Eli Flaxer

Supersensitive Detection of Explosives by Silicon Nanowire Arrays

There has been a great increase in the development of traceand ultra-trace explosive detection in the last decade, mainlybecause of the globalization of terrorist acts, and thereclamationofcontaminatedlandpreviouslyusedformilitarypurposes. In this regard, detection methods for traces ofexplosives continue to be hampered by the low volatility ofthe analytes and thus, the analytical problem remainschallenging.

Supersensitive fingerprinting of explosives by chemically modified nanosensors arrays

The capability to detect traces of explosives sensitively, selectively and rapidly could be of great benefit for applications relating to civilian national security and military needs. Here, we show that, when chemically modified in a multiplexed mode, nanoelectrical devices arrays enable the supersensitive discriminative detection of explosive species. The fingerprinting of explosives is achieved by pattern recognizing the inherent kinetics, and thermodynamics, of interaction between the chemically modified nanosensors array and the molecular analytes under test. This platform allows for the rapid detection of explosives, from air collected samples, down to the parts-per-quadrillion concentration range, and represents the first nanotechnology-inspired demonstration on the selective supersensitive detection of explosives, including the nitro- and peroxide-derivatives, on a single electronic platform. Furthermore, the ultrahigh sensitivity displayed by our platform may allow the remote detection of various explosives, a task unachieved by existing detection technologies.

Non-covalent Monolayer-Piercing Anchoring of Lipophilic Nucleic Acids: Preparation, Characterization, and Sensing Applications

Functional interfaces of biomolecules and inorganic substrates like semiconductor materials are of utmost importance for the development of highly sensitive biosensors and microarray technology. However, there is still a lot of room for improving the techniques for immobilization of biomolecules, in particular nucleic acids and proteins. Conventional anchoring strategies rely on attaching biomacromolecules via complementary functional groups, appropriate bifunctional linker molecules, or non-covalent immobilization via electrostatic interactions. In this work, we demonstrate a facile, new, and general method for the reversible non-covalent attachment of amphiphilic DNA probes containing hydrophobic units attached to the nucleobases (lipid-DNA) onto SAM-modified gold electrodes, silicon semiconductor surfaces, and glass substrates. We show the anchoring of well-defined amounts of lipid-DNA onto the surface by insertion of their lipid tails into the hydrophobic monolayer structure. The surface coverage of DNA molecules can be conveniently controlled by modulating the initial concentration and incubation time. Further control over the DNA layer is afforded by the additional external stimulus of temperature. Heating the DNA-modified surfaces at temperatures >80 °C leads to the release of the lipid-DNA structures from the surface without harming the integrity of the hydrophobic SAMs. These supramolecular DNA layers can be further tuned by anchoring onto a mixed SAM containing hydrophobic molecules of different lengths, rather than a homogeneous SAM. Immobilization of lipid-DNA on such SAMs has revealed that the surface density of DNA probes is highly dependent on the composition of the surface layer and the structure of the lipid-DNA. The formation of the lipid-DNA sensing layers was monitored and characterized by numerous techniques including X-ray photoelectron spectroscopy, quartz crystal microbalance, ellipsometry, contact angle measurements, atomic force microscopy, and confocal fluorescence imaging. Finally, this new DNA modification strategy was applied for the sensing of target DNAs using silicon-nanowire field-effect transistor device arrays, showing a high degree of specificity toward the complementary DNA target, as well as single-base mismatch selectivity.

Laser wavelength effects on the charge state resolved ion energy distributions from laser-produced Sn plasma

The effects of laser wavelength on the charge state resolved ion energy distributions from laser-produced Sn plasma freely expanding into vacuum are investigated. Planar Sn targets are irradiated at laser wavelengths of 10.6 and 1.064 μm and intensities of 1.8×1010 and 3.4×1011 W/cm2, respectively. These parameters are relevant to the extreme ultraviolet x-ray source application. An electrostatic deflection probe and single channel electron multiplier are used to record the charge state resolved ion energy distributions 100 cm from the laser plasma source. At the longer laser wavelength, higher charge state ions are observed. At both laser wavelengths, the peak ion energies increase approximately linearly as a function of charge state, and all ion energies greatly exceed the initial thermal electron temperature. The differences in the ion energy distributions are attributed to the laser wavelength dependence of the laser energy absorption, the resulting plasma density in the corona, and the subsequent rec...

