Fluorocarbon Liquid Research Articles

A microfluidic cell co-culture platform with a liquid fluorocarbon separator

A microfluidic cell co-culture platform that uses a liquid fluorocarbon oil barrier to separate cells into different culture chambers has been developed. Characterization indicates that the oil barrier could be effective for multiple days, and a maximum pressure difference between the oil barrier and aqueous media in the cell culture chamber could be as large as ~3.43 kPa before the oil barrier fails. Biological applications have been demonstrated with the separate transfection of two groups of primary hippocampal neurons with two different fluorescent proteins and subsequent observation of synaptic contacts between the neurons. In addition, the quality of the fluidic seal provided by the oil barrier is shown to be greater than that of an alternative solid-PDMS valve barrier design by testing the ability of each device to block low molecular weight CellTracker dyes used to stain cells in the culture chambers.

Nuclear Magnetic Resonance at the Picomole Level of a DNA Adduct

We investigate the limit of detection for obtaining NMR data of a DNA adduct using modern microscale NMR instrumentation, once the adduct has been isolated at the picomole level. Eighty nanograms (130 pmol) of a DNA adduct standard, N-(2'-deoxyguanosin-8-yl)-2-acetylaminofluorene 5'-monophosphate (AAF-dGMP), in 1.5 μL of D₂O with 10% methanol-d₄, in a vial, was completely picked up as a droplet suspended in a fluorocarbon liquid and loaded efficiently into a microcoil probe. This work demonstrates a practical manual method of droplet microfluidic sample loading, previously demonstrated using automated equipment, which provides a severalfold advantage over conventional flow injection. Eliminating dilution during injection and confining the sample to the observed volume produce the full theoretical mass sensitivity of a microcoil, comparable to that of a microcryo probe. With 80 ng, an NMR spectrum acquired over 40 h showed all of the resonances seen in a standard spectrum of AAF-dGMP, with a signal-to-noise ratio of at least 10, despite broadening due to previously noted effects of conformational exchange. Even with this broadening to 5 Hz, a two-dimensional total correlation spectroscopy spectrum was acquired on 1.6 μg in 18 h. This work helps to define the utility of NMR in combination with other analytical methods for the structural characterization of a small amount of a DNA adduct.

Biofabrication under fluorocarbon: a novel freeform fabrication technique to generate high aspect ratio tissue-engineered constructs.

Bioprinting is a recent development in tissue engineering, which applies rapid prototyping techniques to generate complex living tissues. Typically, cell-containing hydrogels are dispensed layer-by-layer according to a computer-generated three-dimensional model. The lack of mechanical stability of printed hydrogels hinders the fabrication of high aspect ratio constructs. Here we present submerged bioprinting, a novel technique for freeform fabrication of hydrogels in liquid fluorocarbon. The high buoyant density of fluorocarbons supports soft hydrogels by floating. Hydrogel constructs of up to 30-mm height were generated. Using 3% (w/v) agarose as the hydrogel and disposable syringe needles as nozzles, the printer produced features down to 570-μm diameter with a lateral dispensing accuracy of 89 μm. We printed thin-walled hydrogel cylinders measuring 4.8 mm in height, with an inner diameter of ∼2.9 mm and a minimal wall thickness of ∼650 μm. The technique was successfully applied in printing a model of an arterial bifurcation. We extruded under fluorocarbon, cellularized alginate tubes with 5-mm outer diameter and 3-cm length. Cells grew vigorously and formed clonal colonies within the 7-day culture period. Submerged bioprinting thus seems particularly suited to fabricate hollow structures with a high aspect ratio like vascular grafts for cardiovascular tissue engineering as well as branching or cantilever-like structures, obviating the need for a solid support beneath the overhanging protrusions.

Advances in small-angle X-ray scattering for the study of supported catalysts

Ru particle sizes in supported ruthenium catalysts have been studied by small-angle X-ray scattering (SAXS). It has been proposed to use new masking liquids with a relatively low X-ray radiation absorption. Using these liquids it was possible to achieve practically quantitative agreement between SAXS and transmission electron microscopy data. The SAXS technique employing such masking liquids can be used as a quick analytical method for determining the particle size distributions of supported metals. Fluorocarbon liquids can eliminate the scattering signal from any support with a density of 2.5 g cm−3or less. This procedure can be very useful for selective study of separate components in complex samples consisting of carbon materials, silica materials, polymers, some hydroxides, claysetc.

