Enhanced viscoelastic focusing of particle in microchannel

A novel method is reported to enhance the focusing of microparticle in the viscoelastic fluid. Gradually contracted geometry is designed in microchannel, which changes the distribution of the elastic lift force on the cross section. Additionally, it induces the viscous drag force and the Saffman lift force in the lateral direction. Under the combined effect of these forces, microparticles fast migrate to the center of the channel. In comparison to the channel with constant cross section, the present channel significantly enhances the particle's lateral migration, leading to efficient viscoelastic particle focusing in a short channel length. The influence of flow rate, channel length, particle size and fluid property on the particle focusing is also investigated. With simple structure, small footprint and perfect particle focusing performance, the present device has great potential in the particle focusing processes in various lab-on-a-chip applications.     

Reduction in microparticle adsorption using a lateral interconnection method in a PDMS‐based microfluidic device

Microparticle adsorption on microchannel walls occurs frequently due to nonspecific interactions, decreasing operational performance in pressure‐driven microfluidic systems. However, it is essential for delicate manipulation of microparticles or cells to maintain smooth fluid traffic. Here, we report a novel microparticle injection technique, which prevents particle loss, assisted by sample injection along the direction of fluid flow. Sample fluids, including microparticles, mammalian (U937), and green algae (Chlorella vulgaris) cells, were injected directly via a through hole drilled in the lateral direction, resulting in a significant reduction in microparticle attachment. For digital microfluidic application, the proposed regime achieved a twofold enhancement of single‐cell encapsulation compared to the conventional encapsulation rate, based on a Poisson distribution, by reducing the number of empty droplets. This novel interconnection method can be straightforwardly integrated as a microparticle or cell injection component in integrated microfluidic systems.     

Inertial separation in a contraction-expansion array microchannel

We report a contraction-expansion array (CEA) microchannel that allows inertial size separation by a force balance between inertial lift and Dean drag forces in fluid regimes in which inertial fluid effects become significant. An abrupt change of the cross-sectional area of the channel curves fluid streams and produces a similar effect compared to Dean flows in a curved microchannel of constant cross-section, thereby inducing Dean drag forces acting on particles. In addition, the particles are influenced by inertial lift forces throughout the contraction regions. These two forces act in opposite directions each other throughout the CEA microchannel, and their force balancing determines whether the particles cross the channel, following Dean flows. Here we describe the physics and design of the CEA microfluidic device, and demonstrate complete separation of microparticles (polystyrene beads of 4 and 10 μm in diameter) and efficient exchange of the carrier medium while retaining 10 μm beads.     

Trapping and releasing of single microparticles and cells in a microfluidic chip

A microfluidic device was designed and fabricated to capture single microparticles and cells by using hydrodynamic force and selectively release the microparticles and cells of interest via negative dielectrophoresis by activating selected individual microelectrodes. The trap microstructure was optimized based on numerical simulation of the electric field as well as the flow field. The capture and selective release functions of the device were verified by multi-types microparticles with different diameters and K562 cells. The capture efficiencies/release efficiencies were 95.55% ± 0.43%/96.41% ± 1.08% and 91.34% ± 0.01%/93.67% ± 0.36% for microparticles and cells, respectively. By including more traps and microelectrodes, the device can achieve high throughput and realize the visual separation of microparticles/cells of interest in a large number of particle/cell groups.     

Efficient microfluidic enrichment of nano-/submicroparticle in viscoelastic fluid

The enrichment and focusing of the nano-/submicroparticle (e.g., 150–1000 nm microvesicle shed from the plasma membrane) in the viscoelastic fluid has great potentials in the biomedical and clinical applications such as the disease diagnosis and the prognostic test for liquid biopsy. However, due to the small size and the resulting weak hydrodynamic force, the efficient manipulation of the nano-/submicroparticle by the passive viscoelastic microfluidic technology remains a major challenge. For instance, a typically long channel length is often required to achieve the focusing or the separation of the nano-/submicroparticle, which makes it difficult to be integrated in small chip area. In this work, a microchannel with gradually contracted cross-section and high aspect ratio (the ratio of the height to the average width of channel) is utilized to enhance the hydrodynamic force and change the force direction, eventually leading to the efficient enrichment of nano-/submicroparticles (500 and 860 nm) in a short channel length (2 cm). The influence of the flow rate, the particle size, the solid concentration, and the channel geometry on the enrichment of the nano-/submicroparticles are investigated. With simple structure, small footprint, easy operation, and good performance, the present device would be a promising platform for various lab-chip microvesicle-related biomedical research and disease diagnosis.     

