Nazar Ileri

Biotechnical and other applications of nanoporous membranes

Recent advances mean that arrays of nearly uniform cylindrical, conical and pyramidal shaped pores can be produced in several types of substrates. Surface modification of nanopore surfaces can give unique mass transport characteristics that have recently been explored for biomolecule separation, detection and purification. Recent interest has focused on the use of nanoporous membranes for mass transfer diodes that act analogous to solid-state devices based on electron conduction. Asymmetric pores such as conical pores can show superior performance characteristics compared to traditional cylindrical pores in ion rectification. However, many phenomena for membranes with asymmetric pores still remain to be exploited in biomolecular separation, biosensing, microfluidics, logic gates, and energy harvesting and storage.

Nanopillar array on a fiber facet for highly sensitive surface-enhanced Raman scattering

A highly-sensitive optical fiber surface-enhanced Raman scattering (SERS) sensor has been developed by interference lithography. While one facet of the optical fiber is patterned with silver-coated nanopillar array as a SERS platform, the other end of the probe is used, in a remote end detection, to couple the excitation laser into the fiber and send the SERS signal to the spectrometer. SERS performance of the probe is characterized using trans-1,2-bis(4-pyridyl)-ethylene (BPE) monolayer and an enhancement factor of 1.2 × 10(7) can be achieved by focusing the laser directly onto the nanopillar array (front end detection). We also demonstrate that this probe can be used for in situ remote sensing of toluene vapor by the remote end detection. Such a fiber SERS probe shows great potential for molecular detection in various sensing applications.

Effects of pH Strategy on endo- and exo-Metabolome Profiles and Sodium Potassium Hydrogen Ports of β-Lactamase-Producing Bacilluslicheniformis

The effects of pH strategy on endo- and exo-metabolome profiling of beta-lactamase-producing Bacillus licheniformis were investigated at controlled-pH (pH(C) = 6.5, 6.75, 7.0, 7.25, 7.5) and uncontrolled-pH (pH(UC) = 7.5) values using a glucose-based defined medium. The cell concentration profiles were not affected by the pH considerably within the investigated range. The highest enzyme activities were obtained as A = 54 U cm(-)(3) at pH(C) = 6.75 among the controlled-pH operations and as A = 57 U cm(-3) at the uncontrolled-pH pH(UC) = 7.5. At all conditions, oxygen transfer resistances were more effective, whereas the limitation increased in the beta-lactamase production phase. Total intracellular amino acid concentrations ranged between 0.142 and 6.766 kg m(-3) (0.0058-0.277 g g(cell)(-1)), and their concentrations in terms of kg m(-3) were, at most, 580-fold higher than the extracellular concentrations. Methionine/cysteine concentrations were generally higher than the other intracellular amino acids, whereas asparagine concentration was the highest in the fermentation broth. From Na(+), K(+), and H(+) ion profiles, Na(+)-K(+) antiport and Na(+)-H(+) symport were found to be present within the system, and a correlation was found between organic acid transport and Na(+)-H(+) symport. Intracellular organic acid concentrations in terms of kg m(-3) were, at most, 20-fold higher than that of the extracellular, and with the increase in pH, extracellular acetic acid concentration increased and lactic acid concentration decreased. Average permeability coefficient values of organic acids were found to be in the range from 4.10 x 10(-7) to 4.32 x 10(-6) cm s(-1) for the growth phase (0 < t < 6 h) and decreased at least 3-fold in the beta-lactamase production phase (8 < t < 15 h), indicating the considerable structural change of the lipid membrane during the fermentation.

Fabrication of functional silicon-based nanoporous membranes

Macroscopic porous membranes with pore diameter uniformity approaching the nanometer scale have great potential to significantly increase the speed, selectivity, and efficiency of molecular separations. We present fabrication, characterization, and molecular transport evaluation of nanoporous thin silicon-based sieves created by laser interferometric lithography (LIL). This fabrication approach is ideally suited for the integration of nanostructured pore arrays into larger microfluidic processing systems, using a simple all-silicon lithographic process. Submilli-meter-scale planar arrays of uniform cylindrical and pyramidal nanopores are created in silicon nitride and silicon, respectively, with average pore diameters below 250 nm and significantly smaller standard error than commercial polycarbonate track etched (PCTE) membranes. Molecular transport properties of short cylindrical pores fabricated by LIL are compared to those of thicker commercial PCTE membranes for the first time. A 10-fold increase in pyridine pore flux is achieved with thin membranes relative to commercial sieves, without any modification of the membrane surface.