Nucleate boiling from smooth and rough surfaces – Part 1: Fabrication and characterization of an optically transparent heater–sensor substrate with controlled surface roughness

The effect of surface roughness on nucleate boiling heat transfer is not clearly understood. This study is devised to conduct detailed heat transfer and bubble measurements during boiling on a heater surface with controlled roughness. This first of two companion papers discusses details of the fabrication, construction, and operation of the experimental facility. Test pieces are fabricated from 50.8mm×50.8mm×3.18mm borosilicate glass squares that are roughened by abrading with diamond compound with particles of known size and then annealed in order to control small-scale roughness features. Heater/sensor devices are fabricated by depositing indium tin oxide (ITO), a transparent electrically conductive material, on top of the roughened glass surfaces. A method for calibrating the ITO devices for use as temperature sensors is developed. Experimental boiling curves are reported for seven surfaces of different roughness tested in the perfluorinated fluorocarbon liquid, FC-72. The measured receding contact angle for FC-72 on the ITO-coated surfaces is reported. The wall superheat during saturated pool boiling at atmospheric pressure was found not to vary consistently with surface average roughness (Ra) values. Qualitative differences between smooth and rough surface boiling visualizations obtained simultaneously from the side and from below the heaters are discussed.

The investigation of fast neutron Threshold Activation Detectors (TAD)

The detection of fast neutrons is usually done by liquid hydrogenous organic scintillators, where the separation between the ever present gamma rays and neutrons is achieved by the pulse shape discrimination (PSD). In many practical situation the detection of fast neutrons has to be carried out while the intense source (be it neutrons, gamma rays or x-rays) that creates these neutrons, for example by the fission process, is present. This source, or ``flash'', usually blinds the neutron detectors and temporarily incapacitates them. By the time the detectors recover the prompt neutron signature does not exist. Thus to overcome the blinding background, one needs to search for processes whereby the desired signature, such as fission neutrons could in some way be measured long after the fission occurred and when the neutron detector is fully recovered from the overload.A new approach was proposed and demonstrated a good sensitivity for the detection of fast neutrons in adverse overload situations where normally it could not be done. A temporal separation of the fission event from the prompt neutrons detection is achieved via the activation process. The main idea, called Threshold Activation Detection (or detector)-TAD, is to find appropriate substances that can be selectively activated by the fission neutrons and not by the source radiation, and then measure the radioactively decaying activation products (typically beta and γ-rays) well after the source pulse has ended. The activation material should possess certain properties: a suitable half-life; an energy threshold below which the numerous source neutrons will not activate it (e.g. about 3 MeV); easily detectable activation products and has a usable cross section for the selected reaction. Ideally the substance would be part of the scintillator.There are several good candidates for TAD. The first one we have selected is based on fluorine. One of the major advantages of this element is the fact that it is a major constituent of available scintillators (e.g., BaF2, CaF2, hydrogen free liquid fluorocarbon). Thus the activation products of the fast prompt neutrons, in particular, the beta particles, can be measured with a very high efficiency in the detector. Other detectors and substances were investigated, such as 6Li and even common detectors such as NaI.The principles and experimental results obtained with F, NaI and 6Li based TAD are shown. The various contributing activation products are identified. The insensitivity of the fluorine based TAD to (d,D) neutrons is demonstrated. Ways and means to reduce or subtract the various neutron induced activations of NaI detector are elucidated along with its fast neutron detection capabilities. 6Li could also be a useful TAD.

New Method for Fabrication of Fused Silica Emitters with Submicrometer Orifices for Nanoelectrospray Mass Spectrometry

In this paper, we describe a new method for fabrication of nanoelectrospray emitters. The needles were pulled from fused silica capillary tubing, which was melted by means of a plasma, formed by electrical discharges between two pointed platinum electrodes. A key feature of the pulling device is a rotating configuration of the electrodes, which results in an even radial heating of the capillary. The construction of the setup is straightforward, and needles with a variety of shapes can be fabricated, including orifices of submicrometer dimensions. Pulled needles with long tapered tips and an orifice of 0.5 μm were utilized for electrospray ionization mass spectrometry (ESI-MS) of discrete sample volumes down to 275 pL. The picoliter-sized samples were transferred into the tip of the needle from a silicon microchip by aspiration. To avoid a rapid evaporation of the sample, all manipulations were performed under a cover of a fluorocarbon liquid. The limit of detection was measured to be ca. 20 attomole for insulin (chain B, oxidized).

