Microfluidic Separation and Enrichment of Escherichia coli by Size Using Viscoelastic Flows

Viscoelastic Fluid Focusing Chip-ICP-MS Single-Cell Analysis Enables Elucidating the Effect of Extracellular Polymeric Substances on Bioaccumulation of Hg2+/HgS in Microcystis aeruginosa Cell

Understanding the interactions between mercury and microalgae, especially the interactions between inorganic mercury (IHg) and extracellular polymeric substances (EPS, a protective barrier between cells and their external environment), is essential for elucidating mercury's toxicological mechanisms. Given the inherent cell heterogeneity, a novel analysis system of an online viscoelastic fluid focusing chip-time-resolved analysis inductively coupled plasma mass spectrometry has been developed to investigate the bioaccumulation of HgS nanoparticles and Hg2+ in single Microcystis aeruginosa (M. aeruginosa) cells, exploring the interaction mechanisms between HgS/Hg2+ accumulation in algal cells and EPS. The single-cell analysis results reveal minimal bioavailability of HgS within algal cells, with mercury's toxicity to M. aeruginosa being species-dependent. Notably, algal cells exhibited more heterogeneity in HgS uptake than in Hg2+ uptake. Under Hg2+/HgS stress, M. aeruginosa cells with EPS removed (EPS-R algal cells) showed an increased level of bioaccumulation of mercury compared to those with EPS (EPS-C algal cells), highlighting the critical role of EPS in mercury bioaccumulation. Overall, the designed viscoelastic fluid microfluidic focusing chip integrates focusing and cleaning functions, featuring easy fabrication, simple operation, low sample loss, and relatively high throughput. Under the optimal conditions, the sample throughput is 1195 min-1 and the cell recovery is 90%. Besides, this research offers novel insights into the interaction mechanisms between Hg2+/HgS and EPS in microalgal cells and unveils the specific toxic effects of Hg2+/HgS on M. aeruginosa at the single-cell level, contributing to a deeper understanding of mercury's ecological and toxicological impact in aquatic environments.

The use of droplet-based microfluidic technologies for accelerated selection of Yarrowia lipolytica and Phaffia rhodozyma yeast mutants

Microorganisms are widely used for the industrial production of various valuable products, such as pharmaceuticals, food and beverages, biofuels, enzymes, amino acids, vaccines, etc. Research is constantly carried out to improve their properties, mainly to increase their productivity and efficiency and reduce the cost of the processes. The selection of microorganisms with improved qualities takes a lot of time and resources (both human and material); therefore, this process itself needs optimization. In the last two decades, microfluidics technology appeared in bioengineering, which allows for manipulating small particles (from tens of microns to nanometre scale) in the flow of liquid in microchannels. The technology is based on small-volume objects (microdroplets from nano to femtolitres), which are manipulated using a microchip. The chip is made of an optically transparent inert to liquid medium material and contains a series of channels of small size (<1 mm) of certain geometry. Based on the physical and chemical properties of microparticles (like size, weight, optical density, dielectric constant, etc.), they are separated using microsensors. The idea of accelerated selection of microorganisms is the application of microfluidic technologies to separate mutants with improved qualities after mutagenesis. This article discusses the possible application and practical implementation of microfluidic separation of mutants, including yeasts like Yarrowia lipolytica and Phaffia rhodozyma after chemical mutagenesis will be discussed.

A Review of Research Progress in Microfluidic Bioseparation and Bioassay

With the rapid development of biotechnology, the importance of microfluidic bioseparation and bioassay in biomedicine, clinical diagnosis, and other fields has become increasingly prominent. Microfluidic technology, with its significant advantages of high throughput, automated operation, and low sample consumption, has brought new breakthroughs in the field of biological separation and bioassay. In this paper, the latest research progress in microfluidic technology in the field of bioseparation and bioassay is reviewed. Then, we focus on the methods of bioseparation including active separation, passive separation, and hybrid separation. At the same time, the latest research results of our group in particle separation are introduced. Finally, some application examples or methods for bioassay after particle separation are listed, and the current challenges and future prospects of bioseparation and bioassay are discussed.

