Holographic optical tweezers and their relevance to lab on chip devices

During the last decade, optical tweezers have been transformed by the combined availability of spatial light modulators and the speed of low-cost computing to drive them. Holographic optical tweezers can trap and move many objects simultaneously and their compatibility with other optical techniques, particularly microscopy, means that they are highly appropriate to lab-on-chip systems to enable optical manipulation, actuation and sensing.     

Extended nanospace chemical systems on a chip for new analytical technology

Integration of chemical processes on a microchemical chip has gained much attention in the past decade, and the basic concepts of micro-integration and the supporting technologies have been intensively developed. As a result, many analytical and chemical synthesis applications were demonstrated. The superior performances were verified including shortening analysis time, decrease of sample and reagent volume, and easy chemical operations. Now, the micro-technologies are moving toward practical applications by establishing the systems in which the microchemical chip works as chemical central processing unit. Recently, as a new research field, integration is further proceeding to the 10(1)-10(3) nm scale, which we call extended nanospace. The extended nanospace locates the gap between the targets of conventional nanotechnology (10(0)-10(1) nm) and micro-technology (>1 μm), and the fluidics and chemistry have not been explored well due to a lack of fundamental technologies. For these purposes, many methodologies were established in recent years. Unique liquid properties were reported, which were quite different from those in microspace. Some properties can be expected by considering the characteristics of microspace and the downscaling, and the others are unexpected or are difficult to predict. These properties enabled new chemical operations which will be quite important as the next analytical technologies. Now, chemistry and fluidics in the extended nanospace are forming a new research field. In this review, we survey the fundamental technologies for extended nanospace researches and introduce several unique liquid properties. Finally, unique chemical operations are also illustrated leading to new analytical operations.     

Measurement of density and chemical concentration using a microfluidic chip

A new microfluidic product for measuring fluid density, specific gravity and chemical concentration has been developed. At the core of this lab-on-a-chip sensor is a vacuum-sealed resonating silicon microtube. Measurements can be made with under a microliter of sample fluid, which is over 1000x less than is conventionally required. Since the product is MEMS-based the overall system size is a fraction of conventional density meters and it weighs much less than the traditional desk-top, temperature controlled, density meters. The syringe or pipette loaded system includes a dynamic temperature control system that operates between 0 degree C and 90 degree C with an accuracy of less than 0.01 degree C. Density measurement accuracies of 4 to 5 digits have been observed with aqueous solutions. Measurement examples and applications will be discussed.     

Controlling volatility in solid-state, redox-based memory devices using heterojunction barriers to ion transport

In this work, we show the ability to tune the volatility of redox-based memory by designing barriers to ion drift. By changing the nature and properties of the barrier material, the key performance metric (ratio of retention time to read/write time) could be altered to yield ratios in the range of 1 to 10(9).     

Studying electronic transport in polyazulene-ionic liquid systems using infrared vibrational spectroscopy

This paper presents an in situ spectroelectrochemical characterization of polyazulene (PAz) and PAz-C(60) composite films using Fourier Transform Infrared Attenuated Total Reflection (FTIR-ATR) spectroscopy. In situ FTIR-ATR spectra were recorded simultaneously as the films were charged and discharged electrochemically. The aim was to clarify how the use of ILs and the addition of C(60) affected the electronic transport and structural changes occurring in PAz during electrochemical charging. We found that electrosynthesis of PAz in an IL lowered the oxidation potential of the film and improved its electroactivity. The FTIR-ATR data also suggest that PAz with a longer effective conjugation length is obtained during electrosynthesis when using ILs. With in situ FTIR-ATR it is possible to quite accurately determine the onset potential for oxidation/reduction. These values are important since they determine the suitability of the polymer for a specific application. Our experiments indicate that two types of charge carriers are formed during electrochemical oxidation of PAz in an IL. Furthermore, their formation is strongly affected by the addition of C(60) into the film. The type of charge carrier formed affects the electronic and possibly also ionic transport within the film. The inclusion of C(60) into PAz influenced the optical and structural properties considerably. In situ FTIR-ATR is also an extremely useful method for studying the potential stability of an IL during electrochemical cycling. We showed that cathodic decomposition of N,N-butyl-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][Tf(2)N]) occurs at less negative potentials than those determined electrochemically.     

Detection of single ion channel activity on a chip using tethered bilayer membranes

Membrane-bound ion channels are promising biological receptors since they allow for the stochastic detection of analytes at high sensitivity. For stochastic sensing, it is necessary to measure the ion currents associated with single ion channel opening and closing events. However, this calls for stability, high reproducibility, and long lifetimes. A critical issue to overcome is the low stability of the ion channel environment, that is, the bilayer membrane. A promising technique to surmount this is to connect the lower part of the membrane to a surface forming a tethered bilayer membrane. By reconstituting the synthetic ion channel, gramicidin A, into a tethered bilayer as part of a microchip design, we have been able to record the activity of single ion channels. The observed activity was compared with that obtained by a conventional electrophysiology method, tip dipping, to confirm its authenticity. These findings allow for the construction of stable biosensors based on ion channels and provide a novel technique for the characterization of ion channel activity.     