Sheathless hydrodynamic positioning of buoyant drops and bubbles inside microchannels

Particles, bubbles, and drops carried by a fluid in a confined environment such as a pipe can be subjected to hydrodynamic lift forces, i.e., forces that are perpendicular to the direction of the flow. We investigated the positioning effect of lift forces acting on buoyant drops and bubbles suspended in a carrier fluid and flowing in a horizontal microchannel. We report experiments on drops of water in fluorocarbon liquid, and on bubbles of nitrogen in hydrocarbon liquid and silicone oil, inside microchannels with widths on the order of 0.1-1 mm. Despite their buoyancy, drops and bubbles could travel without contacting with the walls of channels; the most important parameters for reaching this flow regime in our experiments were the viscosity and the velocity of the carrier fluid, and the sizes of drops and bubbles. The dependencies of the transverse position of drops and bubbles on these parameters were investigated. At steady state, the trajectories of drops and bubbles approached the center of the channel for drops and bubbles almost as large as the channel, carried by rapidly flowing viscous liquids; among our experiments, these flow conditions were characterized by larger capillary numbers and smaller Reynolds numbers. Analytical models of lift forces developed for the flow of drops much smaller than the width of the channel failed to predict their transverse position, while computational fluid dynamic simulations of the experiments agreed better with the experimental measurements. The degrees of success of these predictions indicate the importance of confinement on generating strong hydrodynamic lift forces. We conclude that, inside microfluidic channels, it is possible to support and position buoyant drops and bubbles simply by flowing a single-stream (i.e., "sheathless") carrier liquid that has appropriate velocity and hydrodynamic properties.

Preparation of asialoglycoprotein receptor-mediated hepatic targeting nano- lipid ultrasound contrast agent and its ultrasound imaging in vitro

Objective To prepare the liver targeting nano-liquid perfluorocarbon ultrasound contrast agent and observe its general characteristics;to observe the targeting combined effects of the human liver cells L02 and the targeted ultrasound contrast agent ;to evaluate the gathering imaging effects of the targeted ultrasound contrast agent. Methods Amine method was used to prepared asialoglycoprotein Gal specific ligand polylysine (Gal-PLL), rotary evaporator and sonicated liquid fluorocarbon were used to prepare nano lipid ultrasound contrast agent. Human liver cell L02 were cultured, the combined effects were observed according to the reacting time of the cells and the targeted nano-lipid ultrasound contrast agent. The nanolipid ultrasound contrast agent and the degassed_ water_ were loaded into cysts and their ultrasound imaging effects were observed by ultrasound diagnostic apparatus Philips iU22. Results The particle size of the liquid fluorocarbon nano-targeted lipid ultrasound contrast agent was extremely small, uniform, cylindrical and spherical. The cysts in vitro showed that the side of the targeted liquid perfluorocarbon nano-lipid ultrasound contrast agent showed high echo. Conclusions The targeted liquid perfluorocarbon nano-lipid ultrasound contrast agent can be effectively targeted to the human liver cells L02 due to carrying home-made Gal-PLL. The targeted ultrasound contrast agents can be imaging by ultrasound and be confirmed in vitro.The size of the contrast agent was small, therefore, it can be considered an ideal ultrasonic molecular probe and achieve the ultrasound molecular imaging in cell level. Key words: Ultrasonography; Microbubbles; Nanotechnology; Gene Targeting

