Nl Min Research Articles

Open nanofluidic films with rapid transport and no analyte exchange for ultra-low sample volumes.

Moving to ultra-low (<100 nL) sample volumes presents numerous challenges, many of which can be resolved by implementation of open nanofluidic films. These nanofluidic films are fabricated using a hexagonal network of gold-coated open microchannels which capture all of the following innovative advantages: (1) sample volumes of <100 nL cm-2; (2) zero analyte exchange and loss with the film materials; (3) rapid and omni-directional wicking transport of >500 nL min-1 per square of film; (4) ultra-simple roll-to-roll fabrication; (5) stable and bio-compatible super-hydrophilicity for weeks in air by peptide surface modification. Validation includes both detailed in vitro characterization and in vivo validation with sweat transport from the human skin. Sampling times (skin-to-sensor) of <3 min were achieved, setting new benchmarks for the field of wearable sweat sensing. This work addresses significant challenges for sweat biosensing, or for any other nano-liter regime (<100 nL) fluid sampling and sensing application.

Direct Infusion Resonance-Enhanced Multiphoton Ionization Mass Spectrometry of Liquid Samples under Vacuum Conditions.

Direct infusion resonance-enhanced multiphoton ionization (DI-REMPI) was performed on liquid samples, which were introduced to the ion source via a direct liquid interface, to enable the investigation of dissolved aromatic compounds. Desolvation and nebulization of the samples were supported by a heated repeller using flow rates in the upper nL min-1 range. The obtained mass spectra of five pure polycyclic aromatic hydrocarbons as well as complex petroleum samples revealed predominantly molecular ions without evidence of solvent or dopant effects as observed in atmospheric pressure photoionization (APPI) and laser ionization (APLI) with limits of detection in the lower pmol range. Furthermore, it is demonstrated by the analysis of different complex oil samples that DI-REMPI covers a larger m/z range than external volatilization of the sample prior to introduction to the ion source by using thermogravimetry (TG) hyphenated to REMPI time-of-flight mass spectrometry (TOFMS). Analogous to reported setups with direct liquid interface and electron ionization, direct-REMPI may be an option for soft ionization in liquid chromatography.

Hybrid polymer composite membrane for an electromagnetic (EM) valveless micropump

In this paper, we report on a hybrid membrane used as an actuator in an electromagnetically driven valveless micropump developed using MEMS processes. The membrane structure consists of the combination of a magnetic polymer composite membrane and an attached bulk permanent magnet which is expected to have a compact structure and a strong magnetic force with maintained membrane flexibility. A soft polymeric material made of polydimethylsiloxane (PDMS) is initially mixed with neodymium magnetic particles (NdFeB) to form a magnetic polymer composite membrane. The membrane is then bonded with the PDMS based microfluidic part, developed using soft lithography process. The developed micropump was tested in terms of the actuator membrane deflection capability and the fluidic flow of the injected fluid sample through the microfluidic channel. The experimental results show that the magnetic composite actuator membrane with an attached bulk permanent magnet is capable of producing a maximum membrane deflection of up to 106 µm. The functionality test of the electromagnetic (EM) actuator for fluid pumping purposes was done by supplying an AC voltage with various amplitudes, signal waves and frequencies. A wide range of sample injection rates from a few µl min−1 to tens of nl min−1 was achieved with a maximum flow rate of 6.6 µl min−1. The injection flow rate of the EM micropump can be controlled by adjusting the voltage amplitude and frequency supplied to the EM coil, to control the membrane deflection in the pump chamber. The designed valveless EM micropump has a very high potential to enhance the drug delivery system capability in biomedical applications.

Hydrodynamic effects created by argon stirring liquid steel in a one-strand tundish

ABSTRACTContinuous casting of steel ensures the flexible production of different grades of slabs intended for the Rolling Mill departments. Therefore, it seems justifiable to search new solutions for tundish metallurgy. This study puts forward a new gas-permeable barrier’s design solution with two circular porous plugs, whose purpose is to punctually agitate the liquid steel in tundish. Two argon injection system locations were tested. The results for the hydrodynamic pattern of liquid steel and bubbles’ behaviour in the tundish were obtained from laboratory experiments with water glass model and computer simulations. Within the framework of the investigation, three argon flow rates, i.e. 5, 10 and 15 NL min−1, were considered. The designed gas-permeable barriers effectively stimulate active flow in the tundish for isothermal and non-isothermal conditions, while reducing the stagnant flow share and the transient zone extent.

