Gas Chemical Microsensor
Selective Gas Chemical Microsensors Based on Coordinational Rare Metal Compounds
Tech Area / Field
- ENV-MIN/Monitoring and Instrumentation/Environment
8 Project completed
Senior Project Manager
State Institute of Rare Metals, Russia, Moscow
- Lomonosov Academy of Fine Chemical Technologies, Russia, Moscow
- University of Arkansas/Center for Sensing Technology and Research, USA, AR, Fayetteville\nUniversity of Linköping / Institute of Physics and Measurement Technology, Sweden, Linköping
Project summaryThe project is pided up into several goals, that are integrated into one ultimate outcome: the manufacture of cheap selective sensors for electron-donating gases such as ammonia, hydrazine, hydroxylamine, amines, and hydrosulfuric acid.
Our scientists have developed a large library of metalloporphyrins over the last several years. Some of these compounds have been reported in Western scientific journals while others have not. This library of compounds provides us with an extensive list of compounds to use as the bases for selective gas sensors.
Studied metalloporphyrins are able to provide better gas selectivity than devices which rely on various types of non-selective dopants. In addition, most porphyrins or other transducing molecules are immobilized on the surface of the sensor by covalent attachment, or trapped in a polymer matrix or self assembling film, providing a stable and reliable device.
Metalloporphyrins are directly deposited onto a silicon-metal or “sital” substrate. Sital an alternative substrate to silicon, and has been used extensively by the engineering community in Russia. Our choice of materials and deposition methods are such that, not only does the catalytic activity in the film provide a selective measure of gaseous compounds, but the film is also stable enough to be used in aggressive media. The durability of these devices should be impressive: practically insoluble in water, resistive to cracking, and chemical attack.
The project makes extensive use of former Russian weapon scientist and technology and material previously unknown to the West. We expect our sensors to meet or exceed the performance of all other sensors currently in use.
The existing means of the atmospheric monitoring are plagued by the high price of existing precision gas analyzers (from $10,000 to $1,000,000 and up). Once returned to the laboratory, samples are expensive to analyze requiring highly qualified personnel operating bulky and expensive equipment. Because atmospheric pollutants typically travel over hundreds of kilometers, numerous samples over a large area often required, but in practice are rarely obtained or analyzed due to the limitations of the current methodology. Clearly new instrumentation and methods for monitoring toxic atmospheric pollutants is needed.
Small, portable, inexpensive, mass-produced chemical sensors for electron donating gases such as ammonia, hydrazine, hydroxylamine, amines, and hydrosulfuric acid, could provide the instrumentation necessary for atmospheric monitoring over large areas.
Numerous types of chemical sensors currently exist, but often do not meet the required, sensitivity, selectivity, speed, reproducibility, and reusability need for continuous and repetitive operation. The fundamental problem with all current systems is found in the transducing element itself, the part of the device which converts the concentration of the gas to a electrical signal which can be measured. Many of these transducers have low sensitivity and selectivity, are unstable, and have a short useful life.
Currently most solid state gas sensors are composed of semiconductor materials operated at high temperatures. Gas selectivity with these devices is achieved by operation at different temperatures, or using alternate dopants, but results have been poor, because of the limited number of materials available for this purpose. Unique to our devices are the use of porphyrin molecules, whose selectivity for different gases can be modified by changing the central metal or modifying the attached ligands. With a distinct advantage over optical methods of transduction, we propose the use of the multi-frequency impedance spectroscopy to probe the response of the sensing film to gas adsorption. We have previously determined that selectivity between different analytes can be enhanced by varying the frequency of the sinusoidal voltage used to interrogate the sensing film. What is proposed here is to develop an alternative transduction principle using films of metalloporphyrin coordinational compounds.
The literature on the synthesis and development of metalloporphyrins is extensive (thousands of references). The most widely known metalloporphyrin is hemoglobin, the oxygen carrying molecule in blood. The vast majority of synthetically made porphyrins have been developed to detect oxygen by a luminescence mechanism. These optically based sensors have been used to develop such unique things as pressure sensitive paint, which is used in the development of airfoils.