Sheathless elasto-inertial particle focusing and continuous separation in a straight rectangular microchannel

Particle focusing in planar geometries is essentially required in order to develop cost-effective lab-on-a-chips, such as cell counting and point-of-care (POC) devices. In this study, a novel method for sheathless particle focusing, called "Elasto-Inertial Particle Focusing", was demonstrated in a straight microchannel. The particles were notably aligned along the centerline of the straight channel under a pressure-driven flow without any additional external force or apparatus after the addition of an elasticity enhancer: PEO (poly(ethylene oxide)) (～O(100) ppm). As theoretically predicted (elasticity number: El≈O(100)), multiple equilibrium positions (centerline and corners) were observed for the viscoelastic flow without inertia, whereas three-dimensional particle focusing only occurred when neither the elasticity nor the inertia was negligible. Therefore, the three-dimensional particle focusing mechanism was attributed to the synergetic combination of the elasticity and the inertia (elasticity number: El≈O(1-10)). Furthermore, from the size dependence of the elastic force upon particles, we demonstrated that a mixture of 5.9 and 2.4 μm particles was separated at the exit of the channel in viscoelastic flows. We expect that this method can contribute to develop the miniaturized flow cytometry and microdevices for cell and particle manipulation.     

Investigation of viscoelastic focusing of particles and cells in a zigzag microchannel

Microfluidic particle focusing has been a vital prerequisite step in sample preparation for downstream particle separation, counting, detection, or analysis, and has attracted broad applications in biomedical and chemical areas. Besides all the active and passive focusing methods in Newtonian fluids, particle focusing in viscoelastic fluids has been attracting increasing interest because of its advantages induced by intrinsic fluid property. However, to achieve a well-defined focusing position, there is a need to extend channel lengths when focusing micrometer-sized or sub-microsized particles, which would result in the size increase of the microfluidic devices. This work investigated the sheathless viscoelastic focusing of particles and cells in a zigzag microfluidic channel. Benefit from the zigzag structure of the channel, the channel length and the footprint of the device can be reduced without sacrificing the focusing performance. In this work, the viscoelastic focusing, including the focusing of 10 μm polystyrene particles, 5 μm polystyrene particles, 5 μm magnetic particles, white blood cells (WBCs), red blood cells (RBCs), and cancer cells, were all demonstrated. Moreover, magnetophoretic separation of magnetic and nonmagnetic particles after viscoelastic pre-focusing was shown. This focusing technique has the potential to be used in a range of biomedical applications.     

Determination of key flavonoid aglycones by means of nano‐LC for the analysis of dietary supplements and food matrices

A method for the analysis of flavonoids (myricetin, quercetin, naringenin, hesperitin, and kaempferol), with interesting bioactivity, has been developed and validated utilizing nano‐LC technique. In order to find optimal conditions, capillary columns (75 μm id × 10 cm) packed with different types of stationary phases, Kinetex® C18 core–shell (2.6 μm particle size), Hydride‐based RP‐C18 (sub‐2 μm particle size), and LiChrospher® 100 RP‐18 endcapped (5 μm particle size) were evaluated. The method was validated using Hydride‐based RP‐C18 stationary phase, with sub‐2 μm particle size. A good chromatographic performance, expressed in terms of repeatability (RSD, in the range 1.63–4.68% for peak area), column‐to‐column reproducibility (RSD not higher than 8.01% for peak area), good linearity and sensitivity was obtained. In particular limit of detection values between 0.07 and 0.31 μg/mL were achieved with on column focusing technique. The method was applied to the determination of studied flavonoids in dietary supplements as well as in food matrices. The amount of quercetin found in the first analyzed dietary supplement, was in agreement to the labeled content. In the other samples, where the content of flavonoids was not labeled, most of the studied flavonoids were determined in amounts somewhere comparable to those reported in literature.     

Impedance‐based viscoelastic flow cytometry

Elastic nature of the viscoelastic fluids induces lateral migration of particles into a single streamline and can be used by microfluidic based flow cytometry devices. In this study, we investigated focusing efficiency of polyethylene oxide based viscoelastic solutions at varying ionic concentration to demonstrate their use in impedimetric particle characterization systems. Rheological properties of the viscoelastic fluid and particle focusing performance are not affected by ionic concentration. We investigated the viscoelastic focusing dynamics using polystyrene (PS) beads and human red blood cells (RBCs) suspended in the viscoelastic fluid. Elasto‐inertial focusing of PS beads was achieved with the combination of inertial and viscoelastic effects. RBCs were aligned along the channel centerline in parachute shape which yielded consistent impedimetric signals. We compared our impedance‐based microfluidic flow cytometry results for RBCs and PS beads by analyzing particle transit time and peak amplitude at varying viscoelastic focusing conditions obtained at different flow rates. We showed that single orientation, single train focusing of nonspherical RBCs can be achieved with polyethylene oxide based viscoelastic solution that has been shown to be a good candidate as a carrier fluid for impedance cytometry.     