Water-head pumps provide precise and fast microfluidic pumping and switching versus syringe pumps

We compare the performance of a water-head pump (WHP) system with that of a syringe pump (SP) system with respect to fluctuation, tunability, and transient response of flow rate. Despite its simplicity, the WHP system has not been as widely adopted as a means of microfluidic control as the SP system, partly because the transient and steady-state flow rates of a WHP in a microfluidic system have not been characterized in detail. We show that the flow-rate fluctuation of the WHP system is at least one order of magnitude smaller than that of the SP system, and that the two systems have similar flow-rate tunability on the order of 1 nL min−1 to 1 mL min−1. In addition, the pressure rise time of the WHP system is at least one order of magnitude faster than that of the SP system. As model experiments, we applied the WHP system to hydrodynamic focusing with a stable focused stream and to fast fluidic switching. The WHP system could be broadly useful versus the SP system and could enable precise, stable, and fast flow-rate control with minimal experimental setup.

Arraying single microbeads in microchannels using dielectrophoresis-assisted mechanical traps

Manipulating and immobilizing single microbeads in flowing fluids is relevant for biological assays and chemical tests but typically requires expensive laboratory equipment and trapping mechanisms that are not reversible. In this paper, we present a highly efficient and reversible mechanism for trapping microbeads by combining dielectrophoresis (DEP) with mechanical traps. The integration of planar electrodes and mechanical traps in a microchannel enables versatile manipulation of microbeads via DEP for their docking in recessed structures of mechanical traps. By simulating the combined effects of the hydrodynamic drag and DEP forces on microbeads, we explore a configuration of periodic traps where the beads are guided by the electrodes and immobilized in recess areas of the traps. The design of the electrode layout and operating configuration are optimized for the efficient trapping of single microbeads. We demonstrated the predicted guiding and trapping effectiveness of the design as well as the reversibility of the system on 10 μm polystyrene beads. Experimental verification used an array of 96 traps in an area of 420 × 420 μm2, reaching a trapping efficiency of 63% when 7 Vpp is applied to the electrodes under 80 nl min−1 flow rate conditions, and 98% of bead release when the voltage is turned off.

An evaporation based digital microflow meter

In this work, we present a digital microflow meter operating in the range 30–250 nl min−1 for water. The principle is based on determining the evaporation rate of the liquid via reading the number of wetted pore array structures in a microfluidic system, through which continuous evaporation takes place. A proof-of-principle device of the digital flow meter was designed, fabricated, and tested. The device was built on foil-based technology. In the proof-of-principle experiments, good agreement was found between set flow rates and the evaporation rates estimated from reading the number of wetted pore structures. The measurement range of the digital flow meter can be tuned and extended in a straightforward manner by changing the pore structure of the device.

TRPV4 mediates flow-induced increases in intracellular Ca in medullary thick ascending limbs.

Medullary thick ascending limbs (mTAL) regulate Na balance and therefore blood pressure. We previously showed that cell swelling and luminal flow activates the mechanosensitive channel TRPV4 in mTAL. We hypothesized that TRPV4 mediates flow-induced increases in intracellular Ca (Cai) in rat mTALs. We performed ratiometric measurements of Cai in perfused mTALs. Increasing luminal flow from 0 to 20 nL min(-1) caused Cai to peak 231 ± 29 nmol L(-1) above basal concentrations (n = 18). The general TRPV inhibitor ruthenium red at 15 and 50 μmol L(-1) reduced peak Cai by 41 ± 9 (P < 0.01; n = 5) and 77 ± 10% (P < 0.02; n = 6). The selective TRPV4 inhibitor RN1734 at 10 and 50 μmol L(-1) reduced peak Cai by 46 ± 11 (P < 0.01; n = 7) and 76 ± 5% (P < 0.02; n = 5) respectively. To specifically target TRPV4, mTALs were transduced with adenoviruses expressing TRPV4 small hairpin (sh) RNA. In non-transduced control mTALs, luminal flow generated a peak increase in Cai of 111 ± 21 nmol L(-1) (n = 8). In TRPV4shRNA-transduced mTALs, the Cai peak was reduced to 56 ± 8 nmol L(-1) (P < 0.03, n = 9). Removing extracellular Ca completely abolished flow-induced increases in Cai. Increasing luminal flow in the presence of hexokinase 20 (U mL(-1) ) to scavenge extracellular ATP did not modify significantly the increases in Cai induced by luminal flow. Finally, we studied the effect of the TRPV4 selective agonist GSK1016790A on Cai. In the absence of luminal flow, GSK1016790A (10 nmol L(-1) ) increased Cai from 60 ± 11 nmol L(-1) to 262 ± 71 nmol L(-1) (P < 0.05; n = 7). We conclude that flow-induced increases in Cai are mediated primarily by TRPV4 in the rat mTAL.

