Multi-temperature zone, droplet-based microreactor for increased temperature control in nanoparticle synthesis

Biosensor for ATP detection via aptamer-modified PDA@POSS nanoparticles synthesized in a microfluidic reactor

This study introduces aptamer-functionalized polyhedral oligomeric silsesquioxane (POSS) nanoparticles for adenosine triphosphate (ATP) detection where the POSS nanoparticles were synthesized in a one-step, continuous flow microfluidic reactor utilizing thermal polymerization. A microemulsion containing POSS monomers was generated in the microfluidic reactor which was designed to prevent clogging by using a continuous oil flow around the emulsion during thermal polymerization. Surfaces of POSS nanoparticles were biomimetically modified by polydopamine. The aptamer sequence for ATP was successfully attached to POSS nanoparticles. The aptamer-modified POSS nanoparticles were tested for affinity-based biosensor applications using ATP as a model molecule. The nanoparticles were able to capture ATP molecules successfully with an affinity constant of 46.5 [Formula: see text]M. Based on this result, it was shown, for the first time, that microfluidic synthesis of POSS nanoparticles can be utilized in designing aptamer-functionalized nanosystems for biosensor applications. The integration of POSS in biosensing technologies not only exemplifies the versatility and efficacy of these nanoparticles but also marks a significant contribution to the field of biorecognition and sample preparation.

Synthesis of Anisotropic Magnetic Polymeric Janus Particles by In Situ Separation of Magnetic Nanoparticles in a Microfluidic Device

Magnetic Janus particles have been studied extensively for medical and biological applications owing to their controllable mobility in fluid media. In this work, we report a novel microfluidic device designed for the synthesis of magnetically anisotropic Janus particles made of poly(ethylene glycol) diacrylate and embedded with magnetic iron oxide nanoparticles. Our method consists of a droplet generation step followed by magnetic separation using an external magnetic field and ultraviolet polymerization. The synthesized particles exhibit a monodisperse size distribution with a standard deviation of less than 3.5%, which is among the best size distributions obtained in the literature for magnetic Janus particles. The anisotropic magnetic property of the particles enable them to rotate about their own axes in the presence of an external magnetic field, introducing another degree of freedom to their motion. This microfluidic technique is simple, one-step, and versatile, offering control over the size distribution to synthesize magnetically anisotropic Janus particles.

Antibacterial properties and osteoblast interactions of microfluidically synthesized chitosan - SPION composite nanoparticles

In this research, a multi-step microfluidic reactor was used to fabricate chitosan - superparamagnetic iron oxide composite nanoparticles (Ch - SPIONs), where composite formation using chitosan was aimed to provide antibacterial property and nanoparticle stability for magnetic resonance imaging (MRI). Monodispersed Ch - SPIONs had an average particle size of 8.8 ± 1.2 nm with a magnetization value of 32.0 emu/g. Ch - SPIONs could be used as an MRI contrast agent by shortening T2 relaxation parameter of the surrounding environment, as measured on a 3 T MRI scanner. In addition, Ch - SPIONs with concentrations less than 1 g/L promoted bone cell (osteoblast) viability up to 7 days of culture in vitro in the presence of 0.4 T external static magnetic field. These nanoparticles were also tested against Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa), which are dangerous pathogens that cause infection in tissues and biomedical devices. Upon interaction of Ch - SPIONs with S. aureus and P. aeruginosa at 0.01 g/L concentration, nearly a 2-fold reduction in the number of colonies was observed for both bacteria strains at 48 h of culture. Results cumulatively showed that Ch - SPIONs were potential candidates as a cytocompatible and antibacterial agent that can be targeted to biofilm and imaged using an MRI.

Microreactor-based micro/nanomaterials: fabrication, advances, and outlook

Micro/nanomaterials are widely used in optoelectronics, environmental materials, bioimaging, agricultural industries, and drug delivery owing to their marvelous features, such as quantum tunneling, size, surface and boundary, and Coulomb blockade effects. Recently, microreactor technology has opened up broad prospects for green and sustainable chemical synthesis as a powerful tool for process intensification and microscale manipulation. This review focuses on recent progress in the microreactor synthesis of micro/nanomaterials. First, the fabrication and design principles of existing microreactors for producing micro/nanomaterials are summarized and classified. Afterwards, typical examples are shown to demonstrate the fabrication of micro/nanomaterials, including metal nanoparticles, inorganic nonmetallic nanoparticles, organic nanoparticles, Janus particles, and MOFs. Finally, the future research prospects and key issues of microreactor-based micro/nanomaterials are discussed. In short, microreactors provide new ideas and methods for the synthesis of micro/nanomaterials, which have huge potential and inestimable possibilities in large-scale production and scientific research.

Microfluidic Methods in Janus Particle Synthesis

Janus particles have been at the center of attention over the years due to their asymmetric nature that makes them superior in many ways to conventional monophase particles. Several techniques have been reported for the synthesis of Janus particles; however, microfluidic-based techniques are by far the most popular due to their versatility, rapid prototyping, low reagent consumption and superior control over reaction conditions. In this review, we will go through microfluidic-based Janus particle synthesis techniques and highlight how recent advances have led to complex functionalities being imparted to the Janus particles.

