A high voltage asymmetric waveform generator for FAIMS

High field asymmetric waveform ion mobility spectrometry (FAIMS) has been used increasingly in recent years as an additional method of ion separation and selection before mass spectrometry. The FAIMS electrodes are relatively simple to design and fabricate for laboratories wishing to implement their own FAIMS designs. However, construction of the electronics apparatus needed to produce the required high magnitude asymmetric electric field oscillating at a frequency of several hundred kilohertz is not trivial. Here we present an entirely custom-built electronics setup capable of supplying the required waveforms and voltages. The apparatus is relatively simple and inexpensive to implement. We also present data acquired on this system demonstrating the use of FAIMS as a gas-phase ion filter interface to an ion trap mass spectrometer.     

A time-coded multi-concentration microfluidic chemical waveform generator for high-throughput probing suspension single-cell signaling

The cellular response to the complex extracellular microenvironment is highly dynamic in time and type of extracellular matrix. Accurately reconstructing this process and analyzing the changes in receptor conformation on the cell membrane surface and intracellular or intercellular signaling has been a major challenge in analytical chemistry and biophysical methodology. In this paper, a time-coded multiconcentration microfluidic chemical waveform generator was developed for the dynamic signaling ...     

A programmable spin-free method for configuration interaction

In this note a method is presented for quick implementation of configuration interaction (CI) calculations in molecules. A spin-free Hamiltonian for anN electron system in a spin stateS, expressed in terms of the generators for the unitary group algebra, is diagonalized over orbital configurations forming a basis for the irreducible representation [2^1/2N-S 1^2S ] of the permutation group S _N . It has been found that the basic algebraic expressions necessary for the CI calculation involve a limited category of permutations. These have been displayed explicitly. On leave from the Indian Institute of Technology, Bombay, India.     

A simple technetium generator

A systematic study on the extraction of⁹⁹Mo and its daughter^99mTc by pure organic diluents and dinonylnaphthalinesulfonic acid (DNNS) is described. The aqueous phases used are H₂SO₄, HCl, KI and their binary mixture solutions. The effect of alcohols on the distribution coefficient has been investigated. As a result of the study, a simple and rapid generator is built for the production of pure^99mTc from⁹⁹Mo.     

A triangular wave form generator

A simple generator for triangular waveforms is described. It uses two operational amplifiers to give triangular waves between 0 V and a preselected voltage. The scan rate and limit can be varied independently.     

A programmable molecular diode driven by charge-induced conformational changes

The 3-nitro-2-(3'-nitro-2'-ethynylpyridine)-5-thiopyridine molecule shows charge-induced conformational switching and a rectifying behavior with a charge-induced controllable switching. This device can be used as a memory operated with an external field interacting with one of the rings local dipole. Alternatively, the molecule can be used as a nano-actuator controlling the rotation of the ring by charging the molecule with a bias voltage.     

A programmable microfluidic cell array for combinatorial drug screening

We describe the development of a fully automatic and programmable microfluidic cell culture array that integrates on-chip generation of drug concentrations and pair-wise combinations with parallel culture of cells for drug candidate screening applications. The device has 64 individually addressable cell culture chambers in which cells can be cultured and exposed either sequentially or simultaneously to 64 pair-wise concentration combinations of two drugs. For sequential exposure, a simple microfluidic diffusive mixer is used to generate different concentrations of drugs from two inputs. For generation of 64 pair-wise combinations from two drug inputs, a novel time dependent variable concentration scheme is used in conjunction with the simple diffusive mixer to generate the desired combinations without the need for complex multi-layer structures or continuous medium perfusion. The generation of drug combinations and exposure to specific cell culture chambers are controlled using a LabVIEW interface capable of automatically running a multi-day drug screening experiment. Our cell array does not require continuous perfusion for keeping cells exposed to concentration gradients, minimizing the amount of drug used per experiment, and cells cultured in the chamber are not exposed to significant shear stress continuously. The utility of this platform is demonstrated for inducing loss of viability of PC3 prostate cancer cells using combinations of either doxorubicin or mitoxantrone with TRAIL (TNF-alpha Related Apoptosis Inducing Ligand) either in a sequential or simultaneous format. Our results demonstrate that the device can capture the synergy between different sensitizer drugs and TRAIL and demonstrate the potential of the microfluidic cell array for screening and optimizing combinatorial drug treatments for cancer therapy.     

