Alonso Castro

Ultrasensitive, direct detection of a specific DNA sequence of Bacillus anthracis in solution.

A very fast and ultrasensitive method has been developed for the detection and quantitation of specific nucleic and sequences of bacterial origin in solution. The method is based on a two-color, single fluorescent molecule detection technique developed in our laboratory. The technique was applied to the detection of Bacillus anthracis DNA in solution.

Solid-phase extraction microfluidic devices for matrix removal in trace element assay of actinide materials

Advances in sample nebulization and injection technology have significantly reduced the volume of solution required for trace impurity analysis in plutonium and uranium materials. Correspondingly, we have designed and tested a novel chip-based microfluidic platform, containing a 100-µL or 20-µL solid-phase microextraction column, packed by centrifugation, which supports nuclear material mass and solution volume reductions of 90% or more compared to standard methods. Quantitative recovery of 28 trace elements in uranium was demonstrated using a UTEVA chromatographic resin column, and trace element recovery from thorium (a surrogate for plutonium) was similarly demonstrated using anion exchange resin AG MP-1. Of nine materials tested, compatibility of polyvinyl chloride (PVC), polypropylene (PP), and polytetrafluoroethylene (PTFE) chips with the strong nitric acid media was highest. The microcolumns can be incorporated into a variety of devices and systems, and can be loaded with other solid-phase resins for trace element assay in high-purity metals.

Optical trapping microfabrication with electrophoretically delivered particles inside glass capillaries.

We have developed a new technique for rapid microfabrication that uses electrophoretically delivered particles and an optical trap. The material particles, micrometer- and nanometer-sized polystyrene beads in aqueous solution, are continuously delivered to an optical trap by means of the electrophoretic effect inside glass capillaries or similar microstructures. The optical trap is used to manipulate and deposit the polystyrene beads onto a substrate. The continuous, on-demand delivery of particles allows for microfabrication in two and three dimensions with high speed and high efficiency and without material waste. This new technique has many potential applications in microelectronics and biotechnology.

Note: Micro-channel array crucible for isotope-resolved laser spectroscopy of high-temperature atomic beams

We present a novel compact design for a multichannel atomic oven which generates collimated beams of refractory atoms for fieldable laser spectroscopy. Using this resistively heated crucible, we demonstrate spectroscopy of an erbium sample at 1300 °C with improved isotopic resolution with respect to a single-channel design. In addition, our oven has a high thermal efficiency. By minimizing the surface area of the crucible, we achieve 2000 °C at 140 W of applied electrical power. As a result, the design does not require any active cooling and is compact enough to allow for its incorporation into fieldable instruments.

Isotope-resolved atomic beam laser spectroscopy of natural uranium

We present our results on the development of a technique for conducting laser absorption spectroscopy of uranium in a collimated atomic beam using a compact and potentially fieldable device. A solid natural uranium metal sample is vaporized in a modest vacuum of several mTorr via resistive heating of a tantalum foil micro-crucible. A temperature of over 2000 °C is reached by applying only 200 W of electrical power to the crucible. At this temperature, the vapor pressure of uranium is large enough to generate a stable atomic beam. A diode laser is tuned around the 861.031 nm uranium transition, which allows the observation of absorption bands from both the 238U and 235U isotopes. The isotopic composition of uranium Standard Reference Material 960 is obtained from the absorption signal, in excellent agreement with the nominal value. Our approach can be readily applied to the isotopic analysis of other actinides, and it is expected to lead to the development of compact, fieldable instrumentation.

Assessment of the excitation temperatures and Mg II:I line ratios of the direct current (DC) arc source for the analysis of radioactive materials

The direct current (DC) arc plasma has been assessed with an emphasis on excitation temperature (Texe) and ionization/excitation efficiency by monitoring magnesium ionic:atomic ratios (Mg II:I). The primary goal is to improve the analytical performance of the DC arc instrumentation such that more sensitive and reproducible measurements can be achieved when analyzing trace impurities in nuclear materials. Due to the variety of sample types requiring DC arc analysis, an understanding of the plasma’s characteristics will significantly benefit the experimental design when moving forward with LANL’s capabilities for trace metal analysis of plutonium metals.

Analytical Chemistry Developmental Work Using a 243Am Solution

This project seeks to reestablish our analytical capability to characterize Am bulk material and develop a reference material suitable to characterizing the purity and assay of 241Am oxide for industrial use. The tasks associated with this phase of the project included conducting initial separations experiments, developing thermal ionization mass spectrometry capability using the 243Am isotope as an isotope dilution spike , optimizing the spike for the determination of 241Pu-241 Am radiochemistry, and, additionally, developing and testing a methodology which can detect trace to ultra- trace levels of Pu (both assay and isotopics) in bulk Am samples .

Analytical Chemistry and Materials Characterization Results for Debris Recovered from Nitrate Salt Waste Drum S855793

Solid debris was recovered from the previously-emptied nitrate salt waste drum S855793. The bulk sample was nondestructively assayed for radionuclides in its as-received condition. Three monoliths were selected for further characterization. Two of the monoliths, designated Specimen 1 and 3, consisted primarily of sodium nitrate and lead nitrate, with smaller amounts of lead nitrate oxalate and lead oxide by powder x-ray diffraction. The third monolith, Specimen 2, had a complex composition; lead carbonate was identified as the predominant component, and smaller amounts of nitrate, nitrite and carbonate salts of lead, magnesium and sodium were also identified. Microfocused x-ray fluorescence (MXRF) mapping showed that lead was ubiquitous throughout the cross-sections of Specimens 1 and 2, while heteroelements such as potassium, calcium, chromium, iron, and nickel were found in localized deposits. MXRF examination and destructive analysis of fragments of Specimen 3 showed elevated concentrations of iron, which were broadly distributed through the sample. With the exception of its high iron content and low carbon content, the chemical composition of Specimen 3 was within the ranges of values previously observed in four other nitrate salt samples recovered from emptied waste drums.

Single-molecule electrophoresis: applications to biomolecular detection

A new method for the detection and identification of biological molecules at the single molecule level of sensitivity has been developed. The technique involves measuring the electrophoretic velocity of each molecule present in a sample. Since different chemical species generally exhibit different electrophoretic velocities, identification is accomplished by classification according to electrophoretic velocity. The solution is contained in a capillary to which an external voltage is applied, and the velocity is determined by measuring the time taken by an individual molecule to travel the distance between two tightly focused laser beams due to the electrophoretic effect. The detection of the migration of individual molecules through each laser beam was accomplished by a modified version of our recently developed technique of single fluorescent molecule detection. Monte Carlo computer simulations of the process were performed beforehand in order to estimate the experimental feasibility of the method, and to determine the optimum values for the various experimental parameters. The method has been applied to the analysis of single-fluorophore molecules such as rhodamine 6G, and to biological macromolecules, such as mixtures of nucleic acids and of proteins. Applications of the technique to the detection of specific DNA sequences are discussed.