Facile Synthesis of Platinum Right Bipyramids by Separating and Controlling the Nucleation Step in a Continuous Flow System

Colloidal synthesis of metal nanocrystals with controlled shapes and internal structures calls for a tight control over both the nucleation and growth processes. Here we report a method for the facile synthesis of Pt right bipyramids (RBPs) by separating nucleation from growth and controlling the nucleation step in a continuous flow reactor. Specifically, homogeneous nucleation was thermally triggered by introducing the reaction solution into a tubular flow reactor held at an elevated temperature to generate singly-twinned seeds. At a lower temperature, the singly-twinned seeds were protected from oxidative etching to allow their slow growth and evolution into RBPs while additional nucleation of undesired seeds could be largely suppressed to ensure RBPs as the main product. Further investigation indicated that the internal structure and growth pattern of the seeds were determined by the temperatures used for the nucleation and growth steps, respectively. The Br^- ions involved in the synthesis also played a critical role in the generation of RBPs by serving as a capping agent for the Pt{100} facets while regulating the reduction kinetics through coordination with the Pt(IV) ions.

Droplet-based lab-on-chip platform integrated with laser ablated graphene heaters to synthesize gold nanoparticles for electrochemical sensing and fuel cell applications

Controlled, stable and uniform temperature environment with quick response are crucial needs for many lab-on-chip (LOC) applications requiring thermal management. Laser Induced Graphene (LIG) heater is one such mechanism capable of maintaining a wide range of steady state temperature. LIG heaters are thin, flexible, and inexpensive and can be fabricated easily in different geometric configurations. In this perspective, herein, the electro-thermal performance of the LIG heater has been examined for different laser power values and scanning speeds. The experimented laser ablated patterns exhibited varying electrical conductivity corresponding to different combinations of power and speed of the laser. The conductivity of the pattern can be tailored by tuning the parameters which exhibit, a wide range of temperatures making them suitable for diverse lab-on-chip applications. A maximum temperature of 589 °C was observed for a combination of 15% laser power and 5.5% scanning speed. A LOC platform was realized by integrating the developed LIG heaters with a droplet-based microfluidic device. The performance of this LOC platform was analyzed for effective use of LIG heaters to synthesize Gold nanoparticles (GNP). Finally, the functionality of the synthesized GNPs was validated by utilizing them as catalyst in enzymatic glucose biofuel cell and in electrochemical applications.

Microfluidic and mathematical modeling of aquatic microbial communities

Aquatic microbial communities contribute fundamentally to biogeochemical transformations in natural ecosystems, and disruption of these communities can lead to ecological disasters such as harmful algal blooms. Microbial communities are highly dynamic, and their composition and function are tightly controlled by the biophysical (e.g., light, fluid flow, and temperature) and biochemical (e.g., chemical gradients and cell concentration) parameters of the surrounding environment. Due to the large number of environmental factors involved, a systematic understanding of the microbial community-environment interactions is lacking. In this article, we show that microfluidic platforms present a unique opportunity to recreate well-defined environmental factors in a laboratory setting in a high throughput way, enabling quantitative studies of microbial communities that are amenable to theoretical modeling. The focus of this article is on aquatic microbial communities, but the microfluidic and mathematical models discussed here can be readily applied to investigate other microbiomes.

Monolithically Integrated Diffused Silicon Two-Zone Heaters for Silicon-Pyrex Glass Microreactors for Production of Nanoparticles: Heat Exchange Aspects

We present the design, simulation, fabrication and characterization of monolithically integrated high resistivity p-type boron-diffused silicon two-zone heaters in a model high temperature microreactor intended for nanoparticle fabrication. We used a finite element method for simulations of the heaters’ operation and performance. Our experimental model reactor structure consisted of a silicon wafer anodically bonded to a Pyrex glass wafer with an isotropically etched serpentine microchannels network. We fabricated two separate spiral heaters with different temperatures, mutually thermally isolated by barrier apertures etched throughout the silicon wafer. The heaters were characterized by electric measurements and by infrared thermal vision. The obtained results show that our proposed procedure for the heater fabrication is robust, stable and controllable, with a decreased sensitivity to random variations of fabrication process parameters. Compared to metallic or polysilicon heaters typically integrated into microreactors, our approach offers improved control over heater characteristics through adjustment of the Boron doping level and profile. Our microreactor is intended to produce titanium dioxide nanoparticles, but it could be also used to fabricate nanoparticles in different materials as well, with various parameters and geometries. Our method can be generally applied to other high-temperature microsystems.

Textured surfaces as a new platform for nanoparticle synthesis

We present a new, surface-based microfluidic platform for the synthesis of nanoparticles. In this platform chemical reagents are carried in separate droplets, then mixed and later transported to a desired location on the surface using surface textured ratchet tracks. This brings the advantages of both synthesizing and transporting nanoparticles in situ without having cross-contamination between samples and addressing each sample independently. This platform is also capable of carrying multiple synthesis reactions concurrently.