Highly selective transport of silver ion through a supported liquid membrane using calix[4]pyrroles as suitable ion carriers

Facilitated transport of silver ion across a supported liquid membrane (SLM) by calix[4]pyrroles, as selective ion carriers, dissolved in kerosene has been investigated. The influences of fundamental parameters affecting the transport of silver ion including ion carrier concentration in the membrane phase, thiosulfate concentration in strip phase, picric acid concentration in the feed phase, stirring speed of aqueous phases, type of membrane solvent and time of transport have been studied. In the presence of thiosulfate as a suitable metal ion acceptor in the strip phase and picrate ion as ion pairing agent in the source phase, transport of silver occurs almost quantitatively after 75 min. The selectivity and efficiency of silver transport from aqueous solution containing Cu²⁺, Mg²⁺, Ni²⁺, Ca²⁺, Zn²⁺, Pb²⁺, Co²⁺, Al³⁺, Hg²⁺, Cd²⁺, Fe³⁺, Fe²⁺ and Cr³⁺ were investigated.     

Extraction and carrier mediated transport of urea using noncyclic receptors through liquid membrane systems

Extraction and carrier mediated transport through bulk liquid membrane and supported liquid membrane systems have wide applications in separation technology. This paper highlights the use of six noncyclic receptors (podands) having variations in chain length and end group for the removal of urea using liquid membrane system. These receptors R_1, R_2, R_3, R_4, R_5, R₆ are diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, diethylene glycol dibenzoate, diethylene glycol, triethylene glycol and tetraethylene glycol respectively. The sequence of extraction and transport of urea by BLM system using various receptors is R₂ > R₃ > R₁ > R₄ > R₅ > R₆ and R₆ ≈ R₃ > R₅ > R₄ > R₁ > R₂ respectively. Receptor R₂ containing butyl end group is best extractant while receptor R₆ with flexible backbone is best carrier and this carrier efficiency is used to remove urea using BLM system from the feed phase by recyclization process up to 88.16%. The experimental results influenced by concentration of receptors and urea. Effect of time was also studied.     

Characterization of the chemical composition of a block copolymer by liquid chromatography/mass spectrometry using atmospheric pressure chemical ionization and electrospray ionization

Liquid chromatography/mass spectrometry (LC/MS) with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in the positive and negative ion modes was used for the characterization of a block copolymer consisting of methoxy poly(ethylene oxide) (mPEO), an epsilon-caprolactone (CL) segment and linoleic acid (LA), used as surfactant in water-based latex paints. Chromatographic separation was obtained based on the number of CL units in the polymer species and the presence of an mPEO and/or LA tail. Different ionization methods were found to be complementary and only their combination allowed the qualitative profiling of the chemical composition. The LC/MS method has proven valuable for following the reaction in time, as well as for comparison of different polymeric surfactants.     

Selective transport of silver ion through a supported liquid membrane using hexathia-18-crown-6 as carrier.

A facile supported liquid membrane (SLM) system for the selective and efficient transport of silver ion is introduced. The SLM used is a thin porous polyvinyldifluoride membrane impregnated with hexathia-18-crown-6 (HT18C6) dissolved in nitrophenyloctyl ether. HT18C6 acts as a specific carrier for the uphill transport of Ag+ ion as its picrate ion paired complex through the SLM. In the presence of thiosulfate ion as a suitable stripping agent in the strip solution, transport of silver occurs almost quantitatively after 4 h. The selectivity and efficiency of silver transport from aqueous solutions containing other Mn+ cations such as Mg2+, Ca2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+, Hg2+, Fe3+ and Cr3+ ions were investigated.     

Effect of a lanthanide ion on the micellation and self-organization of lyotropic liquid crystal systems

Lanthanide-containing lyotropic liquidcrystalline systems were synthesized and their phase behavior, as well as the micellar behavior of aqueous solutions of decaethylene glycol monodecyl ether in the absence and presence of a lanthanide ion, were studied. Tensimetry and conductometry were used to determine the critical micellation concentration, and the values obtained by these methods were found to be in close agreement with each other. Polarization microscopy observations showed that, in concentrated aqueous solutions, ordered lyotropic mesophases arise. The parameters of the phase transitions in the systems under study were determined. The mesophase obtained was demonstrated to have a 2D hexagonal supramolecular structure.     