Neutron threshold activation detectors (TAD) for the detection of fissions

Abstract Prompt fission neutrons are one of the strongest signatures of the fission process. Depending on the fission inducing radiation, their average number ranges from 2.5 to 4 neutrons per fission. They are more energetic and abundant, by about 2 orders of magnitude, than the delayed neutrons (≈3 vs. ≈0.01) that are commonly used as indicators for the presence of fissionable materials. The detection of fission prompt neutrons, however, has to be done in the presence of extremely intense probing radiation that stimulated them. During irradiation, the fission stimulation radiation, X-rays or neutrons, overwhelms the neutron detectors and temporarily incapacitate them. Consequently, by the time the detectors recover from the source radiation, fission prompt neutrons are no longer emitted. In order to measure the prompt fission signatures under these circumstances, special measures are usually taken with the detectors such as heavy shielding with collimation, use of inefficient geometries, high pulse height bias and gamma-neutron separation via pulse-shape discrimination with an appropriate organic scintillator. These attempts to shield the detector from the flash of radiation result in a major loss of sensitivity. It can lead to a complete inability to detect the fission prompt neutrons. In order to overcome the blinding induced background from the source radiation, the detection of prompt fission neutrons needs to occur long after the fission event and after the detector has fully recovered from the source overload. A new approach to achieve this is to detect the delayed activation induced by the fission neutrons. The approach demonstrates a good sensitivity in adverse overload situations (gamma and neutron “flash”) where fission prompt neutrons could normally not be detected. The new approach achieves the required temporal separation between the detection of prompt neutrons and the detector overload by the neutron activation of the detector material. The technique, called Threshold Activation Detection (TAD), is to utilize appropriate substances that can be selectively activated by the fission neutrons and not by the source radiation and then measure the radioactively decaying activation products (typically beta and gamma rays) well after the source pulse. The activation material should possess certain properties: a suitable half-life of the order of seconds; an energy threshold below which the numerous source neutrons will not activate it (e.g., 3 MeV); easily detectable activation products (typically >1 MeV beta and gamma rays) and have a usable cross-section for the selected reaction. Ideally the substance would be a part of the scintillator. There are several good material candidates for the TAD, including fluorine, which is a major constituent of available scintillators such as BaF 2 , CaF 2 and hydrogen free liquid fluorocarbon. Thus the fluorine activation products, in particular the beta particles, can be measured with a very high efficiency in the detector. The principles, applications and experimental results obtained with the fluorine based TAD are discussed.

Kinetics of fluorine binding from gaseous products of thermal decomposition of M-1 fluorocarbon liquid and a telomeric alcohol by alkaline-earth metal oxides and calcium hydroxide

The reactions of products of thermal decomposition of fluorinated compounds with magnesium and calcium oxides and with calcium hydroxide were studied. The kinetic parameters of the processes were determined. Conditions were found for complete binding of fluorine from M-1 fluorocarbon liquid into environmentally safe products, alkaline-earth metal fluorides.

Electrospray ionization mass spectrometry from discrete nanoliter‐sized sample volumes

We describe a method for nanoelectrospray ionization mass spectrometry (nESI-MS) of very small sample volumes. Nanoliter-sized sample droplets were taken up by suction into a nanoelectrospray needle from a silicon microchip prior to ESI. To avoid a rapid evaporation of the small sample volumes, all manipulation steps were performed under a cover of fluorocarbon liquid. Sample volumes down to 1.5 nL were successfully analyzed, and an absolute limit of detection of 105 attomole of insulin (chain B, oxidized) was obtained. The open access to the sample droplets on the silicon chip provides the possibility to add reagents to the sample droplets and perform chemical reactions under an extended period of time. This was demonstrated in an example where we performed a tryptic digestion of cytochrome C in a nanoliter-sized sample volume for 2.5 h, followed by monitoring the outcome of the reaction with nESI-MS. The technology was also utilized for tandem mass spectrometry (MS/MS) sequencing analysis of a 2 nL solution of angiotensin I.

Influence of surface modification on the adhesion between Nitinol wire and fluoropolymer films.