A computer-based storage and retrieval system for electronic absorption spectra

A computer-based system for storage and retrieval of spectra in the ultra-violet region, with absorbance as the observed variable, is described. Differences in concentration between solutions relating to observed and stored spectra are automatically adjusted. The entire spectral curve is stored, not only selected points such as maxima etc.; this makes it possible to investigate the spectral range continuously during the retrieval procedure. The increment between two observations (absorbance values) is 2 nm on the wavelength axis.The input medium is punched cards containing values taken directly from observed (catalogued) spectra. The output is a printed list, giving information about observed and retrieved spectra, system parameters used during the retrieval procedure, etc. An important feature of the system is that displacements between observed and stored spectra are allowed for, in two dimensions during comparison, thus taking into account 'chromic' effects. Information about partial identity between observed and stored (retrieved) spectra is given, even if this partial identity exists in dislocated wavelength regions. To test the program, constructed (test) curves as well as real spectra were used. The system is capable of collecting in groups substances with common spectral characteristics, and thus substances belonging to the same class of chemical compounds. This makes the system a valuable tool not only for identification work but also for the study of spectral behaviour in general.     

Dielectrophoresis-based programmable fluidic processors

Droplet-based programmable processors promise to offer solutions to a wide range of applications in which chemical and biological analysis and/or small-scale synthesis are required, suggesting they will become the microfluidic equivalents of microprocessors by offering off-the-shelf solutions for almost any fluid based analysis or small scale synthesis problem. A general purpose droplet processor should be able to manipulate droplets of different compositions (including those that are electrically conductive or insulating and those of polar or non-polar nature), to control reagent titrations accurately, and to remain free of contamination and carry over on its reaction surfaces. In this article we discuss the application of dielectrophoresis to droplet based processors and demonstrate that it can provide the means for accurately titrating, moving and mixing polar or non-polar droplets whether they are electrically conductive or not. DEP does not require contact with control surfaces and several strategies for minimizing surface contact are presented. As an example of a DEP actuated general purpose droplet processor, we show an embodiment based on a scaleable CMOS architecture that uses DEP manipulation on a 32 x 32 electrode array having built-in control and switching circuitry. Lastly, we demonstrate the concept of a general-purpose programming environment that facilitates droplet software development for any type of droplet processor.     

A new continuous hydride generator for ICP-AES

With the construction of a tubular hydride generator some of the technical inconveniences of the hydride generation technique are overcome. The system allows the determination of hydride forming elements and mercury with a sample uptake rate of 1 ml/min without loss of sensitivity. Due to the small volume of the reactor and the performed neutralization of the reaction mixture in the siphon the memory effect is reduced. The sodium hydroxide used for neutralization also prevents the generation of an excess of hydrogen and therefore removes its negative influence on the plasma discharge.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

A109Cd/109mAg generator

Sorption of Cd and Ag by a cation exchange resin has been studied at different molarities of nitric acid. The sorption capacity of Cd on a cation exchanger has been determined. A¹⁰⁹Cd/^109mAg generator is suggested, based on the sorption of Cd on AG 50W-X8 organic cation exchanger at 0.01M HNO₃.^109mAg is eluted with 0.2M NaCl, physiologically compatible for human use.     

