Toward continuous production of high-quality nanomaterials using microfluidics: nanoengineering the shape, structure and chemical composition

Continuous and Scalable Synthesis of Prussian Blue Analogues with Tunable Structure and Composition in Surfactant-Free Microreactor for Stable Zinc-Ion Storage

We represent a segmented flow surfactant-free microfluidic strategy for continuous synthesis of Prussian blue analogues (PBAs) with high dispersity and high crystallization. Representative zinc hexacyanoferrate (ZnHCF) nanocubes were successfully synthesized in a microfluidic reactor within a few minutes via the cooperation method and possessed lower contents of crystal water and Fe(CN)6 3- vacancies than that of synthesis in bulk solution. The nucleation and particle growth process can be precisely controlled by the exploration of different flow rates and reaction temperatures during the formation of ZnHCF nanocubes in segmented flow microfluidic reactors. High crystallinity, low crystal water and vacancies in the ZnHCF structure were presented at relatively high temperatures for the crystal growth process. High-quality ZnHCF with a low content of crystal water showed excellent electrochemical activity and stability towards zinc-ion storage. The continuous and scalable synthesis approach can be extended to the fabrication of other PBAs such as NiHCF, CoHCF, MnHCF, and CuHCF with high dispersity without using any surfactants. The controllable construction of PBAs with tunable properties in microfluidic reactors provides a promising direction to minimize the gap between commercial reality and laboratory research.

A do-it-yourself benchtop device for highly scalable flow synthesis of protein-based nanoparticles

Synthesis of nanoparticles is typically carried out in batch procedures, which offer limited control of parameters, and a narrow range of possible batch volumes. In contrast, flow synthesis systems, usually having a microfluidic chip as a crucial part, are devoid of these drawbacks. However, large scale devices - millifluidic systems - may offer several advantages over microfluidic systems, such as easier and cheaper production, enhanced throughput, and reduced channel clogging. Here we report a millifluidic system for the generation of protein nanoparticles, using the flow format of the original swift thermal formation technology (STF), which can process batch volume ranging from 100 µl to any practically significant amount. Capabilities of the system are demonstrated with model synthesis of Epirubicin-encapsulated BSA nanoparticles. A better degree of scalability of the synthesis over batch procedure is shown: with a 10-fold working volume increase, hydrodynamic diameter and loading capacity changed by only 10 % and 1 % respectively, compared to 60 % and 30 % for the batch synthesis. Additionally, we provide all engineering drawings, electrical circuits, programming code and nuances of assembly and operation, so that our findings can be easily reproduced. The ease of construction of the device and the superior characteristics of the resulting nanoparticles compared to the batch method indicate application potential in both the biomedical research and industrial spheres.

Oral delivery of RNAi for cancer therapy

Cancer is a major health concern worldwide and is still in a continuous surge of seeking for effective treatments. Since the discovery of RNAi and their mechanism of action, it has shown promises in targeted therapy for various diseases including cancer. The ability of RNAi to selectively silence the carcinogenic gene makes them ideal as cancer therapeutics. Oral delivery is the ideal route of administration of drug administration because of its patients' compliance and convenience. However, orally administered RNAi, for instance, siRNA, must cross various extracellular and intracellular biological barriers before it reaches the site of action. It is very challenging and important to keep the siRNA stable until they reach to the targeted site. Harsh pH, thick mucus layer, and nuclease enzyme prevent siRNA to diffuse through the intestinal wall and thereby induce a therapeutic effect. After entering the cell, siRNA is subjected to lysosomal degradation. Over the years, various approaches have been taken into consideration to overcome these challenges for oral RNAi delivery. Therefore, understanding the challenges and recent development is crucial to offer a novel and advanced approach for oral RNAi delivery. Herein, we have summarized the delivery strategies for oral delivery RNAi and recent advancement towards the preclinical stages.