One of the current challenges for the medical device industry is how to manufacture and assemble biomedical implants consisting of a metallic wire component and a fluorocarbon film without the use of an adhesive. In an attempt to answer this question, samples of Nitinol wire and fluorinated ethylene-propylene (FEP) film were surface modified by various treatments before being thermally bonded into a composite pull-out strength test specimen and mechanically tested to determine their adhesion strength. The two surface treatments for Nitinol wire included mechanical roughening with sandpaper, and adding a fluorocarbon coating followed by polymerization and curing by a helium plasma treatment. The two surface treatments for FEP film included helium plasma and helium-oxygen plasma under atmospheric conditions. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements were also taken to characterize the appearance and chemistry of the surfaces before and after modification. A unique pull-out strength test method was developed to assess the level of adhesion between these various candidates. The pull-out force for untreated Nitinol bonded to untreated FEP film was 30.5 +/- 2.4 N. Significant improvements of up to 14% in this level of adhesion were obtained with the mechanically roughened Nitinol wire bonded to the helium plasma treated films. However, coating the wire with a liquid fluorocarbon monomer mixture (TG-10) was not successful and after thermal bonding to FEP film the level of adhesion decreased by over 80%. Thus, the bonding strength between the wire and the film can be significantly improved by mechanically roughening the Nitinol wire and treating the FEP film with helium plasma prior to thermal bonding.

A high-energy 160-ps pulse generation by stimulated Brillouin scattering from heavy fluorocarbon liquid at 1064 nm wavelength

We have achieved a high compression ratio by stimulated Brillouin scattering (SBS) consisting of two long cells. A 13-ns Nd:YAG laser pulse was temporally compressed to about 160-ps phase-conjugated pulse in heavy fluorocarbon FC-40 liquid at a 1064 nm wavelength. The maximum reflectivity of SBS process was over 80 % without an optical damage. The compressed pulse brightness was about 65-fold higher than that of the incident pulse.

Optical nonlinearities in As_2Se_3 chalcogenide glasses doped with Cu and Ag for pulse durations on the order of nanoseconds

We investigate the dependence of the nonlinear optical properties of Cu-doped and Ag-doped As(2)Se(3) glasses on the incident pulse-width at 1.064 microm using the Z-scan technique. In this work, 11.5-ns optical pulses from a Nd:YAG laser were compressed up to 1.6 ns by using stimulated Brillouin scattering in heavy fluorocarbon liquid. The measurement of the pulse-width dependence of the optical nonlinearities leads to the separation of an ultrafast Kerr nonlinearity and a slow (cumulative) nonlinearity such as a thermal nonlinearity. The measured values of the nonlinear refractive index and the nonlinear absorption coefficient of 4 at.% Cu-doped As(2)Se(3) glass (where the normal photodarkening effect is sufficiently suppressed) and 4 at.% Ag-doped As(2)Se(3) glass were proportional to the pulse width, showing that the cumulative nonlinearity is present in these two glasses. The cumulative nonlinearity of these doped glasses is larger than one of the undoped glass. The origin of such slow nonlinearity is presumably attributed to the photostructural changes inherent in chalcogenide glasses and is directly independent of one of photodarkening.

Subcooled Pool Boiling Experiments on Horizontal Heaters Coated With Carbon Nanotubes

Pool boiling experiments were conducted with three horizontal, flat, silicon surfaces, two of which were coated with vertically aligned multiwalled carbon nanotubes (MWCNTs). The two wafers were coated with MWCNT of two different thicknesses: 9 μm (Type-A) and 25 μm (Type-B). Experiments were conducted for the nucleate boiling and film boiling regimes for saturated and subcooled conditions with liquid subcooling of 0–30°C using a dielectric fluorocarbon liquid (PF-5060) as test fluid. The pool boiling heat flux data obtained from the bare silicon test surface were used as a base line for all heat transfer comparisons. Type-B MWCNT coatings enhanced the critical heat flux (CHF) in saturated nucleate boiling by 58%. The heat flux at the Leidenfrost point was enhanced by a maximum of ∼150% (i.e., 2.5 times) at 10°C subcooling. Type-A MWCNT enhanced the CHF in nucleate boiling by as much as 62%. Both Type-A MWCNT and bare silicon test surfaces showed similar heat transfer rates (within the bounds of experimental uncertainty) in film boiling. The Leidenfrost points on the boiling curve for Type-A MWCNT occurred at higher wall superheats. The percentage enhancements in the value of heat flux at the CHF condition decreased with an increase in liquid subcooling. However the enhancement in heat flux at the Leidenfrost points for the nanotube coated surfaces increased with liquid subcooling. Significantly higher bubble nucleation rates were observed for both nanotube coated surfaces.