Magnetophoresis-Enhanced Elasto-Inertial Migration of Microparticles and Cells in Microfluidics

Microfluidic particle and cell manipulation techniques possess many potentials for biomedicine and healthcare. Many techniques have been developed based on active (e.g., electrical, magnetic, acoustic, and thermal) force fields and passive hydrodynamic forces (e.g., inertial and elastic lift forces). However, techniques based on a single active or passive manipulating physics cannot always meet the demands, and combining multiple physics becomes a promising strategy to promote technique flexibility and versatility. In this work, we explored the physical coupling of magnetophoresis with the elastic and inertial (i.e., elasto-inertial) lift forces for the manipulation of microparticles. Particle lateral migration was studied in a coflowing configuration of viscoelastic ferrofluid/water (sample/sheath). The particles were suspended in the viscoelastic ferrofluid and confined near the channel sidewall by a sheath flow. The coordination of magnetophoresis and elasto-inertial lift forces promoted the cross-stream migration of particles. Besides, we investigated the effect of the flow rate ratio and total flow rate on the migration of particles. Furthermore, we also investigated the effects of fluid elasticity in sample and sheath flows on particle migration using different combinations of sample and sheath flows, including Newtonian ferrofluid/water, Newtonian ferrofluid/viscoelastic fluid, and viscoelastic ferrofluid/viscoelastic coflows. Experimental results demonstrated and ascertained the promoted particle lateral migration in the PEO-based ferrofluid/water coflow. Finally, we demonstrate the proof-of-concept application of the physical coupling strategy for cell cross-stream migration and solution exchange. We envisage that this novel multiphysical coupling scheme has great potential for the flexible and versatile manipulation of microparticles and cells.

Passive microfluidic devices for cell separation

The separation of specific cell populations is instrumental in gaining insights into cellular processes, elucidating disease mechanisms, and advancing applications in tissue engineering, regenerative medicine, diagnostics, and cell therapies. Microfluidic methods for cell separation have propelled the field forward, benefitting from miniaturization, advanced fabrication technologies, a profound understanding of fluid dynamics governing particle separation mechanisms, and a surge in interdisciplinary investigations focused on diverse applications. Cell separation methodologies can be categorized according to their underlying separation mechanisms. Passive microfluidic separation systems rely on channel structures and fluidic rheology, obviating the necessity for external force fields to facilitate label-free cell separation. These passive approaches offer a compelling combination of cost-effectiveness and scalability when compared to active methods that depend on external fields to manipulate cells. This review delves into the extensive utilization of passive microfluidic techniques for cell separation, encompassing various strategies such as filtration, sedimentation, adhesion-based techniques, pinched flow fractionation (PFF), deterministic lateral displacement (DLD), inertial microfluidics, hydrophoresis, viscoelastic microfluidics, and hybrid microfluidics. Besides, the review provides an in-depth discussion concerning cell types, separation markers, and the commercialization of these technologies. Subsequently, it outlines the current challenges faced in the field and presents a forward-looking perspective on potential future developments. This work hopes to aid in facilitating the dissemination of knowledge in cell separation, guiding future research, and informing practical applications across diverse scientific disciplines.

2D Materials Nanoarchitectonics for 3D Structures/Functions

It has become clear that superior material functions are derived from precisely controlled nanostructures. This has been greatly accelerated by the development of nanotechnology. The next step is to assemble materials with knowledge of their nano-level structures. This task is assigned to the post-nanotechnology concept of nanoarchitectonics. However, nanoarchitectonics, which creates intricate three-dimensional functional structures, is not always easy. Two-dimensional nanoarchitectonics based on reactions and arrangements at the surface may be an easier target to tackle. A better methodology would be to define a two-dimensional structure and then develop it into a three-dimensional structure and function. According to these backgrounds, this review paper is organized as follows. The introduction is followed by a summary of the three issues; (i) 2D to 3D dynamic structure control: liquid crystal commanded by the surface, (ii) 2D to 3D rational construction: a metal-organic framework (MOF) and a covalent organic framework (COF); (iii) 2D to 3D functional amplification: cells regulated by the surface. In addition, this review summarizes the important aspects of the ultimate three-dimensional nanoarchitectonics as a perspective. The goal of this paper is to establish an integrated concept of functional material creation by reconsidering various reported cases from the viewpoint of nanoarchitectonics, where nanoarchitectonics can be regarded as a method for everything in materials science.

