Ariel Shemesh

Molecular recognition induced mechanics: isotope effects in the interaction between gas phase substances and polymer-coated microcantilevers

A novel Porous-Silicon-Over-Silicon (PSOS) chemomechanical microcantilever sensor for the isotope discrimination of gas phase substances is presented. A strong isotope effect is observed in the guest induced PSOS microcantilever bending curves of novel poly-4-vinylpyridine (P4VP) coated microcantilevers. Isotopologues of ethanol and water exhibit a clear difference in their time dependent bending response patterns. While the sorption of protiated isotopologues exhibits Langmuir-type sorption curves, deuterated isotopologues exhibit anomalous bending overshoot curves.

NEMS/MEMS cantilever-based biosensors: addressing the open issues

The impressive developments in micro / nano-electro-mechanical-systems (MEMS; NEMS) have led to a new class of chemical and biological sensors based on micro and nano cantilevers. This work focuses on fabrication challenges of flat cantilevers exhibiting well-controlled, uniform and reproducible mechanical performance. Our experimental study is based on cantilevers made of crystalline silicon (c-Si), using SOI wafers as the starting material and using bulk micromachining. Experimental results on fabrication and characterization of composite porous silicon-crystalline silicon microcantilevers made of SOI wafers are also presented, where the porous silicon surface provides an excellent interface for immobilization of the biosensing layer. The optimal geometric design of microcantilevers depending on the application as well on the selected sensing mode (static or dynamic) is considered. The innovative aspects and open issues of NEMS/MEMS cantilever-based biosensors are addressed.

Vertically Integrated MEMS SOI Composite Porous Silicon-Crystalline Silicon Cantilever-Array Sensors: Concept for Continuous Sensing of Explosives and Warfare Agents

This study focuses on arrays of cantilevers made of crystalline silicon (c-Si), using SOI wafers as the starting material and using bulk micromachining. The arrays are subsequently transformed into composite porous silicon-crystalline silicon cantilevers, using a unique vapor phase process tailored for providing a thin surface layer of porous silicon on one side only. This results in asymmetric cantilever arrays, with one side providing nano-structured porous large surface, which can be further coated with polymers, thus providing additional sensing capabilities and enhanced sensing. The c-Si cantilevers are vertically integrated with a bottom silicon die with electrodes allowing electrostatic actuation. Flip Chip bonding is used for the vertical integration. The readout is provided by a sensitive Capacitance to Digital Converter. The fabrication, processing and characterization results are reported. The reported study is aimed towards achieving miniature cantilever chips with integrated readout for sensing explosives and chemical warfare agents in the field.

Detection of Alkylating Agents using Electrical and Mechanical Means

Alkylating agents are reactive molecules having at least one polar bond between a carbon atom and a good leaving group. These often simple molecules are frequently used in organic synthesis, as sterilizing agents in agriculture and even as anticancer agents in medicine. Unfortunately, for over a century, some of the highly reactive alkylating agents are also being used as blister chemical warfare agents. Being relatively simple to make, the risk is that these will be applied by terrorists as poor people warfare agents. The detection and identification of such alkylating agents is not a simple task because of their high reactivity and simple structure of the reactive site. Here we report on new approaches to the detection and identification of such alkylating agents using electrical (organic field effect transistors) and mechanical (microcantilevers) means.

Detection of Alkylating Agents Using Optical, Electrical and Mechanical Means

Alkylating agents, such as methyl iodide, dichloromethane and epichlorohydrin, are commonly used in organic synthesis as reagents and solvents. The alkylating agents, such as methyl bromide, are still used as soil steriliers, while nitrogen mustards are being used as anticancer drugs. Alkylating agents are also dangerous byproducts of the water purification process. Unfortunately, due to their ease of production and storage, those materials are also used as chemical warfare agents. Owing to their ability to react with nucleophiles in our body, most of these materials are toxic, carcinogenic and mutagenic. The combination of simple synthesis with aggressive reaction with biological tissues makes many alkylating agents perfect potential chemical warfare agents for the underdogs and thus a perfect terror inflicting weapon. Therefore, there is a clear need for simple, sensitive and informative tools for the detection and identification of such agents, especially in the gas phase.

Microcantilevers as a sensitive platform for detection of volatile substances and explosives

Microcantilevers are versatile platform for sensing applications. The interaction of APTES coated microcantilevers with different volatile substances and TNT is studied. While the interaction of the studied volatiles with APTES is labile, the interaction of TNT with APTES is strong giving rise to high sensitivity and selectivity. Moreover, the experiments done with TNT are at air atmosphere, showing the strong ability of detection at harsh conditions. These results serve as a corner stone in the development of a small, reliable sensor for explosives.

Microcantilevers as artificial nose platform

In recent years, explosive based terrorism has grown enormously; moreover, chemical warfare is forecasted as the next terror inflicting agents. Detecting such materials is a challenging task. Aiming towards “artificial nose”, we take advantage of highly sensitive porous silicon microcantilevers devices in combination with non specific polymer layers and monitor their interaction with target analytes. Our screening method is through passive and active modes of detection and has been proved effective for distinguishing between different isotopically labeled substances.