Multistep Continuous-Flow Microsynthesis of Magnetic and Fluorescent γ-Fe2O3@SiO2Core/Shell Nanoparticles

Trace Explosive Detection Based on Photonic Crystal Amplified Fluorescence

With increasing demand for public security and environmental protection, it is highly desirable to develop strategies to identify trace explosives (e. g., 2,4,6-trinitrotoluene (TNT)). Herein, we report novel photonic crystal (PC)-based sensor chips for trace TNT detection by using amplification effect of PCs on fluorescence (FL) signals. The sensor chips are constructed by integrating silica nanoparticles (NPs) modified with (3-aminopropyl)triethoxysilane (APTES) and fluorescein isothiocyanate isomer (FITC) and PC substrates. The amino groups on FITC-APTES-silica NPs can specifically bind with TNT molecules to form Meisenheimer complexes and strongly quench the FL signal of neighboring fluorophores FITC through Förster resonance energy transfer. PCs with matched PBG can amplify the FL signal of FITC-APTES-silica NPs about 24.4-fold and significantly improve sensitivity and resolution of trace TNT detection with the limit of detection of 0.23 nM. The PC-based sensor chips are stable, sensitive, and reliable TNT sensing platforms, showing great potential in homeland safety and environmental protection.

CFD Analysis and Life Cycle Assessment of Continuous Synthesis of Magnetite Nanoparticles Using 2D and 3D Micromixers

Magnetite nanoparticles (MNPs) have attracted basic and applied research due to their immense potential to enable applications in fields as varied as drug delivery and bioremediation. Conventional synthesis schemes led to wide particle size distributions and inhomogeneous morphologies and crystalline structures. This has been attributed to the inability to control nucleation and growth processes under the conventional conditions of bulk batch processes. Here, we attempted to address these issues by scaling down the synthesis process aided by microfluidic devices, as they provide highly controlled and stable mixing patterns. Accordingly, we proposed three micromixers with different channel configurations, namely, serpentine, triangular, and a 3D arrangement with abrupt changes in fluid direction. The micromixers were first studied in silico, aided by Comsol Multiphysics^® to investigate the obtained mixing patterns, and consequently, their potential for controlled growth and the nucleation processes required to form MNPs of uniform size and crystalline structure. The devices were then manufactured using a low-cost approach based on polymethyl methacrylate (PMMA) and laser cutting. Testing the micromixers in the synthesis of MNPs revealed homogeneous morphologies and particle size distributions, and the typical crystalline structure reported previously. A life cycle assessment (LCA) analysis for the devices was conducted in comparison with conventional batch co-precipitation synthesis to investigate the potential impacts on water and energy consumption. The obtained results revealed that such consumptions are higher than those of the conventional process. However, they can be reduced by conducting the synthesis with reused micromixers, as new PMMA is not needed for their assembly prior to operation. We are certain that the proposed approach represents an advantageous alternative to co-precipitation synthesis schemes, in terms of continuous production and more homogeneous physicochemical parameters of interest such as size, morphologies, and crystalline structure. Future work should be directed towards improving the sustainability indicators of the micromixers’ manufacturing process.

High Temperature Continuous Flow Syntheses of Iron Oxide Nanoflowers Using the Polyol Route in a Multi-Parametric Millifluidic Device

One of the most versatile routes for the elaboration of nanomaterials in materials science, including the synthesis of magnetic iron oxide nanoclusters, is the high-temperature polyol process. However, despite its versatility, this process still lacks reproducibility and scale-up, in addition to the low yield obtained in final materials. In this work, we demonstrate a home-made multiparametric continuous flow millifluidic system that can operate at high temperatures (up to 400 °C). After optimization, we validate its potential for the production of nanomaterials using the polyol route at 220 °C by elaborating ferrite iron oxide nanoclusters called nanoflowers (CoFe₂O₄, Fe₃O₄, MnFe₂O₄) with well-controlled nanostructure and composition, which are highly demanded due to their physical properties. Moreover, we demonstrate that by using such a continuous process, the chemical yield and reproducibility of the nanoflower synthesis are strongly improved as well as the possibility to produce these nanomaterials on a large scale with quantities up to 45 g per day.

Microfluidic nanomaterials: From synthesis to biomedical applications

Microfluidic platforms gain popularity in biomedical research due to their attractive inherent features, especially in nanomaterials synthesis. This review critically evaluates the current state of the controlled synthesis of nanomaterials using microfluidic devices. We describe nanomaterials' screening in microfluidics, which is very relevant for automating the synthesis process for biomedical applications. We discuss the latest microfluidics trends to achieve noble metal, silica, biopolymer, quantum dots, iron oxide, carbon-based, rare-earth-based, and other nanomaterials with a specific size, composition, surface modification, and morphology required for particular biomedical application. Screening nanomaterials has become an essential tool to synthesize desired nanomaterials using more automated processes with high speed and repeatability, which can't be neglected in today's microfluidic technology. Moreover, we emphasize biomedical applications of nanomaterials, including imaging, targeting, therapy, and sensing. Before clinical use, nanomaterials have to be evaluated under physiological conditions, which is possible in the microfluidic system as it stimulates chemical gradients, fluid flows, and the ability to control microenvironment and partitioning multi-organs. In this review, we emphasize the clinical evaluation of nanomaterials using microfluidics which was not covered by any other reviews. In the future, the growth of new materials or modification in existing materials using microfluidics platforms and applications in a diversity of biomedical fields by utilizing all the features of microfluidic technology is expected.

