density and superior biocompatibility. The attractiveness of these nanostructures is that their formation, size, shape, porosity, pore volume, pore size (textural properties) thickness of mesoporous shell can be precisely tuned owing to the control in their chemistry. In addition, the effective surface modifications impart these nanostructures supplementary role of gate-keeping to prevent premature release of drugs, active targeting, and diagnostic functionalities [1-3]. C/S-MSNs projects its biomedical application as a nano-reserve for the storage of drug in their void or hollow core, controlled (smart/stimuli responsive) and sustained release of encapsulated or adsorbed drug, targeted delivery of drugs with functionalized ligands thus minimizing unfavourable side effects, and ultimately the development of theragnostic nanostructures that aids simultaneous therapeutic and diagnostic functions by utilizing the benefits of mesoporous coreshellnanostructures. Theragnostic nanomaterials are those materials that reduce the gap between therapeutic efficiency and diagnostic potential thus coupling aforementioned different strategies to a single unit. To provide an overview of versatile coreshell mesoporous nanostructures as theragnostic agents in cancer nanotechnology, we aim to discuss major synthetic strategies of C/S-MSNs and recent improvements in the theragnostic (therapeutic and diagnostic) applications for cancer. Firstly, we discuss significant properties and different methodology for the synthesis of coreshell mesoporous silica nanostructures. In the second section, we focus on various therapeutic strategies (targeted chemotherapy, magnetic hyperthermia, photodynamic therapy, gene therapy, immunotherapy, etc.) and diagnostic modalities (optical imaging, magnetic resonance imaging, nuclear imaging, etc.) emerged from the core part of the nanocarrier. Finally, we discuss the major challenges and future perspectives of C/S-MSNs in biomedical regime.
Semiconductor nanocrystals or quantum dots (QDs) are the subject of intensive research, due to a number of novel properties which make them attractive for both fundamental studies and technological applications. 1 − 6 QDs are of particular interest for solar cell applications due to their ability to increase e ﬃ ciency via the generation of multiexcitons from a single photon. 7−9 QDs can be synthesized with a high degree of control using colloidal chemistry. 10,11 Much research e ﬀ ort has been directed toward studying QDs grown from more than one semiconductor, e.g., core/shell heterostructures. 12 − 14 Such core/shellnanostructures provide a means to control the optical properties by tuning the electron − hole wave function overlap which is a ﬀ ected by the alignment of the conduction band (CB) and valence band (VB) edges, as well as the QD shape and size. In contrast to type-I band alignments, type-II alignments have staggered CB and VB edges so the lowest energy states for electrons and holes lie in di ﬀ erent spatial regions, leading to charge separation between the carriers. Type-II core/shell QDs can be classi ﬁ ed according to whether the band alignments tend to localize the hole in the core and electron in the shell (h/e QDs, such as CdTe/CdSe QDs) or the electron in the core and the hole in the shell (e/h QDs, such as CdSe/CdTe QDs). 15 Such staggered band alignments have several useful physical consequences, including longer radiative recombination times for more e ﬃ cient charge extraction in photovoltaic applications, 16,17 optical gaps that can be made smaller than the bulk values of the constituent materials, 12,18,19 and control of the electron − hole wave function overlap which determines the exchange interaction energy. 20 Charge separation in type-II QDs can also be used to increase the repulsion between like-sign charges in biexciton states, 21,22 leading to the possibility of lasing in the single exciton regime. 6,23,24
Commercially pure titanium powder is subjected to mechanical milling (MM)-a severe plastic deformation process-for various periods of time. The MM powder has two diﬀerent kinds of microstructure, which can be controlled by the MM conditions. They include ultra ﬁne and coarse grain structures known as ‘‘shell’’ and ‘‘core’’, respectively. Subsequently, these MM powder is sintered using a hot roll sintering (HRS) process. The HRS materials with the shell and the core have a network structure of continuously connected shells, which is known as a harmonic structure. The HRS materials with the harmonic structure simultaneously demonstrate both high strength and elongation. These outstanding mechanical properties are inﬂuenced by the harmonic structure characteristics such as shell and core grain sizes, and shell fraction and shell network size. Thus, the harmonic structure can be considered as a remarkable design for improving the mechanical properties of commercially pure titanium as well as other metallic materials. [doi:10.2320/matertrans.MB200913]
As most studies only used one voltage value for specific compound cone stabilization, no systematic investigation of this parameter has been done. For a given pair of polymer systems and flow rates, it was found that there exists a narrow range of applied voltage in which a stable compound Taylor cone can be formed (Fig 7b). Below this optimal range, both or any one liquid cannot be driven out and results in discontinuous dripping (Fig 7a) . Due to the increased size of the cone, mixing of the two solutions tended to occur . Voltage above the critical range caused the strength of the electric field to exceed that required for the material and the processing conditions used. Instead of the coaxial jet, separate jets formed from the shell and core solutions (Fig 7c).
