Actively controlled self-assembly of colloidal crystals in microfluidic networks by electrocapillary forces

We report a simple approach to actively control the formation of the self-assembled colloidal crystals in the microfluidic networks using a combination of electrocapillary forces and evaporation-induced self-assembly. Using this scheme, we can not only selectively fabricate the colloidal crystals in the desired channels, but we can also build colloidal crystals with different optical properties in different channels or in the same channel.     

An osmotic micro-pump integrated on a microfluidic chip for perfusion cell culture

A novel microfluidic chip integrating an osmosis-based micro-pump was developed and used for perfusion cell culture. The micro-pump includes two sealed chambers, i.e., the inner osmotic reagent chamber and the outer water chamber, sandwiching a semi-permeable membrane. The water in the outer chamber was forced to flow through the membrane into the inner chamber via osmosis, facilitating continuous flow of fluidic zone in the channel. An average flow rate of 0.33 μL min⁻¹ was obtained within 50 h along with a precision of 4.3% RSD (n = 51) by using a 100 mg mL⁻¹ polyvinylpyrrolidone (PVP) solution as the osmotic driving reagent and a flow passage area of 0.98 cm² of the semi-permeable membrane. The power-free micro-pump has been demonstrated to be pulse-free offering stable flow rates during long-term operation. The present microfluidic chip has been successfully applied for the perfusion culture of human colorectal carcinoma cell by continuously refreshing the culture medium with the osmotic micro-pump. In addition, in situ cell immunostaining was also performed on the microchip by driving all the reagent zones with the integrated micro-pump.     

Algal fluorescence sensor integrated into a microfluidic chip for water pollutant detection

We report the first miniaturized fluorescent sensor based on algae, with an organic light emitting diode (OLED) and an organic photodetector (OPD) integrated into a microfluidic chip. The blue emission OLED was used as the excitation source, while a blend of PTB3/PC(61)BM was used for the fabrication of the organic photodetector. Excitation and emission color filters based on acid/base dyes and a metal complex were developed and assembled with the organic optoelectronic components in order to complete the fluorescent detection system. The detection system was then integrated in a microfluidic chip made from (poly)dimethylsiloxane (PDMS). The complete sensor is designed to detect algal fluorescence in the microfluidic chamber. Algal chlorophyll fluorescence enables evaluation of the toxicity of pollutants like herbicides and metals-ions from agricultural run-offs. The entirely organic bioassay here presented allowed detection of the toxic effects of the herbicide Diuron on Chlamydomonas reinhardtii green algae that gave 50% inhibition of the algae photochemistry (EC(50)) with a concentration as low as 11 nM.     

Measurement of density and chemical concentration using a microfluidic chip

A new microfluidic product for measuring fluid density, specific gravity and chemical concentration has been developed. At the core of this lab-on-a-chip sensor is a vacuum-sealed resonating silicon microtube. Measurements can be made with under a microliter of sample fluid, which is over 1000x less than is conventionally required. Since the product is MEMS-based the overall system size is a fraction of conventional density meters and it weighs much less than the traditional desk-top, temperature controlled, density meters. The syringe or pipette loaded system includes a dynamic temperature control system that operates between 0 degree C and 90 degree C with an accuracy of less than 0.01 degree C. Density measurement accuracies of 4 to 5 digits have been observed with aqueous solutions. Measurement examples and applications will be discussed.     

Rapid protein concentration, efficient fluorescence labeling and purification on a micro/nanofluidics chip

Fluorescence analysis has proved to be a powerful detection technique for achieving single molecule analysis. However, it usually requires the labeling of targets with bright fluorescent tags since most chemicals and biomolecules lack fluorescence. Conventional fluorescence labeling methods require a considerable quantity of biomolecule samples, long reaction times and extensive chromatographic purification procedures. Herein, a micro/nanofluidics device integrating a nanochannel in a microfluidics chip has been designed and fabricated, which achieves rapid protein concentration, fluorescence labeling, and efficient purification of product in a miniaturized and continuous manner. As a demonstration, labeling of the proteins bovine serum albumin (BSA) and IgG with fluorescein isothiocyanate (FITC) is presented. Compared to conventional methods, the present micro/nanofluidics device performs about 10(4)-10(6) times faster BSA labeling with 1.6 times higher yields due to the efficient nanoconfinement effect, improved mass, and heat transfer in the chip device. The results demonstrate that the present micro/nanofluidics device promises rapid and facile fluorescence labeling of small amount of reagents such as proteins, nucleic acids and other biomolecules with high efficiency.     