Fluid absorption in the isolated midgut of adult female yellow fever mosquitoes (Aedes aegypti).

The transepithelial voltage (Vte) and the volume of isolated posterior midguts of adult female yellow fever mosquitoes (Aedes aegypti) were monitored. In all experiments, the initial Vte after filling the midgut was lumen negative, but subsequently became lumen positive at a rate of approximately 1 mV min(-1). Simultaneously, the midgut volume decreased, indicating spontaneous fluid absorption. When the midguts were filled and bathed with mosquito saline, the average rate of fluid absorption was 36.5±3.0 nl min(-1) (N=4, ±s.e.m.). In the presence of theophylline (10 mmol l(-1)), Vte reached significantly higher lumen-positive values, but the rate of fluid absorption was not affected (N=6). In the presence of NaCN (5 mmol l(-1)), Vte remained close to 0 mV (N=4) and fluid absorption was reduced (14.4±1.3 nl min(-1), N=3, ±s.e.m.). When midguts were filled with buffered NaCl (154 mmol l(-1) plus 1 mmol l(-1) HEPES) and bathed in mosquito saline with theophylline, fluid absorption was augmented (50.0±5.8 nl min(-1), N=12, ±s.e.m.). Concanamycin A (10 µmoll(-1)), ouabain (1 mmol l(-1)), and acetazolamide (1 mmol l(-1)) affected Vte in different ways, but all reduced fluid absorption by 60-70% of the value before addition of the drugs.

Bidirectional microfluidic pumping using an array of magnetic Janus microspheres rotating around magnetic disks.

We demonstrate a novel, flexible and programmable method to pump liquid through microchannels in lab-on-a-chip systems without the use of an external pump. The pumping principle is based on the rotation of ferromagnetic Janus microspheres around permalloy disks, driven by an external rotating magnetic field. By placing the disks close to the edge of the microchannel, a pumping rate of at least 0.3 nL min(-1) was measured using tracking microspheres. Geometric programming of the pumping direction is possible by positioning the magnetic disk close to the side wall. A second degree of freedom in the pumping direction is offered by the rotational direction of the external magnetic field. This method is especially suited for flow-controlled recirculation of chemical and biological species in microchannels - for example, medium recirculation in culture chambers - opening the way towards novel, portable, on-chip applications without the need for external fluidic or electrical connections.

The effect of varying temperature and O2 flow rate in ex situ annealed tin-doped indium for fabrication of commercial grade indium tin oxide

In this work, tin-doped indium was deposited on a glass substrate via the electron beam evaporation tech- nique. Then, the as-grown thin films were baked in the presence of oxygen at different O2 flow rates and tempera- tures inside a furnace to obtain transparent conducting oxide thin film structures. The electrical and optical properties of the layers were investigated, the thickness of all samples was kept at 500 nm and the rate of deposition was set at 0.1 nm min -1 . The best optical and electrical properties were obtained at O2 flow rate of 1.5 Nl min -1 and temper- atures of 500 C where above 90 % optical transparency and B4 9 10 -3 ohm cm -1 electrical resistivity were achieved.

Yield enhancement in whispering gallery mode biosensors: microfluidics and optical forces

We analyze the transport of 25 nm polystyrene nanoparticles through a microfluidic geometry housing a microtoroidal whispering gallery mode (WGM) sensor, taking into account diffusion, convection and optical forces. In particular, we look at the effects of tightly confining the flow of nanoparticles near the microtoroid’s equatorial rim, and calculate the average nanoparticle detection time as well as the total yield for passage of a 1 L sample. Compared to purely diffusive transport, flow rates on the order of 2 nL min give yield enhancements of up to 15 , with nanoparticles being detected every 12 s. Even shorter detection times (1.2 s) can be achieved, but at the expense of lower yield. The sensor’s transport properties are further improved due to gradient optical forces exerted on the nanoparticles.