Investigation of Harmattan particulates from Kano and Ife,Nigeria

The size distribution, elemental composition, shape and surface texture of harmattan particulates of distinctly located points have been examined. The characterized particle size ranges are 0.7–16.4 μm and 0.6–19.7 μm for Kano and Ife, respectively. A total of 12 elements (Al, Si, P, S, Cl, K, Ca, Mn, Ti, Fe, Cu, and Zn) were detected with varying degrees of concentration. The plotted element concentration curves favored micron and submicron particle diameters. The particle shapes exhibit high/low sphericity. The plotted size distribution curves exhibited a marked downward shift in particle diameter from Kano to Ife.     

Ultra high-performance liquid chromatography of porphyrins in clinical materials: column and mobile phase selection and optimisation

Ultra high-performance liquid chromatographic (UHPLC) systems on columns packed with materials ranging from 1.9 to 2.7 μm average particle size were assessed for the fast and sensitive analysis of porphyrins in clinical materials. The fastest separation was achieved on an Agilent Poroshell C(18) column (2.7 μm particle size, 50 × 4.6 mm i.d.), followed by a Thermo Hypersil Gold C(18) column (1.9 μm particle size, 50 × 2.1 mm i.d.) and the Thermo Hypersil BDS C(18) column (2.4 μm particle size, 100 × 2.1 mm i.d.). All columns required a mobile phase containing 1 m ammonium acetate buffer, pH 5.16, with a mixture of acetonitrile and methanol as the organic modifiers for optimum resolution of the type I and III isomers, particularly for uroporphyrin I and III isomers. All UHPLC columns were suitable and superior to conventional HPLC columns packed with 5 μm average particle size materials for clinical sample analysis.     

可用于色谱固定相的介孔氧化硅球材料的合成

采用非离子型嵌段高分子表面活性剂EO₂₀PO₃₀EO₂₀ (P65)为结构导向剂, 正硅酸乙酯为硅源, 在酸性介质中, 静置法制备了微米级介孔氧化硅球. 通过改变合成温度、反应时间或者无机盐KCl的加入量, 可以调节介孔氧化硅球的直径(9.0～17.6 μm); 加入1,3,5-三甲苯(TMB)或者调节水热温度, 可以调节介孔氧化硅球的孔径(2.3～4.8 nm). 采用X射线衍射(XRD)、N₂吸附-脱附、扫描电镜(SEM)、激光散射粒度分布和对溶菌酶的吸附等方法, 对介孔氧化硅球的结构、孔性质、形貌、吸附性质等进行了表征. 实验发现, 孔径较小的介孔氧化硅球(≤4.3 nm)对溶菌酶的吸附不明显(≤42 mg/g), 而孔径(4.8 nm)大于溶菌酶直径的材料对溶菌酶有较大的吸附量(192 mg/g), 说明孔径均匀可调的介孔氧化硅球材料可以很好地用作体积排阻色谱柱的固定相.     

Sub-1-micron mesoporous silica particles functionalized with cyclodextrin derivative for rapid enantioseparations on ultra-high pressure liquid chromatography

Mesoporous silica particles of relatively uniform sub-1-micron size (0.6-0.9 μm) were successfully prepared by a modified synthesis strategy and applied in chiral separation in an ultra-high pressure liquid chromatography system. These particles were prepared via a ternary surfactant system (Pluronic P123, F127 and hexadecyltrimethyl-ammonium bromide) and subsequently derivatized with perphenylcarbamoylated-β-cyclodextrin moieties. The mesoporous silica particles, despite their submicron size, enabled low back-pressure operation on an ultra-high pressure liquid chromatography system at a maximum flow rate of 2 ml/min. In addition, the particles possessed high surface area (480 m(2)/g) and thus afforded high cyclodextrin derivative loading (32 μmol/g), demonstrating rapid enantioseparation and good resolution of 6 basic and neutral racemates.     