Microfluidic Synthesis, Control, and Sensing of Magnetic Nanoparticles: A Review

Magnetic nanoparticles have attracted significant attention in various disciplines, including engineering and medicine. Microfluidic chips and lab-on-a-chip devices, with precise control over small volumes of fluids and tiny particles, are appropriate tools for the synthesis, manipulation, and evaluation of nanoparticles. Moreover, the controllability and automation offered by the microfluidic chips in combination with the unique capabilities of the magnetic nanoparticles and their ability to be remotely controlled and detected, have recently provided tremendous advances in biotechnology. In particular, microfluidic chips with magnetic nanoparticles serve as sensitive, high throughput, and portable devices for contactless detecting and manipulating DNAs, RNAs, living cells, and viruses. In this work, we review recent fundamental advances in the field with a focus on biomedical applications. First, we study novel microfluidic-based methods in synthesizing magnetic nanoparticles as well as microparticles encapsulating them. We review both continues-flow and droplet-based microreactors, including the ones based on the cross-flow, co-flow, and flow-focusing methods. Then, we investigate the microfluidic-based methods for manipulating tiny magnetic particles. These manipulation techniques include the ones based on external magnets, embedded micro-coils, and magnetic thin films. Finally, we review techniques invented for the detection and magnetic measurement of magnetic nanoparticles and magnetically labeled bioparticles. We include the advances in anisotropic magnetoresistive, giant magnetoresistive, tunneling magnetoresistive, and magnetorelaxometry sensors. Overall, this review covers a wide range of the field uniquely and provides essential information for designing "lab-on-a-chip" systems for synthesizing magnetic nanoparticles, labeling bioparticles with them, and sorting and detecting them on a single chip.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Synthesis and applications of surface-modified magnetic nanoparticles: progress and future prospects

The growing use of magnetic nanoparticles (MNPs) demands cost-effective methods for their synthesis that allow proper control of particle size and size distribution. The unique properties of MNPs include high specific surface area, ease of functionalization, chemical stability and superparamagnetic behavior, with applications in catalysis, data and energy storage, environmental remediation and biomedicine. This review highlights breakthroughs in the use of MNPs since their initial introduction in biomedicine to the latest challenging applications; special attention is paid to the importance of proper coating and functionalization of the particle surface, which dictates the specific properties for each application. Starting from the first report following LaMer’s theory in 1950, this review discusses and analyzes methods of synthesizing MNPs, with an emphasis on functionality and applications. However, several hurdles, such as the design of reactors with suitable geometries, appropriate control of operating conditions and, in particular, reproducibility and scalability, continue to prevent many applications from reaching the market. The most recent strategy, the use of microfluidics to achieve continuous and controlled synthesis of MNPs, is therefore thoroughly analyzed. This review is the first to survey continuous microfluidic coating or functionalization of particles, including challenging properties and applications.

Process Intensification Approach Using Microreactors for Synthesizing Nanomaterials-A Critical Review

Nanomaterials have found many applications due to their unique properties such as high surface-to-volume ratio, density, strength, and many more. This review focuses on the recent developments on the synthesis of nanomaterials using process intensification. The review covers the designing of microreactors, design principles, and fundamental mechanisms involved in process intensification using microreactors for synthesizing nanomaterials. The microfluidics technology operates in continuous mode as well as the segmented flow of gas–liquid combinations. Various examples from the literature are discussed in detail highlighting the advantages and disadvantages of microfluidics technology for nanomaterial synthesis.

Segmented Microfluidic Flow Reactors for Nanomaterial Synthesis

Microfluidic reactors have remarkably promoted the synthesis and investigation of advanced nanomaterials due to their continuous mode and accelerated heat/mass transfer. Notably, segmented microfluidic flow reactors (SMFRs) are an important class of microfluidic reactors that have been developed to accurately manipulate nanomaterial synthesis by further improvement of the residence time distributions and unique flow behaviors. This review provided a survey of the nanomaterial synthesis in SMFRs for the aspects of fluid dynamics, flow patterns, and mass transfer among and within distinct phases and provided examples of the synthesis of versatile nanomaterials via the use of different flow patterns.