Realizing nano electrospray ionization using disposable pipette tips under super atmospheric pressure

Nano electrospray with a solution flow rate below 100 nL min(-1) is usually performed using a metallized pulled glass capillary with an inner diameter tip of <10 μm. In this paper, we demonstrated that it was possible to achieve a stable solution flow rate of ~10 nL min(-1) for an aqueous solution using a disposable plastic pipette tip with an inner diameter of 100 μm as an ESI emitter. This pipette tip (gel loading tip) was originally designed for the loading of sample onto the gel in gel electrophoresis. The inner and outer diameters were much larger than those of a nanoESI emitter, but the low solution flow rate could be sustained by conducting the electrospray under a super-atmospheric gas pressure. The high pressure condition ensured the absence of electrical discharge which was essential for stable electrospray of aqueous solution. ESI with this low cost tip was equally as sensitive as the standard nanoESI emitter and capable of producing a long lasting signal from a small amount of sample liquid. Due to a small initial droplet size under the low flow rate regime, ESI with the present method exhibited the property of nanoESI where the ion suppression of the hydrophilic analyte by the hydrophobic compound present in the solution was greatly reduced. Furthermore, owing to its larger inner diameter, the tip relatively easily avoided the clogging problem often encountered when dealing with "dirty" samples when compared with a nanoESI emitter made from a fine glass capillary.

Unusual behavior of dynamic hydrogen generation from sodium borohydride

In this study, for the first time, hydrogen gas generation rate is dynamically measured by transferring required amount of sodium borohydride solution to maintain 1 or 2 normal liters of hydrogen gas generation per minute. Three different catalysts (iron, platinum and ruthenium) are used in order to investigate the critical catalyst concentration, catalyst amount and the rate relation and as well as the influence of the sodium borohydride concentration on the rate equations. It has been demonstrated that the linear approximation from the initial hydrogen gas generation data usually reported in the literature is not valid. Moreover, the actual rates reported here are higher and lower than the linear approximations depending on the type of the catalyst. It is about 60 percent lower than linear approximation when iron catalyst is used. Therefore, calculating hydrogen gas generation rate as NL min−1 g−1catalyst is invalid. On the other hand, it has been observed that the rate equation may not be dependent on the amount of the sodium borohydride concentration if the highest catalytic activity is achieved. Hence, most of the rate equations in the literature are only valid for a range, which is limited to the highest catalytic activity. Additionally, it has been concluded that the amount of catalyst and sodium borohydride concentration may be optimized to observe almost 100% efficiencies.

Design and uncertainty assessment of a setup for calibration of microfluidic devices down to 5 nL min−1

This work focuses on the design and characterization of a system for measuring and calibration of liquid micro-flows down to 5 nL min−1. The experimental setup relies on a telecentric imaging system mounted on a high-precision, computer controlled linear stage to track a moving liquid meniscus in a glass capillary. The position of the linear stage can be automatically adjusted to track the motion of the liquid front over distances of up to 15 cm. All fluidic components were placed inside a temperature regulated chamber at 36.0 ± 1.1 °C with a maximum variability ΔT = ± 0.1 °C for time intervals shorter than 1 h. The combined flow-rate uncertainty has been evaluated for measurement times from 15 s to 1 h and nominal flow rates between 5 and 50 nL min−1. At 5 nL min−1, an extended flow-rate uncertainty better that 8.3% can be attained for measurement times equal to or longer than 60 s. The uncertainty approaches asymptotically 5.4% for measurement times longer than 300 s or flow rates higher than 50 nL min−1.

Development of an electrospray-63Ni-differential ion mobility spectrometer for the analysis of aqueous samples

The feasibility of an electrospray coupled with a (63)Ni-differential ion mobility spectrometer (DMS) for the analysis of water samples was proven on examples of 2-hexanone, fluoroacetamide, l-nicotine and 1-phenyl-2-thiourea water solutions. The model substances were selected in order to cover the vapor pressure range of 0.3-1467 Pa. To reduce the inline humidity, which demonstrates a strong influence on the analyte compensation voltage, two units with a desolvation region lengths of 15.5 and 7 mm were examined. The counter gas (heated to 100 °C nitrogen) with flow rates of 100 mL min(-1) and 30 mL min(-1) for short and long desolvation units, respectively, was essential for the efficient reduction of humidity. The reduction of water content in the carrier gas to 2.2-2.4 g m(-3) and to 1.8-2.0 g m(-3) for the short and long desolvation unit, respectively, was achieved at an electrospray flow rate of 1000 nL min(-1). With this adjusted experimental setup, the detection of model substances in the water solutions, in the range of 0.1-50 mg L(-1), was performed. No correlation between the vapor pressure and signal area was observed. The high stability of the inline humidity, and the correspondingly stable carrier gas flow rate, were found to be essential for an acceptable reproducibility.