Interactive manipulation of blood cells using a lens-integrated liquid crystal display based optoelectronic tweezers system

This paper reports a lens-integrated liquid crystal display (LCD)-based optoelectronic tweezers (OET) system for interactive manipulation of polystyrene microspheres and blood cells by optically induced dielectrophoretic force. When a dynamic image pattern is projected into a specific area of a photoconductive layer in an OET, virtual electrodes are generated by spatially resolved illumination of the photoconductive layer, resulting in dielectrophoresis of microparticles suspended in the liquid layer under nonuniform electric field. In this study, the simple-structured OET system has been easily constructed with an OET device, an LCD and a condenser lens integrated in a conventional microscope. By using a condenser lens, both stronger dielectrophoretic forces and higher virtual electrode resolution than previously reported lens-less LCD-based OET platform are obtained. The effects of blurred LCD image and liquid chamber height on the performances of optoelectronic particle manipulation are investigated by measuring the bead velocities according to their sizes. An interactive control program for OET-based microparticle manipulation is also developed by Flash language. The integrated system is successfully applied to the parallel and interactive manipulation of red and white blood cells. Due to its simple structures, cheap manufacturing costs, and high performances, this new LCD-based OET platform may be a widely usable integrated system for optoelectronic manipulation of microparticles including living cells.     

Continuous particle separation in spiral microchannels using Dean flows and differential migration

Microparticle separation and concentration based on size has become indispensable in many biomedical and environmental applications. In this paper we describe a passive microfluidic device with spiral microchannel geometry for complete separation of particles. The design takes advantage of the inertial lift and viscous drag forces acting on particles of various sizes to achieve differential migration, and hence separation, of microparticles. The dominant inertial forces and the Dean rotation force due to the spiral microchannel geometry cause the larger particles to occupy a single equilibrium position near the inner microchannel wall. The smaller particles migrate to the outer half of the channel under the influence of Dean forces resulting in the formation of two distinct particle streams which are collected in two separate outputs. This is the first demonstration that takes advantage of the dual role of Dean forces for focusing larger particles in a single equilibrium position and transposing the smaller particles from the inner half to the outer half of the microchannel cross-section. The 5-loop spiral microchannel 100 microm wide and 50 microm high was used to successfully demonstrate a complete separation of 7.32 microm and 1.9 microm particles at Dean number De = 0.47. Analytical analysis supporting the experiments and models is also presented. The simple planar structure of the separator offers simple fabrication and makes it ideal for integration with on-chip microfluidic systems, such as micro total analysis systems (muTAS) or lab-on-a-chip (LOC) for continuous filtration and separation applications.     

Dielectrophoretic manipulation and separation of microparticles using curved microelectrodes

This paper presents the development and experimental analysis of a dielectrophoresis (DEP) system, which is used for the manipulation and separation of microparticles in liquid flow. The system is composed of arrays of microelectrodes integrated to a microchannel. Novel curved microelectrodes are symmetrically placed with respect to the centre of the microchannel with a minimum gap of 40 μm. Computational fluid dynamics method is utilised to characterise the DEP field and predict the dynamics of particles. The performance of the system is assessed with microspheres of 1, 5 and 12 μm diameters. When a high‐frequency potential is applied to microelectrodes a spatially varying electric field is induced in the microchannel, which creates the DEP force. Negative‐DEP behaviour is observed with particles being repelled from the microelectrodes. The particles of different dimensions experience different DEP forces and thus settle to separate equilibrium zones across the microchannel. Experiments demonstrate the capability of the system as a field flow fraction tool for sorting microparticles according to their dimensions and dielectric properties.     

Model‐based analysis of a dielectrophoretic microfluidic device for field‐flow fractionation

We present the development of a dynamic model for predicting the trajectory of microparticles in microfluidic devices, employing dielectrophoresis, for Hyperlayer field‐flow fractionation. The electrode configuration is such that multiple finite‐sized electrodes are located on the top and bottom walls of the microchannel; the electrodes on the walls are aligned with each other. The electric potential inside the microchannel is described using the Laplace equation while the microparticles' trajectory is described using equations based on Newton's second law. All equations are solved using finite difference method. The equations of motion account for forces including inertia, buoyancy, drag, gravity, virtual mass, and dielectrophoresis. The model is used for parametric study; the geometric parameters analyzed include microparticle radius, microchannel depth, and electrode/spacing lengths while volumetric flow rate and actuation voltage are the two operating parameters considered in the study. The trajectory of microparticles is composed of transient and steady state phases; the trajectory is influenced by all parameters. Microparticle radius and volumetric flow rate, above the threshold, do not influence the steady state levitation height; microparticle levitation is not possible below the threshold of the volumetric flow rate. Microchannel depth, electrode/spacing lengths, and actuation voltage influence the steady‐state levitation height.     

