Vortex fluidic promoted Diels–Alder reactions in an aqueous medium

‘Soft energy’ provided within a thin film microfluidic platform, namely a vortex fluidic device (VFD), is effective in accelerating and promoting Diels–Alder reactions in the absence of any catalyst. Diels–Alder cycloadducts generated from different 9-substituted anthracenes and N-maleimides are formed in high yield in an aqueous medium using the confined mode of operation of the VFD.     

A Versatile Compact Parahydrogen Membrane Reactor

We introduce a Spin Transfer Automated Reactor (STAR) that produces continuous parahydrogen induced polarization (PHIP), which is stable for hours to days. We use the PHIP variant called signal amplification by reversible exchange (SABRE), which is particularly well suited to produce continuous hyperpolarization. The STAR is operated in conjunction with benchtop (1.1 T) and high field (9.4 T) NMR magnets, highlighting the versatility of this system to operate with any NMR or MRI system. The STAR uses semipermeable membranes to efficiently deliver parahydrogen into solutions at nano to milli Tesla fields, which enables ¹H, ¹³C, and ¹⁵N hyperpolarization on a large range of substrates including drugs and metabolites. The unique features of the STAR are leveraged for important applications, including continuous hyperpolarization of metabolites, desirable for examining steady-state metabolism in vivo, as well as for continuous RASER signals suitable for the investigation of new physics.     

Series solutions of nano boundary layer flows by means of the homotopy analysis method

We present here a ‘similar’ solution for the nano boundary layer with nonlinear Navier boundary condition. Three types of flows are considered: (i) the flow past a wedge; (ii) the flow in a convergent channel; (iii) the flow driven by an exponentially-varying outer flows. The resulting differential equations are solved by the homotopy analysis method. Different from the perturbation methods, the present method is independent of small physical parameters so that it is applicable for not only weak but also strong nonlinear flow phenomena. Numerical results are compared with the available exact results to demonstrate the validity of the present solution. The effects of the slip length ?, the index parameters n and m on the velocity profile and the tangential stress are investigated and discussed.     

Measurement of microchannel fluidic resistance with a standard voltage meter

A simplified method for measuring the fluidic resistance (R_fluidic) of microfluidic channels is presented, in which the electrical resistance (R_elec) of a channel filled with a conductivity standard solution can be measured and directly correlated to R_fluidic using a simple equation. Although a slight correction factor could be applied in this system to improve accuracy, results showed that a standard voltage meter could be used without calibration to determine R_fluidic to within 12% error. Results accurate to within 2% were obtained when a geometric correction factor was applied using these particular channels. When compared to standard flow rate measurements, such as meniscus tracking in outlet tubing, this approach provided a more straightforward alternative and resulted in lower measurement error. The method was validated using 9 different fluidic resistance values (from ∼40 to 600 kPa s mm⁻³) and over 30 separately fabricated microfluidic devices. Furthermore, since the method is analogous to resistance measurements with a voltage meter in electrical circuits, dynamic R_fluidic measurements were possible in more complex microfluidic designs. Microchannel R_elec was shown to dynamically mimic pressure waveforms applied to a membrane in a variable microfluidic resistor. The variable resistor was then used to dynamically control aqueous-in-oil droplet sizes and spacing, providing a unique and convenient control system for droplet-generating devices. This conductivity-based method for fluidic resistance measurement is thus a useful tool for static or real-time characterization of microfluidic systems.     

基于介质上电润湿的微流体变焦透镜的研究进展

近年来,微流体变焦透镜的研究已展示出其在光学系统中的应用前景,其中基于介质上电润湿(Electrowet-ting on dielectric,EWOD)的微流体变焦透镜只需改变外加电压便能快速调节透镜焦距,并且具有尺寸小、结构灵活、功耗低、焦距调节范围广等许多突出优点而日益受到注目。在介绍EWOD机理的基础上,综述了目前基于EWOD的微流体变焦透镜的研究进展。     

Vortex amplifier internal geometry and its effect on performance

Consideration of the internal geometry of a vortex amplifier reveals eight geometrical ratios that describe the device. The effects of each of these ratios on the performance of a vortex amplifier are considered and experimental results presented. The most significant ratios when designing for vortex amplifier performance are identified     

Miniaturizing sample spots for matrix-assisted laser desorption/ionization mass spectrometry

The trend of miniaturization in bioanalytical chemistry is shifting from technical development to practical application. In matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), progress in miniaturizing sample spots has been driven by the needs to increase sensitivity and speed, to interface with other analytical microtechnologies, and to develop miniaturized instrumentation.We review recent developments in miniaturizing sample spots for MALDI-MS. We cover both target modification and microdispensing technologies, and we emphasize the benefits with respect to sensitivity, throughput and automation.We hope that this review will encourage further method development and application of miniaturized sample spots for MALDI-MS, so as to expand applications in analytical chemistry, protein science and molecular biology.     

Accelerating Enzymatic Catalysis Using Vortex Fluidics

Enzymes catalyze chemical transformations with outstanding stereo‐ and regio‐specificities, but many enzymes are limited by their long reaction times. A general method to accelerate enzymes using pressure waves contained within thin films is described. Each enzyme responds best to specific frequencies of pressure waves, and an acceleration landscape for each protein is reported. A vortex fluidic device introduces pressure waves that drive increased rate constants (k_cat) and enzymatic efficiency (k_cat/K_m). Four enzymes displayed an average seven‐fold acceleration, with deoxyribose‐5‐phosphate aldolase (DERA) achieving an average 15‐fold enhancement using this approach. In solving a common problem in enzyme catalysis, a powerful, generalizable tool for enzyme acceleration has been uncovered. This research provides new insights into previously uncontrolled factors affecting enzyme function.