Searching lab on a chip literature: the need for a glossary of terms and concepts in a multidisciplinary environment

This paper investigates the problem of searching literature in a multidisciplinary environment. It is found that much relevant literature is not found because other disciplines use a different terminology, different units, or slightly different (but related) concepts. The paper suggests some approaches to enhance interdisciplinary understanding and improve exchange of ideas and literature.     

Perfusion and chemical monitoring of living cells on a microfluidic chip

A microfluidic device that incorporates continuous perfusion and an on-line electrophoresis immunoassay was developed, characterized, and applied to monitoring insulin secretion from single islets of Langerhans. In the device, a cell chamber was perfused with cell culture media or a balanced salt solution at 0.6 to 1.5 microL min(-1). The flow was driven by gas pressure applied off-chip. Perfusate was continuously sampled at 2 nL min(-1) by electroosmosis through a separate channel on the chip. The perfusate was mixed on-line with fluorescein isothiocyanate-labeled insulin (FITC-insulin) and monoclonal anti-insulin antibody and allowed to react for 60 s as the mixture traveled down a 4 cm long reaction channel. The cell chamber and reaction channel were maintained at 37 degrees C. The reaction mixture was injected onto a 1.5 cm separation channel as rapidly as every 6 s, and the free FITC-insulin and the FITC-insulin-antibody complex were separated under an electric field of 500 to 600 V cm(-1). The immunoassay had a detection limit of 0.8 nM and a relative standard deviation of 6% during 2 h of continuous operation with standard solutions. Individual islets were monitored for up to 1 h while perfusing with different concentrations of glucose. The immunoassay allowed quantitative monitoring of classical biphasic and oscillatory insulin secretion with 6 s sampling frequency following step changes in glucose from 3 to 11 mM. The 2.5 cm x 7.6 cm microfluidic system allowed for monitoring islets in a highly automated fashion. The technique should be amenable to studies involving other tissues or cells that release chemicals.     

Determination of nivalenol and deoxynivalenol in wheat using liquid chromatography-mass spectrometry with negative ion atmospheric pressure chemical ionisation.

A new, rapid and sensitive method has been developed for the determination of nivalenol (NIV) and deoxynivalenol (DON) by using HPLC in combination with an atmospheric pressure chemical ionization (APCI)-interface and a single quadrupole mass spectrometer. Different LC and MS parameters have been optimized prior to this in order to obtain better results and sensitivity. The effect of nebulizing temperature on the sensitivity and fragmentation of NIV and DON in an APCI interface was investigated. Also, the influence of the cone voltage on the fragmentation pattern was studied, which was shown to have a tremendous effect. Furthermore, the effect of modifiers such as ammonium acetate, acetic acid and ammonia on the ionisation yield of the above substances have been investigated. The extraction was carried out using acetonitrile-water. A two step purification was then applied on two different Mycosep clean up columns. We have used a modified, rapid and isocratic HPLC method combined with a negative ion APCI-MS for the separation and quantitative determination of NIV and DON in wheat extract. An RP C18 column was used for the separation of selected compounds in wheat extract with water-acetonitrile-methanol (82:9:9, v/v/v) at a flow-rate of 1 ml/min without a split. Calibration curves show good linearity and reproducibility. The detection limit and precision were determined for NIV and DON. Both compounds could be detected down to microg/kg level in wheat using selected ion monitoring of the [M-H]- ions and the main fragments.     

Study of the effect of the membrane composition on ion transfer across a supported liquid membrane

The rate of ion transfer across the supported liquid membrane (SLM) is studied in the rotating diffusion cell (RDC), varying the chemical composition of the SLM from net-cloth supported gel membranes to radiation-grafted polymer membranes. Steady-state current–voltage curves are measured as a function of the rotation rate, and values for the standard rate constant, k⁰, are determined for a series of tetraalkylammonium cations from the analysis of the initial slopes and the diffusion limiting currents. The analysis gives values for k⁰ of the order of 10⁻²–10⁻⁴ cm s⁻¹, which is in rather good agreement with the values found in the literature for this type of the system. As controlled delivery of ionic drugs can be achieved by control of the electric current, whereby the SLM acts as a drug reservoir, the study is extended to the release of the anti-Alzheimer drug Tacrine, where ion-exchange fibers are embedded in the membrane as the drug carrier. Our previous transient experiments are also discussed, and it is suggested that their interpretation is seriously hampered by the non-uniform potential distribution, which brings about high capacitive currents.     

Modelling monopolar and bipolar switching in ferroelectric liquid crystal devices using a three variable theory

The switching process in ferroelectric liquid crystal devices takes place through the formation and evolution of domains, which can be modelled using a three variable approach. Here we discuss details of the model which are necessary in order to reproduce the domain nucleation and switching times as a function of applied voltage for both monopolar and bipolar pulses. We show that in order to reproduce data correctly the model must incorporate a complex empirical elastic stress term.