Direct Integration of Micromachined Pipettes in a Flow Channel for Single DNA Molecule Study by Optical Tweezers

We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap setup (optical tweezers) to study mechanical and structural properties of λ-DNA molecules. The flow cell was realized using silicon micromachining including the so-called buried channel technology to fabricate the micropipettes, the wet etching of glass to create the flow channel,\ud and the powder blasting of glass to make the fluid connections. The volume of the flow cell is 2 µl. The pipettes have a length of 130 m, a width of 5–10 µm, a round opening of 1 um and can be processed with different shapes. Using this flow cell we stretched single molecules (λ-DNA) showing typical force-extension curves also found with conventional techniques. These pipettes can be\ud also used for drug delivery, for injection of small gas bubbles into a liquid flow to monitor the streamlines, and for the mixing of liquids to study diffusion effects. The paper describes the design, the fabrication and testing of the flow cell

Electrically rechargeable REDOX flow cell

A bulk energy storage system is designed with an electrically rechargeable reduction-oxidation (REDOX) cell divided into two compartments by a membrane, each compartment containing an electrode. An anode fluid is directed through the first compartment at the same time that a cathode fluid is directed through the second compartment. Means are provided for circulating the anode and cathode fluids, and the electrodes are connected to an intermittent or non-continuous electrical source, which when operating, supplies current to a load as well as to the cell to recharge it. Ancillary circuitry is provided for disconnecting the intermittent source from the cell at prescribed times and for circulating the anode and cathode fluids according to desired parameters and conditions

The 3D printing of a polymeric electrochemical cell body and its characterisation

An undivided flow cell was designed and constructed using additive manufacturing technology and its mass transport characteristics were evaluated using the reduction of ferricyanide, hexacyanoferrate (III) ions at a nickel surface. The dimensionless mass transfer correlation Sh = aRebScdLee was obtained using the convective-diffusion limiting current observed in linear sweep voltammetry; this correlation compared closely with that reported in the literature from traditionally machined plane parallel rectangular flow channel reactors. The ability of 3D printer technology, aided by computational graphics, to rapidly and conveniently design, manufacture and re-design the geometrical characteristics of the flow cell ishighlighted

Feasibility study: Atmospheric general circulation experiment, volume 1

The atmospheric general circulation experiment (AGCE) uses a rotating fluid flow cell assembly. The key technical areas affecting the feasibility of the design and operation of the AGCE are investigated. The areas investigated include materials for the flow cell assembly, thermal design, high voltage power supply design, effective retrieval and handling of experiment data and apparatus configuration. Several materials, DMSO and m-tolunitrile, were selected as candidate fluids for the flow cell principally for their high dielectric constant which permits the high voltage power supply design to be held to 15 kV and still simulate terrestrial gravity. Achievement of a low dissipation factor in the fluid to minimize internal heating from the applied electrical field depends strongly on purification and handling procedures. The use of sapphire as the outer hemisphere for the flow cell provides excellent viewing conditions without a significant impact on attaining the desired thermal gradients. Birefringent effects from sapphire can be held to acceptably low limits. Visualization of flow fluid is achieved through the motion of a dot matrix formed by photochromic dyes. Two dyes found compatible with the candidate fluids are spiropyran and triarylmethane. The observation of the dot motion is accomplished using a flying spot scanner

Experiments on atmospheric processes

Spacelab technology is examined as applied to the observation of the earth's weather patterns, composition, thermodynamics, and kinematics. An atmospheric cloud physics laboratory and a geophysical fluid flow cell are individually outlined as planned payload experiment efforts

Recent advances in redox flow cell storage systems

Several features which were conceived and incorporated into complete redox systems that greatly enhanced its ability to be kept in proper charge balance, to be capable of internal voltage regulation, and in general be treated as a true multicell electrochemical system rather than an assembly of single cells that were wired together, were discussed. The technology status as it relates to the two application areas of solar photovoltaic/wind and distributed energy storage for electric utility applications was addressed. The cost and life advantages of redox systems were also covered

Single walled carbon nanotube channel flow electrode : hydrodynamic voltammetry at the nanomolar level

The use of single walled carbon nanotube (SWNT) band electrodes in a channel flow cell, for low concentration detection, with hydrodynamic voltammetry is reported. A two dimensional SWNT network electrode is combined with a one piece channel flow cell unit, fabricated by microstereolithography. This configuration provides well defined hydrodynamics over a wide range of volume flow rates (0.05–25 mL min− 1). Limiting current measurements, from linear sweep voltammograms, are in good agreement with the channel electrode Levich equation, for the one electron oxidation of ferrocenylmethyl trimethylammonium (FcTMA+), over a wide concentration range, 1 × 10− 8 M to 2.1 × 10− 5 M, with a detection limit of 5 nM. At the highest flow rates, some influence of the slightly recessed electrode geometry arising from the SWNT electrode fabrication is noted. However, this can be accounted for by a full simulation of the hydrodynamics and solution of the resulting convection–diffusion equation. Application of this hydrodynamic configuration to the voltammetric detection of dopamine is also demonstrated

Photometric detection in flow analysis systems using integrated PEDDs

A novel inexpensive optical-sensing technique has been developed for colorimetric flow analysis. This sensing system employs two LEDs whereby one is used as the light source and the other as a light detector. The LED used as light detector is reverse biased with a 5-V supply so that the photocurrent generated by the incident light discharges the capacitance. Direct digital output is provided by a simple timer circuit that measures the time taken for this discharge process from 5 V (logic 1) to 1.7 V (logic 0). This sensing concept has been applied in flow analysis by constructing an optical flow cell with a pair of LEDs. Calibration of the integrated optical flow cell using a dye resulted in a linear response that obeys the Beer–Lambert law. The flow rate, dynamic range, sensitivity and limits of detection were investigated. The system was also used for pH determination in the range of pH 2.5–6.8 using bromocresol green (BCG). The pKa of BCG was successfully determined by this technique