Synthesis and Surface Engineering of Inorganic Nanomaterials Based on Microfluidic Technology

The controlled synthesis and surface engineering of inorganic nanomaterials hold great promise for the design of functional nanoparticles for a variety of applications, such as drug delivery, bioimaging, biosensing, and catalysis. However, owing to the inadequate and unstable mass/heat transfer, conventional bulk synthesis methods often result in the poor uniformity of nanoparticles, in terms of microstructure, morphology, and physicochemical properties. Microfluidic technologies with advantageous features, such as precise fluid control and rapid microscale mixing, have gathered the widespread attention of the research community for the fabrication and engineering of nanomaterials, which effectively overcome the aforementioned shortcomings of conventional bench methods. This review summarizes the latest research progress in the microfluidic fabrication of different types of inorganic nanomaterials, including silica, metal, metal oxides, metal organic frameworks, and quantum dots. In addition, the surface modification strategies of nonporous and porous inorganic nanoparticles based on microfluidic method are also introduced. We also provide the readers with an insight on the red blocks and prospects of microfluidic approaches, for designing the next generation of inorganic nanomaterials.

Continuous Synthesis of Nanocrystals via Flow Chemistry Technology

Modern nanotechnologies bring humanity to a new age, and advanced methods for preparing functional nanocrystals are cornerstones. A considerable variety of nanomaterials has been created over the past decades, but few were prepared on the macro scale, even fewer making it to the stage of industrial production. The gap between academic research and engineering production is expected to be filled by flow chemistry technology, which relies on microreactors. Microreaction devices and technologies for synthesizing different kinds of nanocrystals are discussed from an engineering point of view. The advantages of microreactors, the important features of flow chemistry systems, and methods to apply them in the syntheses of salt, oxide, metal, alloy, and quantum dot nanomaterials are summarized. To further exhibit the scaling-up of nanocrystal synthesis, recent reports on using microreactors with gram per hour and larger production rates are highlighted. Finally, an industrial example for preparing 10 tons of CaCO₃ nanoparticles per day is introduced, which shows the great potential for flow chemistry processes to transfer lab research to industry.

Continuous Multistage Synthesis and Functionalization of Sub-100 nm Silica Nanoparticles in 3D-Printed Continuous Stirred-Tank Reactor Cascades

The controlled and continuous production of nanoparticles (NPs) with functionalized surfaces remains a technological challenge. We present a multistage synthetic platform, consisting of 3D-printed miniature continuous stirred-tank reactor (CSTR) cascades, for the continuous synthesis and functionalization of SiO₂ NPs. The use of the CSTR platform provides ideal and rapid mixing of precursor solutions, precise injection of additional reagents for multistep reactions, and facile operation when using viscous solutions and handling of syntheses with longer reaction times. To exemplify the use of such custom-designed CSTR cascades, amine- and carbohydrate-functionalized SiO₂ NPs are chosen as model reaction systems. In particular, the intensified flow reactor units allowed for the reproducible formation of SiO₂ NPs with diameters less than 100 nm and narrow size distributions (3-8%). Most importantly, by assembling various 3D-printed CSTR cascades, we synthesized gluconolactone-capped polyethylenimine-modified silica NPs in a fully continuous manner. The inherent control over NP surface charge, reactor scalability, and the significant shortening of processing times (less than 10 min) compared to batch methodologies (several days) strongly indicate the ability of the reactor technology to accelerate continuous nanomanufacturing. In general, it provides a simple route for the reproducible preparation of functionalized NPs, thus expanding the gamut of flow reactors for material synthesis.

Synthesis and characterization of novel γ-Fe2O3-NH4OH@SiO2(APTMS) nanoparticles for dysprosium adsorption

This paper deals with synthesis and characterization of novel γ-Fe₂O₃-NH₄OH@SiO₂(APTMS) nanoparticles formed from magnetic γ-Fe₂O₃ core, stabilized electrostatically in basic media NH₄OH, doped with SiO₂ shell and functionalized with 3-aminopropyltrimethoxysilane. The gradually synthesized nanoparticles are characterized in order to analyze their structural, morphology, thermogravimetry, surface area and charge, and magnetic properties. The novel synthesized γ-Fe₂O₃-NH₄OH@SiO₂(APTMS) nanoparticles are suitable to adsorb dysprosium ions (Dy³⁺), as one of the most critical rare earth elements, from aqueous solution. The Dy³⁺ adsorption from aqueous solution follows a pseudo-second order kinetic model and the adsorption equilibrium data fits well to the Temkin isotherm. Thermodynamic studies imply that the adsorption process is endothermic and spontaneous in nature. The maximum adsorption efficiency for Dy³⁺ from aqueous solution with 2·10^-6M concentration of Dy³⁺ is over 90% at pH 7.

Advances in diagnostic microfluidics

Microfluidics is an emerging field in diagnostics that allows for extremely precise fluid control and manipulation, enabling rapid and high-throughput sample processing in integrated micro-scale medical systems. These platforms are well-suited for both standard clinical settings and point-of-care applications. The unique features of microfluidics-based platforms make them attractive for early disease diagnosis and real-time monitoring of the disease and therapeutic efficacy. In this chapter, we will first provide a background on microfluidic fundamentals, microfluidic fabrication technologies, microfluidic reactors, and microfluidic total-analysis-systems. Next, we will move into a discussion on the clinical applications of existing and emerging microfluidic platforms for blood analysis, and for diagnosis and monitoring of cancer and infectious disease. Together, this chapter should elucidate the potential that microfluidic systems have in the development of effective diagnostic technologies through a review of existing technologies and promising directions.

