Simple analytical model for the magnetophoretic separation of superparamagnetic dispersions in a uniform magnetic gradient

Magnetophoresis-the motion of magnetic particles under applied magnetic gradient-is a process of great interest in novel applications of magnetic nanoparticles and colloids. In general, there are two main different types of magnetophoresis processes: cooperative magnetophoresis (a fast process enhanced by particle-particle interactions) and noncooperative magnetophoresis (driven by the motion of individual particles in magnetic fields). In the case of noncooperative magnetophoresis, we have obtained a simple analytical solution which allows the prediction of the magnetophoresis kinetics from particle characterization data (size and magnetization). Our comparison with new experimental results shows good quantitative agreement. In addition, we show the existence of a universal curve onto which all experimental results should collapse after proper rescaling. The range of applicability of the analytical solution is discussed in light of the predictions of a magnetic aggregation model

Hydrothermal assisted synthesis of iron oxide-based magnetic silica spheres and their performance in magnetophoretic water purification

Porous Magnetic Silica (PMS) spheres of about 400 nm diameter were synthesised by one-pot process using the classical Stӧber method combined with hydrothermal treatment. Maghemite nanoparticles (γ-Fe2O3) were used as fillers and cetyltrimethylammonium bromide (CTAB) was used as templating agent. The application of the hydrothermal process (120 °C during 48 h) before the calcination leads to the formation of homogeneous and narrow size distribution PMS spheres. X-ray diffraction patterns (XRD), Infrared measurements (FTIR) and Transmission Electron microscopy (TEM) methods were used to determine the composition and morphology of the obtained PMS spheres. The results show a homogeneous distribution of the γ-Fe2O3 nanoparticles in the silica matrix with a “hollow-like” morphology. Magnetophoresis measurements at 60 T m−1 show a total separation time of the PMS spheres suspension of about 16 min. By using this synthesis method, the limitation of the formation of silica spheres without incorporation of magnetic nanoparticles is overcome. These achievements make this procedure interesting for industrial up scaling. The obtained PMS spheres were evaluated as adsorbents for Ni2+ in aqueous solution. Their adsorption capacity was compared with the adsorption capacity of magnetic silica spheres obtained without hydrothermal treatment before calcination process. PMS spheres show an increase of the adsorption capacity of about 15% of the initial dissolution of Ni2+ without the need to functionalize the silica surface.Fundação para a Ciência e a Tecnologia (FCT

Stimulus-Responsive Ultrathin Films for Bioapplications: A Concise Review

The term “nanosheets” has been coined recently to describe supported and free-standing “ultrathin film” materials, with thicknesses ranging from a single atomic layer to a few tens of nanometers. Owing to their physicochemical properties and their large surface area with abundant accessible active sites, nanosheets (NSHs) of inorganic materials such as Au, amorphous carbon, graphene, and boron nitride (BN) are considered ideal building blocks or scaffolds for a wide range of applications encompassing electronic and optical devices, membranes, drug delivery systems, and multimodal contrast agents, among others. A wide variety of synthetic methods are employed for the manufacturing of these NSHs, and they can be categorized into (1) top-down approaches involving exfoliation of layered materials, or (2) bottom-up approaches where crystal growth of nanocomposites takes place in a liquid or gas phase. Of note, polymer template liquid exfoliation (PTLE) methods are the most suitable as they lead to the fabrication of high-performance and stable hybrid NSHs and NSH composites with the appropriate quality, solubility, and properties. Moreover, PTLE methods allow for the production of stimulus-responsive NSHs, whose response is commonly driven by a favorable growth in the appropriate polymer chains onto one side of the NSHs, resulting in the ability of the NSHs to roll up to form nanoscrolls (NSCs), i.e., open tubular structures with tunable interlayer gaps between their walls. On the other hand, this review gives insight into the potential of the stimulus-responsive nanostructures for biosensing and controlled drug release systems, illustrating the last advances in the PTLE methods of synthesis of these nanostructures and their applications

Interfacial Transformation of an Amorphous Carbon Nanofilm upon Fe@Ag@Si Nanoparticle Landing and its Colloidal Nanoscrolls: Enhanced Nanocompositing-Based Performance for Bioapplications

We report a novel method for generating magneto-plasmonic carbon nanofilms and nanoscrolls using a combination of two gas-phase synthetic techniques. Ternary Fe@Ag@Si “onion-like” nanoparticles (NPs) are produced by a magnetron sputtering inert gas condensation source and are in situ landed onto the surface of carbon nanofilms, which were previously deposited by a DC arc discharge technique. Subsequently, a polyethylenimine-mediated chemical exfoliation process is performed to obtain carbon nanoscrolls (CNS) with embedded NPs (CNS-NPs). Of note, the carbon nanofilms undergo an interfacial transition upon addition of NPs and become rich in the sp² phase. This transformation endows and enhances multiple functions, such as thermal conductivity and the plasmonic properties of the nanocomposites. The obtained two-dimentional (2D) nanocomposites not only exhibit a highly efficient surface-enhanced Raman scattering property, allowing sensitive detection of malachite green isothiocyanate (MGIT) and adenosine-triphosphate (ATP) molecules at concentrations as low as 1 × 10^–10 M, but also show enhanced near-infrared-responsive photothermal activity when forming stable colloidal 1D CNS-NPs. In addition, the CNS-NPs present an enhanced single- and two-photon fluorescence in comparison with pristine CNS and NPs. These results make them suitable for the rational fabrication of “all-in-one” multifunctional nanocomposites with tubular structures toward a wide range of biomedical solutions