Pinched flow coupled shear-modulated inertial microfluidics for high-throughput rare blood cell separation

Blood is a highly complex bio-fluid with cellular components making up >40% of the total volume, thus making its analysis challenging and time-consuming. In this work, we introduce a high-throughput size-based separation method for processing diluted blood using inertial microfluidics. The technique takes advantage of the preferential cell focusing in high aspect-ratio microchannels coupled with pinched flow dynamics for isolating low abundance cells from blood. As an application of the developed technique, we demonstrate the isolation of cancer cells (circulating tumor cells (CTCs)) spiked in blood by exploiting the difference in size between CTCs and hematologic cells. The microchannel dimensions and processing parameters were optimized to enable high throughput and high resolution separation, comparable to existing CTC isolation technologies. Results from experiments conducted with MCF-7 cells spiked into whole blood indicate >80% cell recovery with an impressive 3.25 × 10(5) fold enrichment over red blood cells (RBCs) and 1.2 × 10(4) fold enrichment over peripheral blood leukocytes (PBL). In spite of a 20× sample dilution, the fast operating flow rate allows the processing of ～10(8) cells min(-1) through a single microfluidic device. The device design can be easily customized for isolating other rare cells from blood including peripheral blood leukocytes and fetal nucleated red blood cells by simply varying the 'pinching' width. The advantage of simple label-free separation, combined with the ability to retrieve viable cells post enrichment and minimal sample pre-processing presents numerous applications for use in clinical diagnosis and conducting fundamental studies.     

Development and in vitro cytotoxicity of microparticle drug delivery system for proteins using <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine polyphosphate

l-Tyrosine polyphosphate (LTP), a “pseudo” poly (amino acid) polymer is characterized by a rapid degradation rate. Subsequently, formulation of a drug delivery system has been investigated by encapsulating fluorescein isothiocyanate–bovine serum albumin (FITC-BSA) within LTP microparticles. Characterization of surface morphology shows a mixture of spherical and discoid particles with a slightly rough surface morphology for all microparticle formulations. Dynamic laser light scattering (DLS) shows a decrease in particle diameters and size distribution upon FITC-BSA encapsulation. LTP microparticles are found to degrade over a period of 7 days, and complete release of FITC-BSA is observed over a period of 6 days. Cytotoxicity evaluation of LTP microparticles indicates that these microparticles do not cause severe cell death in cultured primary human dermal fibroblasts over a period of 10 days. Therefore, the LTP microparticles are promising candidates for short-term protein delivery applications.     

Microparticle collection and concentration via a miniature surface acoustic wave device

The ability to detect microbes, pollens and other microparticles is a critically important ability given the increasing risk of bioterrorism and emergence of antibiotic-resistant bacteria. The efficient collection of microparticles via a liquid water droplet moved by a surface acoustic wave (SAW) device is demonstrated in this study. A fluidic track patterned on the SAW device directs the water droplet's motion, and fluid streaming induced inside the droplet as it moves along is a key advantage over other particle collection approaches, because it enhances microparticle collection and concentration. Test particles consisted of 2, 10, 12 and 45 microm diameter monodisperse polystyrene and melamine microparticles; pollen from the Populus deltoides, Kochia scoparia, Secale cerale, and Broussonetia papyrifera (Paper Mulberry) species; and Escherichia coli bacteria. The collection efficiency for the synthetic particles ranged from 16 to 55%, depending on the particle size and surface tension of the collection fluid. The method was more effective in collecting pollen and the bacteria with an efficiency of 45-68% and 61.0-69.8%, respectively. Pollen collection was strongly influenced by its diameter, size, and surface geometry in a manner contrary to initial expectations. Reasons for the consistent yet unexpected collection results include leaky SAW pressure boundary segregation and shear-induced concentration of larger particles, and the subtle effects of wetting interactions. These results demonstrate a new method for collecting microparticles requiring only about one second per run, and illustrate the inadequacy of using synthetic microparticles as a substitute for their biological counterparts in experiments studying particle collection and behavior.     