Microfluidics for silica biomaterials synthesis: opportunities and challenges

The rational design and controllable synthesis of silica nanomaterials bearing unique physicochemical properties is becoming increasingly important for a variety of biomedical applications from imaging to drug delivery. Microfluidics has recently emerged as a promising platform for nanomaterial synthesis, providing precise control over particle size, shape, porosity, and structure compared to conventional batch synthesis approaches. This review summarizes microfluidics approaches for the synthesis of silica materials as well as the design, fabrication and the emerging roles in the development of new classes of functional biomaterials. We highlight the unprecedented opportunities of using microreactors in biomaterial synthesis, and assess the recent progress of continuous and discrete microreactors and the associated biomedical applications of silica materials. Finally, we discuss the challenges arising from the intrinsic properties of microfluidics reactors for inspiring future research in this field.

Biomimetic human lung-on-a-chip for modeling disease investigation

The lung is the primary respiratory organ of the human body and has a complicated and precise tissue structure. It comprises conductive airways formed by the trachea, bronchi and bronchioles, and many alveoli, the smallest functional units where gas-exchange occurs via the unique gas-liquid exchange interface known as the respiratory membrane. In vitro bionic simulation of the lung or its microenvironment, therefore, presents a great challenge, which requires the joint efforts of anatomy, physics, material science, cell biology, tissue engineering, and other disciplines. With the development of micromachining and miniaturization technology, the concept of a microfluidics-based organ-on-a-chip has received great attention. An organ-on-a-chip is a small cell-culture device that can accurately simulate tissue and organ functions in vitro and has the potential to replace animal models in evaluations of drug toxicity and efficacy. A lung-on-a-chip, as one of the first proposed and developed organs-on-a-chip, provides new strategies for designing a bionic lung cell microenvironment and for in vitro construction of lung disease models, and it is expected to promote the development of basic research and translational medicine in drug evaluation, toxicological detection, and disease model-building for the lung. This review summarizes current lungs-on-a-chip models based on the lung-related cellular microenvironment, including the latest advances described in studies of lung injury, inflammation, lung cancer, and pulmonary fibrosis. This model should see effective use in clinical medicine to promote the development of precision medicine and individualized diagnosis and treatment.

Microfluidic assisted synthesis of PLGA drug delivery systems

Poly(lactic-co-glycolic acid) (PLGA) is a biocompatible and biodegradable polymer that recently attracted attention for use as part of drug delivery systems (DDS). In this context, there is an emerging need for a rapid, reliable and reproducible method of synthesis. Here, microfluidic systems provide great opportunities for synthesizing carriers in a tightly controlled manner and with low consumption of materials, energy and time. These miniature devices have been the focus of recent research since they can address the challenges inherent to the bulk system, e.g. low drug loading efficiency and encapsulation, broad size distribution and burst initial release. In this article, we provide an overview of current microfluidic systems used in drug delivery production, with a special focus on PLGA-based DDS. In this context, we highlight the advantages associated with the use of microchip systems in the fabrication of nanoparticles (NPs) and microparticles (MPs), e.g. in achieving complex morphologies. Furthermore, we discuss the challenges for selecting proper microfluidics for targeted DDS production in a translational setting and introduce strategies that are used to overcome microfluidics shortcomings, like low throughput for production.

Poly(lactic-co-glycolic acid) (PLGA) is a biocompatible and biodegradable polymer that recently attracted attention for use as part of drug delivery systems (DDS).

Characterization of Cotton Ball-like Au/ZnO Photocatalyst Synthesized in a Micro-Reactor

Noble metal/metal oxide nanostructures are an efficient system in photocatalysis. Continuous and scalable production of advanced particle systems will be a requirement for commercial-scale deployment for many applications, including photocatalysis. In this work, Au/ZnO structures were synthesized in a continuous flow micro-reactor at room temperature and the detailed characteristics of the product indicate a specific cotton ball-like core-shell microstructure that showcases specific advantages compared to traditional batch synthesis methods. The formation pathway of the core-shell Au/ZnO structures is discussed with the pH-dependent speciation diagram, and photocatalytic activity was assessed under simulated sunlight, demonstrating the enhanced performance of the cotton ball-like Au/ZnO microstructures in photocatalytic dye degradation. This work describes the application of microreaction technology in the continuous production of metal/metal oxide photocatalysts.

Precise Synthesis of Well-Defined Inorganic-Organic Hybrid Particles

Synthesis of hybrid particles toward precisely designed hierarchical nanoarchitectures is summarized. In order to satisfy the demands for a variety of materials' performances, the selection of materials, composition and synthesis is carefully done. Flow reactors are one of the useful synthetic means to prepare hybrid materials, especially those with hierarchically and precisely designed multi-components hybrid particles, owing to the efficient mixing and heat exchange in the reactor as well as its connectable (both parallel and sequential) feature. In this review article, after the summary of the preparation of hybrids based on oxides and organics through conventional batch reactors, the application of flow reactors to the preparation of various hybrid particles is introduced to highlight the present status and future possibility of the flow reactor synthesis.

