Zhaoxia Zhou

Cubic Molecularly Imprinted Polymer Nanoparticles with a Fluorescent Core

Molecular recognition is a fundamental process for all living systems. Applications of the phenomenon have exploited antibodies as the selective components of immunoassays, affinity phases and biosensors and as therapeutic agents. Molecularly imprinted polymers (MIPs) are one of the leading contenders for alternatives to antibodies. MIPs generally are cross-linked polymers synthesized in the presence of the target compound (the template). After the removal of the template, cavities with complementary size and shape to the template are created, which can recognize and selectively rebind the template. MIPs have been successfully applied to solid-phase extraction and in biosensors. The synthesis of MIPs with architectures which are well defined on the molecular level is a future priority. MIP nanoparticles (NPs) can be prepared by a number of methods. Each of these have some disadvantages including: production of particles with irregular shapes and sizes, heterogeneous binding sites, decreased affinity due to use of surfactants and high polymerization temperatures, long polymerization time, relatively low yield, etc. Here, we have developed a new core–shell approach. In order to detect binding, fluorescence is a promising technique, since fluorescent labeling can be a powerful tool for probing the local environment, as well as for biological imaging. As a site for placement of a fluorescent label, the NP core is a promising location, since it is isolated from the bulk solution by the surrounding polymer shell. There are currently two reported approaches for the incorporation of fluorescent species in the core of MIP NPs. One example involved the creation of a MIP layer over inorganic quantum dots. In the second case two layers were created over silicacoated magnetic particles; the first consisting of a fluorescently labeled polymer and the second, outer layer, was the MIP. In our approach dendrimers were selected as the core from which to graft a MIP shell to form imprinted NPs. Dendrimers are biocompatible, soluble macromolecules possessing highly defined regularly branched structures, a well defined shape, size and number of peripheral functionalities. Using dendrimers as the core in a controlled or “living” polymerization would ensure precise grafting at the molecular level. An earlier example of dendrimer-based MIP NPs was reported by Zimmerman. The monomolecular imprinted NPs formed had only one binding site at the centre of the particles and involved a long and tedious synthesis. The use of dendrimer-based macroinitiators for the synthesis of NPs using atom transfer living radical, nitroxide-initiated and microemulsion polymerizations have been reported. Unfortunately the synthesis conditions are mostly incompatible with the imprinting process (high temperature, presence of ions, etc.). Much more favorable conditions would be associated with use of iniferters (initiator, chain transfer agent, terminator). Here we describe the synthesis of NPs in solution without the use of surfactant and no requirement for high temperatures in 120 s polymerization time. The NPs are dispersible in both aqueous and organic solvents. A unique, versatile and highly controlled technique combining dendrimer-based macroiniferters, living polymerization, nanotechnology, molecular imprinting and novel fluorescent sensing technique is demonstrated. In order to first characterize the properties of dendrimercore NPs, a non-fluorescent core was used. Iniferter units were attached on the periphery of polyamidoamine (PAMAM) dendrimers, generation 4, creating a soluble macroiniferter. This was used as core for the synthesis of NPs (Scheme 1). As iniferter S-(carboxypropyl)-N,N-diethyldithiocarbamic acid (CNDDA) was used and coupled to the peripheral primary amino groups of the dendrimers (Supporting Information). The polymerization was initiated simultaneously from potentially 48 points per dendrimer moiety. Dendrimer-core MIP-shell NPs were synthesized in just two minutes by UV irradiation. The use of UV-initiated living radical polymerization, besides imparting better control over the size distribution, has another fundamental advantage. The polymerization process can be re-initiated by UV exposure, where the already synthesized NPs will act as a macroinitiator, allowing many possibilities for further modification of the particle surface properties. [*] P. K. Ivanova-Mitseva, Dr. A. Guerreiro, Dr. E. V. Piletska, Dr. M. J. Whitcombe, Dr. F. Davis, Prof. S. A. Piletsky Cranfield Health, Vincent Building, Cranfield University Cranfield, MK43 0AL (UK) E-mail: m.whitcombe@cranfield.ac.uk

Structure characterization and tribological study of magnetron sputtered nanocomposite nc-TiAlV(N,C)/a-C coatings