In this paper, we modeled a core/shell/shell structure with cylindrical Schrodinger-Poisson coupled equation when a magnetic field is (and is not) applied along its axis. We showed the electron density is peaked near the outer surface of the channel when the magnetic field is applied. Therefore one may make a nano-device which its electrons move only on its outer surface. Also we applied a gate voltage to the device and showed a higher threshold voltage (to turn on the device) is necessary when a magnetic field is applied. This is because of the increase in the lowest energy level similar to the size quantization. i.e a device with longer channel looks like a device with shorter channel if it is placed in a magnetic field parallel to its axis.
brittle and exhibited a high modulus and low elongation- at-break. In our previous study , an increase of Young’s modulus was achieved with increasing the gelatin content in the shell material for different blending ratios. The crystalline morphology of electrospun polymeric fibers strongly influenced the mechanical properties [51,52], and gelatin mainly contributed to the crystallinity of the electrospun mats [53,54]. In this regard, it was assumed that by combining the gelatin into PCL fibers, in addition to the biological performance, the tensile properties could be enhanced and became more proper for tissue engineering approaches. Moreover, fiber orientation in the thread will affect the interaction between the fibers and consequently influence their mechanical behavior . Compared with un-crosslinked threads, fibrous threads crosslinked with genipin showed improvement in tensile properties with increment in Young’s modulus from 34.20 cN/tex to 40.64 cN/tex (p<0.1) and significant decrement in the strain-at-break from 20.78% to 14.26% (p<0.05). However, a significant improvement (p>0.5) was not observed in terms of the ultimate tensile strength (1.66 cN/tex).
Background: The controlled introduction of covalent linkages between dendrimer building blocks leads to polymers of higher architectural order known as tecto-dendrimers. Because of the few simple steps involved in their synthesis, tecto-dendrimers could expand the portfolio of structures beyond commercial dendrimers, due to the absence of synthetic drawbacks (large number of reaction steps, excessive monomer loading, and lengthy chromatographic separations) and structural constraints of high-generation dendrimers (reduction of good monodispersity and ideal dendritic construction due to de Gennes dense-packing phenomenon). However, the bio- medical uses of tecto-dendrimers remain unexplored. In this work, after synthesizing saturated shellcore–shell tecto-dendrimers using amine-terminated polyamidoamine (PAMAM) generation 5 (G5) as core and carboxyl-terminated PAMAM G2.5 as shell (G5G2.5 tecto-dendrimers), we surveyed for the first time the main features of their interaction with epithelial cells.
decay rates. As such a higher ensemble quantum yield (QY) 72 and higher on-time fractions among single dots can be achieved. 97,146 Indeed, it is possible to routinely achieve near-unity QY in the best-represented material systems such as CdSe/CdS. 62,156 One effect of a shell is to isolate the excited state from the surface by decreasing the wave function overlap with surface states. It is notable that even in samples with shells only a few monolayers thick, in which the excited states are clearly not isolated from the surface, a very high QY can be achieved (for example at the conclusion of QD synthesis). 62 This demonstrates that molecular surface termination can be achieved in which almost no intergap states or resonant excitations are present. As-synthesized colloidal QD samples typically or inherently contain large concentrations of molecules that could coordinate the surface. 157 However, applications almost universally require purification and/or surface modification of as-synthesized QDs. Purification methods have frequently been seen to decrease QY 7,62,97,158 and also to decrease ligand populations. 124,158,159 It is essential to understand whether the changes in QY are reversible, how ensemble QY and decay profiles depend on ligand occupation, and the conditions under which surface structures that support high QY can be maintained or restored. 160
The shape of the PA particles varied significantly from batch to batch. Some particles had generally spherical shape (as in the case of toluene-containing ones), while some were collapsed (as for other solvents). In one batch, particles were either mainly spherical or collapsed. This effect was not solvent-specific; both types of particles were observed for most solvents in different batches. The shape was found to be influenced by the drying procedure. Freeze-dried particles exhibit spherical shape more often than those dried in air, though not always. The effect of the drying procedure on the final shape of PA microparticles/capsules was already discussed in the literature . The phenomenon can be explained by the plasticizing effect of water on PA. In an aqueous medium, the walls of particles are soft and elastic due to the swelling of the polymer in water. Strong mechanical impact experienced by the microobjects during drying due to capillary forces leads to their collapse. Freeze-drying helps to preserve the spherical shape during drying. This hypothesis is supported by the fact that in the suspension most of the PA particles have spherical shape with minor amount of concavities or folds. Although further examination of the parameters influencing mechanical properties of the PA particles might be very useful for their further application, it was not performed here. The main goal here was to investigate the morphology. Appearance of collapsed particles in this sense is advantageous, since it is the direct evidence of the core- shell morphology. For the determination of morphology of particles with well-pronounced spherical shape other methods should be used.
Nanoparticles with average particles size in the range from 1-100 nm have been considered as an alternative tool for cancer diagnosis and therapy at an early stage as they have special physiochemical and unique size-dependent properties. [54,55] The magnetic nanostructures are a vital material used in various applications in sensors, cancer treatment, drug delivery, solar cells, high performance batteries, data storage materials, etc. The advantages of using magnetic nanoparticles are: chemically stable under physiological conditions, functionalized with other materials, and have a high magnetization moment. The disadvantages associated with magnetic nanostructures are: aggregation and instability of nanoparticles. [56-59] Since the nanostructures can oxidize, a non-reactive coating layer is coated on the surface of the magnetic core. By fabricating the core-shell structure, the magnetic core could be isolated from a corrosive environment. The shell can include two major types to protect the core: organic materials (polymer) and inorganic materials (silica). Complex materials can be embedded such as: carbon nanotubes, graphene derivatives, and polymers, etc. [60,61] The synthesis process of the magnetic nanostructures is divided into four different types: co-precipitation , thermal decomposition , and hydrothermal process.  Different processes give out different size and shape of the magnetic nanostructures.