Dynamic Assembly of Microspheres under an Ultrasound Field

The assembly of micro‐nanoparticles is one of the key tasks for controlling and manipulating the structure of materials at micro/‐nanoscale. By carefully designing the ultrasound experiments and comparing the results with acoustic theories, we presented an in‐depth study of the ultrasound‐induced assembly behaviors of micro/‐nanoparticles (microparticle size?wavelength), especially their dynamic interactions between microparticles. The whole assembly processes including floating micro/nanoparticles, single particle communication, assembly to single particle interactions, and reorganization of assembly are fully studied. A rapid response of the ultrasound‐based assembly (0.5 min) shows distinct advantages compared to those of previously used methods such as light‐, electrical‐ and temperature‐based ones. Such an efficient and effective microparticle assembly holds great promise for fabrication of complex structure of materials.     

Identification of137Cs in an individual microparticle by laser desorption/ionization ion trap mass spectrometer

The detection of radiocesium in microparticles was performed by using an ion trap mass spectrometer coupled with laser desorption and ionization. Pulsed laser desorbed particle and the resulted ions were analyzed by an ion trap mass analyzer. The presence of radiocesium, especially about¹³⁷Cs, in microparticles was verified by single as well as successive particle analysis. The detection limit was reached to ≈ag/particle level with a signal-to-background ratio of 4. The inhomogeneous distribution of particle size and the irregular shapes of particle limit the quantitative evaluation of¹³⁷Cs concentration in the microparticle. But this high sensitivity allows to monitor directly the radiocesium from small amounts of a microparticle sample.     

Separation and quantification of imidazoles in atmospheric particles using LC–Orbitrap‐MS

A method using ultra‐high performance liquid chromatography coupled to a high resolution Orbitrap mass spectrometer was developed to identify and quantify imidazoles in aqueous extracts of aerosol particles. The aqueous particle extract was used without further enrichment or sample clean‐up. Five columns were tested for efficient separation of ten imidazoles and the Acquity HSS T3 column was chosen for further optimization. Low limits of detection (<25 nM) and good intraday and interday repeatability (<1.6 and <6%, respectively) were achieved. Investigation of matrix effects showed that external calibration is applicable when the loading of organic carbon in the sample is below 10 µg m^?3. The developed method was applied to ten real samples, and six out of the ten test imidazoles were successfully quantified, while six further imidazoles were qualitatively identified, among them 4‐imidazolecarboxaldehyde and 4‐methyl‐5‐imidazolecarboxaldehyde. Advantages of the method are the minimal sample preparation, the short run time for each sample, and the low detection limits. These allow for a fast and reliable quantification of imidazoles even in a large number of aqueous particle extract samples.     

Zeolitic imidazolate framework‐8 reinforced hollow‐fiber liquid‐phase microextraction of free urinary biomarkers of whole grain intake followed by CE analysis

The whole grain intake is closely associated with human health. In this work, three‐phase dynamic hollow‐fiber liquid‐phase microextraction reinforced with 0.10 mg/mL 30 nm zeolitic imidazolate framework‐8 nanoparticles was introduced for purification and enrichment of free urinary metabolite biomarkers of whole grain intake. Eight milliliters of HCl (pH 3.00) and 8 μL of 300 mM NaOH solutions were used as the donor and acceptor phases, respectively. The temperature and stirring rate were kept at 25℃ and 500 rpm, and the extraction time was 40 min. The extraction process required no further desorption, and the resultant extract was directly used for electrophoretic analysis without derivatization. Based on the synergistic effect of hollow‐fiber liquid‐phase microextraction and the electrophoretic stacking, the enrichment factors of 3,5‐dihydroxybenzoic acid and 3‐(3,5‐dihydroxyphenyl)‐1‐propionic acid reached 1018–1034 times, and their limits of detection achieved 0.33–0.67 ng/mL (S/N = 3) in urine matrix. The developed method has been successfully used for urine analysis, and the sample recovery data were in the range of 97.0–103.5%. This developed method provided an attractive alternative for the determination of urinary metabolite biomarkers of whole grain intake due to its sensitive, fast, low‐cost, and environmental‐friendly features.     