Peptide functionalized magneto-plasmonic nanoparticles obtained by microfluidics for inhibition of β-amyloid aggregation

Synthesis of magneto-plasmonic nanoparticles for the inhibition of β-amyloid fibril formation.

Insights in the Diffusion Controlled Interfacial Flow Synthesis of Au Nanostructures in a Microfluidic System

Continuous segmented flow interfacial synthesis of Au nanostructures is demonstrated in a microchannel reactor. This study brings new insights into the growth of nanostructures at continuous interfaces. The size as well as the shape of the nanostructures showed significant dependence on the reactant concentrations, reaction time, temperature, and surface tension, which actually controlled the interfacial mass transfer. The microchannel reactor assisted in achieving a high interfacial area, as well as uniformity in mass transfer effects. Hexagonal nanostructures were seen to be formed in synthesis times as short as 10 min. The wettability of the channel showed significant effect on the particle size as well as the actual shape. The hydrophobic channel yielded hexagonal structures of relatively smaller size than the hydrophilic microchannel, which yielded sharp hexagonal bipyramidal particles (diagonal distance of 30 nm). The evolution of particle size and shape for the case of hydrophilic microchannel is also shown as a function of the residence time. The interfacial synthesis approach based on a stable segmented flow promoted an excellent control on the reaction extent, reduction in axial dispersion as well as the particle size distribution.

Controllable synthesis of nanocrystals in droplet reactors

In recent years, a broad range of nanocrystals have been synthesized in droplet-based microfluidic reactors which provide obvious advantages, such as accurate manipulation, better reproducibility and reliable automation. In this review, we initially introduce general concepts of droplet reactors followed by discussions of their main functional regions including droplet generation, mixing of reactants, reaction controlling, in situ monitoring, and reaction quenching. Subsequently, the enhanced mass and heat transport properties are discussed. Next, we focus on research frontiers including sequential multistep synthesis, intelligent synthesis, reliable scale-up synthesis, and interfacial synthesis. Finally, we end with an outlook on droplet reactors, especially highlighting some aspects such as large-scale production, the integrated process of synthesis and post-synthetic treatments, automated droplet reactors with in situ monitoring and optimizing algorithms, and rapidly developing strategies for interfacial synthesis.

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

In order to translate nanotechnology into medical practice, magnetic nanoparticles (MNPs) have been presented as a class of non-invasive nanomaterials for numerous biomedical applications. In particular, MNPs have opened a door for simultaneous diagnosis and brisk treatment of diseases in the form of theranostic agents. This review highlights the recent advances in preparation and utilization of MNPs from the synthesis and functionalization steps to the final design consideration in evading the body immune system for therapeutic and diagnostic applications with addressing the most recent examples of the literature in each section. This study provides a conceptual framework of a wide range of synthetic routes classified mainly as wet chemistry, state-of-the-art microfluidic reactors, and biogenic routes, along with the most popular coating materials to stabilize resultant MNPs. Additionally, key aspects of prolonging the half-life of MNPs via overcoming the sequential biological barriers are covered through unraveling the biophysical interactions at the bio-nano interface and giving a set of criteria to efficiently modulate MNPs' physicochemical properties. Furthermore, concepts of passive and active targeting for successful cell internalization, by respectively exploiting the unique properties of cancers and novel targeting ligands are described in detail. Finally, this study extensively covers the recent developments in magnetic drug targeting and hyperthermia as therapeutic applications of MNPs. In addition, multi-modal imaging via fusion of magnetic resonance imaging, and also innovative magnetic particle imaging with other imaging techniques for early diagnosis of diseases are extensively provided.

An engineering approach to synthesis of gold and silver nanoparticles by controlling hydrodynamics and mixing based on a coaxial flow reactor

In this work we present a detailed study of flow technology approaches that could open up new possibilities for nanoparticle synthesis. The synthesis of gold and silver nanoparticles (NPs) in a flow device based on a coaxial flow reactor (CFR) was investigated. The CFR comprised of an outer glass tube of 2 mm inner diameter (I.D.) and an inner glass tube whose I.D. varied between 0.142 and 0.798 mm. A split and recombine (SAR) mixer and coiled flow inverter (CFI) were further employed to alter the mixing conditions after the CFR. The 'Turkevich' method was used to synthesize gold NPs, with a CFR followed by a CFI. This assembly allows control over nucleation and growth through variation of residence time. Increasing the total flow rate from 0.25 ml min^-1 to 3 ml min^-1 resulted initially in a constant Au NP size, and beyond 1 ml min^-1 to a size increase of Au NPs from 17.9 ± 2.1 nm to 23.9 ± 4.7 nm. The temperature was varied between 60-100 °C and a minimum Au NP size of 17.9 ± 2.1 nm was observed at 80 °C. Silver NPs were synthesized in a CFR followed by a SAR mixer, using sodium borohydride to reduce silver nitrate in the presence of trisodium citrate. The SAR mixer provided an enhancement of the well-controlled laminar mixing in the CFR. Increasing silver nitrate concentration resulted in a decrease in Ag NP size from 5.5 ± 2.4 nm to 3.4 ± 1.4 nm. Different hydrodynamic conditions were studied in the CFR operated in isolation for silver NP synthesis. Increasing the Reynolds number from 132 to 530 in the inner tube created a vortex flow resulting in Ag NPs in the size range between 5.9 ± 1.5 nm to 7.7 ± 3.4 nm. Decreasing the inner tube I.D. from 0.798 mm to 0.142 mm resulted in a decrease in Ag NP size from 10.5 ± 4.0 nm to 4.7 ± 1.4 nm. Thus, changing the thickness of the inner stream enabled control over size of the Ag NPs.