Alternating Droplet Formation by using Tapered Channel Geometry

The ability to produce a controlled sequence of alternating droplets from two separate sources inside a microfluidic system brings several advantages in microfluidic analysis. The effectiveness of this technique for use in an application depends on the ability of the device to replicate the pattern continuously and accurately. In this work we studied the effect of the dispersed phase channel geometry on generating a repeating pattern of alternating droplets in a cross junction microfluidic device. By measuring the radius of curvature of a droplet at the time of break up, and calculating the Laplace pressure using these values, we analyzed how the angle of taper of the dispersed phase inlet channel has an influence on the pattern repetition and uniformity of formed droplet size and spacing in between. The performance of devices with different angle of taper values were studied experimentally. This comparative study indicated that the ability of a cross junction device to generate alternating droplets with uniform size and spacing is highly dependent on the angle of taper of the inlet channels; and it improves with larger taper angles.

Continuous low temperature synthesis of MAPbX3 perovskite nanocrystals in a flow reactor

Perovskite nanocrystals prepared at room temperature using a simple flow reactor.

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.

Microdroplet chain array for cell migration assays

Establishing cell migration assays in multiple different microenvironments is important in the study of tissue repair and regeneration, cancer progression, atherosclerosis, and arthritis. In this work, we developed a miniaturized and massive parallel microfluidic platform for multiple cell migration assays combining the traditional membrane-based cell migration technique and the droplet-based microfluidic technique. Nanoliter-scale droplets are flexibly assembled as building blocks based on a porous membrane to form microdroplet chains with diverse configurations for different assay modes. Multiple operations including in-droplet 2D/3D cell culture, cell co-culture and cell migration induced by a chemoattractant concentration gradient in droplet chains could be flexibly performed with reagent consumption in the nanoliter range for each assay and an assay scale-up to 81 assays in parallel in one microchip. We have applied the present platform to multiple modes of cell migration assays including the accurate cell migration assay, competitive cell migration assay, biomimetic chemotaxis assay, and multifactor cell migration assay based on the organ-on-a-chip concept, for demonstrating its versatility, applicability, and potential in cell migration-related research.

Synthesis of Cesium Lead Halide Perovskite Nanocrystals in a Droplet-Based Microfluidic Platform: Fast Parametric Space Mapping

Prior to this work, fully inorganic nanocrystals of cesium lead halide perovskite (CsPbX3, X = Br, I, Cl and Cl/Br and Br/I mixed halide systems), exhibiting bright and tunable photoluminescence, have been synthesized using conventional batch (flask-based) reactions. Unfortunately, our understanding of the parameters governing the formation of these nanocrystals is still very limited due to extremely fast reaction kinetics and multiple variables involved in ion-metathesis-based synthesis of such multinary halide systems. Herein, we report the use of a droplet-based microfluidic platform for the synthesis of CsPbX3 nanocrystals. The combination of online photoluminescence and absorption measurements and the fast mixing of reagents within such a platform allows the rigorous and rapid mapping of the reaction parameters, including molar ratios of Cs, Pb, and halide precursors, reaction temperatures, and reaction times. This translates into enormous savings in reagent usage and screening times when compared to analogous batch synthetic approaches. The early-stage insight into the mechanism of nucleation of metal halide nanocrystals suggests similarities with multinary metal chalcogenide systems, albeit with much faster reaction kinetics in the case of halides. Furthermore, we show that microfluidics-optimized synthesis parameters are also directly transferrable to the conventional flask-based reaction.

Millisecond-Timescale Monitoring of PbS Nanoparticle Nucleation and Growth Using Droplet-Based Microfluidics

The early-time kinetics (<1 s) of lead sulfide (PbS) quantum dot formation are probed using a novel droplet-based microfluidic platform, which allows for high-throughput and real-time optical analysis of the reactive process with millisecond time resolution. The reaction platform enables the concurrent investigation of the emission characteristics of PbS quantum dots and a real-time estimation of their size and concentration during nucleation and growth. These investigations reveal a two-stage mechanism for PbS nanoparticle formation. The first stage corresponds to the fast conversion of precursor species to PbS crystals, followed by the growth of the formed particles. The growth kinetics of the PbS nanoparticles follow the Lifshitz-Slyozov-Wagner model for Ostwald ripening, allowing direct estimation of the rate constants for the process. In addition, the extraction of absorption spectra of ultrasmall quantum dots is demonstrated for first time in an online manner. The droplet-based microfluidic platform integrated with online spectroscopic analysis provides a new tool for the quantitative extraction of high temperature kinetics for systems with rapid nucleation and growth stages.

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).

Nanocrystal synthesis in microfluidic reactors: where next?

The past decade has seen a steady rise in the use of microfluidic reactors for nanocrystal synthesis, with numerous studies reporting improved reaction control relative to conventional batch chemistry. However, flow synthesis procedures continue to lag behind batch methods in terms of chemical sophistication and the range of accessible materials, with most reports having involved simple one- or two-step chemical procedures directly adapted from proven batch protocols. Here we examine the current status of microscale methods for nanocrystal synthesis, and consider what role microreactors might ultimately play in laboratory-scale research and industrial production.