Grown by reactive unbalanced magnetron sputtering in a mixed N2 and CH4 gaseous medium, heterogeneous nanocomposite coatings in the Ti–Al–V–N–C system show extraordinarily excellent tribological performance of coated machining tools. Using analytical high-resolution TEM, EELS, FEG-SEM, XRD, and Raman spectroscopy, this paper reports detailed structural and chemical characterization of the coatings grown at various CH4 : N2 ratios. Meanwhile, the mechanical and tribological properties were also measured, including hardness, Youngs modulus, residual stress and the dry-sliding friction and wear at varying environmental humidity. When CH4 gas was introduced in the deposition, the structure of the coatings has been found to experience a change from nano-scale TiAlN/VN multilayer architecture to a complex mixture of columnar grains of nc-TiAlV(N,C)/a-C nanocomposites and inter-column network of sp2-type amorphous carbon. Carbon incorporation and segregation also shows remarkable influence on the columnar growth model by leading to finer grain size. As compared to the carbon-free nitride coating, the nanocomposite coatings showed substantially reduced residual stress owing to the free-carbon precipitation, whereas the coatings maintained comparable hardness to the carbon-free TiAlN/VN. Their tribological properties were found to be strongly dependent on the environment. In humid air at RH > 30%, the coatings showed low friction coefficient less than 0.4 and extremely low wear rate at a scale of ∼10−17 m3N−1 m−1.

On the structure and composition of nanoscale TiAlN/VN multilayers

The chemical and physical structure of a TiAlN/VN multilayer, of average layer thickness 3.4 ± 0.4 nm, was characterized using a spherical aberration-corrected STEM, utilizing a nominal 0.1-nm beam, by HAADF and EELS. The interface between layers was shown to be rough, with local thickness variations evident in layer thickness. Chemical mixing between layers was identified, consistent with numerical modelling of the deposition flux and layer growth. The implications of the compositional modulation are discussed.

The role of helium ion microscopy in the characterisation of complex three-dimensional nanostructures.

This work addresses two major issues relating to Helium Ion Microscopy (HeIM). First we show that HeIM is capable of solving the interpretation difficulties that arise when complex three-dimensional structures are imaged using traditional high lateral resolution techniques which are transmission based, such as scanning transmission electron microscopy (STEM). Secondly we use a nano-composite coating consisting of amorphous carbon embedded in chromium rich matrix to estimate the mean escape depth for amorphous carbon for secondary electrons generated by helium ion impact as a measure of HeIM depth resolution.

Tracing C changes in a C/CrC PVD coating using Raman spectroscopy and EELS

A C/CrC coating was deposited by unbalanced magnetron sputtering of graphite and Cr metal targets in argon atmosphere for low friction tribological applications. The coating possessed a nanocomposite structure with amorphous carbon embedded in a metastable fcc CrC matrix. The nanocomposite structure was annealed at 750°C in Ar+5%H2 atmosphere for 30 minutes to evaluate its thermal stability. Microstructures of the as-deposited and annealed coating were characterised using Raman spectroscopy and cross sectional transmission electron microscopy coupled with electron energy loss spectroscopy (TEM/EELS). Raman spectroscopy suggested the presence of graphitic carbon in the coating after annealing. EELS (ELNES of C K) combined with HRTEM investigation of the cross sections revealed graphitic C at the very top (~200nm) of the coating and amorphous C at the remaining part of the coating after annealing at 750°C. The advantages and limitations of Raman spectroscopy and TEM techniques in studying C/CrC coating are also discussed.

Synthesis of Gold Nanoparticles Using the Interface of an Emulsion Droplet

A facile and rapid method for synthesizing single crystal gold spherical or platelet (nonspherical) particles is reported. The reaction takes place at the interface of two immiscible liquids where the reducing agent decamethylferrocene (DmFc) was initially added to hexane and gold chloride (AuCl4-) to an aqueous phase. The reaction is spontaneous at room temperature, leading to the creation of Au nanoparticles (AuNP). A flow focusing microfluidic chip was used to create emulsion droplets, allowing the same reaction to take place within a series of microreactors. The technique allows the number of droplets, their diameter, and even the concentration of reactants in both phases to be controlled. The size and shape of the AuNP are dependent upon the concentration of the reactants and the size of the droplets. By tuning the reaction parameters, the synthesized nanoparticles vary from nanometer to micrometer sized spheres or platelets. The surfactant used to stabilize the emulsion was also shown to influence the particle shape. Finally, the addition of other nanoparticles within the droplet allows for core@shell particles to be readily formed, and we believe this could be a versatile platform for the large scale production of core@shell particles.