Viscoelastic microfluidics for enhanced separation resolution of submicron particles and extracellular vesicles

Manipulation, focusing, and separation of submicron- and nanoparticles such as extracellular vesicles (EVs), viruses and bacteria have broad applications in disease diagnostics and therapeutics. Viscoelastic microfluidic technology emerges as a promising technique, and it shows an unparalleled capacity to manipulate and separate submicron particles in a high resolution based on the elastic effects of non-Newtonian mediums. The maximum particle separation resolution for the reported state-of-the-art viscoelastic microfluidics is around 200 nm. To further enhance the reseparation resolution, this work develops a viscoelastic microfluidic device that can achieve a finer separation resolution up to 100 nm, by optimising the operating conditions such as flow rate, flow rate ratio and polyethylene oxide (PEO) concentration. With these optimised conditions, we separated a ternary mixture of 100 nm, 200 nm and 500 nm polystyrene particles, with purities above 90%, 70% and 82%, respectively. Furthermore, we also applied the developed viscoelastic microfluidic device for the separation of cancer cell-secreted extracellular vesicles (EVs) into three different size groups. After single processing, the separation efficiencies for small EVs (sEVs, <150 nm), medium EVs (mEVs, 150-300 nm), and large EVs (>300 nm) were 86%, 80% and 50%, respectively. The enrichment factors for the three EV groups were 2.4, 1.1 and 1.3, respectively. Moreover, we observed an unexpected effect of high PEO concentrations (2000-5000 ppm) on the lateral migration of nanoparticles where nanoparticles of up to 50 nm surprisingly can migrate and concentrate at the middle of the microchannel. This simple and label-free viscoelastic microfluidic device possesses excellent potential for sorting submicron particles for various chemical, biological, medical and environmental applications.

Cascaded elasto-inertial separation of malignant tumor cells from untreated malignant pleural and peritoneal effusions

Separation of malignant tumor cells (MTCs) from large background cells in untreated malignant pleural and peritoneal effusions (MPPEs) is critical for improving the sensitivity and efficiency of cytological diagnosis. Herein, we proposed a cascaded elasto-inertial cell separation (CEICS) device integrating an interfacial elasto-inertial microfluidic channel with a symmetric contraction expansion array (CEA) channel for pretreatment-free, high-recovery-ratio, and high-purity separation of MTCs from clinical MPPEs. First, the effects of flow-rate ratio, cell concentration, and cell size on separation performances in two single-stage channels were investigated. Then, the performances of the integrated CEICS device were characterized using blood cells spiked with three different tumor cells (MCF-7, MDA-MB-231, and A549 cells) at a high total throughput of 240 μL min-1. An average recovery ratio of ∼95% and an average purity of ∼61% for the three tumor cells were achieved. Finally, we successfully applied the CEICS device for the pretreatment-free separation of MTCs from clinical MPPEs of different cancers. Our CEICS device may provide a preparation tool for improving the sensitivity and efficiency of cytological examination.

Elasto-inertial microfluidic separation of microspheres with submicron resolution at high-throughput

Elasto-inertial microfluidic separation offers many advantages including high throughput and separation resolution. Even though the separation efficiency highly depends on precise control of the flow conditions, no concrete guidelines have been reported yet in elasto-inertial microfluidics. Here, we propose a dimensionless analysis for precise estimation of the microsphere behaviors across the interface of Newtonian and viscoelastic fluids. Reynolds number, modified Weissenberg number, and modified elastic number are used to investigate the balance between inertial and elastic lift forces. Based on the findings, we introduce a new dimensionless number defined as the width of the Newtonian fluid stream divided by microsphere diameter. The proposed dimensionless analysis allows us to predict whether the microspheres migrate across the co-flow interface. The theoretical estimation is found to be in good agreement with the experimental results using 2.1- and 3.2-μm-diameter polystyrene microspheres in a co-flow of water and polyethylene oxide solution. Based on the theoretical estimation, we also realize submicron separation of the microspheres with 2.1 and 2.5 μm in diameter at high throughput, high purity (>95%), and high recovery rate (>97%). The applicability of the proposed method was validated by separation of platelets from similar-sized Escherichia coli (E.coli).

Materials Nanoarchitectonics at Dynamic Interfaces: Structure Formation and Functional Manipulation

The next step in nanotechnology is to establish a methodology to assemble new functional materials based on the knowledge of nanotechnology. This task is undertaken by nanoarchitectonics. In nanoarchitectonics, we architect functional material systems from nanounits such as atoms, molecules, and nanomaterials. In terms of the hierarchy of the structure and the harmonization of the function, the material created by nanoarchitectonics has similar characteristics to the organization of the functional structure in biosystems. Looking at actual biofunctional systems, dynamic properties and interfacial environments are key. In other words, nanoarchitectonics at dynamic interfaces is important for the production of bio-like highly functional materials systems. In this review paper, nanoarchitectonics at dynamic interfaces will be discussed, looking at recent typical examples. In particular, the basic topics of "molecular manipulation, arrangement, and assembly" and "material production" will be discussed in the first two sections. Then, in the following section, "fullerene assembly: from zero-dimensional unit to advanced materials", we will discuss how various functional structures can be created from the very basic nanounit, the fullerene. The above examples demonstrate the versatile possibilities of architectonics at dynamic interfaces. In the last section, these tendencies will be summarized, and future directions will be discussed.