Fluorescent Nanocomposites: Hollow Silica Microspheres with Embedded Carbon Dots

Intrinsically fluorescent carbon dots may form the basis for a safer and more accurate sensor technology for digital counting in bioanalytical assays. This work presents a simple and inexpensive synthesis method for producing fluorescent carbon dots embedded in hollow silica particles. Hydrothermal treatment at low temperature (160 °C) of microporous silica particles in presence of urea and citric acid results in fluorescent, microporous and hollow nanocomposites with a surface area of 12 m2/g. High absolute zeta potential (−44 mV) at neutral pH demonstrates the high electrosteric stability of the nanocomposites in aqueous solution. Their fluorescence emission at 445 nm is remarkably stable in aqueous dispersion under a wide pH range (3–12) and in the dried state. The biocompatibility of the composite particles is excellent, as the particles were found to show low genotoxicity at exposures up to 10 μg/cm2.publishedVersio

Reversible aggregation and chemical resistance of magnetic nanoclusters for their recycling and repetitive use in industrial bioprocesses

Magnetic nanclusters are widely used as carriers for biomedical and bioindustrial applications. 12 The chemical resistance of the nanoclusters is a key factor for the recycling the magnetic beads 13 for a repetitive use in the industrial bioprocesses. In this work, a study of the chemical resistance 14 of Fe2O3 silica-coated nanoclusters at different pH is presented. The use of Horizontal Low 15 Gradient Magnetic Field (HLGMF) for the control and separation of the magnetic nanoclusters at 16 diferent magnetic field gradients is also investigated. For these purposes Fe2O3 silica-coated 17 nanoclusters are synthesised and characreized by SQUID, TEM, Zeta potential techniques. The 18 magnetophoresis study was performed at 15 T/m and 30 T/m magnetic field gradients. 19 Recycling aspects of the nanoclusters were estimated by evaluating their resistance to pH 20 variation from acid to basic solutions of about pH 2.5 and 10

Oxidized colloidal h-BN nanoscrolls: Spectroscopic study of the phase transformation upon scrolling process

In comparison to carbon nanostructures, hexagonal boron nitride (hBN) nanostructures show better biocompatibility and lower cytotoxicity. However, research studies on hBN nanostructures for biomedical applications are still in an early stage, which limits the current knowledge about this group of materials, particularly their functionalization. Herein, we report a simple and scalable two-step method for the simultaneous synthesis and functionalization of hBN nanosheets (NSHs) and nanoscrolls (NSCs). The first step is conventional chemical exfoliation under alkaline conditions to weaken the interlayer interactions. The second step is exposure to low-frequency ultrasonic irradiation to obtain partially oxidized NSHs and NSCs. The successful formation of both NSHs and NSCs is confirmed using electron microscopy. The effective incorporation of O atoms into hBN nanostructures was confirmed through (i) the changes in the optical bandgaps deduced from UV–vis absorption, and (ii) the decrease in B atoms bonded to three N atoms and the increase in the BNxOy component observed using high-resolution XPS. Raman spectroscopy was used to analyze the evolution of the active phonon modes upon further exposure to irradiation, and showed a phase transition from sp2 to a mixture of sp2–sp3 bondings at the occurrence of the shape transformation from NSHs to NSCs.R. Miranti thanks to Research Council of Norway for the financial support under FRINATEK Project Nr. 275139. M.S. Qayyum thanks NTNU NanoLab support through the Norwegian Micro- and Nano-Fabrication Facility, NorFab, (Grant No. 245963/F50).Peer reviewe

Improving the binding capacity of Ni2+ decorated porous magnetic silica spheres for histidine-rich protein separation

Biomagnetic immobilization of histidine-rich proteins based on the single-step affinity adsorption of transition metal ions continues to be a suitable practice as a cost effective and a up scaled alternative to the to multiple-step chromatographic separations. In our previous work [12], we synthesised Porous Magnetic silica (PMS) spheres by one-step hydrothermal-assisted modified-stöber method. The obtained spheres were decorated with Ni2+ and Co2+, and evaluated for the capture of a H6-Tagged green fluorescence protein (GFP-H6) protein. The binding capacity of the obtained spheres was found to be slightly higher in the case Ni2+ decorated PMS spheres (PMSNi). However, comparing with commercial products, the binding capacity was found to be lower than the expected. In this way, the present work is an attempt to improve the binding capacity of PMSNi to histidine-rich proteins. We find that increasing the amount of Ni2+ onto the surface of the PMS spheres leads to an increment of the binding capacity to GFP-H6 by a factor of two. On the other hand, we explore how the size of histidine-rich protein can affect the binding capacity comparing the results of the GFP-6H to those of the His-tagged a-galactosidase (a-GLA). Finally, we demonstrate that the optimization of the magnetophoresis parameters during washing and eluting steps can lead to an additional improvement of the binding capacity.Peer Reviewe