HPLC of basic drugs using non‐aqueous ionic eluents: evaluation of a 3 μm strong cation‐exchange material

HPLC columns packed with 3 μm particle size HPLC Technology Techsphere SCX (propylsulfonic acid‐modified) silica offer considerable advantages over 5 μm SCX packings in the analysis of basic drugs using 100% methanol eluents containing an ionic modifier such as ammonium perchlorate. The basic drugs studied included clozapine and norclozapine, olanzapine, quinine and quinidine, and amitriptyline, nortriptyline, imipramine and desipramine. The 3 μm column was not only more efficient for a given column length compared with 5 μm materials, but also elution times were less, a phenomenon observed in reversed‐phase systems. The high efficiencies and excellent peak shapes obtained with the 3 μm SCX‐modified packing together with the relatively low back‐pressures attained show that such materials deserve serious consideration by laboratories involved in the analysis of basic drugs. Manufacturers should offer such packings as a matter of routine. Alternative ionic modifiers such as ammonium acetate are available for use with mass spectrometric detection if required. Copyright © 2009 John Wiley & Sons, Ltd.     

Improvement of size-based particle separation throughput in slanted spiral microchannel by modifying outlet geometry

The inertial microfluidic technique, as a powerful new tool for accurate cell/particle separation based on the hydrodynamic phenomenon, has drawn considerable interest in recent years. Despite numerous microfluidic techniques of particle separation, there are few articles in the literature on separation techniques addressing external outlet geometry to increase the throughput efficiency and purity. In this work, we report on a spiral inertial microfluidic device with high efficiency (>98%). Herein, we demonstrate how changing the outlet geometry can improve the particle separation throughput. We present a complete separation of 4 and 6 μm from 10 μm particles potentially applicable to separate microalgae (Tetraselmis suecica from Phaeodactylum tricornutum). Two spiral microchannels with the same cross section dimension but different outlet geometry were considered and tested to investigate the particle focusing behavior and separation efficiency. As compared with particle focusing observed in channels with a simple outlet, the particle focusing in a modified outlet geometry appears in a more successful focusing manner with complete separation. This simple approach of particle separation makes it attractive for lab-on-a-chip devices for continuous extraction and filtration of a wide range of cell/particle sizes.     

Monodispersed submicron porous silica particles functionalized with CD derivatives for chiral CEC

Rapid and efficient enantioseparation of halogen aryl alcohols and β‐blockers propranolol and pindolol in packed bed CEC (p‐CEC) using as‐prepared submicron porous silica chiral stationary phases (CSPs) has been achieved. Monodispersed 0.66 and 0.81 μm chiral submicron porous silica spheres were prepared using tetramethoxysilane and hexadecyltrimethylammonium bromide, followed by a hydrothermal treatment method with ammonia–ethanol to expand the pore of silica spheres without changing their spherical morphology. A proper specific surface of ca. 230 m²/g and pore sizes average of 6–8 nm were obtained by this method. The submicron porous silica spheres were modified with mono‐6‐phenylcarbamoylated β‐CD via thiol‐en radical addition. They were packed into 9 cm 50 μm id capillary columns with photopolymerized monolithic frits. These submicron CSPs showed greater column efficiency (about 476 000 plates/m for 4‐iodophenyl‐1‐ethanol) and higher resolution than the corresponding 3 μm CSP.     

Synthesis and characterization of pore size-tunable magnetic mesoporous silica nanoparticles

Magnetic mesoporous silica nanoparticles (M-MSNs) are emerging as one of the most appealing candidates for theranostic carriers. Herein, a simple synthesis method of M-MSNs with a single Fe(3)O(4) nanocrystal core and a mesoporous shell with radially aligned pores was elaborated using tetraethyl orthosilicate (TEOS) as silica source, cationic surfactant CTAB as template, and 1,3,5-triisopropylbenzene (TMB)/decane as pore swelling agents. Due to the special localization of TMB during the synthesis process, the pore size was increased with added TMB amount within a limited range, while further employment of TMB lead to severe particle coalescence and not well-developed pore structure. On the other hand, when a proper amount of decane was jointly incorporated with limited amounts of TMB, effective pore expansion of M-MSNs similar to that of analogous mesoporous silica nanoparticles was realized. The resultant M-MSN materials possessed smaller particle size (about 40-70 nm in diameter), tunable pore sizes (3.8-6.1 nm), high surface areas (700-1100 m(2)/g), and large pore volumes (0.44-1.54 cm(3)/g). We also demonstrate their high potential in conventional DNA loading. Maximum loading capacity of salmon sperm DNA (375 mg/g) was obtained by the use of the M-MSN sample with the largest pore size of 6.1 nm.     