Biomaterials Meet Microfluidics: From Synthesis Technologies to Biological Applications

Microfluidics is characterized by laminar flow at micro-scale dimension, high surface to volume ratio, and markedly improved heat/mass transfer. In addition, together with advantages of large-scale integration and flexible manipulation, microfluidic technology has been rapidly developed as one of the most important platforms in the field of functional biomaterial synthesis. Compared to biomaterials assisted by conventional strategies, functional biomaterials synthesized by microfluidics are with superior properties and performances, due to their controllable morphology and composition, which have shown great advantages and potential in the field of biomedicine, biosensing, and tissue engineering. Take the significance of microfluidic engineered biomaterials into consideration; this review highlights the microfluidic synthesis technologies and biomedical applications of materials. We divide microfluidic based biomaterials into four kinds. According to the material dimensionality, it includes: 0D (particulate materials), 1D (fibrous materials), 2D (sheet materials), and 3D (construct forms of materials). In particular, micro/nano-particles and micro/nano-fibers are introduced respectively. This classification standard could include all of the microfluidic biomaterials, and we envision introducing a comprehensive and overall evaluation and presentation of microfluidic based biomaterials and their applications.

Microfluidic Synthesis of Nanohybrids

Nanohybrids composed of two or more components exhibit many distinct physicochemical properties and hold great promise for applications in optics, electronics, magnetics, new energy, environment protection, and biomedical engineering. Microfluidic systems exhibit many advantages due to their unique characteristics of narrow channels, variable length, controllable number of channels and multiple integrations. Particularly their spatial-temporarily splitting of the formation stages during nanomaterials formation along the microfluidic channels favors the online control of the reaction kinetic parameters and in situ tuning of the product properties. This Review is focused on the features of the current types of microfluidic devices in the synthesis of different types of nanohybrids based on the classification of the four main kinds of materials: metal, nonmetal inorganic, polymer and composites. Their morphologies, compositions and properties can be adjusted conveniently in these synthesis systems. Synthesis advantages of varieties of microfluidic devices for specific nanohybrids of defined surfaces and interfaces are presented according to their process and microstructure features of devices as compared with conventional methods. A summary is presented, and challenges are put forward for the future development of the microfluidic synthesis of nanohybrids for advanced applications.

Controllable synthesis of functional nanoparticles by microfluidic platforms for biomedical applications - a review

Nanoparticles have drawn significant attention in biomedicine due to their unique optical, thermal, magnetic and electrical properties which are highly related to their size and morphologies. Recently, microfluidic systems have shown promising potential to modulate critical stages in nanosynthesis, such as nucleation, growth and reaction conditions so that the size, size distribution, morphology, and reproducibility of nanoparticles are optimized in a high throughput manner. In this review, we put an emphasis on a decade of developments of microfluidic systems for engineering nanoparticles in various applications including imaging, biosensing, drug delivery, and theranostic applications.

Magnetic separation of clenbuterol based on competitive immunoassay and evaluation by surface-enhanced Raman spectroscopy

The elimination of β-agonist has attracted considerable interest due to its harmfulness to human health when it existed in pork.

Microfluidic Hydrodynamic Focusing for Synthesis of Nanomaterials

Microfluidics expands the synthetic space such as heat transfer, mass transport, and reagent consumption to conditions not easily achievable in conventional batch processes. Hydrodynamic focusing in particular enables the generation and study of complex engineered nanostructures and new materials systems. In this review, we present an overview of recent progress in the synthesis of nanostructures and microfibers using microfluidic hydrodynamic focusing techniques. Emphasis is placed on distinct designs of flow focusing methods and their associated mechanisms, as well as their applications in material synthesis, determination of reaction kinetics, and study of synthetic mechanisms.