Efficient Nanoporous Silicon Membranes for Integrated Microfluidic Separation and Sensing Systems

Nanoporous devices constitute emerging platforms for selective molecule separation and sensing, with great potential for high throughput and economy in manufacturing and operation. Acting as mass transfer diodes similar to a solid-state device based on electron conduction, conical pores are shown to have superior performance characteristics compared to traditional cylindrical pores. Such phenomena, however, remain to be exploited for molecular separation. Here we present performance results from silicon membranes created by a new synthesis technique based on interferometric lithography. This method creates millimeter sized planar arrays of uniformly tapered nanopores in silicon with pore diameter 100 nm or smaller, ideally-suited for integration into a multi-scale microfluidic processing system. Molecular transport properties of these devices are compared against state-of-the-art polycarbonate track etched (PCTE) membranes. Mass transfer rates of up to fifteen-fold greater than commercial sieve technology are obtained. Complementary results from molecular dynamics simulations on molecular transport are reported.

Phosphate enrichment and fed-batch operation for prolonged β-lactamase production by Bacillus licheniformis

Aims:  Investigation of the phosphate effect and feeding strategy, i.e. linear and exponential feeding, to improve β‐lactamase production by Bacillus licheniformis considering the viability of the cells.

Graphene and nano-diamond synthesis in expansions of molten liquid carbon

Despite their widespread use in high-pressure experiments, little is known about the physical and chemical properties of carbon-containing materials as they expand and cool to ambient conditions. As a result, interpretation of experiments can rely on use of unconstrained models with poor accuracy for the ensuing equation of state properties and final chemical products. To this end, we use quantum simulations to study the free expansion and cooling of carbon from metallic liquid states achieved during shock compression. Expansions from three different sets of shock conditions yielded of a variety of chain and ring structures. We then quantify the relative amounts of graphite-like and diamond-like particles formed during cooling and equilibration. We observe that for all cases, graphene sheets are the majority product formed with more extreme initial conditions producing increasingly larger amounts of diamond particles. Our results can address key needs for future meso-scale models of experiments, where knowledge of material properties and chemical end products can have a pronounced effect on interpreting experimental observables.

Detection of volatile organic compounds by surface enhanced Raman scattering

We present the detection of volatile organic compounds directly in their vapor phase by surface-enhanced Raman scattering (SERS) substrates based on lithographically-defined two-dimensional rectangular array of nanopillars. The type of nanopillars is known as the tapered pillars. For the tapered pillars, SERS enhancement arises from the nanofocusing effect due to the sharp tip on top. SERS experiments were carried out on these substrates using various concentrations of toluene vapor. The results show that SERS signal from a toluene vapor is strongly influenced by the substrate temperature, and the toluene vapor can be detected within minutes of exposing the SERS substrate to the vapor. A simple adsorption model is developed which gives results matching the experimental data. The results also show promising potential for the use of these substrates in environmental monitoring of gases and vapors.

Quantum molecular dynamics simulations of liquid benzene using orbital optimization

The structure of liquid benzene is investigated by quantum molecular dynamics simulations. Results using variationally optimized numerical pseudo-atomic orbitals are compared to those of generic optimized orbitals. The accuracy of the first-principle calculations is compared with recent experimental findings. Simulations using minimal basis sets with optimized orbitals are shown to successfully predict the local structure of liquid benzene, while simulations with non-optimized minimal basis sets have significant errors in the structure of the first solvation shell. The use of a minimal optimized basis set considerably speeds up simulations, while preserving much of the accuracy of a larger basis set formed by generic orbitals. The transferability of the optimized orbitals is also explored under different environmental conditions.

Study of Electrophoretic Mobility of Proteins in Agarose and Poly-Acrylamide Gels

Gel electrophoresis is among the most widely used techniques for separation, characterization, and purification of proteins, nucleic acids, and other molecules including peptides, amino acids, and nucleotides. Electrophoretic measurements can rapidly and reproducibly characterize the size, charge, shape, and purity of these molecules. In this work, we present new measurements of electrophoretic mobility of the protein bovine serum albumin (BSA) in agarose and poly-acrylamide gels, using an optical technique that employs a modified spectrophotometer. The molecular transport rate of BSA due to imposition of a known electric field is investigated in (2-6 %, w/w) agarose gel as well as in (5-15%, w/w) poly-acrylamide gel. By directing the collimated light of the spectrophotometer through a gel/protein matrix, we characterize the molecular motion of the protein under the influence of an applied electric field. We thereby measure the electrophoretic mobility of BSA in agarose gels for the first time, and compare these results directly with the BSA mobility measured in poly-acrylamide gels.This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.