Binary self-assembly of highly symmetric DNA nanocages via sticky-end engineering

Discrete and symmetric three-dimensional(3D)DNA nanocages have been revoked as excellent candidates for various applications,such as guest component encapsulation and organization(e.g.dye molecules,proteins,inorganic nanoparticles,etc.)to construct new materials and devices.To date,a large variety of DNA nanocages has been synthesized through assembling small individual DNA motifs into predesigned structures in a bottom-up fashion.Most of them rely on the assembly using multiple copies of single type of motifs and a few sophisticated nanostructures have been engineered by co-assembling multi-types of DNA tiles simultaneously.However,the availability of complex DNA nanocages is still limited.Herein,we demonstrate that highly symmetric DNA nanocages consisted of binary DNA point-star motifs can be easily assembled by deliberately engineering the sticky-end interaction between the component building blocks.As such,DNA nanocages with new geometries,including elongated tetrahedron(E-TET),rhombic dodecahedron(R-DOD),and rhombic triacontahedron(R-TRI)are successfully synthesized.Moreover,their design principle,assembly process,and structural features are revealed by polyacryalmide gel electrophoresis(PAGE),atomic force microscope(AFM)imaging,and cryogenic transmission electron microscope imaging(cryo-TEM)associated with single particle reconstruction.     

Negative dielectrophoresis-based particle separation by size in a serpentine microchannel

Dielectrophoresis has been widely used to focus, trap, concentrate, and sort particles in microfluidic devices. This work demonstrates a continuous separation of particles by size in a serpentine microchannel using negative dielectrophoresis. Depending on the magnitude of the turn-induced dielectrophoretic force, particles travelling electrokinetically through a serpentine channel either migrate toward the centerline or bounce between the two sidewalls. These distinctive focusing and bouncing phenomena are utilized to implement a dielectrophoretic separation of 1 and 3 μm polystyrene particles under a DC-biased AC electric field of 880 V/cm on average. The particle separation process in the entire microchannel is simulated by a numerical model.     

Three-dimensional focusing of particles using negative dielectrophoretic force in a microfluidic chip with insulating microstructures and dual planar microelectrodes

The focusing of biological and synthetic particles in microfluidic devices is a prerequisite for the construction of microstructured materials, as well as for medical applications. In the present study, a microdevice that can effectively focus particles in three dimensions using a combination of insulator-based and metal-electrode dielectrophoresis (DEP) has been designed and fabricated. The DEP force is employed to confine the particles using a negative DEP response. Four insulating microstructures, which form an X-pattern in the microchannel, were employed to distort the electric field between the insulators in a conducting solution, thereby generating regions with a high electric-field gradient. Two strips of microelectrodes on the top and bottom surfaces were placed in the middle of the microchannel and connected to an electric pole. Two sets of dual-planar electrodes connected to the opposite pole were placed at the sides of the microchannel at the top and bottom surfaces. The results of a transient simulation of tracks of polystyrene particles, which was performed using the commercial software package CFD-ACE? (ESI Group, France), demonstrate that the three-dimensional focusing of particles was achieved when the applied voltage was larger than 35?V at a frequency of 1 MHz. Furthermore, the focusing performance increased with the increased strength of the applied electric field and decreased inlet flow rate. Experiments on particle focusing, employing polystyrene particles 10 μm in diameter, were conducted to demonstrate the feasibility of the proposed design; the results agree with the trend predicted by numerical simulations.     

DNA diffusion in aqueous solution in presence of suspended particles

Although nanoparticles, which are comparable in size to polymer chains, are widely used as fillers to polymer matrices for developing functional and high performance materials, the dynamics of polymers constrained between solid particles has not been well elucidated. In this study, dynamics of individual polymer under such condition was investigated with fluorescent microscopy using DNA solutions as model systems. For individual T4 and λ DNA molecules in aqueous suspensions of spherical polystyrene particles with diameter of 1 μm, it was found that (i) the radius of gyration of DNA is independent of the particle volume fraction, ?_p, (ii) DNA diffusion is not sensitive to ?_p up to a certain critical ?_p where the average distance between particle surfaces is close to DNA size, and (iii) the DNA diffusion becomes slower at higher ?_p. The diffusion coefficient of DNA was larger, by a factor of 2, in the suspensions at intermediate ?_p than in the corresponding confined geometry (channel/slit between fixed walls), whereas this difference asymptotically vanished with increasing ?_p. This result suggested that the DNA diffusion in the suspensions with intermediate ?_p is accelerated by the particle motion. In fact, the diffusion coefficient measured for DNA in the suspensions was semiquantitatively described by the Rouse constraint‐release model considering the matrix effect on the probe chain diffusion. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1103–1111, 2009     