A microfluidic apparatus for the study of ice nucleation in supercooled water drops

This paper describes a microfluidic instrument that produces drops of supercooled water suspended in a moving stream of liquid fluorocarbon, and measures the temperatures at which ice nucleates in the drops. A microfluidic chip containing a monodisperse drop generator and a straight channel with 38 embedded resistance thermometers was placed in contact with a seven-zone temperature-control plate and imaged under a microscope with a high-speed camera. This instrument can record the freezing temperatures of tens of thousands of drops within minutes, with an accuracy of 0.4 degrees C. The ice-nucleation temperatures in approximately 80-microm drops were reported for the freezing of 37 061 drops of pure water, and of 8898 drops of water seeded with silver iodide. Nucleation of ice in pure water was homogenous and occurred at temperatures between -36 and -37.8 degrees C, while water containing silver iodide froze between -10 and -19 degrees C. The instrument recorded the largest sets of individual freezing temperatures (37 061), had the fastest data acquisition rate (75 measurements/s), and the best optical (3 microm) and temporal (70 micros) resolutions among instruments designed to study nucleation of ice. The dendritic growth of ice in 150-microm drops of supercooled water at -35 degrees C was observed and imaged at a rate of 16 000 frames/s.

Non-contact protein microarray fabrication using a procedure based on liquid bridge formation

Contemporary microarrayers of contact or non-contact format used in protein microarray fabrication still suffer from a number of problems, e.g. generation of satellite spots, inhomogeneous spots, misplaced or even absent spots, and sample carryover. In this paper, a new concept of non-contact sample deposition that reduces such problems is introduced. To show the potential and robustness of this pressure-assisted deposition technique, different sample solutions known to cause severe problems or to be even impossible to print with conventional microarrayers were accurately printed. The samples included 200 mg mL(-1) human serum albumin, highly concentrated sticky cell adhesion proteins, pure high-salt cell-lysis buffer, pure DMSO, and a suspension of 5-microm polystyrene beads. Additionally, a water-immiscible liquid fluorocarbon, which was shown not to affect the functionality of the capture molecules, was employed as a lid to reduce evaporation during microarray printing. The fluorocarbon liquid lid was shown to circumvent hydrolysis of water-sensitive activated surfaces during long-term deposition procedures.

Pulse-width dependence of optical nonlinearities in As_2Se_3 chalcogenide glass in the picosecond-to-nanosecond region

We study the dependence of optical nonlinearities in As(2)Se(3) glass on the incident pulse-width using the Z-scan technique. In this work, 11.5-ns optical pulses from a Nd:YAG laser operating at 1.064 mum were compressed up to 1.6 ns by using stimulated Brillouin scattering in heavy fluorocarbon liquid, where the duration of the compressed pulses depends on the pump energy. Moreover picosecond optical pulses with a 1.053-mum wavelength were utilized for the Z-scan experiments. To investigate the pulse-width dependence of the optical nonlinearities leads to the separation of an ultrafast Kerr nonlinearity and a slow (cumulative) nonlinearity such as a thermal nonlinearity because the magnitude of the cumulative nonlinearity should be proportional to the pulse duration. The experimental results clearly show that both the nonlinear refractive index and the nonlinear absorption coefficient increase linearly with pulse width. The origin of such pulse-width dependence is presumably attributed to photostructural changes inherent in chalcogenide glasses, which are induced not by nonlinear absorption such as two-photon absorption or two-step absorption, but by linear absorption in the weak-absorption region.

Effective Method of Characterizing Specific Liquid Fluorocarbon Interactions Using Ultrasound

Several studies have used the analytical results available for structure factor, osmotic pressure, vapor pressure, and suspension viscosity to characterize nanoparticle interactions. In this work a novel attempt has been made to characterize seven different types of liquid per fluorocarbon nanoparticles (LPFC-np) by estimating packing factor, segment diameter, chemical potential, Rao's constant, and adiabatic and isothermal compressibilities using experimental ultrasonic velocity as input. The segment diameter has also been examined by using experimental surface tension and viscosity for comparison. The calculations were extended for different temperatures involving four different equations of state. We have tested the sensitivity of all these parameters to a very small change in the heat capacity ratio. This extensive calculation helps to make a reasonable description about the interactions among the LPFC-np. Also a better correlation could be determined between the interaction of ultrasound with LPFC-np (as a facilitator) and the pure absorption (propagation) of ultrasound by the entire system.