Programmable smart electron emission controller for hot filament.

In electron ionization source, electrons are produced through thermionic emission by heating a wire filament, accelerating the electrons by high voltage, and ionizing the analyzed molecules. In such a system, one important parameter is the filament emission current that determines the ionization rate; therefore, one needs to regulate this current. On the one hand, fast responses control is needed to keep the emission current constant, but on the other hand, we need to protect the filament from damage that occurs by large filaments current transients and overheating. To control our filament current and emission current, we developed a digital circuit based on a digital signal processing controller that has several modes of operation. We used a smart algorithm that has a fast response to a small signal and a slow response to a large signal. In addition, we have several protective measures that prevent the current from reaching unsafe values.

Implementing of a precision fast thermoelectric cooler controller using a personal computer parallel port connection and ADN8830 controller

A complete design of a compact precision and fast thermoelectric cooler (TEC) controller with a parallel port connection to a personal computer (PC), using a pulse width modulation technique by a dedicated smart driver, and digital control designed using very high-speed integrated circuit hardware description language is presented. The design allows replacement of the PC with an “on board” embedded microcontroller. This circuit is demonstrated as a TEC controller for a high-speed electro-optical modulator.

A low-cost, ultra-fast and low-noise preamplifier for micro channel plates

A compact, low-cost, ultra fast, low distortion and low noise preamplifier suitable for data-acquisition applications utilization micro channel plate (MCP) detectors has been built with a new monolithic integrated circuit amplifier in two stages. The gain, bandwidth and noise are optimized to the MCP performance in order to achieve the best rise time, response and stability with minimal jitter. The use of commercial components makes this instrument very low in cost and easy to build.

Multichannels high voltage programmable driver for piezoelectric transducer

A complete design of a compact, high voltage, multichannel programmable waveform generator, using an 8 bit microcontroller, 12 bit digital to analog converter, and high voltage operation amplifier, is presented. The user can generate the waveform by several options: classic waveform, calculator, freehand drawing, and using excel or text file. All the waveform data are stored in a nonvolatile memory of the microcontroller. The generator can work as a stand-alone instrument or conjoined with a personal computer. We used this generator as a controller for piezoelectric inertial slider.

Fast mass programming controller for a supersonic gas chromatography mass spectrometer

In a gas chromatograph mass spectrometer employing a quadrupole mass filter, molecules are ionized and transferred to a mass analyzer, where their mass to charge ratios (m/z) are measured. After the ionization step, the ions pass through a series of ion lenses that focus and guide them into the mass analyzer. The voltages on these lenses can be optimized for each specific m/z value (as the rest of the system is also optimized) to increase the number of ions reaching the mass analyzer. In certain cases, this dynamic mass-dependent optimization of the lenses can increase the signal by a factor of 2 or more. To implement this dynamic optimization, a digital circuit was developed, based on a digital signal controller and high-voltage (HV) amplifiers, that is able to optimize eight independent HV channels ranging between ±150 V at a rate of 100 µs.

An Alternative Approach in Mechatronics Curricular Development at AFEKA — Tel-Aviv Academic College of Engineering and at Tel-Aviv University

The AFEKA – Tel Aviv Academic College of Engineering has developed a program in mechatronics studies designed not just for students of mechanical engineering but for every student in any field of engineering, as well as for experimentalists in natural sciences. This program supplies the students with tools that allow them to gain interdisciplinary insights and to carry out interdisciplinary final projects. In this paper we outline this program and give a detailed description of some unique features of the mechatronics laboratory.