Ballpoint connector‐protected salt‐oil‐salt liquid phase microextraction for concentration and enrichment of trace anthraquinone compounds in rhubarb

This study proposed a new ballpoint connector‐protected salt‐oil‐salt liquid phase microextraction for extraction and enrichment of trace rhein and chrysophanol in rhubarb prior to determination of the analytes by high performance liquid chromatography. In this study, a handy ballpoint connector (between ballpoint tip and ink chamber) was used as extraction device, in which its cavity was filled with n‐octanol, and the bare n‐octanol in its two opening ends was covered with a thin layer of sodium chloride film. The design subtly assembled salt film onto ballpoint connector for extraction and enrichment, which greatly improved the enrichment factors of the target analytes. Moreover, the novel procedure and its extraction mechanism were described and analyzed, and several crucial parameters reflecting the extraction effect were investigated and optimized. Under optimum conditions, high enrichment factors (247 and 127), good linearities with r ≥ 0.9998, limits of detection (0.6–1.1 ng/mL), relative standard deviations of intra‐ and interday (2.2–8.8% and 4.3–8.9%), and average recoveries (97.6–98.1%), were obtained, respectively. The proposed method can not only eliminate the negative effects from viscosity and ion strength at high salt concentration of sample phase, but also make salting‐out effect be focused on small area so as to maximize the extraction effect.     

Study on the discrete dielectrophoresis for particle–cell separation

This paper presents the application of the discrete dielectrophoretic force to separate polystyrene particles from red blood cells. The separation process employs a simple microfluidic device that is composed of interdigitated electrodes and a microchannel. The discrete dielectrophoretic force is generated by adjusting the duty cycle of the applied voltage. The electrodes make a tilt angle with the microchannel to change the moving direction of the red blood cells. By adjusting the voltage magnitude and duty cycle, we investigate the deflection of red blood cells and the variation of cell velocity along electrode edge under positive dielectrophoresis. The experiments with polystyrene particles show that the enrichment of the particles is greater than 150 times. The maximum separation efficiency is 97% for particle-to-cell number ratio equal to 1:2000 in the sample having high cell concentration. Using the appropriate applied voltage magnitude and duty cycle, the discrete dielectrophoretic force can prevent the clogging of microchannel while successfully separating the particles from the cells with high enrichment and efficiency. The proposed principle can be readily applied to dielectrophoresis-based devices for biomedical sample preparation or diagnosis such as the separation of rare or infected cells from a blood sample.     

Composite microparticle drug delivery systems based on chitosan, alginate and pectin with improved pH-sensitive drug release property

Composite microparticle drug delivery systems based on chitosan, alginate and pectin with improved pH sensitivity were developed for oral delivery of protein drugs, using bovine serum albumin (BSA) as a model drug. The composite drug-loaded microparticles with a mean particle size less than 200 μm were prepared by a convenient shredding method. Since the microparticles were formed by tripolyphosphate cross-linking, electrostatic complexation by alginate and/or pectin, as well as ionotropic gelation with calcium ions, the microparticles exhibited an improved pH-sensitive drug release property. The in vitro drug release behaviors of the microparticles were studied in simulated gastric (pH 1.2 and pH 5.0), intestinal (pH 7.4) and colonic (pH 6.0 and pH 6.8 with enzyme) media. For the composite microparticles with suitable compositions, the releases of BSA at pH 1.2 and pH 5.0 could be effectively sustained, while the releases at pH 7.4, pH 6.8 and pH 6.0 increased significantly, especially in the presence of pectinase. These results clearly suggested that the microparticles had potential for site-specific protein drug delivery through oral administration.     

Salt‐assisted dispersive liquid–liquid microextraction for enhancing the concentration of matrine alkaloids in traditional Chinese medicine and its preparations

A fast, simple, and efficient salt‐assisted dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography was developed and introduced for the simultaneous enrichment, extraction, and determination of the trace levels of matrine alkaloids (sophoridine, matrine, and sophocarpine) in Sophorae Flavescentis Radix and Composite Kushen injection. Compared with conventional dispersive liquid–liquid microextraction, the proposed method, with added salt but without dispersant and centrifuging, makes the operation simpler, greener, and leads to a higher enrichment factor. The crucial parameters affecting the enrichment factors of target analytes, such as type and volume of extraction solvent, pH of sample phase, salt concentration, volume of sample phase, and extraction time, were investigated and optimized, meanwhile, the extraction mechanism of the method was analyzed and described. Under the optimized conditions, the enrichment factors of the three matrine alkaloids were 150, 178, and 227, respectively. Good linearities (r² ≥ 0.9992) for all analytes, low limits of detection (less than 0.08 ng/mL), satisfactory precisions (2.1–12.3%), and accuracies (recoveries, 99.3–103.9%) were achieved. The experimental results showed that the approach is a simple, fast, green, eco‐friendly, and sensitive method and can be used for the preconcentration and determination of matrine alkaloids in traditional Chinese medicines and their preparations.