Ali Abou-Hassan

Microfluidics in Inorganic Chemistry

The application of microfluidics in chemistry has gained significant importance in the recent years. Miniaturized chemistry platforms provide controlled fluid transport, rapid chemical reactions, and cost-saving advantages over conventional reactors. The advantages of microfluidics have been clearly established in the field of analytical and bioanalytical sciences and in the field of organic synthesis. It is less true in the field of inorganic chemistry and materials science; however in inorganic chemistry it has mostly been used for the separation and selective extraction of metal ions. Microfluidics has been used in materials science mainly for the improvement of nanoparticle synthesis, namely metal, metal oxide, and semiconductor nanoparticles. Microfluidic devices can also be used for the formulation of more advanced and sophisticated inorganic materials or hybrids.

Multistep Continuous-Flow Microsynthesis of Magnetic and Fluorescent γ-Fe2O3@SiO2 Core/Shell Nanoparticles†

Microreactors are useful tools for optimizing and studying chemical reactions. Compared to conventional reactors, microreactors improve chemical synthesis through advantages offered by their small length scales, such as reaction volumes, and enhanced heat and mass transfer. These advantages can be very important for nanoparticle synthesis. Indeed, several kinds of inorganic particles have been synthesized in microreactors: quantum dots (as CdS or CdSe/ZnS core/shell structures), metallic nanoparticles (Pd, Co, Ag, Au), and oxide nanoparticles (g-Fe2O3, [6,7] a-FeOOH, SiO2, TiO2, [10] and SiO2/TiO2 core/shell nanoparticles). Nanoparticles with tailored structural, magnetic, fluorescence, and chemical properties have a wide range of applications in the biomedical field, including imaging, targeting, and drug delivery. Superparamagnetic g-Fe2O3 nanoparticles (MNPs) are a good example of such multifunctional particles and are used for magnetic separation, drug delivery, magnetic resonance imaging (MRI), and hyperthermia cancer treatment. Most of these applications require proven chemical stability of the nanoparticles, a narrow particle size distribution, and good dispersion of the nanoparticles in the liquid medium to avoid any unspecific aggregation. Encapsulating the MNPs in silica shells provides a protective, biocompatible, inert, and hydrophilic surface with excellent anchoring points for derivatizing molecules. Moreover, incorporation of chromophores in the silica shell provides magnetic and luminescent core/shell nanocomposites with applications as contrast agents for molecular imaging. 20] Chromophores can be organic fluorescent dyes, or luminescent inorganic particles such as quantum dots. Methods reported for formation of MNP/ silica nanocomposites in the bulk include the use of aerosol pyrolysis, 23] emulsions, microemulsions, 26] and reactions performed under St ber conditions. Looking for new methods in synthetic chemistry has led to the development of microreactors for the elaboration of labon-a-chip synthesis platforms. Compared to droplets-based microreactors, continuous-flow microreactors appear to be easier to handle and more representative of bulk conditions with improved homogeneity leading to better control of nanoparticle characteristics. In addition, the chemical composition of the mixture can be continuously varied, as different reagents can be added downstream without any synchronization, in contrast to droplets-based reactors. An additional advantage of these synthesis platforms is that they allow linking of individual reactions into multistep sequences. This enables one reaction to flow into another and thus to combine multiple synthetic steps into a continuous operation. Multistep synthesis in continuous-flow microreactors involving multiple reactions and on-line or off-line separation (workup) were elegantly demonstrated for the synthesis of organic molecules. In the field of inorganic chemistry, the use of microreactors for nanoparticle coating has been described but is limited to single-step modifications of the surface. Herein we report a continuous multistep synthesis of magnetic and fluorescent nanoparticles dedicated to elaboration of a nanoparticle lab-on-a-chip platform. The basic concept of the proposed synthetic process is illustrated in Scheme 1 a. It is based on a continuous multistep

Synthesis of Goethite by Separation of the Nucleation and Growth Processes of Ferrihydrite Nanoparticles Using Microfluidics

Microfluidic synthesis is used to form nanoparticles by separate nucleation and growth processes using two microreactors (see picture) operating under different temperature and flow conditions. Ferrihydrite nanoparticles precipitated in the first microreactor are aged under continuous flow in a second microtubular reactor, leading to goethite nanoparticles. TMAOH = tetramethylammonium hydroxide.

Design of Vesicles Using Capillary Microfluidic Devices: From Magnetic to Multifunctional Vesicles

In the core, in the shell, or both: a microfluidic device is used to design magnetic vesicles (liposomes and polymersomes) through chemical modification of the nanoparticle surface. Hydrophilic, hydrophobic and fluorescent quantum dot nanoparticles are used for elaborating the vesicles. Hybrid vesicles are easily obtained with a very high yield and excellent monodispersity.

Synthesis of cobalt ferrite nanoparticles in continuous-flow microreactors

High quality CoFe2O4 nanoparticles were synthesized only in 16 min, continuously in two coupled microreactors. The first microreactor induced the fast homogenization of the reagents mixture at ambient temperature so Fe3+ and Co2+ hydroxides precipitate, while a second microreactor heated at 98 °C allowed the fast aging and the evolution of amorphous hydroxides into faceted and crystalline CoFe2O4.