C/CrC nanocomposite coating deposited by magnetron sputtering at high ion irradiation conditions

CrC with the fcc NaCl (B1) structure is a metastable phase that can be obtained under the non-equilibrium conditions of high ion irradiation. A nano-composite coating consisting of amorphous carbon embedded in a CrC matrix was prepared via the unbalanced magnetron sputtering of graphite and Cr metal targets in Ar gas with a high ionized flux (ion-to-neutral ratio Ji/Jn = 6). The nanoscale amorphous carbon clusters self-assembled into layers alternated by CrC, giving the composite a multilayer structure. The phase, microstructure, and composition of the coating were characterized using x-ray diffraction, transmission electron microscopy, and aberration corrected scanning transmission electron microscopy coupled with electron energy loss spectroscopy. The interpretation of the true coating structure, in particular the carbide type, is discussed.

Origin of Porosity in Triol Sol-Gel PbZr 53 Ti 47 O 3 Single Layer Thin Films Deposited on Pt/Ti/SiO 2 /Si Substrates

Pb(Zr 53 Ti 47 )O 3 thin films on Pt/Ti/SiO 2 /Si substrates were processed by a triol (1,1,1-tris(hydroxymethyl)ethane) based sol-gel route. Film microstructures were characterised using transmission electron microscope (TEM) equipped with electron energy loss spectroscopy and nano-probe energy dispersive X-ray analysis with the intention of revealing the crystallisation mechanism. Porosity developed in films >75nm, whereas films h 75nm thick were single phase and pore free. An investigation of low temperature heat treatment schedule on phase evolution was carried out to elucidate the origin of the porosity in films >75nm. TEM results indicated that porosity was associated with the formation of Pb-rich precipitates during low temperature pyrolysis (∼400°C). Inhomogeneity of the pyrolysed microstructure is responsible for inhomogeneity in the crystallised film >75nm.

Data related to the mesoscopic structure of iso-graphite for nuclear applications

The data in this article are related to the research article “Mesoscopic structure features in synthetic graphite” (März et al., 2018) [1]. Details of the manufacture of isostatically moulded graphite (iso-graphite), thin foil preparation by focused ion beams (FIB) for analysis, and characterisation methods are provided. The detailed structures of coke filler and binding carbon are presented through scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and Raman spectroscopy characterisation. Atomistic modelling results of mesoscopic structural features are included.

Diffusion Barrier Effect of Ni-W-P and Ni-Fe UBMs during High Temperature Storage

The high temperature storage test (HTST) was conducted on the SnAgCu/Ni-W-P and Ni-Fe solder joints. While the conventional Ni-P solder joints were used as comparison to study the diffusion barrier effect of Ni-W-P and Ni-Fe under bump metallization (UBM). Both cross section and top view for the microstructural evolution of solder joints during 150°C aging were observed by the scanning electron microscope (SEM). After reflow, (Cu, Ni)6Sn5 in the forms of chunky and rod-like was formed with an average thickness of around 1µm in SAC/Ni-P solder joint. During the HTST, bulky (Cu, Ni)6Sn5 grains were formed with a 5µm in diameter due to the interconnections of multiple (Cu, Ni)6Sn5 grains. In terms of SAC/Ni-Fe solder joints, during the reflow process, FeSn2 layer and rod-like (Cu, Ni)6Sn5 grains were formed. During the aging at 150°C, rod-like dispersed (Cu, Ni)6Sn5 grains started to interconnect with each other which finally progressed into an outer IMC layer upon FeSn2 phase. In Ni-W-P solder joints, the morphology and composition of IMCs is similar to it in Ni-P solder joints. The thickness of (Cu, Ni)6Sn5 was much thicker during reflow but turned out to be below it in Ni-P solder joints after 120h aging. Experimentally, both Ni-W-P and Ni-Fe UBM show an excellent diffusion barrier effect to retard the Kirkendall voids formation compared to the conventional Ni-P UBM. Specifically, (Cu, Ni)6Sn5 were formed at the SnAgCu/ Ni-W-P interface with a total thickness around 2µm, while only a 1µm thick FeSn2 layer accompanying with several dispersing (Cu, Ni)6Sn5 grains outside were formed at the SnAgCu/Ni-Fe interface. The addition of Fe elements can dramatically supress the diffusion of Ni and the formation of Ni3Sn4, which shows superior diffusion barrier compared to Ni-P UBM. The addition of W into Ni-P significantly decreases the growth rate of the interfacial IMCs during the aging process, which shows potential for electronic devices operated under long-term aging process.