Hydrothermal Synthesis of TiO2@SnO2 Hybrid Nanoparticles in a Continuous-Flow Dual-Stage Reactor

TiO2@SnO2 hybrid nanocomposites were successfully prepared in gram scale using a dual-stage hydrothermal continuous-flow reactor. Temperature and pH in the secondary reactor were found to selectively direct nucleation and growth of the secondary material into either heterogeneous nanocomposites or separate intermixed nanoparticles. At low pH, 2 nm rutile SnO2 nanoparticles were deposited on 9 nm anatase TiO2 particles; the presence of TiO2 was found to suppress formation of larger SnO2 particles. At high pH SnO2 formed separate particles and no deposition on TiO2 was observed. Ball-milling of TiO2 and SnO2 produced no TiO2@SnO2 composites. This verifies that the composite particles must be formed by nucleation and growth of the secondary precursor on the TiO2 . High concentration of secondary precursor led to formation of TiO2 particles embedded in aggregates of SnO2 nanoparticles. The results demonstrate how nanocomposites may be produced in high yield by green chemistry.

A general strategy for nanohybrids synthesis via coupled competitive reactions controlled in a hybrid process

A new methodology based on core alloying and shell gradient-doping are developed for the synthesis of nanohybrids, realized by coupled competitive reactions, or sequenced reducing-nucleation and co-precipitation reaction of mixed metal salts in a microfluidic and batch-cooling process. The latent time of nucleation and the growth of nanohybrids can be well controlled due to the formation of controllable intermediates in the coupled competitive reactions. Thus, spatiotemporal-resolved synthesis can be realized by the hybrid process, which enables us to investigate nanohybrid formation at each stage through their solution color changes and TEM images. By adjusting the bi-channel solvents and kinetic parameters of each stage, the primary components of alloyed cores and the second components of transition metal doping ZnO or Al2O3 as surface coatings can be successively formed. The core alloying and shell gradient-doping strategy can efficiently eliminate the crystal lattice mismatch in different components. Consequently, varieties of gradient core-shell nanohybrids can be synthesized using CoM, FeM, AuM, AgM (M = Zn or Al) alloys as cores and transition metal gradient-doping ZnO or Al2O3 as shells, endowing these nanohybrids with unique magnetic and optical properties (e.g., high temperature ferromagnetic property and enhanced blue emission).

Synthesis of silver nanoparticles in a microfluidic coaxial flow reactor

The coaxial flow reactor allows tuning of size and dispersity of silver nanoparticles because of its unique mass transfer characteristics.

Continuous chemical operations and modifications on magnetic γ-Fe2O3 nanoparticles confined in nanoliter droplets for the assembly of fluorescent and magnetic SiO2@γ-Fe2O3

An automated droplet microfluidic platform is described for the manipulation of magnetic nanoparticles and their assembly with fluorescent silica nanoparticles.

Reaction engineering strategies for the production of inorganic nanomaterials

The rapid expansion of nanotechnology requires scaled-up production rates to cope with increased nanomaterials demand. However, in many cases, the final uses of nanomaterials impose strict requisites on their physical and chemical characteristics including size, shape, chemical composition and type of functional groups on their surface. Frequently, additional features such as a limited degree of agglomeration are also demanded. These requisites represent a serious challenge to present-day synthesis methods when nanomaterials must be produced in large amounts. Some of the possible solutions from the reaction engineering perspective are discussed in this work for both gas and liquid phase production processes. Special attention will be devoted to enabling technologies, which allow the production of engineered nanoparticles with limited aggregation and with a good control on their nano-scale characteristics.

Preparation of biofunctionalized quantum dots using microfluidic chips for bioimaging

Biofunctionalized quantum dots were prepared using microfluidic chips and were used as optical probes for imaging live cells.

Magnetically recoverable fluorescence chemosensor for the adsorption and selective detection of Hg2+ in water

In order to conveniently and effectively detect the heavy metal ion Hg(2+) existing in water, a magnetic fluorescence chemosensor has been strategically prepared by immobilizing a Rhodamine B derivative RhB-tris(2-aminoethyl)amine on Fe3O4@SiO2-Au@PSiO2 composites via gold particles. The adsorption and detection for Hg(2+) ions were investigated with fluorophotometry. This chemosensor shows high sensitivity and high selectivity for Hg(2+) over other metal cations owing to the ring opening of the rhodamine fluorophore selectively induced by Hg(2+). In addition, the presence of Fe3O4 in the sensor also facilitates the magnetic separation of the Fe3O4@SiO2-Au-Hg(2+)@PSiO2 from the solution.

A microfluidic approach to synthesizing high-performance microfibers with tunable anhydrous proton conductivity

Here, we demonstrate a new approach for the synthesis of ion exchange microfibers with finely tuned anhydrous conductivity. This work presents microfluidics as a system to control the size and phosphoric acid (PA) doping level of the polybenzimidazole (PBI) microfibers. It has been shown that the PA doping level can be controlled by varying the flow ratios in the microfluidic channel. The diameter of the microfibers increased with extending mixing time, whereas the doping level decreased with increasing flow ratio. The highest doping level, 16, was achieved at the flow ratio of 0.175. The anhydrous proton conductivity of the microfibers was found to be adjustable between 0.01 and 0.1 S cm(-1) at 160 °C, which is considerably higher than for conventionally doped PBI cast membranes (0.004 S cm(-1)). Furthermore, molecular dynamic simulation of proton conduction through the microfibers at different doping levels was in good agreement with the experimental results. These results demonstrate the potential of the microfluidic technique to precisely tune the physicochemical properties of PBI microfibers for various electrochemical applications such as hydrogen sensors, fuel cells as well as artificial muscles.