Static Magnetowetting of Ferrofluid Drops

We report results of a comprehensive study of the wetting properties of sessile drops of ferrofluid water solutions at various concentrations deposited on flat substrates and subjected to the action of permanent magnets of different sizes and strengths. The amplitude and the gradient of the magnetic field experienced by the ferrofluid are changed by varying the magnets and their distance to the surface. Magnetic forces up to 100 times the gravitational one and magnetic gradients up to 1 T/cm are achieved. A rich phenomenology is observed, ranging from flattened drops caused by the magnetic attraction to drops extended normally to the substrate because of the normal traction of the magnetic field. We find that the former effect can be conveniently described in terms of an effective Bond number that compares the effective drop attraction with the capillary force, whereas the drops vertical elongation is effectively expressed by a dimensionless number S, which compares the pressure jump at the ferrofluid interface because of the magnetization with the capillary pressure.

Interaction of the Belousov–Zhabotinsky Reaction with Phospholipid Engineered Membranes

Compartmentalized in liposome arrays, the Belousov-Zhabotinsky (BZ) oscillatory reaction might represent a good model for biochemical networks. In order to engineer such liposomes, we used small-angle X-ray scattering (SAXS) to study the effect of individual BZ reactant as well as of the entire BZ mixture on the structural properties of lipid layer(s) formed by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) phospholipids in aqueous media. These properties were compared with those of lipid layers doped with myristic acid (Myr-A), sodium tetradecyl sulfate (STS), and cholesterol (CHOL). In parallel, the effect on the BZ reaction exerted by doped DMPC liposomes was investigated by UV-vis spectroscopy, followed by image analysis of the recorded time series. SAXS experiments showed that chemical species involved in the BZ reaction bring small changes to the internal structure of DMPC bilayers. However, ferroin can reduce the liposome lamellarity by being adsorbed on the surface of lipid layers. Also, the presence of charged dopants such as STS and TA tends to reduce the lamellarity of liposomes, while CHOL brings marked changes in the BZ system due to chemical reaction with oxidant species. In particular, an increase of the oscillation frequency is observed when the BZ reaction is carried out in the presence of CHOL-DMPC liposomes. For this behavior, a possible explanation supported by numerical simulations is bromination of CHOL double bonds by BZ intermediates.

Flow Chemistry to Control the Synthesis of Nano and Microparticles for Biomedical Applications

In this article we review the flow chemistry methodologies for the controlled synthesis of different kind of nano and microparticles for biomedical applications. Injection mechanism has emerged as new alternative for the synthesis of nanoparticles due to this strategy allows achieving superior levels of control of self-assemblies, leading to higher-ordered structures and rapid chemical reactions. Self-assembly events are strongly dependent on factors such as the local concentration of reagents, the mixing rates, and the shear forces, which can be finely tuned, as an example, in a microfluidic device. Injection methods have also proved to be optimal to elaborate microsystems comprising polymer solutions. Concretely, extrusion based methods can provide controlled fluid transport, rapid chemical reactions, and cost-saving advantages over conventional reactors. We provide an update of synthesis of nano and microparticles such as core/shell, Janus, nanocrystals, liposomes, and biopolymeric microgels through flow chemistry, its potential bioapplications and future challenges in this field are discussed.

Lipid-Stabilized Water–Oil Interfaces Studied by Microfocusing Small-Angle X-ray Scattering

Water-in-oil (w/o) simple emulsions are dispersed microconfined systems that find applications in many areas of advanced materials and biotechnology, such as the food industry, drug delivery, and cosmetics, to name but a few. In these systems, the structural and chemical properties of the boundary layer at the w/o interface are of paramount importance in determining functionality and stability. Recently, microfluidic methods have emerged as a valuable tool for fabricating monodisperse emulsion droplets. Because of the intrinsic flexibility of microfluidics, different interfaces can be obtained, and general principles governing their stability are needed to guide the experimental approach. Herein, we investigate the structural characteristics of the region encompassing the liquid/liquid (L/L) interface of w/o emulsions generated by a microfluidic device in the presence of phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and other intercalating amphiphiles (dopants) using microfocused small-angle X-rays scattering (μ-SAXS). We show that phospholipids provide a stable and versatile boundary film of ∼100 μm whose basic units are swollen and uncorrelated DMPC bilayers. The internal arrangement of this interfacial film can be tuned by adding molecules with a different packing parameter, such as cholesterol, which is able to increase the stiffness of the lipid membranes and trigger interbilayer correlation.

Sprouting Droplets Driven by Physical Effects Alone

Combining a partially miscible three-liquid system with interfacially trapped silica colloids, we show that small droplets can exhibit dramatic growth phenomena driven by physical effects alone. The mass dense droplets sprout tubes which grow vertically upward in a gravitational field and respond to the presence of other droplets in their path. Two of the liquids in our system are water and toluene. By varying the third liquid, we are able to relate the growth behavior to the details of the underlying three-fluid phase diagram and the changes to the interfacial tension. Additionally, we introduce a pendant drop in the path of our growing drop. We use this to confirm that growth is driven by the partitioning of solvents, that exchange of solvents between droplets is chemically selective, and that the exchange behavior can itself generate further growth phenomena.