A smart surface in a microfluidic chip for controlled protein separation

The smart surface created in a microfluidic chip has shown the capability of adsorbing and releasing proteins under electrical control. The inner surface of the chip channel was first coated by a thin layer of Au through sputtering and was subsequently modified with loosely packed self-assembled monolayers (SAMs) of thiols with terminal carboxylic or amino groups. Upon application of an external electric potential to the gold substrate, reversible conformational transformation between "bent" and "straight" states for the anchored mercapto chains could be modulated, through the electrostatic effect between the ionized terminal groups and the charged gold substrate. Thus, a hydrophobic or hydrophilic channel surface was established and could be reversibly switched electrochemically. Accordingly, the microchips prepared in this way can reversibly and selectively adsorb and release differently charged proteins under electrical control. Two model proteins, avidin and streptavidin, were demonstrated to be readily adsorbed by the smart chips under negative and positive potential, respectively. Also, more than 90 % of the adsorbed proteins could be released upon an electrical command. Furthermore, these chips were applied to the controlled separation of avidin and streptavidin mixtures with 1:1 and 1:1000 molar ratios. Under specific applied potentials, the chips adsorbed a certain protein from the mixture whereas the other protein was allowed to flow out, after which the adsorbed protein could be released by switching the applied potential. Thus, two eluted protein fractions were obtained and the separation of the two proteins was achieved. For the former mixture, each eluted fraction contained up to approximately 80-90 % avidin or streptavidin. For the latter mixture, the resulting separation efficiency indicated that the molar ratio of avidin and streptavidin could be increased from 1:1000 to about 32:1 after five run separations.     

Formation and shear-induced processing of quantum dot colloidal assemblies in a multiphase microfluidic chip

The controlled self-assembly of polymer-stabilized quantum dots (QDs) into mesoscale aqueous spherical assemblies termed quantum dot compound micelles (QDCMs) using a two-phase gas-segmented microfluidic reactor is described. Self-assembly is initiated by the fast mixing of water (approximately 1 s) with a blend solution of polystyrene-coated QDs and amphiphilic polystyrene-block-poly(acrylic acid) stabilizing chains via chaotic advection within liquid plugs moving through a sinusoidal channel. Subsequent recirculating flow within a post-formation channel subjects the dynamic QDCMs to shear-induced processing, controlled via the flow rate and channel length, before a final quench into pure water. During processing, larger QDCMs within the initial population undergo breakup into smaller particles, resulting in smaller mean particle sizes, smaller relative standard deviations, and more skewed distribution shapes, as the overall shear exposure is increased. For these cases, shear-induced size reduction is sufficient to dominate surface tension-driven growth.     

Screening of protein crystallization conditions on a microfluidic chip using nanoliter-size droplets

Protein crystallization is a major bottleneck in determining tertiary protein structures from genomic sequence data. This paper describes a microfluidic system for screening hundreds of protein crystallization conditions using less than 4 nL of protein solution for each crystallization droplet. The droplets are formed by mixing protein, precipitant, and additive stock solutions in variable ratios in a flow of water-immiscible fluids inside microchannels. Each droplet represents a discrete trial testing different conditions. The system has been validated by crystallization of several water-soluble proteins.     

Enantioselective analysis of melagatran via an LSPR biosensor integrated with a microfluidic chip

The impact of chiral compounds on pharmacological and biological processes is well known. With the increasing need for enantiomerically pure compounds, effective strategies for enantioseparation and chiral discrimination are in great demand. Herein we report a simple but efficient approach for the enantioselective determination of chiral compounds based on a localized surface plasmon resonance (LSPR) biosensor integrated with a microfluidic chip. A glass microfluidic chip with an effective volume of ～0.75 μL was fabricated for this application. Gold nanorods (AuNRs) with an aspect ratio of ～2.6 were self-assembled onto the surface of the inner wall of the chip to serve as LSPR transducers, which would translate the analyte binding events into quantitative concentration information. Human α-thrombin was immobilized onto the AuNR surface for enantioselective sensing of the enantiomers of melagatran. The proposed sensor was found to be highly selective for RS-melagatran, while the binding of its enantiomer, SR-melagatran, to the sensor was inactive. Under optimal conditions, the limit of detection of this sensor for RS-melagatran was found to be 0.9 nM, whereas the presence of 10?000-fold amounts of SR-melagatran did not interfere with the detection. To the best of our knowledge, this is the first demonstration of an LSPR-based enantioselective biosensor.     