Lab-on-a-chip synthesis of inorganic nanomaterials and quantum dots for biomedical applications

The past two decades have seen a dramatic raise in the number of investigations leading to the development of Lab-on-a-Chip (LOC) devices for synthesis of nanomaterials. A majority of these investigations were focused on inorganic nanomaterials comprising of metals, metal oxides, nanocomposites and quantum dots. Herein, we provide an analysis of these findings, especially, considering the more recent developments in this new decade. We made an attempt to bring out the differences between chip-based as well as tubular continuous flow systems. We also cover, for the first time, various opportunities the tools from the field of computational fluid dynamics provide in designing LOC systems for synthesis inorganic nanomaterials. Particularly, we provide unique examples to demonstrate that there is a need for concerted effort to utilize LOC devices not only for synthesis of inorganic nanomaterials but also for carrying out superior in vitro studies thereby, paving the way for faster clinical translation. Even though LOC devices with the possibility to carry out multi-step syntheses have been designed, surprisingly, such systems have not been utilized for carrying out simultaneous synthesis and bio-functionalization of nanomaterials. While traditionally, LOC devices are primarily based on microfluidic systems, in this review article, we make a case for utilizing millifluidic systems for more efficient synthesis, bio-functionalization and in vitro studies of inorganic nanomaterials tailor-made for biomedical applications. Finally, recent advances in the field clearly point out the possibility for pushing the boundaries of current medical practices towards personalized health care with a vision to develop automated LOC-based instrumentation for carrying out simultaneous synthesis, bio-functionalization and in vitro evaluation of inorganic nanomaterials for biomedical applications.

Microfluidic and lab-on-a-chip preparation routes for organic nanoparticles and vesicular systems for nanomedicine applications

In recent years, advancements in the fields of microfluidic and lab-on-a-chip technologies have provided unique opportunities for the implementation of nanomaterial production processes owing to the miniaturisation of the fluidic environment. It has been demonstrated that microfluidic reactors offer a range of advantages compared to conventional batch reactors, including improved controllability and uniformity of nanomaterial characteristics. In addition, the fast mixing achieved within microchannels, and the predictability of the laminar flow conditions, can be leveraged to investigate the nanomaterial formation dynamics. In this article recent developments in the field of microfluidic production of nanomaterials for drug delivery applications are reviewed. The features that make microfluidic reactors a suitable technological platform are discussed in terms of controllability of nanomaterials production. An overview of the various strategies developed for the production of organic nanoparticles and colloidal assemblies is presented, focusing on those nanomaterials that could have an impact on nanomedicine field such as drug nanoparticles, polymeric micelles, liposomes, polymersomes, polyplexes and hybrid nanoparticles. The effect of microfluidic environment on nanomaterials formation dynamics, as well as the use of microdevices as tools for nanomaterial investigation is also discussed.

A sensitive and selective chemosensor for GSSG detection based on the recovered fluorescence of NDPA-Fe₃O₄@SiO₂-Cu(II) nanomaterial

A sensitive and selective sensor for oxidized glutathione (GSSG) detection based on the recovered fluorescence of naphthalimide-DPA (NDPA)-Fe₃O₄@SiO₂-Cu(II) system is reported. NDPA-Fe3Fe₃O₄@SiO₂ was characterized by X-ray power diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR) and fluorophotometry. The fluorescence of NDPA-Fe₃O₄@SiO₂ could be quenched by Cu²⁺ due to the coordination of Cu²⁺ with the tridentate receptor DPA. This coordination process reduced the electron-donating ability of the nitrogen atom in the DPA moiety, thus suppressing the internal charge transfer (ICT) process in NDPA-Fe₃O₄@SiO₂. In the presence of GSSG, the fluorescence of NDPA-Fe₃O₄@SiO₂-Cu(II) was recovered because of strong coordination of Cu²⁺ with GSSG, which promoted the decomplexation between NDPA-Fe₃O₄@SiO₂ and Cu²⁺, and enhanced the ICT process. The NDPA-Fe₃O₄@SiO₂-Cu(II) nanomaterial exhibited high sensitivity towards GSSG, and a good linear relationship was obtained from 5 nM to 60 μM. The limit of detection, based on a signal-to-noise ratio of 3, was 50 pM. In addition, the presence of magnetic Fe₃O₄ nanoparticles (NPs) in NDPA-Fe₃O₄@SiO₂ NPs would also facilitate the magnetic separation of NDPA-Fe₃O₄@SiO₂ from the solution. Through the use of added internal standards, we successfully determined the concentration of GSSG in HEK 293 cell lysate to be 1.15 μM by the prepared chemsensor NDPA-Fe₃O₄@SiO₂-Cu(II). The proposed method is anticipated to fabricate other sensitive fluorescence sensors based on organic-inorganic hybrid magnetic nanoparticles.