Exploitation of elasto-inertial fluid flow for the separation of nano-sized particles: Simulating the isolation of extracellular vesicles

High throughput and efficient separation/isolation of nanoparticles such as exosomes remain a challenge owing to their small size. Elasto-inertial approaches have a new potential to be leveraged because of the ability to achieve fine control over the forces that act on extremely small particles. That is, the viscoelasticity of fluid that helps carry biological particles such as extracellular vesicles (EVs) and cells through microfluidic channels can be tailored to optimize how different-sized particles move within the chip. In this contribution, we demonstrate through computational fluid dynamics (CFD) simulations the ability to separate nanoparticles with a size comparable to exosomes from larger spheres with physical properties comparable to cells and larger EVs. Our current design makes use of an efficient flow-focusing geometry at the inlet of the device in which two side channels deliver the sample, while the inner channel injects the sheath flow. Such flow configuration results in an efficient focusing of all the particles near the sidewalls of the channel at the inlet. By dissolving a minute amount of polymer in the sample and sheath fluid, the elastic lift force arises and the initially focused particle adjacent to the wall will gradually migrate toward the center of the channel. This results in larger particles experiencing larger elastic forces, thereby migrating faster toward the center of the channel. By adjusting the size and location of the outlets, nanoparticles comparable to the size of exosomes (30-100 nm) will be effectively separated from other particles. Furthermore, the influence of different parameters such as channel geometry, flow rate, and fluid rheology on the separation process is evaluated by computational analysis.

Blood component separation in straight microfluidic channels

Separation of blood components is required in many diagnostic applications and blood processes. In laboratories, blood is usually fractionated by manual operation involving a bulk centrifugation equipment, which significantly increases logistic burden. Blood sample processing in the field and resource-limited settings cannot be readily implemented without the use of microfluidic technology. In this study, we developed a small footprint, rapid, and passive microfluidic channel device that relied on margination and inertial focusing effects for blood component separation. No blood dilution, lysis, or labeling step was needed as to preserve sample integrity. One main innovation of this work was the insertion of fluidic restrictors at outlet ports to divert the separation interface into designated outlet channels. Thus, separation efficiency was significantly improved in comparison to previous works. We demonstrated different operation modes ranging from platelet or plasma extraction from human whole blood to platelet concentration from platelet-rich plasma through the manipulation of outlet port fluidic resistance. Using straight microfluidic channels with a high aspect ratio rectangular cross section, we demonstrated 95.4% platelet purity extracted from human whole blood. In plasma extraction, 99.9% RBC removal rate was achieved. We also demonstrated 2.6× concentration of platelet-rich plasma solution to produce platelet concentrate. The extraction efficiency and throughput rate are scalable with continuous and clog-free recirculation operation, in contrast to other blood fractionation approaches using filtration membranes or affinity-based purification methods. Our microfluidic blood separation method is highly tunable and versatile, and easy to be integrated into multi-step blood processing and advanced sample preparation workflows.

Continuous separation of bacterial cells from large debris using a spiral microfluidic device

With the global increase in food exchange, rapid identification and enumeration of bacteria has become crucial for protecting consumers from bacterial contamination. Efficient analysis requires the separation of target particles (e.g., bacterial cells) from food and/or sampling matrices to prevent matrix interference with the detection and analysis of target cells. However, studies on the separation of bacteria-sized particles and defined particles, such as bacterial cells, from heterogeneous debris, such as meat swab suspensions, are limited. In this study, we explore the use of passive-based inertial microfluidics to separate bacterial cells from debris, such as fascia, muscle tissues, and cotton fibers, extracted from ground meat and meat swabs-a novel approach demonstrated for the first time. Our objective is to evaluate the recovery efficiency of bacterial cells from large debris obtained from ground meat and meat swab suspensions using a spiral microfluidic device. In this study, we establish the optimal flow rates and Dean number for continuous bacterial cell and debris separation and a methodology to determine the percentage of debris removed from the sample suspension. Our findings demonstrate an average recovery efficiency of ∼ 80% for bacterial cells separated from debris in meat swab suspensions, while the average recovery efficiency from ground beef suspensions was ∼ 70%. Furthermore, approximately 50% of the debris in the ground meat suspension were separated from bacterial cells.