A modified sorbent for99mTc generator

A modified sorbent for^99mTe generators of higher activities has been developed. The sorbent consists of two layers. The layer in which (F.P.)⁹⁹Mo is adsorbed contains alumina and silica gel mixture in the weight ratio 40∶60%. The underlaying layer contains 0.5% g of pure alumina. The performances of the columns filled with this sorbent are compared to these containing pure alumina with respect to the total elution efficiency of^99mTc and the elution efficiency ratio of subsequent elutions. Radiochemical and radionuclidic purities (⁹⁹Mo breakthrough) of eluates from both kinds of columns have also been determined and compared.     

A personal computer-based data control interface for neutralization-reionization and tandem mass spectrometry

An improved data-acquisition and management system interfaces an IBM-compatible personal computer to a tandem mass spectrometer. In addition to increased spectral resolution and storage, the control system measures the absolute abundance (peak areas) of product ions, and also that of the precursor; these are capabilities critical for collisional activation, metastable ion decomposition and neutralization-reionization mass spectra. Improved experimental control features include multiple mass range and repetitive scan selection, spurious transient rejection and comparative spectral display.     

A new high temperature gas chromatograph incorporating a temperature programmable direct injector

A high temperature gas chromatograph has been developed which is capable of operating at column oven temperatures up to 500°C. In addition, the detector can operate at temperatures up to 500°C, and the injector up to 450°C. The injector on this instrument is a temperature programmable direct injector, designed specifically to introduce labile or high molecular weight samples into the GC without molecular weight discrimination. The design of this GC and injector will be described, and high temperature applications will be discussed.     

A new method for99mTc generator preparation

The authors report here a new approach for making^99mTc generators based on neutron irradiation of metallic molybdates and direct elution eliminating intermediate chemical processing steps. This approach tested using zirconium molybdate was found to yield^99mTc with good yield and purity. This seems to be the simplest way of making column type^99mTc generator even using low flux reactors and merits further detailed evaluation.     

A generator for preparation of carrier-free224Ra

The construction of a dynamic generator for the separation of carrier-free²²⁴Ra is described. The mother²²⁸Th was extracted on the top of the column with di-(2-ethylhexyl)phosphoric acid on hydrophobized Chromosorb W DMCS. The function of the generator was checked during 6 months by measuring the decontamination of²²⁴Ra from²²⁸Th. Simultaneously the yield of²²⁴Ra was determined as a function of the HCl concentration and of the means of milking. The best results were obtained with 0.01–0.1M HCl; the yield was about 75% of the theoretical value, and the²²⁴Ra contained less than 0.01% of²²⁸Th.     

A generator of peroxynitrite activatable with red light

The generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) as “unconventional” therapeutics with precise spatiotemporal control by using light stimuli may open entirely new horizons for innovative therapeutic modalities. Among ROS and RNS, peroxynitrite (ONOO⁻) plays a dominant role in chemistry and biology in view of its potent oxidizing power and cytotoxic action. We have designed and synthesized a molecular hybrid based on benzophenothiazine as a red light-harvesting antenna joined to an N-nitroso appendage through a flexible spacer. Single photon red light excitation of this molecular construct triggers the release of nitric oxide (˙NO) and simultaneously produces superoxide anions (O₂˙⁻). The diffusion-controlled reaction between these two radical species generates ONOO⁻, as confirmed by the use of fluorescein-boronate as a highly selective chemical probe. Besides, the red fluorescence of the hybrid allows its tracking in different types of cancer cells where it is well-tolerated in the dark but induces remarkable cell mortality under irradiation with red light in a very low concentration range, with very low light doses (ca. 1 J cm⁻²). This ONOO⁻ generator activatable by highly biocompatible and tissue penetrating single photon red light can open up intriguing prospects in biomedical research, where precise and spatiotemporally controlled concentrations of ONOO⁻ are required.

Excitation of a molecular hybrid with highly biocompatible red light generates cytotoxic peroxynitrite, produces red fluorescence useful for cell tracking and induces remarkable cancer cell death at very low concentrations and very low light doses.