Comparison of core-shell versus fully porous particle packings for chiral liquid chromatography productivity

A loading and productivity study was done using three racemates on vancomycin and teicoplanin-bonded chiral stationary phases of different particle formats. Two columns were packed with 2.7 μm superficially porous particles and two columns were packed with identically bonded 5 μm fully porous particles. The last two columns were packed with specially synthesized 4.5 μm vancomycin and teicoplanin superficially porous particles. The loading of different chiral compounds showed that the columns filled with 2.7-μm chiral stationary phases were inappropriate for preparative separations due to their very low permeability which precluded high flow rates. However, columns containing 4.5 μm superficially porous (core-shell) particles were as effective for small-scale preparative chiral separations as columns filled with classical 5 μm fully porous particles. Comparing the 4.5 μm superficially porous particles and 5 μm fully porous particles teicoplanin columns, the observed respective productivities of 270 and 265 mg/g chiral phase/h for 5-methyl-5-phenyl hydantoin enantiomers were obtained. Particular attention was given to the peculiar case of the mianserin enantiomeric separation on vancomycin columns that gave observed productivities of 200 and 205 mg/g chiral phase/h on the 4.5 μm superficially porous particles and 5 μm fully porous particles, respectively.     

Free surface electrospinning of fibers containing microparticles

Many materials have been fabricated using electrospinning, including pharmaceutical formulations, superhydrophobic surfaces, catalysis supports, filters, and tissue engineering scaffolds. Often these materials can benefit from microparticles included within the electrospun fibers. In this work, we evaluate a high-throughput free surface electrospinning technique to prepare fibers containing microparticles. We investigate the spinnability of polyvinylpyrrolidone (PVP) solutions containing suspended polystyrene (PS) beads of 1, 3, 5, and 10 μm diameter in order to better understand free surface electrospinning of particle suspensions. PS bead suspensions with both 55 kDa PVP and 1.3 MDa PVP were spinnable at 1:10, 1:5, and 1:2 PS:PVP mass loadings for all particle sizes studied. The final average fiber diameters ranged from 0.47 to 1.2 μm and were independent of the particle size and particle loading, indicating that the fiber diameter can be smaller than the particles entrained and can furthermore be adjusted based on solution properties and electrospinning parameters, as is the case for electrospinning of solutions without particles.     

Influence of parent graphite particle size on the electrochemistry of thermally reduced graphene oxide

Electrochemical applications of graphene are of very high importance. For electrochemistry, bulk quantities of materials are needed. The most common preparation of bulk quantities of graphene materials is based on oxidation of graphite to graphite oxide and subsequent thermal exfoliation of graphite oxide to thermally reduced graphene oxide (TR-GO). It is important to investigate to which extent a reaction condition, that is, composition of the oxidation mixture and size of graphite materials, influences the properties of the resulting materials. We characterised six graphite materials with a range of particle sizes (0.05, 11, 20, 32, 35 and 41 μm) and the TR-GO products prepared from them by use of scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Cyclic voltammetric performance of the TR-GO samples was compared using ferro/ferricyanide and ascorbic acid. We observed no correlation between size of initial graphite and properties of the resultant TR-GO such as density of surface defects, amount of oxygen-containing groups, or rate of heterogeneous electron transfer (HET). A positive correspondence between HET rate and high defect density as well as low amounts of oxygen functionalities was noted. Our findings will have profound influence upon practical fabrication of graphene for applications in sensing and energy storage devices.     

Viscoelastic particle focusing in human biofluids

Saliva and blood plasma are non-Newtonian viscoelastic fluids that play essential roles in the transport of particulate matters (e.g., food and blood cells). However, whether the viscoelasticity of such biofluids alters the dynamics of suspended particles is still unknown. In this study, we report that under pressure-driven microflows of both human saliva and blood plasma, spherical particles laterally migrate and form a focused stream along the channel centerline by their viscoelastic properties. We observed that the particle focusing varied among samples on the basis of sampling times/donors, thereby demonstrating that the viscoelasticity of the human biofluids can be affected by their compositions. We showed that the particle focusing, observed in bovine submaxillary mucin solutions, intensified with the increase in mucin concentration. We expect that the findings from this study will contribute to the understanding of the physiological roles of viscoelasticity of human biofluids.