Hydrodynamic Cell Trapping for High Throughput Single-Cell Applications

The possibility to conduct complete cell assays under a precisely controlled environment while consuming minor amounts of chemicals and precious drugs have made microfluidics an interesting candidate for quantitative single-cell studies. Here, we present an application-specific microfluidic device, cellcomb, capable of conducting high-throughput single-cell experiments. The system employs pure hydrodynamic forces for easy cell trapping and is readily fabricated in polydimethylsiloxane (PDMS) using soft lithography techniques. The cell-trapping array consists of V-shaped pockets designed to accommodate up to six Saccharomyces cerevisiae (yeast cells) with the average diameter of 4 μm. We used this platform to monitor the impact of flow rate modulation on the arsenite (As(III)) uptake in yeast. Redistribution of a green fluorescent protein (GFP)-tagged version of the heat shock protein Hsp104 was followed over time as read out. Results showed a clear reverse correlation between the arsenite uptake and three different adjusted low = 25 nL min−1, moderate = 50 nL min−1, and high = 100 nL min−1 flow rates. We consider the presented device as the first building block of a future integrated application-specific cell-trapping array that can be used to conduct complete single cell experiments on different cell types.

Preparation of ultrafine polyurethane fiber web by laser-electrospinning combined with air blowing

Thermoplastic polyurethane fiber webs were prepared using a laser-heated electrospinning process combined with air blowing. The effect of spinning conditions such as air flow rate and air temperature on fiber diameter and molecular weight was investigated. Although the average fiber diameter decreased with increased air flow rate at each air temperature, the diameter increased when the air flow rate was >15 NL min−1. In addition, the fiber was comparatively thicker with an increase in the air temperature. The variation in the fiber diameter tends to increase with the air flow rate, and a reduction in the molecular weight of the fiber by thermal degradation was suppressed. The thinnest and most uniform fiber with a diameter of 0.9 µm and a diameter coefficient variation of 15% was obtained at an air temperature of 25°C under an air flow rate of 15 NL min−1. This fiber also had a minimum of decreased molecular weight. POLYM. ENG. SCI., 54:2605–2609, 2014. © 2013 Society of Plastics Engineers

Cultivation Process Optimization Of Recombinant Bacillus Subtilis Harbouring Apoptin Gene

The success of recombinan apoptin production in native form in the previous results open the way to develop this anticancer protein production to the larger scale. We optimized cultivation process of recombinant Bacillus subtilis 168 harbouring pOXGW12His8Arg with apoptin gene in a stirred tank fermentor and shake flasks. The parameters to optimize cultivation process are xylose-inducer concentration, agitation speed, and aeration rate. The xylose-inducer concentration variations are carried out in a shake flasks with 100 mL volume broth, while the agitation speed and aeration rate variation is carried out in a stirred tank fermentor with 3 L volume broth. The xylose concentration is varied between 0-5% w/v, while agitation speed and aeration rate are varied between 150-250 rpm and 0.5-1.5 NL min-1 respectively. The best condition in this cultivation is 1% w/v of xylose, 250 rpm of agitation speed and 1,5 NL min-1 of aeration rate giving the specific growth rate value for each parameter of 0.628 h-1; 0.630 h-1; and 0.747 h-1 respectively. The recombinant apoptin were purified by Ni-NTA column using AKTA system. However, the results showed that the optimum condition of producing recombinant apoptin was 1% w/v of xylose, 250 rpm of agitation speed, and 0.5 NL min-1 of aeration.

Highly reproducible chronoamperometric analysis in microdroplets

Here we report a method for highly reproducible chronoamperometric analysis of the contents of microdroplets. Aqueous microdroplets having volumes on the order of 1 nL and separated by a fluorocarbon solvent are generated within a microfluidic device using a T-shaped junction. The key finding is that stable and reproducible quasi-steady-state currents are observed if the electrochemical measurements are made in a narrowed segment of a microchannel. Under these conditions, the microdroplets are stretched, here by a factor of 10, leading to desirable intradroplet mass transfer characteristics. Microdroplet frequencies up to 0.67 s(-1) are accessible using this method. The quasi-steady-state currents resulting from chronoamperometric analysis of microdroplets containing 1.0 mM Ru(NH3)6(3+) have relative standard deviations of just 1.8% and 2.8% at flow rates of 30 nL min(-1) and 60 nL min(-1), respectively. Importantly, the design of the microelectrochemical device ensures direct contact between intradroplet redox molecules and the electrode surface. That is, the fluorocarbon between microdroplets does interfere with inner-sphere electrocatalytic processes such as the oxygen reduction reaction. Finite-element simulations are presented that are in accord with the experimental findings.