Co-electrolysis of seawater and carbon dioxide inside a microfluidic reactor to synthesize speciality organics

We report co-electrolysis of seawater and carbon dioxide (CO₂) gas in a solar cell-integrated membraneless microfluidic reactor for continuous synthesis of organic products. The microfluidic reactor was fabricated using polydimethylsiloxane substrate comprising of a central microchannel with a pair of inlets for injection of CO₂ gas and seawater and an outlet for removal of organic products. A pair of copper electrodes were inserted into microchannel to ensure its direct interaction with incoming CO₂ gas and seawater as they pass into the microchannel. The coupling of solar cell panels with electrodes generated a high-intensity electrical field across the electrodes at low voltage, which facilitated the co-electrolysis of CO₂ and seawater. The paired electrolysis of CO₂ gas and seawater produced a range of industrially important organics under influence of solar cell-mediated external electric field. The, as synthesized, organic compounds were collected downstream and identified using characterization techniques. Furthermore, the probable underlying electrochemical reaction mechanisms near the electrodes were proposed for synthesis of organic products. The inclusion of greenhouse CO₂ gas as reactant, seawater as electrolyte, and solar energy as an inexpensive electric source for co-electrolysis initiation makes the microreactor a low-cost and sustainable alternative for CO₂ sequestration and synthesis of organic compounds.

Ultra-stable blue-emitting lead-free double perovskite Cs2SnCl6 nanocrystals enabled by an aqueous synthesis on a microfluidic platform

Blue emitting Sn-based lead-free halide perovskite nanocrystals (NCs) are considered to be a promising material in lighting and displays. However, industrialised fabrication of blue-emitting NCs still remains a significant challenge due to the use of toxic solvents and optical instability, not mentioning in large-scale synthesis. In this work, a green-route synthesis of blue-emitting lead-free halide perovskite Cs₂SnCl₆ powders is developed, in which deionized water with a small amount of inorganic acid is used as the solvent and the synthesis of the Cs₂SnCl₆ powders is achieved on a microfluidic platform. Using the Cs₂SnCl₆ powders, we prepare Cs₂SnCl₆ NCs via an ultrasonication process. Changing the volume ratio of the ligands (oleic acid to oleylamine) can alter the photoluminescence (PL) characteristics of the prepared NCs, including the PL-peak wavelength, PL-peak intensity and quantum yield. The highest photoluminescence quantum yield (PLQY) of 13.4% is achieved by the Cs₂SnCl₆ NCs prepared with the volume ratio of oleic acid to oleylamine of 40 μL to 10 μL. A long-term PL stability test demonstrates that the as-synthesized Cs₂SnCl₆ NCs can retain a stable PLQY over a period of 60 days. This work opens up a new path for a large-scale green-route synthesis of blue-emitting Sn-based lead-free NCs, such as Cs₂SnX₆ (Cl, Br and I), towards their applications in optoelectronics.

Microfluidic Nanomaterial Synthesis and In Situ SAXS, WAXS, or SANS Characterization: Manipulation of Size Characteristics and Online Elucidation of Dynamic Structural Transitions

With the ability to cross biological barriers, encapsulate and efficiently deliver drugs and nucleic acid therapeutics, and protect the loaded cargos from degradation, different soft polymer and lipid nanoparticles (including liposomes, cubosomes, and hexosomes) have received considerable interest in the last three decades as versatile platforms for drug delivery applications and for the design of vaccines. Hard nanocrystals (including gold nanoparticles and quantum dots) are also attractive for use in various biomedical applications. Here, microfluidics provides unique opportunities for the continuous synthesis of these hard and soft nanomaterials with controllable shapes and sizes, and their in situ characterization through manipulation of the flow conditions and coupling to synchrotron small-angle X-ray (SAXS), wide-angle scattering (WAXS), or neutron (SANS) scattering techniques, respectively. Two-dimensional (2D) and three-dimensional (3D) microfluidic devices are attractive not only for the continuous production of monodispersed nanomaterials, but also for improving our understanding of the involved nucleation and growth mechanisms during the formation of hard nanocrystals under confined geometry conditions. They allow further gaining insight into the involved dynamic structural transitions, mechanisms, and kinetics during the generation of self-assembled nanostructures (including drug nanocarriers) at different reaction times (ranging from fractions of seconds to minutes). This review provides an overview of recently developed 2D and 3D microfluidic platforms for the continuous production of nanomaterials, and their simultaneous use in in situ characterization investigations through coupling to nanostructural characterization techniques (e.g., SAXS, WAXS, and SANS).