Two-dimensional ordered arrays of aligned lipid tubules on substrates with microfluidic networks

Microfluidic networks is a powerful tool for aligning one-dimensional materials over a large area on solid substrates. Here we show that lipid nano- and microtubules can be assembled into two-dimensional (2-D) parallel arrays with controlled separations by combining fluidic alignment with dewetting, which occurs within microchannels. We also demonstrate that lipid tubules can be bent into a well-defined shape at the entrance of the channels by the capillary force. Atomic force microscopy is used to study the structure and stability of the aligned lipid tubules on substrates. The deposition experiments with silica colloidal particles show that the 2-D parallel-aligned tubules can be used as a template to synthesize silica films with controlled morphologies and patterns on substrates in a single-step process.     

In situ photo-immobilised pH gradient isoelectric focusing and zone electrophoresis integrated two-dimensional microfluidic chip electrophoresis for protein separation

A method is introduced for open-column photo-induced site-selective immobilization of pH gradients in a layer of PEG-methacrylate in a multi-dimensional microfluidic chip for use in electrophoresis. It has several attractive features: (a) mixtures of fluorescently labelled proteins carbonic anhydrase, catalase and myoglobin in their native state can be separated by pH-gradient isoelectric focusing (IEF) and zone electrophoresis (CZE) using integrated 2D chip electrophoresis; (b) compared to strip packing or monolithic photo-immobilization, it overcomes the shortcomings of free carrier ampholyte-based 2D chip electrophoresis in an easy way; (c) larger amount of sample can be loaded into the open column-mode electrophoresis (d) immobilized pH gradients can be re-used and the chip can be recycled; (e) a multilayer 3D pH gradient is established by a layer-by-layer assembly technique to further increase the separation capacity. In our perception, this strategy has a large potential in microfluidic chip-based separation schemes because of its simplicity, separation power, re-usability, and separation capacity.

An open-column layer-by-layer photo-immobilised pH gradient was introduced into two-dimensional chip electrophoresis with simplicity, reusability, improved separation performance and separation capacity.

     

基于核酸适配体的微流控芯片酶反应器用于蛋白质的分析

将核酸适配体作为胰蛋白酶固定化介质,制备了一种新型的微流控芯片酶反应器,并与高效液相色谱-串联质谱联用,搭建了在线分析平台;分别使用标准蛋白及混合蛋白样品对芯片的酶解效率及联用平台的分析能力进行了初步评价。结果表明,5 ng肌红蛋白经该平台分析后肽段覆盖率可达到37%;对500 ng混合蛋白进行3次平行分析,肽段覆盖率及相对标准偏差分别为44.3%、6.5%(牛血清白蛋白), 65.0%、2.7%(肌红蛋白)和62.0%、5.6%(细胞色素c);初步实验表明,该在线分析平台具有检测灵敏度高、重现性好、酶解效率高的特点,有望在蛋白质组学分析中发挥重要作用。     

Controlled proteolysis of normal and pathological prion protein in a microfluidic chip

A microreactor for proteinase K (PK)-mediated protein digestion was developed as a step towards the elaboration of a fully integrated microdevice for the detection of pathological prion protein (PrP). PK-grafted magnetic beads were immobilized inside a polydimethylsiloxane (PDMS) microchannel using a longitudinal magnetic field parallel to the flow direction and a magnetic field gradient, thereby forming a matrix for enzymatic digestion. This self-organization provided uniform pore sizes, a low flow resistance and a strong reaction efficiency due to a very thin diffusion layer. The microreactor's performance was first evaluated using a model substrate, succinyl-ala-ala-ala-paranitroanilide (SAAAP). Reaction kinetics were typically accelerated a hundred-fold as compared to conventional batch reactions. Reproducibility was around 98% for on-chip experiments. This microsystem was then applied to the digestion of prion protein from brain tissues. Controlled proteolysis could be obtained by varying the on-chip flow rate, while a complete proteolysis of normal protein was achieved in only three minutes. Extracts from normal and pathological brain homogenates were finally compared and strong discrimination between normal and pathological samples was demonstrated.     

Electrophoresis on a microfluidic chip for analysis of fluorescence-labeled human rhinovirus

We report the analysis of human rhinovirus serotype 2 (HRV2) on a commercially available lab-on-a-chip instrument. Due to lack of sufficient native fluorescence, the proteinaceous capsid of HRV2 was labeled with Cy5 for detection by the red laser (lambda ex 630 nm) implemented in the instrument. On the microdevice, electrophoresis of the labeled virus was possible in a BGE without stabilizing detergents, which is in contrast to conventional CE; moreover, analysis times were drastically shortened to the few 10 s range. Resolution of the sample constituents (virions, a contaminant present in all virus preparations, and excess dye) was improved upon adaptation of the separation conditions, mainly by adjusting the SDS concentration of the BGE. Purity of fractions from size-exclusion chromatography after labeling of virus was assessed, and affinity complex formation of the labeled virus with various recombinant very-low-density lipoprotein receptor derivatives differing in the number of concatenated V3 ligand binding repeats was monitored. Virus analysis on microchip devices is of particular interest for experiments with infectious material because of easy containment and disposal of samples. Thus, the employment of microchip devices in routine analysis of viruses appears to be exceptionally attractive.     

