nL Droplet Research Articles

Simulation and experimentation of a microfluidic device based on electrowetting on dielectric

Electrowetting on dielectric (EWOD) moving fluid by surface tension effects offers some advantages, including simplicity of fabrication, control of minute volumes, rapid mixing, low cost and others. This work presents a numerical model using a commercial software, CFD-ACE+, and an EWOD system including a microfluidic device, a microprocessor, electric circuits, a LCD module, a keypad, a power supply and a power amplifier. The EWOD model based on a reduced form of the mass conservation and momentum equations is adopted to simulate the fluid dynamics of the droplets. The EWOD device consists of the 2 x 2 mm bottom electrodes (Au/Cr), a dielectric layer of 3,000 A nitride, 500 A Teflon and a piece of indium tin oxide (ITO)-coated glass as the top electrode. The complete EWOD phenomenon is elucidated by comparing simulation with the experimental data on droplet transportation, cutting and creation. In transportation testing, the speed of the droplet is 6 mm/s at 40 V(dc). In addition, the droplet division process takes 0.12 s at 60 V(dc) in the current case. Finally, a 347 nl droplet is successfully created from an on-chip reservoir at 60 V(dc).

On Low-Power Droplet Manipulator Employing High-Frequency Surface Acoustic Waves

A droplet manipulator working with low driving power was developed by using the surface acoustic wave (SAW) technology. The manipulator was driven at a relatively high frequency of 350MHz to increase the SAW power density. First, a single phase unidirectional transducer (SPUDT) was designed. Because of its low insertion loss of 1.5 dB and high directivity of 10 dB, the SPUDT successfully conveyed a 100 nl water droplet with RF input power of 18 dBm (60 mW). Second, the SPUDT design was extended to a curved transducer to focus and launch the SAW energy into the narrow waveguide. Owing to the increased SAW power density, the required SAW power was reduced to 15 dBm (30 mW) for the 100 nl droplet manipulation. In addition, fabrication of liquid injectors was discussed for the formation of tiny droplet.

Automated nanoliter solution deposition for total reflection X-ray fluorescence analysis of semiconductor samples

In this study, a BioDot BioJet dispensing system was investigated as a nanoliter sample deposition method for total reflection X-ray fluorescence (TXRF) analysis. The BioDot system was programmed to dispense arrays of 20 nL droplets of sample solution on Si wafers. Each 20 nL droplet was approximately 100 μm in diameter. A 10 × 10 array (100 droplets) was deposited and dried in less than 2 min at room temperature and pressure, demonstrating the efficiency of the automated deposition method. Solutions of various concentrations of Ni and Ni in different matrices were made from stock trace element standards to investigate of the effect of the matrix on the TXRF signal. The concentrations were such that the levels of TXRF signal saturation could be examined. Arrays were deposited to demonstrate the capability of drying 100 μL of vapor phase decomposition-like residue in the area of a typical TXRF detector.

Quantitative extraction using flowing nano-liter droplet in microfluidic system

Quickly extraction system using dispersed droplet in T-shaped microchannel has been constructed and investigated for the determination of aluminum in water. The droplet was generated in T-shaped microchannel with 600 μm wide and 200 μm deep in continuous phase and 70 μm wide and 20 μm deep in dispersed phase by flowing two immiscible solutions, buffer solution containing aluminum and tributyl phosphate as dispersed phase. By varying the flow rate of two solutions, the droplet volume could be controlled in the range from 0.6 to 32 nL. Using this droplet generation in microchannel, aluminum in continuous phase was extracted with 2,2-dihydroxyazobenzene as a metal chelate from buffer solution to tributyl phosphate for 1 s, which was 90 times shorter than that of a conventional extraction method using a separatory funnel. Estimated overall mass transfer coefficient was to be 57 × 10 −4 mm s −1 with 0.6 nL droplet. And quantitative extraction was performed in this extraction system by detecting droplets before it reached to extraction equilibrium. Furthermore, this extraction system was applied to environmental analysis for evaluation of its validity, and the results were in agreement with the conventional extraction method ( r = 0.92).

Electrophysiological, mechanosensitive responses of Xenopus laevis oocytes to direct, isotonic increase in intracellular volume

An intra-oocyte injection method for obtaining the electrophysiological response of follicle-enclosed Xenopus laevis oocytes to an increase in intracellular volume (i.e. stretch) without changing the extracellular medium is described. The response comprised a ‘stretch-activated’ (SA) current which was evoked by injection of an isotonic 14–70 nl droplet and had a transient, smooth profile. Ionic substitution experiments revealed that the current was carried mainly by Na +, K + and Cl − and had a reversal potential of about −2 mV. A similar result was obtained from experiments in which the holding potential was varied between −40 and +10 mV whilst repeatedly inducing the SA current. On average, the channel was blocked 60% by 10 μM gadolinium chloride, 58% by 50 μM amiloride, 11% by 50 μM 4,4′-diisothiocyanatostilbene-2, 2′-disulfonic acid and 63% by 50 μM 4-acetamido-4′-isothiocyanato-stilbene-2-2′-disulfonic acid. Maturation of the oocytes with 100 μM progesterone reduced the mechanosensitivity 12-fold. This injection technique is compared with other methods of eliciting mechanosensitive (MS) currents in X. laevis oocytes. These observed characteristics of the SA current are discussed in relation to the oocytes’ endogenous MS cation and anion channels.

Interaction between 3 alpha-hydroxy-5 alpha-pregnan-20-one and carbachol in the control of neuronal excitability in hippocampal slices of female rats in defined phases of the oestrus.

The effects of 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone) and carbachol on CA1 and dentate gyrus action potentials were studied in hippocampus slices in premature, follicular and luteal phase rats. A 0.5 nL droplet of allopregnanolone (12.5 mumol L-1), carbachol (5 mumol L-1) or a mixed solution of 12.5 mumol L-1 allopregnanolone and 5 mumol L-1 carbachol was applied locally onto the stratum oriens-pyramidale or granular layer. The amplitude of CA1 population spike (POPSP) was reduced by allopregnanolone (-38 +/- 3%) and carbachol (-21 +/- 4%) in the luteal phase slices. The mixture of allopregnanolone and carbachol doubled this inhibition (-77 +/- 6%). The inhibition caused by allopregnanolone and the mixture of allopregnanolone and carbachol in CA1 was significantly larger in the luteal phase than in the follicular phase (P = 0.02 and 0.0002). In the granular layer of the dentate gyrus, these inhibitions showed no significant difference between the phases. Neither in CA1 nor in the dentate gyrus did the carbachol inhibition differ between the phases. Perfusion with 5-10 mumol L-1 carbachol caused an increasing inhibition of the POPSP during the first few minutes. Thereafter the inhibition gradually diminished and was replaced by a facilitation. The local allopregnanolone inhibition was enhanced by simultaneous carbachol perfusion. Picrotoxin (100 mumol L-1) substantially reduced the allopregnanolone but not the carbachol inhibition. Atropine (10 mumol L-1) blocked the carbachol response, but not the allopregnanolone inhibition. Perfusion with a mixed solution of picrotoxin and atropine reduced, but did not block, the inhibition caused by local application of allopregnanolone or by the mixture of allopregnanolone and carbachol. Our data suggest that neuroprogestine modulators of the GABAA-receptor-mediated inhibition may play a significant role in the control of the cholinergic excitation in the hippocampus.