Simultaneous Separation and Detection of Cations and Anions Ion a Microfluidic Device with Suppressed Electroosmotic Flow and a Single Injection Point

A rapid and simultaneous separation of cationic and anionic peptides and proteins in a glass microfluidic device that has been covalently modified with a neutral poly(ethylene glycol) (PEG) coating to minimize protein adsorption is presented. The features of the device allow samples that contain both anions and cations to be introduced from a central flow stream and separated in different channels with different outlets—all in the presence of low electroosmotic flow (EOF) imparted by the PEG coating. The analytes are electrophoretically extracted from a central hydrodynamic stream and electrophoretically separated in two different channels, in which pressure driven flow has been suppressed through the use of hydrodynamic restrictors. Having different outlets for the electrophoretic separation channels that are spatially separated from the injection enables coupling with further downstream functionalities or off-chip detection, such as mass spectrometry. A plug of charged analyte is hydrodynamically pumped to the sampling intersection and anions from the plug migrate electrophoretically toward the anode in one channel while cations migrate toward the cathode in the other channel due to suppressed EOF from the PEG coating. The separations presented here required less than a minute to complete and produced average separation efficiencies of up to about 3,500 plates from a separation length of 2 cm. The extraction efficiency of both cations and anions from the hydrodynamic stream is determined experimentally and compared with a previously reported model that was used to determine anion extraction efficiency. The extraction efficiency is determined to be 87% and 98% for the two sample mixtures analyzed, and the values predicted by the model are within 3.5% of the experimental data. It is anticipated that this basic approach for simultaneous separation of anions and cations with reduced EOF will be integrated into larger microfluidic systems because the design provides separate outlets that can feed downstream processes or linked to off-chip detection

In vitro inhibition of liver forms of the rodent malaria parasite Plasmodium berghei by naphthylisoquinoline alkaloids--structure-activity relationships of dioncophyllines A and C and ancistrocladine

Naphthylisoquinoline alkaloids are derived from Dioncophyllaceae and Ancistrocladaceae species and comprise a new class of promising antimalarials with a demonstrated potential against asexual erythrocytic Plasmodium falciparum and P. berghei stages in vitro. We report herein the pronounced activity of pure naphthylisoquinoline alkaloids against exoerythrocytic malaria parasites. P. berghei-infected human hepatoma cells (Hep G2) were incubated with culture medium containing selected alkaloids at 10 micrograms/ml. The most active compounds, showing inhibitory activity of more than 40%, were dioncophylline A (compound 1), dioncophyllacine A (compound 6), and ancistrobarterine A (compound 12). For structure-activity investigations of dioncophyllines A (compound 1) and C (compound 3) and ancistrocladine (compound 7) a selection of their analogs from natural or synthetic sources was examined. Dioncophylline A (compound 16), 5'-O-demethyl-8-O-methyl-7-epi-dioncophylline A (compound 17), N-formyl-8-O-methyl-dioncophylline C (compound 21), and N-formyl-8-O-benzoyldioncophylline C (compound 24) were found to display high levels of activity as well, although the former two compounds caused damage to the host-cell monolayers. As naphthylisoquinoline alkaloids are also highly active against blood forms of Plasmodium spp., they should be regarded as lead compounds for further development as drugs against erythrocytic and exoerythrocytic stages of Plasmodium spp

A Theoretical and Experimental Study of the Electrophoretic Extraction of Ions from a Pressure Driven Flow in a Microfluidic Device

The electrophoretic extraction of ions from a hydrodynamic flow stream is investigated at an intersection between two microfluidic channels. A pressure gradient is used to drive samples through the main channel, while ions are electrophoretically extracted into the side channels. Hydrodynamic restrictors and a neutral coating are used to suppress bulk flow through the side channels. A theoretical model that assumes Poiseuille flow in the main channel and neglects molecular diffusion is used to calculate the extraction efficiency, η, as a function of the ratio, R, of the average hydrodynamic velocity to the electrophoretic velocity. The model predicts complete extraction of ions (η = 1) for R \u3c 2/3 and a monotonic decrease in η as R becomes greater than 2/3, which agrees well with the experimental results. Additionally, the model predicts that the aspect ratio of the microfluidic channel has little effect on the extraction efficiency. It is anticipated that this device can be used for on-line process monitoring, sample injection, and 2D separations for proteomics and other fields

Fabrication and performance of a microfluidic traveling-wave electrophoresis system

A microfluidic traveling-wave electrophoresis (TWE) system is reported that uses a locally defined traveling electric field wave within a microfluidic channel to achieve band transport and separation. Low voltages, over a range of-0.5 to +0.5 V, are used to avoid electrolysis and other detrimental redox reactions while the short distance between electrodes, ∼25 μm, provides high electric fields of ∼200 V cm -1. It is expected that the low voltage requirements will simplify the future development of smaller portable devices. The TWE device uses four interdigitated electrode arrays: one interdigitated electrode array pair is on the top of the microchannel and the other interdigitated electrode array pair is on the microchannel bottom. The top and bottom substrates are joined by a PDMS spacer that has a nominal height of 15 μm. A pinched injection scheme is used to define a narrow sample band within an injection cross either electrokinetically or hydrodynamically. Separation of two dyes, fluorescein and FLCA, with baseline resolution is achieved in less than 3 min and separation of two proteins, insulin and casein is demonstrated. Investigation of band broadening with fluorescein reveals that sample band widths equivalent to the diffusion limit can be achieved within the microfluidic channel, yielding highly efficient separations. This low level of band broadening can be achieved with capillary electrophoresis, but is not routinely observed in microchannel electrophoresis. Sample enrichment can be achieved very easily with TWE using a device with converging electric field waves controlled by two sets of independently controlled interdigitated electrodes arrays positioned serially along the microchannel. Sample enrichment of 40-fold is achieved without heterogeneous buffer/solvent systems, sorptive, or permselective materials. While there is much room for improvement in device fabrication, and many capabilities are yet to be demonstrated, it is anticipated that the capabilities and performance demonstrated herein will enable new lab-on-a-chip processes and systems. © The Royal Society of Chemistry 2012

Traveling-Wave Electrophoresis for Microfluidic Separations

Models and microfluidic experiments are presented of an electrophoretic separation technique in which charged particles whose mobilities exceed a tunable threshold are trapped between the crests of a longitudinal electric wave traveling through a stationary viscous fluid. The wave is created by applying periodic potentials to electrode arrays above and below a microchannel. Predicted average velocities agree with experiments and feature chaotic attractors for intermediate mobilities