A novel and highly efficient method for the silylation of alcohols with hexamethyldisilazane (HMDS) catalyzed by recyclable sulfonic acid-functionalized ordered nanoporous silica

Silylation of alcohols with hexamethyldisilazane (HMDS) in dichloromethane provides the corresponding silyl ethers in almost quantitative yields at room temperature using 1-3 mol % of sulfonic acid-functionalized silica. Additionally, the catalyst displays a high activity and thermal stability (up to 240 °C) and it can be easily recovered and reused for at least 20 reaction cycles without loss of reactivity.     

Simultaneous sample washing and concentration using a "trapping-and-releasing" mechanism of magnetic beads on a microfluidic chip

Simultaneous washing and concentration of functionalized magnetic beads in a complex sample solution were demonstrated by applying a rotational magnetic actuation system to a microfluidic chip under continuous flow conditions. The rotation of periodically arranged small permanent magnets close to the fluidic channel carrying a magnetic bead suspension allows trapping and releasing of the beads along the fluidic channel in a periodical manner. Each trapping and releasing event resembles one washing cycle. A purification efficiency of magnetic beads out of a mixed magnetic and non-magnetic bead sample solution of 83±4% at a flow rate of 0.5 μL min(-1), and a magnetic bead recovery or concentration efficiency of 91±5% were achieved using a flow rate of 0.2 μL min(-1). The detection performance of the device was experimentally evaluated with two different bioassays, using either streptavidin-coated magnetic beads in combination with biotinylated fluorescent isothiocyanate (FITC), or a mouse antigen (Ag)-antibody (Ab) system.     

New amphiphilic terphenyl liquid crystals for the preparation of highly ordered ultrathin films

Four new amphiphilic liquid crystals have been synthesized, in which terphenyl was used as the mesogenic unit. In order to enable the formation of Langmuir Monolayers at the air/water-interface, the molecules were equipped with slightly polar headgroups such as esters or a carboxylic acid group. All compounds can be transferred onto solid substrates. In addition, it is possible to prepare freely suspended films of at least one compound in the temperature range of the smectic phases. The phases of the different states, bulk, monolayer, freely suspended film, and Langmuir-Blodgett multilayers have been investigated by means of monolayer isotherms, optical textures, differential scanning calorimetry (DSC) and small angle X-ray scattering.     

Generation of concentration gradient by controlled flow distribution and diffusive mixing in a microfluidic chip

We have developed a simple method to generate a concentration gradient in a microfluidic device. This method is based on the combination of controlled fluid distribution at each intersection of a microfluidic network by liquid pressure and subsequent diffusion between laminas in the downstream microchannel. A fluid dynamic model taking into account the diffusion coefficient was established to simulate the on-chip flow distribution and diffusion. Concentration gradients along a distance of a few hundred micrometers were generated in a series of microchannels. The gradients could be varied by carefully regulating the liquid pressure applied to the sample injection vials. The observed concentration gradients of fluorescent dyes generated on the microfluidic channel are consistent with the theoretically predicted results. The microfluidic design described in this study may provide a new tool for applications based on concentration gradients, including many biological and chemical analyses such as cellular reaction monitoring and drug screening.     

Two-dimensional electrophoresis on a microfluidic chip for quantitative amino acid analysis

Analysis of complex biological samples requires the use of high-throughput analytical tools. In this work, a microfluidic two-dimensional electrophoresis system was developed with mercury-lamp-induced fluorescence detection. Mixtures of 20 standard amino acids were used to evaluate the separation performance of the system. After fluorescent labeling with fluorescein isothiocyanate, mixtures of amino acids were separated by micellar electrokinetic chromatography in the first dimension and by capillary zone electrophoresis in the second. A double electrokinetic valve system was employed for the sample injection and the switching between separation channels. Under the optimized conditions, 20 standard amino acids were effectively separated within 20 min with high resolution and repeatability. Quantitative analysis revealed linear dynamic ranges of over three orders of magnitudes with detection limits at micromolar range. To further evaluate the reliability of the system, quantitative analysis of a commercial nutrition supplement liquid was successfully demonstrated. Figure